radio fine tuning b11 (rft)

BSS B11 Radio Fine Tuning Introduction - All Rights Reserved © Alcatel-Lucent 2010

All Rights Reserved © Alcatel-Lucent 2010

GSM B11BSS B11 Radio Fine Tuning

Introduction

STUDENT GUIDE

TMO18097 D0 SG DEN I1.0 Issue 1

All rights reserved © Alcatel-Lucent 2010 Passing on and copying of this document, use and communication of its contents not

permitted without written authorization from Alcatel-Lucent



BSS B11 Radio Fine Tuning IntroductionGSM B11

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Terms of Use and Legal Notices

Switch to notes view!1. Safety WarningBoth lethal and dangerous voltages may be present within the products used herein. The user is strongly advised not to wear conductive jewelry while working on the products. Always observe all safety precautions and do not work on the equipment alone.

The equipment used during this course may be electrostatic sensitive. Please observe correct anti-static precautions.

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All other trademarks, service marks and logos (“Marks”) are the property of their respective holders, including Alcatel-Lucent. Users are not permitted to use these Marks without the prior consent of Alcatel-Lucent or such third party owning the Mark. The absence of a Mark identifier is not a representation that a particular product or service name is not a Mark.

Alcatel-Lucent assumes no responsibility for the accuracy of the information presented herein, which may be subject to change without notice.

3. CopyrightThis document contains information that is proprietary to Alcatel-Lucent and may be used for training purposes only. No other use or transmission of all or any part of this document is permitted without Alcatel-Lucent’s written permission, and must include all copyright and other proprietary notices. No other use or transmission of all or any part of its contents may be used, copied, disclosed or conveyed to any party in any manner whatsoever without prior written permission from Alcatel-Lucent.

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Please refer to technical practices supplied by Alcatel-Lucent for current information concerning Alcatel-Lucent equipment and its operation, or contact your nearest Alcatel-Lucent representative for more information.

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5

Course Outline

About This CourseCourse outlineTechnical supportCourse objectives

1. Topic/Section is Positioned HereXxxXxxXxx

2. Topic/Section is Positioned Here






1. B11 Radio Fine Tuning

1. Typical Radio Problems 3JK12201AAAAWBZZA

2. Idle Mode (Re)Selection 3JK12202AAAAWBZZA

3. Radio Measurements Principles 3JK12203AAAAWBZZA

4. Radio Link Sup and Power Control 3JK12204AAAAWBZZA

5. Handover Algorithms 3JK12205AAAAWBZZA

6. Resources Allocation Management 3JK12206AAAAWBZZA

7. Optimization Methodology 3JK12207AAAAWBZZA

8. Case Studies 3JK12208AAAAWBZZA

9. Annexes 3JK12209AAAAWBZZA

10. Solutions 3JK12210AAAAWBZZA




6

Course Outline [cont.]






7

Course Objectives


Welcome to BSS B11 Radio Fine Tuning Introduction

Upon completion of this course, you should be able to:

By the end of the course, participants will be able, for conventional networks, to: - Characterize the usual radio problems and decide on the appropriate maintenance team; - List and describe BSS radio algorithms and related parameters;List radio parameters and check

conformity with Alcatel-Lucent standards; - Estimate the qualitative impact of an algorithm parameter change; - Propose algorithm parameter setup to solve typical radio problems. Note: Hierarchical, dual-band, frequency hopping and GPRS networks are covered in other trainings.




8

Course Objectives [cont.]






9

About this Student Guide

Switch to notes view!Conventions used in this guide

Where you can get further information

If you want further information you can refer to the following:

Technical Practices for the specific product

Technical support page on the Alcatel website: http://www.alcatel-lucent.com

Note Provides you with additional information about the topic being discussed. Although this information is not required knowledge, you might find it useful or interesting.

Technical Reference (1) 24.348.98 – Points you to the exact section of Alcatel-Lucent Technical Practices where you can find more information on the topic being discussed.

WarningAlerts you to instances where non-compliance could result in equipment damage or personal injury.




10

About this Student Guide [cont.]






11

Self-assessment of Objectives

At the end of each section you will be asked to fill this questionnaire Please, return this sheet to the trainer at the end of the training


Instructional objectives Yes (or globally

yes)

No (or globally

no) Comments

1 To be able to XXX

2

Contract number :

Course title :

Client (Company, Center) :

Language : Dates from : to :

Number of trainees : Location :

Surname, First name :

Did you meet the following objectives ?Tick the corresponding box

Please, return this sheet to the trainer at the end of the training




12

Self-assessment of Objectives [cont.]


Instructional objectives Yes (or Globally

yes)

No (or globally

no) Comments

Thank you for your answers to this questionnaire

Other comments

Section 1 · Module 1 · Page 1

All Rights Reserved © Alcatel-Lucent 20103JK12201AAAAWBZZA Issue 1

Do not delete this graphic elements in here:


Module 1Typical Radio Problems

3JK12201AAAAWBZZA Issue 1

Section 1B11 Radio Fine Tuning

GSM B11BSS B11 Radio Fine Tuning Introduction





GSM B11 · BSS B11 Radio Fine Tuning IntroductionB11 Radio Fine Tuning · Typical Radio Problems

1 · 1 · 2

Blank Page


First editionLast name, first nameYYYY-MM-DD01

RemarksAuthorDateEdition

Document History





1 · 1 · 3

Module Objectives

Upon completion of this module, you should be able to:

Characterize typical radio problems in order to trigger an intervention of the appropriate team





1 · 1 · 4

Module Objectives [cont.]






1 · 1 · 5

Table of Contents

Switch to notes view! Page

1 Presentation 72 Coverage Problem 93 Interference Problem 184 Unbalanced Power Budget Problem 325 TCH Congestion Problem 386 Deducing the Right Team for Intervention 43





1 · 1 · 6

Table of Contents [cont.]







1 · 1 · 7

1 Presentation





1 · 1 · 8

1 Presentation

Justification

Several sources of information can alert RFTM team: QoS indicators Customers complaints Drive tests Other teams information (NSS statistics)

As many symptoms are common to several causes, it can be necessary to: Consolidate standard sources of information Carry out specific examinations Deduce the appropriate team for intervention





1 · 1 · 9

2 Coverage Problem





1 · 1 · 10

2 Coverage Problem

Definition and Symptoms

Definition: Bad coverage A network or cell facing coverage problems presents a bad RxLev and RxQual

at the same time on some areas.

Symptoms: Customers complain about dropped calls or/and “no network” OMC QoS indicators TCH failure rate Call drop rate Low proportion of better cell HO High rate of DL quality HO

A interface indicators High rate of Clear Request messages, cause radio interface failure

No information is available on non-covered parts of the network, as there are non-mobiles making calls over there!

Nevertheless, cells in border of non-covered zones do have a particular behavior:

Cell A will mainly perform Better Cell handovers towards its neighbors, whereas cell B, bordering the non-coverage area, will perform emergency handovers for MSs exiting the network.

For these MSs, mainly DL Quality HO will be triggered:

DL because MS antenna is less efficient than BTS one,

Quality rather than Level since Qual has a greater priority in Alcatel-Lucent HO causes.

AB





1 · 1 · 11

2 Coverage Problem

Examination

Depending on the information sources you have: Radio Measurement Statistics (RMS) – (RxLevel , RxQuality) matrix Radio Link Counter S vector

Number of calls with DL/UL bad coverage (bad RxLev, bad RxQual)

Abis interface (for example with COMPASS) bad quality > 5% bad level RxLev < - 95 dBm and RxQual > 4

OMC-R or A interface unexpected high traffic, induced by call repetition

Billing information High recall rate detected

RMS:

Provides statistics from any area in the network which are available at any time.

Cost-effective.

Easier and cheaper to perform than Drive test or Abis Trace.

The operator can tune 54 parameters (based on RxLev, BFI, C/I, Radio Link Counter S, Path Balance, etc.) to define up to 16 templates (depending on cell type – rural, urban, etc. – for example).

Trigger from the OMC-R.

NPO can save up to 15 days of RMS for the complete network.

Templates can be designed in NPO.

Default result reports are available in NPO.





1 · 1 · 12

2 Coverage Problem

Typical Causes

If the actual coverage is not the one predicted by RNP tools: check antenna system increase or decrease antenna down-tilt check BS_TXPWR_MAX to be increased if value different from RNP power budget

If the actual coverage is OK compared to the predicted ones: indoor traffic, to be handled by specific means if black spot close to cell border, ease outgoing HO





1 · 1 · 13

2 Coverage Problem

Investigation with Abis Trace

Example of an Abis trace analysis

TRX index RxLev_UL RxLev_DL RxQual_UL Path_loss_UL Path_loss_DL delta_Path_loss Delta_quality AV_MS_PWR Nb_of_samplesRxQual_DL

TRX index Qual0 Qual1 Qual2 Qual4 Qual5 Qual6 Qual7 Bad_QualityQual3

TRX index Qual0 Qual1 Qual2 Qual4 Qual5 Qual6 Qual7 Bad_QualityQual3

1 -89.29 -84.67 0.42 123.82 123.67 0.15 -0.01 34.53 30740.43

2 -89.77 -89.09 0.41 124.87 128.09 -3.21 0.03 35.11 10 2530.38

3 -83.15 -79.15 0.17 116.05 121.22 -5.16 -0.16 32.9 53390.33

DISTRIBUTION OF UPLINK QUALITY

1 86.50% 3.19% 2.50% 1.92% 2.08% 0.98% 0.26% 3.32%2.57%

2 88.11% 1.82% 1.91% 2.14% 2.17% 1.15% 0.19% 3.51%2.51%

3 77.70% 4.30% 4.30% 3.56% 3.56% 1.70% 0.17%4.36%

1 88.29% 1.82% 2.05% 1.30% 1.46% 1.76% 0.94% 4.16%2.37%

2 87.50% 2.98% 2.60% 2.11% 1.14% 0.74% 0.50% 2.38%2.43%

3 71.30% 3.82% 4.02% 4.16% 4.30% 4.23% 3.16%4.89%

DISTRIBUTION OF DOWNLINK QUALITY

5.43%

11.73%

It could have been coverage problems if this trace was made for 3 mono-TRX cells. In this case, the 3 lines are uncorrelated. Anyway, delta path loss of frequency 111 is greater than 5dB, showing a problem on this TRX.

If this is a 3-TRX cell, it cannot be a coverage problem as the three TRXs are not impacted. It will be either interference or malfunction of one TRE.

If the trace is done on 3 mono-TRX cells, in that case, it could be a coverage problem. Be careful when interpreting this result table: even if average levels in the UL and the DL are high and a lot of Quality problems are seen, nobody can say that samples with bad quality have a good level! The level seen is just an average…

One should have a look at the next slide…





1 · 1 · 14

2 Coverage Problem

Investigation with Abis Trace [cont.]

Example of an Abis trace analysisThresholds

Bad Coverage

RxLev -95

RxQual > 4

Interference RxLev > -95

RxQual > 4

3-88.0063-95.3331-71.0031-80.0061-80.003 -80.003

571111212

Number_UL: 10 253Number_DL: 10 253

Int_UL: 2BC_UL: 358

Int_DL: 0%

0.02%3.49%

67-104.64

2048-

107.5051

Number_UL: 5339Number_DL: 5339

Int_UL: 0BC_UL: 290

Int_DL: 0%BC_DL: 626

0.00%5.43%

Samples<Lev>BSIC63-101.542

Samples<Lev>BSICNeigh_Cell_Nb

Samples<Lev>BSICNeigh_Cell_Nb

<RxLev_Serving>= -102.17 dBm3.74%BC_DL: 115

57-100.532045-98.7121034-98.036533-98.6137

<RxLev_Serving>= -106.56 dBm

BC_DL: 244 2.38% <RxLev_Serving>= -106.17 dBm

Frequency: 92

Frequency: 111

11.73%

Neigh_Cell_Nb10

All samples are Bad Coverage samples (BC). None is interference, showing that this cell is not facing any interference problem.

By the way, if the cell is:

mono-TRX, this is a coverage problem.

3 TRXs, this is a malfunction of the TRE (shown also by the high value of delta_path_loss).





1 · 1 · 15

2 Coverage Problem

Investigation with RMS

Suspecting a cell coverage problem Distribution of samples per RxQual value and RxLev band

Distribution of samples per RxLev band

0

1

2

4

5

7

[-110,-104[

[-104,-98[

[-98,-92[

[-92,-86[

[-86,-80[

[-80,-74[

[-74,-68[

[-68,-62[

[-62,-56[

[-56,-47[

RxQuality (Nb)

RxLevel(dB)

[0, 14 793]

]14 793, 23 446]

]23 446, 29 586]

]29 586, 34 348]

]34 348, 38 239]

]38 239, 41 529]

]41 529, 44 378]

]44 378, 46 892]

Out of RangeX

Interval of numberof samples

Downlink Samples Matrix in log scale

3

6

Not acceptable coverage limit:too low level

too bad quality

A coverage problem is observed when a significant amount of the traffic of a cell is suffering from both low level and bad quality (RxQual).

To confirm, distribution of samples per RXLEV band should be also considered to know the proportion of calls which are experiencing a low signal level.

If a lot of samples of low level and bad quality are observed for only a sub-part of the TRXs (can be one only) then a BTS hardware problem or a problem on the antenna should be suspected.

If all the TRXs are experiencing a lot of samples of low level and bad quality then a coverage problem must be suspected.

These RMS indicators are provided on the NPO tool per TRX, per Cell:

Matrix of Number of Measurement Results per DL RxQual value and per DL RxLev bandRMQLDSAM = RMS_DL_RxQuality_RxLevel_sample

Vector of Percentage of Samples per DL RxLev bandRMQLDLVDV = RMS_DL_RxLevel_distrib

Vector of Percentage of Samples per DL RxQual bandRMQLDQUDV = RMS_DL_RxQuality_distrib





1 · 1 · 16

2 Coverage Problem

Investigation with RMS [cont.]

Suspecting a cell coverage problem Average TA values per RxQual value and RxLev band

16.00%

14.00%

12.00%

10.00%

8.00%

6.00%

4.00%

2.00%

0.00%

01/1

2/2

001

01/0

1/2

002

02/0

1/2

002

03/0

1/2

002

04/0

1/2

002

05/0

1/2

002

06/0

1/2

002

07/0

1/2

002

08/0

1/2

002

09/0

1/2

002

10/0

1/2

002

11/0

1/2

002

12/0

1/2

002

13/0

1/2

002

14/0

1/2

002

109876543210

%N > TA thres TA max

Maximum Timing Advance and TA > threshold

N > TA thresTA maxTA thresholdAcceptable

coverage limit:sufficient level and

good quality

Not acceptablecoverage limit:

too low level andtoo bad quality

% of TA valueover TA threshold

has also to beconsidered

0

1

2

4

5

7

[-110,-104[

[-104,-98[

[-98,-92[

[-92,-86[

[-86,-80[

[-80,-74[

[-74,-68[

[-68,-62[

[-62,-56[

[-56,-47[

RxQuality (Nb)

RxLevel(dB)

[0, 2]

]2, 4]

]4, 6]

]6, 8]

Out of Range

Interval of averageTiming Advance

Uplink average TA Distribution

3

6

X

Down

In order to know if the coverage problem is due to a big amount of traffic at the cell border or rather to indoor calls, the average TA value per RXQUAL value and RXLEV band as well as the Percentage of TA values over TA threshold should be observed:

Matrix of Average TA per UL RxQual value and per UL RxLev bandRMQLUTAM = RMS_UL_RxQuality_RxLevel_TimingAdvance

Rate of Measurements Results whose TA is greater than the TA thresholdRMTAGTR = RMS_TimingAdvance_greater_threshold_rate

Maximum TA value of all values reported in Measurement Results RMTAMXN = RMS_TimingAdvance_max





1 · 1 · 17

2 Coverage Problem

Investigation with RMS [cont.]

Suspecting a local cell coverage problem RxQual and RxLev per TA bands

5

4

3

2

0

1

2.5

[0,5[ [6,11[ [55,63[[49,54[[43,48[[37,42[[31,36[[25,30[[19,24[

[12,18[

-47

- 60

- 70

- 80

- 110

- 90

- 59

[0,5[ [6,11[ [55,63[[49,54[[43,48[[37,42[[31,36[[25,30[[19,24[

[12,18[

Bad qualityand bad Level

for a specific TA band

Coverage problem

In order to know if the coverage problem is due to a big amount of traffic at the cell border or rather to indoor calls, the average TA value per RXQUAL value and RXLEV band as well as the Percentage of TA values over TA threshold should be observed:

Matrix of Average TA per UL RxQual value and per UL RxLev bandRMQLUTAM = RMS_UL_RxQuality_RxLevel_TimingAdvance

Rate of Measurements Results whose TA is greater than the TA thresholdRMTAGTR = RMS_TimingAdvance_greater_threshold_rate

Maximum TA value of all values reported in Measurement Results RMTAMXN = RMS_TimingAdvance_max





1 · 1 · 18

3 Interference Problem





1 · 1 · 19



Definition: Interference A network facing interference problems presents good RxLev and bad RxQual

at the same time on some areas.

Symptoms Customers complain about bad speech quality (noisy calls) and/or call drops OMC QoS indicators: SDCCH/TCH Drop Low proportion of better cell HO High rate of DL/UL quality HO and interference HO Low HO success rate


DL/UL depends on the way on which the interference is present.

Mainly, interferences are in the DL, due to bad frequency planning introducing interferences in the network. And this problem will not change till the frequency plan is not returned…

Sometimes, interference can be in the UL in very dense area (for example, microcell area), since MSs are very close.

Finally, sometimes interferences are not coming from BS or MS but from another radio equipment, either in the UL or the DL.





1 · 1 · 20


Examination with RMS

Radio Measurement Statistics (RMS) RxQual/RxLev matrix CFE/RxLev matrix C/I vectors for neighbors C/I vectors for MAFA frequencies MAFA is a new standardized GSM feature for mobiles MAFA mobiles can provide C/I measurements from non-neighbor cells

Number of calls with DL/UL interference (good RxLev, bad RxQual) Number of noisy calls (bad RxQual) with bad voice quality (bad FER) A high rate use of the most robust AMR codecs also denounces interferences

problems. But be careful, this can also be due to a pessimistic choice of the thresholds used for codec change.

The feature Radio Measurement Statistics (RMS) is designed to make far easier the work for planning and optimization of the network by providing the operator with useful statistics on reported radio measurements.

In fact these statistics give directly the real cell characteristics by taking into account the MS distribution.

Thanks to this feature, the operator is able to:

detect interfered frequencies.

assess the quality of the cell coverage.

detect and quantify cell unexpected propagation.

assess the traffic distribution in the cell from statistics on reported neighboring cells.

evaluate the voice quality in the cell.

etc.

In regards to the “RTCH Measurements Observation” (measurement type 11), the Radio Measurement Statistics feature (RMS) brings the following advantages:

smaller report files.

the report files always have the same maximum length no matter what the measurement duration is.

every measurement is taken into account (no sampling).

no more need for measurement post-processing tools for statistics. Directly available with NPO.





1 · 1 · 21


Examination with RMS [cont.]

Suspecting a cell interference problem Number of samples per RxQual value and RxLev band

Quality problems are obvious at any level of RMS data

Interference highlighted

Network fine tuning needed

0

1

2

4

5

7

[-110,-104[

[-104,-98[

[-98,-92[

[-92,-86[

[-86,-80[

[-80,-74[

[-74,-68[

[-68,-62[

[-62,-56[

[-56,-47[

RxQuality (Nb)

RxLevel(dB)

[0, 14 793]

]14 793, 23 446]

]23 446, 29 586]

]29 586, 34 348]

]34 348, 38 239]

]38 239, 41 529]

]41 529, 44 378]

]44 378, 46 892]

Out of RangeX


Downlink Samples Matrix in log scale

3

6

Average RxQual value per RXLev bandhas also to be considered

0

1

2

3

4

5

6

[-110,-104[

[-104,-98[

[-98,-92[

[-92,-86[

[-86,-80[

[-80,-74[

[-74,-68[

[-68,-62[

[-62,-56[

[-56,-47[

RxQuality (Nb)

RxLevel(dB)

Downlink average RxQuality per RxLevel

RxQualityAverage

5

Average DL RxQuality = 2.81





1 · 1 · 22



Suspecting a Voice Quality problem Number of samples per BFI band and RxLev band

0

1

2

3

4

5

6

[-110,-104[

[-104,-98[

[-98,-92[

[-92,-86[

[-86,-80[

[-80,-74[

[-74,-68[

[-68,-62[

[-62,-56[

[-56,-47[

Average CFE

RxLevel (dB)

Uplink average Consecutive Frame Erasure per RxLevel

7

8Average RxQual

0

1

2

3

4

5

6CFEAverage

RxQualityAverage

Consecutive Frame Erasure (BFI) is a measurement based on loss of consecutive

speech frames over one SACCH mw.

It is directly linked to Voice Quality.

RxQual to be compared with CFE since Bad RxQual does not always mean bad VQ.

[0, 1[

[1, 2[

[2, 4[

[6, 8[

[8, 10[

[14, 18[

[-110,-104[

[-104,-98[

[-98,-92[

[-92,-86[

[-86,-80[

[-80,-74[

[-74,-68[

[-68,-62[

[-62,-56[

[-56,-47[

CFE (Nb)

RxLevel(dB)

[0, 14 793]

]14 793, 23 446]

]23 446, 29 586]

]29 586, 34 348]

]34 348, 38 239]

]38 239, 41 529]

]41 529, 44 378]

]44 378, 46 892]

Out of RangeX


Consecutive Frame Erasure Matrix in log scale

[4, 6[

[10, 14[

[14, 18[

[14, 18[[22, 25[

[18, 22[

[14, 18[


Matrix of Number of Measurements Results per CFE band (or BFI band) and per UL RxLev band RMFEM = RMS_UL_ConsecutiveFrameErasure_RxLevel_sample

Vector of Average number of Consecutive Frame Erasure per UL RxLev bandRMFEBFAV = RMS_UL_ConsecutiveFrameErasure_avg_per_RxLevel

Vector of Average UL RxQual per RxLev bandRMQLUQUAV = RMS_UL_RxQuality_avg_per_RxLevel





1 · 1 · 23



Suspecting a local interference problem RxQual and RxLev per TA bands

5

4

3

2

0

1

2.5

[0,5[ [6,11[ [55,63[[49,54[[43,48[[37,42[[31,36[[25,30[[19,24[

[12,18[

Bad qualityand good Level

for a specific TA band

interference problem

-47

- 60

- 70

- 80

- 110

- 90

- 59

[0,5[ [6,11[ [55,63[[49,54[[43,48[[37,42[[31,36[[25,30[[19,24[

[12,18[


Matrix of Number of Measurements Results per CFE band (or BFI band) and per UL RxLev band RMFEM = RMS_UL_ConsecutiveFrameErasure_RxLevel_sample

Vector of Average number of Consecutive Frame Erasure per UL RxLev bandRMFEBFAV = RMS_UL_ConsecutiveFrameErasure_avg_per_RxLevel

Vector of Average UL RxQual per RxLev bandRMQLUQUAV = RMS_UL_RxQuality_avg_per_RxLevel





1 · 1 · 24


Typical Causes

GSM interference co-channel adjacent

Non-GSM interference other Mobile Networks other RF sources





1 · 1 · 25


GSM Interference: Adjacent Channels

Adjacent channel interference +6dB are sufficient to interfere (9dB according to GSM)

Level

Frequency

F(BTS1)

6 dB

F(BTS2)F(BTS1) = F(BTS2)+1





1 · 1 · 26


GSM Interference: Adjacent Channels [cont.]

Adjacent channel interference: Symptom Usually downlink interference High rate of quality HO, call drop (due to HO but mainly due to radio) and TCH

assignment failure

Examination Neighbor cells in Abis trace (only for BCCH) Non-neighbor cells in RMS (MAFA frequencies) Frequency planning C/(I adjacent) < -6dB

Correction Downtilt increase of interferer, or even change of antenna orientation Reduction of BS power if necessary, Change of frequency (best solution) Concentric cell implementation (1 extra TRX needed if traffic cannot be supported

by Outer+Inner configuration)





1 · 1 · 27


GSM Interference: Co-Channel

GSM Interference Co-Channel interference -12dB are sufficient (-9dB according to GSM) by Outer+Inner configuration

Level

Frequency

F(BTS1)

-12 dB

F(BTS2)F(BTS1) = F(BTS2)





1 · 1 · 28


GSM Interference: Co-Channel [cont.]

Co-channel interference Symptom Usually downlink interference High rate of quality HO, call drop and call failure

Examination Neighbor cells in Abis trace (only for BCCH) Non-neighbor cells in RMS (MAFA frequencies) Frequency planning C/I < 12 dB

Correction Downtilt increase of interferer, or even change of antenna orientation Reduction of BS power, Change of frequency Concentric cell implementation (1 extra TRX needed if traffic cannot be supported

by Outer+Inner configuration)





1 · 1 · 29


GSM Interference: µcellular

GSM interference: µcellular

BTS1: ARFCN 5 BTS2: ARFCN 6

MS1 indoor RxLev_UL: - 90 dBm

MS2 outdoor, connected to BTS2 1: no level on BTS1

(BTS 1 under-roof) 2: - 80 dBm on BTS1:

interferer UL/DL 3: no level on BTS1 µcell algo prevents BTS2->BTS1 HO

MS 1(indoor)

MS 2(outdoor) 1

2

3

BTS 1(Micro)

BTS 2

When interferences are created by frequency planning, it’s not so hard to detect them. But frequency planning tools mainly consider DL C/I and coverage.

Some problems are more difficult to predict. For example, let’s consider a microcell layer:

A and B are 2 microcells with the coverage described before in dense urban environment.

Even if both cells A & B are using adjacent frequencies (5 and 6), the overlapping area is far from cell A antenna. Thus, in this area C/I is lower than 6 dB.

A “red” MS is connected to cell A. When the MS starts its call, it transmits full power and a PC algorithm quickly reduces MS power as the received level is very good (microcell coverage). When MS A enters the building, it faces a loss of signal of 20 dB. Then, the MS power increases to MS_TXPWR_MAX.

A second mobile “B” is connected to cell B and moves down in the coverage area of cell B. The MS power of B decreases quickly down to MS_TXPWR_MIN as the MS is close to the antenna. But when MS B arrives outside the building where A is sitting, A and B are close and transmitting on adjacent frequencies… Then B has to increase its power to avoid dropping its call. By the way, global level of freq B is increased in all cell B… creating interference in the UL.

A

B





1 · 1 · 30


GSM Interference: Forced Directed Retry

GSM Interference: Forced Directed Retry The MS should connect to cell2, but no TCH

available The MS connects to cell 1 with forced

directed retry The MS is emitting at high level (far from

BTS1) UL interference for BTS 3

BTS 1 is emitting at high level DL interference at BTS 3

Cell 2: 4 5

C ell 3: 23

Ce

ll 1:

2

4

MS

BTS 2

BTS 1

BTS 3

Another more difficult case of interference: FDR

When examining the preceding situation of planning tool: no problem of C/I. No risk of interference.

The FDR algorithm allows an MS connected on an SDDCH on a cell without any free TCH to make an SDCCH-TCH handover (cause 20) so that it takes a TCH on its neighbor. As seen from the user, this is not a handover (call establishment phase, no impact on speech quality), and this algorithm is very efficient to avoid cell congestion cases.

This algorithm is mainly based on neighbor level compared to parameter L_RXLEV_NCELL_DR (n). If the level greater than this threshold, the TCH is to be seized on neighbor.

FDR is mandatory for dual layer or dual band networks (and very easy to configure in this case), since we have capture handovers. Capture handovers send traffic to lower or preferred band cells. In case these cells are congested, calls may not be established, even if upper or non-preferred band cells are free (due to MS idle mode selection, advantaging microcell for example). With the FDR algorithm, the MS takes an SDCCH in the preferred cell, and FDR is used to take a TCH on the non-preferred cell in case of congestion. This situation highlights a good network behavior, since the MS is at the same time in the coverage area of both cells (preferred and not preferred).

The situation described on the slide corresponds to the usage of FDR in a single layer network. This is in that case a heavy-to-tune algorithm presenting of lot of interference and bad quality call risks, since the mobile will be connected to a cell when being not in its service area.

umbrella

microcellFDRcapture





1 · 1 · 31


Non-GSM Interference

Other mobile networks: TACS/AMPS/NMT900 Inter-modulation with GSM BS/MS receiver Spurious RACH for AMPS (AMPS Tx bands close to GSM uplink band) Examination TASC: coverage hole with 600 m from TASC BTS

AMPS => 50% reduction of range if AMPS/GSM BTS collocated

Other RF interferers (Radar, shop anti-theft mechanisms, medical device, etc.)

Other RF interferers:

medical devices: GSM equipment disturb them more than the opposite!

anti-theft mechanisms.

Example:

The Microcell is showing a very high call drop rate. On one frequency, very small call duration.

No problem seen in the frequency plannig. No potential interferer.

Abis trace:

The Spectrum analyzer connected on the antenna feeder highlights a peak on GSM freq 6 in the UL…

Anti-theft mechanism turned off: no more problem…

shop

Microcellantenna

Qual

Level

Qual

Level

DL UL

interference





1 · 1 · 32

4 Unbalanced Power Budget Problem





1 · 1 · 33



Definition: Unbalanced power budget A cell facing unbalanced power budget problems presents a too high path-

loss difference between UL and DL (often DL>UL) Rule: try to have delta as small as possible to avoid access network possible

only in 1 direction (usually BTS->MS: OK and MS->BTS: NOK) Symptoms: OMC QoS indicators High rate of Uplink quality Handover causes Low incoming HO success rate (no HO Access triggered on the uplink) Degradation of TCH failures and OC call drop indicators


O&M Alarms Voltage Standing Wave Ratio BTS Alarm (VSWR) TMA Alarm (in case of G2 BTS or Evolium™ BTS with high power TRE)

UL Quality HO is triggered:

UL since the problem is in the UL.

Quality as Quality has greater priority than level.





1 · 1 · 34


Examination

RMS: Path Balance vector per TRX Number of calls with abnormal bad FER (good RxQual & bad FER)

Abis monitoring: |delta path-loss| > 5dB Check if problem is occurring for 1 TRX or all

Problem on 1 TRX: FU/CU or TRE problem or ANY problem or cables connected to this equipment.

All TRXs: problem on antenna, feeder, jumper or common equipment (e.g., ANX, ANC).





1 · 1 · 35


Abis Trace

Example of an Abis trace analysis

106 -94.52 -87.19 0.43 127.55 130.19 -2.64 0.18 33.03 20660.25

Frequency Qual0 Qual1 Qual2 Qual4 Qual5 Qual6 Qual7 Bad_QualityQual3

Frequency Qual0 Qual1 Qual2 Qual4 Qual5 Qual6 Qual7 Bad_QualityQual3

89 -84.29 -75.17 0.65 115.32 118.17 -2.85 0.21 31.03 20010.44

118 -90.75 -83.36 0.46 123.22 126.36 -3.14 0.04 32.46 31930.41

124 -88.89 -85.30 0.29 120.48 128.30 -0.37 31.59 29310.67

DISTRIBUTION OF UPLINK QUALITY

106 84.75% 4.07% 3.68% 1.36% 1.50% 0.92% 0.53% 2.95%3.19%

89 81.41% 1.70% 2.95% 6.35% 2.55% 1.30% 0.10% 3.95%3.65%

118 83.62% 4.23% 4.23% 1.57% 1.79% 0.97% 0.25%3.35%

106 90.27% 3.44% 2.08% 0.92% 1.36% 0.34% 0.05% 1.74%1.55%

89 80.16% 6.45% 7.00% 1.50% 0.50% 0.45% 0.10% 1.05%3.85%

118 86.78% 2.72% 3.95% 1.41% 1.13% 1.19% 1.00%1.82%

DISTRIBUTION OF DOWNLINK QUALITY

3.01%

3.32%

Frequency RxLev_UL RxLev_DL RxQual_UL Path_loss_UL Path_loss_DL delta_Path_loss Delta_quality AV_MS_PWR Nb_of_samplesRxQual_DL

-7.82

124 90.79% 1.06% 2.18% 1.77% 1.30% 0.48% 0.07%2.35% 1.84%

124 77.14% 4.37% 5.87% 3.48% 1.36% 0.82% 1.02%5.94% 3.21%





1 · 1 · 36


RMS Data

Suspecting a TRX hardware problem Average Path Balance

A fair average Path Balance at Cell level can hide a bad value for one TRX

0

500

1000

1500

2000

2500

3000

[-110,-20[

[-20,-10[

[-10,-6[

[-6,-3[

[-3,0[

[0,3[

[3,6[

[6,10[

[10,20[

[20,110[

Nb Samples

PathBalance(dB)

NbSamples

PathBalance Distribution

Average Cell Path Balance = - 0.9 dB


Vector of the Number of Measurement Results per Path Balance bandRMPBV = RMS_PathBalance_sample

Average Path Balance valueRMPBAN = RMS_PathBalance_avg





1 · 1 · 37


Typical Causes

Antennas or common RF components, TMA (pb common to all TRXs of the BTS)

TRX RF cables/LNA ... if problem located on only 1 FU

Every BTS has its proper architecture and the diagnosis must be adapted.





1 · 1 · 38

5 TCH Congestion Problem





1 · 1 · 39



Definition: TCH Congestion TCH Congestion rate (TCH Assignment Phase) is too high (more than 2%) Rule: try to meet the offered traffic (asked by users) by providing the right

number of resources (TRX extension) Symptoms: Customers complain about ‘Network busy’ OMC QoS indicators High “TCH Congestion rate” Low “incoming Intra/Inter BSC HO success rate” (no TCH available) High “Directed Retry rate” if activated

A interface indicator: “BSS Congestion failure in OC” High rate of Assignment Failure messages, No radio resource available





1 · 1 · 40


Examination and Typical Causes

Examination: TCH Congestion On a per cell basis examination, check the evolution of the TCH Congestion

rate. Typical causes: Special events: Foreseeable: football match, important meeting

Activate some TRXs already installed (and use Synthesized FH) Add special moving BTSs

Not foreseeable: car crash on the highway

Cells on wheel operational by several operators around the world for special events coverage & capacity:

IRMA (SFR) connected to Caen’s BSC.

Orange coverage / Football WC 1998 for Paris « Stade de France »:

Specific cells covering Paris Stadium. During games, only small capacity (using joker frequencies). During breaks, some TRX off-cells around are turned off, and frequencies are reused for stadium cells.





1 · 1 · 41


Typical Causes

Daily periodic problems At peak hour, the cell is not correctly dimensioned.

Hardware solution (refer to Annex)

Estimate the offered traffic: At OMC-R level: Traffic in Erlang/(1- TCH Congestion rate)

Use the B-Erlang law to estimate the number of TCHs required for a 2% blocking rate, thus the target configuration

Add TRXs to reach the new target configuration and find ‘joker frequencies’and / or implement concentric cells

Warning: “offered traffic” is not the capacity delivered by the system but the traffic asked by the users.





1 · 1 · 42


Typical Causes [cont.]

Daily periodic problems At peak hour, the cell is not correctly dimensioned.

Software solution Use specific densification features Half Rate Forced Directed Retry Traffic handover Fast Traffic handover Candidate Cell Evaluation (FREEFACTOR / LOADFACTOR)

Half rate may not only mean “SW” solution. Need of G2 BSC/TC, Evolium TRE or G2 DRFU.





1 · 1 · 43

6 Deducing the Right Team for Intervention





1 · 1 · 44


Process

Problem characterization

Make assumption causes

Check the tuning of default radio parameters

Consult the config. db Choose an (other) classical algo

Identify the tunable parameters

Impact estimation

Standard setting ?

No

Yes

Yes

No

No

Yes

Call expert

- Microcell, multiband- Concentric

=N

No

Yes

No

Yes

No

Yes

Parameters modificationDatabase updating

Impact simulation of aparameter modification

No

- Hopping- Marketing

Yes

QOS alarm on the network,on a BSC or some cells

- Indicators (% call drop)- Field measurements/planning- Subscriber complains

QOS team

DHCPEND

Drive test team

DHCPEND

Dimensionning team

OK

Correctionaction

Maintenance team

Planning team

NOK

Cell corrected ?Neighbor cell ?

RFT team - Interferences- Coverage (indoor)- Power budget- Congestion (TCH, SDCCH)- BSS problemInvestig problem ?

Planning/BSS causes

Standard parameters ?

Onpurpose

Systemproblem ? Simulation

OK ?

Recurrent problem ?

N timesCheck ?

With QOS ?





1 · 1 · 45


Coverage Problem

In case of coverage problem: If the field reality does not match the RNP prediction Maintenance team to change physical configuration (tilt, azimuth, antenna height,

etc.) and drive test team to check it

If the field reality matches the RNP prediction Deployment team to add sites (tri-sector, micro cellular, indoor cells)





1 · 1 · 46


Other Problems

In case of interference problem: Planning team to identify the interference source and correct it (joker

frequency, new frequency planning, etc.)

In case of unbalanced power budget problem: Maintenance team to check the impacted BTS (antennas, TMA, RF cables,

LNA, diversity system, etc.)

In case of TCH congestion problem: Traffic team (theoretically always in relation with the marketing team) to

manage the need of TRX extension, densification policy, etc.





1 · 1 · 47


Exercise

Match the symptoms listed below with the corresponding problem.

High rate of UL QUAL HO causesGood RxLev and Bad RxQual

VSWR alarm (OMC-R) (Voltage Standing Wave Ratio)

Bad RxLev and Bad RxQual

OMC QOS indicators: % TCH ASS failure high % call drop high

% QUAL HO % call drop % call failure

Unbalanced Power Budget

Bad coverage InterferencesTCH

Congestion

High Path-loss difference between UL and DLLow incoming HO success rate

Time allowed:

10 minutes





1 · 1 · 48


Radio Fine Tuning Team

When the detected problem does not concern another team (Networkdesign and frequency planning, Dimensioning, Radio engineering, Maintenance) or when the other teams cannot give any solution (too tight frequency planning, no additional TRX available, no financial budget for new sites, etc.), the Radio Fine Tuning team has to find acompromise between: High traffic density (Erl/km²/Hz) High quality of service (Call drop, CSSR, Speech quality, indoor, etc.)

Its role will be to take charge of radio resources management process This process can be fully described by the following algorithms: Idle Mode Optimization Cell Selection and Reselection Dedicated Mode Optimization: Radio Link Supervision and Power Control Handover Ressources Allocation and Management

In-depth knowledge of these algorithms is required for tuning





1 · 1 · 49

Self-assessment on the Objectives

Please be reminded to fill in the formSelf-Assessment on the Objectivesfor this module

The form can be found in the first partof this course documentation





1 · 1 · 50

End of ModuleTypical Radio Problems





Module 2Idle Mode (Re)Selection








GSM B11 · BSS B11 Radio Fine Tuning IntroductionB11 Radio Fine Tuning · Idle Mode (Re)Selection

1 · 2 · 2

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Document History





1 · 2 · 3

Module Objectives


Describe the Cell Selection and Reselection Algorithm List the associated parameters





1 · 2 · 4







1 · 2 · 5

Table of Contents


1 Idle Mode Cell Selection and Reselection 7





1 · 2 · 6








1 · 2 · 7

1 Idle Mode Cell Selection and Reselection





1 · 2 · 8


Selection and Reselection Principles

At startup (IMSI Attach), the MS selects a cell with: best C1 once “camped on” one cell (in idle mode)…

…the MS can decide to reselect on another one if: C1 criterion is too low the MS cannot decode downlink messages the current cell is becoming forbidden (e.g. barred) the MS cannot access the cell there is a better cell, regarding C2 criterion

Idle Mode Status null: the Mobile Station (MS) is off Status search BCCH: the MS searches a broadcast channel with the best signal level (cell selection and

reselection) BCCH list: up to 36 BCCH frequencies plus BSIC can be saved on SIM per visited network. Look if frequencies of the BCCH list can be used. No entries in the BCCH list, or the location is completely different: scan frequency band.

Status BCCH: the MS is synchronized on a BCCH. The MS camps on a cell. The BTS sends the neighbor cells list (BCCH allocation BA) on BCCH in System Information (SI) 2, 2bis and

2ter if BSS parameter EN_INTERBAND_NEIGH in dual band networks: GSM900 serving cellGSM900 neighbor cells put into SI 2GSM1800 neighbor cells put into SI 2ter/2bis

GSM1800 serving cellGSM900 neighbor cells put into SI 2terGSM1800 neighbor cells put into SI 2/2bis

The MS measures RXLEV from BCCH of the serving and neighbor cells. Camping on a cell is performed using C1 criterion only (the chosen cell is the one with the best C1)

The MS needs to have access to the network. The MS needs to be accessible by the network.

Reselection is done using the mechanisms referenced above. ‘handover algorithms’ in idle mode





1 · 2 · 9


C1 Criteria

C1 ensures that, if a call was attempted, it would be done with a sufficient

downlink and uplink received level based on 2 parameters, broadcasted on BCCH RXLEV_ACCESS_MIN [dBm] MS_TXPWR_MAX_CCH [dBm]

evaluated every 5 sec (minimum) C1 = A - MAX(0,B) > 0 A = RxLev - RXLEV_ACCESS_MIN B = MS_TXPWR_MAX_CCH - P If A > 0 & B < 0 OK, if B > 0, it can be compensated by A A >> 0 means that the MS is closer to the BTS

RXLEV_ACCESS_MIN [dBm] = minimum level to access the cell

MS_TXPWR_MAX_CCH [dBm] = maximum level for MS emitting

A = RxLev - RXLEV_ACCESS_MIN

assess that the MS received level is sufficient

B = MS_TXPWR_MAX_CCH - P

P maximum power of MS

assess that the BTS received level will be sufficient





1 · 2 · 10


C2 Criteria

CELL_RESELECT_PARAM_IND= not present THEN C2=C1 else C2 = C1 + CELL_RESELECT_OFFSET - TEMPORARY_OFFSET (T)

(if PENALTY_TIME 31) if T > PENALTY_TIME, TEMPORARY_OFFSET(T) = 0 used to avoid locating on “transient cell” CELL_RESELECT_OFFSET used to favor cell among other (e.g. micro-cell vs. umbrella,

once T > PENALTY_TIME)

Or C2 = C1 - CELL_RESELECT_OFFSET(if PENALTY_TIME = 31) CELL_RESELECT_OFFSET used to handicap some cells among others

One reselection criterion is compared to C2s C2neighbor > C2current if cells belong to same LA C2neighbor > C2current+Cell_Reselect_Hysteresis if cells from a different LA

Note:

CELL_RESELECT_OFFSET: from 0 to 126 dB, step 2dB

PENALTY_TIME: from 0=20s to 30=620s, step: 20s; 31=infinite

TEMPORARY_OFFSET: from 1=10dB to 6=60dB; 7 = infinite

The use of a second formula (Penalty_time = 31) is restricted to very special cases, as we do not like to penalize a cell. If a cell is parametered with PT=31, it will be penalized compared to ALL its neighbors. To penalize a cell compared to one neighbor, one should better boost the neighbor cell (using the first formula).

The first formula is very useful for favoring indoor cell or microcell.

Cell Selection and Cell Reselection Considering CELL_BAR_QUALIFY

In case of phase 2 MS and CELL_RESELECT_PARAM_IND=1, it is possible to set priorities to cells

CELL_BAR_QUALIFY

Two values:

0 = normal priority (default value)

1 = lower priority

CELL_BAR_QUALIFY Interacts with CELL_BAR_ACCESS (barring cell)

A phase 2 MS selects the suitable cell with the highest C2 (C1>0) belonging to the list of normal priority.

If no cell with normal priority is available then the MS would select the lower priority cell with the highest C2 (C1>0).





1 · 2 · 11


Exercise 1

On this network example List the parameters involved in the selection / reselection process

Time allowed:

5 minutes

Cell

Sectorized cell

CI=6169GSM900

Concentric cell

(8564, 1964)

(8564, 6169)

(8557, 1823)

Cell

CI=6271GSM900

CI=6270, GSM900

CI=1823GSM900

CI=1964GSM900





1 · 2 · 12


Exercise 2

Find the selected cell by the MS

Cell 1

Cell 2

CI=6169GSM900

Cell 3

(8564, 1964)

(8564, 6169)

(8557, 1823)

Cell

CI=6271GSM900

CI=6270, GSM900

CI=1823GSM900

CI=1964GSM900

Measurements RxLev (cell 1) RxLev (cell 2) RxLev (cell 3)

1

2

3

4

5

-80

-84

-88

-88

-89

-96

-90

-90

-87

-85

-104

-100

-87

-82

-78

The same parameters setting is applied in all the cells:

Rxlev_Access_min = -103 dBm for all cells

Cell_Reselect_Offset = 0 dB

Temporary_Offset = 0 dB

Penalty_Time = 0 (20 s)

Cell_Reselect_Hysteresis = 6 dB





1 · 2 · 13








1 · 2 · 14

End of ModuleIdle Mode (Re)Selection





Module 3Radio Measurements Principles








GSM B11 · BSS B11 Radio Fine Tuning IntroductionB11 Radio Fine Tuning · Radio Measurements Principles

1 · 3 · 2

Blank Page




Document History





1 · 3 · 3

Module Objectives


Describe the Radio Measurements Principles List the associated parameters





1 · 3 · 4







1 · 3 · 5

Table of Contents


1 Radio Measurements 72 Radio Measurement Data Processing 20





1 · 3 · 6








1 · 3 · 7

1 Radio Measurements





1 · 3 · 8


Radio Measurement Mechanisms

MS connected (TCH or SDCCH) The serving cell gives the MS the list of the neighbor cells to listen to Every SACCH, the MS reports to the serving cell via a measurement

report message: Received level of 6 best cells

(which can change) DL level and quality

of serving cell

Best cellBest cell

B est cell Bes t c ellC ell

C ell

Best cell

Cell

Best cell

Se

rvin

g cell

SYS_INFO_5message (list)

MS reporting

The BTS sends a SYS_INFO_5 message that contains the list of neighbor cells for connected mode (The SYS_INFO_2 message contains the list of neighbor cells for idle mode).

Sys info 2bis, 2ter, 5bis and 5ter are also used for multiband networks.

MS reporting depends on EN_INTERBAND_NEIGH and on MULTIBAND_REPORTING parameters. The MS may report:

6 strongest cells of any band (MULTIBAND_REPORTING=0), or

5 strongest cells of the serving band + 1 strongest cell of another band (MULTIBAND_REPORTING=1), or

4+2 (MULTIBAND_REPORTING=2), or

3+3 (MULTIBAND_REPORTING=3).

RXLEV

Range: [-110dBm, -47dBm]

Binary range: [0, 63]; 0=-110dBm, 63=-47dBm

The higher the physical or binary value, the higher the receiving level

RXQUAL

Range: [0.14%, 18.10%]

Binary range: [0, 7]; 0=0.14%, 7=18.10%

The lower the physical or binary value, the lower the bit error rate, the better the quality

0-2=excellent; 3=good; 4=ok; 5=bad; 6=very bad; 7=not acceptable





1 · 3 · 9


Radio Measurement Mechanisms [cont.]

For each MS connected to the BTS (TCH or SDCCH) UL received level and quality is

measured every SACCH The Timing Advance (TA) is

computed The UL information is gathered

into the measurement report This is the message result sent by

the BTS to the BSC

BSC

MS

DL measurements

U

L+DL measurements

BTS

Measurementreport

Measurementresult

Candidate cellevaluation

MeasurementsActive channelpreprocessing

Candidate cellevaluationHO & PCdecision

Candidate cellevaluation

PC execution

HO execution

The BSC is computing algorithms usually using average value (sliding window) of these measurements

The BTS starts sending MEASUREMENT RESULT messages as soon as it receives the RL ESTABLISH INDICATION message from the MS.

The BTS stops sending MEASUREMENT RESULT messages upon receipt of one of the two following messages: DEACTIVATE SACCH RF CHANNEL RELEASE

Every SACCH multiframe, the BTS: receives the MEASUREMENT REPORT message from the MS. For power control and handover algorithms, this message

contains downlink measurements and, in the layer 1 header, the power used by the MS. does uplink measurements. reports the uplink and downlink measurements to the BSC in the MEASUREMENT RESULT message. Input flows

Uplink radio signal: radio signal received on the Air interface. BS_TXPWR_CONF: BS transmit power currently used by the BS. DTX_DL: indicator of downlink DTX use.

Output flows: Abis MEASUREMENT RESULT message Internal flows:

Radio measurements. Air MEASUREMENT REPORT message (DL) containing DL MS radio measurements. Uplink radio measurements (quality and level) and a flag indicating whether DTX was used in the downlink (DTX/DL). Timing advance: last TA calculated by the BTS. MS_TXPWR_CONF: last reported value of MS power (reported by the MS). BS_TXPWR_CONF: value of the BS transmit power currently in use. BFI_SACCH: bad frame indicator of the SACCH block produced every SACCH multiframe (# 480ms):

0 = SACCH frame successfully decoded 1 = SACCH frame not successfully decoded





1 · 3 · 10


Structure of a Measurement Result

CHAN_NUMBER_IEID

FREQ(5) / BSIC(5) / RXLEV_NCELL(6)

Meas_result_number_IEIDMeas_result_numberElement IdentifierLength

{2} / RXLEV_UL_SUB_{2} / RXQUAL_UL_FULL / RXQUAL_UL_SUBBS_POWER_IEID{3} / BS_POWERElement IdentifierMS_TXPWR_CONF / R{3}TOA / R{2}Element IdentifierLengthLength

BA_USED / DTX_UL / RXLEV_DL_FULL0 / MEAS_VALID / RXLEV_DL_SUB0 / RXQUAL_DL_FULL / RXQUAL_DL_SUB / NO_NCELL_MNO_NCELL_M / RXLEV_NCELL(1)FREQ(1) / BSIC(1)BSIC(1) / RXLEV_NCELL(2)RXLEV_NCELL(2) / FREQ(2) / BSIC(2)BSIC(2) / RXLEV_NCELL(3)RXLEV_NCELL(3) / FREQ(3) / BSIC(3)BSIC(3) / RXLEV_NCELL(4)

0 / Message Type{7}

RXLEV_NCELL(5) / FREQ(5)


SACCH_BFI / DTX_DL{1} / RXLEV_UL_FULL

CHANNEL_NUMBER


MSG_TYPEMSG_DISK

TI {4} / Prot. Disc{4}

BSIC(4) / RXLEV_NCELL(5)

FREQ(6) / BSIC(6)

L1 Info

L3 Info:

Measurementreport from

the MS

Basically, the MEASUREMENT RESULT message is composed of:

L1 info: SACCH Layer 1 header containing MS_TXPWR_CONF and TOA.

L3 info: MEASUREMENT REPORT from the MS. This message contains the downlink measurements and neighborcell measurements.

Uplink measurements performed by the BTS.

BTS power level used.

SUB frames correspond to the use of DTX:

if the mobile is in DTX, the rxlevsub or rxqualsub is used to avoid measuring the TS where there is nothing to transmit in order not to distort measurements.

else rxlevfull is used that is to say all TSs are measured.

MS TXPOWER CONF: which is the actual power emitted by the MS.

TOA is timing advance.

SACCH BFI: bad frame indicator; 2 values 0 or 1; 0 means that the BTS succeeded in decoding the measurement report.

How the neighbor cells are coded:

BCCH1 index in BA list / BSIC1; BCCH2 index in BA list / BSIC2

why? because it does not receive LAC/CI (too long) but BCCH and replies with BCCH/BSIC





1 · 3 · 11


Extended Measurement Reporting (EMR)

Extended Measurement Reporting mechanisms Extended Measurement

Order includes the MAFA frequencies the MS is asked to measure

EMO sent once to the MS on SACCH after TCH seizure

Extended Measurement Results include the average signal level measured on each MAFA frequency over one SACCH mf duration

EMR received once per call on SACCH

Channel Activation Acknowledge

Assignment RequestPhysical Context Request

Physical Context Confirm

Channel Activation (TCH)(EMO included)

TCH ESTABLISHMENT

TCHAssignment Complete

Assignment CompleteAssignment Complete

SACCH

SACCH

SACCH

SACCH

SACCH (EMO)(MAFA Freq. List)

SACCH (EMR)(MAFA Freq. RxLev)

TCH ASSIGNMENT (OC or TC)

MS BTS BSC MSC

When the BTS receives a CHANNEL ACTIVATION with the Extended Measurement Order (EMO) included, it must send this information on the SACCH to the corresponding mobile only once.

When the BTS has to send this information, it must replace the sending of system information 5, 5bis, 5ter or 6 by this information. At the next SACCH multiframe, the BTS must resume the sending of this system information by the replaced one.

The EMO must be sent after 2 complete sets of SYS_INFO5 and 6, i.e. after the 2nd SYSINFO 6 after the reception of SABM. This guarantees the MS has received a complete set.

Then, the BTS normally receives from the MS an EXTENDED MEASUREMENT RESULT with the level of the frequencies to monitor. The BTS must make the correlation between these levels and the frequencies contained in the latest EMO information, after having decoded them, according to the order of the ARFCN. The ‘EXTENDED_MEASUREMENT_RESULT’ is NOT forwarded to the BSC, instead a ‘MEASUREMENT_RESULT’ with indication ‘no_MS_results’ is sent to the BSC.

In particular, the BTS must identify the level of the BCCH frequency of the serving cell (which must always be part of the frequencies to monitor) and apply it as the RXLEV_DL in the Radio Measurement Statistics. The other frequencies will be considered in the same way as the BCCH frequency of neighbor cells: they will be linked to the neighbor level and C/I statistics.





1 · 3 · 12


Repeated SACCH and Repeated DL FACCH B11

Optional feature EN_REP_DL_FACCH EN_REP_SACCH

Available only for AMR calls Whatever the type of AMR FR or HR NarrowBand or WideBand

Gains Repeated SACCH: Extended Coverage & reduction of call drops Repeated DL FACCH: Improves handover reliability of AMR calls

MS 3GPP release Repeated SACCH is only supported by Rel 6 MS Repeated DL FACCH is mandatory for Rel 6 MS, but can be applied to legacy

MS

Improved voicecoverage with AMR

Signaling coverage

Call drop

Improved coveragewith RepeatedFACCH/SACCH

When AMR speech codecs were introduced, the same ACCH (Associated Control Channels) as those used for traditional TCH/FR and TCH/EFR were re-used The consequence is that, in poor radio conditions, the more protected AMR speech codecs have now better performance (in terms of error rate) than the associated control channels. This results in an imbalance between voice and signaling.

The SACCH is used mainly for the transmission of the radio measurement data. SACCH is also used for SMS transfer during a call.

The BTS sends cell specific information (periodically SYS_INFO 5, 5bis, 5ter, 6) to the MS using SACCH.

A FR TCH uses one TS per TDMA frame, for each frame of the multiframe, except the frames 12 and 25. The TDMA frame 12 is used to carry the SACCH and the TDMA frame 25 is an idle frame.

The SACCH multiframe / block is composed of four SACCH frames/bursts; thus the SACCH period is equal to 480ms.

The FACCH is associated with a TCH, and is required to support the high-speed signaling needed during call establishment, and HO management.

The occurrence of the FACCH is not fixed in the multiframe, as it is for the SACCH Rather, the FACCH occurs on a TDMA frame that is reserved for a TCH.

The multiplexing of TCH and FACCH is possible by means of the frame stealing. This means that a speech frame carried over a TCH can be replaced by a FACCH frame.

Additional flag: REP_DL_FACCH_LEGACY_SUPPORT

0: repeated DL FACCH enabled only for the AMR mobile stations having indicated the support of the feature by repeated ACCH Capability bit = 1

1: repeated DL FACCH enabled for all AMR mobile stations

This parameter is relevant only if repeated downlink FACCH (EN_REP_DL_FACCH) is enabled.

Function available on BSC Evolution only.

The value 1 is used to tackle early implementations, ie for MS with repeated ACCH Capability bit=0 or MS without Repeated ACCH Capability bit (legacy MS).





1 · 3 · 13


Repeated DL FACCH: principle B11

Each DLFACCH frame is sent twice with exactly the same content In case of these 2 DLFACCH frames are not decoded, they are soft-

combined to succeed the decoding

FACCH n FACCH n+1

40ms

TCH

frame

TCH

frame

FA

CC

H n

+2

,1

TCH

frame

FA

CC

H n

+1

,2

TCH

frame

TCH

frame

FA

CC

H n

+3

,1

TCH

frame

FA

CC

H n

+3

,2

TCH

frame

TCH

frame

FA

CC

H n

+1

,2

TCH

frame

FA

CC

H n

+1

,1

TCH

frame

TCH

frame

FACCH

n,2

TCH

frame

FACCH

n,1

TCH

frame

ok

Nok

Nok

Nok

ok

NO

K

okok

FACCH n+2 FACCH n+3

FACCH n+3,2

FACCH n+3,1

Soft Combining

Rel-6 MS

TDMA Multiframe

AMR call

LAPDm

BTSFACCH n+4

FACCH n+4,2FAC

CH

n+4

,1

outcome of

the decoding process

In case of TCH/FR the transmission of the repeated FACCH is done by leaving one TCH frame between the two LAPDm frames.





1 · 3 · 14


Repeated DL FACCH: dynamic activation B11

The FACCH frame is effectively repeated if EN_REP_DL_FACCH = 1 or 2 AND AMR codec mode request (CMR) ≤ REP_DL_FACCH_THRES_AMR_XX XX = FR or HR or WB

codec threshold

FACCH N

Repeated FACCH N

4,75 kbit/s

5,90 kbit/s

7.95 kbit/s

10,2 kbit/s

CM

R

EN_REP_DL_FACCH = 1: enabled for LAPDm command frames.

EN_REP_DL_FACCH = 2: enabled for LAPDm command frames, and also for LAPDm response frames (valid only for the MS having indicated the support of the feature by Repeated ACCH Capability bit=1).

Dynamic activation is done as long as codec mode request CMR <= REP_DL_FACCH_THRES_AMR_XX.





1 · 3 · 15


Repeated DL SACCH: principle B11

If the MS can not decode correctly a DL SACCH, the BTS will resend it To indicate to the BTS the DL SACCH has to be repeated, the MS set the

SRR bit to 1 in the UL SACCH frame

480ms

SAC

CH

n+2

SAC

CH

n+3,1

SAC

CH

n+3,2

SAC

CH

n+4

SAC

CH

n+1,2

SAC

CH

n+1,1

SAC

CH

n

Rel-6 MS

TDMA Multiframe

LAPDm

BTS

SAC

CH

SAC

CH

SRR=1

SAC

CH

SRR=1

SAC

CH

SAC

CH

SRR=1

SAC

CH

Soft CombiningSoft Combining Soft CombiningSoft CombiningSoft CombiningSoft Combining

Rel-6 MSoutcome of

the decoding process

UL

DL

SRR: SACCH Repetition Request





1 · 3 · 16


Repeated UL SACCH: principle B11

If the BTS can not decode correctly a UL SACCH, the MS will resend it To indicate to the MS the UL SACCH has to be repeated, the BTS set the

SRO bit to 1 in the DL SACCH frame480ms

SAC

CH

n+2,1

SAC

CH

n+1,1 SR

O=1

SAC

CH

n,1

Rel-6 MS

LAPDm

BTS

SAC

CH

m+1,2

SAC

CH

m+1,1

SAC

CH

m,1

SACCH f

Rel-6 MS

outcome of

the decoding processinBTS

SACCH m

+7,1

SRO: SACCH Repetition Order





1 · 3 · 17


Repeated SACCH: dynamic activation B11

RDSACCH dynamic activation: The RDSACCH is activated if at least 3 SRR bits set to 1 have been received in the

decision window Decision window size = 10 successive UL SACCH periods

Inversely RDSACCH is deactivated if less than 3 SRR bits set to 1 have been received in the decision window

Additionally, RDSACCH is also activated when UL RLT counter (S) becomes inferior or equal to a given value RADIOLINK_REP_DL_SACCH See Radio Link Supervision part

Similar principle for RUSACCH dynamic activation (see comment)

YES

NO

RDSACCHActivted?

3/102/102/103/104/105/106/106/106/95/85/75/64/53/42/31/20/1SRR Sum

11000000100111110SRR

Value

1716151413121110987654321SACCH Period

YES

NO

RDSACCHActivted?

3/102/102/103/104/105/106/106/106/95/85/75/64/53/42/31/20/1SRR Sum

11000000100111110SRR

Value

1716151413121110987654321SACCH Period

RUSACCH is activated if at least 3 UL SACCH messages have not been correctly received before combining in a window whose size is equal to 10 successive UL SACCH periods (inversely RUSACCH is deactivated if less than 3 UL legacy SACCH messages have not been correctly received before combining in the window, note this means the BTS always try to first decode the SACCH before any combining).

At call start, RUSACCH is disabled by default. At the beginning of the call, the decision window is reduced to the number of elapsed SACCH periods but the threshold remains the same.

Note this means the state of RUSACCH activation is updated in every SACCH period.





1 · 3 · 18


Exercise 1

(BSIC, BCCH index)/(LAC, CI) problem

As LAC and CI information take up too much space, the MS only reports the decoded BSIC and the BCCH index when it sends measurement on theadjacent cell. The BSC makes the correspondence between the couple (BSIC, BCCH index)

and the real neighbor cell concerned [completely defined by (LAC,CI)]. WHAT IS THE RISK?

Time allowed:

5 minutes





1 · 3 · 19


Exercise 2

Explain why cell 2 has a very high outgoing HO unsuccessful rate and a high call drop.

Cell 2

Cell 1

Cell

(7, 62)

CI=1964GSM900

Cell 3

CI=6169GSM900

(7, 62)

(3, 46)

Cell

CI=6169GSM900

2006





1 · 3 · 20

2 Radio Measurement Data Processing





1 · 3 · 21


Name of No Level

BSC

Active ChannelPre-processing

BTS

Radio LinkMeasurements

Assignment of radio measurements data processing functions in the ALCATEL BSS

The active channel pre-processing function calculates average values of signal levels, qualities and timing advance provided by the radio link measurements function.

The pre-processing is based on a sliding window averaging technique. The averaging is either weighted or unweighted depending on the type of the input parameters.





1 · 3 · 22


Active Channel Pre-Processing

Active channel pre-processing

ACTIVATED EACH TIME A MEASUREMENT IS RECEIVED

AVERAGING VALUES OF SIGNAL LEVELS, QUALITIES, TIMING ADVANCE USING “SLIDING WINDOW” TECHNIQUE

BUILDING A BOOK-KEEPING LIST OF neighbor CELLS The MS is reporting the 6 best cells at one time They can change from 1 measurement to another Maximum for 1 call: last 32 best ones (among 64 maximum declared as neighbor)





1 · 3 · 23


Active Channel Pre-Processing - Principles

HANDLED by the BSC ACTIVATED when the BSC receives: ESTABLISH INDICATION from the MS on SAPI 0, or HANDOVER FAILURE from the MS, or ASSIGNMENT FAILURE from the MS (in case of intracell handover)

STOPPED when a HANDOVER COMMAND is emitted in the serving BSC

AVERAGING VALUES OF SIGNAL LEVELS, QUALITIES, TIMING ADVANCE USING “SLIDING WINDOW” TECHNIQUE

BUILDING A BOOK-KEEPING LIST OF neighbor CELLS

The pre-processing function is stopped when a HANDOVER COMMAND is emitted by the serving BSC. At this time, the MEASUREMENT RESULT messages are ignored by the pre-processing function and no update of the book-keeping tables or averaging is done anymore.

The pre-processing function is enabled again (in case of failure of an intracell or intercell handover) after reception of either messages listed above, and the old measurements are kept in the book-keeping list and taken into account in the new averaging.

The pre-processing function is completely handled by the BSC. The input parameters of this function are provided by the BTS every SACCH multiframe in the MEASUREMENT RESULT message.

The function calculates average values of levels, qualities and timing advance. The pre-processing method is based on a sliding window averaging technique. The pre-processing is done for every measurement sample, i.e. every SACCH multiframe. The averaging intervals are expressed in terms of SACCH multiframe periods and their range is between 1 and 31.

The averaging process for any variable can start as soon as A_YYYY_XX (YYYY stands for “LEV”, “QUAL”, “PBGT”or “RANGE” and XX for “HO”, “DR”, “PC” or “MCHO”) samples, each with MEAS_VALID bit set to 0 (validity indicator reported by the MS in the MEASUREMENT REPORT message), are actually available except in case of the averaging of the received level from the neighbor cells and the averaging of AV_RXLEV_PBGT_HO, AV_BS_TXPWR_HO and AV_BS_TXPWR_DR.





1 · 3 · 24


Measurement Averaging

Avoid reacting too early to some “atypical” measurements

75.00

80.00

85.00

90.00

95.00

100.00

105.00-------

The calculation of levels, qualities and timing advance (i.e. distance information) uses a variety of averaging window sizes as well as specific weighting factors for quality estimates.

One separate window exists for:

power control on the uplink and the downlink (A_LEV_PC , A_QUAL_PC),

emergency handover (A_LEV_HO , A_QUAL_HO , A_RANGE_HO),

fast emergency handover for microcells (A_LEV_MCHO),

better cell handover and better zone handover (A_PBGT_HO) for intra-layer, interlayer and interzonehandovers,

forced directed retry (A_PBGT_DR),

neighbor filtering and ranking for all HOs (A_PBGT_HO),

codec adaptation (A_QUAL_CA_HR_FR , A_QUAL_CA_FR_HR).





1 · 3 · 25


Measurement Averaging [cont.]

Objective: average measurements to avoid reacting to transient degradation Principle: sliding window: level/quality/distance values are averaged for N

last samples N = A_LEV_HO samples for uplink and downlink level N = A_QUAL_HO samples for uplink and downlink quality N = A_RANGE_HO samples for distance N = A_PGBT_HO for level used in power budget equation

Example (A_LEV_HO=6, A_QUAL_HO=4, A_PBGT_HO=8)

Experiences some experiments have shown that the number of HOs is very sensitive to

modification of these values

DL Level

AV-RxLev

AV-Lev-PGBT

DL Qual

AV-RxQual

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24Meas

2 3 3 4

3

7

4

-95

7

5

-99-90 -92 -93 -98 -100 -98 -90 -80

-97 -96 -94

-95 -94

7 5 2

6 7 5

-75 -72 -71 -110 -70

-90 -86 -81 -83 -80

-92 -89 -86 -87 -83

1 1 0 6 0

4 2 1 2 2

-69

-78

-80

0

2

-68 -78 -88 -95

-77 -78 -81 -78

-77 -77 -78 -81

0 0 1 2

2 0 0 1

-98

-83

-85

3

2

-100 -110 -110

-88 -95 -100

-83 -88 -93

6 7 7

3 5 6

-110

-104

-99

7

7

At BSC level, Input flows

MEASUREMENT RESULT Control flows

active channel pre-processing configuration parameters for PC: A_LEV_PC, W_LEV_PC, A_QUAL_PC and W_QUAL_PC,

active channel pre-processing configuration parameters for HO: A_LEV_HO, W_LEV_HO, A_PBGT_HO, W_PBGT_HO, A_QUAL_HO, W_QUAL_HO, A_RANGE_HO, A_LEV_MCHO,

W_LEV_MCHO, A_PBGT_DR. cells list for book-keeping:

BA_IND_SACCH: indicator of the change of the BA_allocation, NBR_ADJ: number of declared adjacent cells of the serving cell denoted by n, for n=1 to NBR_ADJ: BSIC(n) and FREQ(n).

Output flows Averaged measurements for power control:

AV_RXQUAL_UL_PC ; AV_RXLEV_UL_PC: MS power control/threshold comparison, AV_RXQUAL_DL_PC ; AV_RXLEV_DL_PC: BS power control/threshold comparison.

Averaged measurements for handover detection: AV_RXQUAL_UL_HO, AV_RXQUAL_DL_HO, AV_RXLEV_UL_MCHO, AV_RXLEV_UL_HO, AV_RXLEV_DL_HO, AV_RXLEV_DL_MCHO, AV_LOAD , averaged traffic load AV_BS_TXPWR_HO, AV_RANGE_HO, AV_RXLEV_PBGT_HO, AV_RXLEV_NCELL(n), AV_RXLEV_NCELL_BIS(n). AV_RXLEV_PBGT_DR, AV_RXLEV_NCELL_DR(n), n=1..BTSnum. BFI_SACCH AV_RXQUAL_xx_CA_HR_FR, AV_RXQUAL_xx_CA_FR_HR

MS_TXPOWER_CONF / BS_POWER: last power level reported by the MS and transmit power currently used by the BS.





1 · 3 · 26


Neighbor Cell Measurement Book-Keeping

BUILDING A BOOK-KEEPING LIST OF neighbor CELLS The MS reports the measurements of the NO_NCELL_M ( 6) best cells every

multi-frame The adjacent cells reported by the MS can change from one measurement to

another The book-keeping function keeps a table of the last 32 reported adjacent

cells Clearing process of non-reported neighbors during 10s (signal level=0)

An MS is required to measure the BCCH power level of a number of BCCH frequencies. These measurements are used for the power budget computation in the BSC and the candidate cell evaluation in the BSC.

The MS reports to the BTS, in the MEASUREMENT REPORT message, the measurements of the NO_NCELL_M (NO_NCELL_M <= 6) best cells it receives (RXLEV_NCELL, BCCH frequency index and BSIC number) for each multiframe. In case of multiband capability, the mobile reports the best cells of each supported frequency band (if available). This reporting is allowed at BSS level by the flag EN_INTERBAND_NEIGH and it is specified by the parameter MULTIBAND_REPORTING.

The adjacent cells reported by an MS can change over the averaging interval. The book-keeping function keeps a table composed of the last 32 reported adjacent cells, the maximum number of which is NBR_ADJ. The total number of adjacent cells for which measurements reported by the MSs are available within the average interval is BTSnum.

The BSC G1 maintains a table of up to 150 cells, from which up to 64 can be declared as adjacent cells to a given cell.

The BSC G2 maintains a list of up to 1000 cells, from which up to 64 can be declared as adjacent cells to a given cell.

Because the maximum number of adjacent cells may be greater than 32, the number of adjacent BCCH frequencies is limited to 32. Moreover, a mechanism for overwriting obsolete entries in the book-keeping table, when new cells are reported, is provided.

When the variable BTSnum reaches its maximum value of 32 and at least one new cell has to be entered in the list, then the BSC sorts out all cells in the book-keeping list, which have been reported with signal level = 0 forthe last 20 measurements (10 seconds).

This is done by summing the raw measurement values over the last 20 samples. All the corresponding cell entries are cleared from the bookkeeping list, BTSnum is decreased by the number of cleared entries and some of the vacant entries are used to include the new cells.

The end of the comment is on the next page...





1 · 3 · 27


Exercise

Measurements averaging With ‘averaging window’

excel sheet: Compute averaging on quality,

distance and level Make charts with different sliding

averaging windows

Time allowed:

10 minutes

Raw measurements

Average measurements

AV_RXLEV_DL_HO

A_LEV_HO=8

A_LEV_HO=2

2 3 4 5 6 7 8 9 10 11 12 13 14 151-75

-80

-85

-90

-95

Number ofmeasurements

Level

AV_RXQUAL_DL_HO

3

A_QUAL_HO=8

A_QUAL_HO=2

2 3 4 5 6 7 8 9 10 11 12 13 14 151

4

3

2

1

0

Quality

AV_RANGE_HO

10

12

15

A_RANGE_HO=8

A_RANGE_HO=2

2 3 4 5 6 7 8 9 10 11 12 13 14 151

25

20

15

10

5

Distance

DL LevelA_LEV_HO=8A_LEV_HO=4A_LEV_HO=2

DL LevelA_QUAL_HO=8A_QUAL_HO=4A_QUAL_HO=2

DL LevelA_RANGE_HO=8A_RANGE_HO=4A_RANGE_HO=2

-80

2

10

-78

2

11

-84

3

9

-87

3

11

-80

2

13

-75

1

12

-77

4

14

-94

4

15

-79

3

16

-77

1

17

-78

2

18

-84

3

17

-89

3

19

-90

3

20

-91

4

19

DL Level

DL Quality

Distance

-80

-76

-82

-82

-86

-82

-81

-87

-82

-82

-78

-81

-82

-78

-81

-80

-81

-82

-82

-87

-84

-85

-90

-85

-89

-91-81

-82

-86

-82

-84

-82

-78-79A_LEV_HO=4



32

3

32

3

33

3

33

4

33

4

33

4

33

2

33

2

3

3

2

2

3

32 3

A_QUAL_HO=4 3

13

14

16

13

16

17

15

17

18

15

17

18

16

18

18

17

19

20

18

19

20

11

12

11

13

13

13

14

11 10

A_RANGE_HO=4 10

Fill up the table with average function. The chart will be automatically processed

The fact that there may not be enough cleared entries to store new measurements is excluded, see justification below:

Because the MS must resynchronize at most every 10s with the neighbor cells it monitors, it is useless to keep cells in the book-keeping list which have not been reported for more than 10s, it will be impossible to make a handover towards these cells.

Therefore, the overwriting mechanism described above will function correctly if there are less than 32 cells reported in every 10s, which makes an average rate of 3 new cells per second.

The potentiality of overflow of the book-keeping list is therefore excluded.

The book-keeping is performed according to the BSIC and BCCH frequency couple. This function updates the table every multiframe except if the measurement report is missing or Measurement Valid Bit is set to not valid. When the level of a cell is not reported, a zero must be entered as measurement value. For each multiframeand for each of the NO_NCELL_M cell measurements it receives, the function has to check the BSIC number and the BCCH frequency index (FREQ(n)).

When the couple (BSIC, BCCH frequency) is not in the reference list (received from the OMC), the corresponding measurements should be discarded.

The BTSnum variable is updated every multiframe except if the measurement report from the MS is missing. It is incremented by the number of new couples (BSIC number, BCCH frequency index) registered as described above.

Remark: Two cells can have the same BSIC number or the same BCCH frequency index. Therefore, the couple of these parameters is needed to define a cell.





1 · 3 · 28








1 · 3 · 29

End of ModuleRadio Measurements Principles





Module 4Radio Link Sup and Power Control








GSM B11 · BSS B11 Radio Fine Tuning IntroductionB11 Radio Fine Tuning · Radio Link Sup and Power Control

1 · 4 · 2

Blank Page




Document History





1 · 4 · 3

Module Objectives


Describe Radio Link Supervision and Power control algorithms List the associated parameters





1 · 4 · 4







1 · 4 · 5

Table of Contents


1 Radio Link Supervision 72 Power Control 18





1 · 4 · 6








1 · 4 · 7

1 Radio Link Supervision





1 · 4 · 8


Functional Entities

Assignment of PC functions in the ALCATEL BSS

BSCBTS

Radio LinkSupervision

PC CommandPC ThresholdComparison

Radio LinkCommand



The two main functions specified in this document and implemented in the Alcatel-Lucent BSS are:

Radio link supervision and radio link command:

These functions handle the detection of the radio link failure so that calls which fail either from loss of radio coverage or unacceptable interference are satisfactorily handled by the network. The radio link supervision is responsible for detection of the loss of the radio link, based on incorrectly received SACCH frames. The radio link command is responsible for commanding to set the power at a maximum level for radio link recovery or to clear the call when the radio link has failed.

The radio link recovery can be activated or not, depending on a configuration flag (EN_RL_RECOV). The radio link failure procedure is always running and clears the call when the radio link has failed.

Power control:

This function handles the adaptive control of the RF transmit power from the MS and the BS. The RF power control aims at minimizing the co-channel interference and also at reducing the DC power consumption of the MS. This function is in charge of detecting a need for a power command and then of applying this power command. Therefore it can be divided into two processes: PC threshold comparison and PC command. MS and BS power control are operating independently, they can be activated or not, depending on configuration flags (EN_MS_PC and EN_BS_PC).

All these functions require directly or indirectly input parameters provided by the function in charge of the radio link measurements.

Most of the input data required by the power control functions are provided by the Active channel pre-processing function.

The figure depicts in a general way:

the interconnections between all these functions,

the implementation of these functions in the Alcatel-Lucent BSS.





1 · 4 · 9


Principles

Detection (by BTS) of a radio link failure with an MS notification to BSC for radio resource release

Try to recover an MS when radio becomes poor optional mechanism “radio link recovery” by requiring BTS and MS to transmit at maximum power

Equivalent mechanism in MS for Radio Link Failure detection

The determination of the radio link failure is based on a counter. According to the GSM Technical Specification 05.08 for the BSS, the criterion for incrementing/decrementing this counter should be based:

either on the error rate on the uplink SACCH,

or on RXLEV/RXQUAL measurements of the MS.

In the Alcatel-Lucent BSS, it is based on the number of SACCH frames which cannot be decoded.

It must be stressed that this criterion is related to the first one recommended above but it is not exactly the same. The Alcatel-Lucent criterion is in fact the one recommended by the GSM Technical Specification 05.08 for the MS.





1 · 4 · 10


Principles [Cont.]

For each active radio channel, a counter “S” is: decremented by 1 each time an SACCH frame cannot be decoded (BFI=1) incremented by 2 each time a valid SACCH frame is received

There is one counter “S” at MS side and another one at BTS side The value of S gives a measure of the “quality” of uplink radio link

The initial value of S is RADIO_LINK_TIMEOUT_BS (at BTS side) and RADIO_LINK_TIMEOUT (at MS side) if S reaches N_BSTXPWR_M, a radio link recovery is triggered (optional) if S reaches 0, a radio link failure is detected

RADIOLINK_TIMEOUT_BS RADIOLINK_TIMEOUT is important because the mobile must release the radio channel first

New Radio link Timeout parameters has been introduced for AMR MSs RADIO_LINK_TIMEOUT_BS_AMR RADIO_LINK_TIMEOUT_AMR

The radio link supervision function is performed in the BTS and it uses three parameters given to the BTS in the TRX configuration data message:

EN_RL_RECOV: flag enabling/disabling the sending of CONNECTION FAILURE INDICATION by the BTS when the need for radio link recovery is detected.

N_BSTXPWR_M: threshold for the radio link recovery.

RADIOLINK_TIMEOUT_BS: threshold (number of SACCH messages) for the radio link failure.

RADIOLINK_TIMEOUT_BS_AMR: threshold (number of SACCH messages) for the radio link failure of calls using an AMR codec.

In addition, the function handles a counter named S. RADIOLINK_TIMEOUT_BS is the initial and maximum value of S.

For each SACCH not decoded, S is decremented by 1 while for each SACCH decoded, it is incremented by 2. The incrementation or decrementation is performed if the following condition is met: RADIOLINK_TIMEOUT_BS(_AMR) >= counter S >= 0.

As soon as the counter S is equal to the threshold N_BSTXPWR_M, the radio link recovery is triggered if EN_RL_RECOV = ENABLE. Therefore, in the case where the shadowing is so strong that all SACCH frames are lost, the radio link recovery will be triggered after (RADIOLINK_TIMEOUT_BS(_AMR) - N_BSTXPWR_M) SACCH periods.

The parameter N_BSTXPWR_M must be set according this simple behavior.

If the radio link recovery is not successful, as soon as S reaches 0, the radio link failure procedure is applied.

As soon as a radio link failure is detected, the radio link supervision must be started again in the BTS.





1 · 4 · 11


Principles [Cont.]

SACCHnumber

S value

29282726252423222120191817161514131211109876543210

5

10

15

20

25

RADIO_LINK_TIMEOUT_BS

N_BSTXPWR_M

SBFI

S = f [ BFI(t) ]

1

Received Events

Activate supervision: activation of the radio link supervision from the BTS telecom layer 3,

SACCH, BFI = 1: not decoded SACCH frame,

SACCH, BFI = 0: decoded SACCH frame.

Note: the BFI flag is internal to the BTS and does not deal with the BFI flag defined by the GSM.

Deactivate supervision: deactivation of the radio link supervision by the BTS telecom layer 3.

Transmitted Events

Radio link recovery: indication sent to the radio link command function in order to set the BS and MS powers to the maximum.

Radio link failure: indication sent to the radio link command function in order to release the call.

These events are sent to the BSC in the CONNECTION FAILURE INDICATION message:

In case of Radio link recovery, the BTS sends only once (to avoid overload of the Abis interface) the CONNECTION FAILURE INDICATION message to the BSC with cause "set MS/BS-TXPWR-M” (value: '001 1111', reserved for National use). This action (message formatting) is performed by the GSM layer 3.

In case of Radio link failure, the BTS sends the CONNECTION FAILURE INDICATION message with cause 'Radio link Failure' to the BSC.

Thus, the CONNECTION FAILURE INDICATION message on Abis is not showing any call drop. One should look at the cause of CONFAIL.





1 · 4 · 12


Principles [Cont.]

RLT = 18

RLT_AMR = 18 AMR an non AMR Call Drop

Start of AMR communication

Audio degradation

Start of non AMR communication Audio degradation

VQ improvment

provided by AMR

Non AMR Call DropRLT = 18RLT_AMR = 26

AMR Call Drop

Start of non AMR

communication Audio degradation

Start of non AMR

communication Audio degradation


Audio degradation


Audio degradation

Extension of the degradation period





1 · 4 · 13


AMR call B11

2 different mechanisms in case of AMR calls Either usage of specific threshold: RADIOLINK_TIMEOUT_BS_AMR if AMR is used AND RSACCH is NOT activated (EN_REP_SACCH = Disabled) OR RDFACCH is NOT activated (EN_REP_DL_FACCH = Disabled)

Or usage of RADIOLINK_TIMEOUT_BS if Repeated SACCH (RSACCH) is activated AND Repeated Downlink FACCH (RDFACCH) is activated THEN S is decremented by 1 only after the soft combining DRSACCH is dynamically activated depending on S value (See next slide)

This means that for an AMR call with RSACCH and RDFACCH are both activated, RADIOLINK_TIMEOUT_BS is used.

It may not be enough secured to come back to the RADIOLINK_TIMOUT_BS value when only RSACCH is activated, because RDFACCH improves also the handover in poor radio conditions





1 · 4 · 14


AMR call with RSACCH activated B11

SACCHnumber

S value

29282726252423222120191817161514131211109876543210

5

10

15

20

25

RADIO_LINK_TIMEOUT_BS

N_BSTXPWR_M

SBFI

1

RADIOLINK_REP_DL_SACCH

RLR

RepeadtedDL SACCH





1 · 4 · 15


Radio Link Recovery

The BTS sends a Connection Failure Indication message Cause ‘001 1111’ reserved for national usage (Alcatel-Lucent: RLR) On K1205: “set MS/BS_TXPWR_MAX (Alcatel-Lucent only)”

The BSC sends BS and MS POWER CONTROL messages Required for maximum possible values The MS required level is embedded in the SACCH header in the downlink

Optional mechanism EN_RL_RECOV =ENABLE useless without power control “master” vs. power control

The action consists in increasing the power of the MS and of the BTS to their maximum, in a single step, if the link is failing, i.e. the BTS is not able to decode the SACCH anymore for some period of time.

This functionality is performed upon reception of the CONNECTION FAILURE INDICATION message (cause “set MS/BS-TXPWR-M”) from the BTS. This message can be sent by the BTS only if EN_RL_RECOV = ENABLE. Upon reception of this message, the radio link command function:

1. sends to the BTS a power increase command up to BS_TXPWR_MAX (BS_TXPWR_MAX_INNER if the MS is on the inner zone of a concentric or multiband cell) in the BS POWER CONTROL message.

2. sends to the MS a power increase command up to min(MS_TXPWR_MAX,P) (min (MS_TXPWR_MAX_INNER,P) if the MS is in the inner zone of a concentric or multiband cell) in the message MS POWER CONTROL.

When a radio link recovery occurs, the radio link command function gives an indication to the power control function once the power increase has been commanded.

The maximum power increase of the MS is 2dB per 60 ms. Thus, if MS_TXPWR_MAX=33dBm and MS_TXPWR_MIN=13dBm, the MS coming from MIN to Max will take 600 ms.

Note: the BS Power Control process does not interfere with the recovery procedure since the former comes to a halt when no SACCH multiframe is received. Thus, the BS power control process does not take into account the radio link recovery event.





1 · 4 · 16


Radio Link Failure

The BTS sends a Connection Failure Indication message Cause ‘radio link failure’

The BSC notifies the loss to the MSC Usually Clear Request “radio interface failure”

The BSC releases locally the radio resource (TCH or SDCCH) Radio frequency Channel Release message sent to BTS

The call is dropped!

The task of the radio link command consists in informing the call control function to release the call.

Concentric Cell or Multiband Cell

The power value BS_TXPWR_MAX_INNER is applied in case of radio link recovery for an MS in the inner zone. The power value BS_TXPWR_MAX is applied in case of radio link recovery for an MS on an outer zone channel.

Note: the radio link supervision procedure will function also if SACCH frames are not lost continuously, but with a longer reaction time.





1 · 4 · 17


Exercise

With the “RLS” excel sheet, taking into account the measurements with BFI and the parameter values (N_BSTXPWR_M and RADIOLINK_TIMEOUT_BS), indicate when: A radio link recovery is triggered A radio link failure is triggered

Time allowed:

5 minutes

0

1

1000

01111

1101

0111111101

1

1

0

1

0

1

1

1

1

1

18

5

17181818

1817161514

12111312

1211109876576

10

6

8

17

18

4

11

7

3

13 Radio Link Recovery

BFI S Action

Radio Link Supervision

N_NSTXPWR_MAXRLTO_BS

1318

Parameters:

N_BSTXPWR_M





1 · 4 · 18

2 Power Control





1 · 4 · 19

2 Power Control

Justification

Power Control aims at:

Reducing emitted power to the minimum possible Minimum power levels: GSM: 11dBm, 9dBm, 7dBm and 5dBm DCS: 2dBm, 0dBm

Ensuring quality and received level of peer entity

Power Adaptation in real-time For Uplink PC: decrease UL interference

and save MS battery For Downlink PC, decrease DL

interference

Output Power (dBm)GSM-900

Output Power (dBm)DCS-1800

Powerlevel

14

15

16

17

18

19

15

13

11

9

7

5

2

0

-

-

-

-

BTS MS

Uplink

RXLEV_UL

MS_TXPWRDownlink

BS_TXPWR

RXLEV_DL

The main objective of the power control, in connection with handover algorithms, is to allow a maximum number of MSs to operate in the network while maintaining a minimum interference level.

The algorithms must ensure that any mobile is connected with the cell in which the output powers from the MS and the BS are as low as possible (to reduce MS power consumption and interference in the network) while keeping a satisfactory link quality.

When on a sufficient duration, the propagation conditions keep worsening, then action must be taken.

The first action is to increase the output power levels at the MS or the BS. When the maximum allowed value has been reached, a handover may become necessary.

To reflect this philosophy in macrocells (not in microcellular environment), the algorithm allows for handover on quality and strength reasons only when the last step of power control has been reached. If propagation conditions worsen rapidly when the MS is at low power, the power control algorithm allows to reach quickly the maximum power.

Nevertheless great care must be taken in choosing the relative values of the thresholds for power control and handover as well as the averaging window sizes (smaller window size and higher threshold for power control than for handover). It must be remembered that, although it is desired that the MS transmits with the lowest possible power, it is more important not to lose a call. Thus early triggering for the power control is possible by choosing small values for the averaging window sizes and higher comparison thresholds.





1 · 4 · 20

2 Power Control

Principles

Based on a threshold comparison mechanism

Decrease emitted power when received level AND quality measured by peer entity are better than a given value

Increase emitted power when the received level OR quality is lower than a given value

Does not decrease power if the resulting level is below the low level threshold

FEATURE REAL FAST PC GIVES REACTIVITY TO THE ALGORITHMS

The threshold comparison process detects the need to change the MS power level. This detection is done by comparison between the averaged values produced by the active channel pre-processing function and thresholds.





1 · 4 · 21

2 Power Control

Power Control Detection

MS Power control (for BS PC, replace MS by BS and UL by DL)

U_RXQUAL_UL_P

L_RXQUAL_UL_P

1

2

-95 -93 -85

L_RXLEV_UL_P

POW_RED_STEP_SIZE

U_RXLEV_UL_P

Quality

Level

-90 -75-86

3

2

A need for a PC command is detected when one of the conditions above is true. Then, the information for the execution of the PC command is given to the ‘PC command’ process.

The MS power control function can be disabled with a flag EN_MS_PC. This flag is changeable from the OMC-R.

Note: The GSM coding of quality is contra-intuitive, since the value 0 codes for the best quality and 7 for the worst. Thus, the comparison between two quality values must be understood in the opposite way in terms of quality.

Note: POW_RED_STEP_SIZE is used in two ways: for PC_COMMAND (decrease of MS power) and for PC_THRESHOD_COMPARISON (to avoid ping-pong effect).





1 · 4 · 22

2 Power Control

MS PC Threshold Comparison

MS Power increase: If AV_RXQUAL_UL_PC > L_RXQUAL_UL_P + OFFSET_RXQUAL_FH AV_RXQUAL_UL_PC L_RXQUAL_UL_P + OFFSET_RXQUAL_FH

and AV_RXLEV_UL_PC < L_RXLEV_UL_PThen PC_COMMAND(MS, INC, MS_P_INC dB, <min(MS_TXPWR_MAX, P))

Power decrease: If AV_RXQUAL_UL_PC < U_RXQUAL_UL_P

and AV_RXLEV_UL_PC >= L_RXLEV_UL_P + POW_RED_STEP_SIZE

AV_RXQUAL_UL_PC L_RXQUAL_UL_P + OFFSET_RXQUAL_FHand AV_RXQUAL_UL_PC U_RXQUAL_UL_P and AV_RXLEV_UL_PC > U_RXLEV_UL_P

Then PC_COMMAND(MS, RED, MS_P_RED dB, >MS_TXPWR_MIN)

OFFSET_RXQUAL_FH is an internal variable that is equal to 0 in case of Non-Hopping cell and OFFSET_HOPPING_PC in case of BBH or RH.





1 · 4 · 23

2 Power Control

MS Power Control Command

MS Power command philosophy:

Target received level TARGET_RXLEV_UL middle threshold between U_RXLEV_UL_P and L_RXLEV_UL_P

Adaptive power step size According to the average received level Limited power step size to MAX_POW_INC and MAX_POW_RED If only Quality problem: fixed power step size

POW_INC_STEP_SIZE and POW_RED_STEP_SIZE Two weighting factors to modify the algorithm reactivity when level problem

POW_INC_FACTOR for power increase POW_RED_FACTOR for power decrease

Whenever any of the threshold conditions occurs, a PC command must be sent to the MS over the air interface.

In order to compute the adaptive power step size, the middle threshold between the upper threshold U_RXLEV_UL_P and the lower threshold L_RXLEV_UL_P is considered.

This threshold is regarded as the target received level around which the MS should always stay. The following algorithm tries to maintain and bring the MS power closer to this target threshold. The size of the power step is limited to MAX_POW_INC for an increase of the MS power and MAX_POW_RED for a decrease of the MS power.

When the received level is between the two thresholds U_RXLEV_UL_P and L_RXLEV_UL_P (i.e. no need to change the level) and a power control on quality cause is triggered, fixed power step sizes are applied: POW_INC_STEP_SIZE for power increase and POW_RED_STEP_SIZE for power decrease.

Two weighting factors POW_INC_FACTOR (for power increase) and POW_RED_FACTOR (for power decrease) allow to modify the reactivity of the algorithm (the more POW_INC_FACTOR is nearby 1, the greater the reactivity of the algorithm is and the larger the power step size is).

The target received level is TARGET_RXLEV_UL for the uplink path.

TARGET_RXLEV_UL corresponds to the next higher multiple of 1 dB from (U_RXLEV_UL_P + L_RXLEV_UL_P)/2.





1 · 4 · 24

2 Power Control

Fast and Normal Comparison

Example: Example

4800 960 1440 1920 2400

-110

-100

-90

-80

20 dB

Time(ms)

Power level(dB)

6 dB (POW_INC_STEP_SIZE)

4 SACCH =1 Measurement Report (MR)

MR 2 MR 3 MR 4

Need for PC Command detected

PC Command

Normal Power Control

Fast Power Control





1 · 4 · 25

2 Power Control

MS Power Increase Command Computation

PC_COMMAND (MS, INC, MS_P_INC dB, < power max) If MS_TXPWR < power max

then increase MS_TXPWR by min(MS_P_INC, MAX_POW_INC, powermax-MS_TXPWR) Where MS_P_INC is evaluated by the following algorithm:

if (AV_RXLEV_UL_PC < L_RXLEV_UL_P) (problem of level)if (AV_RXQUAL_UL_PC L_RXQUAL_UL_P + OFFSET_RXQUAL_FH) (sufficient

quality)then MS_P_INC = roundup[ POW_INC_FACTOR* (TARGET_RXLEV_UL -

AV_RXLEV_UL_PC)]else MS_P_INC = roundup[ MAX ( POW_INC_FACTOR * (TARGET_RXLEV_UL -

AV_RXLEV_UL_PC ), POW_INC_STEP_SIZE )]else (problem of quality)

MS_P_INC = POW_INC_STEP_SIZE

In the equations:

MS_TXPWR is the last MS_TXPWR_CONF value reported by the BTS.

‘roundup’ means ‘round to its next higher multiple of 2 dB’.

‘rounddown’ means ‘round to its next lower multiple of 2 dB’.

The rate of change of MS power is required to be one nominal 2 dB step every 60 msec. Thus a 30 dB step change should be accomplished in 900 msec. The operator should be warned of this as it may impact on the choice of settings for MS_P_CON_ACK and MS_P_CON_INT.

Then the ordered value of the MS transmit power, called MS_TXPWR, is sent to the MS as follows:

The BSC sends the MS POWER CONTROL message to the BTS (i.e. to the TRX handling the relevant channel) which then forwards the PC command to the MS in the Layer 1 header.

The MS applies the PC command and confirms this action by transmitting the applied power value (MS_TXPWR_CONF) on the uplink SACCH in the layer 1 header.

On SACCH channel, the MS may not send the MEASUREMENT REPORT message (e.g. in case of transmission of Short Message).

In this case, the BSC receives a MEASUREMENT RESULT message which does not contain the MEASUREMENT REPORT. The BSC takes into account the MS_TXPWR_CONF variable.





1 · 4 · 26

2 Power Control

MS Power Decrease Command Computation

PC_COMMAND (MS, RED, MS_P_RED dB, > power min) If MS_TXPWR > power min

then decrease MS_TXPWR by min(MS_P_RED, MAX_POW_RED, MS_TXPWR-power min) Where MS_P_RED is evaluated by the following algorithm:

if (AV_RXLEV_UL_PC > U_RXLEV_UL_P) (good level)if (AV_RXQUAL_UL_PC U_RXQUAL_UL_P) (sufficient quality)then MS_P_RED = rounddown[ MAX(POW_RED_FACTOR* (AV_RXLEV_UL_PC-

TARGET_RXLEV_UL), 2dB)]else MS_P_RED = rounddown[ MAX ( POW_RED_FACTOR * (AV_RXLEV_UL_PC-

TARGET_RXLEV_UL), POW_RED_STEP_SIZE )]else (good quality)

MS_P_RED = POW_RED_STEP_SIZE





1 · 4 · 27

2 Power Control

Frequency Hopping Cases

OFFSET_RXQUAL_FH

This variable allows to take into account the frequency hopping in the RxQualevaluation (see Annex)

Defined on a per cell basis

Algorithm:If Frequency hopping applied then OFFSET_RXQUAL_FH = Offset_hopping_PC Else OFFSET_RXQUAL_FH = 0

In order to take into account the frequency hopping in the RXQUAL evaluation, the variable OFFSET_RXQUAL_FH is introduced.

If Frequency hopping is applied on the corresponding channel then OFFSET_RXQUAL_FH = Offset_Hopping_PCotherwise OFFSET_RXQUAL_FH = 0

Offset_Hopping_PC is a parameter defined on a per cell basis.

PC Downlink in Frequency Hopping Case

In this case, the BSC inhibits the BS power control on all the channels which use the BCCH carrier. The entity performing the BS power control in the BSC gets all the information concerning a new channel and decides whether to activate the BS power control for this channel. The power control must be inhibited when the frequency used by the new channel is the same as the frequency used for the BCCH in the BTS (cell) in which the channel is activated.

For any channel which has the BCCH frequency in its hopping sequence (MA), the MS is measuring a very good downlink level each time it hops on the BCCH. To avoid that this results in a too optimistic average, it is possible to require from the MS not to include the BCCH measurement in the averages. This is achieved by setting the PWRC flag to 1 in the SYSTEM INFORMATION type 6 message sent by the BSS on the SACCH.

If the channel is hopping only on the BCCH frequency (after a transmitter failure), it is considered as a non-hopping channel and it is concerned by the non-frequency hopping case.





1 · 4 · 28

2 Power Control

Power Control Timers

Timers

T_SDCCH_PC allows the inhibition of PC on SDCCH

When a new power is required, the confirmation is awaited: MS_P_CON_ACK BS_P_CON_ACK

As soon as the new power is acknowledged, a fixed duration is awaited to trigger a new change of power, if necessary: MS_P_CON_INT BS_P_CON_INT

The timer T_SDCCH_PC allows to inhibit the MS and BS power control on SDCCH:

This timer is changeable at the OMC-R level on a per cell basis. It is triggered upon receipt of the ESTABLISH INDICATION message after SDCCH activation for immediate assignment procedure. As long as the timer runs, the power control is inhibited on SDCCH.

If the timer expires, the power control will be enabled again on SDCCH.

If the timer is running at the sending of the RF CHANNEL RELEASE message, the timer is stopped.

T_SDCCH_PC is useful in case of long SDCCH phases.

During SDCCH for call establishment, PC disabled should be preferred with a view to secure call setup. Nevertheless, if SMS usage is very high, SDCCH phases may be long. In this case, to avoid interference, PC will be enabled after T_SDCCH_PC expiry (about 5s).

After any PC command is sent to the MS, some time must be expected before MS_TXPWR_CONF (power confirmation sent by the MS on the uplink SACCH) can reach the desired value. The timer MS_P_CON_ACK is triggered after any power modification command to monitor that the desired transmission power MS_TXPWR is reached.

If MS_P_CON_ACK elapses before the expected value of MS_TXPWR_CONF is received, the power control decision process is resumed immediately with the last MS_TXPWR_CONF received.

If the expected value of MS_TXPWR_CONF is received before the timer MS_P_CON_ACK is elapsed, the timer MS_P_CON_ACK is stopped and the timer MS_P_CON_INT is triggered. Then the MS PC threshold comparison process is resumed with MS_TXPWR_CONF for the same MS as soon as MS_P_CON_INT expires.





1 · 4 · 29

2 Power Control

Power Control Timers [cont.]

IF xx_P_CON_ACK is expiring, it is a system problem: Wrong setting of xx_P_CON_ACK (too short) No reception of power command by the MS a radio link recovery can be activated

Problem on Abis repetition of BS power command

The expiry of P_CON_INT is a normal mechanism





1 · 4 · 30

2 Power Control

Extra Information

LEVEL and QUALITY USED in EQUATION are average ones with window size A_QUAL_PC and A_LEV_PC

BS POWER CONTROL INHIBITED ON BCCH frequency BCCH must be emitted at the maximum level

MS dynamic constraint minimum 2dB every 60 ms

Emitted power can be changed by radio link supervision algorithm Radio link supervision has a greater priority

Activation of power control can slow down HO decision some causes can be triggered only if the MS (BTS) is emitting at the maximum

power

PC Thresholds in case of AMR calls If RSACCH and RFACCH are activated then L_RXQUAL_UL_P_AMR_RXACCH is replaced by L_RXQUAL_UL_P_AMR_RXACCH L_RXQUAL_DL_P_AMR_RXACCH is replaced by L_RXQUAL_DL_P_AMR_RXACCH

B11

Modified B11

Interaction with Radio Link Command

The MS power control function is informed of a radio link recovery by the radio link command function. Once the indication is received, the PC command process is resumed immediately:

timer MS_P_CON_ACK is started (or reset and started if running),

If MS_P_CON_ACK elapses before the expected value of MS_TXPWR_CONF is received, the power control decision process is resumed immediately with MS_TXPWR_CONF = min(MS_TXPWR_MAX,P).

According to GSM Technical Specification 05.08 section 7.1, the BCCH carrier must be broadcast with a constant power in the cell. In this release of the Alcatel-Lucent BSS, this constant value is set to the maximum power allowed in the cell that is defined by the parameter BS_TXPWR_MAX.

This means that all dedicated channels (TCH, SDCCH) which are on the BCCH frequency must always be transmitted with the maximum power, i.e. the BCCH power must not be changed by the BS power control function.





1 · 4 · 31

2 Power Control

Exercise

Power control UL(Remark: Use the default parameters document) What happens if we do not use Frequency Hopping? Why is it better to have A_LEV_PC=A_LEV_HO/2? Thresholds: Lower QUAL of RX uplink = 3 High QUAL of RX uplink = 2 Lower LEV of RX uplink = -90dBm Upper LEV of RX uplink = -75dBm POW_RED_STEP_SIZE= 4 POW_INC_STEP_SIZE= 6

Put the right threshold in the next slide chart

Time allowed:

25 minutes





1 · 4 · 32

2 Power Control

Exercise [cont.]

Power control UL For each case: PC triggered? Step size value?

With POW_INC_FACTOR = 0,6and POW_RED_FACTOR = 0,6and MAX_POW_INC = MAX_POW_RED = 8

Quality

Level

Nb of case

AV RXQUAL UL PC

AV RXLEV UL PC

Power control

Delta value

1 2 3 4 5 6

0 1 2 6 3 4

-98 -80 -73 -69 -86 -91





1 · 4 · 33

2 Power Control

Exercise [cont.]

Power control DL Thresholds:

L_RXLEV_DL_P = -85dBm POW_INC_FACTOR = 0.6U_RXLEV_DL_P = -75dBm POW_RED_FACTOR = 0.8L_RXQUAL_DL_P = 2.9 MAX_POW_INC = 16dBU_RXQUAL_DL_P = 1 MAX_POW_RED = 16dBA_QUAL_PC = 4 BS_P_CON_ACK = 3sA_LEV_PC = 4 BS_TXPWR_MIN = -16dB

Using the Trace Abis Excel file, find each parameter value:POW_INC_STEP_SIZE = ? BS_P_CON_INT = ?POW_RED_STEP_SIZE = ? OFFSET_RXQUAL_FH = 0 or 1 ?

Which phenomenon can you observe as regards the successive PC commands?





1 · 4 · 34








1 · 4 · 35

End of ModuleRadio Link Sup and Power Control





Module 5Handover Algorithms








GSM B11 · BSS B11 Radio Fine Tuning IntroductionB11 Radio Fine Tuning · Handover Algorithms

1 · 5 · 2

Blank Page




Document History





1 · 5 · 3

Module Objectives


Describe the Power control and Handover algorithms List the associated parameters





1 · 5 · 4







1 · 5 · 5

Table of Contents


1 Handover Detection 72 Handover Candidate Cell Evaluation 913 Exercise 101





1 · 5 · 6







1 · 5 · 7

1 Handover Detection





1 · 5 · 8


Handover Main Objective

Send connected MS to another cell When needed: “rescue/emergency” handover If useful: “better cell” handover

Toward the “best” cell From a radio point of view Power budget Level

From a traffic point of view Less loaded target

From a dynamic point of view MS speed “History” of the call

From an operator point of view

Emergency Intercell Handovers

These handovers are triggered when the call conditions deteriorate significantly in order to rescue the call. The causes are:

"too low quality" ,

"too low level",

" too long MS-BS distance",

“too short MS-BS distance”,

"consecutive bad SACCH frames",

"level dropping under high threshold".

Better Cell HO

These handovers are triggered to improve the overall system traffic capacity. This spans: interference reduction, signaling load reduction, traffic unbalance smoothing. The basic assumption for these handovers is that they should respect the cell planning decided by the operator.

The causes are:

"power budget",

"high level in neighbor lower layer cell for slow mobile",

"high level in neighbor cell in the preferred band" ,

“traffic handover”.





1 · 5 · 9


Principle

The BSC analyzes averaged measurement results: active channel pre-processing (measurements averaging and book-keeping)

To detect need/utility to handover Handover detection process

To choose/rank target cells according to several criteria Candidate cell evaluation process

To perform the handover Handover management process





1 · 5 · 10


Functional Entities

BSCBTS


HO Detection


HO Preparation

HO CandidateCell Evaluation

HO Management

HO Protocol

MSC

Assignment of HO functions in the ALCATEL BSS

The HO Preparation function can also be named "handover algorithms" as the algorithms described are the "heart" of this function.

The Alcatel-Lucent handover preparation is derived from the basic algorithm found in Annex A of the GSM Technical Specification 05.08.

The handover preparation is in charge of detecting a need for handover and proposing a list of target cells. Therefore it can be divided into two processes: handover detection and handover candidate cell evaluation.

The handover detection process analyzes the radio measurements reported by the BTS and triggers the candidate cell evaluation process each time a handover cause (emergency or better cell type) is fulfilled.

The handover candidate cell evaluation works out a list of possible candidate cells for the handover. This list is sorted according to the evaluation of each cell as well as the layer they belong to (in a hierarchical network) and the frequency band they use (in a multiband network).Once the handover preparation is completed, the handover decision and execution (handover management entity) is performed under the MSC or BSC control. The directed retry preparation is performed by the handover preparation function. Once the directed retry preparation is completed, the directed retry is performed either under the BSC control (internal directed retry) or under the MSC control (external directed retry).

An example of implementation of these functions except for directed retry is given in the GSM Technical Specification 05.08.

The handover preparation requires indirectly input parameters provided by the function in charge of the radio link measurements.

Most of the input data required by the handover functions are provided by a function called: Active channel pre-processing.

The figure above depicts in a general way:

the interconnections between these functions,

the implementation of these functions in the Alcatel-Lucent BSS.





1 · 5 · 11


Handover Causes Detection

Based on the contents of the measurement results

The BSC is computing the need or utility to trigger a handover

25 HO causes, split into 2 main categories: Emergency handover quality, level, distance, etc.

Better cell handover power budget, traffic, etc.

Some are specific to hierarchical and concentric architectures

The process is achieved in the BSC.

Each time a set of pre-processed (averaged) measurements is available, this process checks whether a handover is needed. If the need for a handover is detected, the target cell evaluation process is triggered.

In case of a handover alarm, the handover detection process gives to the cell evaluation process:

the preferred target cell layer: lower, upper or none.

the raw candidate cell list, which can be either all neighbors, or the subset which verifies the handover causes (plus other specific cells in particular cases). With each cell is given one of the handover causes which have been verified.

The cause of handover.

Four main handover categories are provided, depending on the cause of handover and the context of application. The context of application for a handover is either "intercell" (the handover is performed between two different cells) or "intracell" (the handover is performed in the same cell).

The detection of a need for handover is performed through handover causes which are going to be detailed.

The cause of handover is based either on a situation of emergency (this cause is therefore called "emergency cause") or on the existence of better conditions. In this last case, the name of the cause depends on the context of application: for intercell handovers, it is called "Better cell cause". For intracell handovers, it is called "Better zone cause", as it is applied only in the case of interzone handovers in concentric or multiband cells.





1 · 5 · 12


Handover Causes

16 HO causes for standard networks (26 on the whole)

Emergency HO

Cause 2

Cause 3

Cause 4

Cause 5

Cause 6

Cause 15

Cause 16

Cause 26

Too low quality on the uplink

Too low level on the uplink

Too low quality on the downlink

Too low level on the downlink

Too long distance between the

MS and the BTS

High interference on the uplink

(intracell HO)

High interference on the downlink

(intracell HO)AMR channel adaptation HO

(HR to FR)

Better conditions HO

Cause 12

Cause 20

Cause 23

Cause 24

Cause 27

Cause 28

Cause 29

Power budget evaluation

Forced directed retry

Traffic

General capture

AMR channel adaptationHO (FR to HR)

Fast traffic HO

TFO HO

30 Move from PS to CS zone

B11

Modified B11

HO causes for Extended Cells:

Emergency causes:

cause 22: too short MS-BTS distance

HO causes for hierarchical or multiband network:

Emergency causes

cause 7: consecutive bad SACCH frames received in a microcell

cause 17: too low level on the uplink in a microcell compared to a high threshold

cause 18: too low level on the downlink in a microcell compared to a high threshold

Better causes

cause 14: high level in neighbor lower layer cell for slow mobile

cause 21: high level in neighbor cell in the preferred band

HO causes for Concentric cells:

Emergency causes

cause 10: too low level on the uplink in the inner zone

cause 11: too low level on the downlink in the inner zone

Better causes

cause 13: Outer zone level uplink and downlink

HO causes inter techno:

Cause 31: 2G to 3G HO





1 · 5 · 13


Handover Causes 2: UL Quality

CAUSE 2: too low quality on the Uplink

AV_RXQUAL_UL_HO > L_RXQUAL_UL_H + OFFSET_RXQUAL_FHand AV_RXLEV_UL_HO <= RXLEV_UL_IHand MS_TXPWR = min (P, MS_TXPWR_MAX)and EN_RXQUAL_UL= ENABLE

Size of window for averaging quality: A_QUAL_HO Size of window for averaging level: A_LEV_HO

Quality

Level

Quality and Level causes (2, 3, 4, 5, 15, 16)

The aim of these causes is to keep the call going when the radio link is degrading otherwise the radio link failure might be detected and the call released. These causes wait generally for the power control process to increase the BTS and MS power to their maximum values, except for the causes specific to microcellular environment.

Handover on "too low level" is used to avoid situations where the interference level is low, while the attenuation is quite high. These conditions may appear for example in big city streets which enable a line of sight propagation from the BTS antenna. There is in this case a risk of abrupt quality degradation, if the MS moves away from the line of sight street.

In case of simultaneous low-level and low-quality signals, an intercell handover is requested.





1 · 5 · 14


Handover Causes 3: UL Level

CAUSE 3: too low level on the uplink

AV_RXQUAL_UL_HO <= L_RXQUAL_UL_H + OFFSET_RXQUAL_FHand AV_RXLEV_UL_HO < L_RXLEV_UL_Hand MS_TXPWR = min (P, MS_TXPWR_MAX)and EN_RXLEV_UL= ENABLE


Quality

Level





1 · 5 · 15


Handover Causes 4: DL Quality

CAUSE 4: too low quality on the downlink

AV_RXQUAL_DL_HO > L_RXQUAL_DL_H + OFFSET_RXQUAL_FHand AV_RXLEV_DL_HO <= RXLEV_DL_IHand BS_TXPWR = BS_TXPWR_MAXand EN_RXQUAL_DL= ENABLE


Quality

Level





1 · 5 · 16


Handover Causes 5: DL Level

CAUSE 5: too low level on the downlink

AV_RXQUAL_DL_HO <= L_RXQUAL_DL_H + OFFSET_RXQUAL_FHAV_RXLEV_DL_HO < L_RXLEV_DL_HBS_TXPWR = BS_TXPWR_MAXand EN_RXLEV_DL= ENABLE


Quality

Level





1 · 5 · 17


Handover Causes 6: Distance

CAUSE 6: Too long distance between the MS and the BTS

AV_RANGE_HO > U_TIME_ADVANCEand EN_DIST_HO= ENABLE

Size of window for distance averaging: A_RANGE_HO

Too long distanceBTSGood level but …

This cause is used when a dominant cell provides a lot of scattered coverages inside other cells, due to propagation conditions of the operational network. The consequence of these spurious coverages is the probable production of a high level of co-channel interference.

This cause is different from the others as it is more preventive. It does not make use of the propagation conditions of a call. It just does not allow an MS to talk to a BTS if it is too far away.

It may happen for example that some peculiar propagation conditions exist at one point in time that provide exceptional quality and level although the serving BTS is far and another is closer and should be the one the mobile should be connected to if the conditions were normal.

It may then happen that these exceptional conditions suddenly drop and the link is lost, which would not have happened if the mobile had been connected to the closest cell. So for these reasons, this cause does not wait for the power control to react.





1 · 5 · 18


Handover Causes 12: Power Budget

Cause 12 (Power Budget) principle Decision based mainly on comparison of serving and neighbor cells for: downlink level of serving and neighbor cells maximum emitting level of MS

Aiming at decreasing UL & DL emitted power

Should be the “normal” handover type no matter of emergency

In this case, there is another cell with a better power budget i.e., the link quality can be improved or maintained with a reduced transmit power of both the MS and the BTS. The radio link is not degraded but there is the opportunity to decrease the overall interference level by changing the serving cell of the given MS.

In conjunction with power control, it presents the advantage to keep the interference as low as possible, since it minimizes the path loss between the BTS and the MS.

This cause is especially designed to cope with the requirement that the mobile should be connected with the cell with which the lowest possible output powers are used. To assess which of the cells is this "best cell", the algorithm performs every measurement reporting period the comparison of the path loss in the current and in the neighbor cell. This is a feature special to GSM which is made possible because the mobile measures the adjacent cell signal levels and reports the six best ones.

This power budget gives the difference in path loss between the current cell and the adjacent cells reported by the mobile.

When PBGT(n) is greater than 0, then the path loss from cell n is less than the path loss from the serving cell and thus the radiated power in the downlink direction, and therefore in the uplink direction as well, will be lower in cell n than in the current cell.

However it would not be advisable to hand over the MS to another cell as soon as PBGT is greater than 0, because the MS would probably oscillate between the two adjacent cells as the propagation conditions vary. An hysteresis mechanism is implemented to avoid this undesirable effect.

No PBGT between different layers.

Ok between different bands if EN_INTERBAND_PBGT_HO = 1





1 · 5 · 19


Handover Causes 12: Power Budget [cont.]

Power Budget computation

PBGT(n) = AV_RXLEV_NCELL(n) - AV_RXLEV_PBGT_HO - (BS_TXPWR_MAX – AV_BS_TXPWR_HO)- (MS_TXPWR_MAX(n) – MS_TXPWR_MAX)- PING_PONG_MARGIN(n, call_ref)

The MS may be handed over from the serving cell indexed 0 to a neighbor cell indexed n only if the power budget exceeds the handover Margin(0,n). The handover Margin(0,n) can be modified according to the traffic situation in the serving cell and the neighbor cell n. In this way, power budget handover can be delayed towards a loaded cell and traffic load handover can be triggered from a loaded cell. Once the MS is handed over, the same algorithm is applied in the new cell, and a new PBGT is computed (which will be close to the opposite value of PBGT in the old cell) and compared to a new HOMargin. (Thus, the global hysteresis (from cell 0 to cell n and back to cell 0) is the sum of the two HOMargins).

However, it is still possible that a ping-pong mechanism is created by different handover causes, for instance a handover may be triggered towards a neighbor cell for bad quality, but in the neighbor cell, a handover back may be triggered for power budget reasons. In order to avoid this, an additional anti-ping-pong mechanism is implemented in the power budget calculation. It enables to penalize for a certain time the cell on which the call has been before.

In case of handover from SDCCH to SDCCH, this cause does not take the traffic situation into account.

In multiband cell environment, the mobile can operate in a different band than the frequency band of the BCCHs. This can lead to circular ping-pong handovers from the inner zone if the new band is DCS 1800 or to the impossibility to trigger PBGT handovers from the inner zone if the preferred band is GSM 900.

To avoid this problem, when the MS is in the inner zone of a multiband cell, it may be handed over from the serving cell indexed 0 to a neighbor multiband cell indexed n only if the power budget exceeds the handover Margin(0,n) plus the offset handover margin which allows to handicap or favor the PBGT (In the inner zone, the cause “power budget” is only checked between multiband cells, in a way to maintain the MS in the preferred band).

The offset handover margin can possibly be used in concentric cells.





1 · 5 · 20



Power Budget Variables

AV_RXLEV_NCELL received level of BCCH of neighbor cell

AV_RXLEV_PBGT_HO received level of serving cell (BCCH or not)

AV_RXLEV_NCELL - AV_RXLEV_PBGT_HO the highest is the best neighbor cell but serving might not be at the maximum level (with DL power control)

necessity to have a corrective factor


BCCH = AV_RXLEV_NCELL(n) - (AV_RXLEV_PBGT_HO + C)

with C = BS_TXPWR_MAX - AV_BS_TXPWR_HO.

This corresponds to the difference of received BCCH signal levels.

A correction factor C is taken into account for the serving cell, because the received signal level (i.e. AV_RXLEV_PBGT_HO) may not be measured on BCCH.





1 · 5 · 21



Receive Level correcting factor

BS_TXPWR_MAX – AV_BS_TXPWR_HO

BS_TXPWR_MAX are attenuations, not absolute level = (“bts_max_power”+BS_TXPWR_MAX) -

(“bts_max_power”+AV_BS_TXPWR_HO)

AV_BS_TXPWR_HO: average of BS_POWER over A_PBGT_HO measurements corrective factor used to compensate for the fact that the serving cell may not emit

at the maximum level

AV_RXLEV_NCELL-[AV_RXLEV_PBGT_HO+(BS_TXPWR_MAX-AV_BS_TXPWR_HO)] compare received level of neighbor and serving cells as if the serving one was

emitting at the maximum level






1 · 5 · 22



Power Budget parameters

MS_TXPWR_MAX(n) maximum emitting power for the MS in neighbor cell n

MS_TXPWR_MAX maximum emitting power for the MS in the serving cell

MS_TXPWR_MAX(n) - MS_TXPWR_MAX Corrective factor to compensate for the difference of maximum power of each cell

MS_TXPWR_MAX(n) - MS_TXPWR_MAX = bts_max_power(n) - bts_max_power which should be the case if delta_path_loss is equilibrated if not exact, can be corrected with HO_MARGIN(0,n)


Then, another correction factor must be taken into account because the maximum BS powers of the serving and neighbor cells may be different:

TXPWR= MS_TXPWR_MAX(n) - MS_TXPWR_MAX.

As the first step of calculation is based on the downlink parameters, this correction factor should be based on the maximum BS powers used in the serving and neighbor cells.

Two reasons (which are not completely de-correlated) for not using the BS powers can be envisaged:

for a given cell, the GSM does not specify formally the maximum BS power of the neighbor cells. Only BS_TXPWR_MAX is defined (it is sent on the air interface),

it is not easy for the evaluating BSC to know the maximum BS powers of the neighbor cells.

The use of the maximum MS powers requires that the difference of MS powers is equal to the difference of BS powers. This condition is met in most cases. If it is not the case, the difference can be corrected by the operator with the HO_MARGIN(0,n) parameter (HO hysteresis).

PBGT >0: the neighbor cell is more advantageous as the path loss is lower than in the current cell.

PBGT <0: the serving cell is more advantageous than the current cell.





1 · 5 · 23



CAUSE 12: Power budget

Hysteresis to avoid ping-pong HO

Static hysteresis defined for each couple of cells:HO_MARGIN (0,n) can also be used to correct delta_path_loss

“Dynamic” penalty for call coming from cell n: ping_pong_margin(n,call_ref) penalty PING_PONG_HCP applied during a limited duration: T_HCP not used if call arrived with a forced directed retry penalty defined on a cell basis


The main drawback of this handover category is the risk of "ping-pong " effect, which is an oscillating back and forth handover between two (or three) cells. As the "better cell" handovers are meant to find the "best cell", the variation of the radio conditions will trigger a big amount of better cell handovers, if the algorithms have a too sensitive reaction. Hence, some mechanisms are forecast, in order to prevent these oscillations from occurring repeatedly at given places.

PING_PONG_MARGIN(n,call_ref) is a penalty put on the cell n if:

it is the immediately precedent cell on which the call has been,

this cell belongs to the same BSC as the serving cell,

the call has not performed a forced directed retry towards the serving cell,

less than T_HCP seconds have elapsed since the last handover.

In this case PING_PONG_MARGIN(n,call_ref) = PING_PONG_HCP

If the call was not precedently on cell n, or if the preceding cell was external, or if the call has just performed a forced directed retry, or if the timer T_HCP has expired, then PING_PONG_MARGIN(n,call_ref) = 0





1 · 5 · 24



CAUSE 12: Power budget ping_pong_margin example

Cell Cell Cell

Case 1

Case 3

Case 2

OK1

Ping-pong case A OK with Static margin (HO_MARGIN)

Not a ping-pong case

OK due to T_HCP expiry

2

3 Ping-pong case B

This chart shows the efficiency of the anti-ping-pong mechanism.

But, never forget that the anti-ping-pong mechanism distorts the serving areas of the cells.

This is why interference problems might occur when enabling this mechanism. Tuning PING_PONG_HCP parameter is thus very important.

Warning: this mechanism is not applied for emergency handovers (new mechanism in B7 exists for capture HO, based on T_INHIBIT_CPT timer).





1 · 5 · 25



CAUSE 12 (Power budget) detection

EN_PBGT_HO = ENABLE

AND AV_RXLEV_PBGT_HO RXLEV_LIMIT_PBGT_HO

AND If EN_TRAFFIC_HO(0,n) = DISABLEPBGT(n) > HO _MARGIN(0,n)

+OFFSET_HO_MARGIN_INNER

Else PBGT(n) > HO_MARGIN(0,n) + OFFSET_HO_MARGIN_INNER+ max(0, DELTA_HO_MARGIN(0,n))

(n=1…BTSnum)

Size of window for level averaging: A_PBGT_HO

Cause 12 HO is correlated with HO cause 23. This is why there are two equations according to the activation of HO cause 23 (EN_TRAFFIC_HO).





1 · 5 · 26



Mechanism to avoid PBGT HO if the level from the serving cell is high enough

RXLEV_LIMIT_PBGT_HO: threshold above which it is not necessary to trigger a handover on power budget

AV_RXLEV_PBGT_HO: average of the received levels over A_PBGT_HOmeasurements

Specific to particular algorithms (not mentioned in this course) OFFSET_HO_MARGIN_INNER: offset which allows to take into account

the radio differences between outer and inner zones (especially in case of multi-band cells)

RXLEV_LIMIT_PBGT_HO: Dense Network Handover Regulator features

The feature aims at optimizing the better cell handovers, especially in the microcellular environment.

In very dense networks, there is a lot of overlapping between adjacent cells: a better cell handover will be realized very often. Since B6, the Alcatel-Lucent BSS tunes the number of handovers performed to the accurate need by taking into account the level received by the serving cell.

Therefore, the best trade-off between quality of speech and intempestive handovers is achieved.

Why?

Especially in microcellular environment (where cell radius is smaller), the better cell HO (based on Power Budget) is likely to be performed at a high rate to the detriment of the quality.

But it is necessary to maintain the better cell HO.

How?

With a modification of the power budget triggering cause.

Principles

HO cause 12 (Power Budget HO) is modified and takes into account the received downlink level of the serving cell (new criterion): if the received level is high enough, there is no need to perform an HO.

Consequence

Less HOs when the number of overlapping cells is high.





1 · 5 · 27



Specific to traffic considerations

DELTA_HO_MARGIN(0,n): evaluated according to the traffic situation of the serving cell and the neighbor cell n (Traffic_load(n)) in the following way:If Traffic_load(0) = high and Traffic_load(n) = low,

DELTA_HO_MARGIN(0,n) = - DELTA_DEC_HO_margin

If Traffic_load(0) = low and Traffic_load(n) = high,DELTA_HO_MARGIN(0,n) = DELTA_INC_HO_margin

Else DELTA_HO_MARGIN(0,n) = 0

PhilosophyThis mechanism aims at penalizing cause 12 detection when the traffic in the serving cell is low and is high in the cell n.

DELTA_HO_MARGIN(0,n) is evaluated according to the traffic situation of the serving cell and the neighbor cell n (Traffic_load(n)) in the following way:

If Traffic_load(0)=high and Traffic_load(n)=low

DELTA_HO_MARGIN(0,n)= -DELTA_DEC_HO_margin

If Traffic_load(0)=low and Traffic_load(n)=high

DELTA_HO_MARGIN(0,n)= DELTA_INC_HO_margin

else DELTA_HO_MARGIN(0,n)=0

where DELTA_DEC_HO_margin allows the cause 23 (traffic handover) detection.

When the traffic in the serving cell is high and is low in the cell n:

DELTA_INC_HO_margin allows to penalize the cause 12 detection when the traffic in the serving cell is low and is high in the cell n.

Note:In the case of concentric or multiband cells, if the channel is in the inner zone (ZONE_TYPE = INNER), BS_TXPWR_MAX and MS_TXPWR_MAX in equation must be replaced by BS_TXPWR_MAX_INNER and MS_TXPWR_MAX_INNER respectively.

If the channel is in the outer zone (ZONE_TYPE = OUTER), the formulation of equation is not changed.

Note: The value of PBGT(n) is calculated every SACCH period for each neighbor cell n whose measures are kept in the book-keeping list.





1 · 5 · 28



Traffic_load() is a function managed for every cell of a BSC Traffic_load() can have three values: high: cell is loaded low: cell is unloaded indefinite: cell is neither loaded nor unloaded

Traffic_load() value is modified according to the long-term traffic evaluation algorithm using the following parameters: A_TRAFFIC_LOAD, N_TRAFFIC_LOAD, HIGH_TRAFFIC_LOAD,

IND_TRAFFIC_LOAD, LOW_TRAFFIC_LOAD: can be modified per cell TCH_INFO_PERIOD: cannot be modified

TCH_INFO_PERIOD = 5s period used by the BSC to count the number of free TCHs.

More details are provided in Annex.





1 · 5 · 29


Handover Causes 23: Traffic

CAUSE 23: Traffic Handover

DELTA_HO_MARGIN(0,n) < 0dB

AND PBGT(n) > HO_MARGIN(0,n) + OFFSET_HO_MARGNIN_INNER + DELTA_HO_MARGI (0,n)

(n=1…BTSnum)

AND EN_TRAFFIC_HO(0,n) = ENABLE

Size of window for level averaging: A_PBGT_HO

The principle of this handover is to reduce the size of the serving cell when it is high-loaded relatively to a low-loaded cell.

When the mobile moves away from the BTS, the power budget will increase and a better cell handover will be triggered earlier.

It is recommended to inhibit Traffic handover towards 1-TRX cells. These cells do not have enough resources to receive incoming handovers due to congestion of neighbor cells. Moreover because of the great variation of traffic in the 1-TRX cells, traffic load is never considered as low.

This cause is inhibited for handover from SDCCH to SDCCH.

Cause 23 is checked over all the neighboring cells belonging to the same layer. It means that it is checked between cells whose CELL_LAYER_TYPE is single or upper, between cells whose CELL_LAYER_TYPE is lower, and between cells whose CELL_LAYER_TYPE is indoor.

In addition to the condition on the cell layer type, the cell frequency band condition for checking Cause 23 is as follows whether or not the MS is in the inner zone of a multi-band cell:

a) The MS is not in the inner zone of a multi-band cell:

If the flag EN_MULTI-BAND_PBGT_HO is set to “disabled”, Cause 23 must not be checked between cells which use different frequency bands (i.e cells having different CELL_BAND_TYPE).

If the flag EN_MULTI-BAND_PBGT_HO is set to “enabled”, Cause 23 will be checked over all the neighboring cells without any cell frequency band restriction.

b) The MS is in the inner zone of a multi-band cell:

If the flag EN_MULTI-BAND_PBGT_HO is set to “disabled”, Cause 23 is checked over all the neighboring cell multi-band cells (FREQUENCY_RANGE= PGSM-DCS1800 or EGSM-DCS1800) which belong to the same BSC as the serving cell.

If the flag EN_MULTI-BAND_PBGT_HO is set to “enabled”, Cause 23 will be checked over all the neighboring cells without any cell frequency band restriction.





1 · 5 · 30


Handover Causes 23: Traffic [cont.]

CAUSE 23: Traffic Handover

DELTA_HO_MARGIN(0,n) computation is already described in Cause 12 HO

DELTA_HO_MARGIN(0,n) < 0dB means that

The serving cell is loaded

The target cell is unloaded

PBGT(n) > HO_MARGIN(0,n) + OFFSET_HO_MARGIN_INNER

+ DELTA_HO_MARGIN(0,n) (n=1…BTSnum)

This constraint is less discriminative than Cause 12

In specific traffic distribution, this cause is triggered before cause 12





1 · 5 · 31


Handover Causes 12 & 23 Interworking

Cause 12 & 23: A dynamic way to handle traffic loadPBGT (n2)

PBGT (n1)

Traffic_loadTraffic_load(n2)=high

Traffic_load(n1)=low

Other cases Traffic_load(n2)=low

Traffic_load(n1)=high

HO_MARGING(n1, n2) + DELTA_INC_HO_margin

HO_MARGING(n1, n2)

HO_MARGING(n1, n2) - DELTA_DEC_HO_margin

HO_MARGING(n2, n1) - DELTA_DEC_HO_margin

HO_MARGING(n2, n1)

HO_MARGING(n2, n1) + DELTA_INC_HO_margin

PBGT Handover

PBGT Handover

2 x HO_MARGIN+ DELTA_INC_HO_margin- DELTA_DEC_HO_margin

2 x HO_MARGIN

PBGT Handover

Traffic Handover

PBGT Handover

Traffic Handover

Handover from n1 to n2

Handover from n2 to n1

N2 loaded

N1 loaded

The figure represents the triggering areas of PBGT and traffic handovers according to the traffic load in the serving cell and in the neighbor cell.





1 · 5 · 32


Directed Retry Principles

Directed Retry is: an SDCCH to TCH intercell handover Triggered during call setup procedure

If the serving cell is completely congested, the MS is allocated an SDCCH

If no TCH is available, the MS is queued Under certain conditions, the MS obtains TCH in another cell

SDCCH-TCH handover on: better condition or emergency causes = Directed Retry cause 20 = Forced Directed Retry

Internal and External Directed Retries are possible (since B6.2)





1 · 5 · 33


Directed Retry

Directed Retry

Set on a per cell basis with parameter EN_DR

Same behavior as TCH HO

Intercell handover causes are checked (i.e. all HO causes except 10, 11 and 13 (concentric cells) and causes 15 and 16 (intracell HO))

Candidate cell evaluation process: same as for TCH HO





1 · 5 · 34


Forced Directed Retry: Cause 20

CAUSE 20: Forced Directed Retry

AV_RXLEV_NCELL_DR(n) > L_RXLEV_NCELL_DR(n)

And EN_FORCED_DR = ENABLE

EN_FORCED_DR value is only relevant if EN_DR = true

AV_RXLEV_NCELL_DR(n) is calculated with A_PBGT_DR window

if less than A_PBGT_DR samples are available, the average value is calculated with the available samples and the averaging window is filled in with -110 dBm





1 · 5 · 35


Forced Directed Retry: Cell Candidate Evaluation

Pre-ranking using PREF_LAYER, PRIORITY(0,n), frequency band

Filtering process AV_RXLEV_NCELL_DR(n) > RXLEVmin(n)

+max(0,MS_TXPWR_MAX(n) - P)

Number of free TCHs t(n) > FREElevel_DR(n)

Remaining cells are sorted according totheir PBGT_DR(n) (averaging window A_PBGT_DR)

PBGT_DR(n) = AV_RXLEV_NCELL_DR(n) - AV_RXLEV_PBGT_DR - (BS_TXPWR_MAX - BS_TXPWR)

- (MS_TXPWR_MAX(n) - MS_TXPWR_MAX)





1 · 5 · 36


Forced Directed Retry: Parameters

L_RXLEV_NCELL_DR(n): level required in the neighbor cell n The parameter considered is the one set in the neighbor cell The default value depends on network architecture See next slide

Freelevel_DR(n): number of free TCH channels required in the neighbor cell n The parameter considered is the one set in the neighbor cell Default value = 0 to 4 TCHs (linked to the nb of TRXs)

A_PBGT_DR: Averaging window Default value = 4 SACCHs





1 · 5 · 37


Cause 24: General Capture

CAUSE 24: general capture

Capture handover Modified in B8: Inhibition of capture handovers for “Single layer serving cell”

May be triggered From all cells Towards all cells except serving Can be used to capture traffic by any cell, whatever its type, band, etc.

Serving cellCell

Cell

Cell

Cell





1 · 5 · 38


Cause 24: General Capture [cont.]

CAUSE 24: general capture

AV_RXLEV_NCELL(n) > L_RXLEV_CPT_HO(0,n) + max (0, [MS_TXPWR_MAX(n) - P])

and Traffic_load(0) = CAPTURE_TRAFFIC_CONDITIONand Traffic_load(n) HIGHand EN_GENERAL_CAPTURE_HO = ENABLE

Size of window for averaging level: A_PBGT_HO CAPTURE_TRAFFIC_CONDITION can take 3 values: ANY_LOAD (default),

HIGH, NOT_LOW Anti ping-pong: not checked if T_INHIBIT_CPT is running

Case the serving cell is in the upper or single layer (CELL_LAYER_TYPE(n0) = upper or single):

Condition 1:

The immediately preceding cell n-1 is in the indoor or lower layer, i.e. CELL_LAYER_TYPE(n–1) = lower or indoor, or the frequency band of the immediately preceding cell n-1 is different from the frequency band of the serving cell n0, i.e. CELL_BAND_TYPE(n–1) <> CELL_BAND_TYPE(n0).

Condition 2:

The call has previously performed i) an emergency internal handover on quality (Cause 2, 4, and 7) towards the serving cell or ii) an external handover with the A interface GSM cause “uplink quality or downlink quality” and there is a bi-directional adjacency link between the preceding external cell n-1and the serving cell n0.

If Conditions 1 and 2 are fulfilled the timer T_INHIBIT_CPT is started





1 · 5 · 39


Handover Cause 28: Fast Traffic HO

CAUSE 28: Fast Traffic HO

Push out of a cell a mobile in dedicated mode to allow a queued request to be served in the serving cell Complement the current traffic HO (Cause 23), for sudden traffic peaks (no

averaging window used) More efficient where the overlap of adjacent cells is reduced

Most appropriate MSto be pushed out

New call attempt

CongestedServing cell

Neighbor cell Cell

Neighbor cell Cell

Upper layer cell

HO

HOMost appropriate MSto be pushed out

New call attempt

CongestedServing cell

AV_RXLEV_NCELL( n) > L_RXLEV_NCELL_DR( n) + max(0,[MS_TXPWR_MAX( n)-P])

The threshold L_RXLEV_NCELL_DR(n) is the observed level from the neighbor cell n at the border of the area where fast traffic handovers are enabled. This threshold fixes the size of the overlapping area where fast traffic handovers can be performed. It should be greater than RXLEVmin(n).

And t(n) > FREElevel_DR(n)

FREElevel_DR(n) is the minimum threshold of free TCHs in the neighbor cell n for forced directed retry and fast traffic handover.

t(n) is the absolute number of free (dual rate) TCHs in the neighbor cell n.

For external cells, t( n) is fixed to the arbitrary value t(n) = 255. Therefore, setting FREElevel_DR(n) to 255 for an external cell inhibits outgoing external fast traffic handover towards this cell. Setting FREElevel_DR(n) to any other value will allow outgoing external fast traffic handover towards this cell.

EN_CAUSE_28 = enable

The flag EN_CAUSE_28 is not an OMC flag but a HOP flag.





1 · 5 · 40


Handover Cause 28: Fast Traffic HO [cont.]

CAUSE 28: Fast Traffic Handover

Cause 28 is only checked if the channel of the candidate MS can support the channel rate (HR or FR) required by the queued request:

HO is triggered when a request is queued at the top of the queue

If the MS is E-GSM capable then the G1 TRXs of the target cells are also considered

FR FR (Whatever the TRX type)

HR , or FR on dual rate TRX

Queued Request Candidate MS

HR

B11

Modified B11





1 · 5 · 41



CAUSE 28: Fast Traffic Handover equation

AV_RXLEV_NCELL(n) > L_RXLEV_NCELL_DR(n) + max(0,[MS_TXPWR_MAX(n)-P])

AND t(n) > FREElevel_DR(n)AND EN_CAUSE_28 = ENABLEAND EN_FAST_TRAFFIC_HO = ENABLE

Size of window for averaging level: A_PBGT_DR

Same thresholds and window as Cause 20 (Forced Directed Retry) EN_CAUSE_28 is an internal HOP process variable





1 · 5 · 42



CAUSE 28: Fast Traffic Handover process

DHCPEND

- Cause number 28- Reference of the call to handover(which corresponds to the firstcandidate MS received)

Start HO

Assignment request queued - Queued request reference- Channel rate of queued request

Fast Traffic HO Request

Yes

EN_CAUSE_28=enable

EN_CAUSE_28=disable

HO alarm:cause 28?

NOK

DHCPEND

Requeststill queued?

Resource AllocationManagement

HandoverPreparation

T_FILTERis started

HandoverManagement

OK

Check first2 conditions of cause 28

- Queued request reference- Reference of MS can perform HO

Fast Traffic HO Acknowledge

Yes

No

NO

- Channel band of the queued request

B11

Modified B11

HO cause 28 process:

If EN_FAST_TRAFFIC_HO = enable, when an assignment request (or external emergency HO request) is queued, the RAM process sends to the HOP process a Fast Traffic HO request which contains the queued request reference and its channel rate.

Then, HO cause 28 becomes checkable (EN_CAUSE_28=enable).

Once an HO alarm for cause 28 is triggered, the flag EN_CAUSE_28 is set to “disable” so as not to perform more than one handover. In the same time, the HOP process gets back to the RAM process a Fast Traffic HO Acknowledge which contains the queued request reference and the reference of the MS that can perform HO.

If several answers are sent to the RAM process, only the first one corresponding to the queued request is taken into account. The RAM process checks if the request is still queued. If that is so, the RAM process asks the HOP process to start HO for this mobile; otherwise the process is stopped.

Once the HOP process receives this message, the first two conditions of Cause 28 (good enough level, enough free resources in the target cell) are checked one more time. If the conditions are fulfilled, the HOP process sends an alarm to the HOM entity and the timer T_FILTER is started ; otherwise the process is stopped.

Note: the first two conditions of cause 28 are tested twice in order to be sure that the candidate cells are still valid when the « cause 28 start HO » message is received from the RAM process.





1 · 5 · 43


Handover Cause 15: UL Interference

CAUSE 15: High interference on the uplink Intracell HO

AV_RXQUAL_UL_HO > THR_RXQUAL_CAUSE_15 +OFFSET_RXQUAL_FH

AND AV_RXLEV_UL_HO > RXLEV_UL_IHAND EN_CAUSE_15 = ENABLEAND [ no previous intracell handover for this connection failed

OR EN_INTRACELL_REPEATED = ENABLE ] Size of window for averaging quality: A_QUAL_HO Size of window for averaging level: A_LEV_HO

THR_RXQUAL_CAUSE_15 and EN_CAUSE_15 are not parameters but variables defined just after.

In B7:

New causes (26 & 27) introduced due to AMR support

Cause 26 is an emergency condition:

Intracell HO: speech codec from AMR-HR to AMR-FR

Cause 27 is a better condition

Intracell HO: speech codec from AMR-FR to AMR-HR

Causes 15 & 16 are modified due to AMR support

Specific enablers and thresholds for AMR calls

AMR emergency HO (cause 26) is triggered if cause 15 or 16 has already been triggered

Cause 29 is created for intracell handover due to TFO

Codec sharing and optimization for MTM calls





1 · 5 · 44


Handover Cause 16: DL Interference

CAUSE 16: High interference on the downlink

Intracell HOAV_RXQUAL_DL_HO > THR_RXQUAL_CAUSE_16 + OFFSET_RXQUAL_FH

AND AV_RXLEV_DL_HO > RXLEV_DL_IHAND EN_CAUSE_16 = ENABLEAND [ no previous intracell handover for this connection failed

OR EN_INTRACELL_REPEATED = ENABLE ] Size of window for averaging quality: A_QUAL_HO Size of window for averaging level: A_LEV_HO

THR_RXQUAL_CAUSE_16 and EN_CAUSE_16 are not parameters but variables defined after.





1 · 5 · 45


New Parameters for Causes 15 & 16

CAUSE 15 and CAUSE 16: THR_RXQUAL_CAUSE_15 (or 16) and EN_CAUSE_15 (or 16) are specific to HOP THR_RXQUAL_CAUSE_15 (or 16) = L_RXQUAL_XX_H for a non AMR call (same threshold as CAUSE 2 or CAUSE 4) L_RXQUAL_XX_H_AMR for an AMR call

EN_ CAUSE _15 (or 16) = EN_INTRA_XX for a non AMR call EN_INTRA_XX_AMR for an AMR call

XX = UL or DL

For a non-AMR call, the thresholds used are identical to the ones used for CAUSE 2 and CAUSE 4.

In this case and if EN_INTRACELL_REPEATED = DISABLE, when aN HO CAUSE 15 (or 16) fails, it can be modified as UPLINK (or DOWLINK) QUALITY, HO CAUSE 2 (respectively HO CAUSE 4).





1 · 5 · 46


GSM Standard Codecs

Principles: Two consecutive encodings: speech coding and channel coding With current codecs, the share of each coding is FIXED (not optimized)

Speech protection"against degradation"

22.8 Kbit/s (FR TS)

Speech protection"against degradation"

11.4 Kbit/s (HR TS)

Channel coding

Channel coding

FIXEDFIXEDFIXED

Radio

Radio

Speech coding

Speech information "useful part"

13 Kbit/sou 12.2 Kbit/s

(FR)(EFR)

Speech information "useful part"

5.6 Kbit/s (HR)

Speech coding

Voice

Voice

Speech coding contains speech information (the “useful” part).

Channel coding protects speech information (against radio degradations).

The main speech codec currently used in GSM networks, speech Full Rate, is quite old. It has been specified more than 10 years ago. Around 1992, to increase network capacity, GSM has specified a half rate speech codec. But this codec showed strong limitations in terms of speech quality, especially for mobile to mobile calls (double transcoding degrades very much the speech quality of the half rate codec) and under poor radio conditions.

Recently, studies on AMR have been launched to provide a solution to:

Increase speech quality in full rate and half rate,

Increase network capacity by offering a good half rate solution,

Use a long-term solution, to avoid adding more and more codecs handled independently from the others.





1 · 5 · 47


Adaptative Multi-Rate

Speech frame (20 ms)

Speech coding

N bits

Channel coding

456 (FR) or 228 (HR) bits

FR AMR WideBand:

N =

132 6.6 kbit/s

177 8.85 kbit/s

253 12.65 kbit/s

FR AMR (NarrowBand):

N =

95 4.75 kbit/s

103 5.15 kbit/s

118 5.9 kbit/s

134 6.7 kbit/s

148 7.4 kbit/s

159 7.95 kbit/s

204 10.2 kbit/s

244 12.2 kbit/s

HR AMR (NarrowBand):

N =

95 4.75 kbit/s

103 5.15 kbit/s

118 5.9 kbit/s

134 6.7 kbit/s

148 7.4 kbit/s

159 7.95 kbit/s

In order to adapt the intermediate rate, a set of speech codecs has been defined by ETSI to be used by AMR:

When radio conditions are good, increases speech information.

When radio conditions are bad, protects speech information.

Full Rate AMR-NB: Alcatel-Lucent implementation is fully compliant with GSM recommendations. All these AMR FR codec modes are supported. In particular, the Alcatel-Lucent BSS has implemented the 7.95, 5.9 and 4.75 codec modes which use polynomials of constraint length 7 to ensure a high protection.

Half Rate AMR-NB: Alcatel-Lucent implementation supports 5 out of 6 AMR HR codec modes (AMR HR 7.95 is not supported) which are fully compliant with GSM recommendations. In particular, the Alcatel-Lucent BSS has implemented the 4.75 codec mode which uses polynomials of constraint length 7 to ensure a high protection.

AMR-WB: Defined in 3GPP Release 5, it’s described in 3GPP TS 26.171 as follow:

OFR AMR-WB : known as FR sv4 [Not supported in ALU BSS B10]

Uses a FR channel with 8-PSK

5 codec modes are defined : 23.85 kbit/s, 15.85 kbit/s, 12.65 kbit/s, 8.85 kbit/s, 6.60 kbit/s

FR AMR-WB : known as FR sv5

Uses a FR channel with GMSK

3 codec modes are defined : 12.65 kbit/s, 8.85 kbit/s, 6.60 kbit/s

OHR AMR-WB : known as HR sv4 [Not supported in ALU BSS B10]

Uses a HR channel with 8-PSK

Same codec modes as FR AMR-WB





1 · 5 · 48

SF(20 ms)

SpeechCoding

ChannelCoding

N bitsbit rate

R

456 (FR)or

228 (HR) bits

AMR-NB Sampling rate: 8 kHzAMR-WB Sampling rate: 16 kHz

The main difference between AMR WideBand (AMR-WB) and AMR-NB is the sampling rate.

In 2G, AMR-WB allows to improve voice quality and enables 3G service continuity.

The AMR-WB feature is used with the new MT-120WB transcoder board. TFO is a prerequisite for AMR-WB. Indeed, without TFO, all benefits from WB

speech coding are lost because of transcoding from AMR-WB to AMR-NB.


Adaptative Multi-Rate: [Cont.]

For AMR-NB, during a call, only a subset out of the 8 codecs (in case of FR) or 6 codecs (in case of HR) is used.

The Active Codec Set (ACS) can include from 1 to 4 codecs. It is up to the operator to define its own codec subset with the following O&M parameters: AMR_FR_SUBSET and AMR_HR_SUBSET.

The ACS will be relevant only if FR AMR-NB is activated: EN_AMR_FR = Enable (resp HR AMR-NB is activated: EN_AMR_HR = Enable)

In particular, he can define a codec subset limited to the common codec modes supported by all the BSSs of its network (some BSSs may not be able to support all of them due to implementability problems).The codec subset defined by the operator is the same in the uplink and in the downlink.

For AMR-WB, there is no need to define an ACS. Only the flag EN_AMR-WB_GMSK to be set to Enable

Codec Mode Adaptation:

dynamic change from one codec to another, using the same channel (FR or HR).

metric used: C/I (Carrier over interference ratio).

Channel Mode adaptation:

change from one FR channel to an HR one and vice-versa independently from the codec mode.

metric used: RX_QUAL uplink and downlink.





1 · 5 · 49


Codec Mode Adaptation

Based on adaptive trade-off between the share of throughput given to speech coding and the one given to channel coding (speech protection)

Depends on radio conditions estimated in real-time

Mediumradio conditions

Badradio conditions

Goodradio conditions

Speech coding = speech information

Channel coding = speech protection

The AMR principle is to have a set of codecs and, for any radio conditions, to use the one with the best speech quality.

Under good radio conditions, a codec with a high bit rate is used. Speech is encoded with more information so the quality is better. In the channel coding, only little place is left for redundancy.

Under poor radio conditions, a codec with a low bit rate is chosen. Speech is encoded with less information, but this information can be well protected due to redundancy in the channel coding.

The BSS adapts dynamically the codec in uplink direction and in downlink direction, taking into account the C/I measured by the BTS (for uplink adaptation) and by the MS (for downlink adaptation).

The codec used in the uplink and used in the downlink can be different: the adaptation is independent in each direction.

This permits to use an optimal codec for each C/I value of each direction, as indicated in the figure below.





1 · 5 · 50


Codec Mode Adaptation [Cont.]

For AMR-NB, only a subset of 4 codecs can be used per channel type (FR/HR)

The same codec subset is used for Uplink and Downlink For both AMR (NB and WB), codec mode adaptation is performed as

follow: In Uplink, for each SACCH frame, the BTS compares C/I value to the threshold

corresponding to the current codec (belonging to the codec subset defined by the operator) In downlink, it’s the same process as uplink adaptation. Nevertheless, the

BTS remains the master Unrelated processes uplink and downlink codecs may be different at

a given time





1 · 5 · 51


Codec Mode Adaptation: AMR-NB

The Codec mode can be modified on one frame out of two (CMI / CMC-CMR).

Decision based on thresholds (OMC-R settable), for the uplink and the downlink.

CODEC_MODE_4(less robust)

CODEC_MODE_3

CODEC_MODE_2

CODEC_MODE_1(most robust)

High

Low

C/I norm

AMR_FR_THR_1 + AMR_FR_HYST

AMR_FR_THR_1


AMR_FR_THR_2


AMR_FR_THR_3





1 · 5 · 52


Codec Mode Adaptation: AMR-WB

The Codec mode can be modified on one frame out of two (CMI / CMC-CMR).

Decision based on thresholds (OMC-R settable), for the uplink and the downlink.

C/I norm

High

Low

AMR_WB_GMSK_THR_2 + AMR_WB_GMSK_HYST_2

AMR_WB_GMSK_THR_2

AMR_WB_GMSK_THR_1 + AMR_WB_GMSK_HYST_1

AMR_WB_GMSK_THR_1

CODEC_MODE_3(less robust)

CODEC_MODE_2

CODEC_MODE_1(most robust)





1 · 5 · 53


Codec Mode Adaptation

Uplink adaptation

Downlink adaptation

Codec Mode Request(new codec mode)

Codec Mode Indication(new codec mode)

Codec Mode Request(new codec mode)

MS BTS TC


C/I evaluation &thresholds comparison


Codec Mode Command(new codec mode)

MS BTS TC


C/I evaluation &thresholds comparison





1 · 5 · 54


AMR-NB Channel Mode Adaptation

The choice between HR AMR-NB and FR AMR-NB is called: Channel mode adaptation

It’s done at call setup and during the call through HO causes 26 & 27





1 · 5 · 55


AMR Gain

AMR: always gives end user the best satisfaction Comparison between different codecs in terms of capacity and quality:

FR

EFR

HR

FR AMR-NB

HR AMR-NB

FR AMR-NB + HR AMR-NB

FR AMR-WB without TFO

FR AMR-WB with TFO

Speech qualityrequirement

Capacityrequirement

The main speech codec currently used in GSM networks, speech Full Rate, is quite old. It has been specified more than 10 years ago.

Around 1992, to increase network capacity, GSM has specified a half-rate speech codec. But this codec showed strong limitations in terms of speech quality, especially for mobile-to-mobile calls (double transcoding degrades very much the speech quality of the half-rate codec) and under poor radio conditions.

A few years later, when GSM started to be introduced in North America, American operators asked for an improved speech codec for full rate channels. Indeed speech quality was a major argument for customers used to have a good speech quality with analog systems. For that issue, EFR was specified for GSM.

Recently, studies on AMR have been launched to provide a solution to:

Increase speech quality in full rate and half rate,

Increase network capacity by offering a good half rate solution,

Use a long-term solution, to avoid adding more and more codecs handled independently from the others,

Take into account Tandem Free Operation (TFO), especially between MSs on half rate on one side and on full rate on the other side.





1 · 5 · 56


AMR: TCH Allocation

FR / HR discrimination Cell load AV_LOAD() computed from load samples = NB_BUSY_TS / NB_TS * 100 non sliding window (LOAD_EV_PERIOD) averaging process

THR_FR_LOAD_U_SV1=80%

THR_FR_LOAD_U_SV3=60%

THR_FR_LOAD_L_SV1=50%

THR_FR_LOAD_L_SV3=40%

AV_LOAD

Time

100%

FR for any MS

HR for AMR MSFR for other MS

HR for any MS

HR for AMR MSFR for other MS

FR for any MS

Load samples are computed by the BSC every TCH_INFO_PERIOD = 5 seconds.

LOAD_EV_PERIOD is the averaging window size for cell load computation. It is equal to 12 but can be changed at the OMC-R level on a per cell basis. Therefore cell load process has a periodicity of 1mn by default (TCH_INFO_PERIOD*LOAD_EV_PERIOD). The allocation of Half rate resources is decided upon the load evaluation in the serving cell.

AMR HR (HR SV3) offers a better speech quality than HR SV1. The Alcatel-Lucent BSS offers thus the possibility to define a set of thresholds specific for AMR. If the load increases, AMR HR capable MSs can be the first to be allocated in HR (HR SV3) for load reasons, and if the load still increases, then all the HR capable MSs can be allocated in HR (HR SV1 & HR SV3) for load reasons.

This is why two variables of load are defined: LOAD_SV3 and LOAD_SV1.

Each load variable is calculated through its own threshold set: the thresholds related to the variable LOAD_SV3 (THR_FR_LOAD_U_SV3 and THR_FR_LOAD_L_SV3) are less restrictive than the ones related to the variable LOAD_SV1 (THR_FR_LOAD_U_SV1 and THR_FR_LOAD_L_SV1).

As a consequence, if the load of the cell increases, then the variable LOAD_SV3 will first equal TRUE, and if the load still increases, the variable LOAD_SV1 will then equal TRUE.

The variable LOAD_SV1 corresponds to a level of load where it is important to put as many MSs on half rate TCH as possible: HR SV3 or HR SV1.

The same computation is done to compute LOAD_SV3 with the thresholds: THR_FR_LOAD_U_SV3 and THR_FR_LOAD_L_SV3 with the following relations:

THR_FR_LOAD_L_SV3 THR_FR_LOAD_U_SV3

THR_FR_LOAD_U_SV3 THR_FR_LOAD_U_SV1

THR_FR_LOAD_L_SV3 THR_FR_LOAD_L_SV1

Previous stateAV_LOAD

LOAD_SV1 = FALSE LOAD_SV1 = TRUE

AV_LOAD £ THR_FR_LOAD_L_SV1 LOAD_SV1 = FALSE LOAD_SV1 = FALSETHR_FR_LOAD_L_SV1 <

AV_LOAD £THR_FR_LOAD_U_SV1

LOAD_SV1 = FALSE LOAD_SV1 = TRUE

THR_FR_LOAD_U_SV1 < AV_LOAD LOAD_SV1 = TRUE LOAD_SV1 = TRUE





1 · 5 · 57


Cause 26: AMR HR to FR HO

CAUSE 26: AMR channel adaptation HO (HR to FR)

Cause 26 is triggered if : Current channel rate is HR Current channel is dual rate and changes are allowed AMR_FR speech codec is allowed:EN_AMR_FR = ENABLE





1 · 5 · 58


Cause 26: AMR HR to FR HO [cont.]

CAUSE 26: AMR channel adaptation HO (HR to FR) equation [ a previous intracell HO cause 15 or 16 has been triggered for this call

in the serving cellOR

EN_INTRA_DL_AMR = DISABLE and EN_INTRA_UL_AMR = DISABLE] AND

AV_RXQUAL_UL_CA_HR_FR > THR_RXQUAL_CA + OFFSET_CA+ OFFSET_RXQUAL_FH and AV_RXLEV_UL_HO > RXLEV_UL_IH

ORAV_RXQUAL_DL_CA_HR_FR > THR_RXQUAL_CA + OFFSET_CA+ OFFSET_RXQUAL_FH and AV_RXLEV_DL_HO > RXLEV_DL_IH

AND EN_AMR_CA_HR_FR = ENABLE

Size of window for averaging quality: A_QUAL_CA_HR_FR

2 different flags in order to activate cause 26 and cause 27 separately.

In B10, EN_AMR_CA has been removed and replaced by 2 parameters:

EN_AMR_CA_FR_HR

EN_AMR_CA_HR_FR

HO algorithms in the BSC is modified so that cause 26 and cause 27 are enabled separately.

EN_AMR_CA_HR_FR: This flag enables/disables intracell HO for AMR channel adaptation (Handover Cause 26) (cell parameter)





1 · 5 · 59




THR_RXQUAL_CA and OFFSET_CA are set as follows:if LOAD_SV3(0) = false then

THR_RXQUAL_CA = THR_RXQUAL_CA_NORMALOFFSET_CA = OFFSET_CA_NORMAL

if LOAD_SV3(0) = true thenTHR_RXQUAL_CA = THR_RXQUAL_CA_HIGHOFFSET_CA = OFFSET_CA_HIGH





1 · 5 · 60




Calculation of LOAD_SV3(0):If previous value of LOAD_SV3 = false then

If AV_LOAD > THR_FR_LOAD_U_SV3 thenLOAD_SV3 = true

Else LOAD_SV3 = false

Else (if previous value of LOAD_SV3 = true then)If AV_LOAD <= THR_FR_LOAD_L_SV3 then

LOAD_SV3 = falseElse LOAD_SV3 = true






1 · 5 · 61


Cause 27: AMR FR to HR HO

CAUSE 27: AMR channel adaptation HO (FR to HR)

Cause 27 is triggered if:

Current channel rate is FR Current channel is dual rate and changes are allowed AMR_HR speech codec is allowed:EN_AMR_HR = ENABLE





1 · 5 · 62


Cause 27: AMR FR to HR HO [cont.]

CAUSE 27: AMR channel adaptation HO (FR to HR) equationAV_RXQUAL_UL_CA_FR_HR <= THR_RXQUAL_CA+ OFFSET_RXQUAL_FH

ANDAV_RXQUAL_DL_CA_FR_HR <= THR_RXQUAL_CA

+ OFFSET_RXQUAL_FHAND EN_AMR_CA_FR_HR = ENABLE

Size of window for averaging quality: A_QUAL_CA_FR_HR

2 different flags in order to activate cause 26 and cause 27 separately.

In B10, EN_AMR_CA has been removed and replaced by 2 parameters:

EN_AMR_CA_FR_HR

EN_AMR_CA_HR_FR

HO algorithms in the BSC is modified so that cause 26 and cause 27 are enabled separately.

EN_AMR_CA_FR_HR: This flag enables/disables intracell HO for AMR channel adaptation (Handover Cause 27) (cell parameter)





1 · 5 · 63


Cause 26 & 27 Interworking

THR_RXQUAL_CA_NORMAL

Quality

THR_RXQUAL_CA_NORMAL +OFFSET_CA_NORMAL

THR_RXQUAL_CA_HIGH

THR_RXQUAL_CA_HIGH +OFFSET_CA_HIGH

Bad quality: 7

Good quality: 0

Load = False Load = True

Half Rate

Full Rate

Half Rate

Full Rate

HO cause 26

HO cause 27

HO cause 26

HO cause 27





1 · 5 · 64


Introduction to TFO

Tandem Free Operation (TFO) solution

ITU-T G.711 A-Law/? -Law

Compressed Speech Compressed Speech

TranscodingFunction

TranscodingFunction

DecodingEncoding

Encoding Decoding

MS BMS A

GSM Codec at 8 or 16 Kbit/s GSM Codec at 8 or 16 Kbit/sPSTN Codec at 64 Kbit/s

Double Transcoding without TFO

Compressed Speech Compressed Speech

TranscodingFunction

TranscodingFunction

TFOTFO

Encoding Decoding

MS BMS A

No Transcoding with TFO

Compressed Speech

EFR, FR, HR, FR AMR-WB

The Tandem Free Operation (TFO) feature is a way to avoid double transcoding in mobile to mobile speech calls.

Indeed, without TFO one GSM codec type is used between the first mobile and the first transcoder, then the speech is transcoded into A/ law between transcoders and finally this speech is transcoded again into a second GSM codec type (which may be the same as the first one) between the second transcoder and the second mobile.

With TFO, after call establishment, both BSSs at each side are able to negotiate a common GSM codec type which is then used from one mobile to the other mobile. This negotiation is performed through in-band signaling between transcoders.





1 · 5 · 65


Introduction to TFO [cont.]

Applicability: Only MS-to-MS speech calls TFO is based on information exchanged between transcoders

TRAU

MS MSBTS

64 Kbit/s Speech Sample carrying:

- TFO frames on the LSB containing: - compressed speech samples - control bits - TFO messages

- original PCM speech samples on the MSB

TRAU

BSC

IPE

MSC

IPE

MSC

BTS

BSC





1 · 5 · 66


TFO Principles

In the case of first allocation (normal assignment at call setup, inter-BSS handover, intra-BSS handover where no TFO was previously on-going):

Exchange of Codec capabilities

New call setup

Match

Found

Yes No

Look for common codec

NoYes

Normal operationTFO mode ON

Intracell HO





1 · 5 · 67


Cause 29: TFO HO

CAUSE 29: TFO HO

Intracell HO used in case of codec mismatch between two MSs calling, in order to match their speech codec No radio measurements needed No priority and may be triggered at any

time Conditions:

HO_INTRACELL_ALLOWED = ENABLEAND

EN_TFO_MATCH = ENABLE





1 · 5 · 68


Cause 29: TFO Parameters

EN_TFO enables/disables the feature, per cell

EN_TFO_MATCH enables/disables resolution of codec mismatch, per cell

EN_TFO_OPT enables/disables codec optimization, per cell

FORCE_TFO_VS_AMR enables/disables the basic functions of TFO for GSM EFR, FR and HR codec

types when the current codec is AMR FR or AMR HR FORCE_TFO_HR_WHEN_LOADED controls the establishment of TFO in HR when the cell is loaded

KEEP_CODEC_HO indicates if the BSC tries to keep the same codec in case of internal intercell

HO

Codec Mismatch

At call setup for a mobile-to-mobile speech call, when both BSSs do not use the same codec type, a codec mismatch occurs. If a common codec type can be found, either one or possibly both BSSs perform an intracellhandover to use the common codec type found. Afterwards TFO can be started using this common codec type. Codec mismatch resolution is authorized in the BSC using an O&M flag: EN_TFO_MATCH. This flag is forwarded to the TC, via the BTS.

Codec Optimization

At call setup for a mobile-to-mobile speech call, it can occur that a first common codec type can be found but a better speech quality would be provided with another common codec type. Once both BSSs operate in Tandem Free, they exchange their complete codec capabilities, to try to find a better codec type than the current one. Codec optimization is authorized in the BSC using an O&M flag : EN_TFO_OPT. This flag is forwarded to the TC, via the BTS.

Classification of Codec Types

In all cases, TFO is considered better as any tandeming configuration. In TFO, EFR is considered as better than FR, considered as better than HR.Force TFO vs. AMRTFO + AMR is not supported in this implementation of TFO. In the normal operation, a call established with AMR will not initiate a TFO negotiation. The goal of the function Force TFO vs. AMR is to allow a call, established with AMR to initiate a TFO negotiation and, if possible, to change of codec type to FR, HR or EFR to establish TFO.

In-Path Equipment (IPE)

TFO can only be activated if TFO frames (at 8 or 16 Kbit/s) can be sent transparently through the public switching network. In-path equipments are equipments such as echo cancelers or A/ law converters that modify the 64 Kbit/s speech signal. Such equipment need to be deactivated for TFO calls.





1 · 5 · 69


Cause 29: TFO Parameters [cont.]

EN_TFO_OPT: enables/disables codec optimization, per cell Allows new TFO negotiation on an on-going MTM call to find a better common

codec For example, HR is used on both sides, but FR is possible too HO cause 29 will be triggered on both sides towards the best codec

EN_TFO_AMR_WB : enable, disable the use of TFO in case of AMR WideBand, per cell

EN_TFO_AMR_NB : enable, disable the use of TFO in case of AMR NarrowBand, per cell

B11





1 · 5 · 70



FORCE_TFO_VS_AMR: TFO AMR-NB not specified Call setup in AMR is not followed by TFO negotiation FORCE_TFO_VS_AMR enables HO cause 29 after AMR call establishment towards the

best TFO codec

EFR + TFOThe MS A can only use HR/EFR/FR

The MS B can use HR/EFR/FR

Cell cap: Cell cap:

The MS A using AMR-NB, could use HR/EFR/FR


MS A MS B

TFO not possible

Enable (Alcatel patent)

FORCE_TFO_VS_AMR

Disabled(ETSI implementation)

AMR-NB / HR / FR / EFR HR / FR / EFR





1 · 5 · 71



FORCE_TFO_HR_WHEN_LOADED: Gives control on load regulation precedence vs. TFO 3 values: TFO_HR_NOT_FORCED, TFO_HR_ONLY, TFO_HR_PREFERRED enable

different behaviours in case of loaded cell

HR + TFOThe MS A can only use HR


Loaded cellMS/cell cap:

Unloaded cellMS/cell cap:

The MS A can use HR/EFR/FR


MS A MS B

EFR + TFO

Enable (Alcatel patent)

FORCE_TFO_HR_WHEN_LOADED

Disabled(ETSI implementation)

H/EFR/FR HR/EFR/FR





1 · 5 · 72



KEEP_CODEC_HO keeps the same codec type in the new cell in case of internal intercell HO in

order to avoid resolving a new mismatch codec situation Avoids double speech quality transition:

TFO --> non-TFO --> TFO 3 possible behaviors: TFO_CALLS_ONLY: codec is preferably kept in case of internal intercell HO for TFO

calls only ALL_CALLS: codec is preferably kept in case of internal intercell HO for all calls

(whatever the TFO state) FREE: the choice of the codec type is free and depends on the situation in the target

cell





1 · 5 · 73



B7, Only TFO for legacy codecs (EFR, FR & HR) is supported B10, TFO for AMR-WB No TFO for AMR-NB

MS 1 MS 2

BSS 1 BSS 2

TC1

TC2

MSCserver

MSCserver

AMR-NB AMR-NB G711 G711G711 over IP

IP

AMR-NB AMR-NB

NoTFO

NoTFO

G711oIPrequires

highbandwidth

DegradedSpeech Quality

due to 3 transcodingstages

MG MG

B11





1 · 5 · 74



EN_TFO_AMR_NB B11, TFO for AMR-NB

Avoid 3 trancoding stages

B11

MS 1 MS 2

BSS 1 BSS 2

TC1

TC2

MSCserver

MSCserver

IP

AMR-NB AMR-NB AMR-NB AMR-NBAMR-NB AMR-NB AMR-NB

TFO TFOTrFOAMR over IP

Transcoding FunctionsBypassed

High transmissionsavings in NGN

BetterSpeech Quality

MG MG

Transcoder Free Operation (TrFO) is a Core Network protocol, applicable to the NGN architecture.

TrFO allows to transport speech in the Core Network using GERAN/UTRAN codecs over IP, rather than G.711. Advantages:

Gain in transmission bandwidth.

Gain in speech quality if the same codec is used over the complete path.

Contrarily to TFO, TrFO is out-of-band, i.e. negotiation is not done in the User Plane (embedded in speech frames), but in the Control Plane, on a specific interface.

The AMR +TFO feature improves the speech quality of mobile-to-mobile calls and TFO-TrFO interaction in the NGN core network.

AMR-WB without TFO does not make sense.





1 · 5 · 75


Cause 29: TFO Parameters [cont.]AMR Codec Adaptation with TFO

The Codec mode adaptation is performed independently on each direction. But for one direction, the same codec mode is used from one MS to the

other MS. Codec mode adaptation is always performed for the side having the worst

radio conditions

ULdowngrading

DLdowngrading

ULupgrading

DLupgrading

MS1 BTS1 TRAU1 TRAU2 BTS2 MS2

The BTS detectsa bad uplink quality

CMC: new codec(lower rate)

The MS1 usesimmediately

the new codec

CMI: new codec CMI:new codec CMI:

new codec CMI:new codec CMI:

new codec

TFO establishment with original codec

TFO establishment with new codec

B11





1 · 5 · 76


Cause 30: Move from PS to CS Zone

If EN_RETURN_CS_ZONE_HO = enableAND a CS call is inside both The Non pre-emptable zone and The MAX_SPDCH_LIMIT_ZONE thenAn intra cell HO cause 30 is triggered

TRX3 TRX1

BCCHSDCCHPS PS PS PSCS CS CS

Non pre-emptable zone

MAX_SPDCH_HIGH_LOAD zone

MAX_SPDCH_LIMIT zone

PS traffic zone

HO cause 30

PS PS

The enabling/disabling of Cause 30 is independent of the flag HO_INTRACELL_ALLOWED.

MAX_SPDCH_HIGH_LOAD zone: this zone corresponds to the MAX_SPDCH_HIGH_LOAD consecutive PS capable timeslots that are preferred for PS allocation. In this zone, allocated TBFs cannot be pre-empted. If the value of MAX_SPDCH_HIGH_LOAD is not modified, this zone remains unchanged.

Non pre-emptable PS zone: this zone is always inside the MAX_SPDCH_HIGH_LOAD zone. In this latter zone, we search for the rightest timeslot allocated to the MFS and used. Then, all timeslots situated at its left define this non pre-emptable PS zone.

MAX_SPDCH_LIMIT zone: this zone corresponds to the MAX_SPDCH_LIMIT consecutive PS capable timeslots that are preferred for PS allocation.

PS traffic zone: this zone corresponds to the larger zone between the non pre-emptable PS zone and the MAX_SPDCH_LIMIT zone.





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Handover Causes Priorities

Emergency Handover

Uplink Quality Cause 2

Downlink Quality Cause 4

Uplink Level Cause 3

Downlink Level Cause 5

Distance Cause 6

Too Low Level UL Inner Cause 10

Too Low Level DL Inner Cause 11

HR to FR Channel Adaptation Cause 26 intracell

Uplink Interference Cause 15 intracell

Downlink Interference Cause 16 intracell

Better Condition Handover

Capture Handover Cause 24

Power Budget Cause 12

Traffic Cause 23

Outer UL/DL Level Cause 13

FR to HR Channel Adaptation Cause 27 intracell

Forced Directed Retry Cause 20

Fast Traffic HO Cause 28

HANDOVER PRIORITIES

The causes 24, 12 and 23 have the same priority. Nevertheless, if a cell is a candidate for both causes, triggered at the same time, it is kept only for cause 12.

Dealing with all available causes, we get the following list:

Emergency: 7 > 17 > 18 > 2 > 4 > 3 > 5 > 6 > 22 > 10 > 11 > 26 > 15 > 16

Better conditions: 21=14=24=12=23 > 13 > 27 > 20 > 28

29,30 and 31 has no priority (can be detected at any time)





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Exercise 1

Emergency causes What is the HO cause 2? Which is the flag to activate the HO cause 2?

Time allowed:

45 minutes





1 · 5 · 79


Exercise 2

Emergency causesComplete the diagram below and fill in the chart with:

L_RXQUAL_UL_H = 3RXLEV_UL_IH = -70 dBmP=MS_TXPWR_MAX=33dBm

Quality

Level

Nb of case

AV_RXQUAL_UL_HO

AV_RXLEV_UL_HO

Current MS power

HO cause 2: YES/NO?

1 2 3 4 5 6

4 1 3 4 4 4

-81 -79 -75 -70 -69 -72

33 33 33 33 33 29(0.8 w)





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Exercise 3

Better condition causes (simple case) There are only 2W cells and 2W MS EN_TRAFFIC_HO(0,n) =Disable No Ping-Pong margin HO_MARGIN(0,n) =5 dB NO DL PC,

RXLEV_LIMIT_PBGT_LIMIT=-47dBm,The serving is not a concentric cell.

Fill in the chart:

Nb of case

AV_RXLEV_NCELL(n)

AV_RXLEV_PBGT_HO

PBGT(n)

HO cause 12: YES/NO?

1 2 3 4 5 6

-70 -70 -80 -70 -70 -75

-80 -70 -75 -75 -79 -96

Serving cell N cell





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Exercise 4

Better condition causes (ping-pong case) EN_TRAFFIC_HO(0,n) =Disable Ping-Pong margin

PING_PONG_HCP=15dbT_HCP =15s HO_MARGIN(0,n) =5 dB

A_PBGT_HO = 8 SACCHA n to 0 HO has just been triggered, what happens after 4s?

N cellServing cell?

Nb of case

AV_RXLEV_NCELL(n)

AV_RXLEV_PBGT_HO

PBGT(n)

HO cause 12: YES/NO? PBGT>HO margin

PING_PONG_HCP=15 -> PBGT(n)

HO cause 12:YES/NO?

1 2 3 4 5 6

-70 -70 -80 -70 -70 -75

-80 -70 -75 -75 -79 -96

10 0 -5 5 9 21

YES NO NO NO YES YES





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Exercise 5

Handover Detection Better condition causes (traffic case) EN_TRAFFIC_HO(0,n) =Enable No Ping-Pong margin HO_MARGIN(0,n) =5 dB DELTA_DEC_HO_margin =5dB DELTA_INC_HO_margin =5dB

N cellServing cell

HO





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Exercise 6

Better condition causes (traffic case)

Fill in the chart: N cellServing cell

HO ?

Nb of case

AV_RXLEV_NCELL(n)

AV_RXLEV_PBGT_HO

Traffic distribution

PBGT(n)

DELTA_HO_MARGIN (0, n)

Cause 12 HO: YES/NO?

Cause 23 HO: YES/NO?

1 2 3 4

-71 dBm -71 dBm -76 dBm -71 dBm

-80 dBm -80 dBm -80 dBm -80 dBm0: traffic lowN: traffic high

0: traffic highN: traffic low

0: traffic highN: traffic low

0: traffic lowN: traffic low





1 · 5 · 84


Exercise 7

Channel adaptation (cause 26 and cause 27) Why is it recommended to have A_QUAL_CA_FR_HR A_QUAL_CA_HR_FR? An operator may be willing to:

- Under normal load, use only HR calls for quality 0- Under high load, use HR calls for qualities 0 to 3, with an hysteresis of 1

Find the thresholds and offsets for normal and high load:THR_RXQUAL_CA_NORMAL = ? OFFSET_CA_NORMAL = ?THR_RXQUAL_CA_HIGH = ? OFFSET_CA_HIGH = ?





1 · 5 · 85


Exercise 8

Channel adaptation (cause 26 and cause 27) EN_INTRA_XX_AMR = Disable RXLEV_XX_IH = -110 dBm OFFSET_RXQUAL_FH = 0 A_QUAL_CA_FR_HR =4 and A_QUAL_CA_HR_FR = 2

Use the previous thresholds and fill in the chart:

UL_QUAL 0 1 2 3 3 1 1 0 0 1

DL_QUAL 0 0 1 1 1 0 0 2 4 3

LOAD_SV3 False False False False True True True True True True

AV_RXQUAL_UL_CA_HR_FR

AV_RXQUAL_DL_CA_HR_FR

AV_RXQUAL_UL_CA_FR_HR

AV_RXQUAL_DL_CA_FR_HR

CHANNEL TYPE FR FR FR





1 · 5 · 86


Exercise 9

Capture HO (Cause 24 ) There are only 2W cells and 2W MS L_RXLEV_CPT_HO(0,n) = -85dBm EN_GENERAL_CAPTURE_HO = ENABLE

Fill in the chart:

N cellServing cell

HO ?

Nb of case 1 2 3 4 5 6

AV_RXLEV_NCELL(n) - 70 - 70 - 80 - 70 - 70 - 85

CAPTURE_TRAFFIC_CONDITION NOT_LOW HIGH ANY_LOAD HIGH HIGH

TRAFFIC_LOAD(0) HIGH LOW INDEFINITE HIGH LOW HIGH

TRAFFIC_LOAD(n) HIGH LOW INDEFINITE LOW LOW LOW

HO cause 24: YES/NO?

NOT_LOW





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Exercise 10

Fast Traffic HO (cause 28) Find the appropriate candidate MS for this queued request: Channel rate required: HR L_RXLEV_NCELL_DR(n) = -85 dBm (whatever n) FREElevel_DR(n) = 1 (whatever n) Channel rate: MS1FR on Full rate TRX, MS2HR, MS3FR on Dual rate TRX t(n) for neighbor cells: t(1)=1, t(2)=2, t(3)=2 AV_RXLEV_NCELL(n) in dBm:

Neighbors

MS 1

MS 2

MS 3

1 2 3

- 82 dBM

- 79 dBM

- 90 dBM

- 85 dBM

- 86 dBM

- 82 dBM

- 78 dBM

- 92 dBM

- 89 dBM





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Exercise 11

TFO HO (cause 29): after call setup

Find the 2 speech version types of the following MS-to-MS call: EN_TFO = enable, EN_TFO_MATCH = enable FORCE_TFO_HR_WHEN_LOADED = TFO_HR_NOT_FORCED



MS A MS B

TCH = ? TCH = ?

TCH = ? TCH = ?

Aftercall setup

After TFOnegociation

HR/EFR/FR EFR/FR





1 · 5 · 89


Exercise 12

TFO HO (cause 29): after call setup Find the 2 speech version types of the following MS-to-MS call: EN_TFO = enable, EN_TFO_MATCH = enable FORCE_TFO_HR_WHEN_LOADED = TFO_HR_ONLY



MS A MS B

TCH = ? TCH = ?

TCH = ? TCH = ?

Aftercall setup


HR/EFR/FR EFR/FR





1 · 5 · 90


Exercise 13


Find the 2 speech version types of the following MS-to-MS call: EN_TFO = enable, EN_TFO_MATCH = enable FORCE_TFO_HR_WHEN_LOADED = TFO_HR_PREFERRED



MS A MS B

TCH = ? TCH = ?

TCH = ? TCH = ?

Aftercall setup


HR/EFR/FR EFR/FR





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Exercise 14


Find the 2 speech version types of the following MS-to-MS call: EN_TFO = enable, EN_TFO_MATCH = enable FORCE_TFO_HR_WHEN_LOADED = TFO_HR_ONLY



MS A MS B

TCH = ? TCH = ?

TCH = ? TCH = ?

Aftercall setup


HR/EFR/FR HR/EFR/FR





1 · 5 · 92


Exercise 15

TFO HO (cause 29): after handover Find the speech version types of the following MS-to-MS call: EN_TFO = enable, EN_TFO_MATCH = enable FORCE_TFO_HR_WHEN_LOADED = TFO_HR_ONLY1. KEEP_CODEC_HO = TFO_CALLS_ONLY 2. KEEP_CODEC_HO = FREE

??



MS 1


MS 2

HO

?

MS 2Call setup +

TFO negociation

MS 2HO

?TFO

?TFO

HR/EFR/FR HR/EFR/FR HR/EFR/FR





1 · 5 · 93


Exercise 16

TFO HO (cause 29): after handover Find the speech version types of the following MS-to-MS call: EN_TFO = enable, EN_TFO_MATCH = enable FORCE_TFO_HR_WHEN_LOADED = TFO_HR_ONLY KEEP_CODEC_HO = TFO_CALLS_ONLY1. EN_TFO_OPT = disable2. EN_TFO_OPT = enable

??



MS 1


MS 2

HO

?

MS 2Call setup +

TFO negociation

MS 2HO

?TFO

?TFO

HR/EFR/FR HR/EFR/FR HR/EFR/FR





1 · 5 · 94

2 Handover Candidate Cell Evaluation





1 · 5 · 95


Principles

Used to rank potential target cells:

Ranking based on radio characteristics

Ranking based on operator preferences

Ranking based on traffic intensity

Handover Candidate Cell Evaluation

The process is performed in the BSC.

Once a need for handover is detected, this process looks for possible target cells (except if it is an intracellhandover or an interzone handover) and provides the BSC entity in charge of the HO decision and execution entity with a list of candidate cells and their respective HO cause.





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Evaluation Process

MeasurementPreprocessing

A_LEV_HOA_QUAL_HOA_PBGT_HOA_RANGE_HO

HO Detection

Cause 2: uplink qualityCause 3: uplink levelCause 4: downlink qualityCause 5: downlink levelCause 6: distanceCause 12: power budget

Performed every SACCHPerformed every SACCH

Pre-ranking

Priority (0, n) = 0Cell 2: cause C2Cell 3: cause C2Cell 4: cause C2

Priority (0, n) = 1Cell 1: cause C2

Priority (0, n) = 2Priority (0, n) = 3

Cell 5: cause C2Cell 6: cause C2Cell 7: cause C2Cell 8: cause C2



Priority (0, n) = 1Priority (0, n) = 2Priority (0, n) = 3

Cell 6: cause C2Cell 8: cause C2


PBGT filteringHO_MARGIN_XX(0,n)

Grade





Order





Cell evaluation process (Order or Grade)

HO Candidate Cells Evaluation

Max

every SACCH

Preprocessmeasurement

Measurementresult

Raw cell list

Cell 1: cause C2Cell 2: cause C2Cell 3: cause C2Cell 4: cause C2Cell 5: cause C2Cell 6: cause C2Cell 7: cause C2Cell 8: cause C2... max 32 cells

The HO candidate evaluation process is run after all intercell handover alarms.

In case of intracell handover alarm (HO causes 10, 11, 13, 15, 16), the candidate cell evaluation process is skipped: the target cell is the serving cell.

The handover detection gives as indication the raw cell list (built from book-keeping list) and the preferred layer for the handover. In case of emergency handover alarms or cause 20 alarm, the cell evaluation will order the cells given in the raw list, putting in the first position the cells belonging to the preferred layer, having the highest priority (if EN_PRIORITY_ORDERING=ENABLE) and/or having the same frequency band type as the serving cell. In case of an intercell handover alarm, if the serving cell belongs to the raw cell list (emergency handover from the DCS 1800 inner zone of a multiband cell), this cell is put at the end of the candidate cell list with the MS zone indication OUTER.

In case of better condition handover alarms (except cause 20), the cell evaluation will order the cells given in the raw list, putting in the first position the cells belonging to the preferred layer and having the highest priority (if EN_PRIORITY_ORDERING=ENABLE).





1 · 5 · 97


Pre-Ranking

Pre-ranking in hierarchical or multi-band networks: For emergency handover and causes 20 and 28 only.

Priority(0,n) = 0Cell_layer_type = Pref_layer

Cell_band_type = serving_cell

Priority(0,n) = 1

Priority(0,n) = 5

Cell_band_type = serving_cell

Priority(0,n) = 0Cell_layer_type = Pref_layer

Priority(0,n) = 1

Priority(0,n) = 5

List ofcandidate

cells n

Cell_band_typenot applicable

to comfort causes

!





1 · 5 · 98


Pre-Ranking [cont.]

With priority(0,n) settings, the operator can, for each couple of cells: tag the target cell with a defined priority (from 0 = max to 5 = min) this definition has an higher priority than usual order/grade ranking

Especially useful for multi band/hierarchical architectures: a simple way to force a target cell whatever its RxLev level and PBGT nevertheless can be skipped over by filtering processes low interest for standard networks

RxLev: - 90 dBmPBGT: + 5 dB

Serving cell

Candidate cell 1

Candidate cell 2

RxLev: - 70 dBmPBGT: + 10 dB

Priority

P1

P0

Cell Ordering according to Target Layer and Target Band

In hierarchical or multiband environment, cells are characterized by the layer they belong to or/and the frequency band they use. The candidate cell evaluation process takes into account these characteristics in the candidate cell ordering.

In hierarchical environment, the HO detection process can indicate a preferred layer where the handover must be directed to. If this indication is used, the candidate cell evaluation puts in the first places of the list, the candidate cells belonging to the preferred layer. They are followed by the cells of the other layer, providing they are also correct candidates.

After this possible distinction, in each part of the list, the candidate cell evaluation sorts the candidate cells according to the parameter PRIORITY(0,n) (parameter on line changeable from the OMC-R).

The cells having the highest priority are put in the first place of the list. They are followed by the cells having the lowest priorities. The PRIORITY(0,n) is only used when the flag EN_PRIORTY_ORDERING is set to “enable”.

In case of emergency handover, for each category (preferred layer and other layer) and between cells having the same priority, the candidate cell evaluation sorts the candidate cells according to the frequency band they use: the cells which use the same frequency band as the serving cell are put first and they are followed by the cells which use the other frequency band.

The cell evaluation function is then applied to the different candidate cell lists defined from the preferred layer indication, the PRIORITY(0,n) parameter and the frequency band of the serving cell (only in case of emergency handover).





1 · 5 · 99


PBGT Filtering

Characteristics: optional, flag EN_PBGT_FILTERING filter out cells from the target list inhibited for better cell handovers based on of cells

power budget per couple was needed for multiband architecture

PBGT(n) > HO_MARGIN_XX (0,n) + OFFSET_HO_MARGIN_INNER

HO_MARGIN_XX (0,n) = HO_MARGIN_QUAL (0,n)for cause 2,4 HO_MARGIN_XX (0,n) = HO_MARGIN_LEV (0,n) for cause 3,5 HO_MARGIN_XX (0,n) = HO_MARGIN_DIST (0,n) for cause 6 OFFSET_HO_MARGIN_INNER is only applied when the MS is in the inner zone of a

concentric or multi band cell The averaging window is A_PBGT_HO

The filtering process allows to filter out cells from the target list before sending them to the ORDER or GRADE evaluation process.

It can be enabled/disabled on-line on a per cell basis from the OMC-R with the flag EN_PBGT_FILTERING.

The candidate cells are filtered on their power budget in relation to a handover margin threshold based on the handover cause.

Note: the averaging window used for this process is A_PBGT_HO (even for emergency handovers, where a handover alarm could have been raised through A_LEV_HO or A_QUAL_HO samples)





1 · 5 · 100


Order Evaluation

ORDER cell evaluation processCell "n" is ranked among other accordingly:If EN_LOAD_ORDER = ENABLE and cell n is internal to the BSC

ORDER (n) = PBGT(n) + LINK_FACTOR(0,n) + FREEfactor(n)- FREEfactor(0)- HO_MARGIN_XX(0,n)

· Link_factor (0,n) is an operator parameter to give a bonus/penalty to a cellex: avoid external HO, decrease incoming flow of HO to a cell from another

· FREEfactor is TCH traffic based bonus/penalty to rank cells

If EN_LOAD_ORDER = DISABLE or cell n is external to the BSCORDER (n) = PBGT(n) + LINK_FACTOR(0,n) - HO_MARGIN_XX(0,n)

Cell "n" is kept if:AV_RXLEV_NCELL (n) > RXLEVmin (n)+ max [0;(MS_TXPWR_MAX(n)-P)] [dBm]

Two types of cell evaluation algorithms can be used: ORDER and GRADE.

ORDER and GRADE are two different methods of cell ranking. They both consist in giving a mark or ’figure of merit’ to each candidate cell.

The basic differences between ORDER and GRADE are that:

with ORDER:

The candidate cell evaluation process interacts with the handover detection by use of cause-dependent handover margins.

The candidate cell evaluation process takes into account the number of free TCHs in the candidate cells.

with GRADE:

The candidate cell evaluation process does not interact with the handover detection.

The candidate cell evaluation process takes into account the relative load of traffic channels in the candidate cells.

The type of cell evaluation is chosen by the operator on a (serving) cell basis and is provided to the BSC with the parameter CELL_EV.

For any handover cause, the first cell in the list is taken as a target cell, i.e. the cell with the highest value of ORDER(n). The cells do not need to fulfill any other condition.

If no cell fulfills the condition and the serving cell does not belong to the target cell list, the target cell list is empty and no further action is carried out.

Note: the A_PBGT_HO averaging window is used for this process.





1 · 5 · 101


GRADE Evaluation

GRADE cell evaluation processCell "n" is ranked among other accordingly:If EN_LOAD_ORDER = ENABLE and cell n is internal to the BSC

GRADE (n) = PBGT(n) + LINK_FACTOR(0,n) + LOADfactor(n)

· Link_factor (0,n) is an operator parameter to give a bonus/penalty to a cell· LOADfactor(n) is a weighting factor that takes into account the relative load of

traffic channels in a cell

If EN_LOAD_ORDER = DISABLE or cell n is external to the BSC

GRADE (n) = PBGT(n) + LINK_FACTOR(0,n)

Cell "n" is kept if:AV_RXLEV_NCELL (n) > RXLEVmin(n)+ max [0;(MS_TXPWR_MAX(n)-P)]

LINKfactor(0,n) is a parameter set by OMC command for each cell(n).

LINKfactor(n1,n2) allows the operator to handicap or to favor the cell n1 with respect to its neighbor cell n2. In particular, it can be used to disadvantage an external cell when an internal cell is also a possible candidate.

For any handover cause, the first cell in the list is taken as a target cell, i.e. the cell with the highest value of GRADE(n). If no cell fulfills the condition and the serving cell does not belong to the target cell list, the target cell list is empty and no further action is carried out.

Note: the A_PBGT_HO averaging window is used for this process.






1 · 5 · 102


Exercise 1

Emergency HO detected With the “Candidate evaluation.xls” excel sheet... Filtering simulation for a list of candidate cells Ranking simulation for a list ofcandidate cells

Candidate Cell Evaluation

Serving cell Cell 1 Cell 2 Cell 3 Cell 4 Cell 5 Cell 6RxLev_cell1Mk RxLev_DL Cell_Nb1 BSIC_cell1 Cell_Nb2 BSIC_cell2RxLev_cell2 Cell_Nb3 BSIC_cell3RxLev_cell3 Cell_Nb4 BSIC_cell4RxLev_cell4 Cell_Nb5 BSIC_cell5RxLev_cell5 Cell_Nb6 BSIC_cell6RxLev_cell6

-102** 0 0 -110 0 0 -110 0 0 -110 0 0 -110 0 0 -110-99** 0 0 -110 0 0 -110 0 0 -110 0 0 -110 0 0 -110-99** 0 0 -110 0 0 -110 0 0 -110 0 0 -110 0 0 -110-98AssCmd 0 0 -110 0 0 -110 0 0 -110 0 0 -110 0 0 -110

-110AssCmp 0 0 -110 0 0 -110 0 0 -110 0 0 -110 0 0 -110-76** 0 0 -110 0 0 -110 0 0 -110 0 0 -110 0 0 -110-96** 0 0 -110 0 0 -110 0 0 -110 0 0 -110 0 0 -110-95** 14 3 -91 0 0 -110 0 0 -110 0 0 -110 0 0 -110-93** 14 3 -92 0 0 -110 0 0 -110 0 0 -110 0 0 -110-93** 1 0 -89 14 3 -91 0 0 -110 0 0 -110 0 0 -110-93** 1 0 -90 14 3 -94 0 0 -110 0 0 -110 0 0 -110-93** 1 -0 -88 14 3 -94 3 1 -101 0 0 -110 0 0 -110-94** 8 7 -93 1 0 -93 14 3 -96 3 1 -103 0 0 -110-96** 1 0 -93 8 7 -95 14 3 -99 3 1 -106 0 0 -110-96** -1 0 -91 8 7 -95 14 3 -99 3 1 -104 0 0 -110-98** 1 0 -92 14 3 -98 8 7 -99 3 1 -107 0 0 -110

-101** 8 7 -97 1 0 -97 14 3 -102 3 1 -107 0 0 -110-101HOCMD 8 7 -96 1 0 -99 14 3 -103 3 1 -108 0 0 -110

0 0 -1100 0 -1100 0 -1100 0 -1100 0 -1100 0 -1100 0 -1100 0 -1100 0 -1100 0 -1100 0 -1100 0 -1100 0 -1100 0 -1100 0 -1100 0 -1100 0 -1100 0 -110

HO Cause

A_PBGT_HO

GRADE EVALUATION

Priority(0,n)

HO_MARGIN_LEV(0,n)RX_LEV_MIN(n)

LINK_FACTOR(0,n)

LoadFactor(n)

DL Level

6

0 for all neighbor cell

0-100

0 for all neighbor cell

0

Time allowed:

15 minutes





1 · 5 · 103


Exercise

Emergency HO detected

1 Book-keeping list

Book-keeping list(14;3) (1;0) (8;7) (3;1)

2 Averaging measurement

Averaged measurements and PBGT(n)AV_RXLEV_PBGT_HO

AV_RXLEV_PBGT_HO

(14;3)

(1;0)

(8;7)

(3;1)

-100

-95

-96

-106

PBGT(n)

-2

3

2

-8

3 PBGT Filtering

PBGT(n)

(1;0)

(8;7)

3

2

PBGT Filtering

4 GRADE evaluation process

GRADE(n)

(1;0)

(8;7)

3

2

GRADE evaluation process

5 Target Cell

(1;0)

? ?

?

?

?





1 · 5 · 104

3 Exercise





1 · 5 · 105

3 Exercise

Exercise

List all the parameters involved in the detection of cause 23 List all the causes impacted by the parameter DELTA_INC_HO_MARGIN List all the causes impacted by the parameter L_RXQUAL_UL_H List all the causes impacted by the parameter BS_TXPWR_MAX List all the causes impacted by the parameter BS_P_CON_ACK

Time allowed:

10 minutes





1 · 5 · 106








1 · 5 · 107

End of ModuleHandover Algorithms





Module 6Resources Allocation Management








GSM B11 · BSS B11 Radio Fine Tuning IntroductionB11 Radio Fine Tuning · Resources Allocation Management

1 · 6 · 2

Blank Page




Document History





1 · 6 · 3

Module Objectives


Describe TCH resource allocation List the associated parameters





1 · 6 · 4







1 · 6 · 5

Table of Contents


1 TCH Resource Allocation Algorithm 7





1 · 6 · 6








1 · 6 · 7

1 TCH Resource Allocation Algorithm





1 · 6 · 8


Radio Allocation and Management

Radio resource Allocation and Management (RAM) aims at: Managing pools of TCH radio resources by: defining TCH radio timeslots as a function of the cell radio configuration from the

operator sorting these TCH TSs according to their radio capabilities (FR or DR, frequency band

(G1 or GSM/DCS))

Allocating dedicated TCH radio resources by: selecting the TCH pool in which the TCH should be chosen according to:

the requested channel rate (FR or HR) the radio capability of the mobile the TRE DR capability and the TRE band

selecting the best TCH resource among the available TCH channels of this pool according to several criteria





1 · 6 · 9


Radio Timeslot of a Cell: Operator View

On the OMC-R the operator can configure the following Radio TS per cell: Main BCCH timeslot (BCC): TS carrying FCCH + SCH + BCCH + CCCH Main combined BCCH timeslot (CBC): TS carrying FCCH + SCH + BCCH + CCCH

+ SDCCH/4 + SACCH/4 Main combined BCCH with CBCH (CBH) : TS carrying FCCH + SCH + BCCH +

CCCH + SDCCH/3 + SACCH/3 + CBCH Secondary BCCH timeslot (CCH) : TS carrying BCCH + CCCH Static SDCCH timeslot (SDC): TS carrying SDCCH/8 + SACCH/8 Static SDCCH timeslot combined with CBCH (SDH): TS carrying SDCCH/7 +

SACCH/7 + CBCH Dynamic SDCCH/8 timeslot (SDD): TS carrying TCH + SACCH or SDCCH/8 +

SACCH/8 TCH timeslot (TCH): TS carrying TCH + SACCH or used as a PS timeslot (PDCH)

The operator has to choose between a Combined BCCH (CBC TS) or a Non-combined BCCH configuration (BCC TS).

A PDCH is a radio timeslot used for PS traffic or signaling.

It can carry either PS traffic or PS signaling but not both.

If it carries traffic it is called a Slave PDCH (SPDCH) TS and it carries the logical channels PDTCH+PACCH+PTTCH.

If it carries signaling it is called a Master PDCH (MPDCH) TS and it carries:

either the logical channels PBCCH+PPCH+PAGCH+PRACH: it is then called a Primary MPDCH

or only PPCH+PAGCH+PRACH: it is then called a Secondary MPDCH

SDD TS can carry either TCH or SDCCH channels but not both at the same time.

TCH TS can carry either CS traffic channel TCH or PS logical channels but not both at the same time.





1 · 6 · 10


Radio Timeslot of a Cell: RAM View

In the BSS the RAM software module maps the OMC-R cell radio configuration to its own types of TS: Pure BCCH timeslot: BCC TS carrying only common CS signalling

(BCCH+CCCH) Pure SDCCH timeslot: CBC or SDC TS carrying only dedicated CS signalling

(SDCCH) Pure TCH timeslot: TCH TS carrying only TCH traffic TCH/SDCCH timeslot: SDD TS carrying either CS traffic (TCH) or dedicated CS

signalling (SDCCH) TCH/SPDCH timeslot: TCH TS carrying either CS traffic (TCH) or PS traffic

(SPDCH channels) MPDCH timeslot: TCH TS carrying common PS signalling (PBCCH+PCCCH or

PCCCH only)





1 · 6 · 11

NB_TS_MPDCH MPDCH TS are defined on the BCCH TRX: on the timeslots configured as TCH TS on the OMC-R having the lowest timeslot index

TCH/SPDCH TS are defined as being part of an SPDCH group Pure TCH timeslots are OMC-R TCH TS neither defined as MPDCH TS nor

in an SPDCH group


Radio Timeslot: OMC-R / RAM Mapping

OMC-Rradio TS

RAMradio TS

BCC

CCH

CBC

SDC

SDD

TCHC

Pure BCCH

Pure SDCCH

TCH/SDCCH

TCH/SPDCH

MPDCH

Pure TCH

MPDCH TS are defined on the BCCH TRX even if the corresponding TRX_PREF_MARK is different from 0.





1 · 6 · 12


Definition of a TCH/SPDCH TS

For PS traffic resource allocation, an SPDCH group is defined on a per TRX basis and is made up of consecutive timeslots: mapped on OMC-R TCH TS located on a PS capable TRX (TRX_PREF_MARK = 0) not defined as MPDCH TS having the same radio configuration (MA, MAIO)

If several SPDCH groups can be defined on a given TRX, the BSS chooses the SPDCH group of timeslots having the highest number of consecutive timeslots.

A radio timeslot belonging to one of the different SPDCH groups of the cell is identified in RAM as a TCH/SPDCH timeslot.

The timeslots shall be consecutive on a given TRX, which means that there shall be no hole in the SPDCH group.

If several SPDCH groups can be defined on the same TRX and having the same number of consecutive timeslots then the group that is located on the left side of the TRX (i.e. the timeslots having the lowest index) shall be chosen.





1 · 6 · 13


Definition of a TCH/SPDCH TS [cont.]

A non-hopping cell is configured on the OMC-R

Find the radio TS configuration in RAM if NB_TS_MPDCH= 0

BCC TCH SDC TCH

SDD TCH SDC TCH

TCH TCH TCH TCH

TCH TCH TCH TCH

TCH TCH TCH TCH TCH TCH TCH TCH


TRX1

TRX2

TRX3

TRX4

TRX_PREF_MARK

0

0

0

1

0 1 2 3 4 5 6 7

TRX1

TRX2

TRX3

TRX4

0 1 2 3 4 5 6 7

MPDPBCPSDPTCTSDTSP

: MPDCH: Pure BCCH: Pure SDCCH: Pure TCH: TCH/SDCCH: TCH/SPDCH

The timeslots shall be consecutive on a given TRX, which means that there shall be no hole in the SPDCH group.

If several SPDCH groups can be defined on the same TRX and having the same number of consecutive timeslots then the group that is located on the left side of the TRX (i.e. the timeslots having the lowest index) shall be chosen.





1 · 6 · 14


TCH Pools

3 pools of TCH resources are managed per cell: G1 pure TCH pool: contains all the free TCH sub-channels (FR or HR) free on

the pure TCH TS of the G1 TRXs GSM/DCS pure TCH - TCH/SPDCH pool: contains all the free TCH sub-channels

(FR or HR) free on the pure TCH TS and on the TCH/SPDCH TS of the GSM/DCS TRXs GSM/DCS TCH/SDCCH pool: contains all the free TCH sub-channels (FR or HR)

free on the TCH/SDCCH TS of the GSM/DCS TRXs

Any pure TCH, TCH/SPDCH, TCH/SDCCH TS can be: Busy: if it is not free to serve an FR TCH request Free: if it is free to serve an FR TCH request

A DR TS (timeslot on a DR TRX) is free if no FR TCH or HR TCH is allocated for a call on this timeslot.

A DR TS is busy if at least one TCH is allocated for a call on this timeslot:

1 FR TCH, or

1 HR TCH (HR 0 TCH or HR 1 TCH), or

2 HR TCHs (HR 0 TCH and HR 1 TCH).





1 · 6 · 15


TCH Sub-Pools

FR TCH channels can be allocated on both FR and DR TRXs whereas HR TCH channels can only be allocated on DR TRXs

Each of the three TCH pools is divided in three sub-pools: FR sub-pool: contains all the free FR TCH sub-channels available on the FR

TRX DR: sub-pool: contains all the free FR TCH sub-channels available on the DR

TRX HR sub-pool: contains all the free HR TCH sub-channels whose mate HR TCH

sub-channel is busy(always located on the DR TRX)





1 · 6 · 16


TCH Allocation Process

TCH Request

TCH Allocation

- Radio capability of the mobile- Channel type (FR, HR, DR)- Speech version (FR, HR, EFR, AMR FR, AMR HR)- Request type (NA or HO)

- Cell channel type capability- Cell codec type capability- Cell load

TCH selected

TCH free?

Yes

Queuing?

Select a TCH sub-pool

Select a TCH in this sub-pool

TCH rejectedTCH queued

Yes No

No

Inputs for TCH allocation function:

radio capability of the MS:

The BSS knows the radio capability of the mobile from the MS CLASSMARK after the Radio Link Establishment procedure

requirements from the MSC:

Channel type (mandatory) is one of the following:

List of preferred speech version (optional):

GSM full rate speech version 1 = FR

GSM full rate speech version 2 = EFR

GSM full rate speech version 3 = AMR FR

GSM half rate speech version 1 = HR

GSM half rate speech version 3 = AMR HR

capabilities of the cell:

FR TCHs only if only FR TRXs / FR+HR TCHs if some DR TRXs

codec supported among: FR, EFR, AMR FR, HR, AMR HR

FR Full Rate onlyHR Half Rate onlyDR FR P N CA Dual Rate Full Rate Preferred N o Changes Allowed after first channel allocation

as a result of the requestDR FR P CA Dual Rate Full Rate Preferred Changes Allowed after first channel allocation as a

result of the requestDR HR P N CA Dual Rate Half Rate Preferred N o Changes Allowed after first channel allocation

as a result of the requestDR HR P CA Dual Rate Half Rate Preferred Changes Allowed after first channel allocation as a

result of the requestDR SV P N CA Dual Rate N o Changes of channel rate Allowed after first channel allocation as a

result of the requestDR SV P CA Dual Rate Changes of channel rate Allowed after first channel allocation as a

result of the request





1 · 6 · 17


TCH Allocation Process [cont.]

TCH Allocation

TCH free?

Queuing?

TCH selected

Select a TCH sub-pool

Select a TCH in this sub-pool

TCH rejectedTCH queued

Yes No

Yes No

ALLOC_ANYWAYT11T11_FORCEDT_QHO

NUM_TCH_EGNCY_HO

The timer T11 corresponds to normal assignment with queuing authorised.

The timer T11_FORCED corresponds to normal assignment:

either when the queuing is not authorized by the MSC but forced by the BSC (QUEUE_ANYWAY = TRUE),

or when the queuing is not authorized but the request has its pre-emption indicator set and has already forced the release of a lower priority pre-emptable on-going call.

The QUEUE_ANYWAY flag is checked by the Normal Assignment (NASS) entity.

The timer T_QHO corresponds to an external channel change with queuing authorized or to an external channel change when the queuing is not authorized but the request has its pre-emption indicator set and has already forced the release of a lower priority pre-emptable on-going call.

NUM_TCH_EGNCY_HO: Number of RTCHs reserved for incoming HO. These RTCHs cannot be allocated for call establishment. (from the user point of view, it can be better to avoid a drop rather than to allow a new call).

ALLOC_ANYWAY: set to “TRUE”, it allows to use an RTS normally reserved for incoming HO (NUM_TCH_EGNCY_HO) for call establishment. But only after having passed by the queue.

3 queues: 3 different timers

T11: maximum time a request can be kept in queue.

T11_FORCED: maximum time a request can be kept in queue when the queue is forced.

T_QHO: maximum time an incoming HO request can be kept in queue.





1 · 6 · 18


TCH Sub-Pool Selection

The BSS selects the TCH sub-pools in which a TCH channel can be allocated according to: The requested channel rate and the cell load situation favour HR if cell is loaded

A priority given to generic resources1. G1 pool (E-GSM mobile only) on non PS capable TRX2. GSM/DCS pure TCH - TCH/SPDCH pool on non PS capable TRX3. GSM/DCS pure TCH - TCH/SPDCH pool on PS capable TRX4. G1 pool (E-GSM mobile only) on PS capable TRX 5. GSM/DCS TCH/SDCCH pool

An optimisation of FR/HR resources favour FR pool over DR pool for a FR TCH request favour HR pool over DR pool for an HR TCH request

The availability of a TCH channel in the sub-pool

TCH allocation without list of preferred speech versions:

FR request: FR pool DR pool

HR request: HR pool DR pool

DR FR preferred request:

cell load=False: FR pool DR pool HR pool

cell load=True: HR pool DR pool FR pool

DR HR Pref. request: HR pool DR pool FR pool

TCH allocation with a list of preferred speech versions:

FR SV then HR SV: FR pool DR pool HR

HR SV then FR SV: HR pool DR pool FR

FR SV only: FR pool DR pool

HR SV only: HR pool DR pool

From B9 and due to the new feature “Enhanced E-GSM band handling”, a new parameter has to be set:

EGSM_RR_Alloc_Strategy = 0 (default) (Different behavior for EGSM-capable MS):The BSS handles differently EGSM capable MS from PGSM only capable MS in EGSM cells; this means that not all GSM900 MS in the network are assumed to be E-GSM capable. G1 and PGSM TRX are not managed in the same way.

EGSM_RR_Alloc_Strategy = 1 (Same behavior for EGSM capable MS):The BSS handles in the same way PGSM capable only MS as EGSM-capable MS in EGSM cells; this means that all GSM900 MS in the network are assumed to be E-GSM capable. No difference made between a G1 TRX and a PGSM TRX.

So, if PGSM only capable MS have to be supported, the parameter must be set to the value 0. Otherwise 1.

As (E)GPRS service was not supported on G1 TRX (B7.2, B8). Consequently, new pools have to be taken into account:Capable or not capable PS TRX in G1 and in GSM/DCS bands.

Independently of the E-GSM preference, a TCH request is preferentially allocated firstly on TCH/VGCH timeslots, secondly on TCH/SPDCH/VGCH timeslots. Finally, TCH requests are served on TCH/SDCCH timeslots, which timeslots can also be used for SDCCH allocations (i.e. TCH requests are preferentially not served on TCH/SDCCH timeslots).VGCH: Voice Group Call Channel





1 · 6 · 19


TCH Selection

PS traffic resources optimization TCH allocated on TRX of highest TRX rank and on TS of highest TS index

SPDCH allocated on TRX of lowest TRX rank and on TS of lowest TS index

2 modes of TCH selection On pure TCH or TCH/SDCCH timeslots On TCH/SPDCH timeslots

TCH selection on pure TCH or TCH/SDCCH timeslots if:

there is at least one candidate TCH free on pure TCH TS

OR

there is no candidate TCH free on TCH/SPDCH TS: only the candidate TCH sub-channels available on pure TCH TS and on TCH/SDCCH TS are kept as candidate

TCH selection on TCH/SPDCH timeslots if:

there is at least one candidate TCH free on a TCH/SPDCH TS

AND

there is no candidate TCH free on pure TCH TS: only the candidate TCH sub-channels available on TCH/SPDCH TS are kept as candidate





1 · 6 · 20


TCH Selection on Pure TCH or TCH/SDCCH TS

The TCH is chosen from the selected sub-pool according to the following criteria:

Non hopping cellBiggest Mobile AllocationEN_MA_SELECTION = true

TCH selected

Highest TS index

HR 0 TCH sub-channel

TCH candidates of the selectedTCH sub-pool

Highest TRX_PREF_MARK

FR allocation orHR allocation on busy TS

Best Interference Band

Highest TRX Identity

The BSS attempts to offer the best quality of service for TCH calls in accordance with the privileged order between the groups of TRXs (if any) defined by the operator. Among a group of TRXs, the BSS attempts to allocate traffic channels that have the best quality characteristics (channels using frequency with low reuse factor, large hopping frequency sets, low measured interference).

The benefits from this type of allocation are that the operator has the possibility to define groups of TRXs and to favor (or to disadvantage) them on the other if he wants to do so. Among a group of pure TCH or TCH/SDCCH timeslots, the overall interference is kept as low as possible, thus the user will perceive a better quality of service.

The BSS chooses the best TCH among the sub-channels of the selected TCH sub-pool applying criteria below in the specified order of priority:

1. TCH on TS with the highest TRX Preference Mark

According to the frequency plan, the coverage and interference probability of a cell (or according to measurements), the operator may know which TRX should be a priori favored for TCH selection. For that purpose, it is possible for operators to give a preference mark to each TRX of a cell. This mark is given through the parameters TRX_PREF_MARK (TPM) changeable at OMC-R side per TRX. The range of TRX_PREF_MARK will be from 0 (lowest priority) to 7 (highest priority). The TCH selection function favors the channels with the highest TPM.

Note that a few Pure TCH TS should be available in a cell on a TRX of TRX_PREF_MARK value of 0 since TCH/SPDCH TS may also be defined on this TRX according to PS radio resource configuration.

2. TCH on TS with the biggest Mobile Allocation (for hopping cell only)

Considering that the number of frequencies is a key factor for the average quality of channels, the TCH selection function favors the TS with the biggest MA (i.e. with the most frequencies in their frequency hopping sequence). This selection criterion is enabled/disabled via the flag EN_MA_SELECTION changeable at the OMC-R side on a per cell basis.

3. TCH on TS from the best Interference Band

Considering that the uplink received level measured by the BTS on an idle channel is a means to assess the quality when in connected mode, the TCH selection function favors the TS belonging to the best Interference Band (IB). Five IBs are defined through 5 parameters INTFBD1 to INTFBD5 where INTFBD(i)< INTFBD(i+1) and INTFBD5 = -47 all changeable at the OMC-R side on a per BTS basis.

4. TCH on TRX with the highest TRX identity

5. TCH on TS with the highest TS index

6. HR 0 TCH if the two sub-channels remaining candidates are the 2 HR TCHs of the same free TS





1 · 6 · 21


TCH selection on TCH/SPDCH TS

The TCH is chosen from the selected sub-pool according to the following criteria:

TRX rank is determined by the TRX Ranking algorithm described in the GPRS & EGPRS Radio Algorithms Description training course

Highest TRX Rank

TCH selected

FR allocation orHR allocation on busy TS

HR 0 TCH sub-channel

Highest TS index

TCH candidates of the selectedTCH sub-pool

The BSS tends to allocate to the MFS the TCH/SPDCH timeslots so as to avoid conflicts between CS and PS allocations on PS capable TRX.

In order to be able to allocate as much slave PDCHs as possible to a given TBF, it is important to avoid any mix ofallocation between TCHs and SPDCHs (e.g. avoid on a TRX a configuration such as TCH – TCH – SPDCH – SPDCH –TCH – SPDCH – SPDCH – SPDCH). For that purpose, a TRX rank is assigned to each PS capable TRX. The TRX having the highest TRX rank is preferentially selected for TCH allocations, whereas TRX having the lowest TRX rank is preferentially selected for SPDCH allocations

This rule only applies on PS capable TRX. On a given PS capable TRX, TCH are preferentially allocated on the right side of the TRX (highest TS index), whereas SPDCH are preferentially allocated on the left side (lowest TS index).





1 · 6 · 22


Exercise 1

A cell is configured on the OMC-R and TREs are mapped by BSS.

Time allowed:

10 minutes

BCC SDC TCH TCH

SDD TCH TCH TCH

TCH TCH TCH TCH

TCH TCH TCH TCH

SDC TCH TCH TCH TCH TCH TCH TCH


TRX1

TRX2

TRX3

TRX4

TRX_PREF_MARK

0

0

1

0

0 1 2 3 4 5 6 7

TCH TCH TCH TCH TCH TCH TCH TCHTRX51

TRE

G4 MP FR

G4 MP DR

G3 DR

G4 MP FR

G3 DR





1 · 6 · 23


Exercise [cont.]


MPD MPDCH

PBC Pure BCCH TS

PSD Pure SDCCH TS

PTC Pure TCH TS

TSD TCH/SDDCH TS

TSP TCH/SPDCH TS

TRX1

TRX2

TRX3

TRX4

TRX_PREF_MARK

0

0

1

0

0 1 2 3 4 5 6 7

TRX51

TRE

G4 MP FR

G4 MP DR

G3 DR

G4 MP FR

G3 DR





1 · 6 · 24


Exercise [cont.]

Find which TCH sub-channel is allocated:1. For MS1: E-GSM, DR2. For MS2: GSM/DCS, DR3. For MS3: GSM, FR4. For MS4, MS5, …., MSn: E-GSM, DR

n = ?

Pure TCH TS

TCH/SPDCH TS

TCH/SDDCH TSas TCH TS

FHP

Cell load = true

: FR TCH call: HR TCH call: SPDCH TS

TSD P P P

P P P

P F

F F F F F F

P P P P P P P

TRX1

TRX2

TRX3

TRX4

TRX_Rank

2

3

-

1

0 1 2 3 4 5 6 7

F FTRX5-

TRE

GSM/FR

GSM/DR

GSM/DR

GSM/FR

G1/DR

H

H HHHHHH





1 · 6 · 25








1 · 6 · 26

End of ModuleResources Allocation Management





Module 7Optimization Methodology








GSM B11 · BSS B11 Radio Fine Tuning IntroductionB11 Radio Fine Tuning · Optimization Methodology

1 · 7 · 2

Blank Page




Document History





1 · 7 · 3

Module Objectives


Estimate qualitatively the impact of parameters change





1 · 7 · 4







1 · 7 · 5

Table of Contents


1 Presentation 72 Examples and Exercises 9

2.1 Overview 102.2 Optimization of Handover Algorithms 112.3 Power Control Algorithms Optimization 162.4 Traffic Load Sharing 19





1 · 7 · 6








1 · 7 · 7

1 Presentation





1 · 7 · 8

1 Presentation

Justification

Tuning is not an exact science The optimizer has to control every parameter change and predict

qualitatively what the consequences will be Note: Each change of parameter and its justification have to be

registered in a database for operation convenience





1 · 7 · 9

2 Examples and Exercises





1 · 7 · 10


2.1 Overview

Example 1: Optimization of handover algorithms Sliding averaging window

Example 2: Optimization of power control algorithms Sliding averaging window

Example 3: Traffic load sharing Parameters qualitative influence





1 · 7 · 11


2.2 Optimization of Handover Algorithms

Search for best tuning of HO parameters to decrease call drop

Call drop

HO/Call





1 · 7 · 12


2.2 Optimization of Handover Algorithms [cont.]

Main Objective: make the HO algorithm as efficient as possible Minimize call drop rate trigger HO soon enough toward the “best” neighbour

While keeping a good speech quality avoid HO due to quality: “too late” avoid having HO/call rate too high





1 · 7 · 13



Method Collect Abis trace chart Search for HO level to avoid quality lower than 4 (or even 3) sufficient number of “bad quality” samples low standard deviation problem when HO already activated

Then tune according to QoS indicators (OMC-R) by repetitive process A_PBGT_HO/A_LEV_HO/A_QUAL_HO L_RXLEV_UL_H, L_RXLEV_DL_H, L_RXLEV_UL_P, L_RXLEV_DL_P OK as soon as HO success rate stabilized

< R x Q u a l _ D L > = f ( A V _ R x L e v _ D L )

0

1

2

3

4

5

6

7

N b _ s a m p l e s

0

2 0 0

4 0 0

6 0 0

S t a n d a r d D e v i a t i o n

0

0 .5

1

1 .5

2

< R x Q u a l _ U L > = f ( A V _ R x L e v _ U L )

0

1

2

3

4

5

6

7

N b _ s a m p l e s

02 0 04 0 06 0 08 0 0

1 0 0 0

S t a n d a r d D e v i a t i o n

0

1

2

3

Never forget that Abis information takes into account the traffic distribution in the cell. Any parameter tuning done after an Abis study has to be checked periodically as the distribution in the cell can change from one week to another.

Use the pivot table function (Excel) to build this graph.





1 · 7 · 14



Neighbouring relationship cleanup Remove useless relationships (A interface statistics, PM Type 180) Remove the common BCCH/BSIC couple Add new relationships when a new site is created

Finally, check the main QoS indicators Call drop rate HO failure rate HO/call rate Radio Link Failure rate

(the strong rate of radio link failure can denounce a lack of vicinity relation between cells)





1 · 7 · 15



According to the Abis results and some parametersalready set, tune qualitatively the sliding averaging windows: A_QUAL_HO A_LEV_HO

Time allowed:

5 minutes

Level at RxQual=3 - 80 dBm - 96 dBm - 90 dBm

L_RXLEV_DL_H

A_QUAL_HO

A_LEV_HO

- 85 dBm

6

?

- 90 dBm

6

?

- 90 dBm

?

4





1 · 7 · 16


2.3 Power Control Algorithms Optimization

Optimization of Downlink Power Control Decrease of downlink interference Risks of delay of HO (without fast power control)

Optimization of Uplink Power Control Decrease of Uplink interference MS battery saving Risks of delay of HO (without fast power control)





1 · 7 · 17


2.3 Power Control Algorithms Optimization [cont.]

The main tuning problem is the interaction with handover, which can slow down HO decision, and debase call drop rate Power control threshold must be within HO ones Dynamic step size must be activated if possible

In the example below, a dynamic MS PC is activated. The MS power changes are really reactive and control the UL level between -80 and -90dBm. In this example, the HO threshold is -98 dBm.





1 · 7 · 18


2.3 Power Control Algorithms Optimization [cont.]

Explain qualitatively the impacts of some parameter changes

What happens if: we increase POW_INC_FACTOR? we increase MAX_POW_INC? We increase A_LEV_PC?

Time allowed:

5 minutes





1 · 7 · 19


2.4 Traffic Load Sharing

Used to unload cell with too high traffic, without HW extension

Trade-off between traffic sharing/radio quality Different algorithms Fast Traffic Handover: Cause 28 Traffic Handover: Cause 23 and 12 with DELTA_HO_MARGIN(0,n) Static (couple of cells): HO_MARGIN, LINK_FACTOR On a local traffic basis: Load_Factor/Free_Factor Forced Directed Retry





1 · 7 · 20


2.4 Traffic Load Sharing [cont.]

Fast Traffic HO Useful in case of sudden traffic peaks as the process response is

instantaneous (no averaging window) The principle is to force handover towards neighbour cells which

have lower traffic when a request is queued in the serving cell. Interaction with Forced DR due to the use of same thresholds Optimization method (repetitive process) Tunes L_RXLEV_NCELL_DR(n), FREElevel_DR(n) Applies new values, checks traffic peaks, QoS indicators





1 · 7 · 21



The Pros and cons of Fast Traffic HO Efficiency depends on: Traffic location in the loaded cell Capacity of neighbour cells

Increase of the number of HO/callIncrease of incoming HOs fail rate (risk of ping-pong effect) In case of internal HO: use PING_PONG_HCP with T_HCP

or/and enable HO CAUSE 23Heavy to tune (has to be done for each couple of cells)

Adapted to instantaneous traffic modificationCan be used to send traffic towards a cell external to the serving BSCAdapted to hierarchical network, but also to standard ones





1 · 7 · 22



DELTA_HO_MARGIN (0,n)

CHANGE DYNAMICALLY TRAFFIC DISTRIBUTION WITH HO: Traffic HO Cause 23 Ease outgoing better condition HO on a traffic point of view

Slow down outgoing better cell HO (to be tuned for a given couple of cells) When the better cell in radio condition is the worst cell in traffic terms

Optimization method (repetitive process) Tune DELTA_DEC_HO_MARGIN and DELTA_INC_HO_MARGIN Apply new values, check traffic, QoS indicators and possibly speech

quality





1 · 7 · 23



The Pros and cons of DELTA_HO_MARGIN (0,n) method Efficiency depends on: Traffic location in the loaded cell Cells overlap Capacity of neighbour cells

Increase the number of HO/callCannot be used to send traffic toward a cell external to the serving BSCThe call has to be first established on a loaded cell, before being “exported” It can be rejected

Easy to tune (dynamic process)Adaptability to instantaneous and long-term traffic modifications





1 · 7 · 24



HO_MARGIN / LINK_FACTOR

CHANGE STATICALLY TRAFFIC DISTRIBUTION WITH HO: Ease outgoing better cell HO (to be tuned for a given couple of

cells) Decrease HO_MARGIN (can make a cell “candidate”) Increase LINK_FACTOR (used to rank candidate cells)

Optimization method (repetitive process) Look for neighbour cells able to carry extra traffic Use Abis trace to check if these cells are candidate

if yes, use LINK_FACTOR to favor them if not, use HO_MARGIN and LINK_FACTOR

Apply new values, check traffic, QoS indicators and possibly speech quality





1 · 7 · 25



The Pros and cons of LINK_FACTOR/HO_MARGIN Can be efficient (up to 20% increase of capacity) in some cases Cell overlap Capacity of neighbour cells

Increase the number of HO/callThe call has to be first established on a loaded cell, before being “exported” It can be rejected

Heavy to tune (has to be done for each couple of cells)No adaptability to instantaneous and long-term traffic modifications

Can be used to send traffic toward a cell external to the serving BSC





1 · 7 · 26



FREE_FACTOR/LOAD_FACTOR

Taking into account the current load of cells, send the MS toward the less loaded cell with HO Ease outgoing better cell HO, according to: Load_Factor (% of TCH occupancy) of serving and “target” cells Free_Factor (number of free TCHs) of serving and target cells (order only) cannot make a “candidate” cell, only change ranking

Tuning method (repetitive) to be activated locally for each cell with default parameter setting look for QoS indicators (esp. traffic intensity and blocking rate) tune tables accordingly





1 · 7 · 27



The Pros and cons of load/free factors method

Lower efficiency compared to LINK_FACTOR/HO_MARGINCalls have to be established on a loaded cell before being “exported”Tuning is performed on a cell-per-cell basisCannot be used to send traffic toward an external cell

Adapted to dynamic change of traffic and capacity (for Load_Factor)No increase of HO/call rate





1 · 7 · 28



Forced directed retry method Mechanisms The MS is connected on an SDCCH of cell1 It must switch on TCH No TCH is free on cell1 There is at least 1 neighbour cell which has: sufficient DL level seen by the MS enough free TCHs

The MS is handed over to TCH towards this cell if there are several cells, the one with the best PBGT is selected





1 · 7 · 29



Method: trade-off between traffic and radio quality

Mainly L_RXLEV_NCELL_DR(n)parameter to tune the lower, the better the traffic sharing the lower, the higher the interference

risks

QoS indicators and field tests (speech quality) are necessary for tuning

Cell 2: 45Cell 3: 23

Ce

ll 1:

2

4

Forced Directed Retry

The following condition is checked every measurement reporting period and if at least one input pre-processed parameter AV_RXLEV_NCELL_DR(n) is available.

CAUSE = 20 (high level in neighbour cell for forced directed retry)

AV_RXLEV_NCELL_DR(n) > L_RXLEV_NCELL_DR(n) (n = 1 ... BTSnum)

and EN_FORCED_DR = ENABLE

The threshold L_RXLEV_NCELL_DR(n) is the observed level from the neighbour cell n at the border of the area where forced directed retry is enabled. This threshold fixes the size of the overlapping area where forced directed retry can be performed. It should be greater than RXLEVmin(n).





1 · 7 · 30



The Pros and cons of Forced directed retry

Highest efficiency (up to 30%)No increase of HO/call rateCan be used to send traffic toward an external cellAdapted to dynamic change of traffic Adapted to hierarchical networks, but also to standard ones

Tuning is performed on a cell-per-cell basis





1 · 7 · 31



Draw qualitatively the new serving areas on the pseudo map when enabling traffic HO with: DELTA_DEC_HO_MARGIN=6dB DELTA_INC_HO_MARGIN=4dB

PBGT(0) = 5

05 5PBGT(0) PBGT(n)

PBGT(n) = 5

Traffic_load

Loaded cell 0 Unloaded cell n

EN_TRAFFIC_HO = 0

Cause 12Cause 12

Time allowed:

5 minutes





1 · 7 · 32



What happens when EN_FAST_TRAFFIC_HO = ENABLE and EN_TRAFFIC_HO(n,0) = DISABLE?

Time allowed:

5 minutes

QueuedAssignment

Request

PBGT(0) = 5

05 5PBGT(0) PBGT(n)

PBGT(n) = 5

Traffic_load


Av_Rxlev_Ncell(n) = -82 dBm Av_Rxlev_Ncell(0) = -74 dBmAv_Rxlev_PBGT_HO = -82 dBm

L_RLEV_NCELL_DR(n) = -85 dBm





1 · 7 · 33



What happens when EN_FAST_TRAFFIC_HO = ENABLE and EN_TRAFFIC_HO(n,0) = ENABLE?

Time allowed:

5 minutes

QueuedAssignment

Request

PBGT(0) = 9

09 -1PBGT(0) PBGT(n)

PBGT(n) = -1

Traffic_load


Av_Rxlev_Ncell(n) = -82 dBm Av_Rxlev_Ncell(0) = -74 dBmAv_Rxlev_PBGT_HO = -82 dBm

5 5





1 · 7 · 34








1 · 7 · 35

End of ModuleOptimization Methodology





Module 8Case Studies








GSM B11 · BSS B11 Radio Fine Tuning IntroductionB11 Radio Fine Tuning · Case Studies

1 · 8 · 2

Blank Page




Document History





1 · 8 · 3

Module Objectives


propose a set of parameters to solve typical radio problems





1 · 8 · 4







1 · 8 · 5

Table of Contents


1 Theoretical Presentation 72 Eight Case Studies 9

2.1 Tunnel Case 102.2 Radar Case 112.3 Tower Case 122.4 Resurgence Case 132.5 Forest Case 142.6 Highway Case 152.7 TCH/SDCCH Congestion Case 162.8 Indoor Cell Congestion Case 17





1 · 8 · 6








1 · 8 · 7

1 Theoretical Presentation





1 · 8 · 8

1 Theoretical Presentation

Justification

Some typical problems due to particular field configuration always occur in a GSM network





1 · 8 · 9

2 Eight Case Studies





1 · 8 · 10


2.1 Tunnel Case

Radiating cable in a tunnel Question: Risks of such a configurationTune the right parameters for the tunnel cellCatch quickly car traffic Avoid the pedestrian traffic

Indoor BTS

Outdoor BTS

Pedestrianmobile





1 · 8 · 11


2.2 Radar Case

Radar situation A “radar” cell situated on top

of a hill provides a wide coverage area. An industrial zone in the

valley is covered by small cells but also by the “radar”cell. The serving areas in the IZ are not clearly defined.

Objective Give a parameter set to

prevent the radar cell from catching any traffic in the industrial zone by HO assignment





1 · 8 · 12


2.3 Tower Case

Tower situation The indoor mobile selects in idle mode the

outdoor cell (same LA)

Objective Define a set of parameters to avoid that

effect

Outdoor cell

Indoorantenna

Indoormobile





1 · 8 · 13


2.4 Resurgence Case

Resurgence situation In rural network, especially

in hilly landscape, many resurgences occur from very far cells.

Objective Define a set of parameters

to avoid radio link establishment to those cells and TCH traffic on those cells

Cell A

Resurgencefrom cell A

Cell B

25 Km





1 · 8 · 14


2.5 Forest Case

Forest situation: a highway crosses a forest High call drop rate (radio cause) on the cell and drive tests: strong level

attenuation at the entrance of the forest Objective Define a set of parameters to avoid radio link failure

-75 dBm

-90 dBm

Forest(ATT = 10 dB every 100 m)

Hig

hw

ay

BTS





1 · 8 · 15


2.6 Highway Case

Highway situation: A highway is slightly covered (best coverage on 200m) by an ‘orthogonal’

cell (cell C on the map) Objective Define a set of parameters to avoid traffic in the ‘orthogonal cell’





1 · 8 · 16


2.7 TCH/SDCCH Congestion Case

SDCCH congestion situation A railway station is located at the frontier of two LAs. Every train stopping

in this station comes from LA 1 and then returns to LA 1 after the stop. Objective Define a set of parameters to avoid

SDCCH congestion on cell B (LA 2)

LA frontier

LA 1

LA 2

Cell A

Cell B





1 · 8 · 17


2.8 Indoor Cell Congestion Case

An indoor microcell has been introduced within a multi-layer network (macro + micro)

When the indoor microcell is congested, FDR may not be working as some the MSs can be covered only by this cell Define parameter settings to find a

good solution in case of indoor cell congestion

City center

Micro-cells

Macro-Cell

Macro-CellMacro-Cell





1 · 8 · 18








1 · 8 · 19

End of ModuleCase Studies





Module 9Annexes








GSM B11 · BSS B11 Radio Fine Tuning IntroductionB11 Radio Fine Tuning · Annexes

1 · 9 · 2

Blank Page




Document History





1 · 9 · 3

Module Objectives


…





1 · 9 · 4







1 · 9 · 5

Table of Contents


1 Erlang B law 72 Frequency Hopping influence on PCHO process 213 Load & Traffic evaluation 264 Handover Management 375 LCS 466 Dynamic SDCCH Allocation 637 Handover Detection for Concentric Cells 73





1 · 9 · 6







1 · 9 · 7

1 Erlang B law




GSM B11 · BSS B11 Radio Fine Tuning IntroductionB11 Radio Fine Tuning · Annexes1 · 9 · 8

1 Erlang B law

Erlang definition

ERLANG: unit used to quantify traffic

Example: 1 TCH is observed during 1 hour one can observe 1 call of 80 sec and 1 call of 100 sec the observed traffic is T = (80+100)/3600 = 0.05 ERLANG

Erlang definition

T = total observation duration

resource usage duration(Erlang)





ERLANG <-> CALL MIX

CALL MIX EXAMPLE

350 call/hour 3 LU/call TCH duration: 85 sec SDCCH duration: 4.5 sec

ERLANG COMPUTATION

TCH = (350 * 85)/3600 = 8.26 ERLANG SDCCH = [ (350 + 350*3) * 4.5 ] / 3600 = 1.75 ERLANG

1 Erlang B law

Call mix definition

350 calls * 85 sec / 1 hour(3600 sec):

TCH = (350 * 85)/3600 = 8.26 ERLANGS

350 calls means 350 SDCCH phases.

3 LU/call means 3 * 350 LUs so 1050 SDCCH phases more.

1 SDCCH phase is 4.5 sec:

SDCCH = [ (350 + 350*3) * 4.5 ] / 3600 = 1.75 ERLANG





1 Erlang B law

Erlang B (1/5)

Erlang B law Relationship between offered traffic number of resources blocking rate

In a telecom system, call arrival frequency is ruled by the POISSON LAW

1 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 970

1

2

3

4

5

6

7

8

9

10

Call

Second

The offered traffic is the traffic asked by the customers.

The graph gives the number of connection requests per second during 35 seconds.

83/30s => 83 * 2 * 60 = about 10 000 / hour

Real example in Paris on 1 BSC (LA FOURCHE).





1 Erlang B law

Erlang B (2/5)

Call request arrival rate (and leaving) is not stable Number of resources = average number of requests * mean duration Is sometime not sufficient => probability of blocking

=> 1 Erlang B law Pblock: blocking probability N: number of resources E: offered traffic [Erlang] Good approximation when

the blocking rate is low (< 5%) Pblock = N

k=0Ek

k !

EN

N !

Erlang B law





There is two different ways to use this law

Using Abacus

Using SW (here Excel) Pblock = f (T, Nc) Offered = f (Nc, Pblock) Channels = f (T, Pblock)

1 Erlang B law

Erlang B (3/5)





1 Erlang B law

Erlang B (4/5)

Example:

We have a BTS of 8 TRXs (about 60 channels (Nc))We do not want more than 2% of blocking (Pblock)=> The traffic is not to be greater than 50 Erlangs (T)

83% of resources used to reach 2% of blocking





1 Erlang B law

Erlang B (5/5)

But be careful, the law is not linear:

In B4, we use for example a combined BCCH with a micro BTS.4 SDCCHs, Pblock = 2% => T = 1.1 E25% of resources used to reach 2% of blocking

In B5, if we decide to provide SMSCB (Cell Broadcast information)1 subchannel SDCCH is therefore used.3 SDCCHs, Pblock = 2% => T = 0.6 E25% of resources less => 50% of Traffic less !!





CELL DIMENSIONING

Given an Offered traffic, compute the number of TRXs (and SDCCHs) needed to carry it

Default blocking rate RTCH: 2% SDCCH: 0.5% (TTCH: 0.1%)

1 Erlang B law

Cell dimensioning (1/5)





CELL DIMENSIONING

To handle an offered traffic of 12 Erlangs (TCH), compute the number of channels, then the number of TRXs

Channels (12;2%) = 19

Example: 3 TRXs , 21 TCHs, 1 BCCH, 2 SDCCH8

1 Erlang B law






CELL DIMENSIONING, based on field measurement

One is measuring a traffic of 15 Erlangs, with a blocking rate of 10% How to dimension the cell?

Offered traffic = 15 / (1-10%) = 16.7 Erlangs !!!! Channels (16.7;2%) -> 25 TCHs -> 4 TRXs needed

1 Erlang B law






FORECASTING TRAFFIC/CRITICAL TRAFFIC

Traffic forecasting must be calculated according to offered traffic not directly on measured traffic

In order to plan necessary actions soon enough, one must calculate regularly the date when the traffic of a cell will become critical

Critical traffic: when offered traffic will induce 2% of blocking

1 Erlang B law






1 Erlang B law


WARNING: in case of too high blocking rate

First check that there is no outage on the BTS

Before starting a dimensioning/tuning action





1 Erlang B law

Training exercise

Training exercise Complete this form in order to get less than 2% of blocking in all cases.

Erlang TCHoffered traffic

450 call/hourMean TCH call duration: 80 sec

Blocking rate TCH: 0.8%12,743 10.08 Erlang TCH

30% offered trafficincrease

13.1 Erlang TCH -> 20 TCH3 TRX

Call mix infoCell Traffic forecast Proposed configuration

12,675

12,865


Blocking rate TCH: 4%


Blocking rate TCH: 8%



cell call mix info Erlang TCH traffic forecast proposed config

12, 743 450 call/hourmean TCH call duration : 80secblocking rate TCH : 0.8%

10 Erlang TCH

(450*80)/3600=1010/.992=10.081

30 % TCH increase

10,081*1.3=13.1

13,1 Erlang TCH - > 20TCH

3 TRX

12,675 330 call/hourmean TCH call duration 129secblocking rate 4%

(330*129)/3600=11.825/0.96=12.3177

30 % TCH increase

12.3177*1.3 =16

16 Erlang TCH -> 24 TCH

4 TRX

12,865 600 call/hourmean TCH call duration 96secblocking rate 8 %

(600*96)/3600=16/.92 = 17.4

30 % TCH increase

17.4*1.3 = 22.6

22.6 Erlang TCH -> 31 TCH

5 TRX





1 · 9 · 21

2 Frequency Hopping influence on PCHO process






(1/4)

Signal decoding process In a GSM system, the number of frames that are not erased are sent as an

input to the voice decoder

Inside the mobile station

Decoder

Encoder

DeinterleaveError Correction

Frame ErasureDecision

RXQUAL Frame Erasure Rate

Demod.Voice

Decoder

Air





Quality impact of frequency hopping on the reception chain

In non-hopping networks, the RXQUAL and voice quality are correlated

In hopping networks, the voice quality is sooner correlated to the FER. This is due to interferer averaging and due to the non-linear mapping of BER to RXQUAL values.


(2/4)





Quality impact of frequency hopping on the reception chain FER is improved when frequency hopping is activated (cyclic or random) RxQual is not impacted whereas the speech quality is better


(3/4)

0

0.2

0.4

0.6

0.8

1

1.2

1.4

RxQ Average

0.00%

0.50%

1.00%

1.50%

2.00%

2.50%

FER Average

Ref Cyclic RandomRxQ AverageFER Average





Conclusion

When frequency hopping is activated We can accept in Power Control and Handover processes, a threshold

increase: OFFSET_HOPPING_PC and OFFSET_HOPPING_HO


Conclusion (4/4)





1 · 9 · 26

3 Load & Traffic evaluation






Cell TCH radio resource evaluation usage

FREEfactorLOADfactor

Loadevaluation

Speed discrimination for hierarchical networkFull Rate/Half Rate channel allocation

Power budget HandoverTraffic Handover

Multiband capture HandoverGeneral capture Handover

N_TRAFFIC_LOAD x A_TRAFFIC_LOAD x TCH_INFO_PERIOD

Shortterm

Mediumterm

Longterm

LOAD_EV_PERIOD x TCH_INFO_PERIOD

TCH_INFO_PERIOD

Period Usage






Load evaluation (1/5)

Nb of free TCHsLOADfactorsFREEfactors

Load evaluation

TCH_INFO_PERIOD sec

LOAD_EV_PERIOD

Non-sliding average

Medium term measurement of the load of a cell Corresponds to function AV_LOAD(cell) A new sample of the “Nb free TCH” in the cell is available every

TCH_INFO_PERIOD seconds AV_LOAD() is a non-sliding window load average from Nb free TCH samples

updated every LOAD_EV_PERIOD x TCH_INFO_PERIOD sec







AV_LOAD(cell n) calculated from N Nb free TCH samples available during LOAD_EV_PERIOD x TCH_INFO_PERIOD sec

LOADfactors and FREEfactors also determined from Nb free TCH samples every TCH_INFO_PERIOD seconds (short term evaluation) LOADlevels are boundaries of load intervals associating a LOADfactor (db) to

a Nb of free TCH samples FREElevels are boundaries of Nb of free TCH intervals associating a

FREEfactor (db) to a Nb of free TCH samples

AV_LOADdefinition

AV_LOAD = Nsamples

1 Nsamples

i = 1

(1 - Nb total TCH (n)

Nb free TCH (n)) x 100







LOADfactor determination:

LOADlevel in % LOADfactor in dB

LOADfactor

LOADfactor_1

LOADfactor_2

LOADfactor_3

LOADfactor_4

LOADfactor_5

t = (1 - Nb free TCH/Total Nb TCH) x 100

t <= LOADlevel_1

LOADlevel_1 < t <= LOADlevel_2



LOADlevel_4 < t







FREEfactor determination:

FREElevel in absolute number of TCH FREEfactor in dB

FREEfactor

FREEfactor_1

FREEfactor_2

FREEfactor_3

FREEfactor_4

FREEfactor_5

Nb free TCH

t <= FREElevel_1

FREElevel_1 < t <= FREElevel_2



FREElevel_4 < t







Example: cells with 4 TRXs (28 TCHs)

In cell evaluation of cell n for outgoing HO from cell 0: In GRADE(n): + LOADfactor(n) = +0 = 0 dB In ORDER(n): + FREEfactor(n) – FREEfacfor(0) = +7 – (-8) = +15 dB

LOADfactor

+10 dB

+5 dB

0 dB

-10 dB

-15 dB

Load = (1 - Nb free TCH/Total Nb TCH) x 100

t <= 10%

10% < t <= 25%

25% < t <= 50%

50% < t <= 80%

80% < t

FREEfactor

-16 dB

-8 dB

0 dB

+7 dB

+10 dB

Nb free TCH

t <= 3

3 < t <= 8

8 < t <= 15

15 < t <= 21

21 < t

Cell nCell 0

HO ?Nb free TCHs = 4Load = 85.7%

LOADfactor(0) = -15 dBmFREEfactor(0) = -8 dBm

Nb free TCHs = 20Load = 28.6%

LOADfactor(n) = 0 dBmFREEfactor(n) = +7 dBm






Traffic evaluation (1/4)

Long term measurement of the load of a cell Corresponds to function Traffic_load(cell) Traffic_load() value is determined from a number N_TRAFFIC_LOAD of

consecutive non-sliding window load averages AV_TRAFFIC_LOAD calculated from Nb of free TCH samples updated every A_TRAFFIC_LOAD x TCH_INFO_PERIOD sec

Nb of free TCHsLOADfactorsFREEfactors

Traffic evaluation

TCH_INFO_PERIOD sec

A_TRAFFIC_LOAD(N_TRAFFIC_LOAD non-sliding average)

TRAFFIC_EV_PERIOD







3 possible values for Traffic_load(): high, low, indefinite Initialization: Traffic_load() = indefinite Traffic_load() becomes:

High if the last N_TRAFFIC_LOAD consecutiveAV_TRAFFIC_LOAD load averages are all greater than HIGH_TRAFFIC_LOAD threshold

Low if the last N_TRAFFIC_LOAD consecutiveAV_TRAFFIC_LOAD load averages are all lower than LOW_TRAFFIC_LOAD threshold

Traffic loadThresolds comparisonwith N_TRAFFIC_LOAD

averages

AV_TRAFFIC_LOADAveraging onA_TRAFFIC_LOAD

load samples

Load samples

HIGH_TRAFFIC_LOAD

LOW_TRAFFIC_LOAD

IND_TRAFFIC_LOAD





Traffic_load() becomes indefinite if: Traffic_load() was high and the last AV_TRAFFIC_LOAD load average is

lower than LOW_TRAFFIC_LOAD (or IND_TRAFFIC_LOAD if not 0%) Traffic_load() was low and the last AV_TRAFFIC_LOAD load average is

greater than HIGH_TRAFFIC_LOAD (or IND_TRAFFIC_LOAD if not 0%)

Traffic_load(n) is always equal to indefinite if cell n is external to BSC

HIGH_TRAFFIC_LOAD IND_TRAFFIC_LOAD LOW_TRAFFIC_LOAD









HIGH_TRAFFIC_LOAD

Variation ofAV_TRAFFIC_LOAD

IND_TRAFFIC_LOAD

LOW_TRAFFIC_LOAD

Traffic_load = high

Traffic_load =indefinite


Traffic_load = low Traffic_load = low



Traffic_load = high

IND_TRAFFIC_LOAD = 0IND_TRAFFIC_LOAD <> 0

Example with N_TRAFFIC_LOAD = 3





1 · 9 · 37

4 Handover Management





Handover Management made up of: Cell Filtering Process (according to call history) Handover Decision (according to the best cell in the list)

Handover Management followed by: Handover Protocol


Principles

RadioLink Measurements

ActiveChannelPre-processing

BTS BSC

HO DetectionHO CandidateCell Evaluation

HO management

MSC

HO protocol

HO Preparation






Global Handover Process

Handover preparation

Handoverdetection

Handover management

Cellfilteringprocess

Handoverprotocol

Externalor internalchannelchange

Candidate cell

evaluation

Handoverdecision

Rawcell list

Orderedtargetcell list

Filteredtargetcell list

Executiontarget

cell list





Three cell lists:

Ordered target Cell list

target cells provided by Candidate Cell Evaluation

REJ_CELL_LIST

cells internally rejected by the MSC or BSC

MS_CELL_REJ_LIST

cells to which the MS failed to hand over


Cell Lists usage

Since B6 release, some changes have been provided to the HO management process which is in charge of the HO execution triggering, when the need of handover is detected by the HO preparation process.

These changes are :

use of the T_FILTER parameter in a different way than for B5,

the parameter NBR_HO_ATTEMPTS which was used for internal HO in B5 is removed,

use of the T7 parameter and of the REJ_CELL_LIST list also for internal HO in B7,

same behavior in case of internal and external HO in B7,

immediate attempt after rejection or failure without waiting for a new alarm in case of internal and external HO in B7,

implicit rejection of cells in B7 with the help of the target cell identity in the HO command received from the MSC.





T_FILTER: controls the global handover procedure started: when a cell list is to be sent by Candidate Cell Evaluation expiry empty target cell list sent to the Handover Management

T7: controls the clean-up of REJ_CELL_LIST started: when a target cell list is to be sent to Handover Protocol expiry empty REJ_CELL_LIST

T_MS_CELL_REJ: clean-up of MS_CELL_REJ_LIST started: when an MS reports a failure to seize the target channel expiry empty MS_CELL_REJ_LIST

T_HO_REQ_LOST: to supervise answer of MSC (no HANDOVER REQUIRED REJECT message sent) Started: HO REQUIRED sent Stopped: HO COMMAND received Expiry external channel change procedure is terminated.


Timers usage

If the candidate cell list provided by the candidate cell evaluation process is different from the previous one (the number of cells is different or same number of cells but new cells in the list), an alarm is sent to the HOM process. In B7, if T_FILTER expires, it means that the HO is no more necessary.

For both internal and external HOs in case of HO failure from the MS, the cell is filtered until the expiry of the T_MS_CELL_REJ timer. When the T_MS_CELL_REJ timer expires, the rejected cell may be a candidate.

In B7 release, T7 timer is used to manage the REJ_CELL_LIST list and a subsequent HO REQUIRED can be sent to the MSC before T7 expiry if the target cell list has changed (new cell or removed cell).

The REJ_CELL_LIST list is used for both internal and external Hos.

T_HO_REQD_LOST Expiry

This timer is used to supervise response from the MSC. It is started when sending the first HANDOVER REQUIRED to the MSC and it is stopped in the following cases:

when HANDOVER COMMAND is received from the MSC or

when HANDOVER REQUIRED REJECT is received from the MSC only if the same number of HANDOVER REQUIRED REJECT messages have been received from the MSC than the number of HANDOVER REQUIRED messages sent to the MSC for this channel change procedure) (i.e. no message crossing over A interface).

In case where more HANDOVER REQUIRED messages have been sent to the MSC, the timer T_HO_REQD_LOST is not stopped upon HANDOVER REQUIRED REJECT receipt, as there is no way for the BSC to know if the received HANDOVER REQUIRED REJECT is a response to the last HANDOVER REQUIRED message or a response to a previous one (message crossing over A interface).

On expiry, an O&M error report is raised only when no message has been received from the MSC since the last HANDOVER REQUIRED message, and the external channel change procedure is terminated.






Handover Execution Process

Handover preparation

Cell filtering process

remove cells previously rejectedfrom MSC or BSC

remove cells previously rejectedfor MS failure reason

remove cells not suitable due toO&M reason

Filteredtarget

cell list

Cell 4

Cell 2

Cell 8

Filteredtarget

cell list

Cell 2

InternalHandover

InternalHandover

Handoverprotocol

Handover decision

Relevant handover protocol ischosen according to the type ofGSM procedure ongoing and thefirst target cell of the list

T7 is started

List of cellspreviously rejected

for MS failure

Cell 8

MS_CELL_REJ_LIST listcleared atT_MS_CELL_REJ expiry

List of cellspreviously rejectedfrom MSC or BSC

Cell 4

REJ_CELL_LIST listcleared at T7 expiry






HO execution example

Handover management

Orderedtarget cell list

Cell 1Cell 2Cell 3

Rejected lists

MS emptyBSC/MSC empty


Cell 1Cell 2Cell 3

Update

Cell 1 -> MSrejected list

Handover management


Cell 1Cell 2Cell 3

Rejected lists

MS cell 1BSC/MSC empty


Cell 1Cell 2Cell 3

Handoverprotocol

HO failson cell 2

ROC

Update

T_MS_CELL_REJexpires

MS rejected listempty

Update

Cell 2 -> MSrejected list

Cell 1 -> BSCrejected list

Handover management


Cell 1Cell 2Cell 3

Rejected lists

MS cell 2BSC/MSC cell 1


Cell 1Cell 2Cell 3

Handoverprotocol

HO tocell 3

Handoverprotocol

HO failson cell 1

ROC





End of Handover procedure = T_FILTER timer expiry

T_FILTER restarted each time a target cell list is to be sent by Candidate Cell

Evaluation to the Handover Management (same list than the one previously

sent or not)

The target cell list is sent to the Handover Management if different from the

last target cell list previously sent

T_FILTER expiry means no handover is needed anymore


T_FILTER controls HO procedure (1/2)






T_FILTER controls HO procedure (2/2)

Is T_FILTER running?

YesNo

Restart T_FILTER

New candidate cell list from thecandidate cell evaluation function

Start T_FILTER:an HO alarm containing thecandidate cell is sent to the

HO management entity

YesNo

Is the candidate cell listdifferent from the previous one?

Restart T_FILTER:an HO alarm containing thecandidate cell is sent to the

HO management entity

No Handover is on-going A Handover is on-going

A Handover is now on-going

T_FILTER is restartedeach time the alarm is still on





1 · 9 · 46

5 LCS





1 · 9 · 47

5 LCS

Definitions

New end-user services which provide the geographical location of an MS: On MS request to know its own location On network request (especially during Emergency calls) On external request (LCS Client)

Several positioning methods: Cell-ID or Cell-ID + TA (Timing Advance) Conventional (standalone) GPS Assisted GPS (with A-GPS server help to compute location) MS-based (MB): the MS is able to perform a pre-computation MS-assisted (MA): the MS sends info, Network computes

Assisted GPS Method:

Mobile-based: The MS performs OTD signal measurements and computes its own location estimate. In this case, the network provides the MS with the additional information such as BTS coordinates and the RTD values. These assistance data can be either broadcast on the CBCH (using SMSCB function) or provided by the BSS in a point-to-point connection (either spontaneously or on request from the MS).

Mobile-assisted: The MS performs and reports OTD signal measurements to the network and the network computes the MS’s location estimate.

With

OTD: Observed Time Difference: the time interval that is observed by an MS between the receptions of signals (bursts) from two different BTSs.

RTD: Real Time Difference: This means the relative synchronization difference in the network between two BTSs.

Finally, 4 methods are possible for positioning:

Cell ID+ TA.

This is the simplest method for determining the location of a mobile. It relies on the hypothesis that the geographical coverage of a cell corresponds to that predicted by radio coverage studies. When an active mobile is connected to a base station, the mobile is assumed to be located geographically within the area predicted to be best served by this base station

Conventional (MS equipped with GPS System).

MS-based Assisted GPS.

MS-Assisted GPS.





1 · 9 · 48

5 LCS

Architecture

MS Request1

Network Request2

External Request3

A-GPSGMLCLCSSMLC

: Assisted GPS: Gateway Mobile Location Center: Location Services: Serving Mobile Location Center

BTS

Abis

MFS

BTS

OSP

SMLC

A-GPSserver

GPS receiversreference network

GMLCExternal

LCS clientMSC

BSC

HLR

Abis

A Lg Le

Lh

Lb

Emergency call

2 3

SAGI

Where isthe accident?

Where ismy son?

Where am I?

1

SMLC function integrated in MFS:- receives the location request from the GMLC through the MSC/BSC- schedules all the necessary actions to get MS location- computes MS location- provides the result back to the GMLC





1 · 9 · 49

5 LCS

LCS Positioning Procedure

BTS

MFS

BTS

OSP

SMLC

GMLCMSC

BSC

HLR

Locationrequest

1

Routinginformation

2

Providesubscriber

location3

Paging,authentication,

ciphering,notification

4

Providesubscriber location

5

Individualpositioning

6 Location report7 7Locationresponse

8

If the MS is in idle mode, the MSC first performs a CS paging, authentication and ciphering in order to establish an SDCCH with the MS. The MS subscriber is not aware of it, i.e. no ringing tone, except towards GPRS MS in Packet Transfer Mode which may suspend its GPRS traffic in order to answer to the CS Paging (i.e. not fully transparent for the subscriber).

When the MS is in dedicated mode (after a specific SDCCH establishment for location, or during an on-going call), the MSC sends the location request to the BSC in the existing SCCP connection for the current call, which forwards it to the SMLC.





1 · 9 · 50

5 LCS

LCS Protocols

BSCSMLC(MFS)

Um Lb

L1-GSL

L2-GSL

BSSLAP

L2-GSL

BSSAP-LE

L1-GSLL1

L2(LAPDm)

RR

Relay

RRLP(04.31)

BSSLAP(08.71)

BSSAP-LE(09.31)

Target MS

L1

RR(04.18)

L2(LAPDm)

RRLP(04.31)





1 · 9 · 51

5 LCS

LCS Protocols [cont.]

Example: Mobile terminated location request success (External request)MS BTS BSC SMLC MSC GMLC HLR

Adequate positioning methodchosen by SMLC with

optional additional scenario

StartsT_Location

StopT_Location

LCS Service Request

Send_Routing_Info request

Send_Routing_Info response

Provide_Subscriber_Location

Authentication + Ciphering

BSSMAP Perform_Location_Request

BSSAP-LE Perform_Location_Request

BSSAP-LE Perform_Location_Response

BSSMAP Perform_Location_Response

Provide_Subscriber_Location Result

LCS Service Response

MSSMAP Clear Command and Release

LCS client

Paging

T_location_Longer used in case of optional additional scenario (see graph):

Upon receipt of the MS POSITION COMMAND message from the SMLC (optional additional scenario), the BSC stops the T_Location timer, and starts instead the T_Location_Longer timer. This timer is stopped only at the end of the location procedure in the BSC, i.e. when an 08.08 PERFORM LOCATION RESPONSE message is sent back to the MSC.

Aborts:

Abort by MSC

Depending on the location procedure and its current state of execution, upon PERFORM LOCATION ABORT message receipt, the BSC sends immediately to the MSC a PERFORM LOCATION RESPONSE message (when no exchange on the Lb interface is on-going), or to the SMLC either a PERFORM LOCATION ABORT or an ABORT message. The BSC starts the timer T_Loc_abort to supervise the SMLC response.

Abort by BSS

The BSC must send either a PERFORM LOCATION ABORT message or a ABORT message to the SMLC and starts the timer T_Loc_abort, if an ongoing location request is interrupted at the BSC level for the following reasons:

by an inter-BSC handover, or

if the main signaling link to the target MS is lost or released, or

the SCCP connection on the A interface is released, or

if the timer T_Location expires,

The useful B8 content of the received PERFORM LOCATION REQUEST message is:

Location type,

Classmark information 3,

Requested QoS: provides service requirement concerning geographic positioning and response time

accuracy, the response time category (Low Delay or Delay Tolerant),

Current Cell Id + TA information are always provided to the SMLC.

The time of transfer of the assitance data on the SDCCH is estimated about 14s for a 1000 octets information.





1 · 9 · 52

5 LCS

Positioning Methods: CI+TA Positioning

Principles of CI + TA Positioning Method

LCS_LONGITUDE

LCS_LATITUDE

LCS_AZIMUTH(Main Beam Directiongiven by the azimuth)

HALFPWR_BEAM_W

IDTH

Serving cell (CI)

TA

3dB pointgiven by the azimuth

and the HPBW

3dB pointgiven by the azimuth

and the HPBW

553 m

MSestimated location

With the TA positioning method, no signaling exchange is required between the SMLC and the MS (i.e. RRLP protocol is not required). The TA positioning method is applicable to all the MSs (supporting LCS or not).

Based on:

Cell Identity (CI) of the serving cell and

Timing Advance (TA) value reported by MS

intersection point of a line from the BTS antenna in its main direction with a circle which radius is corresponding with the propagation delay (timing advance) is the MS estimated position

Omni-directional cells: MS position = site position

Parameters:

EN_LCS – flag to enable/disable the Location Services per BSS

0 = Enabled; 1= Disabled; Default = 0

IF EN_LCS=1, CI+TA method is enabled in all the BSS cells

LCS_LATITUDE: Latitude of the BTS supporting the cell

LCS_LONGITUDE: Longitude of the BTS supporting the cell

LCS_AZIMUTH: Antenna direction orientation for the sector supporting the cell

HALFPWR_BEAM_WIDTH: Antenna half power beamwidth for the sector supporting the cell

Optimization parameters: ARC_SIZE_FACTOR: Factor used in the computation of the width in degree of the ellipsoid arc returned by the MFS when computing location estimate based on TA positioning method. MIN_RADIUS_FACTOR: Factor used in the computation of the minimum radius of the ellipsoid arc returned by the MFS when computing location estimate based on TA positioning method. MAX_RADIUS_FACTOR: Factor used in the computation of the maximum radius of the ellipsoid arc returned by the MFS when computing location estimate based on TA positioning method.





1 · 9 · 53

5 LCS

Positioning Methods: Conventional Positioning

Conventional GPS location procedure This optional location procedure is chosen by the SMLC (if the MS supports

it) upon reception of a Perform Location Request message from the BSC

PerformLocationRequest

MS BTS BSC SMLC

Measurement Position Request

Measurement Position Response (X,Y)

PerformLocation

Response (X,Y)(X,Y):

computed position

(X,Y)

LocationRequest

LocationResponse

The MS continuously computes its position.

The terminal searches for satellites, acquires all the GPS data, computes its own position and finally provides the location estimation to the SMLC.





1 · 9 · 54

5 LCS

Positioning Methods: Assisted GPS Positioning

Assisted GPS Positioning Method (A-GPS) Assisted GPS Positioning Method is split into: MS Based A-GPS method MS Assisted A-GPS method

- GPS acquisition assistance- Navigation model (almanac, ephemeris)- Ionospheric model- Time integrity

GPS MS A-GPSserver

GPS receiversreference network

Assistance data on request

Assistance data gathered from a GPS reference network receiver is broadcast to the GPS MS.

Flags/Parameters

EN_LCS = 1

EN_MS_BASED_AGPS – enables/disables the positioning method MS Based A-GPS per CELL

0 = disabled; 1 = enabled; default = 0

EN_MS_ASSISTED_AGPS – enables/disables the positioning method MS Assisted A-GPS per CELL

0 = disabled; 1 = enabled; default = 0





1 · 9 · 55

5 LCS

Positioning Methods: Assisted GPS Positioning [cont.]

A-GPS location procedure / MS Based A-GPS


MS BTS BSC SMLC

LocationRequest

A-GPSServer

GPS infoRequest

GPS infoResponse


Assistance Data

Assistance Data Acknowledge

Measurement Position Response (X,Y)

PerformLocation

Response (X,Y)

LocationResponse

PositionRequest

PositionResponse

AssistanceData

(X,Y)

(X,Y):computed position

Positioning calculation:latitude, longitude

and altitude

Using assistance data, the MS computes by itself the position and sends it back to the SMLC.





1 · 9 · 56

5 LCS

Positioning Methods: Assisted GPS Positioning [cont.]

AA--GPS location procedure / MS Assisted AGPS location procedure / MS Assisted A--GPSGPS

(X,Y):computed position

Pseudo-rangemeasurements (M)

PositionResponse


MS BTS BSC SMLC

LocationRequest

A-GPSServer

GPS infoRequest

GPS infoResponse


Assistance Data

Assistance Data Acknowledge

PerformLocation

Response (X,Y)

LocationResponse

PositionRequest

AssistanceData

(X,Y)

Measurement Position Response (M)

GPS LocationRequest (M)

GPS LocationResponse (X,Y)

Using a reduced set of assistance data, the MS makes pseudo–range measurements and sends the result to the A-GPS server, which fixes the position in the end.





1 · 9 · 57

5 LCS

LCS Impact on HO

HO preparation Inhibition of “better cell handovers” Other HO

MS BTS BSC SMLC MSC GMLC HLR

StartsT_Location

EmergencyHO

detection

LCS Service Request

Send_Routing_Info request

Send_Routing_Info response

Provide_Subscriber_Location

Authentication + Ciphering


BSSAP-LE Perform_Location_Request

LCS client

Paging

BSSLAP - Reset

HO needed during LCS procedure





1 · 9 · 58

5 LCS

LCS Impact on HO [cont.]

HO management Internal HO

MS BTS BSC SMLC MSC GMLC HLR

HOcomplete



LCS client

BSSLAP - Reset

Intra BSCHO

on going

BSSMAP perform location response (cause = "Intra-BSC Handover Complete)

Mobile in communication





1 · 9 · 59

5 LCS

LCS Impact on HO [cont.]

HO management External HO

MS BTS Serving BSC SMLC MSC GMLC HLR

ExternalBSC HO

BSSAP-LE Perform_Location_Abort

LCS client


BSSMAP HO required






1 · 9 · 60

5 LCS

BSS Parameters

Timers

T_Location

T_Location_longer

T_Loc_Abort

T_LCS_delay_tolerant

T_LCS_LowDelay

T_RRLP_low_delay

T_RRLP_delay_tolerant

FLAGS

EN_LCS

EN_SAGI

OPTIMIZATION DATA

ARC_SIZE_FACTOR

MIN_RADIUS_FACTOR

MAX_RADIUS_FACTOR

BSS PARAMETERS EN_LCS (BSC)

Flag which enables or disables the LCS feature in the BSS. EN_SAGI

Flag indicating whether SAGI is configured or not for this BSS. T_Location:

BSC timer on a per call basis to guard the response from the SMLC in case of Location Request, when no RRLP exchange is triggered with the MS.

T_Location_longer: BSC timer on a per call basis to guard the response from the SMLC in case of Location Request, when an RRLP exchange is triggered with

the MS. Replace T_Location timer in case of Conventional GPS, MS-Assisted A-GPS, MS-Based A-GPS. T_Loc_Abort

BSC timer to guard the response from the SMLC in case of Location Abort. T_LCS_LowDelay

SMLC timer to guard the calculation of the MS position (including the RRLP message exchange with the target MS) in case of a Low Delay Location Request.

T_LCS_DelayTolerant SMLC timer to guard the calculation of the MS position (including the RRLP message exchange with the target MS) in case of a Delay

Tolerant Location Request. T_LCS_LowDelay

SMLC timer to guard the calculation of the MS position (including the RRLP message exchange with the target MS) in case of a Low Delay Location Request.

T_RRLP_Low_delay Timer to guard the RRLP exchange between the SMLC and the MS.

T_RRLP_delay_tolerant Timer to guard the RRLP exchange between the SMLC and the MS.

Optimization data: ARC_SIZE_FACTOR

Factor used in the computation of the width in degree of the ellipsoid arc returned by the MFS when computing location estimate based on TA positioning method.

MIN_RADIUS_FACTOR Factor used in the computation of the minimum radius of the ellipsoid arc returned by the MFS when computing location estimate based

on TA positioning method. MAX_RADIUS_FACTOR

Factor used in the computation of the maximum radius of the ellipsoid arc returned by the MFS when computing location estimate based on TA positioning method.





1 · 9 · 61

5 LCS

Cell Parameters

SITE DATA

LCS_LATITUDE

LCS_LONGITUDE

LCS_SIGNIFICANT_GC

LCS_AZIMUTH

HALF_POWER_BANDWIDTH

EN_CONV_GPS

EN_MS_ASSISTED_AGPS

EN_MS_BASED_AGPS

FLAGS

CELL PARAMETERS EN_CONV_GPS

Flag to enable/disable the Conventional GPS positioning method. EN_MS_ASSISTED_AGPS

Flag to enable/disable the MS Assisted A-GPS positioning method. EN_MS_BASED_AGPS

Flag to enable/disable the MS Based A-GPS positioning method. LCS_LATITUDE

Latitude of the BTS supporting the cell (used by the MFS to compute location estimate based on TA positioning method).

LCS_LONGITUDE Longitude of the BTS supporting the cell (used by the MFS to compute location estimate based on TA

positioning method). LCS_SIGNIFICANT_GC

Indicates whether latitude and longitude are significant or not. LCS_AZIMUTH

Antenna direction orientation for the sector supporting the cell (used by the MFS to compute location estimate based on TA positioning method).

HALF_POWER_BANDWIDTH Half power beam width of the antenna for the sector supporting the cell (used by the MFS to compute

location estimate based on TA positioning method).

Remark: To have LCS supported for a cell, the operator must activate LCS on the BSS handling this cell but he must also activate GPRS for this cell (i.e. setting of MAX_PDCH to a value > 0, the cell being kept locked for GPRS if the operator does not want to have GPRS running on this cell) and configure all the required transmission resources (Ater and Gb resources) on the GPU(s) connected to this BSC.





1 · 9 · 62

5 LCS

Positioning Methods: CI+TA Positioning

Ellipsoid arc definition:

Point (O)= serving BTS site coordinate

= serving cell antenna azimuth - /2 =A*width of serving cell sector in [°],

calculated from bisector anglesof co-sited antenna azimuths r1= inner radius of

TA ring-(B-0.5)*554 in [m] R2=(B+C)*554 in [m] A: ARC_SIZE_FACTOR B: MIN_RADIUS_FACTOR C: MAX_RADIUS_FACTOR

Serving cell (CI)

E

North

S

W

r1

r2

Point (O)

An ellipsoid arc is a shape characterized by the co-ordinates of an ellipsoid point o (the origin), inner radius r1, uncertainty radius r2, both radii being geodesic distances over the surface of the ellipsoid, the offset angle () between the first defining radius of the ellipsoid arc and North, and the included angle () being the angle between the first and second defining radii. The offset angle is within the range of 0 to 359,999… while the included angle is within the range from 0,000…1 to 360. This is to be able to describe a full circle, 0 to 360

For CI+TA method which is default one, the answer is given by description of "ellipsoid arc".

Optimization parameters: ARC_SIZE_FACTOR

Factor used in the computation of the width in degree of the ellipsoid arc returned by the MFS when computing location estimate based on TA positioning method.

MIN_RADIUS_FACTOR Factor used in the computation of the minimum radius of the ellipsoid arc returned by the MFS when

computing location estimate based on TA positioning method. MAX_RADIUS_FACTOR

Factor used in the computation of the maximum radius of the ellipsoid arc returned by the MFS when computing location estimate based on TA positioning method.





1 · 9 · 63

6 Dynamic SDCCH Allocation





1 · 9 · 64


Purpose

SDCCH/8 time slots can be dynamically allocated on demand on a cell-per-cell basis.

“Dynamic SDCCH/8 time slots” “Static SDCCH time slots”

Min

Max

Static SDCCHtimeslots

AllocatedDynamic SDCCH/8

timeslots

0

TCH Capacity

A Static SDCCH timeslot is a physical timeslot fixed allocated on the air interface. It contains 3, 4, 7 or 8 SDCCH sub-channels depending on whether the timeslot is an SDCCH/3, SDCCH/4, SDCCH/7, or SDCCH/8 timeslot.





1 · 9 · 65


Principles

Principles Too few SDCCH time slots could result in high blocking rate on SDCCH

(Configuration 1) Too many SDCCH time slots could lead to a lack of TCH resources

(Configuration 2)

SDCCHtime slots

TCH CAPACITY

SDCCHtime slots

TCH CapacityTCH Capacity

Configuration 1 Configuration 2

Low signaling capacity

More TCH capacity

High signaling capacity

Less TCH capacity

Definition

An SDCCH is a logical SDCCH sub-channel mapped on a Static SDCCH timeslot or a Dynamic SDCCH/8 timeslot.

Signaling Load Cases

Timeslot split between signaling and traffic channels depends on the network signaling load. The main cases are:

Normal signaling load cells:

Rural area cells in center of Location Areas

(e.g. 1 SDCCH timeslot for a 3-TRX cell)

High signaling load cells:

Urban or suburban area cells in the center of a Location Area

Rural area cells at the border of Location Areas

(e.g. 2 SDCCH time slots for a 3-TRX cell)

Very high signaling load cells:

Urban or suburban area cells at the border of a Location Area

Cells with high SMS load (more than one SMS per call)

(e.g. 3 SDCCH time slots for a 3-TRX cell)





1 · 9 · 66


Principles [cont.]

Allocation and de-allocation of Dynamic SDCCH/8 time slots An additional dynamic SDCCH/8 timeslot is allocated by the BSC if there is no

SDCCH sub-channel free in the cell. A dynamic SDCCH/8 timeslot is de-allocated by the BSC after

T_DYN_SDCCH_HOLD (10s) delay if all of its SDCCH sub-channels become free

BCC SDC TCH TCH

TCH TCH TCH TCH

TCH TCH TCH TCH

TCH TCH TCH TCH

TCH TCH TCH TCH TCH TCH TCH TCHCell

Allocation ofDynamic SDCCH/8

times slots

BCC SDC

SDD TCH

TCH TCH

BCC SDC

SDD TCH

SDD TCH

BCCSDCSDD

: BCCH: Static SDCCH: Dynamic SDCCH

The location of the Dynamic SDCCH/8 time slots are fixed by O&M configuration.





1 · 9 · 67


Timeslot Types

NEW TIMESLOT TYPES: SDCCH

Pure SDCCH or “ static SDCCH “ TCH

Pure TCH TCH/SDCCH

“ dynamic SDCCH” TCH/SPDCH

MPDCH

The OMC-R provides the BSC with the following O&M type of radio timeslots:

Main BCCH timeslot (BCC): It is a timeslot carrying FCCH + SCH + BCCH + CCCH.

Main combined BCCH timeslot (CBC): It is a timeslot carrying FCCH + SCH + BCCH + CCCH + SDCCH/4 + SACCH/4.

Static SDCCH timeslot (SDC): It is a timeslot carrying SDCCH/8 + SACCH/8.

Dynamic SDCCH/8 timeslot (SDD): It is a timeslot carrying TCH + SACCH or SDCCH/8 + SACCH/8.

TCH timeslot (TCH): It is a timeslot carrying TCH + SACCH or PDCH.

From RAM point of view, a radio timeslot can be defined as:

Pure BCCH timeslot: The BCCH timeslot is the radio timeslot configured as BCC by O&M. Such a timeslot only carries common CS signaling.

Pure SDCCH timeslot: A pure SDCCH timeslot is a timeslot configured as a CBC or SDC by O&M. Such a timeslot can carry SDCCH traffic.

Pure TCH timeslot: A pure TCH timeslot is a timeslot configured as TCH by O&M. Such a timeslot only carries TCH traffic.

TCH/SDCCH timeslot: A TCH/SDCCH timeslot is a timeslot configured as SDD by O&M. Such a timeslot is dynamically allocated as TCH or as SDCCH depending on the usage of the timeslot. It can carry TCH traffic or SDCCH traffic.

TCH/SPDCH timeslot: A TCH/SPDCH timeslot is a timeslot configured as TCH by O&M. Such a timeslot is dynamically allocated as TCH or as SPDCH depending on the usage of the timeslot. It can carry TCH traffic or PS traffic.

MPDCH timeslot: A MPDCH timeslot is a timeslot configured as TCH by O&M. Such a timeslot can only carry common PS signaling.

A pure SDCCH timeslot can carry x SDCCH sub-channels where x equal to:

4 in case of combined CCCH and when CBCH is not configured on the timeslot,

7 in case of non-combined CCCH and when CBCH is configured on the timeslot,

3 in case of combined CCCH and when CBCH is configured on the timeslot,

8 for a normal SDCCH timeslot.

When allocated as SDCCH, a TCH/SDCCH timeslot can carry up to 8 SDCCH sub-channels.





1 · 9 · 68


Allocation Algorithms

SDCCH Request

SDCCH mapped on "TCU very high load state" removal

Are they any free SDCCH sub-channelamong Static SDCCH timeslots?

Selection of oneSDCCH sub-channel

Yes No

Are they any free SDCCH sub-channelamong Dynamic SDCCH/8 already allocated?

Selection oneSDCCH sub-channel

Yes

Are they any Dynamic SDCCH/8 timeslotsavailable and free in the cell?

No

Allocate one DynamicSDCCH/8 timeslot

Yes No

SDCCH Requestrejected!!!

Principle 1: Preference is given to pure SDCCH timeslots

Principle 2: Balance TCU processor load between different TCUs

In fact before entering in this algorithm (see slide) the first step is: Removal of all the SDCCH subchannels mapped on TCU in « Very High Overload » state.

Principle 3: FR TRX preference





1 · 9 · 69


SDCCH Sub-Channel Selection

Pure SDCCH Timeslot TS with LOWEST TCU LOAD TS with MAXIMUM FREE SDCCH Sub channels TS with lowest index on TRX with lowest TRX_ID

TCH/SDCCH TS allocated as SDCCH TS on FR TRX TS with lowest index on TRX with lowest TRX_ID

TCH/SDCCH TS allocated as TCH TS with LOWEST TCU LOAD TS on FR TRX TS with lowest index on TRX with lowest TRX_ID

Note that a SDCCH request cannot access the timeslots reserved by NUM_TCH_EGNCY_HO. If all remaining TCH/SDCCH timeslots are reserved by NUM_TCH_EGNCY_HO, then the SDCCH request shall be rejected.





1 · 9 · 70


De-Allocation Algorithm

GENERAL CASE: all SDCCH sub-channels of a TCH/SDCCH timeslot become back free. the T_DYN_SDCCH_HOLD timer (10s, not tunable) is started. If the timeslot is still free of SDCCH sub-channel when the timer expires, it is

de-allocated (it becomes back TCH). SPECIAL CASE: Several TCH/SDCCH timeslots are allocated as SDCCH One of them becomes free of SDCCH sub-channels. Its timer starts. A subsequent one becomes free of SDCCH sub-channels too before expiration

of the first one’s timer (10s). One of them is immediately de-allocated (the one with “lowest priority”: see

previous slide in reverse order) and becomes back TCH. For the last one, its timer is restarted (it will be de-allocated in 10s).

The de-allocation algorithm ensures that:

TCH/SDCCH timeslots are not allocated too fast to TCH after de-allocating them

TCH/SDCCH timeslots are not re-allocated too frequently to SDCCH

Note: while T_DYN_SDCCH_HOLD is running:

the dynamic SDCCH/8 timeslot marked as “HOLD” is still considered as allocated to SDCCH (and cannot be allocated to TCH).

If a subsequent dynamic SDCCH/8 timeslot (used as SDCCH and in the same cell) becomes free:

If this just freed dynamic SDCCH/8 timeslot has a higher priority, T_DYN_SDCCH_HOLD is re-started and precedent dynamic SDCCH/8 timeslot in “HOLD” state is de-allocated immediately.

If this just freed dynamic SDCCH/8 timeslot has lower priority, and T_DYN_SDCCH_HOLD is re-started and the just freed dynamic SDCCH/8 timeslot is de-allocated immediately.





1 · 9 · 71


O&M Configuration

Selection of static or dynamic SDCCH Timeslot configuration menu

BTS

BTS

BTS

BTS

2

4

7

3

1

10

9

6

12

8

5

11

Massive modification by script 10 templates Template customization Template launched through PRC

Dynamic SDCCH Rules

The CBCH must be configured on a static SDCCH/8 or SDCCH/4 timeslot.

Combined SDCCHs (SDCCH/4 + BCCH) are always static.

To avoid incoherent allocation strategy between SDCCH and PDCH, a dynamic SDCCH/8 timeslot cannot have the characteristic of being a PDCH (it cannot carry GPRS traffic).

The operator must configure at least one static SDCCH/8 or SDCCH/4 timeslot on BCCH TRX in a cell.

In cells with E-GSM, only the TRX, which do not belong to the G1 band, can support dynamic and static SDCCHs.

In multiband and concentric cells, only the TRX, which belongs to the outer zone, can support dynamic and static SDCCHs.

Up to 24 static/dynamic SDCCH sub-channels can be configured per TRX.





1 · 9 · 72


O&M Configuration [cont.]

Default configuration for a cell which has only Full rate TRX

Number of TRXin the cell

Number ofStatic SDCCH

Number ofDynamic SDCCH

Total numberof SDCCH

MaximumSDCCH/TRX

ratio

Is BCCH/CCCHcombined with

SDCCH?

1

2

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

4

4

8

8

8

8

8

16

16

16

16

16

16

16

24

24

24

8

8

16

16

24

24

24

24

24

32

32

32

40

40

40

48

48

12

12

24

24

32

32

32

40

40

48

48

48

56

56

64

72

72

12.0 (note 1)

6.0

12.0

8.0

8.0

6.4

5.3

5.7

5.0

5.3

4.8

4.4

4.7

4.3

4.6

4.8

4.5

Yes

Yes

No

No

No

No

No

No

No

No

No

No

No

No

No

No

No

Note1: For one TRX, dynamic SDCCHs are over-dimensioned because of the granularity of 8. According to the Alcatel-Lucent traffic model, all dynamic SDCCHs will not be used.

Note2: An additional dynamic SDCCH/8 must be provided for each DR TRX (these are expected mainly on small cells).

Rules:

At least one static SDCCH/4 or SDCCH/8 on BCCH TRX.

Up to 24 static/dynamic SDCCH sub-channels per TRX.

Up to 32 static/dynamic SDCCH sub-channels per TCU.

Up to 88 static/dynamic SDCCH sub-channels per CELL.





1 · 9 · 73

7 Handover Detection for Concentric Cells





1 · 9 · 74


Algorithms

Emergency handovers specific to concentric cells Intracell handovers from inner to outer zone cause 10: too low level on the uplink in inner zone cause 11: too low level on the downlink in inner zone

May be triggered From inner zone of a concentric cell Towards outer zone, same cell

Concentric cellI n n e r z o n e

Outer zone





1 · 9 · 75


HandoverAlgorithm Cause 10

CAUSE 10: too low level on the uplink in the inner zone

AV_RXLEV_UL_HO < RXLEV_UL_ZONEand MS_TXPWR = min (P, MS_TXPWR_MAX_INNER)

Averaging window: A_LEV_HO





1 · 9 · 76



CAUSE 11: too low level on the downlink in the inner zone

AV_RXLEV_DL_HO < RXLEV_DL_ZONEand BS_TXPWR = BS_TXPWR_MAX_INNER

Averaging window: A_LEV_HO





1 · 9 · 77



CAUSE 13: too high level on UL and DL in the outer zone Better condition intracell handover If the cell is a multi-band cell, cause 13 is checked only for multi-band MSs

May be triggered From outer zone of a concentric cell Towards inner zone, same cell

Concentric cellI n n e r z o n e

Outer zone





1 · 9 · 78


HandoverAlgorithm Cause 13 [cont.]

CAUSE 13: too high level on UL and DL in the outer zone

AV_RXLEV_UL_HO > RXLEV_UL_ZONE +

+ ZONE_HO_HYST_UL +

+ (MS_TXPWR -

MS_TXPWR_MAX_INNER) +

+ PING_PONG_MARGIN(0,call_ref)and AV_RXLEV_DL_HO > RXLEV_DL_ZONE +

+ ZONE_HO_HYST_DL ++ (BS_TXPWR -

BS_TXPWR_MAX_INNER) ++ PING_PONG_MARGIN(0,call_ref)

and AV_RXLEV_NCELL_BIS(n) <= neighbour_RXLEV(0,n)and EN_CAUSE_13 = ENABLE (B7)and EN_BETTER_ZONE_HO = ENABLE

Averaging windows: A_LEV_HO and A_PBGT_HO (for n)





1 · 9 · 79



ZONE_HO_HYST_UL UL static hysteresis for interzone HO from outer to inner In case of multi-band cell, should take into account the difference of propagation

between GSM and DCS

Added to cause 10 threshold RXLEV_UL_ZONE

ZONE_HO_HYST_DL DL static hysteresis for interzone HO from outer to inner In case of multi-band cell, should take into account the difference of propagation

between GSM and DCS and the difference of BTS transmission power in the two bands

Added to cause 11 threshold RXLEV_DL_ZONE





1 · 9 · 80



PING_PONG_MARGIN(0,call_ref) Penalty PING_PONG_HCP put on cause 13 if The immediately preceding zone in which the call has been is the inner zone of the

serving cell And The last handover was not external intracell And T_HCP is still running

PING_PONG_MARGIN(0,call_ref) = 0 If the call was not previously

in serving’s inner zone Or T_HCP has expired

Concentric cell

I n n e r z o n e

Outer zone





1 · 9 · 81



neighbour_RXLEV(0,n)

Concentric cells are designed to create an INNER zone protected from external interferers and creating no interferences on other cells … to be able to face more aggressive frequency reuse in INNER zone TRXs

neighbour_RXLEV(0,n) tuning enables to avoid handovers if the MS position will lead to interferences the condition is checked towards all neighbor cells belonging to the same

layer and band as the serving cell

Concentric cellOuter zone

?

Inner zoneinterferer 1

Inner zoneinterferer 2Inner zone





1 · 9 · 82



EN_CAUSE_13 Load balance between inner and outer zones may be allowed by setting

EN_LOAD_BALANCE = ENABLE

If EN_LOAD_BALANCE = ENABLE If INNER zone is less loaded than OUTER,

EN_CAUSE_13 = ENABLE If INNER zone is more loaded than OUTER,

EN_CAUSE_13 = DISABLE

If EN_LOAD_BALANCE = DISABLE EN_CAUSE_13 = ENABLE





1 · 9 · 83


Outgoing Intercell Handovers from Concentric Cell

Outgoing intercell handovers from concentric cells As explained here before, the MS located in a concentric cell can make

intercell, emergency or better condition HO regardless their current zone

For example, an MS locatedin the INNER zone of aconcentric cell can makedirectly an HO cause 12towards another cell,WITHOUT having totrigger any cause 10 or 11to the OUTER zone before.


Inner zone


Inner zone


Inner zone

The only restrictions are linked to EN_MULTI-BAND_PBGT_HO and EN_BI-BAND_MS parameters.





1 · 9 · 84


Incoming Intercell Handovers from Concentric Cell

Incoming intercell handovers towards a concentric cell In case an MS makes an incoming handover towards a concentric cell (due to

outer PBGT measurements,etc.), a TCH may be allocated either in the INNER or in the OUTER zone, as for call setup depending on radio conditions

In case of a multi-band cell, if the MS is not multi-band, it will always be sent to the OUTER zone


Inner zone

Cell

??





1 · 9 · 85


Incoming Intercell Handovers from Concentric Cell [cont.]

Use part of Handover cause 13 algorithm on each potential target IF Cell(n) is external The MS is directed to the OUTER zone of (n)

ELSE (cell(n) is internal) IF

AV_RXLEV_NCELL(n) > RXLEV_DL_ZONE + ZONE_HO_HYST_DL ++ (BS_TXPWR - BS_TXPWR_MAX_INNER)

and EN_BETTER_ZONE_HO = ENABLE

The MS is directed towards the INNER zone ELSE The MS is directed towards the OUTER zone





1 · 9 · 86








1 · 9 · 87

End of ModuleAnnexes





Module 10Solutions








GSM B11 · BSS B11 Radio Fine Tuning IntroductionB11 Radio Fine Tuning · Solutions

1 · 10 · 2

1 Exercises solution





1 · 10 · 3


1.1 Typical radio Problems

Unbalanced Power Budget

Bad Coverage Interferences TCH Congestion

High ratio of UL QUAL HO cause

Good RXLEV and Bad RXQUAL

Alarm VWSR (OMC-R) (Voltage Standing Wave Ratio)

Bad RXLEV and Bad RXQUAL

High Path-loss difference between UL and DL

DL>UL

Low incoming HO success rate

TCH Congestion rate

OMC QOS indicators: % TCH failure high % call drop high

Path loss VWSR UL Qual HO

No network Low prop Better cell High % DL Qual HO

Low HO success rate DL/UL Qual HO Interference HO

% QUAL HO % call drop

Adjacent Co-channel





1 · 10 · 4


1.2 MS Re-selection Algorithms

Important Parameters RXLEV_ACCESS_MIN [dBm] -103dBm for G3

MS_TXPWR_MAX_CCH [dBm] 33dBm

CELL_RESELECT_OFFSET 0 dB

TEMPORARY_OFFSET 0 dB

PENALTY_TIME 0 s

CELL_RESELECT_HYSTERESIS 6dB

CI=6169GSM900

CI=1823GSM900

CI=1964GSM900

CI=6270GSM900

CI=6271GSM900 Cell (8557, 1823)

Cell (8564,6169)Cell (8564, 1964)





1 · 10 · 5


1.2 MS Re-selection Algorithms [cont.]

Find the selected cell by MS?

CI=6169GSM900

CI=1823GSM900

CI=1964GSM900

CI=6270GSM900

CI=6271GSM900

Cell 3(8557, 1823)

Cell 2(8564,6169) Cell 1

(8564, 1964)

5

4

3

2

1

Measurements

-78-85-89

-82-87-88

-87-90-88

-100-90-84

-104-96-80

RxLev (3)RxLev (2)RxLev (1)

LU

Case 5:

LU because cell_reselect_hysteresis = 6dB

C2=-78dB > -85 + 6 = -79 dB

(the best one!)





1 · 10 · 6


1.3 Measurements Principle

The risk is that the correspondence table implemented at OMC is wrong and a distant cell with the same (BSIC, BCCH) couple can be seen as the cell associated to the measurement results.

The BSC can trigger a HO toward this cell whereas the measurements are not the target cell measurements.

OR 2 (BSIC, BCCH) couple are identical or similar : (BSICn, BCCHn) = (BSICm, BCCHm). The BSC can decode (BSICn, BCCHn) as (LACm, CIm) and trigger an HO toward the wrong cell.





1 · 10 · 7


1.4 Measurements Averaging





1 · 10 · 8


1.5 Radio Link Supervisionmk1

mk1 Moctar KARIDJO; 21/04/2009





1 · 10 · 9


1.6 Power Control

Nb of case ---> 1 2 3 4 5 6

AV_RXQUAL_UL_PC 0 1 2 6 3 4

AV_RXLEV_UL_PC -98 -80 -73 -69 -86 -90

Power control

MS_P_INC or RED 10dB 4dB 6dB 6dB - 6dB

RxQual

Lev

2

3

-90 -86 -75

1

6

5

4

3

2





1 · 10 · 10


1.6 Power Control [cont.]

Using the Trace Abis Excel file, find each parameter value : POW_INC_STEP_SIZE = 6 dB BS_P_CON_INT = 1s POW_RED_STEP_SIZE = 2 dB OFFSET_RXQUAL_FH = 1 Which phenomenon can you observe as regards the successive PC

commands ? We can observe a PC ping-pong effect

A increase PC command is triggered because of bad quality and just after a decrease PC command is triggered because of too good level

Most of samples present bad RxQual with good RxLev Solution : tune L_RXLEV_DL_P and U_RXLEV_DL_P





1 · 10 · 11


1.7 HO Detection

Emergency causes HO Cause 2 Recall :

AV_RXQUAL_UL_HO > L_RXQUAL_UL_H + OFFSET_RXQUAL_FH and AV_RXLEV_UL_HO <= RXLEV_UL_IH and MS_TXPWR = min (P, MS_TXPWR_MAX)





1 · 10 · 12


1.7 HO Detection [cont.]

Nb of case ---> 1 2 3 4 5 6 AV_RXQUAL_UL_HO 4 1 3 4 4 4 AV_RXLEV_UL_HO - 81 - 79 - 75 - 70 - 69 - 72 Power m ax of MS 33 33 33 33 33 29

(0,8 w) HO cause 2 : YES/NO ? YES NO NO YES NO WAIT PC

QUAL

LEV-70

3

Emergency causes Complete the diagram then fill in the chart:





1 · 10 · 13



Better condition causes Recall

PBGT(n) = AV_RXLEV_NCELL(n) - AV_RXLEV_PBGT_HO - (BS_TXPWR_MAX – AV_BS_TXPWR_HO) - (MS_TXPWR_MAX(n) – MS_TXPWR_MAX) - PING_PONG_MARGIN(n, call_ref)





1 · 10 · 14



Better condition causes (simple case)What does it mean if there is only 2W cells c=0What happens if DL_PWC is disabled b=0No Ping-Pong margin d=0HO_MARGIN(0,n)=5 dbmFill in the chart:

Nb of case ---> 1 2 3 4 5 6

AV_RXLEV_NCELL(n) - 70 - 70 - 80 - 70 - 70 - 75

AV_RXLEV_PBGT_HO - 80 - 70 - 75 - 75 - 79 - 96

PBGT(n) « a » only 10 0 - 5 5 6 21

HO cause 12: YES/ NO ? PBGT > HO margin

YES NO NO NO YES YES

Serving cell

Ncell





1 · 10 · 15



Better condition causes (ping-pong case)EN_TRAFFIC_HO(0,n)=DisablePing-Pong margin PING_PONG_HCP=15db T_HCP =10s

HO_MARGIN(0,n)=5 dBA_PBGT_HO = 8 SACCHA n to 0 HO has been triggered, what happens after 4s?

N b o f ca se - - - > 1 2 3 4 5 6

AV_RXLEV _N C ELL(n ) - 7 0 - 7 0 - 8 0 - 7 0 - 7 0 - 7 5

AV_RXLEV _PBG T_H O - 8 0 - 7 0 - 7 5 - 7 5 - 7 9 - 9 6

PBG T(n ) « a » o n ly 1 0 0 - 5 5 9 2 1

H O ca u se 1 2 : YES/ N O ?P B G T > H O m arg in

YES N O N O N O YES YES

PIN G _PO N G _H C P= 1 5 - 5 - 1 5 - 2 0 - 1 0 - 6 6

H O ca u se 1 2 : YES/ N O ? N O N O N O N O N O YES

Serving cell

Ncell





1 · 10 · 16



Better condition causes (traffic case) Fill in the chart:

0dB-5dB-5dB5dBDELTA_HO_MARGIN(0,n)

YESNOYESNOCause 12 HO: YES/NO?

NOYESYESNOCause 23 HO: YES/NO?

9dB4dB9dB9 dBPBGT(n)

0: tr lowN: tr low

0: tr highN: tr low

0: tr highN: tr low

0: tr lowN: tr high

Traffic distribution

-80 dBm-80 dBm-80 dBm-80 dBmAV_RXLEV_PBGT_HO

-71 dBm-76 dBm-71 dBm-71 dBmAV_RXLEV_NCELL(n)

4321Number of case





1 · 10 · 17



Channel adaptation (cause 26 and cause 27) Find the thresholds and offsets for normal and high load :

THR_RXQUAL_CA_NORMAL = 0 OFFSET_CA_NORMAL = 0 THR_RXQUAL_CA_HIGH = 2 OFFSET_CA_HIGH = 1 Use the previous thresholds and fill up the chart :

UL_QUAL 0 1 2 3 3 1 1 0 0 1 DL_QUAL 0 0 1 1 1 0 0 2 4 3 LOAD_SV3 false false false false true true true true true true AV_RXQUAL_UL_CA_HR_FR 0,5 1,5 2,5 3 2 1 0,5 0 0,5 AV_RXQUAL_DL_CA_HR_FR 0 0,5 1 1 0,5 0 1 3 3,5 AV_RXQUAL_UL_CA_FR_HR 1,5 2,3 2,3 2 1,3 0,5 0,5 AV_RXQUAL_DL_CA_FR_HR 0,5 0,8 0,8 0,5 0,8 1,5 2,3 CHANNEL TYPE FR FR FR FR HR HR HR FR





1 · 10 · 18



Fast Traffic HO (cause 28)Find the appropriate candidate MS for this queued request :

MS Neighbors 1 2 3

1 -82 -85 -78

2 -79 -86 -92

3 -90 -82 -89





1 · 10 · 19



TFO HO (cause 29) : after call set-up Find the 2 speech version types of the following MS to MS call EN_TFO = enable, EN_TFO_MATCH = enable FORCE_TFO_HR_WHEN_LOADED = TFO_HR_NOT_FORCED

Loaded cellMS / cell cap : HR/EFR/FR

Unloaded cell MS / cell cap : EFR/FR

After call set-up TCH = HR TCH = EFR

After TFO negotiation TCH = EFR TCH = EFR

MS can use HR/EFR/FR

MS can use EFR/FR EFREFR

TFO ON





1 · 10 · 20



TFO HO (cause 29) : after call set-up Find the 2 speech version types of the following MS to MS call EN_TFO = enable, EN_TFO_MATCH = enable FORCE_TFO_HR_WHEN_LOADED = TFO_HR_ONLY




After TFO negotiation TCH = HR TCH = EFR

MS can use HR

MS can use EFR/FR EFRHR

TFO OFF





1 · 10 · 21



TFO HO (cause 29) : after call set-up Find the 2 speech version types of the following MS to MS call EN_TFO = enable, EN_TFO_MATCH = enable FORCE_TFO_HR_WHEN_LOADED = TFO_HR_PREFERRED




After TFO negotiation TCH = EFR TCH = EFR

MS can use HR

MS can use EFR/FR

TFO ON

MS can use HR/EFR/FR EFREFR





1 · 10 · 22



TFO HO (cause 29) : after call set-up Find the 2 speech version types of the following MS to MS call EN_TFO = enable, EN_TFO_MATCH = enable FORCE_TFO_HR_WHEN_LOADED = TFO_HR_ONLY


Unloaded cell MS / cell cap : HR/EFR/FR


After TFO negotiation TCH = HR TCH = HR

MS can use HR

MS can use HR/EFR/FR

TFO ON

HRHR





1 · 10 · 23



TFO HO (cause 29) : after handover Find the 2 speech version types of the following MS to MS call EN_TFO = enable, EN_TFO_MATCH = enable FORCE_TFO_HR_WHEN_LOADED = TFO_HR_ONLY


MS1



MS2

call set-up+ TFO negociation

HR

HRTFO ON

MS2

HO

EFR then HR with TFO negociation

KEEP_CODEC_HO = FREE

TFO ON





1 · 10 · 24



TFO HO (cause 29) : after handover Find the speech version types of the following MS to MS call EN_TFO = enable, EN_TFO_MATCH = enable FORCE_TFO_HR_WHEN_LOADED = TFO_HR_ONLY


MS1



MS2

call set-up+ TFO negotiation

HR

HRTFO ON

MS2

HO

HR without TFO negotiation

KEEP_CODEC_HO = TFO_CALLS_ONLY

TFO ON





1 · 10 · 25



TFO HO (cause 29) : after handover Find the speech version types of the following MS to MS call EN_TFO = enable, EN_TFO_MATCH = enable FORCE_TFO_HR_WHEN_LOADED = TFO_HR_ONLY KEEP_CODEC_HO = TFO_CALLS_ONLY

HR after HO

TFO ON

MS2

HO

TFO ON

Unloaded cellMS / cell cap : HR/EFR/FR

MS1

Loaded cell MS / cell cap : HR/EFR/FR


MS2

call set-up+ TFO negociation

HR

HRTFO ON

EN_TFO_OPT = enable

EFR

EFR after TFO optimisation





1 · 10 · 26


1.8 HO candidate cells Evaluation

Emergency HO detected With the “Candidate evaluation.xls”

excel sheet... Filtering simulation for a list of

candidate cell Ranking simulation for a list of

candidate cell

Book-keeping list1-





1 · 10 · 27


1.8 HO candidate cells Evaluation [cont.]

Emergency HO detectedAveraging

measurement

PBGT Filtering

GRADE evaluation process

Target Cell

2-

3-

4-

5-





1 · 10 · 28


1.9 Algorithms Dynamic Behavior

According to the Abis results and some parameters already set, tune qualitatively the sliding averaging windows: A_QUAL_HO A_LEV_HO

462A_LEV_HO

646A_QUAL_HO

-90dBm-90dBm-85dBmL_RXLEV_DL_H

-90dBm-96dBm-80dBmLevel at RxQual=3

1st Case:

The DL level HO is triggered whereas the quality is already bad (at –80dB, rxQual=3!)

If the sliding averaging window has been set to 6 for quality causes, the sliding averaging window for level causes has to be accelerated;

So, A_LEV_HO = 2. BUT A_QUAL_HO and L_RXLEV_DL_H are very badly tuned !

2nd Case:

The DL level HO is triggered whereas the quality is good

If the sliding averaging window has been set to 4 for quality causes, the sliding averaging window for level causes can be slowed down;

So, A_LEV_HO = 6.

3rd Case:

The DL level HO is triggered whereas the quality starts being degraded

If the sliding averaging window has been set to 4 for level causes, the sliding averaging window for quality causes can not be slowed down anyway. The purpose is not to perform a level handover in place of quality one. Aim is to avoid bad quality calls.

So, A_QUAL_HO = 4 or 6





1 · 10 · 29


1.9 Algorithms Dynamic Behavior [cont.]

Training exercise (1) Solution


PBGT(n) = 5PBGT(0) = 5

PB

GT

(n)

= -

1

Cause 23 Cause 12Cause 12

PB

GT

(0)

= 9

EN_TRAFFIC_HO = 1New traffic

for cell n





1 · 10 · 30



Training exercise (2) HO Ping-Pong effect

Unloaded cell n

PBGT(n) = 5PBGT(0) = 5P

BG

T(0

)=P

BG

T(n

)=0

Queued Ass Req

L_RLEV_NCELL_DR(n) = -85dBm

Cause 28

Cause 12

Av_Rxlev_Ncell(n) = -82dBmAv_Rxlev_Ncell(0) = -74dBmAv_Rxlev_PBGT_HO = -82dBm

First, a HO cause 28 is triggered from cell 0 to cell n because :

- AV_RxLev_Ncell(n) > L_RXLEV_NCELL_DR(n)

-82dBm > -85dBm

- and because cell n is unloaded, we assume that t(n) > FREE_LEVEL_DR(n)

Just after, a HO cause 12 is triggered from cell n to cell 0 because :

- PBGT(0) > HO_MARGIN(n,0)

AV_Rxlev_Ncell(0) – AV_Rxlev_PBGT_HO > HO_MARGIN(n,0)

-74dBm - -82dBm > 5dB

8dB > 5dB





1 · 10 · 31



Training exercise (3) When FAST_TRAFFIC_HO is enabled, activate HO CAUSE 23, it represents a

good means to avoid ping-pong effect


PBGT(0) = 5

PB

GT

(n)

= -

1

PB

GT

(0)

= 9

Queued Ass Req

Av_Rxlev_Ncell(n) = -82Av_Rxlev(0) = -74

Cause 28

In this case, no ping-pong effect because : PBGT(0) = 8dB is not higher than HO_MARGIN(n,0) + DELTA_INC_HO_MARGIN (=5dB + 4dB).

The triggering of HO cause 12 from cell n to cell 0 is delayed because the cell 0 is loaded and the cell n is unloaded.





1 · 10 · 32


1.10 TCH Resources Allocation

A non hopping cell is configured on the OMC-R

TRX1 PBC PSDTSP TSP TSP TSP TSP TSP

TRX2 PSDSDCTSD PTC TSP TSP TSP TSP TSP

TRX3 TSP TSP TSP TSP TSP TSPTSPTSP

TRX4 PTC PTC PTC PTC PTC PTCPTC PTC

TRX30 TCH TCH TCH TCH TCH TCHTCHTCH

TRX_PREF_MARK 0 1 2 3 4 5 6 7

TRX1 BCC SDC0 TCH TCH TCH TCH TCH TCH

TRX2 SDC0 SDCSDD TCH TCH TCH TCH TCH TCH

TRX41 TCH TCH TCH TCH TCH TCHTCH TCH


PBC: Pure BCCH

PSD: Pure SDCCH

TSD: TCH/SDCCH

TSP: TCH/SPDCH

MPD: MPDCH

PTC: Pure TCH





1 · 10 · 33


1.10 TCH Resources Allocation [cont.]

A cell is configured on the OMC-R and TRE are mapped by BSS

0 1 2 3 4 5 6 7TRX1 BCC TCHSDC TCH TCH TCH TCH TCH

TRX2 TCHSDCSDD TCH TCH TCH TCH TCH TCH

TRX3 TCH TCH TCH TCH TCH TCHTCHSDC

TRX4 TCH TCH TCH TCH TCH TCHTCH TCH

TRX5

TRX_PREF_MARK

0

0

1

0

1 TCH TCH TCH TCH TCH TCHTCH TCH

TRE

G4 MP FR

G4 MP DR

G3 DR

G4 MP FR

G3 DR





1 · 10 · 34




0 1 2 3 4 5 6 7TRX1 PBC TSPPSD TSP TSP TSP TSP TSP

TRX2 TSPSDCTSD TSP TSP TSP TSP TSP TSP

TRX3 PTC PTC PTC PTC PTC PTCPTCPSD

TRX4 TSP TSP TSP TSP TSP TSPTSP TSP

TRX5

TRX_PREF_MARK

0

0

1

0

1 PTC PTC PTC PTC PTC PTCPTC PTC

TRE

G4 MP FR

G4 MP DR

G3 DR

G4 MP FR

G3 DR

PBCPure BCCH TS

PSDPure SDCCH TS

TSDTCH/SDDCH TS

PTC

TSP

MPD

Pure TCH TS

TCH/SPDCH TS

MPDCH





1 · 10 · 35



Find which TCH sub-channel is allocated:1. For MS1: E-GSM, DR2. For MS2: GSM/DCS, DR3. For MS3: GSM, FR4. For MS4, MS5, …., MSn: E-GSM, DRn = 16

Pure TCH TS

TCH/SPDCH TS

P: SPDCH TS

F: FR TCH callH: HR TCH call

Cell load = true

TCH/SDDCH TS as TCH TS

0 1 2 3 4 5 6 7TRX1 12 P P P 3

TRX2 P P P P

F F F F F FTRX3

P P P P P P PTRX4

F FTRX5

TRX Rank

2

3

-

1

-

TRE

GSM/FR

GSM/DR

GSM/DR

GSM/FR

G1/DRH H1 HH HH H 6 7 4 5

2 8

FH 910 1115 16

14

13





1 · 10 · 36

2 Case Studies solution





1 · 10 · 37


2.1 Tunnel Case

Radiating cable in a tunnel Question: Risks of such a configuration : The pedestrian mobile receives a good level from the

tunnel BTS (unfortunately, the propagation is not confined in the tunnel). The propagation conditions are very hard to predict and the risk is a conflict in the

serving area (in RNP) of the outdoor BTS.

Tune the right parameters for the tunnel cell Catch quickly car traffic Avoid the pedestrian traffic Indoor BTS

Outdoor BTS

Pedestrianmobile

HO_margin (outdoor, tunnel) = -5 dB (car arriving fast, no Ping-Pong)

HO_margin (tunnel, outdoor) = 5 dB

To avoid ping-pong HO when pedestrian mobile are close to the tunnel, the anti ping-pong mechanism has to be activated:

And Ping_Pong_Margin =50 dB and T_HCP =60sEventually speed-up averaging process in tunnel cell

in order to secure HO when going out of the tunnel (decrease of A_QUAL_HO, A_LEV_HO, A_PBGT_HO).





1 · 10 · 38


2.2 Radar Case

Radar situation A “radar” cell situated on top of a hill provides a wide

coverage area. An industrial zone in the valley is covered by small cells but

also by the “radar” cell. The serving areas in the IZ are not clearly defined.

Objective Give a parameter set to prevent the radar cell from catching

any traffic in the industrial zone by HO assignment

When a HO is triggered in an industrial zone cell, we have to encourage other IZ cells and discourage the “radar” cell in the candidate cell evaluation process.

The pre-ranking procedure is the most adapted to satisfy those requirements.

By setting the PRIORITY(0,N) from any IZ cell to the “radar” cell to 1 whereas it is set to 0 for every IZ couple, the target list will favour the IZ cell face to the “radar” cell.

PRIORITY(IZ Cell, Radar Cell) = 1PRIORITY(IZ Cell, IZ Cell) = 0In idle mode use C2 criteria on cell reselection.

A multilayer architecture can also be used in this case (IZ set as MINI, Radar as UMBRELLA). Cause 14 activated to capture traffic from Radar to IZ. FDR in case of congestion.

To stick to « single » layer architecture, to grab more traffic in IZ cells, Cause 24 (general capture) can be used from Radar to IZ. In the other way (IZ to Radar), PBGT will be disabled by setting HO_MARGIN to +127dB





1 · 10 · 39


2.3 Tower Case

Tower situation The indoor mobile selects in idle mode the outdoor cell (same LA)

Objective Define a set of parameters to avoid that effect

Outdoor cell

Indoorantenna

Indoormobile

The question is : would we rather advantage the indoor cell or disadvantage the outdoor one ?

As the parameter CELL_RESELECT_OFFSET is not set on a cell couple basis but on a cell basis, if we disadvantage the outdoor one, it will be disadvantaged in regard to the other outdoor cells. This is not the purpose.

We’d rather advantage the indoor cell.

In Idle mode, the set of parameters is then:CELL_RESELECT_OFFSET = 10 dBTEMPORARY_OFFSET = 20 dBPENALTY_TIME = 1 (20s = minimum, we need

PENALTY_TIME different from 31 )

In connected mode we can favor the indoor cell by :

- increasing the HO margin from indoor to outdoor cells

- enable distance HO when connected to far outdoor cells

Another idea is to put this cell in INDOOR layer , behaviour like microcell

• Advantaging the indoor cell means: increase artificially its C2 criterion.

We have to introduce a temporary component to increase the C2

C2=C1+ CELL_RESELECT_OFFSET

If there is no temporary component, the C2 is disadvantaged:

C2=C1- CELL_RESELECT_OFFSET





1 · 10 · 40


2.4 Resurgence Case

Resurgence situation In rural network, especially

in hilly landscape, many resurgences occur from very far cells.

Objective Define a set of parameters

to avoid radio link establishment to those cells and TCH traffic on those cells

Cell A

Resurgencefrom cell A

Cell B

25 Km

•To avoid SDCCH connection to this cell:Apply RACH filtering procedure in cell A:RACH_TA_FILTER = 40 (d >> 22km. TA =1 => d =553m)C2 criteria on cell reselection is less easy to tune and can have side effects on surrounding

cells reselection.•To avoid TCH traffic on this cell: Use Cause 6 HO in cell A: A_RANGE_HO = 6 ; U_TIME_ADVANCE = 40 (d >> 22km. TA =1 => d =553m) Risk of PING_PONG HO if the resurgence is strong: activate the anti ping-pong mechanism...Note : RACH_TA_FILTER is anyway a “bad” mechanism. If resurgence of cell A corresponds

to a coverage hole of cell B, due to RACH_TA_FILTER, no call will be possible anymore in this zone…





1 · 10 · 41


2.5 Forest Case

Forest situation: a highway crosses a forest High call drop rate (radio cause) on the cell and drive tests: strong level

attenuation at the entrance of the forest Objective Define a set of parameters to avoid radio link failure

-75 dBm

-90 dBm

Forest(ATT = 10 dB every 100 m)

Hig

hw

ay

BTS

The parameters to set are the Radio Link Supervision parameters:

Radio_Link_Timeout_BS = 68

Radio_Link_Timeout = 64

En_RL_Recov = Enable





1 · 10 · 42


2.6 Highway Case

Highway situation: A highway is slightly covered (best coverage on 200m) by an ‘orthogonal’

cell (cell C on the map) Objective Define a set of parameters to avoid traffic in the ‘orthogonal cell’

The problem involve the pre-ranking and the ORDER/GRADE evaluation processes.

First, Case 1: a mobile is connected to cell A (car in the highway):When the BSC detected a HO, cell B must be advantaged compared to cell

C (the small village BTS).Pre-ranking: •Priority (A, B) = 0•Priority (A, C) = 1Case 2: a mobile is connected to cell B (car in the highway):When the BSC detected a HO, cell A must be advantaged compared to cell

C (the small village BTS).Pre-ranking: •Priority (B, A) = 0•Priority (B, C) = 1Case 3: a mobile is connected to cell C (pedestrian mobile in the

village):The BSC must avoid as far as possible to handover the pedestrian mobile to

cell A or B. Action can be done for better condition HO only (!)HO detection and PBGT filtering•HO_MARGIN (C,A) and HO_MARGIN (C,B) up to 10 dB





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2.7 TCH/SDCCH Congestion Case

SDCCH congestion situation A railway station is located at the frontier of two LAs. Every train stopping

in this station comes from LA 1 and then returns to LA 1 after the stop. Objective Define a set of parameters to avoid

SDCCH congestion on cell B (LA 2)

LA frontier

LA 1

LA 2

Cell A

Cell B

Avoid the LU for all the travellers ’mobile.

C2 criterion is directly concerned by this objective.

If you disadvantage re-selection from one cell to another belonging to a different location area you will avoid inopportune Location Update.

The parameter to tune is CELL_RESELECT_OFFSET ON CELL B.

To define the right value, an Abis trace has to be performed.

Let’s define CELL_RESELECT_OFFSET= 20 dB on cell B. (And PENALTY_TIME = 31)





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2.8 Indoor Cell Congestion Case

An indoor microcell has been introduced within a multi-layer network (macro + micro)

When the indoor microcell is congested, FDR may not be working as some the MSs can be covered only by this cell Define parameter settings to find a

good solution in case of indoor cell congestion

City center

Micro-cells

Macro-Cell

Macro-CellMacro-Cell

Activate FDR and cause 28 ( fast traffic HO)

En_DR(Micro) = Enable

EN_Forced_DR(Micro) = Enable

En_Fast_Taffic_HO(Micro) = Enable

L_Rxlev_Ncell_DR(Macro) = - 85 dBm

Free_Level_DR(Macro) = 1

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