gsm handover

GSM Handover Algorithm N-1

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Copyright © 2009 Huawei Technologies Co., Ltd. All rights reserved.

GSM Handover Algorithm



Page2Copyright © 2009 Huawei Technologies Co., Ltd. All rights reserved.

Foreword

Handover is a key technology of mobile communication system and

make continued conversation possible.

Handover algorithm in Huawei product is flexible and powerful.




Objectives

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

Outline the types of handover

Master handover judgment flow

Understand algorithm of different handovers

Explain HO data configuration




Contents

1. Introduction of Handover

2. HO Algorithm Process




Contents






Purposes of HO

To keep a continuous communication with a moving MS

To improve network service performance

To reduce the call drop rate

To reduce the congestion rate

Handover can maintain the communication continuity of MS which moves across different cells and lower the call drop rate and provide better communication service.




Classification by Reason

No DL MR Emergency HOTiming Advance (TA) HOInterference HORx_Level_Drop HOBad Quality (BQ) HO

Emergency HO

Enhanced Dual Band HO

Load HO

Normal HO

1

2

3

4

Classification by

ReasonEDGE HO PBGT HOLayer HO MS Fast Moving HOConcentric Cell HOAMR HO




Classification by Synchronization

CELL

Case 1

Synchronous Handover: the target BTS shall not send PHY INFO message

Case 2

Asynchronous Handover: the target BTS shall send PHY INFO message

Case 3 Case 4 Case 5

MSC

BSC

BTS

BSC BSC

MSC

BTS BTS BTS BTS

NSS Network

Synchronous handover: source and target cell belong the same BTS

Asynchronous handover: source and target cell belong the different BTS




Classification by Equipment and Channel

SDCCH SDCCH →→ TCHTCH(Direct Retry)(Direct Retry)

SDCCH SDCCH →→ SDCCHSDCCH

Intra Intra –– Cell Cell HOHO

Inter Inter –– Cell HOCell HO

Intra Intra –– BSC HOBSC HO

Intra Intra –– MSC HOMSC HO

Inter Inter –– MSC HOMSC HO

TCH TCH →→ TCHTCH




Contents






Contents


2.1 General HO Process

2.2 Measure and Measurement Result Report

2.3 Measurement Report Preprocessing

2.4 Handover Judgment

2.5 Handover Implementation




General HO Process

MS Goes into New Dedicated Mode

MS Goes into Dedicated Mode

Measure and Measurement Result Report1

Measurement Report Preprocessing2

Handover Judgment3

Handover Implementation4




General HO Process





Handover Judgment3





The downlink measurement reportof the neighbor cell (BCCH)

Measurement Report

Uplink MR includes uplink receiving level and quality.

Downlink MR includes downlink receiving level, downlink receiving

quality of the serving cell and other downlink receiving levels from

the neighbor cells.

Serving cell

Neighbor cell

The uplink MR

The downlink MR

In dedicated mode, the system performs handover and power control judgment based on measurement reports. The downlink MR are reported to the network via uplink SACCH channel.

Downlink--In dedicated mode, MS reports MR via uplink SACCH channel periodically. The report includes the receiving level, received quality, TA, power class and whether DTX is used. At the same time, MS will perform pre-synchronization to neighbor cell defined by the system to obtain BCCH frequencies and BSIC, measure their received signal level and report the six max. neighbor cells with the highest received signal level.

Uplink--The uplink measurement report is measured by BTS, including the receiving level and receiving quality from the MS.

Both parts are sent by BTS to BSC for further processing at the same time.




Measurement Report

There are two values in the measurement report: FULL MR and SUB MR.

FULL--Averaging 100 TCH bursts (except the four idle frames in the four 26-multiframes)

SUB--Averaging 12 bursts (four SACCH bursts and eight TCH bursts in specific position).

SUB should be selected when the Discontinuous Transmission (DTX) function is activated.

RXQUAL level in MR Huawei value BER behind 0 0 Less than 0.2% 1 10 0.2% ~ 0.4% 2 20 0.4% ~ 0.8% 3 30 0.8% ~ 1.6% 4 40 1.6% ~ 3.2% 5 50 3.2% ~ 6.4% 6 60 6.4% ~ 12.8% 7 70 Greater than 12.8%




Period of Measurement Report

The downlink MR is sent to BTS in SACCH uplink

The interval is 480ms/per time when MS is on TCH

The interval is 470ms/per time when MS is on SDCCH

12TCH 12TCH1SACCH 1 Idle

480ms 4 TCH Multi-frames

SACCH is a bidirectional channel.It sends the downlink measurement report to BTS in uplink SACCH.It sends SYS.INFO. 5 and SYS. INFO. 6 to MS in downlink SACCH.

1. The SACCH measurement report period varies with the channel occupied by MS in dedicated mode.

2. When associated with SDCCH, SACCH measurement period is 470ms, this is because there is an entire SACCH message block in 2 SDCCH 51-multiframes.

3. When associated with TCH, SACCH measurement period is 480ms, this is because there is an entire SACCH message block in 4 TCH 26-multiframes

A complete measurement report is formed by four consecutive SACCH bursts. In SDCCH channel the four bursts are transmitted continuously. In TCH channel there is only one SACCH burst in each 26-multiframe, therefore only four 26-multiframe can constitute a complete measurement report.




General HO Process



Measurement Report Preprocessing

Handover Judgment3



2




MR Preprocessing

MR Preprocessing

Interpolation

Recover the lost

measurement report

Filtering

Smooth the instantaneous

fading point

MR preprocessing consists of two steps: interpolation and filtering.




MR Interpolation

MR

MR

No. n

No. n+4

Continuous MR Flow

MRMR

MR

Missing by some reasons

…

…

MR Interpolation – recover the lost measurement report

BTS may fail to receive the MR from MS, and it needs to recover the lost measurement reports. If the lost MR amount is within the allowed range (Allowed MR Number Lost), then recovers the lost MR according to the specific algorithm.

Service cell: linear algorithm

Neighboring cell: the lowest value defined in GSM specification (-110dBm)

The continuity of measurement report is judged by measurement report number. Each measurement report has a serial number. If the serial numbers of received measurement reports are not consecutive, there must be missing measurement reports, and the system will make them up according to the interpolation algorithm.

As shown in the diagram, the network receives measurement reports n and n+4, whose serial numbers are not consecutive, so the system will make up for the missing measurement reports n+1, n+2 and n+3 with a certain algorithm.




MR Filtering

MR

MRContinuous MR Flow MR

MR

MR

…

…Filter----Average several consecutive MRs

MR

Filtering – smooth the instantaneous fading point

Calculate the average value within the filter window

When the network receives the measurement report, it can not judge the current condition of MS according to just one measurement report due to the signal fluctuation. Therefore, filtering, a more suitable method is applied.

Different filters are applied in receiving level, receiving quality and TA of uplink and downlink.




Data Configuration of MR Preprocessing

[MR Preprocessing]

•Value Range: Yes, No

•Default Value: No

•Description: This parameter indicates whether the BTS pre-processes the MR.

This parameter determines the location where power control is performed. If this parameter is set to Yes, power control is performed by the BTS. Otherwise, the power control is performed by the BSC.

When this parameter is set to No, the MR is processed by the BSC, in which case, both Transfer original MR, Transfer BS/MS power class and Sent Freq of preprocessed MR are invalid.

When this parameter is set to Yes, the load over Abis interface and that over the BSC are reduced, thus shortening the response time and improving the network performance.

[Transfer Original MR]



•Description: This parameter indicates whether the original MR is transferred to the BSC after the BTS pre-processes the MR.

When the parameter is set to Yes, the BTS transfers to the BSC both the processed MR and the original MR.

•Remarks:In case of 4:1 configuration, this parameter must be set to No if SDCCH/8 is greater than 2.





[Transfer BS/MS Power Class]


•Default Value: Yes

•Description: This parameter indicates whether the original BS/MS power class is transferred to the BSC.

•Remarks:When MR pre-processing is enabled, uplink and downlink balance measurement is affected if this parameter is set to No. In addition, power compensation handovers, such as PBGT handovers, load handovers, and Concentric Cell handovers, may become abnormal.

[Sent Freq of Preprocessed MR]

•Value Range: Do not Report, Twice every second, Once every second, Once every two seconds, Once every four seconds

•Default Value: Twice every second

•Description: This parameter indicates the frequency that the BTS transfers the preprocessed MR to the BSC. After the MR is preprocessed by BTS, the BTS transfers the preprocessed MR to the BSC. For example, if this parameter is set to Twice every second, the BTS transfers the preprocessed MR to the BSC twice per 0.5 second.





[Allowed MR Number Lost]

•Value Range: 0~31

•Default Value: 4

•Description: This parameter indicates the number of MRs allowed to be lost in succession. When this threshold is not reached, the lost MR is estimated via the linear interpolation basing on the first and the last MRs received. When this threshold is reached, all previous MRs are discarded, and calculations are made again when new MRs are received.

•Remarks: MRs fail to be decoded correctly when the signal strength in the serving cell is poor. When this threshold is reached, all previous MRs are discarded and handover may fail. Thus, it is advised to assign this parameter with a greater value to enable emergency handover.

[Filter Length for TCH Level]


•Default Value: 4

•Description: This parameter indicates the number of MRs used for averaging the TCH signal strength.

This parameter helps to avoid sharp drop of signal levels caused by Raileigh Fading and to ensure correct handover decisions.

•Remarks: When this parameter is too large, the impact of sudden changes is reduced, and the response is delayed, thus affecting the network performance.

[Filter Length for TCH Qual]


•Default Value: 4

•Description: This parameter indicates the number of MRs used for averaging the TCH signal quality.





[Filter Length for SDCCH Level]


•Default Value: 2

•Description: This parameter indicates the number of MRs used for averaging the SDCCH signal strength.

It is recommended that you assign this parameter with a lower value because the SDCCH occupation time is shorter than the TCH occupation time.

[Filter Length for SDCCH Qual]


•Default Value: 2

•Description: This parameter indicates the number of MRs used for averaging the SDCCH signal quality.

It is recommended that you assign this parameter with a lower value because the SDCCH occupation time is shorter than the TCH occupation time.

[Filter Length for Ncell RX_LEV]


•Default Value: 4

•Description: This parameter indicates the number of MRs used for averaging the signal strength in neighboring cells. This parameter helps to avoid sharp drop of signal levels and to ensure correct handover decisions.

•Remarks: When this parameter is too large, the impact of sudden changes is reduced, and the response is delayed, thus affecting the network performance.

[Filter Length for TA]


•Default Value: 4

•Description: This parameter indicates the number of MRs used for TA averaging.




General HO Process


MS Goes intoDedicated Mode


MR. Preprocessing2

Handover Judgment3


TA HO

Interference HO

Rx_Level_Drop HO

Bad Quality HO

Load HO

Edge HO

Layer HO

PBGT HO

AMR HO

No DL MR HO

Concentric Cell HO

MS Fast Moving HO


Penalty Processing

Ranking Processing

OM Forced HO

Direct Retry

Emergency HO

Normal HO




Penalty Processing

Intra-cell HO

HO Fails Emergency (TA&BQ)HO

MS Fast Moving

HO

Concentric Cell HO

Penalty

Punish on the target cell

Punish on the original cell

Punish on other high priority layer cells

AMR HOFails

There are several kinds of penalty process

Penalty on target cell when a HO fails.

Penalty on source cell when an emergency HO (BQ and TA ) is performed.

Penalty on other high priority layer cells after fast moving HO is performed.

Penalty for concentric cell HO

Penalty for intra-cell HO

Penalty for AMR HO




Penalty for Handover Failure

Punish the target cell when a HO fails.

This is to avoid the MS to select this cell again in next HO judgment.

Cell A

BTSHO Fail

BSC

Cell B

BTS

When MS fails to handover to a target cell, a penalty will be given on the signal level of this target cell during a so called “handover failure penalty time” period. That is, when ranking the neighbor cells in the cell list, the corresponding neighbor cell with a failure record within the penalty time will be penalized by cutting certain value on the reported signal level.




Data Configuration of Penalty for Handover Failure

[Penalty Level after HO Fail]


•Unit: dB

•Default Value: 30

•Description: This parameter indicates the penalty level given to a target cell. A penalty level is given to a target cell to avoid further attempts when a handover fails due to any of the following reasons:

Cell congestion

A message indicating internal handover refusal is received.

A message indicating Um interface handover failure is received during out-going BSC handover.

A message indicating Um interface handover failure is received during internal handover.

•Remarks: This parameter is valid only before the penalty time of handover failure expires.




Data Configuration of Penalty for Handover Failure

[RscPenaltyTimer]


•Unit: Seconds

•Default Value: 5

•Description: This parameter indicates the length of the penalty timer for handover failure between adjacent cells due to cell congestion.

[UmPenaltyTimer]


•Unit: Seconds


•Description: This parameter indicates the length of the penalty timer for handover failure between adjacent cells due to failed air interface connection.

[CfgPenaltyTimer]


•Unit: Seconds


•Description: This parameter indicates the length of the penalty timer for handover failure between adjacent cells due to incorrect data configuration.




Cell A

Cell B

BTSBQ&TA HO

BSC

Penalty for Emergency Handover

Punish the original cell when an emergency HO ( due to BQ and TA)

occurs.

In case of BQ emergency handover, the original serving cell will be penalized (called signal level penalty by BQ HO ), during BQ HO penalty time, to avoid MS to be handed back to the original serving cell again within certain time.

It is the same for TA handover, i.e. the original serving cell is penalized (signal level penalty by TA HO ) during TA HO penalty time.




Data Configuration of Penalty for Emergency Handover

[Penalty Level after BQ HO]


•Unit: dB


•Description: This parameter indicates the penalty level given to the original serving cell where emergency handover is performed due to bad quality. After emergency handover is performed due to bad quality, the receive level of the original serving cell is decreased by the penalty level. Thus, other cells are given higher priority and handover to the original serving cell is not allowed.

•Remarks: This parameter is valid only before the penalty time of handover due to bad quality expires.

[Penalty Time after BQ HO (s)]


•Unit: Seconds


•Description: This parameter indicates the penalty time given to the original serving cell where emergency handover is performed due to bad quality. During the penalty time, the receive level of the original serving cell is decreased by the penalty level. Thus, other cells are given higher priority and handover to the original serving cell is not allowed.




Data Configuration of Penalty for Emergency Handover

[Penalty Level after TA HO]


•Unit: dB


•Description: This parameter indicates the penalty level given to the original serving cell where emergency handover is performed due to TA. After emergency handover is performed due to TA, the receive level of the original serving cell is decreased by the penalty level. Thus, other cells are given higher priority and handover to the original serving cell is not allowed. This parameter is valid only before the penalty time of handover due to TA expires.

[Penalty Time after TA HO(s)]


•Unit: Seconds

•Default Value:30

•Description: This parameter indicates the penalty time given to the original serving cell where emergency handover is performed due to TA. During the penalty time, the receive level of the original serving cell is decreased by the penalty level. Thus, other cells are given higher priority and handover to the original serving cell is not allowed.




Back? No way!Back? No way!

Umbrella

Micro cell

Penalty for MS Fast-moving Handover

Giving penalty on the other three layers(Non-umbrella Layer ) after MS

handovers to Umbrella cell by fast-moving-HO.

This is to keep MS staying in the umbrella cell and avoid frequent HO.

Purpose of such penalty: When MS crosses continuously several micro cells, it handover to the umbrella cell with lower hierarchical priority level, to avoid too frequent handovers which will affect the communication quality between those cells. At the same time, penalty is started to avoid handover back to original cell again. A possible example is that a fast moving car is running on a highway.




Data Configuration of Penalty for MS Fast-moving Handover

[Penalty on MS Fast Moving HO]


•Unit: dB

•Default Value:30

•Description: This parameter indicates the penalty given to the level in a neighboring cell when an MS is moving fast. Only the cells in the umbrella layer can give penalty to the cells in other three layers.

•Remarks: This parameter is valid only before the penalty time of fast moving expires.

[Penalty Time on Fast Moving HO]


•Unit: Seconds


•Description: This parameter indicates the period during which penalty is performed on the neighboring cells of the fast moving MS. During this period, penalty on the neighboring cells (on only the other three layers except the umbrella layer) of fast moving MS is valid.




Underlaid

Overlaid Do not attempt again during penalty time

after one failed HO(O->U)!

Penalty for Concentric Cell

A new concentric cell HO is prohibited within a penalty time after a

concentric cell HO failure.

Do not attempt again after N failed

HO(U->O)!

Huawei concentric cell HO failure means the failure of handover from the Underlaid to the Overlaid, or from the Overlaid to the Underlaid.




Data Configuration of Penalty for Concentric Cell

[Penalty Time after UtoO HO Fails(s)]

•Value Range: 10~255 Unit: Seconds Default Value: 40

•Description: After a UL to OL handover fails, no UL to OL handover request is allowed before the penalty time expires.

[Penalty Time after OtoU HO Fails(s)]


•Description: After an OL to UL handover fails, no OL to UL handover request is allowed before the penalty time expires.

[MaxRetry Time after UtoO Fail]

•Value Range: 0~8 Default Value: 3

•Description: This parameter indicates the threshold of UL to OL handover failures. UL to OL handover is not allowed if the number of handover failures reaches this threshold.

•Remarks: When this parameter is set to 0, not this threshold but the penalty time restricts the permission of handover.




Underlaid

OverlaidDo not

attempt back too fast!

Penalty for Enhanced Concentric Cell

A new U O HO is prohibited within a penalty time after a

O U HO is performed successfully.

This penalty is valid only for Enhanced Concentric Cell.




Data Configuration of Penalty for Enhanced Concentric Cell

[Penalty Time of UtoO HO(s)]


•Unit: Seconds


•Description: This parameter indicates the penalty time for forbidding ping-pong handovers. After an OL to UL handover is performed, UL to OL handover is not allowed before the penalty time expires. If this parameter is set to 0, a UL to OL handover is allowed when required.

•Remarks: This parameter is valid only when Enhanced Concentric Cell is allowed.




Penalty for Intra-cell HO

A new intra-cell HO is prohibited if it occurs too frequently.

3 7 12 32 T (s)0

Penalty time

Intra-cell HO Time

2nd.3rd.

4th.

Max. consecutive HO times: 3

Forbidden time after Max. times: 20s

Interval for consecutive HO Jud: 6s

1st.

Because of the co-channel interference and other interference, the voice quality of a MS on certain frequency may lower than the handoverthreshold, now, the voice quality can be satisfied if the MS hands over to another frequency in the same cell. On the other side, the signaling flow of this kind of intra-cell handover is less and handover successful ratio is higher.

But under some specific condition (for example: several frequency are all interfered in a cell), then continual intra-cell handover may occurred. So it is necessary to control the frequency of intra-cell handover.




Data Configuration of Penalty for Intra-cell HO

[Max Consecutive HO Times]

•Value Range:1~20

•Default Value: 3

•Description: This parameter indicates the maximum number of consecutive intra-cell handovers allowed. If the interval of two continuous intra-cell handovers is less than a specified threshold, the two handovers are regarded as consecutive handovers.Intra-cell handover is forbidden if the number of consecutive handovers exceeds this threshold.

[Forbidden Time after Max Times]


•Unit: Seconds


•Description: This parameter indicates the timer that starts when the threshold of maximum consecutive intra-cell handovers is reached. Intra-cell handovers is allowed only when the timer expires.

[Interval for Consecutive HO Jud.]


•Unit: Seconds

•Default Value: 6

•Description: This parameter indicates the period for judging whether two continuous intra-cell handovers are consecutive.




Data Configuration of Penalty for AMR FR HR Handover Failure

[Penalty Time after AMR TCHF-H HO Fails(s)]


•Unit: Seconds


•Description: This parameter indicates the penalty time for AMR full rate to half rate (FR-to-HR) handovers. Before the timer expires, no AMR FR-to-HR handover request is allowed if the previous full-half handover fails due to channel unavailability or channel mismatch.




General HO Process




MR. Preprocessing2

Handover Judgment3


TA HO

Interference HO

Rx_Level_Drop HO

Bad Quality HO

Load HO

Edge HO

Layer HO

PBGT HO

AMR HO

No DL MR HO

Concentric Cell HO

MS Fast Moving HO


Penalty Processing

Ranking Processing

OM Forced HO

Direct Retry

Emergency HO

Normal HO




Ranking Processing

M rule

K rule

Basic ranking

16 bits ranking

Network feature adjustment

The ranking result: target cell selection of handover

Ranking processing of cells are major parts of the HO judgment.

The ranking result is used for target cell selection of handover.

The ranking processing includes:

Basic ranking

M rule

K rule (Integrated with 16bits ranking, will be discussed together with 16bits ranking)

Network feature adjustment

16 bits ranking




M Rule Begin

Finish to all neighbor cells?

An BSC external neighboring cell& the current channel is

SDCCH ?

No

Yes

Direct retry? [Inter-BSC SDCCH HO Allowed] (S) is Yes?

Delete the cell from the cell list?

the cell overload ?

Yes No

Yes

No

RX_LEV_DL(n) < [Min DL Poweron HO Candidate Cell](n)+

[Min Access Level Offset](s->n)?

RX_LEV_UL(n) < [Min UP Power on HO Candidate Cell](n)+

[Min Access Level Offset](s->n)?

Delete this cell from the cell list

Yes

No

No

No

No

Yes

End

For service cell: Min Access Level Offset=0

M rule will remove the neighbor cells from the candidate cell listaccording to the flow.

Yes

Yes

M rule will remove the cells from the candidate cell list according to the following conditions:

Under the condition of non-direct retry, if “Inter-BSC SDCCH HO Allowed” is No, and this is an external neighboring cell, and the current channel is SDCCH

If the cell is overload

RX_LEV_DL < Min DL Power on HO Candidate Cell + Min Access Level Offset

RX_LEV_UL < Min UL Power on HO Candidate Cell + Min Access Level Offset

For service cell: Min Access Level Offset is 0.




Data Configuration of M Rule

[Inter-BSC SDCCH HO Allowed]



•Description: This parameter indicates whether an inter-BSC SDCCH handover is allowed. An inter-BSC SDCCH handover is triggered when an MS succeeds in requesting SDCCH but fails to request TCH in a BSC.




Data Configuration of M Rule

[Min UP Power on HO Candidate Cell]

•Value Range: 0~63 (-110 dBm to -47 dBm) Default Value: 10

•Description: The M criterion supports the minimum value constraint of uplink received level of the neighbor cell. Expected uplink level of the neighbor cell >= (the minimum uplink power of the candidate cell for handover + the minimum access level offset)The M criterion is satisfied only when the expected downlink level of the neighbor cell >= (the minimum downlink power of the candidate cell for handover + the minimum access level offset).0-63 with 0 indicating -110 dBmand 63 indicating -47 dBm.

[Min DL Level on Candidate Cell]


•Description: This parameter indicates the lower threshold of downlink receive level when a cell becomes a candidate cell.

•Remarks: This parameter must be appropriately specified. If it is too high, some desired cells may be excluded from the candidate cells. If it is too low, an unwanted cell may become the target cell, thus leading to handover failures or call drops. A cell can become a candidate cell only when the receive level minus this parameter is greater than the minimum access level offset.

[Min Access Level Offset]

•Value Range: 0~63 Unit: dB Default Value: 0

•Description: This offset is based on the Min DL level on Candidate Cell. For different adjacent cells, different offsets can be defined. Only when the receiving level of an adjacent cell > Min DL Level on Candidate Cell + Min Access Level Offset, then this cell become a candidate cell.




Network Feature Adjustment

After network feature adjustment, all the candidate cells have their own

16 bits value.

The smaller the value is, the higher the handover priority and position of

the cell are in the candidate cell list, then it is possible to be the

candidate cell.

The Lowest

Weight

The Highest

Weight16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1





The 1st~3rd bits

The bit value indicates the priority of downlink receiving level according to

the cell signal level and the penalty process taking place beforehand.

The values come from max. 6 candidate cells and 1 serving cell

according to the level ranges from 000~110. The value for the cell with

the strongest signal level is 000, for the cell with second strongest signal

level is 001 and so on.

Actually that is the core of K rule.

141516 12345678910111213





The 4th bit: [Inter-cell HO hysteresis] bit.

141516 12345678910111213

serving cell?

Always set to 0

No

RX_LEV_DL (n) >=RX_LEV_DL (s) +

[Inter-cell HO hysteresis] (s->n) ?

Yes

Set to 0Yes

Set to1

No

Service cell: always 0

Neighboring cell: when RX_LEV_DL (n) >= RX_LEV_DL (s) + Inter-cell HO hysteresis, bit 4th is set to 0. Otherwise, set to 1




Data Configuration of Inter-cell HO Hysteresis

[Inter-cell HO Hysteresis]


•Unit: dB

•Default Value: 5

•Description: This parameter indicates the handover hysteresis between adjacent cells of the same layer. The purpose of setting this parameter is to reduce the "Ping-Pong" handovers. The value of this parameter is invalid if cells are not on the same layer. 4 dB for populous urban areas and 8 dB for suburbs.





The 5th~10th bits

The bit value is decided according to their position in Huawei hierarchical

network structure.

Huawei cell layers can be divided into 4 layers and each layer can be

further divided into 16 different priorities.

So there are 64 different priorities in Huawei hierarchical cell structure.

141516 12345678910111213




Hierarchical Cell Structure

GSM900 Cell

Micro Cell

Umbrella Cell GSM 900

GSM1800 GSM1800GSM1800

GSM 900

GSM900GSM900

GSM1800GSM1800

GSM1800 Cell

GSM 900

GSM900GSM900

GSM1800GSM1800

Layer 4（low）

Layer 3

Layer 2

Layer 1（high）

The handover algorithm of Huawei divides the whole network into four layers, each of which further divided into 16 levels. The lower the layer is, the higher the handover priority level will be. The “Micro Cell” layer has the highest priority level.




Data Configuration of Cell Hierarchical Network Structure

[Cell Layer]

•Value Range:1~4 (mapping to the PICO layer, the MICRO layer, the MACRO layer, and the UMBRELLA layer)

•Unit: Layer

•Default Value: 3

•Description: The framework of Huawei network is divided into four layers: Umbrella layer, Macro layer, Micro layer, and Pico layer. Each layer is designed with 16 priorities. The Umbrella layer refers to the GSM900 layer with a large coverage area. It implements the high-layer coverage and the connection of MSs moving at a high speed. The Macro layer carries most traffic on the GSM900 band. The Micro layer carries most traffic on the DCS1800 band. It solves the problem of insufficient resources. The Micro layer is a main cell layer for dual-band MSs in the future. The Pico layer is a microcell layer on the GSM900 and DCS1800 bands. It meets the requirements for the provisioning of traffic at hot spots and dead zones.

•Remarks: You can set multiple priorities (a maximum of 16 priorities) for each layer. From the aspect of traffic priority, if the layer and level of a cell is low, the priority is high.

[Cell Priority]

•Value Range:1~16

•Unit: Level

•Default Value:1

•Description: This parameter controls handover between cells at the same layer. Generally, the cells at the same layer have the same priority. If the cells at the same layer have different priorities, the cell with a smaller value has a higher priority.





The 11th bit: The bit value is decided by cell-load-sharing criterion.

This bit is affected by 14th bit.

141516 12345678910111213

System load>=[System Flux Threshold for Load HO](s) or [Load HO Allowed](s) =No ?

Yes 11th bit is turned off

serving cell?

set to 0

NoYes

Cell load >= [Load HO Threshold](s)?

set to 1 set to 1

cell load >=[ Load Req. on Candidate Cell](n)?

set to 0

Yes

No

Yes

No

No

The 11th bit: bit value is decided by cell-load-sharing criterion. And this bit will be turned off when the system load is higher than System Flux Threshold for Load HO or Load HO Allowed is set to NO

Service cell: if cell load >= Load HO Threshold, bit 11th is set to 1. Otherwise, set to 0

Neighboring cell: if cell load >= Load Rep. on Candidate Cell, bit 11th is set to 1. Otherwise, set to 0




Data Configuration of Cell-load-sharing

[Load HO Allowed]

• Value Range: Yes, No

• Default Value: No

• Description: This parameter indicates whether a traffic load-sharing handover is allowed. Load-sharing helps to reduce cell congestion, improve the success rate of assignment, and balance the traffic load among cells. Load-sharing functions only within the same BSC or in cells of the same layer. It applies to only TCH. If load handover is frequently required, TRX configuration and network planning should be properly adjusted.

• Remarks: In areas with tight frequency reuse, extra interference may occur if Load HO Allowed is set to Yes.

[System Flux Threshold for Load HO]

• Value Range: 0~11

• Default Value: 10

• Description: System Flux Threshold for Load HO is obtained based on message load, CPU load, and so on. The system flow level is the current flow control level of the system.

0~11:It is the system flux control level when the alarm module send out alarms information. Level 11 is the highest and level 0 is the lowest.

A load handover is allowed only when the system flow is lower than this threshold. Otherwise, unexpected situations may occur. Therefore, this parameter must be set properly.

Flow control threshold for the CPU to start to discard the channel access messages and paging messages: 80%

Flow control threshold for the CPU to discard all the channel access messages and paging messages: 100%

CPU usage smaller than 80% corresponds to level 0. CPU usage equal to or greater than CPU flow control threshold 80% corresponds to level 2.

An increase of 5% means an increase of 2 levels.

Level 10 is the highest. The level value can be 0, 2, 4, 6, 8, and 10.




Data Configuration of Cell-load-sharing

[Load HO Threshold]

Value Range: 0~100(%)

Default Value: 85

Description: When the load handover is switched on, it is recommended that the Load HO Threshold is set to 85.The cell load refers to TCH usage. When the cell load exceeds the value of Load HO Threshold, the BSC starts the load handover. That is, the BSC starts the load handover after the TCH in the cell are proportionally occupied.

Remarks: Even if the Load HO Allowed is set to Yes, the Load HO Threshold and Load Req. on Candidate Cell affect the queuing of the candidate cell handover. Therefore, when the cell is overloaded, the handovers such as PBGT cannot be performed if this parameter is not properly set.

[Load Req. on Candidate Cell]

Value Range: 0~100(%)

Default Value: 75

Description: If the cell load is lower than the value of this parameter, the cell accepts users that are handed over to the cell due to their cell load. If the cell load is not lower than the value of this parameter, the cell refuses the users.

Remarks: The same as that of Load HO Threshold




Network Feature Adjustment12th bit and 13th bit: Whether share the same BSC or MSC.

141516 12345678910111213

serving cell?NoYes

Both 12th and 13th set to 0

12th set to 113th set to 0

Is [Co-BSC/MSC Adj] (s)yes?

Yes

No

Co-BSC?

Co-MSC?

No

Yes


No

Yes

Turn off 12th &13th bit


12th bit: if neighbor cell is co-BSC with the serving cell, 12th bit is set to 0. Otherwise, set to 1

13th bit: if neighbor cell is co-MSC with the serving cell, 13th bit is set to 0. Otherwise, set to 1

Service cell: is always set to 0

These two bits will be turned off when Co-BSC/MSC Adj. is set to NO




Data Configuration of Co-BSC&MSC

[Co-BSC/MSC Adj]



•Description: This parameter indicates whether the sequence of candidate cells is adjusted. After the sequence is adjusted, the handover within the same BSC/MSC takes priority.




The 14th bit: [Inter-layer HO Threshold/Hysteresis] adjustment bit.


141516 12345678910111213

The 15th/16th bits are reserved

Yes

serving cell?

set to 0

NoYes

Bit 14th set to 1, and bit 5th ~13th are turned off

set to 0

Yes

RX_LEV_DL >= [Inter-layer HO Threshold](s) – [Inter-layer HO Hysteresis](s)?

RX_LEV_DL >= [Inter-layer HO Threshold](n) + [Inter-layer HO Hysteresis](s->n)?

No No

The 14th bit: Layer HO threshold adjustment bit

Serving cell: RX_LEV_DL >= Inter-layer HO Threshold – Inter-layer HO Hysteresis, bit 14th is set to 0

Neighboring cell: RX_LEV_DL >= Inter-layer HO Threshold + Inter-layer HO Hysteresis, bit 14th is set to 0.

If the above criterion is not met, then bit 14th is set to 1. At the same time, bit 5th- 13th bits are turned off.

The 15th/16th bits are reserved




Data Configuration of Layer HO Threshold Adjustment

[Inter-layer HO Threshold]

•Value Range: 0~63(-110 dBm to -47 dBm)


•Description: In BSC handover algorithm, the M criterion is used to rank the handover candidate cells. The M criterion includes 16 bits. This parameter is one bit of the 16 bits and it affects the rank of a candidate cell. When the downlink level of a cell is lower than this threshold, the cell takes low priority as far as comprehensive sequence is concerned.

•Remarks: Make sure that the receive level of the destination cell is higher than this threshold in inter-layer handover or load handover. Otherwise, the MS may be handedfrom a cell with heavy load and high level (high priority cell) to a cell with light load and low level (low priority cell), thus leading to call drops.

[Inter-layer HO Hysteresis]


•Unit: dB

•Default Value: 3

•Description: This parameter indicates the hysteresis of an inter-layer or inter-priority handover. It is used to avoid inter-layer ping-pong handovers. Actual Inter-layer HO Threshold of a serving cell = Inter-layer HO Threshold C Inter-layer HO hysteresis Actual Inter-layer HO Threshold of a neighboring cell = Inter-layer HO Threshold + Inter-layer HO hysteresis




General HO Process




MR. Preprocessing2

Handover Judgment3


TA HO

Interference HO

Rx_Level_Drop HO

Bad Quality HO

Load HO

Edge HO

Layer HO

PBGT HO

AMR HO

No DL MR HO

Concentric Cell HO

MS Fast Moving HO


Penalty Processing

Ranking Processing

OM Forced HO

Direct Retry

Emergency HO

Normal HO




No DL MR HO

Serving Cell Neighboring Cell

When the quality of Um interface become worse and worse, it is for

the worse uplink quality that MS can not deliver downlink MR, while

the downlink quality is not bad enough for MS to receive the

downlink message normally.

Baduplink quality

When the quality of Um interface become worse and worse, it is for the worse uplink quality that MS can not deliver downlink MR, while the downlink quality is not bad enough for MS to receive the downlink message normally. Under this kind of urgency condition, in order to save this call, the network send handover command to MS.




Position of No DL MR HO



Measure and Measurement Result Report

1

MR. Preprocessing2

Handover Judgment3


TA HO

Interference HO

Rx_Level_Drop HO

Bad Quality HO

Load HO

Edge HO

Layer HO

PBGT HO

AMR HO

Concentric Cell HO

MS Fast Moving HO


Penalty Processing

Ranking Processing

OM Forced HO

Direct Retry

Emergency HO

Normal HO

No DL MR HO

Attention: After MR. Preprocessing, the No DL MR handover is triggered if trigger condition is satisfied.




No DL MR HO

Begin

Report 1 DL MR at least?

[No Dl Mr. HO Allowed](s) Yes ?

<=[Cons.No Dl Mr.Ho Allowed Limit](s)?

serving cell?Select the candidate cell with the highest priority,

exluding serving cell

Trigger No DL Mr. HO

No

End

No

No

Yes

No

Yes

signal quality filter length:For TCH:[Filter Length for TCH Qual]For SDCCH:[Filter Length for SDCCH Qual]

No Dl Mr. in current Mr.?

Yes

UL_Qua. (after filtering)>=[No Dl Mr.Ul Qual

HO Limit](s)?

Yes

Only one cadidate cell?

Within Penalty Time

Yes

No

No

Yes

Yes

Yes

No

[Intracell HO Allowed](s)?

Yes

No

No

Triggering condition

No DL information in current MR

Stored UL Rx_Qual Value Number >= Filter Length for TCH/SDCCH Qual

UL Rx_Qual >= No DL MR HO UL Rx_Qual Threshold

Number of Lost DL MR < Cons. No DL MR HO Allowed Limit

Object cell selection

Prefer neighboring cell

If choose the service cell, it cannot in the penalty time for intra-cell handover.




Data Configuration of No DL MR HO

[No Dl Mr. HO Allowed]



•Description: This parameter is used to control the handover algorithm without downlink measurement report. If this parameter is set to 0, the no handover algorithm without downlink measurement report is disabled. Therefore, handover decision without downlink measurement report is not allowed in this cell. If this parameter is set to 1, the no downlink measurement report handover algorithm is enabled. Therefore, handover decision without downlink measurement report is allowed in this cell.

[No Dl Mr. Ul Qual HO Limit]

•Value Range: 0~70 (mapping to RQ (0~7)×10)


•Description: This parameter indicates the uplink receive quality threshold of triggering an emergency handover when no measurement result on downlink channels is contained in the MR. The emergency handover is allowed only when the filtered uplink receive quality crossed this threshold. When an emergency handover is triggered, inter-cell handover takes priority. Intra-cell handover, however, is triggered if no candidate cell is available and intra-cell handovers are allowed.

[Cons. No Dl Mr. HO Allowed Limit]


•Default Value: 8

•Description: This parameter indicates the upper threshold of consecutive MRs containing no downlink measurement result for a call. Each call is configured with a global timer, which counts the number of consecutive MRs containing no downlink measurement. When the timer exceeds thisthreshold, the handover is disabled and the timer is reset.




TA(Time Advance) HO


[TA Threshold](s)

Time

TA(s)

HandoverTriggering

[TA Threshold](n)

or

Handover Triggering ZoneTA(n)

Because a MS is far away from its serving BTS, the practice TA value is more than TA threshold configured in data configuration, TA handover is triggered.




TA(Time Advance) HO

TriggerTA handover

Begin

The actual TA >=[TA Threshold](s)?

[TA HO Allowed] Yes ?

Any neighbour cell exist?

serving cell?

Select the cell with the highest priority in the

cadidate cell list

Suitable cell exist?

Yes

No

End

No

No

YesYes

No

No

Yes

Yes

Yes

No

[TA Threshold](n,in the same BTS) <= [TA Threshold](s)


The actual TA >= TA Threshold


The cell must be of the highest priority in the candidate cell sequence and meet the following restrictions.

Restriction

The service cell cannot be the object cell.

HO is not allowed when TA Threshold of the neighboring cell with the same BTS is equal or smaller than that of the service cell.




Data Configuration of TA HO

[TA HO Allowed]



•Description: The parameter indicates whether a Timing Advance (TA) handover is allowed. A TA handover is triggered when the TA is higher than the triggering threshold. TA is calculated based on the distance between the MS and the BTS. The longer the distance is, the greater the TA is.

[TA Threshold]


•Unit: Bit period (A bit period corresponds to 0.55 km.)


•Description: This parameter indicates the TA threshold of triggering emergency handover. Emergency handover is triggered when TA is equal to or greater than this threshold.




Interference Handover

Lev_Thr

Rx_Qual

RX_Lev

Qual_Thr

InterferenceOrigin


Handover Triggering Zone

For a MS or a BTS, when the receiving quality is lower than the interference quality threshold and receiving level is higher than the interference level threshold, it is considered that interference exists in serving cell, so interference handover is triggered.




Interference HOBegin

UL or DL receiving

Quality(s)>=A?

[Interference HO Allowed] Yes ?


serving cell?


cadidate cell list

Rx_Level(n)>= [Inter-layer HO Threshold](n) +

[Inter-layer HO Hysteresis](s->n)?

Yes

No

End

No

No

Yes No

NoYes

None AMR FR: A = RXQUALn, 1<=n<=12 AMR FR:A = RXQUAL1, n=1; A = RXQUALn + RXLEVoff, 2<=n<=12

[Intracell HO Allowed](s) yes& cell not punished?

Any suitable cell exist?

Trigger interference handover

No

Yes

Yes

Yes

Yes

No


UL/DL receiving quality>=A

None AMR FR

A = RXQUALn, 1<=n<=12

AMR FR

A = RXQUAL1, n=1; A = RXQUALn + RXLEVoff, 2<=n<=12


The cells must be of the highest priority in the candidate cell sequence and meet the following restrictions.

Restriction

The service cell that is not in the penalty time for intra-cell handover.

The neighboring cell with the receiving level higher than the inter layer HO Thrsh + Hysteresis.For none AMR FR, if one of the following conditions is met, the system will judge that interference occur:

1. Rx_lev <= 30, and Rx_qual > RXQUAL 1

2. Rx_lev = 31, and Rx_qual > RXQUAL 2

3. Rx_lev is within [32,35], and Rx_qual > RXQUAL3

4. Rx_lev is within [36,38], and Rx_qual >RXQUAL 4








12. Rx_lev >= 63, and Rx_qual > RXQUAL12




Data Configuration of Interference HO

50>=63RXQUAL12

5159~62RXQUAL11

5256~58RXQUAL10

5353~55RXQUAL9

5449~52RXQUAL8

5546~48RXQUAL7

5642~45RXQUAL6

5739~41RXQUAL5

5836~38RXQUAL4

5932~35RXQUAL3

60=31RXQUAL2

70<=30RXQUAL1

Receiving QualityReceiving Level(-110dBm)Parameter

Default Value




Data Configuration of Interference HO

[Interference HO Allowed]



•Description: The parameter indicates whether an interference handover is allowed. An interference handover is triggered when the receive level is higher than the receive threshold, but the transmission quality is lower than the handover triggering threshold.

•Remarks: Both downlink and uplink interference is judged, and inter-cell handover takes priority. If no target cell is available, intra-cell interference handover can be implemented in the serving cell if intra-cell handovers are allowed.

[RXQUAL1] ~ [RXQUAL12]


•Description: Quality threshold 1~12 for the interference handover of nonCAMR FR voice services. The value corresponds to (quality level 0~7) x 10.See the next slide

[RXLEVOff]


•Default Value: 5

•Description: The quality level offset of the interface handover of the AMR FR service relative to non-AMR services or the AMR HR service (x 10).




Rx_Level_Drop HO

Rx_Level_Drop HO will be triggered when receiving level drops fast because of barrier such as high building.




Rx_Level_Drop HOBegin

Satisfy the Formula& The latest RX_LEV_UL(s) <

[Edge HO UL RX_LEV Threshold](s)?

[Rx_Level_Drop HO Allowed] Yes ?


serving cell?


cadidate cell list

Yes

No

End

No

No

Yes

NoYes

Formula:

Is priority higher than serving cell?

Trigger Rx_Level_Drop handover

Yes

Yes

( ) ( ) ( ) ( )( ) ( ) ( ) ( ) BXAXAXAXA

XAXAXAXA−<−+−+−+−

+−+−+−+−

88776655

44332211

1010101010101010

End No


The lastest RX_LEV_UL < Edge HO UL RX_LEV Threshold

C1（nt）=(A1-10)X1＋(A2-10)X2+(A3-10)X3＋…＋(A8-10)X8<－B


The neighboring cell with the highest priority and whose priority is higher than that of the service cell in the candidate cell group.

Restriction

The service cell cannot be the object cell.

Filter Parameter A1–A8 and Filter Parameter B work together to decide whether the rapid drop of the receive level must be reflected in one or multiple MRs.

The conditions to trigger a rapid level dropping handover are as follows;

C1（nt）=(A1-10)X1＋(A2-10)X2+(A3-10)X3＋…＋(A8-10)X8，

In the algorithm above, X1, X2, X3, X4, X5, X6, X7, and X8 indicate the uplink receive levels of the last eight MRs in the queue.

Filter Parameter A1–A8 must meet the following conditions: A1+A2+A3+A4+A5+A6+A7+A8=80

For example, if you want to reflect the rapid drop of the cell level in a MR, you can set A3–A8 equal to 10, A1 to 0, and A2 to 20.




Data Configuration of Rx_Level_Drop HO

[Rx_Level_Drop HO Allowed]

•Value Range: Yes, No Default Value: No

•Description: The parameter indicates whether the emergency handover algorithm is allowed. The emergency handover algorithm is used to prevent call drops when the receive level of the MS drops rapidly. Generally this algorithm is not enabled until the conditions are met. To enable this algorithm, original MR is required for the BSC.

[Filter Parameter A1~A8]


•Description: Filter Parameter A1~A8 and Filter Parameter B work together to decide whether the rapid drop of the receive level must be reflected in one or multiple MRs. The conditions to trigger a rapid level dropping handover are as follows; In the algorithm above, X1, X2, X3, X4, X5, X6, X7, and X8 indicate the uplink receive levels of the last eight MRs in the queue. Filter Parameter A1~A8 must meet the following conditions: A1+A2+A3+A4+A5+A6+A7+A8=80. For example, if you want to reflect the rapid drop of the cell level in a MR, you can set A3-A8 to greater than 10, A1 to 0, and A2 to 20.

[Filter Parameter B]


•Description: This is one of the parameters that determine whether a handover is required due to fast dropping levels.Thisparameter indicates the drop trend of the receive level within a period. The greater the parameter B is, a more rapid level drop is required for triggering a rapid level dropping handover.See Filter Parameter A1-A8.

[Edge HO UL RX_LEV Threshold]


•Description: The parameter indicates the uplink receive level threshold of an edge handover. An edge handover will be triggered if the uplink receive level is constantly lower than "Edge HO UL RX_LEV Thrsh." for a period longer than Edge HO Valid Time(s) within Edge HO Watch Time(s). If PBGT handover is enabled, the corresponding edge handover threshold can be lowered. If PBGT handover is disabled, this parameter must be properly specified to avoid overlapping coverage and channel interference. This parameter should be adjusted based on the performance statistics and actual networks to achieve uplink-downlink balance.

•Remarks: Edge handover uplink/downlink receive level threshold < Uplink/downlink signal strength lower limit of HUAWEI II power control




BQ(Bad Quality) HO

Begin

Is [BQ HO Allowed] Yes ?


serving cell?


cadidate cell list

Yes

No

End

No

No

Yes

NoYes

Yes

UL_Rx_Q(s)>=[UL Qual. Threshold](s) or DL_Rx_Q(s)>=[DL Qual. Threshold](s)?

RX_LEV_DL (n) > RX_LEV_DL (s) + Inter-cell HO hysteresis(s->n)

-BQ HO Margin(s->n) ?

[Intracell HO Allowed](s) yes& cell not punished?


Trigger BQ handover

Yes

Yes

Yes

No

No

No

When the receiving level of a MS or a BTS is lower than the quality threshold, bad quality handover will be triggered.


UL receiving quality >= UL Qual. Threshold

OR DL receiving quality >= DL Qual. Threshold

For AMR call, the quality threshold is DL/UL Qual. Limit AMR FR/HR


The cells must be of the highest priority in the candidate cell sequence and meet the following restrictions.

Restriction

Prefer neighboring cell. If the number of neighboring cell is more than one, it is required that RX_LEV_DL (n) > RX_LEV_DL (s) + Inter-cell HO hysteresis - BQ HO Zone

If there is no neighboring cell, handover can occur to the service cell, and the channel at different frequency band, different MA, different TRX or different channel (from left to right) is preference.




Data Configuration of BQ HO

[BQ HO Allowed]



•Description: The parameter indicates whether a Bad Quality (BQ) handover is allowed. BQ handover is triggered when Bit Error Ratio (BER) over uplink/downlink channels is higher than the triggering threshold. If BER rises, or signal strength drops, suspect that the signal power is low or channel interference increases.

•Remarks: Inter-cell BQ handover is preferentially performed. If no target cell is available, intra-cell BQ handover can be implemented in the serving cell if intra-cell handovers are allowed.

[DL Qual. Threshold]

•Value Range: 0~70 (RQ (0~7) 10)


•Description: This parameter indicates the downlink receive quality threshold of triggering an emergency handover. When the receive quality of the downlink is greater than DL Qual Threshold, an emergency handover is triggered. When frequency hopping or DTX of the cell is enabled, it is recommended that you set this parameter to 70. When an emergency handover is triggered, inter-cell handover takes priority. An intra-cell handover, however, is triggered if no candidate cell is available and intra-cell handovers are allowed.

[UL Qual. Threshold]

•Value Range: 0~70 (RQ (0~7)10)


•Description: This parameter indicates the uplink receive quality threshold of triggering an emergency handover. When the receive quality of the uplink is greater than UL Qual Threshold, an emergency handover is triggered due to bad quality. When frequency hopping or DTX of the cell is enabled, it is recommended that you set this parameter to 70.When an emergency handover is triggered, inter-cell handover takes priority. An intra-cell handover, however, is triggered if no candidate cell is available and intra-cell handovers are allowed.





[DL/UL QuaLimitAMRFR]



•Description: This parameter indicates the urgent switchover downlink/uplink quality control for the AMR FR service. The values of this parameter match quality levels 0-7 multiplying 10. The urgent switchover is triggered only when the downlink/uplink receiving quality of the MS is greater than the switchover threshold, that is, the receiving quality is poor.

[DL/UL QuaLimitAMRHR]



•Description: This parameter indicates the urgent switchover downlink quality control for the AMR HR service. The values of this parameter match quality levels 0-7 multiplying 10. The urgent switchover is triggered only when the downlink receiving quality of the MS is greater than the switchover threshold, that is, the receiving quality is poor.





[BQ HO Margin]

•Value Range: 0~127 (-64 dB to +63 dB)


•Description: A Margin in BQ handover algorithm used to judge whether to perform BQ handover. When BQ Handover Allowed is set to Yes and Inter-cell HO Hysteresis > "Inter-cell HO Hysteresis-BQ HO Margin", the Inter-cell HO Hysteresis will act instead of the BQ HO Margin. When "Inter-cell HO Hysteresis-BQ HO Margin" is assigned with a value smaller than 64, MS can hand over to a lower level neighboring cell. 69 for popular urban areas, 72 for suburbs.

•Remarks: If the data is updated from M900/M1800 BSC to HUAWEI BSC6000,the default value of this parameter is 5.Then it's necessary to modify the value of this parameter to 69,otherwise the BQ HO algorithm will be invalid.




General HO Process




MR. Preprocessing2

Handover Judgment3


TA HO

Interference HO

Rx_Level_Drop HO

Bad Quality HO

Load HO

Edge HO

Layer HO

PBGT HO

AMR HO

No DL MR HO

Concentric Cell HO

MS Fast Moving HO


Penalty Processing

Ranking Processing

OM Forced HO

Direct Retry

Emergency HO

Normal HO





Two single band cells which are configured as bi-directional neighbor

cell relationship can be configured as enhanced dual band cell to each

other.

Purpose

During the procedure of channel assignment and handover, the

two single band cells can share their resource.

Assign the channel with low load in UL to MS preferentially.

Make MS handover from the high load cell to the low load cell.




Channel Assignment of Enhanced Dual Band

RX_LEV_OL>= [Incoming OL Subcell HO level Threshold(dB)](o) andRX_LEV_UL – RX_LEV (n) >[Distance Between Boundaries of UL and OL Subcells(dB)] Attention:RX_LEV (n): RX_LEV of the strongest neighboring cell which has the same frequency band and layer with underlaid subcell, but locates in a different BTS. If there is no such a cell, this value is -110dBmIf [ATCBHoSwitch] is [Close], the second condition is turn off.

A:

TCH assignment (SDCCH channel in UL)Begin

from UL

[Assignment Optimization of UL Subcell Allowed

or not] (u) ?

Cell load of UL >[UL Subcell General

Overload Threshold(%)](u)?

Yes

AYes

No

Any idle TCH Available in OL?

Assign TCHin OL

Yes

No

Yes

Assign TCH in ULor direct retry identification

or queuing

No

No

TCH assignment (SDCCH channel in underlaid)

If Assignment Optimization of UL Subcell Allowed or not is set to NO, assign TCH in underlaid as the normal assignment procedure

If Assignment Optimization of UL Subcell Allowed or not is set to YES, assign TCH in overlaid when the following conditions are met

Cell load of underlaid > UL Subcell General Overload Threshold

RX_LEV_OL >= Incoming OL Subcell HO level Threshold

RX_LEV_UL – RX_LEV (n) > Distance Between Boundaries of UL and OL Subcells－Distance Hysteresis Between Boundaries of UL and OL Subcell(dB)

RX_LEV (n): RX_LEV of the strongest neighboring cell which has the same frequency band and layer with underlaid subcell, but locates in a different BTS. If there is no such a cell, this value is -110dBm




Data Configuration of Channel Assignment

[ATCBHoSwitch]

•Value Range: Close, Open

•Default Value: Open

Description: The switch of the ATCB handover algorithm.

[Assignment Optimization of UL Subcell Allowered Or Not]



•Description: This parameter indicates whether the access request originated in the underlaidsubcell is preferably assigned between overlaid subcell cell and underlaid subcell cell according to the Out Cell Low Load Thred.

[UL Subcell General OverLoad Threshold(%)]


•Unit: %


•Description: If the ratio of underlaid subcell channel occupancy is greater than the value of this parameter, some calls in the underlaid subcell are handed over to the overlaid subcell. Moreover, calls originated in the underlaid subcell are preferably assigned to the channel in overlaid subcell.





[Distance Between boundaries of UL And OL Subcells(dB)]

•Value Range:0~63

•Unit: dB


•Description: This parameter indicates the distance between the overlaid subcell and underlaid subcell. The value of this parameter is comparative. The greater the value is, the longer the distance is. The enhanced dual-band network handover algorithm refers to the boundary between underlaid subcell and overlaid subcell based on the comparative value of signal strength of serving cell and neighboring cell. Suppose the signal strength of serving cell is SS(s), and neighboring cell SS(n). If SS(s) is equal to SS(n), the cell is in the underlaid subcell boundary. If the value of SS(s) - SS(n) is larger than the value of ”Distance Between boundaries of UL And OL Subcells(dB)”, the cell is in the overlaid subcell.

[Incming OL Subcell HO Level Threshold(dB)]


•Unit: dB


•Description: This parameter indicates the lowest threshold of overlaid subcell level of the handover from underlaid subcell to overlaid subcell. When the MS receive level is higher than the value of this parameter, the BSC allows the handover of overlaid subcell cell.




Begin from OL

[Assignment Optimization of OL Subcell Allowed or

not ](o) No ?

Cell load of UL< [UL Subcell LowerLoad Threshold](u)?

Yes

Yes

No

Assign TCHin UL

Any idle TCH Available in UL?

Assign TCHin UL

Any idle TCH Available in OL?

Assign TCHin OL

Yes No

Yes

Assign TCH in OLor direct retry identification

or queuing

No

No

TCH assignment (SDCCH channel in OL)

Channel Assignment of Enhanced Dual Band

TCH assignment (SDCCH channel in overlaid)

If Assignment Optimization of OL Subcell Allowed or not is set to NO, assign TCH in overlaid as the normal assignment procedure

If Assignment Optimization of OL Subcell Allowed or not is set to YES

Assign TCH in underlaid, if cell load of underlaid < UL Subcell Lower Load Threshold

Assign TCH in overlaid, if cell load of underlaid >= UL Subcell Lower Load Threshold





[UL Subcell Lower Load Threshold(%)]


•Unit: %


•Description: If the underlaid subcell channel occupancy ratio is smaller than the value of this parameter, some calls of the overlaid subcell is handed over to the underlaid subcell. Moreover, the MS that requests for the overlaid subcell channel is preferably assigned to the underlaid subcellchannel.

[Assignment Optimization of OL Subcell Allowered Or Not]



•Description: This parameter indicates whether the channel request in the overlaid subcell is preferably assigned between overlaid subcell and underlaid subcell according to the Out Cell Low Load Thred.





Classification of TCH HO in enhanced dual band HO

OL to UL for low load in UL

UL to OL for high load in UL

OL to UL for moving

There are three kinds of handover for enhanced dual band network:

•UL to OL for high load in UL

•OL to UL for moving

•OL to UL for low load in UL




Enhanced Dual Band HO(U O )

Triggering condition for TCH Load HO from UL to OL for high load in UL

The order of handover is from the MS who is near the OL to the MS who is far away from OL.




Enhanced Dual Band HO(U O )Triggering condition for TCH Load HO from UL to OL for high load in UL

RX_LEV_OL >= [Incoming OL Subcell HO level Threshold(dB)] (o)andRX_LEV_UL – RX_LEV (n) > [Distance Between Boundaries of UL and OL Subcells(dB)]A:

Cell load of UL>=[UL SubcellSerious Overload Threshold(%)](u)?

Begin [Load HO From UL Subcell

to OL Subcell Allowed](u) Yes ?

Cell load of UL>=[UL SubcellGeneral Overload Threshold(%)](u)?

No

A & Satisfy P/N &not within penalty time?

Trigger UL to OL

Yes No

Adjust HO zone basing on HO step and HO period

Refresh cell load per second

BB-C

Yes

Any MS in HO zone?

Yes

No

No

Yes

Yes No

End

Cell load of OL>=[Inner Cell Serious Overload

Threshold(%)](o)?Yes

No

B=[UL Subcell Load Hierarchical HO Period(s)]

C=[Modified Step Length of UL Load HO Period(s)]

HO step: [Step Length of UL Subcell Load HO(dB)]

HO zone: [Incoming OL Subcell HO level Threshold(dB)]~-47dBm

HO Period: [UL Subcell Load Hierarchical HO Period(s)]

Triggering condition for TCH Load HO from underlaid to overlaid

Load HO of UL Subcell to OL Subcell Enable is YES

Cell load of underlaid > UL Subcell General Overload Threshold

RX_LEV_OL >= Incoming OL Subcell HO level Threshold

RX_LEV_UL – RX_LEV (n) > Distance Between Boundaries of UL and OL Subcells(dB)

Satisfying P/N rule

HO zone is from Incoming OL Subcell HO level Threshold to -47dBmAttention:

RX_LEV (n): RX_LEV of the strongest neighboring cell which has the same frequency band and layer with underlaidsubcell, but locates in a different BTS. If there is no such a cell, this value is -110dBm




Data Configuration of Enhanced Dual Band HO(U O )

[UL Subcell General OverLoad Threshold(%)]


•Unit: %


•Description: If the ratio of underlaid subcell channel occupancy is greater than the value of this parameter, some calls in the underlaid subcell are handed over to the overlaid subcell. Moreover, calls originated in the underlaid subcell are preferably assigned to the channel in overlaid subcell.

[UL Subcell Serious OverLoad Threshold(%)]


•Unit: %


•Description: If the ratio of the underlaid cell channel occupancy is greater than the value of this parameter, the period of handover from underlaid subcell to overlaid subcell is reduced by the value of Out Cell Load HO Modify Step every second based on the value of Out Cell Load Classification HO Period. Thus the handover from underlaid subcell to the overlaid subcell speeds up.

[Load HO From UL Subcell to OL Subcell Allowed]



•Description: When the ratio of underlaid subcell channel occupancy is high, whether some calls in the overlaid subcellare allowed to be handed over to the overlaid subcell.

[Incming OL Subcell HO Level Threshold(dB)]


•Unit: dB


•Description: This parameter indicates the lowest threshold of overlaid subcell level of the handover from underlaidsubcell to overlaid subcell. When the MS receive level is higher than the value of this parameter, the BSC allows the handover of overlaid subcell cell.




Data Configuration of Enhanced Dual Band HO(U O )

[UL Subcell Load Hierarchical HO Period(s)]

• Value Range: 1~255 Unit: Seconds Default Value: 5

• Description: This parameter indicates the period of the hierarchical handover from underlaid subcell to overlaid subcell. When the ratio of underlaid subcell cell channel occupancy is greater than the value of En Iuo Out Cell General OverLoad Thred, all the calls in the cell request for handover at the same time. The BSC load is sharply increased. Thus the call may drop because the target cell is congested. Therefore the algorithm of hierarchical handover is applied to hand over the calls in the cell hierarchically to the overlaid subcell.Thisparameter indicates the time duration of every hierarchical handover.

[Step Length of UL Subcell Load HO(dB)]

• Value Range: 0~63 Unit: dB Default Value: 5

• Description: This parameter indicates the level step of the hierarchical handover from underlaid subcell to overlaid subcell.

[Modified Step Lenghth of UL Load HO Period(s)]


• Description: If underlaid subcell load is higher than the value of Out Cell Serious OverLoad Thred, the period of handover from underlaid subcell cell to overlaid subcell cell is shortened by the value of Out Cell Serious OverLoad Thred every second based on the value of the Out Cell Load classification HO Period.

[Total Number of ]


• Description: P/N criterion: In P measurement reports, N measurement results meet handover requirements. Handover is started. This parameter indicates the P in P/N criterion.

[Satisfy Condition Time]


• Description: P/N criterion: In P measurement reports, N measurement results meet handover requirements. Handover is started. This parameter indicates the N in P/N criterion.




Enhanced Dual Band HO(O U )Triggering condition for TCH HO from OL to UL for moving

RX_LEV_OL <[Outgoing OL Subcell HO level Threshold(dB)](o) orRX_LEV_UL – RX_LEV (n) < [Distance Between Boundaries of UL and OL Subcells(dB)] –

[Distance Hysteresis Between Boundaries of UL and OL Subcells(dB)]

A:

Satisfy P/N?

Begin

A

Yes

End

Trigger OL to UL

Yes

Select Neighbor cellwith the highest priority

No

Yes

No

[Inner Cell Edge HO Enable] (o)Yes ?

RX_LEV_OL < RX_LEV_UL

Yes

No

No

Triggering condition for TCH Moving HO from overlaid to underlaid

RX_LEV_OL < Outgoing OL Subcell HO level Threshold

OR RX_LEV_UL – RX_LEV (n) < Distance Between Boundaries of UL and OL Subcells(dB) - Distance Hysteresis Between Boundaries of UL and OL Subcells(dB)

Satisfying P/N rule


The cell with highest priority. It could be underlaid subcell or normal neighboring cell

Attention:

RX_LEV (n): RX_LEV of the strongest neighboring cell which has the same frequency band and layer with underlaidsubcell, but locates in a different BTS. If there is no such a cell, this value is -110dBm




Data Configuration of Enhanced Dual Band HO(O U )

[Distance Between boundaries of UL And OL Subcells(dB)]

•Value Range:0~63 Unit: dB Default Value: 10

•Description: This parameter indicates the distance between the overlaid subcell and underlaid subcell. The value of this parameter is comparative. The greater the value is, the longer the distance is. The enhanced dual-band network handover algorithm refers to the boundary between underlaid subcell and overlaid subcell based on the comparative value of signal strength of serving cell and neighboring cell. Suppose the signal strength of serving cell is SS(s), and neighboring cell SS(n). If SS(s) is equal to SS(n), the cell is in the underlaid subcell boundary. If the value of SS(s) - SS(n) is larger than the value of ”Distance Between boundaries of UL And OL Subcells(dB)”, the cell is in the overlaid subcell.

[Distance Hysterisis Between Boundaries of UL And OL Subcell(dB)]


•Description: To prevent ping-pong handover, the BSC determines whether the handover of the MS from overlaid subcell cell to underlaid subcell cell based on the value of this parameter. Suppose the signal strength of serving cell is SS(s), and neighboring cell SS(n). If the value of SS(s) - SS(n) is smaller than the value of Distance Between Out And Inn Cell boundary - Distance Hyst Between Out And Inn Cell boundary, the MS handover from overlaid subcell cell to underlaid subcell cell is allowed.

[Outgoing OL Subcell HO level Threshold(dB)]


•Description: This parameter indicates the lowest threshold of overlaid subcell level of the handover from overlaid subcell to underlaid subcell. When the MS receive level is lower than the value of this parameter, the BSC allows the handover from overlaid subcell cell to underlaid subcell.

[Total Number of ]


•Description: P/N criterion: In P measurement reports, N measurement results meet handover requirements. Handover is started. This parameter indicates the P in P/N criterion.

[Satisfy Condition Time]


•Description: P/N criterion: In P measurement reports, N measurement results meet handover requirements. Handover is started. This parameter indicates the N in P/N criterion.




Enhanced Dual Band HO(O U )

Triggering condition for TCH Load HO from OL to UL for low load in UL

The order of handover is from the MS who is near the UL to the MS who is far away from UL.




Enhanced Dual Band HO(O U )Triggering condition for TCH Load HO from OL to UL for low load in UL

HO zone: [Outgoing OL Subcell HO Level Threshold(dB)](o) ~ -47dBmHO step: [Step Length of OL Subcell Load HO(dB)](o)A: RX_LEV_UL >= Inter-layer HO Threshold(u) + Inter-layer HO Hysteresis(o->u)

Begin

[Load HO of OL Subcellto UL Subcell Enable](o) Yes ?

Cell load of UL <[UL SubcellLower Load Threshold(%)](u)?

Yes

NoEnd

Satisfy P/N?

Yes

No


The object cell must be the underlaid subcell

and satisfy condition A

Any MS in HO zone?

Yes

Trigger OL to UL

No

Yes

No


Triggering condition for TCH Load HO from overlaid to underlaid

Load HO of OL Subcell to UL Subcell Enable is YES

Cell load of underlaid < UL Subcell Lower Overload Threshold

Satisfying P/N rule

HO zone is from Outgoing OL Subcell HO level Threshold to -47dBm



RX_LEV_UL >= Inter-layer HO Threshold + Inter-layer HO Hysteresis




Data Configuration of Enhanced Dual Band HO(O U )

[Out Cell Low Load Thred]

•Value Range: 0~100 Unit: % Default Value: 50

•Description: If the underlaid subcell channel occupancy ratio is smaller than the value of this parameter, some calls of the overlaid subcell is handed over to the underlaid subcell. Moreover, the MS that requests for the overlaid subcell channel is preferably assigned to the underlaid subcell.

[Load HO of OL Subcell to UL Subcell Enable]


•Description: This parameter indicates whether the load handover from overlaid subcell to underlaidsubcell is allowed.

[OL Subcell Load Diversity HO Period(s)]

•Value Range: 1~255 Unit: Seconds Default Value:10

•Description: This parameter indicates the period of the hierarchical handover from underlaidsubcell to overlaid subcell.When the ratio of overlaid subcell cell channel occupancy is greater than the value of En Iuo Out Cell General OverLoad Thred, all the calls in the cell request for handover at the same time. The BSC load is sharply increased. Thus the call may drop because the target cell is congested. Therefore the algorithm of hierarchical handover is applied to hand over the calls in the cell hierarchically to the underlaid subcell.This parameter indicates the time duration of every hierarchical handover.

[Step Length of OL Subcell Load HO(dB)]


•Description: This parameter indicates the level step of the load handover from overlaid subcell to underlaid subcell.




General HO Process




MR. Preprocessing2

Handover Judgment3


TA HO

Interference HO

Rx_Level_Drop HO

Bad Quality HO

Load HO

Edge HO

Layer HO

PBGT HO

AMR HO

No DL MR HO

Concentric Cell HO

MS Fast Moving HO


Penalty Processing

Ranking Processing

OM Forced HO

Direct Retry

Emergency HO

Normal HO




Load HOHandover triggering zone

[Load HO Threshold]

Time

Load of Serving Cell

[Load Req. on Candidate Cell]

Load of Neighboring Cell

Congested CellCongested Cell

Congested CellNormal Cell

Normal CellNormal Cell

Normal Cell




Load HO

As load HO may trigger several HOs, we need to consider the

CPU load (system flow level) before triggering it. In addition,

load HO is executed step by step, that is, the edge HO thrsh.

raises according to certain step and period and will stop when

out of the Load HO Zone.

A handover band is defined in load handover, in the range of edge handover threshold ~ edge handover threshold + load handover bandwidth. The handover band itself is divided into multiple equalized handover step sizes, MS (falling within edge handover threshold + N*handover step sizes) are handover to adjacent cells one by one from low to high. Once load of the serving cell decreases (as lower than the load handover start threshold) or load of the adjacent cell increases to a certain extent (as higher than the load handover received threshold), the handover stops.

Load handover is an emergency measure, which mainly applicable to abnormal traffic peak in part of the radio network. It should not be used as the major means to solve the traffic congestion problem. If load handover always occurs to some area of a network, TRX re-configuration and network topology re-design is the right way.

Related parameters: Handover - [Load handover table]

System flux Thrsh. for load HO

Load HO Thrsh.

Load HO Req. on candidate cell

Load handover bandwidth (dB)

Load HO step level (dB)

Load HO step period (second)




Load HO

Congested Cell

Normal Cell

Normal Cell

Normal Cell

The handover bandwidth is gradually wider and wider.




Load HO Begin

[Load HO Allowed] (s)Yes ?

BSC internal cell?

Select the cell with the highest priority in the cadidate cell list

End

No

No

Yes

NoYes

Yes

Current system flux<=[System Flux Threshold

for Load HO](s)?

C & D


Trigger load handover

Yes

Yes

Yes

End No

Load of service cell >= [Load HO Threshold](s)?

Yes

No

Yes

Load HO timer T overflow?

Yes

StepPeriod

T×+ )1( [Load HO Bandwidth](s)

B

Yes

serving cell?

No

No

B: [Edge HO_DL_RX_LEV Threshod](s)<DL_RX_Lev(s) < [Edge HO_DL_RX_LEV Threshod](s)+A

C: RX_LEV (n)>= [Inter-layer HO Threshold](n) + [Inter-layer HO Hysteresis](s->n)

D: load(n)< Load Req. on Candidate Cell(n)Step: [Load HO Step Level](s)Period: [Load HO Step Period](s)

CNo

A=

No

Yes

Load HO timer T begin?

No

No

Star timer T

PeriodStep

TAStep ×−≤≤⇒≤≤ )1Bandwidth] HO [Load(0 Bandwidth] HO [LoadA T

Yes

A=


The CPU load of system <= System Flux Threshold for Load HO

The load of service cell >= Load HO Threshold

The DL receiving level is in the load HO zones


The service cell cannot be the object cell

If the service cell is a enhanced dual band cell, the other cell in this group cannot be the object cell

The load of object cell < Load Req. on Candidate Cell (Only valid for internal neighboring cell)

RX_LEV of object cell >= Inter-layer HO Threshold + Inter-layer HO Hysteresis

Restriction

It is not available with SDCCH.




Data Configuration of Load HO

[Load HO Bandwidth]


•Unit: dB


•Description: Together with Edge HO DL RX_LEV Threshold, this parameter indicates whether a load handover is allowed. Only when the receive level of the serving cell is within the range of (Edge HO RX_LEV Threshold, Edge HO RX_LEV Threshold + Load HO bandwidth), a load handover is allowed.

[Load HO Step Period]

•Value Range:1~255

•Unit: Seconds


•Description: This parameter indicates the period required for each level of load handover. When the load of the cell is equal to or greater than the Load HO Thrsh, all connections in the cell may send handover requests simultaneously, thus leading to sudden increase of CPU load and possible call drops when the target cell is congested. Therefore, these requests are divided into steps based on the receive strength.

[Load HO Step Level]


•Unit: dB

•Default Value: 5

•Description: This parameter indicates the bandwidth of each step during level-based load handover. In a layer load handover, starting from the Downlink Edge Handover Threshold, the upper limit of the load handover band of increases by a Layer Load Handover Step every one Layer Load Handover Period. Go on like this, all calls whose receive levels are between Edge HO RX_LEV Threshold and Edge HO RX_LEV Threshold + Load HO bandwidth in the current serving cell are switched out through level by level handover.

•Remarks: This parameter must be less than Load HO Bandwidth.




General HO Process




MR. Preprocessing2

Handover Judgment3


TA HO

Interference HO

Rx_Level_Drop HO

Bad Quality HO

Load HO

Edge HO

Layer HO

PBGT HO

AMR HO

No DL MR HO

Concentric Cell HO

MS Fast Moving HO


Penalty Processing

Ranking Processing

OM Forced HO

Direct Retry

Emergency HO

Normal HO




Edge HandoverHandoverTriggering

P/N


P: Watch TimeN: Valid Time

RX_LEV Thr

Time

RX_Lev

As a MS moves to the edge of a cell, when the receiving level of MS or BTS is lower than the edge handover threshold, handover is triggered in order to look for a better serving cell.




Edge HOBegin

[Fringe HO Allowed](s) Yes ?

End

No

Yes

Yes

UL_Rx_Lev(s) < [Edge HOUL RX_LEV Threshod](s)?

Yes

Any neighbor cell?No

Refreshits timer

Yes

Satisfy P/N rule(s)?

DL_Rx_Lev(s) < [Edge HODL RX_LEV Threshod](s)?

No

Refreshits timer

Yes

Satisfy P/N rule(s)?

No

Select cell(n) whose 16 bit priority ishigher than serving cell and

whose level satifys P/N rule(n)basing on A

Trigger Edge handover

No

No

Yes

A: DL_Rx_Lev(n)>DL_Rx_Lev(s)+[Inter-cell HO Hysteresis](s->n)


The DL receiving level < Edge HO DL RX_LEV Thrsh.

OR The UL receiving level < Edge HO UL RX_LEV Thrsh.

Satisfying P/N rule



The neighboring cell with the highest priority and whose priority is higher than that of the service cell




Data Configuration of Edge HO

Should be lower than the[Outgoing OL Subcell HO Level Threshold(dB)] in

enhance dual band data table

[Edge HO UL/DL RX-LEV Threshold]<[UL/DL RX_LEV Lower

Threshold] in HWII/III power control tabel

[Fringe HO Allowed]



•Description: The parameter indicates whether a fringe handover is allowed. A fringe handover is used to prevent call drops in cell edges and initiated when the downlink level in the serving cell is lower than Edge HO DL RX_LEV Threshold or the uplink level in the serving cell is lower than Edge HO UL RX_LEV Threshold.

•Remarks: To implement fringe handover, the comprehensive sequence of the target cell must be higher than that of the serving cell.

[Edge HO UL RX_LEV Threshold]

•Value Range: 0~63 (-110 dBm to -47 dBm)

•Default Value:10

•Description: The parameter indicates the uplink receive level threshold of an edge handover. An edge handover will be triggered if the uplink receive level is constantly lower than "Edge HO UL RX_LEV Thrsh." for a period longer than Edge HO Valid Time(s) within Edge HO Watch Time(s). If PBGT handover is enabled, the corresponding edge handover threshold can be lowered. If PBGT handover is disabled, this parameter must be properly specified to avoid overlapping coverage and channel interference. This parameter should be adjusted based on the performance statistics and actual networks to achieve uplink-downlink balance.

25: urban areas without PBGT handover

20: suburbs with a single BTS

20: urban areas with PBGT handover

•Remarks: Edge handover uplink/downlink receive level threshold < Uplink/downlink signal strength lower limit of HW-II/III power control

[Edge HO DL RX_LEV Threshold]



•Description: The parameter indicates the downlink receive level threshold of an edge handover. An edge handover will be triggered if the downlink receive level is lower than "Edge HO UL RX_LEV Thrsh." for a period longer than Edge HO Valid Time(s) within Edge HO Watch Time(s). If PBGT handover is enabled, the corresponding edge handover threshold can be lowered. If PBGT handover is disabled, this parameter must be properly specified to avoid manual overlapping coverage and channel interference. This parameter should be adjusted based on the performance statistics and actual networks to achieve uplink-downlink balance.

30: Urban areas without PBGT handover

25: Suburbs with a single BTS





[Edge HO Watch Time(s)]


•Unit: Seconds

•Default Value: 3

•Description: This parameter indicates the period when uplink/downlink receive levels are measured to determine whether an edge handover is triggered.

[Edge HO Valid Time(s)]


•Unit: Seconds

•Default Value: 2

•Description: To trigger an edge handover, the receive level of the uplink or downlink should constantly remain lower than their corresponding edge handover thresholds within Edge HO Watch Time(s). This parameter indicates this duration.

[Edge HO AdjCell Watch Time(s)]


•Unit: Seconds

•Default Value: 3

•Description: This parameter indicates the period when uplink/downlink receive levels are measured to determine whether an edge handover neighbor cell is triggered.

[Edge HO AdjCell Valid Time(s)]


•Unit: Seconds

•Default Value: 2

•Description: During the edge handover continuance time, the UL/DL receive level should remain higher than the corresponding UL/DL edge handover threshold for a period. This parameter indicates the period.





[Inter-cell HO Hysteresis]


•Unit: Levels

•Default Value: 5

•Description: This parameter indicates the handover hysteresis between adjacent cells of the same layer. The purpose of setting this parameter is to reduce the "Ping-Pong" handovers. The value of this parameter is invalid if cells are not on the same layer.4 dB populous urban areas and 8 dB for suburbs.




MS Fast-Moving Handover

Handover Triggering

TimeThreshold

Umbrella Cell

Time

P/NP: Watch CellsN: Valid Cells

1 1 2 3

Micro Cell

Cells Number

The condition of MS Fast-Moving Handover is that a MS is moving fast (for example

moving on a highway), and the area is covered by two layers, that is micro cell and

macro cell.

MS Fast-Moving Handover is mainly used to solve the handover of MS during fast-

moving, that is to say, to avoid MS handover to the micro cell to increase handover time

and signaling flow, thereby increase service quality

MS Fast-moving time Thrsh——If the time used by MS to pass this cell is less

than this threshold, it means that MS passes the cell quickly.

MS Fast-moving watch cells P —— The total number of cells for judging whether

a MS is fast moving or not.

MS Fast-moving valid cells N —— Total N of actual cells that MS fast passes.

When N equal to or more than P cells that MS lately passes are fast passing

ones, the fast moving handover algorithm will be started.




MS Fast-Moving HandoverBegin

[MS Fast Moving HO Allowed](s) Yes ?

End

No

Yes

Yes

the servingcell on layer 4?

Satisfy P / N rule?No Select the neighbor cell with the highest priority &

on the 4th layer & satisfy RX_LEV(n)>= [Inter-layer HO threshold](n) + [Inter-layer HO hysterisis](s->n)

Any cell satisfy the condition above?

Trigger MS fast-moving handover

No

Yes

Refresh timer(s)

No

Yes

Triggering conditionMS moves through P cells (watch cells), and the speed for Q cells (valid cells) among these p cells

is fast

The layer of service cell must be less than four

Object cell selectionThe service cell cannot be the object cell

The neighboring cell with the highest priority

The layer of the object cell must be the 4th layer

RX_LEV of the object cell >= Inter-layer HO threshold + Inter-layer HO hysterisis




Data Configuration of MS Fast-moving Handover

•[MS Fast Moving HO Allowed]



•Description: This parameter indicates whether a fast moving handover is allowed. The fast moving handover enables a fast moving MS to hand over rapidly to a macro cell, thus reducing handovers. It is recommended that this algorithm be applied only to special areas, such as highways, to reduce the CPU load.[MS Fast-moving Watch Cells]

•Value Range:1~10

•Default Value:3

•Description: During the moving, the MS passes P micro cells. According to the P/N rule, when the MS fast crosses N ones among the P micro cells, the BSC starts to trigger a fast-moving micro cell handover.

•Remarks: If this parameter is excessively high, it is difficult to reduce the system load effectively. If this parameter is excessively low, the judgment is inaccurate.

[MS Fast-moving Valid Cells]


•Default Value: 2

•Description: Suppose that the actual number of the micro cells that the MS fast crosses is N. According to the P/N rule, when the MS fast crosses N ones among the P micro cells, a fast moving handover is triggered by the BSC when this parameter satisfies the required conditions.

[MS Fast-moving Time Threshold]


•Unit: Seconds


•Description: This parameter indicates the threshold for judging whether an MS moves fast across a cell. The threshold is obtained based on the cell radius and specified velocity. If the time for crossing a cell is lower than this threshold, the MS is regarded as moving fast.

•Remarks: Conditions for triggering fast-moving handover are as follows:

The serving cell does not belong to level-4.

The optimum target cell does belong to level-4.

A neighboring cell has a macro cell




Layer HO

Neighboring CellServing Cell

GSM900 Cell（Lay 3） GSM1800 Cell

（Lay 2）

The goal of layer handover is to control the destination cell of handover more flexibly, make a MS hand over to the most reasonable cell to reduce the occurrence of latter handover in order to save all kinds of system resources, and also effectively increase handover successful ratio, reduce call drop during handover, improve voice quality and service level.




Begin

[Level HO Allowed](s) Yes ?

End

No

Yes

Yes

Any neighbor cell exit?

16 bit value(n)<16 bit value(s)?

A & ( layer(n)< layer(s) or level(n)<level(s) )?

Satisfy P/N rule(n)?No

Trigger layer handover

Yes

No

Yes

No

A: RX_LEV(n)>= [nter-layer HO threshold](n) + [Inter-layer HO hysterisis](s->n)

Yes

Identify the next cell

No

Layer HO


The layer or level of object cell is lower than that of the service cell

RX_LEV_DL of the object cell >= Inter-layer HO threshold + Inter-layer HO hysteresis

Satisfying P/N rule



The neighboring cell with the highest priority and whose priority is higher than that of the service cell




Data Configuration of Layer HO

[Level HO Allowed]



•Description: The parameter indicates whether the layer level handover is allowed.AnInter Layer HO is realized by setting different layers and levels for the cells. It is used to guide the traffic to the cell that has a high priority. When this parameter is set to Yes, traffic is routed to a cell with a higher priority.

•Remarks: The lower the layer is, the higher the priority is. The higher the level is, the lower the priority is. Layer level handover is not implemented when the comprehensive sequence (including basic sequence and network sequence) of the serving cell is the highest or when the level of the target cell is not greater than the Inter-layer HO Threshold.

[Layer HO Watch Time(s)]


•Description: Compare the candidate cells that are better than the current serving cell so as to decide whether to trigger a layer handover. This parameter indicates the duration to make the decision.

[Layer HO Valid Time(s)]


•Description: If a cell is ranked 1 of the candidate cells for a whole segment of measurement period, this cell is called the best cell.












•Default Value: 3

•Description: This parameter indicates the hysteresis of an inter-layer or inter-priority handover. It is used to avoid inter-layer ping-pong handovers.

Actual Inter-layer HO Threshold of a serving cell = Inter-layer HO Threshold - Inter-layer HO hysteresis

Actual Inter-layer HO Threshold of a neighboring cell = Inter-layer HO Threshold + Inter-layer HO hysteresis




PBGT HO


PBGT HO Threshold

Time

Path Loss (dB)

126dB 119dB

5

126-119=7dB>5dB

HandoverTriggering

P/NP: Watch Time N: Valid Time

In areas with densely distributed cells, the actual radio coverage range has become far larger than the distance between BTS. If MSkeeps the conversation within a cell, it will not be effectively handed over to a nearby cell with low transmission power and that will lead to over shooting, thus increasing the interference of radio environment and complicating network planning and optimization. To solve this problem, Huawei develops PBGT handover algorithm thatis based on path loss.

PBGT handover algorithm is intended for the handover based on path loss, in real time, it seeks a cell with lower path loss and meeting certain system requirements, and judges whether it’s necessary to perform handover.




Begin [PBGT HO

Allowed] (s)Yes ?

End

No

Yes

current channel signaling channel?

Satisfy P / N rule?

No

Yes

Search next neighborcell

layer(n)=layer(s)&level(n)=level(s)?

Path loss (s) – Path loss (n) >PBGT HO Threshold(s->n)

Refresh timer(s)

Trigger PBGT HO

Yes

No

Yes

No

Yes

No

PBGT HO

NOTES: whichever the greater of the

[inter-cell HO hysteresis] and

[PBGT HO threshold], that value will be

used in the PBGT HO.

Triggering conditionThe layer and level of the object cell are the same as those of the service cell.

Path loss (service cell) – Path loss (neighbor cell) > PBGT HO Threshold

Satisfying P/N rule

Object cell selectionThe service cell cannot be the object cell.

The neighboring cell with the highest priority and whose priority is higher than that of the service cell.

RestrictionIt is not available with SDCCH.




Data Configuration of PBGT HO

[PBGT HO Allowed]



•Description: The parameter indicates whether a POWER BUDGET (PBGT) handover is allowed.Based on path loss, PBGT handover is used to search for a desired cell in real time and to judge whether handover is performed. The cell must provide less path loss and meet other requirements.To avoid ping-pong handovers, PBGT handover applies to only cells of the same level on the same layer and is triggered only over TCH. On a SDCCH, it is not allowed to trigger a PBGT handover.Proper use of PBGT handover helps to reduce over-cell coverage and co-channel interference.

[PBGT Watch Time(s)]


•Unit: Seconds

•Default Value: 3

•Description: This parameter indicates the period when the path losses of neighboring cells are measured. Thus, operators can determine whether a PBGT handover is triggered.

PBGT Valid Time(s)


•Unit: Seconds

•Default Value: 2

•Description: This parameter indicates the period that satisfies PBGT handover.




Data Configuration of PBGT HO

[PBGT HO Threshold]

•Value Range: 0~127 (-64 dB to +63 dB)


•Description: A threshold in PBGT handover algorithm used to judge whether to perform PBGT handover. When PBGT Handover Allowed is set to Yes and Inter-cell HO Hysteresis > PBGT HO Thresh., the Inter-cell HO Hysteresis will act instead of the PBGT HO Thresh. When this parameter is assigned with a value smaller than 64, MS can hand over to a lower level neighboring cell. 68 for popular urban areas, 72 for suburbs.

•Remarks: When PBGT handover is enabled, and Inter-cell HO Hysteresis> PBGT HO Thresh, the Inter-cell HO hysteresis instead of the PBGT HO Thresh works. PBGT HO Thresh must be adjusted as per handover performance statistic result and actual network.




Concentric CellPurposes

Maximize coverage area

Reduce interference and improve frequency reuse density

Construction methods

Different combiner loss

Different propagation loss

Modify the transmission power of TRX, the down tilt of antennas, etc.

By HO parameters

Overlaid

Underlaid




Classification and HO Judgment of Concentric Cell

Receiving level

Time advance

Quality

…

Receiving level

Time advance

Quality

ATCB

Cell load of underlaid

…Normal concentric cell Enhance concentric cell

There are two kinds of concentric cell handover:

•Normal concentric cell handover

•Enhance concentric cell handover

The difference of these two handovers is that enhance concentric cell handover takes into account the cell load of underlaid.




Data Configuration of Concentric Cell

[Concentric Circles HO Allowed]



•Description: The parameter indicates whether a concentric cell handover is allowed. A concentric cell handover is implemented to achieve mass coverage in the underlaid subcelland tight frequency reuse in the overlaid subcell, thus improving the system capability and service performance. A concentric cell handover consists of inward handover and outward handover.

[Enhenced Concentric Allowed]



•Description: This parameter indicates whether a enhenced concentric circle handover is allowed.

While the Enhanced Concentric Cell Allowed is set as "Yes", compare the receive level of the MS with O to U HO Receive Level Threshold and U to O HO Receive Level Threshold to decide whether to trigger an O to U HO or a U to O HO.

While the Enhanced Concentric Cell Allowed is set as "No", compare the receive level of the MS with RX_LEV Threshold so as to decide whether to trigger an enhanced concentric cell HO. It is required to consider the load of the UL when deciding whether to trigger a U to O HO.




Normal Concentric Cell HO

Division of underlaid and overlaid is decided by MS downlink receive

level ,TA value and quality.

underlaid

overlaid

Receiving Level Threshold

Receiving Level Hysteresis

Receiving Qaulityl Threshold

TA Threshold

TA Hysteresis

An illustration of how to define the border between the underlaid and the overlaid.




Normal Concentric Cell HO

U to O O to U




Normal Concentric Cell HO(O U )Flow for TCH HO from overlaid to underlaid

Begin within Penalty Time End Yes

No

[RX_LEV for UO HO Allowed] Yes?

Yes

[OL to UL HO Allowed] Yes ?

NoYes

[RX_QUAL for UO HO Allowed] Yes?

Yes

Rx_Dl_Quality>=[RX_QUAL Treshold]? Current TA>=[TA Threshold]+

[TA Hysteresis]?

[TA for UO HOAllowed] Yes?

Trigger OL to UL

P/N rule?

Yes Yes

Yes

Yes

No

NoNo

No No No

End

Rx_Dl_Level<=[RX_LEV thshold]-[RX_LEV Hysteresis]

NoYes

Criterion for TCH HO from overlaid to underlaid:

TA value >= TA Threshold + TA Hysteresis

OR RX_LEV <= RX_LEV Threshold －RX_LEV Hysteresis

OR Quality >= RX_QUAL Threshold

Satisfying P/N rule




Normal Concentric Cell HO(U O )Criterion for TCH HO from underlaid to overlaid

Begin

With Penalty Time ? End Yes

No

Current TA<=[TA Threshold]-[TA Hysteresis]?


Yes

Yes

No

No[RX_LEV for UO HO Allowed] Yes?

Rx_Dl_Level >=[RX_LEV Threshold] + [RX_LEV Hysteresis]

No


Rx_Dl_Qual<=[RX_QUAL Treshold]?

Yes

P/N rule?

Yes

No

No

No

Yes

Yes

No

[UL to OL HO Allowed] Yes ?

End

Yes

No

Trigger UL to OL

Criterion for TCH HO from underlaid to overlaid:

TA value <= TA Threshold － TA Hysteresis

AND RX_LEV >= RX_LEV Threshold + RX_LEV Hysteresis

AND Qua. <= RX_QUAL Threshold

Satisfying P/N rule




Data Configuration of Normal Concentric Cell HO

[UL to OL HO Allowed]

•Value Range: Yes, No Default Value: Yes

•Description: This parameter indicates whether an underlay (UL) to overlay (OL) handover is allowed.

[OL to UL HO Allowed]


•Description: This parameter indicates whether an OL to UL handover is allowed.

[RX_LEV for UO HO Allowed]


•Description: This parameter indicates whether the downlink receive level is used to determine a Concentric Cell handover.

[RX_QUAL for UO HO Allowed]

•Value Range: Yes, No Default Value: The default value is generally set to Yes. When the cell is a dual-timeslot cell, the default value is set to No.

•Description: This parameter indicates whether the downlink receive quality is used to determine a Concentric Cell handover.

[TA for UO HO Allowed]


•Description: This parameter indicates whether the TA is used to determine a Concentric Cell handover.





[UO Signal Intensity Difference]


•Default Value: 0

•Description: This parameter indicates the signal intensity compensation between the overlaid and underlaidsubcells. It equals the sum of power difference between overlaid and underlaid power amplifiers, insertion loss difference between combiners, path loss difference caused by antennas, and path loss difference caused by frequencies.The parameter is invalid when Enhanced Concentric Cell is allowed.

[RX_LEV Threshold]


•Default Value: 35: This parameter is greater than the sum of fringe handover threshold and UO signal intensity difference. 0: The cell is a dual-timeslot extended cell. 40: The cell is a mixed cell. Description: This is one of the parameters that determine the regions of overlaid and underlaid subcells. It is invalid when Enhanced Concentric Cell is allowed.When Enhanced Concentric Cell is not allowed, the regions are co-determined by RX_LEV Threshold, RX_LEV Hysteresis, RX_QUAL Threshold, TA Threshold, and TA Hysteresis.

[RX_LEV Hysteresis]


•Default Value: 5 When the cell is a dual-timeslot cell, the default value is set to 0.DescriptionThis is one of the parameters that determine the regions of overlaid and underlaid subcells. It is invalid when Enhanced Concentric Cell is allowed.When Enhanced Concentric Cell is not allowed, the regions are co-determined by RX_LEV Threshold, RX_LEV Hysteresis, RX_QUAL Threshold, TA Threshold, and TA Hysteresis.

[RX_QUAL Threshold]

•Value Range: 0~70 (RQ (0-7) 10)

•Default Value: The default value is 60, but it is 70 when the cell is a dual-timeslot extended cell.

•Description: This is one of the parameters that determine the regions of overlaid and underlaid subcells. When Enhanced Concentric Cell is not allowed, the regions are co-determined by RX_LEV Threshold, RX_LEV Hysteresis, RX_QUAL Threshold, TA Threshold, and TA Hysteresis. When Enhanced Concentric Cell is allowed, the regions are co-determined by RX_QUAL Threshold, UtoO HO Receive Level Threshold, OtoU HO Receive Level Threshold, TA Threshold, and TA Hysteresis.





[TA Threshold]


•Unit: Bit period (a bit period denotes 0.55 km)

•Default Value: 63 Note: TA threshold is not used to distinguish the boundary between overlaid and underlaidsubcells.

•Description: This is one of the parameters that determine the regions of overlaid and underlaid subcells. When Enhanced Concentric Cell is not allowed, the regions are co-determined by RX_LEV Threshold, RX_LEV Hysteresis, RX_QUAL Threshold, TA Threshold, and TA Hysteresis.When Enhanced Concentric Cell is allowed, the regions are co-determined by RX_QUAL Threshold, UtoO HO Receive Level Threshold, OtoU HO Receive Level Threshold, TA Threshold, and TA Hysteresis.

•Remarks: This parameter must be less than the TA threshold of an emergency handover. When set to 63, this parameter can be used to distinguish the boundary of Underlaid subcell and OverLaid subcell of a dual-slot concentric cell instead of the boundary of a normal concentric cell.

[TA Hysteresis]


•Unit: Bit period (a bit period corresponds to 0.55 km)

•Default Value: The default value is generally set to 0. When the cell is a dual-timeslot cell, the default value is set to 3.

•Description: This is one of the parameters that determine the regions of overlaid and underlaid subcells. When Concentric Circles HO Allowed is set to No, the regions are co-determined by RX_LEV Threshold, RX_LEV Hysteresis, RX_QUAL Threshold, TA Threshold, and TA Hysteresis. When Concentric Circles HO Allowed is set to Yes, the regions are co-determined by RX_QUAL Threshold, UtoO HO Receive Level Threshold, OtoUHO Receive Level Threshold, TA Threshold, and TA Hysteresis.

[UO HO Watch Time]


•Unit: Seconds

•Default Value: 5

•Description: This parameter indicates the duration during which the BSC counts the duration when the conditions for an concentric cell handover are met to decide whether to trigger a concentric cell handover.

[UO HO Valid Time]


•Unit: Seconds

•Default Value: 4




Enhance Concentric Cell HO

Division of underlaid and overlaid is decided by MS downlink receive

level, quality, TA value and cell load of underlaid.

underlaid

overlaid

U to O HO Receiving Level Threshold

O to U HO Receiving Level Hysteresis

Receiving Qaulityl Threshold

TA Threshold

TA Hysteresis




Enhance Concentric Cell HO

Classification of TCH HO in enhance concentric cell HO

O to Ufor low load in U

U to Ofor high load in U

O to Ufor moving




Enhance Concentric Cell HO(U O )

A: RX_LEV_UL – RX_LEV (n) >[Distance Between Boundaries of UL and OL Subcells(dB)] RX_LEV (n): RX_LEV of the strongest neighboring cell which has the same frequency band and layer with underlaid subcell, but locates in a different BTS. If there is no such a cell, this value is -110dBm

Flow for TCH HO from underlaid to overlaid for high load in UL

Begin

Within Penalty Time ? End Yes

No

Current TA<[TA Threshold]-[TA Hysteresis]?

[ATCBHoSwitch] Open?


Go to the user selection flow in the next slide

Yes

Yes

No


Rx_Dl_Level>[UtoO HO Received Level Threshold]

No

AYes

No


Rx_Dl_Qual<[RX_QUAL Treshold]?

Yes

P/N rule? YesNo

No

No

No

Yes

Yes

Yes

Yes

[UL to OL HO Allowed] Yes ?

End

Yes

No

Criterion for TCH HO from underlaid to overlaid

RX_LEV > UtoO HO Received Level Threshold

And RX_LEV_UL – RX_LEV (n) > Distance Between Boundaries of UL and OL Subcells(dB)

And RX_QUAL < RX_QUAL Threshold

And TA < TA Threshold – TA Hysteresis

Satisfying P/N rule




Enhance Concentric Cell HO(U O ) (Con.)

User selection flow from UL to OL for high load in UL

Cell load of UL>=[En Iuo OutCell Serious OverLoad Thred]?

Begin [UtoO Traffice

HO Allowed] Yes ?

Cell load of UL>=[En Iuo Out Cell General OverLoad Thred]?

Trigger UL to OL

Yes No



B(B-1)/second

Yes

B=[Underlay HO Step Period(s)]HO step: [Underlay HO Step Level]HO period: B-x or BHO zone: begin from -47dBm

Any MS in HO zone?

Yes

No

Yes

No

End

No




Enhance Concentric Cell HO(O U )

Flow for TCH HO from overlaid to underlaid for low load in underlaid

HO period: [En Iuo in Cell Load Classification HO Period]HO step: [En Iuo in Cell Load Classification HO Step]HO zone: begin from [OtoU HO Received Level Threshold] to -47dBm

Begin [[OL to UL HO Allowed] Yes ?

Cell load of UL<[En Iuo Out Cell Low Load Thred]?

No

Trigger UL to OL



Yes

Any MS in HO zone?

Yes

No

Yes

No

End

Criterion for TCH HO from overlaid to underlaid for underlaid low load

Cell load of underlaid < En Iuo Out Cell Low Load Threshold

HO Zone is from OtoU HO Received Level Threshold~-47dBm






Enhance Concentric Cell HO(O U )Flow for TCH HO from overlaid to underlaid for moving

No

Begin With Penalty Time ? End Yes

No

[ATCBHoSwitch] Open?


Rx_Dl_Level<[OtoU HO Received Level Threshold] A

Yes

[OL to UL HO Allowed] Yes ?

NoYes


YesRx_Dl_Qual>

[RX_QUAL Treshold]? Current TA>[TA Threshold]+[TA Hysteresis]?


Trigger OL to UL

P/N rule?

Select the underlaid subcell or the neighbour cell with the highst priority in 16 bits list

Yes Yes Yes

Yes

No

Yes

No No

No No

NoEnd

A: RX_LEV_UL – RX_LEV (n) < [Distance Between Boundaries of UL and OL Subcells(dB)]－[Distance Hysteresis Between Boundaries of UL and OL Subcells(dB)]

Criterion for TCH HO from overlaid to underlaid for moving

RX_LEV < OtoU HO Received Level Threshold

OR RX_QUAL > RX_QUAL Threshold

OR TA > TA Threshold + TA Hysteresis

OR RX_LEV_UL – RX_LEV (n) < Distance Between Boundaries of UL and OL Subcells(dB) – Distance Hysteresis Between Boundaries of UL and OL Subcells(dB)

Satisfying P/N rule


The cell with highest priority. It could be underlaid subcell or normal neighboring cell




Data Configuration of Enhance Concentric Cell HO

[ATCBHoSwitch]

•Value Range: Closed Open Unit: None Default Value: Open

•Description: The switch of the ATCB handover algorithm.

[UL to OL HO Allowed]


•Description: This parameter indicates whether an U to O handover is allowed.

[OL to UL HO Allowed]


•DescriptionThis parameter indicates whether an OL to UL handover is allowed.

[RX_LEV for UO HO Allowed]



•Description: This parameter indicates whether the downlink receive level is used to determine a Concentric Cell handover.

[RX_QUAL for UO HO Allowed]


•Default Value: The default value is generally set to Yes. When the cell is a dual-timeslot cell, the default value is set to No.

•Description: This parameter indicates whether the downlink receive quality is used to determine a Concentric Cell handover.

[TA for UO HO Allowed]


•Description: This parameter indicates whether the TA is used to determine a Concentric Cell handover.





[RX_QUAL Threshold]

•Value Range: 0~70 (RQ (0-7) 10)

•Default Value: The default value is 60, but it is 70 when the cell is a dual-timeslot extended cell.

•Description: This is one of the parameters that determine the regions of overlaid and underlaid subcells. When Enhanced Concentric Cell is not allowed, the regions are co-determined by RX_LEV Threshold, RX_LEV Hysteresis, RX_QUAL Threshold, TA Threshold, and TA Hysteresis. When Enhanced Concentric Cell is allowed, the regions are co-determined by RX_QUAL Threshold, UtoO HO Receive Level Threshold, OtoU HO Receive Level Threshold, TA Threshold, and TA Hysteresis.

[TA Threshold]

•Value Range: 0~255 Unit: Bit period (a bit period denotes 0.55 km)

•Default Value: 63 Note: TA threshold is not used to distinguish the boundary between overlaid and underlaidsubcells.

•Description: This is one of the parameters that determine the regions of overlaid and underlaid subcells. When Enhanced Concentric Cell is not allowed, the regions are co-determined by RX_LEV Threshold, RX_LEV Hysteresis, RX_QUAL Threshold, TA Threshold, and TA Hysteresis.When Enhanced Concentric Cell is allowed, the regions are co-determined by RX_QUAL Threshold, UtoO HO Receive Level Threshold, OtoU HO Receive Level Threshold, TA Threshold, and TA Hysteresis.

•Remarks: This parameter must be less than the TA threshold of an emergency handover. When set to 63, this parameter can be used to distinguish the boundary of Underlaid subcell and OverLaid subcell of a dual-slot concentric cell instead of the boundary of a normal concentric cell.

[TA Hysteresis]

•Value Range: 0~255 Unit: Bit period (a bit period corresponds to 0.55 km)

•Default Value: The default value is generally set to 0. When the cell is a dual-timeslot cell, the default value is set to 3.

•Description: This is one of the parameters that determine the regions of overlaid and underlaid subcells. When Concentric Circles HO Allowed is set to No, the regions are co-determined by RX_LEV Threshold, RX_LEV Hysteresis, RX_QUAL Threshold, TA Threshold, and TA Hysteresis. When Concentric Circles HO Allowed is set to Yes, the regions are co-determined by RX_QUAL Threshold, UtoO HO Receive Level Threshold, OtoUHO Receive Level Threshold, TA Threshold, and TA Hysteresis.





[UO HO Watch Time]


•Unit: Seconds

•Default Value: 5

•Description: This parameter indicates the duration during which the BSC counts the duration when the conditions for an concentric cell handover are met to decide whether to trigger a concentric cell handover.

[UO HO Valid Time]


•Unit: Seconds

•Default Value: 4

•Description: This parameter indicates the duration when the conditions for a concentric cell handover are met within UO HO Watch Time.





[OtoU HO Received Level Threshold]


•Description: This is one of the parameters that determine the regions of overlaid and underlaid subcells. When Enhanced Concentric Cell is allowed, the regions are co-determined by RX_QUAL Threshold, UtoO HO Receive Level Threshold, OtoU HO Receive Level Threshold, TA Threshold, and TA Hysteresis.

[UtoO HO Received Level Threshold]


•Description: This is one of the parameters that determine the regions of overlaid and underlaid subcells.When Enhanced Concentric Cell is allowed, the regions are co-determined by RX_QUAL Threshold, UtoO HO Receive Level Threshold, OtoU HO Receive Level Threshold, TA Threshold, and TA Hysteresis.

[UtoO Traffic HO Allowed]

•Value Range: Yes, No Default Value: No: dual-timeslot cells Yes: other cells

•Description: This parameter indicates whether the traffic in the underlaid subcelldetermines the underlaid to overlaid (UL to OL) handover.When this parameter is set to Yes, the handover is allowed only when the traffic in the underlaid cell is equal to or greater than Traffic Threshold of Underlay.When this parameter is set to No, the traffic is not taken into consideration.






[Underlay HO Step Period(s)]


•Description: This parameter indicates the interval between two grades of level-based handovers. When multiple UL to OL handover requests are initiated simultaneously, it is possible that calls with low level are handed over. This does not conform to the principle that the call with the best quality should be handed over firstly. Thus, level grade-based handover is used to hand over high-level calls with higher priority.


[Underlay HO Step Level]


•Description: This parameter indicates the length of a grade in level grade-based UL to OL handover. Thus, high-level calls are handed over with higher priority.After a step period of UL to OL handover, the handover band is decreased by the length of a grade.This parameter and Underlay HO Step Period control the level band of the step-by-step handover from underlaid subcells to overlaid subcells together. The time for the handover band to step down for Underlay HO Step Level is Underlay HO Step Period.






[En Iuo Out Cell Low Load Thred]


•Description: If the ratio of the underlaid subcell channel occupancy is smaller than the value of this parameter, some calls in the overlaid subcell are handed over to the underlaid subcell.

[En Iuo Out Cell General OverLoad Thred]

•Value Range: 0-100 Unit: % Default Value: 85

•Description: If the ratio of the underlaid subcell channel occupancy is greater than the value of this parameter, some calls in the underlaid subcell are handed over to the overlaid subcell.

[En Iuo Out Cell Serious OverLoad Thred]


•Description: If the ratio of the underlaid cell channel occupancy is greater than the value of this parameter, the period of hierarchical handover from underlaid subcell to overlaid subcell is shorten. That is, the value of Out Cell Load HO Modify Step is reduced every second based on the value of Out Cell Load Classification HO Period. Thus the handover from underlaid subcell to the overlaid subcell speeds up.

•Remarks: The value of this parameter must be greater than that of the En Iuo Out Cell General OverLoad Thred.

[En Iuo In Cell Load classification HO Period]


•Description: When the ratio of overlaid subcell cell channel occupancy is greater than the value of En Iuo Out Cell General OverLoad Thred, all the calls in the cell request for handover at the same time. The BSC load is sharply increased. Thus the call may drop because the target cell is congested. Therefore the algorithm of hierarchical handover is applied to hand over the calls in the cell hierarchically.This parameter indicates the time duration of every hierarchical handover.

[En Iuo In Cell Load classification HO Step]

•Value Range: 0-63 Unit: Db Default Value: 5

•Description: This parameter indicates the level step of the hierarchical handover from underlaid subcell to overlaid subcell.





[Distance Between Boundaries of UL And OL Subcell(dB)]


•Description: This parameter indicates the distance between the overlaid subcelland underlaid subcell. The value of this parameter is comparative. The greater the value is, the longer the distance is.The enhanced dual-band network handover algorithm refers to the boundary between underlaid subcell and overlaid subcellbased on the comparative value of signal strength of serving cell and neighboring cell. Suppose the signal strength of serving cell is SS(s), and neighboring cell SS(n). If SS(s) is equal to SS(n), the cell is in the underlaid subcell boundary. If the value of SS(s) - SS(n) is larger than the value of Distance Between Out And Inn Cell boundary, the cell is in the overlaid subcell.

[Distance Hysterisis Between Boundaries of UL And OL Subcell]


•Description:To prevent ping-pong handover, the BSC determines whether the handover of the MS from overlaid subcell cell to underlaid subcell cell based on the value of this parameter. Suppose the signal strength of serving cell is SS(s), and neighboring cell SS(n). If the value of SS(s) - SS(n) is larger than the value of Distance Between Out And Inn Cell boundary - Distance Hyst Between Out And Inn Cell boundary, the MS handover from overlaid subcell cell to underlaidsubcell cell is allowed.




Channel Assignment strategies of Concentric Cell

Channel Assignment Strategies of Concentric Cell

Immediate Assignment Assignment

Intra-BSC Inter-cell

Handover

Incoming Cell

Handover




The preferred SDCCH channel in two layers is controlled by parameter

“TA pref. Of Imme-Assign Allowed ”

If "No", system prefers the channel in Underlaid subcell

If “Yes", system prefers the channel according to in Channel

Request message

TA smallerTA bigger

Immediate Assignment

When “TA pref. Of Imme-Assign Allowed ” is set as “Yes”, if the TA is larger than the “TA Threshold of Imme-Assignment Pref.”, the underlay cell is assigned first. if the TA is smaller than the threshold, the overlay cell is assigned first.




Data Configuration of Immediate Assignment

[TA Pref of Imme-Assign Allowed]



•Description: This parameter indicates whether access_delay is used in the channel request message for immediate assignment. When this parameter is set to No, a channel in the underlaidsubcell is assigned. When this parameter is set to Yes, a channel in the overlaid subcell is assigned if access_delay is less than TA Threshold of Imme-Assign Pref. If not, a channel in the underlaidsubcell is assigned.

[TA Threshold of Imme-Assign Pref]



•Default Value: 63: Dual-timeslot extended cells 0: Other cells

•Description: This parameter indicates the threshold of overlaid cell-based immediate assignment. If TA Pref of Imme-Assign Allowed is set to Yes, the system prefers the channel in overlaid subcell while ACCESS_DELAY is smaller than TA Thrsh. of Imme- Assign pref. Otherwise, the system prefers the channel in Underlaid subcell.




Preferred assignment in the overlay or underlay cell

Assign the channel of overlay or underlay cell according to

the Rx_level and TA in the measurement report

TA smaller and Rx-level higher

Assignment

The channel of overlay cell is assigned first only when the Rx level on the SDCCH is equal to or larger than the “Assign-optimum-level Threshold” and the TA is smaller than the “TA Threshold of Assignment Pref.”. Otherwise, the channel of underlay cell is assigned first to ensure the successful assignment.




Data Configuration of Assignment

[Assign Optimum Layer]

•Value Range: System Optimization, Overlaid Subcell, Underlaid Subcell, No Preference

•Default Value:

Underlaid Subcell: The cell system is GSM900&DCS1800 and enhanced concentric cell.

System Optimization: The cell system is not GSM900&DCS1800.

•Description: This parameter indicates the method of TCH assignment a concentric cell.

System Optimization: The system selects the optimum serving layer according to the MR provided through the SDCCH.

Underlaid Subcell: Channel assignment in the underlaid subcell has higher priority.

Overlaid Subcell: Channel assignment in the overlaid subcell has higher priority.

No Preference: No specific instruction is given.



[Assign-optimum-level Threshold]


•Default Value: When the uplink and the downlink are not balanced, the default value = receive level + balance margin for uplink and downlink When the uplink and the downlink are balanced, the default value can be set to 35, which is the same as RX_LEV Threshold. When the cell is a dual-timeslot cell, the default value is set to 0. When the cell is a hybrid cell, the default value is set to 40.

•Description: When the optimal layer is selected through system optimization, the current SDCCH level can be estimated (inserted/filtered) based on the uplink measurement result in the previous SDCCH MR. Then, overlaid and underlaid subcells are allocated by comparing this parameter with the receive level of SDCCH, and by comparing TA with the TAthreshold of optimum assignment. The MS is allocated with overlaid subcell only when the receive level is greater than level threshold and TA is smaller than the TA threshold. Otherwise, the MS is allocated with the underlaid cell.

[TA Threshold of Assignment Pref.]



•Default Value:63

•Description: When the optimal layer is selected through system optimization, the current SDCCH level can be estimated (inserted/filtered) based on the uplink measurement result in the previous SDCCH MR. Then, overlaid and underlaid subcells are allocated by comparing this parameter and the receive level of SDCCH, and by comparing TA and the TA threshold of optimum assignment. The MS is allocated with overlaid subcell only when the receive level is greater than level threshold and TA is smaller than the TA threshold. Otherwise, the MS is allocated with the underlaid cell.

•Remarks: When this parameter is set to 0, the MS is allocated with the underlaid cell.




Intra-BSC Inter-Cell HandoverIn the case of intra-BSC inter-cell handover, the MS can be handed

over to the underlay or overlay cell first.

If “System Optimization” is selected, the preferred assignment is

conducted according to the level value in the measurement report.

overlaid

Underlaid

OverlaidAccording to the Rx-level

If the Rx level is higher than the “Rx level threshold”, the MS will be handed over to the overderlay cell. Otherwise, the MS will be handed over to the underlay cell




Data Configuration of Intra-BSC Inter-Cell Handover

[Pref. Subcell in HO of Intra-BSC]

•Value Range: System Optimization, Overlaid Subcell, Underlaid Subcell, No Preference

•Default Value: The default value is System Optimization. For a dual-timeslot extended cell or a hybrid cell, the default value is Underlaid Subcell.

•Description: This parameter indicates the method of channel assignment for intra-BSC handover in a concentric cell.

System Optimization: The BCCH of the target cell is specified in the handover request. Then, the target cell compares only the receive level with RX_LEV Threshold, thus selecting the layer with higher priority.

UnderLaid Subcell: Channel assignment in the underlaid subcell has higher priority.

OverLaid Subcell: Channel assignment in the overlaid subcell has higher priority.

No Preference: Channels are assigned based on routine algorithms.




Inter-BSC Handover

For the inter-BSC Handover, if the target cell is concentric cell , the

channel of underlay cell should be assigned first.

overlaid

Underlaid

Overlaid

BSC1 BSC2

Assign underlaid first




Data Configuration of Inter-BSC Inter-Cell Handover

[Incoming-to-BSC HO Optimum Layer]

•Value Range: Overlaid Subcell, Underlaid Subcell, No Preference

•Default Value:

Underlaid Subcell (common networks)

Overlaid Subcell (dual-frequency networks)

Underlaid Subcell (dual-frequency networks with decreasing success rate of handover)

•Description: This parameter indicates the method of selecting an optimum layer for an incoming handover.

•Remarks: The BCCH carrier must be configured in the underlaid subcell. The SDCCH must be configured in the underlaid subcell. Concentric Cell handover is forbidden if both RX-LEV Threshold and RX-LEV Hysteresis (or both TA Threshold and TA Hysteresis) are set to 63. The data configuration for a dual-timeslot extended cell adopts Concentric Cell techniques.




AMR Handover FlowBegin

Are [Intracell HO Allowed] & [Intracell F-H HO

Allowed］ Yes ?

Yes

Is current channel TCH & version3?

No

A: Cell load > [AMR TCH/H Prior Cell Load Threshold]

During [Penalty Time after AMR TCHF-H HO

Fail(s)]?

Yes

Yes

current channel is FR

Satisfy P/N rule? Trigger internal cellAMR handover

Yes

NoEnd

RQI/2 >[F2H HO th] & A RQI/2 <[H2F HO th] End

Yes Yes

NoNo

No

No

No

Yes




Data Configuration of AMR HO

[Intracell HO Allowed]


•Description: This parameter indicates whether an intra-cell handover is allowed. After an intra-cell handover, the timeslot and TRX that the MS occupies change.

•Remarks: This parameter does not affect concentric cell handovers and forced handovers. During an AMR handover, an interference handover, and a bad quality handover, an intra-cell handover is unavailable if this parameter is set to No.

[Intracell F-H HO Allowed]


•Description: This parameter indicates whether the handover between full-rate channels and half-rate channels in the cell is allowed. Only the value of the Intracell HO Allowed is set Yes, this parameter is valid. Only when this parameter is set to Yes, the BSC makes an AMR handover decision. Otherwise, the BSC makes no decision.

[Intracell F-H HO State Time(s)]


•Description: This parameter indicates the time threshold that satisfies full rate to half rate handover.

[Intracell F-H HO Last Time]


•Description: This parameter indicates the period that satisfies full rate to half rate handover.

[F2H HO th]

•Value Range: 0~39 Unit: dBm Default Value: 25

•Description: This parameter indicates the threshold of a handover from full rate data TCH (TCHF) to half rate data TCH (TCHH). For AMR calls, intra-cell TCHF to TCHH handover is triggered when TCHF is in use and Radio Quality Indication (RQI) is constantly higher than this threshold.

[H2F HO th]

•Value Range: 0~39 Unit: dBm Default Value: 10

•Description: This parameter indicates the threshold of TCHH to TCHF handover. For an AMR call, if the current channel is a HR channel and the RQI is constantly lower than H2F HO th within a period, a TCHH to TCHF handover is triggered.




Data Configuration of AMR HO

[AMR TCH/H Prior Allowed]



•Description: This parameter indicates whether the TCH/H prior function is allowed during the channel assignment. Yes—allowed; No—prohibited.

The channel type to be assigned is decided according to the channel types that are allowed by the MSC and the percentage of seized TCHs in the cell.

During the channel assignment, the TCHF or TCCH, TCHH Prior channels are required when:

Half rate and full rate channels are allowed to be assigned by the MSC.

The AMR TCH/H Prior Allowed is set to Yes.

The percentage of seized TCHs in the cell is greater than the value of AMR TCH/H Prior Cell Load Threshold.

In other cases, the TCHF or TCCH, TCHF Prior channels are required.

[AMR TCH/H Prior Cell Load Threshold]



•Description: The channel type to be assigned is decided according to the channel types that are allowed by the MSC and the percentage of seized TCHs in the cell.

During the channel assignment, the TCHF or TCCH, TCHH Prior channels are required when:

Half rate and full rate channels are allowed to be assigned by the MSC.

The AMR TCH/H Prior Allowed is set to Yes.

The percentage of seized TCHs in the cell is greater than the value of AMR TCH/H Prior Cell Load Threshold.

In other cases, the TCHF or TCCH, TCHF Prior channels are required.




General HO Process





Handover Judgment3





Handover Implementation

No power control during handover in order to make sure the handover is successful

Begin

[Power boost befor HO enabled or not］(s)Yes ?

BTS(s) uses the max. power output

Yes No

BSC send “HO Command” to MS

HO execute

BTS(s) keeps current power output

BTS(s) keeps current power output For BTS

[Power boost befor HO enabled or not］

•Value Range: StartUp,not StartUp,None

•Default Value: not StartUp

•Description: When the MS is in a corner, the receive level may decrease swiftly. Handover may be triggered. At this time, the BSC cannot adjust the power of the MS and BTS in time. The MS cannot receive the handover command. Thus call drop occurs. So the power boosting is necessary before HO.




Data Configuration of Handover Implementation(BTS)




Handover Implementation

No power control during handover in order to make sure the handover is successful

Begin

[MS Power Predictionafter HO］(s) Yes ?

BSC predict power

Yes No

BSC send “HO Command” to MS

HO execute

MS uses the highest power to access For MS

MS will use this predict power in new cell after finishing this handover




Data Configuration of Handover Implementation(MS)

[MS Power Prediction after HO]



•Description: This parameter indicates whether the MS uses the optimum transmit power to access a new channel after the handover. Using the optimum transmit power helps to reduce interference and improve the service performance.




Data Configuration of Handover Implementation(MS)

UL Expected Level at HO Access

•Value Range: 0~63(-110 dBm ~ -47 dBm)

•Unit: dB


•Description: This parameter indicates the expected uplink receive level on a new channel after an MS is handed over to a new cell.This parameter is consistent with UL RX_LEV Upper Threshold in G-II power control.




Summary

In this course, we have learned:

Classification of HO

HO general procedure

HO judgment algorithm

HO implementation process

HO data configuration



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