gsm optimization

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Copy Rights © LEGEND Co. 2010

Prepared by Legend Technical Team


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RF people work in either

RF Planning RF Optimization

Responsibilities

− Nominal Plan Design.

− Sites Survey.

− Validation from field.

− Set RF design (Structure, Azimuth,

Height, Tilt, Cables type).

− Frequency Plan.

− Neighbor Plan.

− Sites Acceptance.

RF Planning KPIs: To provide

coverage outdoor & indoor and to offer

traffic with acceptable grade of service.

Responsibilities

− Maintain the Network„s Accessibility

KPIs.

− Maintain the Network‟s Retainability

KPIs.

− Maintain the Network‟s Service

Integrity KPIs.

− Study and Apply new features.

− Try to think of innovative solutions to

maximize the Network capacity.

They have to maintain the

performance of

the Network as good as possible.

RF People


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Course Outlines:

− Planning Process and Procedures.

− Sites and Hardware Equipment.

− Technical Site Survey & Validation.

− Coverage and Capacity Dimensioning.

− Frequency and Neighbor Planning.

Part I: Radio Network Planning


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What will be our concern during this part of the course?

RF Optimization

How the RF Optimization people can maintain the KPIs?

By studying the different radio network features and studying the controlling parameters of each feature and how to tune them in a smart way to achieve the target KPIs.

What are we going to study during this part of the course?

Most of the Radio Network features and their controlling parameters.

KPIs monitoring and analysis.

Trouble shooting and Tuning.

Part II- Radio Network Optimization


Course Outlines:

− Idle Mode Behavior.

− Handover.

− HCS (Hierarchical Cell Structure).

− Concentric & Multi Band Cells.

− CLS ( Cell Load Sharing).

− Frequency Hopping.

− Intra Cell Handover.

− Dynamic HR Allocation.

− Power Control.

− GSM to UMTS Cell Reselection and Handover.

− Trouble Shooting and KPIs monitoring.

Part II- Radio Network Optimization

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• GSM stands for “ Global System for Mobile Communication”

• GSM – Second Generation for Mobile System.

– Digital System.

– Efficient Use of the Spectrum.

– Speech privacy and security.

– Better resistance to interference (Introducing the frequency Hopping)

– Efficient use of the power battery (Introducing the power control)

– GSM Networks are called “PLMN: Public Land Mobile Networks” i.e. the Radio Sites are located on land, not using satellites.

GSM Revision


• GSM System can work in different bands as follows:

– DCS: Digital Cellular System PCS: Personal Communication Services.

• But what do we mean by frequency Band?

• What is the DL and UL?

• Why DL is higher than UL band?

Frequency Band-Down Link Frequency Band-Up Link

GSM 800 869 894 MHz 824 849 MHz

E-GSM (Extended GSM) 925 935 MHz 880 890 MHz

P-GSM 900 (Primary GSM) 935 960 MHz 890 915 MHz

GSM 1800 (DCS) 1805 1880 MHz 1710 1785 MHz

GSM 1900 (PCS) 1930 1990 MHz 1850 1910 MHz

GSM Revision

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• Frequency Band – The range of frequencies which the operator is allowed to use for

transmission and reception.

• Down Link and Up link bands – DL band is the range of frequencies used by the Base station when

transmitting to the MS while the UL band is the range of frequencies used by the Mobile station when transmitting to the Base Station.

GSM Revision


• Why DL band is higher than the UL band?

– As freq then attenuation with air

– Since Power BaseStation > Power MobileStation then it is wise to configure the higher frequencies that will be attenuated fast to the side that is using higher power (BTS).

GSM Revision

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What do we mean by Multiple Access techniques? These are the Techniques through which many MSs can access the shared media

which is the air interface.

i. FDMA ( Frequency Division Multiple Access) − Each MS is assigned a dedicated frequency through which he can

talk.

ii. TDMA (Time Division Multiple Access) − All MSs are using the same frequency but each of them will be

utilizing it only over a certain period of time called Time Slot (TS)

In GSM System we’re using TDMA over FDMA where the frequency band is divided into no. of frequencies each of which is shared among no. of MSs, where each MS will be assigned a certain TS on certain frequency.

Access Techniques


• For P-GSM (GSM 900) – UL Band 890MHz 915MHz, DL Band 935MHz 960MHz

– Each Band is 25 MHz

– Guard Band between DL and UL is 20 MHz

– Duplex Distance = 45 MHz

– Carrier separation = 200 KHz

– No. of frequencies = 124

GSM 900 Frequency Allocation

F (MHz) 915 890

Uplink 1 2 3 4 121 122 123 124

F (MHz)

Downlink

960 935

1 2 3 4 121 122 123 124

890.2

890.4

890.6

935.2

935.4

935.6

200 KHz

1

1

121

121

Downlink 935 – 960 MHz

Uplink 890 – 915 MHz

GSM Revision

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• For the all GSM Bands

System P-GSM 900 E-GSM 900 GSM(DCS) 1800 GSM(PCS) 1900

Uplink (MS BS) Downlink(BS MS)

890 – 915 MHz 935 – 960 MHz

880 – 915 MHz 925 - 960 MHz

1710 – 1785 MHz 1805 - 1880 MHz

1850 – 1910 MHz 1930 - 1990 MHz

Wavelength 33 cm 33 cm 17 cm 16 cm

Bandwidth 25 MHz 35 MHz 75 MHz 60 MHz

Duplex distance 45 MHz 45 MHz 95 MHz 80 MHz

Carrier separation 200 kHz 200 kHz 200 kHz 200 kHz

No. of carriers 124 174 374 299

Channel rate 270.8 kbps 270.8 kbps 270.8 kbps 270.8 kbps

GSM Revision


GSM Network Architecture

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MSC (Mobile Switching Center)

– Routing/Switching of calls between 2 end users within the GSM Network.

– Charging & Billing.

– Paging of MSs is originated from the MSC

– Access to PSTN (Public Switched Telephone Network)

– Act as a Gateway for other networks.

– Controls no. of BSCs connected to it.

Core Network (NSS: Network Switching System)


HLR (Home Location Register) – Centralized Network data base stores and manages all mobile subscriptions.

– Example: IMSI, MSISDN, MSRN, Services subscribed/restricted for that user. IMSI,MSISDN.ppt

VLR (Visitor Location Register) – It is co-located with the MSC.

– Stored in it a copy of the user’s profile on temporary basis.

AUC (Authentication Center) – Provides the HLR with the authentication parameters and ciphering Keys used

by the MSC/VLR to authenticate certain user. (Triplets: RAND, SRES, Kc) Authentication.ppt

EIR (Equipment Identification Register) – Used to authenticate the user equipment through the IMEI.

IMEI = International Mobile Equipment Identification

Core Network (NSS: Network Switching System)

IMSI,MSISDN.ppt

Authentication.ppt

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BSC (Base Station Controller) – It controls the air interface, it takes the decisions based on the reports came

from the MS and BTS.

– Channel Allocation.

– Controls the Handover Process.

– Dynamic Power Control.

– Frequency Hopping.

BTS (Base Transceiver Station) – It is the Hardware equipment needed to provide the radio coverage.

– Speech Coding/Channel Coding/Interleaving/Ciphering/Burst formatting/Modulation all these are done within the BTS (RBS=Radio Base Station)

– Equipment: Cabinet, jumpers, feeders, combiners, antennas.

BSS (Base Station System)


Mobile Equipment – Transmit the radio waves.

– Speech coding and decoding.

– Call control.

– Performance measurement of radio link.

SIM card (Subscriber Identification Module) – Stores user addresses (IMSI, MSISDN, TMSI).

– Stores authentication key Ki, authentication algorithm A3 and ciphering algorithm A8&A5

– Stores the subscribed services.

MS (Mobile Station)

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• Over the Air Interface

– Frequency Band is divided into no. of frequencies.

– Each frequency is divided into 8 Time slots (TS)

– Each user will be assigned 1 TS.

– One time slot duration = duration of 156.25 bits

– 1 Bit duration=3.7 µsec

– Time slot duration =156.25x3.69 µsec= 0.577 msec

– 1 Frame = 8 TSs

– Frame duration=0.577x8= 4.616 msec

– Bit rate on the air interface is 270 Kbps, but for each user it is 33.8 Kbps


Physical channel: Time slot is called the physical channel.

Logical channel: It is the content that will be sent over the physical channel.

Physical Channels vs. Logical Channels

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Logical Channels

Control Channels Traffic Channels

Half Rate Full Rate

Synchronization Channel

Broadcast Control Channel

Frequency Correction Channel

Standalone Dedicated Control Channel

Slow Associated Control Channel

Fast Associated Control Channel

Cell Broadcast Control Channel

Broadcast Dedicated

Common

Random Access Channel

Access Grant Channel

Paging Channel

Logical Channels


Full Rate Channels (FR) – Carries user’s speech traffic or user data DL and UL.

– Each user is assigned 1 TS.

– Transmission rate is 13 Kbit/s.

Half Rate Channels (HR) – Carries user’s speech traffic or user data DL and UL.

– 2 users will share 1 TS (physical channel), each of them will be utilizing it each frame.

– Transmission rate is 6.5 Kbit/s

Traffic Channels

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These are used to carry signaling or synchronization data, they’re divided into three types: – Broadcast Channels (BCH)

– Common Control Channels (CCCH)

– Dedicated Control Channels (DCCH)

Control Channels


i. Frequency Correction Channel (FCCH) – Pure signal is transmitted to help the MS to lock on the frequency of

the BTS and synchronize to its frequency. (DL channel)

ii. Synchronization Channel (SCH) – Carries the TDMA frame number.

– BSIC (Base Station Identification Code) of the cell. (DL Channel)

iii. BCCH (Broad Cast Control Channel) – LAI (Location Area Identity)

– Cell parameters (used power, Idle mode parameters,…..etc)

– List of BCCH carries of the neighbor cells i.e. “BA List” (DL Channel)

BCH (Broad Cast Control Channels)

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i. Paging Channel (PCH) – Used to inform the MS of an incoming call or sms, where the MS’s

IMSI/TMSI will be sent over it. (DL channel)

ii. Random Access Channel (RACH) – Used by the MS to ask for an SDCCH to respond to the request send on

the paging channel /initiate a call/location update/IMSI attach-detach. (UL Channel)

iii. AGCH (Access Grant Channel) – Used by the network to assign an SDCCH sub-channel for the MS. (DL

channel)

CCCH (Common Control Channels)


i. Standalone Dedicated Control Channel (SDCCH) – Used for signaling purposes: call setup, location update, IMSI attach-detach

– Used to send/receive SMSs in idle mode. (DL/UL channel)

ii. Slow Associated Control Channel (SACCH) – Always allocated in conjunction with traffic channel/SDCCH channel to

transmit measurement reports.

– DL measurement reports will include commands from the network to the MS to adjust its power level.

– Information about the Time Advance.

– UL measurement reports will include information about the MS own power, received SS & Quality from serving cell and SS from neighbor cells.

– Used to send SMSs in active mode. (DL/UL channel)

DCCH (Dedicated Control Channels)

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iii. Fast Associated Control Channel (FACCH) – Used to send necessary Handover information.

– Work in stealing Mode such that 1 TCH channel is replaced by FACCH to send the HO information. (DL/UL channel)

iv. Cell Broad Cast Channel (CBCH) – It is sent point to multi point i.e. from the cell to the mobiles attached

to it, this channel may carry information about the traffic, weather reports,…etc. (DL channel)

DCCH (Dedicated Control Channels)


Mapping on TS0/BCCH carrier (DL)

51 consecutive control frames = 1 Control multi frame Where F:FCCH, S:SCH, B:BCCH, C:PCH/AGCH

Mapping of Logical Channels on the Physical channels

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Mapping on TS0/BCCH carrier (UL)

TS0 in UL is reserved for the RACH, for the MS to access the system.



Mapping on TS1/BCCH carrier (DL)

Where D:SDCCH, A:SACCH


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Mapping on TS1/BCCH carrier (UL)



Mapping on TS2/BCCH carrier (DL/UL) if it will be used by certain MS in active mode

26 consecutive Traffic frames = 1 Traffic multi frame


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Traffic Multi Frames – Traffic Multi Frame = 26 consecutive traffic frames (4.61msec x 26

=120msec)

Control Multi Frames – Control Multi Frame = 51 consecutive Control frames (4.61msec x 51

=235msec)

• Super Frame

51 consecutive Traffic Multi Frames or 26 consecutive Control Multi Frames

– Super Frame = 6.12 seconds

• Hyper Frame

2048 consecutive super Frames – Hyper Frame = 3 hours and 29 minutes nearly.

TDMA Multi Frames Structure


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IMSI : International Mobile Subscriber Identity IMSI = MCC + MNC + MSIN

MCC= Mobile Country Code (3 digits)

MNC= Mobile Network Code (2 digit )

MSIN= Mobile Subscriber Identification Number (10 digits)

Ex: IMSI = MCC-MNC-MSIN = 602-03-1234567890 where,

602 Egypt Country Code

03 Etisalat Network Code

1234567890 Mobile Subscriber Identification Number

MCC (3 digits)

MNC

(2 digits)

MSIN

(10 digits)

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MSISDN : Mobile Station Integrated Services Digital Network MSISDN = CC + NDC + SN

CC= Country Code (2-3 digits)

NDC= Network Destination Code (2-3 digit )

SN= Subscriber Number ( max 10 digits)

Ex: MSISDN = CC-NDC-SN =+20-10-1234567 where,


10 Vodafone Network Code

1234567 Subscriber Number

CC (2-3 digits)

NDC

(2-3 digits)

SN

(max. 10 digits)


LAI : Location Area Identity LAI = MCC + MNC + LAC

MCC= Mobile Country Code (2-3 digits)

MNC= Mobile Network Code (2-3 digit )

LAC= Location Area Code ( max 5 digits)

Ex: LAI= MCC-MNC-LAC = 602-01-12345 where,


01 Mobinil Network Code

12345 Location Area Code

MCC (2-3 digits)

MNC

(2-3 digits)

LAC

(max.5 digits)

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CGI : Cell Global Identity CGI = LAI + CI = MCC + MNC + LAC + CI

MCC = Mobile Country Code (2-3 digits)

MNC = Mobile Network Code (2-3 digit )

LAC = Location Area Code ( max 5 digits)

CI = Cell Identity ( max 5 digits)

Ex: CGI = MCC-MNC-LAC-CI = 602-01-12345-11223 where,


01 Mobinil Network Code

12345 Location Area Code

11223 Cell Identity

MCC (2-3 digits)

MNC

(2-3 digits)

LAC

(max. 5 digits)

CI

(max. 5 digits)


IMEI : International Mobile Equipment Identification IMEI = TAC + FAC + SNR + spare (15 digits)

TAC = Type Approval Code, determined by a central GSM body(6 digits)

FAC = Final Assembly Code, identified the manufacturer (2 digit )

SNR = Serial Number( 6 digits)

spare = A spare bit for future use, when transmitted by MS it is always zero.

( 1 digit)

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AUC : Authentication Center - In the AUC the below table is stored, such that for each user there is a unique

authentication key (Ki)

- On authenticating certain user, the AUC will generate the triplets: RAND,SRES,Kc

- AUC generates a random no. “RAND” and send it to the MS

- Both the AUC and the MS will use RAND + Ki and Algorithm A3 to produce the SRES(Signed Response)

- VLR will take the results from AUC and MS and if:

(SRES1)_AUC = (SRES2)_MS then the MS is Authenticated

User# IMSI Authentication Key

User1 MCC+MNC+MSIN1 Ki1




RAND1

Ki1 (SRES1)_AUC A3

RAND1

Ki1 (SRES1)_MS A3

AUC side MS Side

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AUC : Authentication Center - The AUC is responsible also for generating the ciphering Key (Kc) for each user.

- Kc_AUC should be equal Kc_MS, so the data encrypted by the network can be

de-ciphered by the MS.

Ciphering Process:

RAND1

Ki1 Kc_AUC A8

RAND1

Ki1 Kc_MS A8

AUC side MS Side

+

A5

TDMA Frame no. Kc_AUC

Speech +

A5

TDMA Frame no. Kc_MS

Speech Ciphered Speech

Network side MS side


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• MS in Idle Mode

– Doesn’t have a dedicated channel, but able to access the Network and able to be reached by the Network.

– MS will always try to camp on the best cell based on the signal strength criterion.

– MS will continuously monitor the serving and neighbor BCCH carriers to decide which cell to camp on.

– The purpose behind studying the Idle Mode Behavior is to always ensure that the MS is camped on the cell where it has the highest probability of successful communication.

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• MS Tasks during Idle Mode

– PLMN Selection.

– Cell Selection.

– Cell Reselection.

– Location Updating.

– Monitor the Incoming Paging.



– PLMN Selection

– Cell Selection.




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• PLMN Selection Criterion – PLMN identity is defined as “MCC+MNC” which is part of the LAI,

where LAI=MCC+MNC+LAC.

MCC: Mobile Country Code - MNC: Mobile Network Code - LAC: Location Area Code

– When the MS is powered “ON”, it will check if it needs to perform a Location Update by comparing the new LAI with the old stored one.

– An MS will need to make a PLMN selection only incase:

1. MS is powered “ON” for the 1st time i.e. No PLMN was registered on before

(No Information on MCC&MNC is stored on SIM)

2. Old PLMN is not available any more (Out of coverage/Roaming)


• PLMN Selection Criterion – When the MS has to do a PLMN selection due to one of the previous

cases, the selection mode will depend on the MS settings either Automatic or Manual.

– Automatic PLMN Selection Mode steps:

1. Home PLMN.

2. Each PLMN stored on the SIM card in priority order.

3. Other PLMNs have Signal Strength > -85 dBm.

4. All other PLMNs in order of decreasing Signal Strength.

– Manual PLMN Selection Mode:

1. Home PLMN.

2. All other available PLMNs and give the user the choice to select.

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• PLMN Selection Criterion National Roaming

– If National Roaming is permitted then a MS can register on a PLMN in its home country other than its home PLMN.

– National Roaming may be allowed on a certain location areas (LAs) of the visitor PLMN.

– MS should periodically try to access back his home PLMN, but this periodic attempts will occur only on automatic selection mode.



– PLMN Selection.

– Cell Selection




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• Cell Selection Criterion

– The Cell Selection algorithm tries to find the most suitable cell in the selected PLMN and make the MS camp on.

– Cell Selection is done by the MS itself.

– During Idle Mode the Network doesn’t know the cell which the MS is camping on, it only knows the Location Area where the mobile registed himself in.


• Cell Selection Criterion

MS will synchronize to the BCCH

frequency and read system

information (LAI,BA List,…etc)

Scan RF Frequencies one by

one and calculates the Average

received signal strength over 3

5 seconds

Tune to the RF Frequency with

the highest average received

signal strength

Camp on the Cell

Check if the chosen frequency is a

BCCH carrier frequency or not

Check if C1 > 0 or not

Check if Cell is barred or not

Check if PLMN is desired or not

Tune to the next higher

frequency that wasn‟t tried

before

Yes

Yes

No

Yes

No

Yes

No

No

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• Cell Selection Criterion – Scanning RF Frequencies may occur in 2 ways:

1. Normal Scanning: Scan all Frequencies in the band ex:124 freq. in GSM900 Band.

2. Stored List Scanning: Scan the Frequencies in the Idle BA list (BCCH Allocation) stored on the MS SIM before being switched off.

(BA list can have maximum 32 frequencies)

If MS found cell belongs to the desired PLMN but not suitable, the MS will start to scan the Idle BA list of this cell.


• Cell Selection Criterion – Cell is said to be suitable if:

1. Cell belongs to the desired PLMN

If at least 30 strongest frequencies from GSM900 band were tried and no suitable

cell was found, then the MS will try another PLMN based on PLMN criterion.

2. Cell is not Barred ( CB = NO)

Some cells can be barred for access at selection and reselection or given lower

priority based on settings of parameters: CB

3. C1 > 0

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• Cell Selection Criterion – C1 is called “Cell Selection Quantity”

– It is calculated at the MS based on the below equation:

C1 = (Received SS – ACCMIN) – max (CCHPWR-P,0)

ACCMIN Minimum allowed DL received SS at the MS in order to access the system

CCHPWR Maximum allowed transmitting power by the MS in the UL.

P Maximum out put power of the MS according to its class.

N.B:

1. ACCMIN and CCHPWR are cell parameters sent to the MS at the BCCH channel.

2. If CCHPWR > P then C1 will decrease and so the Received SS should be large enough to keep C1 > 0 (May be this cell is not designed for this MS class)

3. ACCMIN, CCHPWR, P are all measured in dBm, where C1&C2 are measured in dBs



– PLMN Selection.

– Cell Selection.

– Cell Reselection



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• Cell Reselection Criterion – After a cell has been selected, the MS will start the cell reselection

measurements to know if it is better to stay on the current cell or to camp on another cell.

– Cell reselection measurements:

1. Monitors the SS (Signal Strength) of the BCCH carrier of the serving cell.

2. Monitors the SS of the BCCH carrier of all defined neighbors in the Idle BA list.

3. Continuously read system information sent on the serving BCCH carrier at least every 30 seconds.

4. Continuously read system information sent on the BCCH carrier for the six strongest neighbors at least every 5 minutes.

5. Try to decode BSIC of the six strongest neighbors every 30 seconds to assure that it is still monitoring the same cells.


• Cell Reselection Criterion – Cell reselection measurements summary

BSIC BCCH Data (System Information)

Serving Cell - Every 30 Seconds

Six Strongest Neighbors Every 30 Seconds

Every 5 Minutes

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• Cell Reselection Criterion – When Cell Reselection will occur ?

1. Serving Cell became barred ( CB = YES )

2. C1 serving cell falls below zero for more than 5 seconds.

3. MS tried to access the network through this cell unsuccessfully for the allowed no. of times defined by the parameter MAXRET

4. C2 neighbor cell ( one of the six strongest neighbors) became greater than C2 serving cell for more than 5 seconds.

5. MS detects Downlink Signaling Failure.


• Cell Reselection Criterion – What will happen when the MS needs to make cell reselection?

The MS will camp on the cell that has the highest C2 value.

– C2 is called “Cell Reselection Quantity”

C2 = C1 + CRO – TO * H( PT – T ) where PT ≠ 31

C2 = C1 – CRO where PT = 31

0 , X < 0

Where H(x)

1 , X ≥ 0

CRO Cell Reselection Offset, unit = 2 dB, value range = 0 to 63

TO Temporary Offset, unit = 10 dB, value range = 0 to 7

PT Penalty Time during which TO is valid

T Initiated from zero when the MS places the neighbor in the list of the Six Strongest

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• Cell Reselection Criterion – CRO : defines a signal strength offset to encourage or discourage MSs

to reselect that cell.

– TO : defines a negative temporary offset for certain time according to settings of PT (Practically this is useful to prevent fast moving MS from camping on microcells)

– PT: If PT is set to 31, this means that a (–ve) SS offset “CRO” will be applied to this cell and it appears less favorite for cell reselection.


• Cell Reselection Criterion Down Link Signaling Failure Algorithm

– The Algorithm of type “Leaky Bucket” and used a counter “D”, where D = 90/MFRMS

– MFRMS is a cell parameter defines the no. of multiframes between the transmission of each paging group i.e. if MFRMS=4 then a MS attached to a certain paging group will wait in sleeping mode for 4 multiframes (4*235msec) until it is up again to listen to paging.

– When the MS is up to listen to its paging group, if the message is not decoded successfully then D is decremented by 4 and if the message is decoded correctly then D is incremented by 1.

– If D reaches zero, then a Down Link Signaling Failure is detected and cell reselection took place.

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• Cell Reselection Criterion Down Link Signaling Failure Algorithm

– Ex: Assume that MFRMS = 4

Downlink signaling failure counter is initialized: D = round(90/MFRMS)=22.

If the MS unsuccessfully decodes a paging message, then: D = D - 4 = 18.

If the MS successfully decodes a paging message, then: D = D + 1 = 19.

If D reaches zero, then a Down Link Signaling Failure is detected and

cell reselection took place.

N.B: D can’t exceed the bucket size given by round(90/MFRMS)


• Cell Reselection Criterion CRH ( Cell Reselection Hysteresis )

– Cell Reselection between two cells lie in two different Location Areas, will be accompanied by Location Update.

– At the border between cells the Signal level may be comparable, cell reselection may occur many times accompanied by many location updating leading to huge signaling load.

– To avoid this, a parameter CRH is introduced such that a cell in another location area LA2 should have C2LA2

should greater than C2LA1 of

serving cell lie in LA1 by at least CRH in order to be selected.

– If C2LA1 = 5 dB, CRH = 4 dB, then C2LA2

≥ 9 dB in order to be selected.

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– PLMN Selection.

– Cell Selection.


– Location Updating



• Location Updating – To make it possible for the mobile subscriber to receive a call and

initiate a call whenever needed, the network must know where the MS is located whenever it moves that’s why Location Updating is needed.

– In the Idle Mode, the Network knows the location of the MS on a Location area resolution not on a cell resolution.

– There are three different types of location updating defined:

1. Normal Location Updating.

2. Periodic registration.

3. IMSI attach & IMSI detach (when the MS informs the network when it enters an inactive state)

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• Location Updating

1. Normal Location Updating

– Initiated by the MS when it enters a cell belongs to a new Location Area (LA).

– The MS will compare the LAIold stored on the SIM with the LAInew broadcasted from the new cell and it will found them different so it’ll perform Location Update type normal.



2. Periodic Registration

– Regularly the MS should update the Network with its current location Area.

– The Network will inform the MS how often it should report the location Area he is registering himself in.

– Based on the value of the Parameter T3212 the MS will know how frequent it should make periodic registration.

– T3212 take values from 1 (6min) to 255 (25.5 Hours), default = 40 (4 Hours)

– MSC has a supervision time = BTDM+GTDM if it doesn’t hear from the MS during this period, the MSC will consider the MS implicitly detached.

– BTDM+GTDM should > T3212 , to not consider the MS detach before periodic location update is performed.

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3. IMSI Attach/Detach

– IMSI attach/detach operation is an action taken by the MS to inform the Network either it will go to inactive state (Power off) or it returned back to idle mode.

– ATT is a cell parameter that will inform the MS whether IMSI attach/detach is operational or not.

– If ATT=Yes, then before the MS will be switched off, it will send an IMSI detach request to the Network, so no paging messages will be sent to this MS while it is in this state.

– When the MS is switched on again it will send an IMSI attach request to the Network so now paging messages can be sent normally to this MS.



– PLMN Selection.

– Cell Selection.



– Monitor the Incoming Paging

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• Monitor the Incoming Paging Let us revise the DL logical channels and their mapping:

I) BCH(Broadcast Channels): including

FCCH(Frequency Correction Channel)

SCH(Synchronization Channel) Always Mapped on TS0/C0

BCCH(Broadcast Control Channel)

II) CCCH(Common Control Channels): including

PCH(Paging Channel) Always Mapped on TS0/C0

AGCH(Access Grant Channel)

III) DCCH(Dedicated Control Channels): including

SDCCH(Stand Alone Dedicated Control Channel) May be Mapped on either

SACCH(Slow Associated Control Channel) TS1/C0 or TS0/C0

CBCH(Cell Broadcast Channel)

FACH(Fast Associated Control Channel) “ Work in Stealing mode by replacing the TCH time slot”


C B B B B S F

2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50

F S F S F S F S F S I

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51

0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

Frame 1 Frame 2 Frame 3 Frame 4 Frame 5 Frame 6 Frame 7

Default Mapping on TS0/C0 (BCH+CCCH) “Non

Combined Mode”

51 TDMA Frames = 1 Control Multi-frame

B

C

C

C

C

C

C

C

C

C

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Default Mapping on TS1/C0

(SDCCH+SACCH+CBCH(optional))


• Monitor the Incoming Paging Combination of Control channels (Different Mapping Criteria)

− Mapping on TS0/C0 is controlled by Parameter called BCCHTYPE

− BCCHTYPE = NCOMB (Non Combined, BCH&CCCH)TS1/C0 will carry SDCCH+SACCH

= COMB (Combined, BCH&CCCH&SDCCH/4) TS1/C0 will be free for TCH

= COMBC (Combined with cell broadcast channel CBCH is in use,

BCH&CCCH&SDCCH/4&CBCH) TS1/C0 will be free for TCH

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− SDCCH may have on of the following 4 configurations based on parameter SDCCH

− SDCCH = (i) SDCCH/8 (8 SDCCH Sub-channels i.e. make call setup for 8 users)

= (ii) SDCCH/8 including CBCH (7 SDCCH Sub-channels + 1 CBCH)

For these two cases, the BCCHTYPE=NCOMB and the mapping of the SDCCH channel is done on TS1/C0

= (iii) SDCCH/4 (4 SDCCH Sub-channels)

= (iv) SDCCH/4 including CBCH(3 SDCCH Sub-channels + 1 CBCH)

For these two cases, the BCCHTYPE=COMB or COMBC and the mapping of the SDCCH channel is done on TS0/C0



Non Default Mapping on TS0/C0 (BCH+CCCH)

2*51 TDMA Frames = 2 Control Multi-frame

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The Table below summarizes all the previous details

Default Mapping (Non Combined) Non Default Mapping (Combined)

BCH+CCCH on TS0/C0 and SDCCH+SACCH+CBCH on TS1/C0

BCH+CCCH+SDCCH+SACCH+CBCH on TS0/C0

CBCH doesn't exist CBCH exist CBCH doesn't exist CBCH exist

1 block for BCCH 1 block for BCCH 1 block for BCCH 1 block for BCCH

9 blocks for CCCH 9 blocks for CCCH 3 blocks for CCCH 3 blocks for CCCH

8 blocks for SDDCH 7 blocks for SDDCH 4 blocks for SDDCH 3 blocks for SDDCH

1 block for CBCH 1 block for CBCH


• Monitor the Incoming Paging Paging Groups

− The MS will monitor the incoming paging in only specific times, and the rest of the time it will remain in sleeping mode.

− In this way we save the MS battery and we decrease the UL interference on the system.

− The MS will monitor the incoming paging when the “Paging Group” assigned for this MS is transmitted only.

− The CCCH block can be used by either PCH or AGCH.

− When the CCCH block is used for paging it will be called “Paging Block”

− The Paging Block consists of 4 consecutive Time slots lie in 4 consecutive frames.

− The Paging Block can be used to page 4/3/2 users according to IMSI or TMSI is used when paging the MS ( Length IMSI = 2 TS, Length TMSI = 1 TS)

− The group of users belong to the same paging block will be called “Paging Group”

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C B B B B S F

2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50

F S F S F S F S F S I

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 49 51

0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

Frame 1 Frame 2 Frame 3 Frame 4 Frame 5 Frame 6 Frame 7

Default Mapping on TS0/C0 (BCH+CCCH) “Non

Combined Mode”

51 TDMA Frames = 1 Control Multi-frame

B

C

C

C

C

C

C

C

C

C



− As appeared the MS will listen to paging in only specific times.

− The MS will utilize the time between the 4 TS that lie in 4 consecutive frames to make the required measurements on the neighbor cells.

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− How many Paging Groups we have? This will depend on a parameter MFRMS

− MFRMS is a parameter defined per cell and it defines how frequent the paging group assigned for certain MS will be transmitted.

− MFRMS takes values from 1 to 9,

if MFRMS=1 then the paging group assigned for certain MS will be transmitted every 1 control Multiframes=235 msec

if MFRMS=9 then the paging group assigned for certain MS will be transmitted every 9 control Multiframes = 9*235msec=2.3 seconds.

− If MFRMS is large:

Positive Side: The MS battery life time will increase coz the MS remains in sleeping mode for longer time + paging capacity will increase.

Negative Side: Call setup time will increase coz the paging won’t be sent to the MS except when the time of its paging group came.


• Monitor the Incoming Paging Paging Strategies

− Paging Strategies are controlled by parameters in the MSC.

− Setting of parameters will decide whether the paging will be local paging (within the LA) or global paging (within the MSC service area).

− Setting of parameters will decide also whether paging will be done via IMSI or TMSI.

− Using the parameters we can decide also how the second paging will be incase the first paging failed, ex: If 1st paging was local with TMSI then we can set the 2nd paging to be global with IMSI.

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• Related Feature to the Idle Mode Behavior

Adaptive Configuration of Logical Channels (ACLC)

− As we know the SDCCH channel is used for signaling i.e. call setup, while the TCH channel is used to carry real user traffic (speech/data).

− As per the GSM standards, the GOS for TCH=2% i.e. within 100 calls if 2 of them are blocked then this will be acceptable, for the SDCCH/8 the GOS=0.5% and for the SDCCH/4 the GOS=1%

− As we know in the default settings for frequency C0, TS0 is used to carry BCH+CCCH and TS1 used to carry SDCCH+SACCH, and TS2TS7 used to carry speech/data



Adaptive Configuration of Logical Channels (ACLC) − Now if the signaling load is high, ex: many users need to make call setup, then

high blocking will occur exceeding the acceptable value = 0.5%

− To solve the blocking we have 2 ways:

i) Static configuration of a TCH TS to be used as SDCCH forever

( Now TS1&TS2 used for SDDCH+SACCH and TS3TS7 used to carry speech/data)

But in this case we lost 1 TCH channel i.e. 5 users can talk simultaneously instead of 6

ii) Adaptive configuration of a TCH TS to be used as SDCCH/8 when there is high SDCCH utilization only

( Now TS1&TS2 used for SDDCH+SACCH and TS3TS7 used to carry speech/data, but when the utilization is back to its normal trend, TS2 will be configured back automatically as a TCH and used to carry speech/data)

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Adaptive Configuration of Logical Channels (ACLC)

Main Controlling Parameters:

ACSTATE: Activates/Deactivates the feature on cell basis, values: ON/OFF

SLEVEL: No. of Idle SDCCH sub-channels below which the feature will work.

The conditions that should be fulfilled for the ACLC feature to work:

1) ACSTATE=ON

2) No. of Idle SDCCH sub-channels ≤ SLEVEL (Indication for high utilization)

3) No. of already defined SDCCH channels/8 < Max. allowed configuration of SDCCHs in the cell.

4) No. of Idle TCHs > 4


• Parameters Summary

SCH Parameters

Parameter Name Value Range Recommended Value Unit

BSIC NCC: 0 to 7 BCC: 0 to 7 ─ ─

RACH Control Parameters


MAXRET 1,2,4,7 4 ─

Control Channel Parameters


BCCHTYPE COMB COMBC NCOMB NCOMB ─

SDCCH 0 to 16 (0: No SDCCH/8

configured-combined mode) 1 ─

IMSI Attach/Detach Parameters


ATT Yes, No Yes ─

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Paging Parameters and Periodic Update

Parameter Name

Value Range Recommended Value Unit

MFRMS 2 to 9 6 Control Channel Multi

frame

AGBLK 0 or 1 0 ─

T3212 0 to 255 (0: infinite-No periodic

registeration) 40 6 minutes

Cell Selection and Reselection Parameters

Parameter Name


ACCMIN − 47 dBm to −110 dBm −110 dBm dBm

CCHPWR GSM900: 13 to 43 in steps of 2 GSM1800: 4 to 30 in steps of 2

GSM900: 33 dBm GSM1800: 30 dBm

dBm

CRO 0 to 63 0 2 dB

TO 0 to 7 (7:infinite) 0 10 dB

PT 0 to 31 0

CRH 0 to 14 in steps of 2 dB


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• Handover (Locating) Algorithm

– The Handover (Locating) Algorithm is the basic feature to provide mobility in the Radio Network.

– Aims At? i) Keep the continuity of a current call with acceptable quality.

ii) Cell size control in-order to decrease total interference in the system.

– Implemented where? In the BSC.

– Location process initiated when? After Hand Over (HO), Assignment or Immediate Assignment.

– Inputs to the Algorithm? Signal Strength, Quality measurements &TA for serving cell and Signal Strength measurements for neighbor cells.

– Output from the Algorithm? List of candidates which the algorithm judges to be possible candidates for HO (List of HO candidates are ranked and sorted in descending order)

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– What types of Handover (locating) algorithm we have?

i) SS & Path Loss based Algorithm: Follows the GSM specifications. HO decision is taken based on both Signal Strength (SS) and Path Loss.

ii) SS based Algorithm: HO decision is taken based on Signal Strength only and this leads to better performance.

It is less complex, uses less parameters and easy to be maintained in the Radio Network.


• Handover (Locating) Algorithm – The main Flow of the Handover (locating) Algorithm goes as follow:

Filtering Basic

Ranking

Urgency Conditions

Handling Initiations

Auxiliary Radio Network

Features Evaluation

Organizing the List

Sending the List

& Allocation

Reply

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– Initiation

– Filtering.

– Basic Ranking.

– Urgency Conditions Handling.

– Auxiliary Radio Network Features Evaluation.

– Organizing the List.

– Sending the List & Allocation Reply


• Initiation of the Handover (Locating) Process/Algorithm The Locating Process is initiated when one of the following occurs:

1. Handover: Normal, Intra Cell HO (IHO), Sub-cell change (OLUL or ULOL)

2. Assignment: Allocation of TCH channel after completing call setup on SDCCH.

3. Immediate assignment: You are assigned SDCCH to make call setup, or a TCH to make call setup on when no free SDCCH channels exist.

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– Initiation

– Filtering

– Basic Ranking.






• Filtering

− Simply it is the process of collecting the required data on Signal Strength (SS), Quality and Time Advance (TA) for serving and neighbor cells and average these consecutive measurements over a specified period to rank these cells.

− This is accomplished in two steps:

1. Measurements preparation

2. SS, Quality and TA filtering

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• Filtering

1. Measurements preparation

− Data that is measured:

− The MS can measure the SS of up to 32 neighbor frequencies but only the six strongest neighbors (which it succeeded to decode its BSIC over the last 10 seconds) are reported and considered candidates for HO.

Cell on which measurements are reported

Measured Quantity Who makes the measurements?

Serving Cell

SS DL MS

Quality DL (rxqual_DL) MS

Quality UL (rxqual_UL) BTS

TA BTS

6 Strongest neighbor cells SS DL MS


• Filtering

1. Measurements Preparation

− SS measurements are delivered as integer values 0 63 corresponds to real SS from

-110 dBm - 47 dBm

− Quality is measured based on the BER and it may be represented in two forms:

i) Integers 0 (Best) 7 (Worst)

ii) Decitransformed Quality units (dtqu) from 0 (Best) 70 (Worst)

− Time Advance (TA) is reported as values between 0 63 bit period.

N.B: If TA=1 then the MS is at nearly 0.5 km from the cell

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• Filtering

2. SS, Quality and TA filtering:

− The consecutive measurements for SS, Quality and TA are averaged in some way based on the equation of the filter used.

− We’ve 5 Types of Filters that may be used, each one has its own equation or its way to produce output results from the collected consecutive measurements:

A. General FIR filters (Finite Impulse response)

B. Recursive Straight Average filter

C. Recursive exponential filter

D. Recursive 1st order Butterworth filter

E. Median filter


• Filtering

2. SS, Quality and TA filtering:

− In addition to the way each filter use to produce output results from the consecutive measurements, each filter has what we call filter length which is the period over which measurements are considered.

− We have controlling parameters on cell basis to select the type of filter used and the length of the filter.

− Also the type of the filter used in signaling (call setup) and dedicated phases may be configured separately as we’ll see.

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– Initiation

– Filtering

– Basic Ranking






• Basic Ranking

− It is called “Basic” coz in this stage ranking is done before handling the urgency conditions and evaluation of the auxiliary radio network features.

− As mentioned earlier, two algorithms are available for basic ranking (SS&Path loss based Algorithm and SS based Algorithm) and they’re selected according to the parameter EVALTYPE

− EVALTYPE=1, SS & Path loss based Algorithm is used for basic ranking taking into consideration both Signal Strength measurements and the path loss.

− EVALTYPE=3, SS based Algorithm is used for basic ranking taking into consideration Signal Strength measurements only.

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• Basic Ranking Basic Ranking Algorithm following the SS based Algorithm will be done on four steps:

A. Correction of Base Station output power. Common for

B. Evaluation of the minimum signal strength condition for neighbors. Both

C. Subtraction of signal strength penalties. Algorithms

D. Rank the Candidates after applying Offsets and Hysteresis.


• Basic Ranking Basic Ranking Algorithm following the SS based Algorithm

A. Correction of Base Station output power

The location algorithm aims at making the Pure traffic frequencies to control the cell

borders and not the BCCH frequencies, coz most of the time the seized TCH Time slot will be located on a TCH frequency.

BSPWR is a parameter to set the output power of the BCCH carrier and

BSTXPWR is a parameter to set the output power of the TCH frequencies.

Correction for the output power will done for both:

(A-i) Correction for Neighbor Cells.

(A-ii) Correction for Serving Cell.

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(A-i) Correction for Neighbor Cells

− The MS is informed by the BCCH frequencies of the neighbors cells on which he has to perform his measurements via the Active BA list.

− SS_corrected_DLneighbor = SS_measured_DLneighbor - ( BSPWR - BSTXPWR )




(A-ii) Correction for Serving Cell

1) TCH Time Slot (TS) is on the BCCH frequency

SS_corrected_DLservingcell = SS_measured_DLservingcell - ( BSPWR - BSTXPWR )

2) TCH TS is hopping between a BCCH frequency and a TCH frequency:

SS_corrected_DLservingcell = SS_measured_DLservingcell - ( BSPWR - BSTXPWR )/N ,

Where N is the no. of the hopping frequencies

3) TCH TS is on the OL (Over Laid sub cell)

SS_corrected_DLUnderLaid = SS_measured_DLOverLaid+ ( BSTXPWR Under Laid – BSTXPWROverLaid )

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B. Evaluation of the minimum Signal Strength condition for Neighbors

− Not all the neighbors are allowed to be ranked!!

− The neighbor should pass the minimum signal strength condition in order to be ranked.

− SS_corrected_DLneighbor will be compared with respect to parameter called MSRXMIN,

If SS_corrected_DLneighbor ≥ MSRXMIN this neighbor will be included in ranking

If SS_corrected_DLneighbor < MSRXMIN this neighbor will be excluded from ranking

− If UL measurements are included then SS_corrected_ULneighbor will be compared with respect to parameter called BSRXMIN,

If SS_corrected_ULneighbor ≥ BSRXMIN this neighbor will be included in ranking

If SS_corrected_ULneighbor < BSRXMIN this neighbor will be excluded from ranking



B. Evaluation of the minimum Signal Strength condition for Neighbors

− Example: Assume that a MS is connected to cell A that has five neighbors B,C,D,E&F, the MSRXMIN for all the cells is -104 dBm and the SS_corrected_DLneighbor for each cell after correcting the BTS o/p power is given in the below Table

Neighbors SS_corrected_DLneighbor

B -85 dBm

C -110 dBm

D -87 dBm

E -70 dBm

F -100 dBm

Cell C will be excluded

from ranking and won‟t be

considered in the next stage

and the MS will never HO to it

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C. Subtraction of signal strength penalties

− Penalties or Punishments will be applied on cells that are for some reasons temporarily undesirable.

− A Penalty value will decrease the rank of some cells for certain penalty time.

− SS_punished_DL = SS_corrected_DL – Locating Penalties – HCS Penalties

− In the coming slides we’ll talk about the two types of penalties:

(C-i) Locating Penalties

(C-ii) HCS Penalties





1) Due to HO failure: If HO to a neighbor cell failed then we’ve to apply a penalty value for some time on this neighbor so when basic ranking is done again we don’t go back to this cell.

Penalty value will be configured using parameter PSSHF (default 63 dB)

Penalty time will be configured using parameter PTIMHF (default 5 sec)

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2) Due to Bad Quality (BQ) Urgency HO:

If a cell was abandon due to BQ, then it should have been the best cell from SS point of view so without penalties using the basic ranking we’ll be back to this cell.

Penalty value will be configured using parameter PSSBQ (default 7 dB) Penalty time will be configured using parameter PTIMBQ (default 5 seconds)

3) Due to Excessive TA Urgency HO:

Handled in the same manner like the BQ case.

Penalty value will be configured using parameter PSSTA (default 63 dB) Penalty time will be configured using parameter PTIMTA (default 30 seconds)




(C-ii) HCS Penalties

− It is related to the HCS (Hierarchical Cell Structure) feature when a MS is detected as a fast moving mobile (If fast moving mobile feature is activated)

− A penalty will be applied on lower layer cells so in ranking we will prioritize cells in the same layer of the serving cell and cells in higher layers and in this way unnecessary HO’s are prevented ( ex: layer2 cells will be prioritized than layer1 cells)

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D. Rank the Candidates after applying Offsets and Hysteresis

− Ranking for neighbor cells will be done after

applying Offsets and Hysteresis.

– Offset: Displace the cell border as compared to

The border strictly given by SS.

Controlling parameter: OFFSET (default: zero dB)

– Hysteresis: To reduce the risk of ping pong HO

a region for Hysteresis is applied

around the cell border.




− If the Hysteresis value is too high there will be a risk that the MS will be connected to the cell of low SS for long time and if the Hysteresis is too low then there will be a risk that ping pong HO’s occur.

− So the applied value of Hysteresis will be variable based on the received SS of the serving cell.

− SS_corrected_DLservingcell will be compared to value HYSTSEP (default -90 dBm),

If SS_corrected_DLservingcell > HYSTSEP, then the serving cell is strong enough and high value of Hysteresis will be applied such that Hysteresis value=HIHYST (default 5 dB)

If SS_corrected_DLservingcell < HYSTSEP, then the serving cell is not strong enough and low value of Hysteresis will be applied such that Hysteresis value=LOHYST (default 3 dB)

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• Basic Ranking

Basic Ranking Algorithm following the SS based Algorithm


SS_corrected_DLservingcell > HYSTSEP

Yes

HYST=HIHYST

Now,

Rankservingcell = SS_corrected_DLservingcell

Rankneighbor= SS_punished_DLneighbor – OFFSETneighbor – HYSTneighbor

HYST=LOHY

ST

Output from

Basic Ranking

N

o



– Initiation

– Filtering

– Basic Ranking

– Urgency Conditions Handling




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• Urgency Conditions Handling

− After the Basic Ranking stage a check is made on the serving cell to know if Urgency conditions are detected or not.

− We have two types of Urgency HO:

1. Bad Quality (BQ) Urgency HO

2. Excessive Time Advance (TA) Urgency HO

− If Urgency conditions are detected then the serving cell should be abandon as fast as possible, but some of the neighbors will be removed from the candidate list and the MS will not be able to HO to them as we will see later.

− As seen before, cells that were abandon due to Urgency HO will be subjected to punishment/penalty.



1. Bad Quality (BQ) Urgency HO

− The Quality measured at the DL and UL for the serving cell will be compared with two parameters QLIMDL & QLIMUL (default 50 dtqu) and if:

rxqual_DL > QLIMDL

rxqual_UL > QLIMUL

− The Quality may drop like that as a result of Co-Channel Interference or when the SS became very low.

− When Urgency condition is detected the MS has to leave the cell and make HO to other cell, but in this case the serving cell is the one that has the highest SS so the MS has to HO to a cell of worse SS, but is the MS allowed to HO to any worse cell?

Or Urgency HO due to BQ should be

performed

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• Urgency Conditions Handling 1. Bad Quality (BQ) Urgency HO

− Is the MS allowed to HO to any worse cell? No, this will be based on a parameter called BQOFFSET which will ensure that far neighbors won’t be selected.

− If Rankservingcell – Rankneighbor ≤ BQOFFSET+HYST, then this neighbor is near to the serving cell and it is not much worse than the serving cell and it can be candidate for HO.

− If Rankservingcell – Rankneighbor > BQOFFSET+HYST, then this neighbor is far from the serving cell and it will be removed from the candidate list.

− Ex: If Urgency condition is detected where Rankservingcell = -75 dBm and the neighbors: RankB = -79 dBm ,RankC = -90 dBm ,RankD = -87 dBm and BQOFFSET=5dB,HYST=0 dB

Rankservingcell – RankB =4dB<BQOFFSET= 5dB Cell B is kept in the candidate list

Rankservingcell –RankC=15dB>BQOFFSET= 5dB Cell C is removed from the candidate list

Rankservingcell – RankD = 8dB > BQOFFSET=5dB Cell D is removed from the candidate list



2. Excessive Time Advance (TA) Urgency HO

− TA can be used as a measure for the distance between the BTS and the MS.

− If TA > TALIM (63 bit period) Urgency HO due to TA is initiated.

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• After Basic Ranking and Evaluation of the Urgency Conditions, the Serving cell and Neighbor cells will be divided into 3 Groups

Categorization #1

Better Cell

Serving Cell

Worse Cell



– Initiation

– Filtering

– Basic Ranking


– Auxiliary Radio Network Features Evaluation



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• Auxiliary Radio Network Features Evaluation

1. Assignment to Another Cell Evaluation

2. Cell Load Sharing Evaluation

3. Over Laid/Under Laid sub-cell Evaluation

4. IHO Evaluation

5. HCS Evaluation

After these Evaluations, some candidates will be removed from the HO candidate list and

Categorization#2 will be performed.




− The Locating Algorithm may be initiated after immediate assignment to know whether it is better for the MS to take a TCH time slot on the current cell or not.

− If during the signaling phase a better cell was found after ranking, then

“Assignment to Better Cell” will be initiated.

− If during the signaling phase no better cell was found, then the MS will normally be assigned a TCH time slot on the current cell.

− If the Better/Serving cells were congested then “Assignment to Worse Cell” will be initiated if possible.

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− Is the MS allowed to take TCH time slot on any worse cell? No, this will be based on a parameter called AWOFFSET which will ensure that far neighbors won’t be selected.

− Only if Rankservingcell – Rankneighbor ≤ AWOFFSET+HYST, then this neighbor is near to the serving cell and it is not much worse than the serving cell and assignment to it can be done.

− If Rankservingcell – Rankneighbor > AWOFFSET+HYST, then this neighbor is far from the serving cell and it will be removed from the candidate list.



2. Cell Load Sharing (CLS) Evaluation

− This feature is used to reduce congestion on the serving cell.

− When CLS is activated and the load on the serving cell becomes higher than certain threshold then:

i) Valid CLS HO candidates are defined

ii) Re-calculation of their ranking values will be performed.

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2. Cell Load Sharing (CLS) Evaluation

i) Valid CLS HO candidates are defined as follow:

− Load on neighbor cells < CLS load threshold

− Internal cells: lies in the same BSC

− Same Layer

ii. Re-calculation of their ranking values will be performed

− We’re going to recalculate the Ranking values of the valid CLS neighbors with reduced Hysteresis so these worse neighbors will appear with higher SS than they really are and the MS can make HO to them and relief the congestion on the current cell.

This feature will be discussed in details afterwards.



3. OL/UL Sub-Cell Evaluation

− The OL/UL feature provides a way of increasing the traffic capacity in a cellular network without building new sites.

− Since OL subcell serves smaller area than the corresponding UL subcell a smaller reuse distance can be used in in the OL subcell than in the under laid.

− The OL/UL evaluation may result in a recommendation to change the subcell from the one currently in use, this evaluation is based on:

DL SS, TA serving Cell, Distance to cell border, Traffic Load in the cell


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• Auxiliary Radio Network Features Evaluation 4. Intra Cell HO (IHO) Evaluation

− The IHO feature provides a way to improve the speech quality during the conservation when bad quality is detected while the SS is high.

− This is can be accomplished by changing the channel the connection is currently using within the same cell.




5. Hierarchical Cell Structure (HCS) Evaluation

− The HCS feature provides the possibility to give priority to cells that are not strongest but provide sufficient SS.

− The priority of a cell is given by associating a layer to the cell.

− We have 8 layers from layer 1 (Highly prioritized) to layer 8 (least prioritized).

− Micro cells are prioritized than Macro cells for capacity purposes.

− Cells of lower layers will be ranked higher than cells of higher layers in the HO candidate list.


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• After the Auxiliary Radio Network features evaluation some candidates may be prioritized and the order of the candidate list will

be modified.

The Serving cell and Neighbor cells will be divided into 3 Groups

Categorization #2

Above S

Serving Cell

(SC) Below S



– Initiation

– Filtering

– Basic Ranking



– Organizing the List


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• Organizing the List

− The final list will contain maximum up to six neighbors + the serving cell and categorized as follows: Serving Cell (SC), Above S, Below S

− To reach the final form before sending the list the following steps will be done:

A. Removal of Candidates

B. Ordering the Candidate list based on the Current Conditions.



A. Removal of Candidates

Some Candidates may be removed coz:

− Some Controlling timers are active and preventing HO to certain cell:

TALLOC: This timer prevents HO on a target cell for some time after assignment/HO failure due to congestion on target cell. (N.B: No penalties are applied on this cell)

TURGEN: This timer prevents HO on a target cell for some time after urgency HO failure due to congestion on target cell. (N.B: No penalties are applied on this cell)

N.B: TALLOC and TURGEN are BSC parameters (Default Values= 2 SACCH periods

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B. Ordering the Candidate list based on the Current Conditions

− Means what? Means in what order the 3 categories (Above S, S, Below S) will be arranged before sending the candidate list. This will be based on some condition flags.

− Condition flags: 1 Assignment Request Arrived

2 Assignment to Worst Cell is in use

3 Excessive TA detected

4 BQ Urgency HO

5 OL/UL Subcell load change or IHO


• Organizing the List B. Ordering the Candidate list based on the Current Conditions

Condition flags: 1 Assignment Request Arrived 2 Assignment to Worse Cell is in use 3 Excessive TA detected 4 BQ Urgency HO 5 OL/UL Subcell load change or IHO

Case Condition Flags

Ordering Comment 1 2 3 4 5

1 0 x 0 0 0 Above S Normal Case

2 0 x 0 1 0 Above S Below S Serving Cell has BQ so it should be abandon

either to the Above S or Below S cell

3 1 0 0 0 0 Above S S An Assignment request came and the AW flag is

not raised

4 1 1 0 0 0 Above S S Below S An Assignment request came and the AW flag is

raised

5 0 x 0 1 1 Above S S Below S

Serving Cell has BQ so it should be abandon but coz the OL/UL subcell change flag is raised, then

the serving cell is included coz this subcell change may solve the issue with no need to go

for a below worse cell

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– Initiation

– Filtering

– Basic Ranking



– Organizing the List



• Sending the List & Allocation Reply

− The resulting candidate list will form the basis on which HO will be performed.

− Empty list means that no options are better than remaining on the current cell and no HO will occur.

− The channel allocation reply may be success or failure.

− Failure may be due to congestion or signaling failure on the target cell.

− Based on the result of allocation either success/failure, some actions will be taken like applying some penalties or enabling of certain timers as we saw previously.

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• Example1: − Assume that the o/p from the Filtering stage for the SS measurements is as below

and we want to prepare the Basic Ranking Candidate list for HO:

Where,

BSPWR = BSTXPWR, MSRXMIN = -90 dBm,

Cell A was abandon due to BQ urgency HO (PSSBQ=7dB)

SS based Algorithm is in use where OFFSET=0, HYSTSEP= -90 dBm,

HIHYST= 5 dB, LOHYST= 3 dB

Cell SS(dBm)

A -70

B (Serving Cell) -74

C -78

D -68

E -80

F -92

G -95


• Solution:

A) Correction of Base Station output power:

− Since BSPWR = BSTXPWR then the current measurements will be kept as it is.

− SS_corrected_DLneighbor = SS_measured_DLneighbor

− SS_corrected_DLserving = SS_measured_DLserving

B) Evaluation of the minimum Signal Strength condition for Neighbors

− The SS for neighbors will be compared against MSRXMIN = -90 dBm

Cell F and Cell G have SS < MSRXMIN then they will be

removed from the list and can’t be candidates for HO.

Cell SS(dBm)

A -70


C -78

D -68

E -80

F -92

G -95

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• Solution:

C) Subtraction of signal strength penalties

− Since Cell A was abandon due to BQ urgency HO (PSSBQ=7dB) then it will be punished,

SS_punished_DL Cell A = SS_corrected_DL – PSSBQ = -70 – 7 = -77 dBm

− The candidate list will now be in the following form:

Cell SS(dBm)

A -77


C -78

D -68

E -80


• Solution: D) Rank the Candidates after applying Offsets and Hysteresis

Since SSServing cell B = -74 dBm > HYSTSEP= -90 dBm, then it is

better to stay on the current cell and high Hysteresis will be

applied

i.e. HYST = HIHYST = 5 dB

Rankservingcell B = -74 dBm “Serving Cell”

RankA= -77 dBm – OFFSET – HYST = -77 – 0 – 5 = -82 dBm “Worse Cell”

RankC= -78 dBm – OFFSET – HYST = -78 – 0 – 5 = -83 dBm “Worse Cell”

RankD= -68 dBm – OFFSET – HYST = -68 – 0 – 5 = -73 dBm “Better Cell”

RankE= -80 dBm – OFFSET – HYST = -80 – 0 – 5 = -85 dBm “Worse Cell”

Cell SS(dBm)

A -77


C -78

D -68

E -80

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• Solution:

− Now the final list according to Categorization#1 will be arranged as follows:

Categorization#1

Cell RANK(dBm) Category

D -73 Better Cell

B -74 Serving Cell

A -82 Worse Cell

C -83 Worse Cell

E -85 Worse Cell


• Disconnection Criteria

− The Disconnection algorithm is not part of the locating algorithm but for completeness, the topic is treated here.

− The Disconnection algorithm manages when the connection between the MS and the Network shall be dropped when signaling failure is detected.

− The Disconnection criterion can be made in both the DL and the UL such that:

In the DL: managed by the MS and in the UL: managed by the BSC.

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• Disconnection Criteria

− In DL:

Controlled by a parameter RLINKT (max. bucket size) , when the MS couldn’t decode a SACCH message (0.48 sec), the bucket will be decreased by 1 unit, when the MS successfully decodes a SACCH message, the bucket will be increased by 2 units, if the bucket reached value = Zero then disconnection will occur, recommended value RLINKT=16

− In UL:

The disconnection algorithm will run in the same way, the BSC will make the evaluation, and the controlling parameter is called RLINKUP, , recommended value RLINKUP=16

N.B: The bucket can’t have values larger than the max. value given by RLINKT/ RLINKUP



Algorithm Selection

Parameter Name


EVALTYPE 1 or 3 3 ─

Flow Control Parameters

Parameter Name


TALLOC 0 to 120 2 SACCH period=480 msec

TURGEN 0 to 120 2 SACCH period=480 msec

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Signal Strength based Basic Ranking Parameters


HYSTSEP −150 to 0 -90 dBm

LOHYST 0 to63 3 dB

HIHYST 0 to63 3 dB

OFFSET −63 to 63 0 dB

Handover Failure Parameters (Signaling Failure)


PSSHF 0 to 63 63 dB

PTIMHF 0 to 600 5 Seconds



Urgency Conditions Parameters


QLIMUL 0 to 100 55 dtqu

QLIMDL 0 to 100 55 dtqu

BQOFFSET 0 to 63 3 dB

PSSBQ 0 to 63 7 dB

PTIMBQ 0 to 600 15 Seconds

TALIM 0 to 63 62 Bit Period (0.577msec)

PSSTA 0 to 63 63 dB

PTIMTA 0 to 600 30 Seconds

Disconnection Algorithm Parameters


RLINKT 4 to 64 in steps of 4 16 SACCH period=480 msec

RLINKUP 1 to 63 16 SACCH period=480 msec

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• HCS Evaluation Algorithm

– HCS feature provides the ability and flexibility to give priority to cells that are not strongest but provide sufficient Signal Strength.

– The priority of a cell is given by associating an HCS layer to the cell where each cell will be belonging to an HCS band.

– The lower the layer ( and the HCS band), the priority is higher,

i.e. layer 1 has higher priority than layer 2, layer 3, layer 4, …..

layer 2 has higher priority than layer 3, layer 4, layer 5, …..

– Up to 8 layers (in up to 8 bands) may be defined, where one or several layers can be assigned to the same HCS band.



– The lower HCS bands will only include lower layers compared to a higher HCS bands.

– A mixture of small micro cells (lower layers) and large macro (higher layers) cells will achieve both high capacity and good coverage.

– Micro cells will be used for capacity issues while macro cells will be used to provide coverage, fill coverage holes and handle the fast moving mobiles.

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– With Basic Ranking only, micro cells will be ranked as the strongest server in very small area, so to let micro cells serve in an area where acceptable SS is guaranteed then HCS should be used.



− The idea with a layered cell structure is to let lower layer cells serve MSs that receive sufficient SS even if there is other cells with strongest received SS in the area.

− But how to decide if the lower layer cell has sufficient SS to be prioritized over strongest cells?

This will be according to two thresholds LAYERTHR (Layer Threshold) and HCSBANDTHR (HCS Band Threshold)

− LAYERTHR: Decides if the cell should be prioritized over stronger cells lie in the same HCS band or not.

− HCSBANDTHR: Decides if the cell should be prioritized over stronger cells from different HCS bands or not.

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− The input to the HCS Evaluation Algorithm is the Basic Ranking list we prepared from the locating process.

− The output will be in the form of two lists: HCS prioritized list (on Top) then Basic Ranking list.

− HCS prioritized list: will include cells that fulfilled the HCS conditions & rules and will be ranked according to HCS evaluation (layered ranking)

− Basic Ranking list: will include cells that didn’t fulfill the HCS conditions and will be ranked according to basic ranking rules (SS ranking)

HCS Evaluation

Algorithm

HCS Prioritized

Cell List

Basic Ranking List

Basic Ranking List Input Outp

ut


• HCS Evaluation Algorithm Mechanism of the HCS Algorithm

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(A) Band Evaluation: In order to be a candidate in the HCS evaluation process, then the SS of serving and neighbor cells should be greater than their band threshold ( HCSBANDTHR )

SSservingcell > HCSBANDTHRservingcell – HCSBANDHYSTservingcell

SSneigbhorcell > HCSBANDTHRneighborcell + HCSBANDHYSTneighborcell

Cells that will not fulfill the above condition will go to be sorted in the Basic Ranking list in priority order according to SS.

Cells that will fulfill the criterion will pass to the next step in the HCS evaluation.

N.B: HCSBANDTHR and HCSBANDHYST are BSC parameters.



(B) Define the strongest Cell (SS) in each Band

− Cells that passed the band evaluation in step (A) will be moved to the next step.

− In this stage, the strongest cells in each Band from SS point of view will be identified.

− Strongest cells will pass direct to be HCS Ranked

− The rest of cells that are not strongest within the band will be moved to Step (C)

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(C) Layer Threshold Evaluation

− Cells that passed the band evaluation in step (A) and they are not strongest within their own band, their SS will be checked against the Layer threshold (LAYERTHR)

SSservingcell ≥ LAYERTHRservingcell – LAYERHYSTservingcell

SSneigbhorcell ≥ LAYERTHRneighborcell + LAYERHYSTneighborcell

Cells that will not fulfill the above condition will go to be sorted in the Basic Ranking list in priority order according to SS.

Cells that will fulfill the criterion will pass to the next step in the HCS evaluation



(D) Identify the Strongest Cells within each layer

− Now we will deal with cells that passed the band evaluation (in Step A) and they were not strongest within their own band (in Step B) and they passed the layer threshold condition (in Step C)

− Cells that are strongest within their own layer will be identified and they’ll pass direct to be HCS ranked.

− Cells that are not strongest within their own layer will be moved to the next step.

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(E) Check how many cells from each layer are allowed to pass to be HCS ranked

− Now we will deal with cells that passed the band evaluation (in Step A) and they were not strongest within their own band (in Step B) and they passed the layer threshold condition (in Step C) and they are not strongest within their own layer (in step D)

− MAXCELLSINLAYER: will identify how many cells from each layer can pass to be HCS ranked, ex: if MAXCELLSINLAYER = 2 then two cells only are allowed to pass to be HCS ranked.

− MAXDBDEVINLAYER: will identify how the next strongest cell in the layer is far from the strongest cell in the layer.

i.e. if SS_Strongest Celllayer x - SS_next strongest celllayer x ≤ MAXDBDEVINLAYER

then the next strongest cell is not weak and it will pass to be HCS ranked.



(F) Form the Final list

− Now all cells that succeeded to pass to be HCS ranked, will be sorted in ascending order according to their layer not SS (as in Basic Ranking) i.e. layer1 cells, then layer2 cells, …… and these cells will form an HCS prioritized list that will lie on Top.

− All cells that failed to pass to be HCS ranking, will go to be sorted in a Basic Ranking list and this list will lie after the HCS prioritized list

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• HCS Evaluation Algorithm Example:

Assume that the output from the Basic Ranking is as below, where for all cells have HCSBANDTHR = - 90 dBm, LAYERTHR = - 80 dBm,

HCSBANDHYST= LAYERHYST= 0,

MAXCELLSINLAYER = 3, MAXDBDEVINLAYER = 3

Cell SS(dBm) Band Layer

G -68 Band 8 Layer 7

E -72 Band 8 Layer 6

B (Serving) -73 Band 4 Layer 4

A -74 Band 4 Layer 3

C -75 Band 8 Layer 7

F -75 Band 4 Layer 4

D -95 Band 4 Layer 4


• HCS Evaluation Algorithm Solution: (A) Band Evaluation: In order to be a candidate in the HCS evaluation process,

then the SS of serving and neighbor cells should be greater than their band threshold (HCSBANDTHR )

SSservingcell > HCSBANDTHRservingcell – HCSBANDHYSTservingcell

SSneigbhorcell > HCSBANDTHRneighborcell + HCSBANDHYSTneighborcell

HCSBANDTHRservingcell = HCSBANDTHRneighborcell = -90 dBm

HCSBANDHYSTservingcell = HCSBANDHYSTneighborcell = 0 dBm

Cell SS(dBm) Band Layer



B (Serving) -73 Band 4 Layer 4





Cell D didn‟t fulfill the condition (SS_CellD = -95 dBm < -90 dBm) so it will be out of

the HCS evaluation and it will go to be sorted in the Basic Ranking list.

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• HCS Evaluation Algorithm Solution: (B) Define the strongest Cell (SS) in each Band

− Cells that passed the band evaluation in step (A) will be moved to the next step.

− In this stage, the strongest cells in each Band from SS point of view will be identified.

− Strongest cells will pass direct to be HCS Ranked

− Now Cells G & B will go direct to be HCS evaluated, while cells E,A,C&F will be examined in the next steps.

Cell SS(dBm) Band Layer Comment

G -68 Band 8 Layer 7 Strongest in Band 8 - Go direct to HCS Evaluation list

E -72 Band 8 Layer 6 Will go to the next step: Layer Evaluation

B -73 Band 4 Layer 4 Strongest in Band 4 - Go direct to HCS Evaluation list

A -74 Band 4 Layer 3 Will go to the next step: Layer Evaluation

C -75 Band 8 Layer 7 Will go to the next step: Layer Evaluation

F -75 Band 4 Layer 4 Will go to the next step: Layer Evaluation

D -95 Band 4 Layer 4 Out of the HCS Evaluation – Back to the Basic Ranking list


• HCS Evaluation Algorithm Solution: (C) Layer Threshold Evaluation

− Cells E,A,C&F that are not strongest within their own band, their SS will be checked against the Layer threshold (LAYERTHR) if

SSservingcell ≥ LAYERTHRservingcell – LAYERHYSTservingcell

SSneigbhorcell ≥ LAYERTHRneighborcell + LAYERHYSTneighborcell

LAYERTHRservingcell = LAYERTHRneighborcell = - 80 dBm

LAYERHYSTservingcell = LAYERHYSTneighborcell = 0 dBm



E -72 Band 8 Layer 6 SS > LAYERTHR = -80 dBm, Will go to the next step


A -74 Band 4 Layer 3 SS > LAYERTHR = -80 dBm, Will go to the next step

C -75 Band 8 Layer 7 SS > LAYERTHR = -80 dBm, Will go to the next step

F -75 Band 4 Layer 4 SS > LAYERTHR = -80 dBm, Will go to the next step


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Solution: (D) Identify the Strongest Cells within each layer

− After Cells E,A,C&F all of them passed the layer threshold condition (LAYERTHR), Cells that are strongest within their own layer will be identified and they’ll pass direct to be HCS ranked.

− Cells E&A are strongest within their own layer so they will go direct to be HCS ranked.

− Cells C&F are not the strongest within their own layer, so they will be examined in the next step to know if they can pass to be HCS ranked or not



E -72 Band 8 Layer 6 Strongest in Layer 6 - Go direct to HCS Evaluation list


A -74 Band 4 Layer 3 Strongest in Layer 3 - Go direct to HCS Evaluation list

C -75 Band 8 Layer 7 Not Strongest in Layer-Will be examined in the next step

F -75 Band 4 Layer 4 Not Strongest in Layer-Will be examined in the next step



• HCS Evaluation Algorithm Solution: (E) Check how many cells from each layer are allowed to pass to be HCS

ranked

− MAXCELLSINLAYER: will identify how many cells from each layer can pass to be HCS In our example MAXCELLSINLAYER = 3 then three cells only are allowed to pass to be HCS ranked.

− MAXDBDEVINLAYER: will identify how the next strongest cell in the layer is far from the strongest cell in the layer.

i.e. if SS_Strongest Celllayer x - SS_next strongest celllayer x ≤ MAXDBDEVINLAYER = 3 dB

then the next strongest cell is not weak and it will pass to be HCS ranked.

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• HCS Evaluation Algorithm Solution: (E) Check how many cells from each layer are allowed to pass to be HCS

ranked

Cell C:

Check1: Lies in layer 7 and ranked as the 2nd strongest cell in the layer and since 3 cells are

allowed to be ranked according to MAXCELLSINLAYER then Check1 is passed.

Check2: Is SS_Strongest Celllayer 7 - SS_next strongest celllayer 7 < MAXDBDEVINLAYER=3dB

SSCell G - SSCell C = -68-(-75) = 7 dB > MAXDBDEVINLAYER=3dB then Check2 failed.






C -75 Band 8 Layer 7 Out of the HCS Evaluation – Back to the Basic Ranking list




• HCS Evaluation Algorithm Solution:(E)Check how many cells from each layer are allowed to pass to be HCS

ranked

Cell F:

Check1: Lies in layer 4 and ranked as the 2nd strongest cell in the layer and since 3 cells are allowed to be ranked according to MAXCELLSINLAYER then Check1 is passed.

Check2:Is SS_Strongest Celllayer 4 - SS_next strongest celllayer 4<MAXDBDEVINLAYER=3dB

SSCell G - SSCell C = -73-(-75) = 2 dB < MAXDBDEVINLAYER=3dB then Check2 is passed.






C -75 Band 8 Layer 7 Out of the HCS Evaluation – Back to the Basic Ranking list

F -75 Band 4 Layer 4 2nd Strongest in Layer4-Go to HCS Evaluation list


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• HCS Evaluation Algorithm Solution: (F) Form the Final list

− Now all cells that succeeded to pass to be HCS ranked, will be sorted in ascending order according to their layer not SS (as in Basic Ranking) i.e. layer1 cells, then layer2 cells, …… and these cells will form an HCS prioritized list that will lie on Top.

− All cells that failed to pass to be HCS ranking, will go to be sorted in a Basic Ranking list and this list will lie after the HCS prioritized list

Final List



HCS prioritized list (Layer Ranking)

B(Serving) -73 Band 4 Layer 4




C -75 Band 8 Layer 7 Basic Ranking list (SS Ranking)




HCS Traffic Distribution Concept

− This feature is useful In order to control the traffic distribution between cells.

− If this feature is active then some cells that were prioritized due HCS ranking (layer ranking) will be removed if they already have enough traffic.

− HCSTRAFDISSTATE: Is a BCS parameter that shows if HCS Traffic Distribution is enabled within the cells in the BCS or not.

– If the HCS traffic distribution is allowed then two checks will be made:

(i) Check on the serving cell’s availability vs. parameter on cell level called HCSOUT

(ii) Check on the neighbor cells’ availability vs. parameter on cell level called HCSIN

− The Availability means: the percentage of free (non-occupied) Full Rate Time Slots.

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HCS Traffic Distribution Concept

(i) Check on the serving cell’s availability:

− If AvailabilityServingCell > HCSOUT, then this cells has too many free Time slots and it is not preferred to leave this cell.

(ii) Check on the neighbor cell’s availability:

− If AvailabilityneighborCell < HCSIN, then this cells has few free Time slots and it can’t accept HO’s due to HCS prioritization.


• HCS Evaluation Algorithm Mechanism of the HCS Algorithm when HCS Traffic Distribution is in use

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• HCS Evaluation Algorithm I) Example when HCS Traffic Distribution is enabled (AvailabilityServingCell<HSCOUT)

− After ordinary HCS evaluation we formed the below list from the previous example.

− Assume HCSOUT=50%, HCSIN=30%, Availability of Cell B (serving) = 40%

and availability of Cell F (neighbor cell) = 10% only, while all other cells have availability = 45 %

− What will be the final list form ?

Final List










Final List











• HCS Evaluation Algorithm Solution:

− Availability of Serving Cell (B) = 40% < HCSOUT (50%), then the serving cell has few free Time Slots and we can leave this cell i.e. outgoing HO from this cell is enabled.

− Availability of Neighbor Cell F=10% < HCSIN (30%), then this cell can’t accept HO’s due to HCS prioritization coz it has few free TS i.e. this cell is congested.

This cell will be removed from the HCS prioritized list and it will be moved to the Basic Ranking List.

Final List










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− The final list will be as below:

Final List








Basic Ranking list (SS Ranking) C -75 Band 8 Layer 7



• HCS Evaluation Algorithm II) Example when HCS Traffic Distribution is enabled (AvailabilityServingCell > HSCOUT)

− If the serving cell has a channel availability above HCSOUT it is considered to be taking too little traffic so it is decided to not allow handovers out due to HCS from the cell.

− Instead, all the remaining HCS prioritized candidate cells, fulfilling the HCSIN criterion and that are in a lower layer or in the same layer as the serving cell, will be basic ranked among themselves and added to a “Prioritized basic ranked cells list” that will be put above the other basic ranked cells in the final candidate list.

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• HCS Evaluation Algorithm II)Example when HCS Traffic Distribution is enabled(AvailabilityServingCell>HSCOUT)

− After ordinary HCS evaluation we formed the below list from the previous example.

− Assume HCSOUT=50%, HCSIN=30%, Availability of Cell B (serving) = 60%

and availability of Cell F (neighbor cell) = 10% only, while all other cells have availability = 45 %

− What will be the final list form ?

Final List



From HCS prioritized list (Layer Ranking)









− Availability of Serving Cell (B) = 60% > HCSOUT (50%), then the serving cell has Too many Time slots and HO out from this cell due to HCS is not allowed.

− Availability of Neighbor Cell F=10% < HCSIN (30%), then this cell can’t accept HO’s due to HCS prioritization coz it has few free TS i.e. this cell is congested.

This cell will be removed from the HCS prioritized list and it will be moved to the Basic Ranking List.

− Cells E&G are layers 6&7 respectively i.e. they are of higher layers than the serving cells.

These cells will be removed from the HCS prioritized list and it will be moved to the Basic Ranking List.

− Now cells A&B will be ranked according to SS “Prioritized Basic Ranking list”

cells C,D,E,F&G will be ranked according to SS “Basic Ranking list”

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Final List



From HCS prioritized list (Layer Ranking)









− The final list will be as below:

Final List


B(Serving) -73 Band 4 Layer 4 Priotirized Basic Ranking List



Basic Ranking list (SS Ranking)





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• HCS Evaluation Algorithm Optimizing a problematic Traffic Case:

− Assume we have the below case with 3 Macro cells (layer 4) and 1 Micro cell (layer2) and all of them belong to the same HCS band, HCSBAND 1

− One of the Macro cells carries very high traffic and it is about to congest, how could we solve this case?

Macro Cell

(L4) Macro Cell

(L4)

Micro

Cell

(L2)

Macro Cell

(L4)


• HCS Evaluation Algorithm Solution 1: Direct more Traffic to the Micro Cell

− We can decrease the LAYERTHR of the Micro cell (Layer 2) from -75dBm to -80dBm for example, so the micro cell will capture more traffic from the congested macro cell.

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• HCS Evaluation Algorithm Solution 2: Direct more Traffic to the adjacent Macro Cells

− We can increase the Layer of the congested Macro cell (Layer 4 Layer 5) so it will appear less prioritized with respect to the adjacent neighbor cells and it will offload its traffic to them.


• HCS Evaluation Algorithm Solution 3: Direct more Traffic to one of the adjacent Macro Cells

− We can decrease the Layer of one of the adjacent Macro cell (Layer 4 Layer 3) so it will appear more prioritized with respect to the congested cell and it will capture some of its traffic.

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Fast Moving MSs

− If cell parameter FASTMSREG is “ON” and MS made no. of HOs >NHO (default=3) in time window THO (default=30sec) then MS is considered as fast moving MS.

− The stronger cells according to Basic Ranking in all higher layers within the same system type are given priority.

− For example: 1800 candidates are in Layers 1,2&3 while 900 candidates are in Layers 4&5, if the MS is considered as fast in layer1, then candidates in layers 2&3 of higher basic ranking than the serving cell are given priority.

− Highest priority is given for the strongest cell regardless of its layer.

− To prevent HO back to lower layer cells, a penalty PSSTEMP (0 to 63) is applied for a time PTIMTEMP (0 to 600s) on all neighbor cells within the current system type and all cells in other system types.


• HCS Evaluation Algorithm − Parameters Summary

1 For reduced HCS functionality we have only 2 bands HCS Band1 and HCS Band2 (default)

2 For reduced HCS functionality we have only 3 layers

HCS Algorithm Control Parameters

Parameter Name Value Range Default Value Recommended Value Unit

HCSBAND 1 to 8 1 2 2 ─

HCSBANDTHR 150 to 0 95 ─ dBm (–ve)

HCSBANDHYST 0 to 63 2 2 dB

LAYER 1 to 8 2 2 ─ ─

LAYERTHR 150 to 0 75 ─ dBm (–ve)

LAYERHYST 0 to 63 2 2 dB

MAXCELLSINLAYER 1 to 31 1 1

MAXDBDEVINLAYER 0 to 63 3 3 dB

HCSTRAFDISSTATE 0,1 0 1 ─

HCSIN 0 to100 0 ─ %

HCSOUT 0 to100 100 ─ %

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• Concentric Cells (Overlaid Underlaid Subcells)

− Traffic Capacity of a cellular network can be increased by either adding more frequencies or reducing the frequency reuse distance.

− One approach is to apply a second frequency re-use pattern with a tighter frequency reuse (Overlay) on the existing pattern.

− These cells should be restricted in size, so shorter reuse distance can be accomplished without causing Co-channel/Adjacent channel interference.

− They are termed Overlaid (OL) Subcells, whereas the original cells will be called Underlaid(UL) Subcells.

− Now by having more frequencies per cell, then Network capacity is increased.

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− The fundamental idea behind the OL/UL subcells is to let the traffic close to the site to be moved to the OL subcell, while traffic close to the cell border to be moved to the UL subcell.

− In that way of treading the traffic, the frequencies in the OL subcell can have tighter frequency reuse.



− Example: Assume that cell A has frequencies: f1&f2, cell B has frequencies: f3&f4 and now cell A has increase in the traffic, so we’re going to assign cell A frequency f4 also.

− Now high Co-channel interference will occur on f4 at the border between the two cells, coz f4 is reused between two adjacent cells.

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− Using the OL/UL concept we can solve the case as follows:

− f4 will be used in the OL subcell and it will be restricted to serve in a small area only near to the site so interference from the neighbor cell will be minimized and a good C/I can be enjoyed.



− To maintain the service area of the OL subcell restricted to a certain region we have three thresholds we can play with:

A. Path Loss Threshold

B. Timing Advance Threshold

C. Distance to Cell Border Threshold

− With the ordinary OL/UL subcells, the MS near the cell will camp on the overlaid subcell but even if the OL subcell got high utilized there is no way to push traffic to the UL subcell.

− Using Subcell Load Distribution (SCLD) Concept, we can configure the cell to use the OL as the preferred subcell initially and when traffic on the OL increased beyond certain load, any extra traffic will be offloaded to the UL subcell.

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Algorithm

(I) OL/UL Subcell Change with Subcell Load Distribution Deactivated

− As we stated before, the service area of the OL subcell can be defined based on one of three criteria: Path Loss, Time Advance and Distance to cell border.

1. Path Loss Criterion:

− Controlling parameters are the path loss threshold LOL and the path loss hysteresis LOLHYST

− DL path loss L= (BSTXPWR - BTS power reduction) – Received_SS_DLfiltered

− BSTXPWR: BTS output power for the TCH frequencies.

− DL path loss L will be checked vs. LOL (path loss threshold) and LOLHYST to know whether a subcell change from OLUL or ULOL is needed.



Algorithm


2. Time Advance Criterion:

− Time Advance can be used as a measure for the distance between the BTS and MS.

− Controlling parameters are the time advance threshold TAOL and the time advance hysteresis TAOLHYST

− The “TA” of the MS will be measured via BTS and checked vs. TAOL and TAOLHYST to know whether subcell change is needed or not.

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Algorithm


3. Distance to Cell Border Criterion:

− DTCBSC: Is a BSC parameter that enables/disables the distance to cell border evaluation criterion on whole cells on the BSC.

− Controlling parameters are the distance to cell border threshold DTCB and the distance to cell border hysteresis DTCBHYST

− The cell border is defined as the difference between the Received_SSServingCell and the Received_SSStrongest Neighbor ,where this strongest neighbor should meet the following: Non-Cosited, Same System type (900/1800), Same HCS Layer.



Algorithm


3. Distance to Cell Border Criterion:

− Received_SSServingCell - Received_SSStrongest Neighbor will be checked vs. DTCB and DTCBHYST to see whether subcell change is needed or not.

− But for the evaluation to be triggered (initiated), the serving cell should have number of neighbor cells > NNCELLS (if NNCELLS=2, at least 2 neighbor cells) that are measured by the MS having enough SS such that:

Received_SSServingCell - Received_SSNeighbor < DTCB+DTCBHYST+NDIST where,

NDIST is a threshold measured in dBs.

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Algorithm


OL UL Subcell change: for a subcell change from OL UL then one of the following should be fulfilled.

L (Path Loss) > LOL + LOLHYST “OR”

ta (Time Advance) ≥ TAOL + TAOLHYST “OR”

SSServing - SSNeighbor < DTCB - DTCBHYST

Strongest, Non Cosited, Same type, Same HCS Layer

But as mentioned before, for this evaluation to be initiated then,

No. of neighbor cells ≥ NNCELLS should be reported meeting the following

equation:

SSServing - SSNeighbor < DTCB + DTCBHYST + NDIST

Non Cosited, Same type, Same HCS Layer



Algorithm


UL OL Subcell change: for a subcell change from UL OL then one of the following should be fulfilled.

L (Path Loss) ≤ LOL - LOLHYST“and”ta (Time Advance) < TAOL - TAOLHYST “and”

SSServing - SSNeighbor ≥ DTCB + DTCBHYST


But as mentioned before, for this evaluation to be initiated then,


equation:

SSServing - SSNeighbor > DTCB + DTCBHYST + NDIST

Non Cosited, Same type, Same HCS Layer

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Algorithm


N.B:

− If parameter TAOL is set to its maximum value = 61 bit periods and DTCB is set to its minimum value = - 63 dB then the OL/UL subcell change will only be controlled by the path loss using LOL coz:

OLUL: Time Advance & Distance to cell border conditions will never be met and so the path loss only using LOL will control the evaluation.

ULOL: Time Advance & Distance to cell border conditions will always be met and so the path loss only LOL will control the evaluation.

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• Concentric Cells (Overlaid Underlaid Subcells) Algorithm

(II) OL/UL Subcell Change with Subcell Load Distribution Activated

− A subcell load distribution is used to control the traffic between the OL/UL subcells, so if the initially preferred cell got congested we will try to allocate resources in the other subcell. (Activated by setting cell parameter SCLD = ON)

− SCLDSC: Is a cell parameter used to define the preferred cell in allocation whether UL or OL i.e. the subcell which will carry traffic first.

− N.B: if the OL subcell is the preferred one, i.e. if SCLDSC=OL, then the below conditions should be met otherwise a TCH on the UL subcell will be allocated.

L < LOL – LOLHYST and ta < TAOL – TAOLHYST and

SSServing - SSNeighbor ≥ DTCB + DTCBHYST

is



equation:SSServing - SSNeighbor < DTCB + DTCBHYST + NDIST

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− A subcell change may occur due to load based on the settings of the parameters SCLDLUL an SCLDLOL

− Example: If serving cell is the OL subcell and the following occur

Percentage of idle TCHs in the OL subcell < SCLDLOL and

Percentage of idle TCHs in the UL subcell > SCLDLUL

then subcell change from OLUL due to SCLD will occur.




− A subcell change may occur due to load based on the settings of the parameters SCLDLUL an SCLDLOL

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− If some traffic will be moved from the OL UL subcell due to load distribution, then the MSs with the high path loss will be chosen first i.e. MSs that are near to cell border.

− If some traffic will be moved from the UL OL subcell due to load distribution, then the MSs with the low path loss will be chosen first i.e. MSs that are near to the site.

− Apart from the subcell change due to SCLD, as we mentioned before the MS can also request to move from OL UL because of path loss, TA or distance to cell border criterion and in this case the load is not checked coz the thresholds : SCLDLUL&SCLDLOL are only controlling the load incase of subcell change due to load distribution.

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• Concentric Cells (Overlaid Underlaid Subcells) Parameters Summary

Overlaid/Underlaid Control Parameters


SCTYPE UL,OL − − −

LOL 0 to 200 − − dB

LOLHYST 0 to 63 3 3 dB

TAOL 0 to 61 − − Bit Periods (3.69 µsec)

TAOLHYST 0 to 61 − − Bit Periods (3.69 µsec)

DTCBSC 0,1 0 − −

DTCB −63 to 63 -63 − dB

DTCBHYST 0 to 63 2 2 dB

NDIST 0 to 63 10 − dB

NNCELLS 1 to 5 3 1 −

SCLD ON,OFF OFF − −

SCLDLOL 0 to 99 20 − %

SCLDLUL 0 to 99 20 − %

SCLDSC UL,OL UL OL −

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Multi Band Cells (MBC)


• Multi Band Cells (MBC)

− A multi band network consists of cells from different frequency bands for example: 900/1800 MHz

− By combining these frequencies in the same cell with 1 common BCCH, the radio performance and traffic capacity are improved where the no. of cells and neighbor relations are significantly reduced.

− Using 1 BCCH instead of two will increase the no. of time slots that will be used for traffic.

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− Using MBC concept with only 1 BCCH, this will reduce the no. of defined neighbors to 50% leading to better accuracy for the measurement reports coz there will be more time available for measurements for each neighbor.

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− The Dynamic OL/UL subcells (Concentric cells) is a prerequisite feature for the Multi Band Cells.

− Mostly the frequency band with “Better coverage” (i.e. lower frequency band) is configured as the Underlaid subcell while the other frequency band with “Worse coverage” (i.e. higher frequency band) is configured as the Overlaid Subcell.

− Ex: 900MHz frequency band UL, while 1800MHz frequency band OL

− It is recommended to select the BCCH frequency to lie in the “Better Coverage” i.e. UL subcell.

− for the previous example then BCCH frequency will belong to the 900MHz band

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− A parameter CSYSTYPE defines the band of the used BCCH frequency in a multi band cell.

− A parameter BAND defines the band of the Channel Group, where the channel group consists of no. of frequencies as will be seen later.

− As mentioned before, the path loss/Distance to cell border/time advance criteria will define the coverage limit of the frequency band used in the OL subcell vs. UL subcell, (In this case the OL&UL will belong to two different bands)

− Also the traffic load can be maintained between the two subcells (that belong to two different bands) using the subcell load distribution feature where the SCLDSC parameter will define which subcell is preferred first.

is



− The propagation of the radio waves depend on the used frequency band, i.e. the reported signal strength from one MS will differ depending on the frequency band used.

is

M

S

M

S

MS is in the same

location but the reported

SS differs depend on the

used frequency band

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− So to locate the MS correctly regardless of the band it is using we have 2 possible ways:

1. Applying a frequency Band Offset:

If OL subcell is on 1800MHz band and the UL is on the 900MHz band so when the MS is located on the OL subcell and report a certain SS then it should be compensated for the UL subcell.

2. Includes the BCCH carrier frequency in the Active BCCH Allocation (BA) list:The Active BA list is the list which the serving cell uses to inform the MS the neighbors which he has to monitor and make measurements on while it is in dedicated mode and in this way no compensation is needed.

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Applying a frequency Band Offset:

− FBOFFS (Frequency Band Offset): is the parameter that determines the difference between the path loss between bands (BCCH Frequency Band Group and the Non-BCCH Frequency Band Group), it is measured in dBs and take values between -40 40 dBs

− If the MS is served by 1800 band frequency and reporting SS 1800 band = -85 dbm and FBOFFS=7dB then the compensated SS if the MS was served by the 900 band frequency will be SS 900 band = -85 dbm + 7 = -78 dBm

− FBOFFS has to be adjusted in a correct way coz: a. It will be used to locate the MS correctly with respect to neighbors

b. It will be used to locate the MS correctly in the Subcell change Evaluation

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Applying a frequency Band Offset: a. FBOFFS will be used to locate the MS correctly with respect to neighbors

Ex: MS is on the OL subcell (1800 band) and reporting SS_Serving_cellA1800 band = -85 dBm FBOFFS =7dB, and after applying the offset and Hysteresis SS_neighbor_cellB900 band = -83dBm

is

Without applying FBOFFS

SS_Serving_cellA 1800 band

<SS_neighbor_cellB900 band

HO from Cell A Cell B will occur

Wrong Decision

With applying FBOFFS

SS_Serving_cellA 900band = SS_Serving_cellA1800

band+ 7 dB

SS_Serving_cellA 900band = -78 dBm

SS_Serving_cellA 900 band > SS_neighbor_cellB900 band

Cell A will remain the serving cell but subcell

change may occur if needed.

Right Decision




b) FBOFFS will be used to locate the MS correctly during the Subcell change Evaluation

When the MS is served by the OL 1800 band subcell (non-BCCH Band), the path loss in this case will be checked vs. LOL – LOLHYST + FBOFFSET

Ex: Assume a MS is served by the OL 1800 subcell and reporting SS1800 band = -90 dBm, BSTXPWR=46dBm, FBOFFSET=7dB, LOL=131dB, LOLHYST=zero

is

-85

dBm

-92

dBm

Subcell change OLUL

-90

dBm

-83

dBm

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b) FBOFFS will be used to locate the MS correctly during the Subcell change Evaluation

c) Ex: Assume a MS is served by the OL 1800 subcell and reporting SS1800 band = -90 dBm, BSTXPWR=46dBm, FBOFFSET=7dB, LOL=131dB, LOLHYST=zero

• Without applying FBOFFS

Path loss= BSTXPWR - SS1800 band = 46-(-90)=136 dB Path loss=136 dB > LOL – LOLHYST=131 dB

Sub cell change from OL UL will occur

Wrong Decision Right Decision

is

With applying FBOFFS

Path loss= BSTXPWR - SS1800 band = 46 ( 90)=136dB

Path loss=136 < LOL LOLHYST+

FBOFFSET=138dB

− The MS will stay on the OL sub cell



Parameters Summary:

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Multi Band Cells Control Parameters

Parameter Name

Value Range Default Value Recommended

Value Unit

BAND GSM800, GSM900, GSM1800,

GSM1900 − − −

CSYSTYPE GSM800, GSM900, GSM1800,

GSM1900 − − −

FBOFFS −40 to 40 0 − dB

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Cell Load Sharing (CLS)

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• Cell Load Sharing

– The purpose of the Cell Load Sharing feature is to distribute some of a cells traffic load to surrounding cells during peaks in traffic.

− This is achieved by moving established connections to neighboring cells that have idle resources.

− Cell Load Sharing increases the number of handovers in the part of the network where the traffic load is unevenly distributed.



– Cell Load Sharing is activated on the BSC level via parameter LSSTATE (Active/Inactive) and activated on cell level via parameter CLSSTATE (Active/Inactive)

– The traffic load (amount of idle full rate TCHs) on each cell is examined by the BSC every CLS time Interval defined by a parameter CLSTIMEINTERVAL (default=100msec)

− If the percentage of idle full rate traffic channels is ≤ parameter CLSLEVEL, then this cell will try to get rid of some traffic by initiating cell load sharing handovers to neighbors.

− For a neighbor cell to accept HOs due to cell load sharing then parameter HOCLSACC should be set to “ON”

− The traffic load on the neighbor cells should also be examined so handovers due to cell load sharing will only be done to neighbors having enough idle full rate TCHs ( percentage of idle full rate TCHs > CLSACC inorder to accept HO due to CLS)

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– CLS evaluation is performed after normal locating evaluation for neighboring cells.

– The normal Basic ranking evaluation was done as follows:

Rankservingcell = SS_DLservingcell

Rankneighbor= SS_DLneighbor – OFFSETneighbor – HYSTneighbor

− Now when the % idle full rate TCHs < CLSLEVEL, then the HYST for neighbors will be recalculated with reduced values based on parameter RHYST

− Rankneighbor= SS_DLneighbor – OFFSETneighbor – HYSTnew neighbor

Where HYSTnew neighbor = HYSTneighbor [1-2 (RHYST/100)]


• Cell Load Sharing − Rankneighbor= SS_DLneighbor – OFFSETneighbor – HYSTnew neighbor

Where HYSTnew neighbor = HYSTneighbor [1-2 (RHYST/100)]

RHYST Hysteresis Reduction

0 No reduction of the Hysteresis

area

50 Cell Border is reduced to the

nominal cell border

100 All the Hysteresis area is

removed

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• Cell Load Sharing − For a neighbor cell to be candidate for HO due to CLS, then it should satisfy the

following:

− Lies in the same BSC as the source cell.

− Has the same HCS layer.

− Can Accept HO due to CLS i.e. HOCLSACC= ON

− % Idle full rate TCHs > CLSACC

− The settings for CLSLEVEL and CLSACC should be adjusted such that

CLSACC > CLSLEVEL in order to not having unstable situation.

100% idle TCHs

CLSACC=5

0%

CLSLEVEL=30

%

Accept Incoming HOs due

to CLS

Make Outgoing HOs due to

CLS


• Cell Load Sharing Parameters Summary

Parameter Default Value Recommended Value Value Range Unit

CLSLEVEL 20 − 0 to 99 %

CLSACC 40 − 1 to 100 %

HOCLSACC OFF ON ON/OFF

RHYST 75 100 0 to 100 %

CLSTIMERINTERVAL 100 100 100 to 1000 ms

LSSTATE Inactive Active Active/Inactive

CLSSTATE Inactive Active Active/Inactive

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Thank You


Intra Cell Handover (IHO)

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• Intra Cell Handover

− Intra Cell means within the same cell.

− Intra Cell Handover aims at maintaining good quality of a current connection by performing handover to a new channel within the same cell when bad quality is detected.

− When a connection suffers from bad quality and at the same time the Signal Strength is still high, there is a reason to believe that the bad quality is due to interference.

Channel suffering

from bad quality

New channel

f1

f2

TS

1

TS

2

TS

3

TS

4

TS

5

TS

6

TS

7

TS

8

TS

1

TS

2

TS

3

TS

4

TS

5

TS

6

TS

7

TS

8

Same

Cell



− Changing the serving channel on a certain cell to another channel within the same cell may be useful due to the fact that most likely the interference on different channels is not the same, and the reason for this could be:

The cell that interferes a certain connection (channel/call) may be not fully loaded and not transmitting on all its channels.

If power control is in use in the interferer cell, then power used on each channel will differ based on the MS location from the BTS.

For uplink interference, the MSs connected to the interferer cell will be located in different places from the cell causing different levels of interference.

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− After Intra cell handover is performed, the quality of a connection will be enhanced if the radio conditions on the new channel is better than the old channel, and this may be expected when intra cell handover is performed at high signal strength while the quality (rxqual) is bad.

− Intra Cell Handover can be triggered due to bad quality either in the downlink or in the uplink.

− But at which conditions Intra Cell Handover will be triggered ?



− At which conditions Intra Cell Handover will be triggered ?

Intra cell handover is triggered/initiated when signal strength is high and at the same time the quality is bad based on the following equation:

rxqual_DL > QOFFSETDL + FQSS (RXLEV_DL + SSOFFSETDL)

Or

rxqual_UL > QOFFSETUL + FQSS (RXLEV_UL + SSOFFSETUL)

− FQSS is a quality vs. signal strength function that specify at each signal level the quality beyond which an intra cell handover should be triggered.

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• Intra Cell Handover Conditions at which Intra Cell Handover is initiated:

rxqual_DL > QOFFSETDL + FQSS (RXLEV_DL + SSOFFSETDL) Or

rxqual_UL > QOFFSETUL + FQSS (RXLEV_UL + SSOFFSETUL)

− RXLEV_DL and RXLEV_UL both are

measured in rxlev units 0 63, which

corresponds to -110 dBm - 47 dBm

− Example: If RXLEV_DL = 57 and

QOFFSETDL=SSOFFSETDL= zero, then

when rxqual_DL > 52 dtqu an intra cell

handover will be initiated.

The FQSS Table. The rxqual Values Is Given in dtqu

(deci Transformed Quality Units)

RXLEV Rxqual

<=30 infinity

31 60

32 - 35 59

36 - 38 58

39 - 41 57

42 - 45 56

46 - 48 55

49 - 52 54

53 - 55 53

56 - 58 52

59 - 62 51

>=63 50



− SSOFFSETDL & SSOFFSETUL are signal strength offset parameters, increasing them will make the measured signal strength to appear better than the actual situation causing the intra cell handover to be triggered more often.

− QOFFSETDL & QOFFSETUL are quality offset parameters, decreasing them will trigger the intra cell handover more often.

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Selection of a new channel at IHO

− The primary target is to find a new channel that differs as much as possible from the currently used channel.

− The selection of a new channel will depend on whether frequency hopping is used or not.



Selection of a new channel at IHO

(A) With frequency hopping not used

− Among the idle channels, select a channel that lies on a different frequency than the current channel is using.

− If no idle channels were found then select one of the idle timeslots that are on the same frequency as the current channel.

Interfered

Channel

1st choice at IHO

(Change

frequency) 2nd choice at IHO

(Change Time Slot

on the same

frequency)

f1

f2

f3

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• Intra Cell Handover Selection of a new channel at IHO

(B) With frequency hopping in use

− Select one of the idle channels that belongs to a different CHGR than the current channel.

− If no idle channels were found or only 1 CHGR is defined then select one of the idle timeslots that are on the same CHGR as the current channel.

− If no idle channels were found select idle channels on the same CHGR and time slot as the current channel.

1st choice at IHO(Change

CHGR)

2nd choice at IHO (Change

Time Slot within the same

CHGR )

Interfered Channel

f2

f3

f4

f1

CHGR1

CHGR0

3rd choice at IHO

(Same CHGR, same TS but

different channel)



− If quality is not improved after making number of consecutive IHOs, this means that all channels are suffering from poor quality and may be a part of the cell is subjected to high interference.

− We can limit the number of consecutive IHOs for certain connection to certain number using parameter MAXIHO ex: If MAXIHO=3, then the maximum number of allowed consecutive IHOs=3 and if the MS tried to make the 4th IHO it will be disabled and a timer TIHO will start to inhibit any further attempts to make IHO until this timer is released.

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− Intra cell handover and bad quality urgency are both triggered at poor quality situations.

− Intra cell handover has higher priority over bad quality urgency handover, i.e. if the criteria for both are fulfilled then IHO will be triggered/initiated first.

− If the dynamic OL/UL subcell feature is in use and if the number of consecutive IHOs reached its maximum based on the settings of the parameter MAXIHO, then a subcell change from OLUL or ULOL will be attempted.


• Intra Cell Handover Parameters Summary

Intra Cell Handover Control Parameters


IHO ON,OFF OFF ON −

SSOFFSETDL −30 to 30 0 0 dB

SSOFFSETUL −30 to 30 0 −10 dB

QOFFSETDL −50 to 50 0 − dtqu

QOFFSETUL −50 to 50 0 − dtqu

MAXIHO 0 to 15 3 3 −

TIHO 10 to 60 10 10 Seconds

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Thank You


Dynamic HR Allocation

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• Dynamic HR Allocation

− In high load situations it is important that the allocation of a traffic channel is done efficiently for a new connection.

− This will result in high utilization of the channels while keeping good speech quality for the existing connections.



− For a new connection the Dynamic HR Allocation Algorithm evaluates the traffic load in the cell and based on this decides the connection mode: FR, HR or AMR HR

− To Activate the feature, set the parameter: DHA to “ON”

− The feature differentiates between AMR and NAMR MSs and can be controlled on cell level.

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New Connection

Dual Rate MS ? (Supports HR?)

Support AMR HR?

No. of Idle TCHs Total no. of TCHs

< DTHNAMR No. of Idle TCHs Total no. of TCHs

< DTHAMR

AMR HR Allocation HR Allocation

FR Allocation

Yes

Yes

Yes Yes

No

No

No % %



− DTHAMR: The threshold below which the Dynamic HR Allocation starts for AMR supported MSs

− DTHNAMR: The threshold below which the Dynamic HR Allocation starts for Non AMR supported MSs

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• Dynamic HR Allocation Parameters Summary

Intra Cell Handover Control Parameters


DHA ON,OFF OFF ON −

DTHAMR 0 to 100 30 30 %

DTHNAMR 0 to 100 15 15 %


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Frequency Hopping


• Frequency Hopping

− During a call connection, a time slot (burst) can easily be lost when the mobile station happens to be located in a fading dip for that particular frequency or if it is subjected to interference.

− If the next time slot is sent on another frequency, there is high probability that this time slot will be received correctly and this can be done via frequency hopping.

− With frequency hopping:

Tighter frequency reuse can be implemented and so higher capacity can be maintained.

More robust environment can be obtained.

There will be a possibility to give subscribers more uniform speech quality.

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− In frequency hopping, a set of predefined frequencies is used in each cell and the MS will be allowed to transmit on different frequency every TDMA frame (4.61 msec) i.e. The MS will change its frequency 217 times per second

− With frequency hopping we can get:

i. Frequency Diversity

ii. Interference Diversity


• Frequency Hopping i. Frequency Diversity

− Frequency hopping can solve the multipath fading (fast fading) problem.

− The multipath fading results from reflections from the surrounding buildings resulted in low signal strength fading dips.

− The multipath fading is frequency and location dependent.

− With frequency hopping, slow and non-moving MS won’t still in a low signal strength fading dip more than 1 TDMA frame.

F1

F2

Average

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• Frequency Hopping ii. Interference Diversity

− Frequency hopping can also offer better quality when the currently used frequency is interfered.

− Interference depends on the time, frequency and the MS location.

− With frequency hopping, certain MS will experience interference only for 1 time during number of hops i.e. if a MS will hop on 4 frequencies one of them is interfered, then the MS will be subjected to interference 1 time every 4 hops.

− Using frequency hopping will result in spreading the interference on many MSs which will lead to a radio environment that is more even (symmetric).

− The interference diversity can be expressed as a gain in the C/I ratio.


• Frequency Hopping Channel Group Concept (CHGR)

− Each number of frequencies (Transmitters) in the cell are grouped in what we called channel group (CHGR), some parameters are defined per the CHGR and not per cell, for example: within the same cell frequency hopping can be enabled on certain CHGRs and disabled on others.

− HOP: Is a parameter that is used to enable or disable frequency hopping on certain CHGR, it has two values either ON/OFF

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− Frequency hopping is applied on Traffic channels (TCHs), on SDCCHs and packet data channels but it is not applied on Broadcast and Common control channels which are mapped on TS#0 on F0

− Methods of Hopping: we have two methods of hopping

A. Base Band Hopping (BB Hopping)

B. Synthesized frequency Hopping (SY Hopping)

FHOP: Is a parameter to specify the method of hopping, it takes values: BB/SY


• Frequency Hopping A. Base Band Hopping (BB Hopping)

− Each Transmitter is assigned certain frequency and connected to many MSs, each Time slot out of the transmitter will belong to different MS but at the same frequency.

− From MS prospective, each MS will transmit each TS on different frequency.

Transmitter

F1

Transmitter

F2

Transmitter F3

Transmitter

F4

TRX

1

TRX

2

TRX

3

TRX

4

TS

1

TS

2

TS

3 MS

1

TS

1

TS

2

TS

3 MS

2

MS1-TS1-

F1

MS2-TS1-

F2

MS1-TS2-

F2

MS3-TS1-

F3

MS2-TS2-

F3

MS1-TS3-

F3

TS

1

TS

2

TS

3 MS

3

Bus for routing the time slots

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• Frequency Hopping B. Synthesizer Frequency Hopping (SY Frequency Hopping)

− With Synthesized frequency hopping, the MS will receive all its time slots via only 1 transmitter and the transmitter will change its frequency consequently every TDMA frame based on certain sequence.

Trans

F1…….Fn

Trans

F1…….Fn

Trans F1……..Fn

Trans

F1………Fn

TRX1

TRX2

TRX3

TRX4

TS

1

TS

2

TS

3 MS

1

TS

1

TS

2

TS

3 MS

2 MS3-TS1-

F3

MS2-TS2-

F4

MS1-TS3-

F5

TS

1

TS

2

TS

3 MS

3

MS1-TS1-

F1

MS1-TS3-

F3 MS1-TS2-

F2

MS2-TS1-

F2

MS2-TS3-

F4 MS2-TS2-

F3



− The Advantage of Synthesized frequency hopping is that the number of hopping frequencies can be larger than the number of the already existing transmitters causing the hopping gain to increase without a need to use more hardware.

Modes of Hopping

i. Cyclic Frequency Hopping

ii. Random Frequency Hopping

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• Frequency Hopping Modes of Hopping

i. Cyclic Frequency Hopping

− With this type of hopping, frequencies are changed every TDMA frame in a consecutive order starting with the frequency of the lowest Absolute Radio Frequency Channel Number (ARFCN).

− For P-GSM (UL 890-915 MHz, DL 935-960MHz), ARFCNs: 1,2,3,4,…… 124

− For example for four frequencies the cyclic hopping between them will appear as follow: f1, f2, f3, f4, f1, f2, f3, f4, f1, f2, f3, f4, f1, ………

− HSN (Hopping Sequence Number) : Is a parameter defined per CHGR (number of frequencies) that will be used to specify the mode of hopping, it take values from 0 63

− When HSN = 0, this means that Cyclic frequency hopping will be used.


• Frequency Hopping Modes of Hopping

ii. Random Frequency Hopping

− With this type of hopping, frequencies are changed every TDMA frame randomly based on a pseudo-random sequence. The sequence is stored in a look-up table in the MS as well as the BTS and up to 63 independent sequences can be defined.

− Based on the settings of the parameter HSN (163), one of the 63 independent random sequences will be used.

− A random hopping sequence for four frequencies may appear as follow:

……, f1, f4, f4, f3, f1, f2, f4, f1, f3, f3, f2,……….

− The period of the Random sequence=6 minutes, i.e. the random sequence repeats itself once every 6 minutes.

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• Frequency Hopping Synthesizer Frequency Hopping (SY Frequency Hopping)

MAIO Concept

− As we mentioned before that HSN is defined per CHGR, so if a CHGR contains 4 Transmitters and HSN=0, then this means that cyclic hopping will be used over these 4 transmitters.

− But in order for the transmitters within the same CHGR to not interfere each other they must start their hopping with different frequencies.

− And in order to do so a MAIO

(Mobile Allocation Index Offset) will be

assigned for each transmitter so each

of them will start the hopping sequence

either cyclic/random from a different

starting point, based the MAIO assigned

to it.

Transmitter#1

(f0,f1,f2,….fn)

Transmitter#1

(f0,f1,f2,….fn)

Transmitter#1

(f0,f1,f2,….fn)

Transmitter#1

(f0,f1,f2,….fn)

Same CHGR, HSN=0 f0,f1,f2,f3,f4,f5

,f0,….

f1,f2,f3,f4,f5,f0

,f1….

f2,f3,f4,f5,f0,f1

,f2….

f3,f4,f5,f0,f1,f2

,f3….


• Frequency Hopping B. Synthesizer Frequency Hopping (SY Frequency Hopping)

MAIO Concept

− We have different MAIOs, i.e. there are different ways through which each transmitter will start the cyclic/random hopping.

− Using the default MAIO, the even MAIO values in increasing order are picked first then the odd values, example: for a CHGR of 4 Transmitters, the default MAIO list is 0,2,4,1

Transmitter#1

(f0,f1,f2,….fn)

Transmitter#1

(f0,f1,f2,….fn)

Transmitter#1

(f0,f1,f2,….fn)

Transmitter#1

(f0,f1,f2,….fn)

Same

CHGR,

HSN=0

f0,f1,f2,f3,f4,f5,f0,

….

f2,f3,f4,f5,f0,f1,f2

….

f4,f5,f0,f1,f2,f3,f4

….

f1,f2,f3,f4,f5,f0,f1

….

N.B: Number of used

frequencies can

exceed the no. of

Transmitters.

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• Frequency Hopping Parameters Summary

Frequency Hopping Control Parameters


HOP ON,OFF OFF ON −

FHOP BB,SY − − −

HSN 0 to 63 − − −

MAIO 0 to 31 or Default Default − −


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Dynamic Power Control


• Dynamic Power Control

− In this chapter we’ll talk on both BTS and MS Dynamic Power Control.

− The aim with Power Control is to increase the number of connections while maintaining good C/I (Carrier to Interference Ratio)

− Why Power Control is important ?

i. Decreases the total interference in the system ( Interference ) − So when Traffic increases (no. of MSs) then good C/I can be maintained.

− When Traffic is normal, C/I is improved.

− When Interference is low, MSs with poor quality will be able to successfully complete their calls.

ii. Decreases the consumption of the MS battery and the BTS

backup batteries when the main supply is down.

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I- Dynamic BTS Power Control


• Dynamic BTS Power Control − The Algorithms for both BTS and MS dynamic power control are the same.

− The below graph shows the relation between BTS o/p power and the measured (received) signal strength at the MS vs. the path loss between BTS and MS

1 2

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• Dynamic BTS Power Control

− For the area before point 1, the received power at the MS in the DL is very good

and sufficient, however the BTS can’t make any sort of down regulation and sends with power less than its minimum power.

− As the MS is moving away from the BTS, the received power is decreasing, so after crossing point 1, the BTS will start up regulating its power in steps to compensate for the path loss.

− At point 2, the BTS can’t up regulate its power for a value above the max. allowed power level even if the received power in the MS is deteriorated or the path loss increased.



− For Quality measurements the below graph shows the up regulations in the BTS o/p power when quality is deteriorated (SS is not into consideration here)

− As the Quality got worse ( 0 7), the BTS will try to increase its power to compensate for the quality drop.

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Algorithm: The Dynamic BTS Power Control algorithm is done on 3 stages

1. Preparation of the Input Data.

2. Filtering of measurements.

3. Calculation of Power Order.


• Dynamic BTS Power Control Algorithm: 1) Preparation of the Input Data

− Dynamic Power Control is made on TCHs time slots as well as on the SDCCH time slots(on TCH carriers), while the BCCH frequency with all its time slots is sent with max. power with no power control.

− Type of measurements

− Both SS_DL and Quality_DL measurements will be used in the equation through which the next power order is calculated.

Measurement Source

SS_DL MS

Quality_DL MS

power level used by the BTS_DL BTS

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− REGINTDL: A parameter that defines the minimum time period between two consecutive power orders in the DL. Measured in SACCH periods (0.48 Seconds) from 1 to 10 SACCH periods i.e. Regulating Interval in DL. (It is a BSC parameter)

− The BTS is able to changes its output power , the resolution in o/p power is in the form of steps of 2 dBs and maximum change is 30 dBs.

(ex: 2dBs, 4dBs,………. , max to 30 dBs)

− When power control is in use the BTS output power level will be given as:

Down Regulation: BTS o/p powernew (dBm) = BTS o/p powerold – 2*PLused , PLused = 0 to 15

PLused is the power regulation step



− SSDESDL: A parameter that defines the desired Signal Strength in DL which we aim to maintain using power control. Measured in dBm

− The SS measured will be checked against SSDESDL to know if Down regulation in the BTS power or up regulation is needed

− QDESDL: A parameter that defines the desired Quality in DL which we aim to maintain using power control. Measured in dtqu ( 0 to 70)

− The Quality measured will be checked against QDESDL to know if Down regulation in the BTS power or up regulation is needed.

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− The equation used to calculate the power order in the next SACCH period contains information on SSDESDL−SS_DLmeasured and QDESDL−Quality_DLmeasured.

− SSDESDL− SS_DLmeasured is measured in dBm, while QDESDL− Quality_DLmeasured is measured in dtqu so to be used in the same equation some sort of mapping should be done,

i.e. QDESDL−Quality_DLmeasured should be represented in the form of dBs as well

QDESDL (dtqu) 0 10 20 30 40 50 60 70

Quality_DLmeasured 0 1 2 3 4 5 6 7

dB transformation C/I calculation (dB)

23 19 17 15 13 11 8 4



SS Compensation

− We aim to get the SS of the pure TCH time slot compensated for both frequency hopping when BCCH frequency is included and compensated for power control.

i. Compensating for frequency hopping:

When the MS is using a TS on BCCH carrier

SS_DLTCH = SS_DLMeasured – [ BSPWR – (BSTXPWR - 2*PLused) ]

SS_DLTCH = SS_DLMeasured – ( BSPWR – BSTXPWR + 2*PLused )

When the MS is using a TS on TCH frequency

SS_DLTCH = SS_DLMeasured

By Averaging the results then:

SS_DLTCH = SS_DLMeasured – ( BSPWR – BSTXPWR + 2*PLused )/ Nf ,

Nf = no. of hopping frequencies

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SS Compensation

ii. Compensating for power control:

SS_DLCompensated = SS_DLTCH + 2*PLused

Now in further calculations SS_DLCompensated will be used, where SSCompensated is the signal

strength compensated for both frequency hopping and power regulations.

Quality Compensation

− Quality_DLCompensated is calculated in the same way such that:

Quality_DLCompensated = Quality_DLmeasured (in dBs) + 2*PLused

Where the Quality_DLmeasured (in dBs) is the Quality_DLmeasured (07) after transforming it into dBs







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• Dynamic BTS Power Control Algorithm: 2) Filtering of measurements

− Filtering for both SS and Quality is done with exponential non-linear filters in order to eliminate variations of temporary nature.

(A) Filtering of SS Measurements

− SS_DLFiltered (k) = b* SS_DLCompensated (k) + a* SS_DLFiltered (K-1), k is the SACCH period

− a & b (b=1-a) are the non-linear filter’s coefficients and “a” will define the length of the filter “L”, where each filter length “L” corresponds to certain value of “a”

− But how the length of the non-linear filter is calculated?




− SS_DLFiltered (k) = b* SS_DLCompensated (k) + a* SS_DLFiltered(K-1), k is the SACCH period

If SS_DLCompensated (k) <

SS_DLFiltered(K-1)

then L = SSLENDL where,

SSLENDL = 3 15 SACCH

periods

In this case “up regulation is

needed” and it should be done

very fast in order to not lose the

connection.

If SS_DLCompensated (k) >

SS_DLFiltered(K-1)

then L = SSLENDL

*UPDWNRATIO/100 where,

SSLENDL = 3 15 SACCH periods

UPDWNRATIO = 100 700

In this case “Down regulation is

needed” and it should be done in a

smooth way, coz decreasing the

power suddenly may harm the

connection.

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(B) Filtering of Quality Measurements

− Quality_DLFiltered (k) = b* Quality_DLCompensated (k) + a* Quality_DLFiltered(K-1),

k is the SACCH period

If Quality_DLCompensated (k) <

Quality_DLFiltered(K-1)

then L = QLENDL where,

QSLENDL = 1 20 SACCH periods

In this case “up regulation is needed”

and it should be done very fast in order

to not lose the connection.

If Quality_DLCompensated (k)

>Quality_DLFiltered(K-1)

then L = QSLENDL


QSLENDL = 1 20 SACCH periods


In this case “Down regulation is needed”

and it should be done in a smooth way,

coz decreasing the power suddenly may

harm the connection.



− SS_DLFiltered(K-1) is set initially = SSDESDL, that will lead to start power regulations immediately after the first valid measurement report.

− Also Quality_DLFiltered(K-1) is set initially = QDESDL, that will lead to start power regulations immediately after the first valid measurement report.

− SSDESDL: has value range from -110 to -47 dbm and default value is -90 dbm

− QDESDL: has value range from 0 to 70 dtqu and default value is 30 dtqu

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• Dynamic BTS Power Control Algorithm:

Till now we finalized two stages from the algorithm:



SS_DLmeasured SS_DLCompens

ated SS_DLFiltered Compensation Filtering

Q_DLmeasured

(Quality Units)

Q_DLCompensated Q_DLFiltered

Compensation

Filtering

Quality units to

dB

transformation

Q_DLmeasured(

dB)







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• Dynamic BTS Power Control Algorithm: 3) Calculation of Power Order (PU)

− This will be done on three stages:

(A) Calculating the two basic Power Orders

(B) Applying the Power Orders constraints

(C) Conversion of output data.




pui = αi * (SSDESDL - SS_DLFiltered) + βi * (QDESDL - Q_DLFiltered)

i = 1,2 and α1 & β1 are parameters to compensate for the path loss and quality.

α1 = LCOMPDL/100, β1 = QCOMPDL/100, α2 = 0.3, β2 = 0.4

pu1 is calculated according to settings of α1 & β1 ( The operator will set the proper values from his point of view for LCOMPDL & QCOMPDL),

Default values: LCOMPDL=5 and COPMDL=55

pu2 is calculated according to recommended settings of α2 & β2 based on trials and field measurements.

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pui = αi * (SSDESDL - SS_DLFiltered) + βi * (QDESDL - Q_DLFiltered)


pu1 and pu2 both of them aim to maintain the SS within the desired value defined according to SSDESDL and to maintain the Quality within the desired value defined according to QDESDL but each will calculate the path loss in different way.

pu_used = max (pu1,pu2), max of pu1 and pu2 will be used as the desired power order in the next measurement report coz the max of both of them will mean lower down regulation/higher up regulation.


• Dynamic BTS Power Control Algorithm: 3) Calculation of Power Order (pu)

(B) Applying Power Order constraints

− The highest allowed power order pu_used = zero, which means keeping the output power at maximum value with no power control.

− The lowest allowed power order is given by the minimum of the following:

pu_used= minimum (30 dB, BSPWRT- minimum BTS o/p power)

i.e. it is not allowed to decrease the o/p power or increase it by a value > 30 dB

(C) Conversion of output data

− pu_used will be interpreted into final form PL_used which takes from015

− PL_used =Integer(-pu_used/2)

− ex: if PL_used = 3 and Down regulation for power is required, then in the next measurement report the BSC will inform the BTS to decrease its current power by 2* PL_used = 6 dBs

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• Dynamic BTS Power Control Parameters Summary

Dynamic BTS Power Control Parameters

Parameter Name Value Range Default Value Recommended

Value Unit

SSDESDL −110 to −47 −90 −90 dBm

QDESDL 0 to 76 30 30 dtqu

SSLENDL 3 to 15 3 3 SACCH period (0.48 Seconds)

QLENDL 1 to 20 8 3 SACCH period (0.48 Seconds)

LCOMPDL 0 to 100 5 5 −

QCOMPDL 0 to 100 55 55 −

UPDWNRATIO 100 to 700 200 300 −

REGINTDL 1 to 10 1 1 SACCH period (0.48 Seconds)


II- Dynamic MS Power Control

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• Dynamic MS Power Control − The Objective of the MS power control algorithm is to adjust the output power of

the MS so that a desired signal strength is received in the BTS

− The below graph shows the relation between MS o/p power and the measured (received) signal strength at the BTS vs. the path loss between BTS and MS

1 2


• Dynamic MS Power Control

− For the area before point 1, the received power at the BTS in the UL is very good

and sufficient, however the MS can’t make any sort of down regulation and sends with power less than its minimum power.

− As the MS is moving away from the BTS, the received power is decreasing, so after crossing point 1, the MS will start up regulating its power in steps to compensate for the path loss.

− At point 2, the MS can’t up regulate its power for a value above the max. allowed power level even if the received power in the MS is deteriorated or the path loss increased.

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− For Quality measurements the below graph shows the up regulations in the MS o/p power when quality is deteriorated (SS is not taken into consideration here)

− As the Quality got worse ( 0 7), the MS will try to increase its power to compensate for the quality drop.



Algorithm: The Dynamic MS Power Control algorithm is done on 3 stages




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• Dynamic MS Power Control Algorithm: 1) Preparation of the Input Data

− Dynamic Power Control is made on TCHs time slots as well as on the SDCCH time slots.

− Type of measurements

− Both SS_UL and Quality_UL measurements will be used in the equation through which the next power order is calculated.

Measurement Source

SS_UL BTS

Quality_UL BTS

power level used by the MS_UL MS



− REGINTUL: A parameter that defines the minimum time period between two consecutive power orders. Measured in SACCH periods (0.48 Seconds) from 1 to 30 SACCH periods.

− The BTS is able to changes its output power in the form of steps of 2 dBs

(ex: 2dBs, 4dBs,………. , max to 16 dBs)

− When power control is in use the MS output power level will be given as:

MS o/p powernew (dBm) = MS o/p powerold – 2*PLused where PLused = 0 to 8

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− SSDESUL: A parameter that defines the desired Signal Strength in UL which we aim to maintain using power control in the UL. Measured in dBm

− The SS measured will be checked against SSDESUL to know if Down regulation in the MS power or up regulation is needed

− QDESUL: A parameter that defines the desired Quality in UL which we aim to maintain using power control in the UL. Measured in dtqu ( 0 to 70)

− The Quality measured will be checked against QDESUL to know if Down regulation in the MS power or up regulation is needed.



− The equation used to calculate the power order in the next SACCH period contains information on SSDESUL−SS_ULmeasured and QDESUL−Quality_ULmeasured.

− SSDESUL− SS_ULmeasured is measured in dBm, while QDESUL− Quality_ULmeasured is measured in dtqu so to be used in the same equation some sort of mapping should be done,

i.e. QDESUL−Quality_ULmeasured should be represented in the form of dBs as well

QDESUL (dtqu) 0 10 20 30 40 50 60 70

Quality_ULmeasured 0 1 2 3 4 5 6 7

dB transformation (dB)

23 19 17 15 13 11 8 4

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SS Compensation

− Compensating for power control:

SS_ULCompensated = SS_ULmeasured + 2*PLused

Now in further calculations SS_ULCompensated will be used, where SSCompensated is the signal

strength compensated for power regulations.

Quality Compensation

− Quality_ULCompensated is calculated in the same way such that:

Quality_ULCompensated = Quality_ULmeasured (in dBs) + 2*PLused

Where the Quality_ULmeasured (in dBs) is the Quality_ULmeasured (07) after transforming it into dBs







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• Dynamic MS Power Control Algorithm: 2) Filtering of measurements

− Filtering for both SS and Quality is done with exponential non-linear filters in order to eliminate variations of temporary nature.


− SS_ULFiltered (k) = b* SS_ULCompensated (k) + a* SS_ULCompensated(K-1), k is the SACCH period

− a & b (b=1-a) are the non-linear filter’s coefficients and “a” will define the length of the filter “L”, where each filter length “L” corresponds to certain value of “a”

− But how the length of the non-linear filter is calculated?




− SS_ULFiltered (k) = b* SS_ULCompensated (k) + a* SS_ULFiltered(K-1), k is the SACCH period

If SS_ULCompensated (k) <

SS_ULFiltered(K-1)

then L = SSLENUL where,

SSLENUL = 3 15 SACCH

periods

In this case “up regulation is

needed” and it should be done

very fast in order to not lose the

connection.

If SS_ULCompensated (k) >

SS_ULFiltered(K-1)

then L = SSLENUL


SSLENUL = 3 15 SACCH periods


In this case “Down regulation is

needed” and it should be done in a

smooth way, coz decreasing the

power suddenly may harm the

connection.

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(B) Filtering of Quality Measurements

− Quality_ULFiltered (k) = b* Quality_ULCompensated (k) + a* Quality_ULFiltered(K-1),

k is the SACCH period

If Quality_ULCompensated (k) <

Quality_ULFiltered(K-1)

then L = QLENUL where,

QSLENUL = 1 20 SACCH periods

In this case “up regulation is needed”

and it should be done very fast in order

to not lose the connection.

If Quality_ULCompensated (k)

>Quality_ULFiltered(K-1)

then L = QLENUL *UPDWNRATIO/100

where,

QLENUL = 1 20 SACCH periods


In this case “Down regulation is needed”

and it should be done in a smooth way,

coz decreasing the power suddenly may

harm the connection.



− SS_ULFiltered(K-1) is set initially = SSDESUL, that will lead to start power regulations immediately after the first valid measurement report.

− Also Quality_ULFiltered(K-1) is set initially = QDESUL, that will lead to start power regulations immediately after the first valid measurement report.

− SSDESUL: has value range from -110 to -47 dbm and recommended value is -92 dbm

− QDESUL: has value range from 0 to 70 dtqu and recommended value is 30 dtqu

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• Dynamic MS Power Control Algorithm:

Till now we finalized two stages from the algorithm:



SS_ULmeasured SS_ULCompens

ated SS_ULFiltere

d

Compensation Filtering

Q_ULmeasured

(Quality Units)

Q_ULCompensat

ed

Q_ULFiltered

Compensation

Filtering

Quality units to

dB

transformation

Q_ULmeasured(

dB)



Algorithm: The Dynamic MS Power Control algorithm is done on 3 stages




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• Dynamic MS Power Control Algorithm: 3) Calculation of Power Order (PU)

− This will be done on three stages:


(B) Applying the Power Orders constraints

(C) Conversion of output data.




pui = αi * (SSDESUL - SS_ULFiltered) + βi * (QDESUL - Q_ULFiltered)


α1 = LCOMPUL/100, β1 = QCOMPUL/100, α2 = 0.3, β2 = 0.4

pu1 is calculated according to settings of α1 & β1 ( The operator will set the proper values from his point of view for LCOMPUL & QCOMPUL)

pu2 is calculated according to recommended settings of α2 & β2 based on trials and field measurements.

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pui = αi * (SSDESUL - SS_ULFiltered) + βi * (QDESUL - Q_ULFiltered)


pu1 and pu2 both of them aim to maintain the SS within the desired value defined according to SSDESUL and to maintain the Quality within the desired value defined according to QDESUL but each will calculate the path loss in different way.

pu_used = max (pu1,pu2), max of pu1 and pu2 will be used as the desired power order in the next measurement report coz the max of both of them will mean lower down regulation/higher up regulation


• Dynamic MS Power Control Algorithm: 3) Calculation of Power Order (pu)

(B) Applying Power Order constraints

− The highest allowed power order pu_used = zero, which means keeping the output power at maximum value with no power control.

− The lowest allowed power order is given by the minimum of 16 dB i.e. it is not allowed to decrease the o/p power or increase it by a value > 16 dB

(C) Conversion of output data

− pu_used will be interpreted into final form PL_used which takes values from 0 8

− PL_used =Integer(-pu_used/2)

− ex: if PL_used = 3 and Down regulation for power is required, then in the next measurement report the BSC will inform the MS to decrease its current power by 2* PL_used = 6 dBs

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• Dynamic MS Power Control Parameters Summary

Dynamic BTS Power Control Parameters

Parameter Name Value Range Default Value Recommended

Value Unit

SSDESUL −110 to −47 −92 −92 dBm

QDESUL 0 to 76 30 30 dtqu

SSLENUL 3 to 15 3 3 SACCH period (0.48 Seconds)

QLENUL 1 to 20 3 3 SACCH period (0.48 Seconds)

LCOMPUL 0 to 100 6 6 −

QCOMPUL 0 to 100 75 75 −

UPDWNRATIO 100 to 700 200 300 −

REGINTUL 1 to 30 1 1 SACCH period (0.48 Seconds)


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GSM to UMTS Cell Reselection and Handover


• GSM to UMTS Cell Reselection and Handover

− All 3G user equipments (UEs) can support Multi RATs(Radio Access Technology) i.e. Both GSM and UMTS.

− With feature GSM-UMTS cell reselection and HO feature an operator can make use of both GSM and UMTS systems to complement each other.

− Multi RAT users can have good coverage even in areas where no UMTS coverage and this can be accomplished using UMTS-GSM cell reselection and HO.

− COEXUMTS: Is a BSC parameter used to activate the feature GSM-UMTS cell reselection and Handover.

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New concepts will be introduced to understand how the feature works:

− CPICH Ec/No: Common Pilot Channel - Energy per chip/Noise level power density

Used as a measure of the Quality of the neighbor UMTS cell.

− CPICH RSCP: Common Pilot Channel - Received Signal Code Power

Used as a measure of the SS of the neighbor UMTS cell after dispreading.



Measurements on UMTS Cells

− Inorder to be able to make cell reselection or HO to a UMTS neighbor cell, the multi RAT UE should be able to make measurements on this neighbor as well as the ordinary GSM cells.

− But when or at which conditions the UE will perform measurements on the UMTS neighbors?

This will be based on the settings of the parameters QSI and QSC.

− QSI: used to manage the conditions of measuring the UMTS cell in Idle Mode

QSC: used to manage the conditions of measuring the UMTS cell in Active Mode

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• GSM to UMTS Cell Reselection and Handover Measurements on UMTS Cells

Example: If QSC=8, then the UE in

dedicated mode is allowed to

measure the neighbor UMTS cell

only when the SS of the serving

GSM Cell > -78 dBm

When to start measuring the neighbor UMTS cell ?

QSI/QSC Signal Strength of the serving GSM Cell

0 to 6 "Below" -98dBm to -74 dBm in steps of 4 dB

7 Always

8 to 14 "Above" -78dBm to -54 dBm in steps of 4 dB

15 Never

-90 dBm

─

SS(dB

m)

time

-78

dBm

GSM&UMTS

measurements

GSM

measurements

GSM

measurement

s

GSM&UMTS

measurements


• GSM to UMTS Cell Reselection and Handover (I) GSM to UMTS Cell Reselection: This is controlled through set of parameters

QSI: Which defines at which conditions the UMTS cell will be measured in idle mode, because there won’t be any kind of cell reselection without performing measurements.

FDDQMIN: Defines the minimum quality of a UMTS cell inorder to be candidate for cell reselection i.e. this condition should be satisfied CPICH Ec/No >FDDQMIN condition#1

default value = 5 (-10 dB)

FDDRSCPMIN: Defines the minimum SS of a UMTS cell inorder to be candidate for cell reselection i.e. this condition should be satisfied CPICH RSCP >FDDRSCPMIN condition#2

default value= 6 (-102 dBm)

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(I) GSM to UMTS Cell Reselection: This is controlled through set of parameters

FDDQOFF: It is the key parameter to control the behavior of the cell reselection provided that condition#1 and condition#2 are fulfilled.

If CPICH RSCP > RLA (S+N) + FDDQOFFS for at least 5 sec condition#3then “Cell reselection will occur”

RLA (S+N): It is the Received Level Average of the signal strength of the serving+neighbor GSM cells measured in dBm, averaging is made on at least 5 measurements over a period of 35 seconds.

N.B: If the criteria for inter system cell reselection from GSM to UMTS is fulfilled then the multi RAT UE will perform cell reselection to the UMTS cell even if the criteria for selection another ordinary GSM cell is fulfilled.


• GSM to UMTS Cell Reselection and Handover (II) GSM to UMTS Handover:

FDDMRR: The multi RAT UE is informed on how many UMTS cells (03) he should report in the measurement report using this parameter.

− Upon receiving the measurements from the multi RAT UE, the BSC will handle the GSM and UMTS cells separately by filtering out the UMTS measurements before the GSM locating algorithm.

GSM

Evaluatio

n

Sending the list

and allocation

reply

Filtering

Basic Ranking

Urgency

Condition Aux. Radio

features

Organizing the

list

% idle TCHs ≤ ISOLEV

Ec/No > MRSL

Filtering out the UMTS cells

Add UMTS cells to

Candidate list

UMTS

Evaluation

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• GSM to UMTS Cell Reselection and Handover (II) GSM to UMTS Handover: This is controlled through set of parameters

QSC: Which defines at which conditions the UMTS cell will be measured in active mode, because there won’t be any kind of cell reselection without performing measurements.

MRSL: It is a BSC parameter that gives the minimum threshold for the quality (Ec/No) for a UMTS neighbor cell in order to be added to the HO candidate list, recommended value= -9 dB

ISHOLEV: It is a Cell parameter. The percentage of idle TCHs in the serving GSM cell will be compared vs. ISHOLEV to decide if the UMTS will be added to the HO candidate list or not.

Conditions that should be fulfilled for a UMTS cell to be added to the HO candidate list:

(1) No. of Idle TCHsGSM ServingCell ≤ ISHOLEV, or urgency conditions are detected in the GSM

serving cell either due to BQ or TA

(2) CPICH Ec/No UMTS Neighbor ≥ MRSL



(II) GSM to UMTS Handover:

− Now all the valid neighboring UMTS cells will be sorted in order of decreasing CPICH Ec/No in order to form the UMTS candidate list.

− But how the two lists, the GSM and UMTS will be sorted?

Ans.: this will depend on the urgency conditions and the load as follow

− N.B: To have balance between the behavior in the idle & active modes it is recommended to set the values for FDDQMIN (idle) = MRSL (active)

Non-Urgency HO Condition Urgency HO Condition

No Load Load No Load Load

GSM list UMTS list GSM list

GSM list UMTS list

UMTS list GSM list

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Parameters Summary

GSM-UMTS Cell Reselection and HO Control Parameters


COEXUMTS 0(OFF),1(ON) 0(OFF) 1(ON) −

QSI

0 to 6(Below:-98dBm t o -74dBm) 7(Always)

8 to 14(Above:-78dBm to -54dBm) 15 (Never)

15 − −

QSC

0 to 6(Below:-98dBm t o -74dBm) 7(Always)

8 to 14(Above:-78dBm to -54dBm) 15 (Never)

15 − −

FDDQMIN 0 to 7 (-20dB, -18dB,

-16dB, -14dB, 12dB -10dB, -8dB, -6dB) 0 (-20dB) 5(-10dB) −

FDDRSCPMIN 0 to 15(-114 dBm to -84 dBm in steps of 2dBm) 6(-102 dBm) 6(-102 dBm) −

FDDQOFF 0 to 15 (-inf, -28dB to 28dB in steps of 4 dB) 8(0 dB) 0(-inf) −

FDMRR 0 to 3 0 1 or 2 −

MRSL 0 to 49 − 30 (-9 dB)

ISHOLEV 0 to 99 20 − %


Thank You

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Trouble Shooting and KPIs Monitoring


• Trouble Shooting & KPIs monitoring

− The Quality of service means that how the subscriber is satisfied with the overall

service.

− To keep the quality of service good as much as possible, we have to enhance the following:

(A) Accessibility: The ability of users to access the network.

(B) Retainability: The ability of users to successfully continue their connections with the network until it is terminated in a normal way.

(C) Service Integrity: The ability to keep the quality of the service good enough during the connection with the network.

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− KPIs: “Key Performance Indicators” it is a general term used to define the keys or observations through which you can judge if the performance is good or not.

(A) Accessibility KPIs:

Paging Success Rate

Random Access

SDCCH Congestion (Blocking)

TCH Blocking

SDCCH Drop



(B) Retainability KPIs:

TCH Drop Rate

Handover Success Rate

(C) Service Integrity KPIs:

Rxqual (Received Signal Quality)

SQI (Speech Quality Indicator)

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• Trouble Shooting & KPIs monitoring (A) Accessibility KPIs:

(1) Paging

− On MSC level there is counters to count:

No. of attempts of paging to the Location Area

No. of paging response to first paging

No. of paging response to the repeated paging.

Using these counters we can form the equation to calculate the paging success rate.



(1) Paging: The Paging Success rate on certain LA as appeared from the statistics:

Paging

Attempts

Paging Success

Rate

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(1) Paging

What are the causes of bad paging performance?

− Implicit detach is not used: parameter ATT is set to “Off”

− Low Signal Strength

− Not optimized paging strategy

− Use of combined BCCH mapping in high traffic location areas.

− Location area dimensioning

− Using of IMSI most of the time instead of TMSI



(2) Random Access

− A failure in the random access doesn’t mean a call setup failure because the MS sends many random access bursts each time it tries to access the network.

− There are counters to count the no. of accepted random access requests, and the no. of discarded requests (incremented for random access requests that are received with too high Time Advance) through which the random access success rate can be calculated.

− Causes of low random access success rate may be due to:

Too high Time Advance (TA)

High Interference

Bad BSIC Planning

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(3) SDCCH Congestion

− It is the failure of call/connection setup due to high signaling load.

− There are counters to count the no. failed allocations due to SDCCH congestion and the no. of call attempts through which the SDCCH congestion rate can be calculated.

− Causes of high SDCCH congestion? This is may be due to:

Location Area border cell.

High SMS Traffic.

Hardware Availability.

No. of configured SDCCHs is low.



(4) TCH Blocking

− It is the failure of setup a call/connection due to TCH congestion.

− There are counters to count the no. of released connections on SDCCH due to TCH congestion and the no. of assignment attempts on TCH channel through which the TCH blocking rate can be calculated.

− Causes of high TCH Blocking may be due to:

Hardware problem.

Too few TCH resources defined.

Missing neighbor cell definition.

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(4) TCH Blocking: The TCH Blocking as appeared from the Statistics

TCH Blocking was solved after expansion (adding new frequency)

FR Traffic

TCH Blocking

Defined TCH

Channels

HR

Traffic



(5) SDCCH Drop

− It is the failure of setup a call/connection due to SDCCH channel drop.

N.B: when a connection is dropped at call setup it will affect the accessibility KPIs

− There are counters to count the no. of dropped connections on SDCCH and the no. of successful MS channel establishments on SDCCH through which the SDCCH drop rate can be calculated.

− Causes of high SDCCH drop rate may be due to:

Bad Coverage.

Interference.

Hardware problems.

Wrong parameters’ settings

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• Trouble Shooting & KPIs monitoring (B) Retainability KPIs:

(1) TCH Drop

− It is the drop of the connection on the traffic channel which was assigned to the MS

− There are counters to count the no. of dropped connections and the initiated connections on TCH channels through which the TCH drop rate can be calculated.

− Causes of high TCH drop rate may be due to:

Bad coverage.

Interference.

Hardware problems.

Missing Neighbors or Incomplete Active BA lists.

Wrong parameters‘ settings.



(1) TCH Drop: The TCH drop as appeared from the statistics.

High drop rate was solved after fixing a hardware problem.

TCH Traffic

TCH Drop

Rate

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(1) TCH Drop: The TCH drop reasons as appeared from the statistics.

Main drop reason is due to BQ in downlink

BQ Both Links

BQ Downlink

BQ Uplink

Low SS Both

Links

Low SS

Downlink

Low SS Uplink

Sudden Lost



(1) TCH Drop: The TCH drop reasons as appeared from the statistics.

Main drop reason is due to low SS Both link

BQ Both Links

BQ Downlink

BQ Uplink

Low SS Both

Links

Low SS

Downlink

Low SS Uplink

Sudden Lost

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(2) Handover Success Rate

− There are counters to measure the number of Handover attempts from cell to cell and the Handover success rate.

− Poor Handover Success rate may be due to:

Bad Frequency plan.

Wrong definitions and missing neighbors.

Wrong parameters settings.

Hardware problems.

− Handover failure does not mean a drop call will occur.


• Trouble Shooting & KPIs monitoring (C) Service Integrity KPIs:

(1) Rxqual:

− It is obtained by averaging the Bit Error Rate over a certain period ~ 0.5 sec and it is

measured in both the Downlink and Uplink

− Rxqual take values from 0 (Best) 7 (Worst) and gives indication for the quality of the radio environment.

− There are counters to measure the no. of samples that received with Rxqual 0,1,2,….7

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• Trouble Shooting & KPIs monitoring (C) Service Integrity KPIs:

(2) SQI (Speech Quality Index):

− Is a good measure for the end user perceived speech quality.

− The algorithm used for calculation the SQI takes into account the BER, the distribution of BER, the FER (Frame Erasure Rate) and the codec used (HR, FR, EFR). The output values are measured on a dBQ scale.

− Typically, the SQI take values from 0 (Worst) 30 (Best), on HR connection SQImax=17dBQ, FR connection SQImax=22dBQ, AMR HR SQImax=28dBQ, EFR connection SQImax=30dBQ

− N.B: HR ≡ Half Rate, FR ≡ Full Rate, EFR ≡ Enhance Full Rate


gsm optimization

Documents

pgsm gsm

gsm revision gsm system

gsm revision frequency

link gsm

gsm bandssystem pgsm

egsm extended gsm

primary gsm

link frequency band