omf010002 handover issue1.5

Course ContentsSummary of Handover HO Algorithm processHO Data ConfigurationHO Signaling process

Summary of HOPurposes of HOPurposes of HOTo keep a continuous communication with a moving MSTo improve network service performanceTo reduce the call drop rateTo reduce the congestion rate

Classification of HO: Emergency HOTiming Advance (TA) Emergency HOBad quality (BQ) Emergency HO Rx_Level_Drop Emergency HOInterference Emergency HO load HONormal HOEdge HOLayer HOPower Budget (PBGT) HOSpeed-sensitive HO (Fast moving MS HO)Concentric Cell HOSummary of HOClassification of HO

Course ContentsSummary of Handover (HO)HO Algorithm processHO Data ConfigurationHO Signaling process

General HO processMeasurement report preprocessingPenalty processingBasic ranking and Secondary ranking HO judgmentHO Algorithm process

General process of HO Algorithm

HO Algorithm processGeneral HO processMeasurement report preprocessingPenalty processingBasic ranking and secondary ranking HO judgment

Measurement Report PreprocessingMeasurement Report (MR): 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.

Measurement Report Preprocessing

Measurement Report PreprocessingPeriod of measurement reportThe downlink MR is sent to BTS in SACCH uplink The interval is 470ms/per time when MS is on SDCCH The interval is 480ms/per time when MS is on TCH

Measurement Report PreprocessMR interpolation Every time BSC receives a measurement report, there will be an update to the basic rank of the cells.BTS may fail to receive the measurement report from MS. Before the rank-update, BSC needs to recover the lost measurement reports according to Filter Table. If the lost MR amount is within the allowed range, then recovers the lost MR according to the algorithm.

Measurement Report PreprocessHow to interpolate MR?

Measurement Report PreprocessingHow to filter MR?

Filter----Average several continuous MR.

General HO processMeasurement report preprocessingPenalty processingBasic ranking and secondary ranking HO judgmentHO Algorithm process

Penalty ProcessingThere are altogether four types of penalty process (second step of HO algorithm process ) Penalty on the target cell when a HO fails. Penalty on the original serving cell when an emergency HO ( base on BQ and TA ) is performed. Penalty on other high priority layer cells after a fast moving HO is performed. A new HO attempt is prohibited within the penalty time after an overlaid/underlaid HO fails.

Penalty Processing Penalty on the target cell:Punish the target cell when a HO fails. This is to avoid the MS to select this cell again in next HO judgment. BTSHO failureBSCCell ACell B

Penalty Processing Penalty on the serving cell:Punish the original serving cell when an emergency HO ( due to BQ and TA) occurs. BTSBQ& TA HOBSCCell ACell B

Penalty Processing Giving penalty on the other three layers after MS handovers to Umbrella cell by fast-moving-HO. This is to keep MS staying in the umbrella cell and avoid frequent HO.

Penalty Processing A new Overlaid/underlaid HO is prohibited within a penalty time after an Overlaid/Underlaid HO failure.

Underlaid OverlaidDo not attempt again after a failed HO!

HO Algorithm processGeneral HO processMeasurement report preprocessingPenalty processingBasic ranking and secondary ranking HO judgment

Basic Ranking and Secondary RankingBasic ranking and secondary ranking of cells are major parts of the HO judgment. Ranking is made through 16bits-algorithm. The serving cell and the neighbor cells will be listed in a cell list according to their 16bits value. The ranking processes include:M ruleK rule16bits ranking

Basic ranking and Secondary rankingM rule:Only the cells with received signal level satisfy the following conditions can be put into the candidate cell list. For serving cell: RX_LEV (o) >MSRXMIN(o) + MAX(0,Pa(o))i.e : RX_LEV(o) MSRXMIN(o)-MAX(0,Pa(o)) > 0 .. ( 1 ) For Neighbor cell: RX_LEV (n) > MSRXMIN(n)+ MAX(0,Pa(n))+ OFFSET

i.e : Having the same formula as abovePa(0) : MS_TXPWR_MAX(0) PPa(n) : MS_TXPWR_MAX(n) PMS_TXPWR_MAX( ) : The appointed MS transmitting power by the BSS.P : Max_Power_of_MSMax_Power_of_MS : MS maximum transmitting power

K rule Criterion:After the M rule , the serving cell and candidate neighbor cells are ranked in descending order according to the receiving level only.

Basic Ranking and Secondary Ranking

The 16bits ruleBoth the serving cell and the neighbor cells have their own 16bits value. The smaller the value is, the higher the priority and position the cell is in the cell list.

The 1st-3rd bits: bit value is decided 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.

Basic Ranking and Secondary Ranking

The 4th bit: bit value is determined by inter-cell HO ( of the same layer ) hysteresis.The 4th bit of the serving cell is always 0,The receiving signal level of the neighbor cell >= The receiving level of the serving cell + Inter-cell HO ( of the same layer ) hysteresis, bit 4th is set to 0.The receiving level of the neighbor cell < The receiving level of the serving cell + Inter-cell HO ( of the same layer ) hysteresis, bit 4th is set to 1.Note: In PBGT HO, whichever the greater of the inter-cell ( of the same layer ) hysteresis and PBGT threshold, that value will be used in the PBGT HO.Basic ranking and Secondary ranking

The 5th-10th bits: bit value is decided according to their position in Huawei hierarchical network structure.When the signal level of the neighbor cells or the serving cell is lower than the layer HO threshold and hysteresis, this function is turned off and all bits are set to 0.That is to say only when the above criterions are met, then this function take effect. 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.Basic ranking and Secondary ranking

Hierarchical cell structureBasic ranking and Secondary ranking

The 11th bit: bit value is decided by cell-load-sharing criterion.Serving cell: if Cell Load>= Start threshold of load HO, bit 11th is set to 1, otherwise is set to 0.Neighbor cell: if Cell Load>=Receive threshold of load HO, bit 11th is set to 1, otherwise is set to 0.Refer to Load HO Table for the load HO threshold and load req. on candidate cell.Clue : When the cell load is higher than the threshold, then the bit 11th is set to 1.This is done in order to put the cell in a lower part of the cell list.Basic Ranking and Secondary Ranking

12th bit: bit value is decided by co-BSC criterion.Serving cell: is always set to 0.Neighbor cell: if co-BSC with the serving cell, 12th bit is set to 0, otherwise is set to 1.When the signal level from the neighbor cell or the serving cell is lower than layer HO threshold and hysteresis. This function is turned off and the value is set to 0. If the parameter Co-BSC/MSC Adj. in the HO control table is set to No, then this function is turned off and the value is 0. 13th bit : Bit value is decided by Co-MSC parameter, having the same concept as the 12th bit.Basic Ranking and Secondary Ranking

The 14th bit: Layer HO threshold adjustment bitServing cell criterion: Receive level >= layer HO threshold layer HO hysteresis, bit 14th is set to 0. At the same time, bit 13th, 12th and 10th5th bits are set to 0.If the above criterion is not met, then bit 14th is set to 1.Example : 20-5 = 15 ( -95 dBm )Basic Ranking and Secondary Ranking

Basic Ranking and Secondary RankingNeighbor cell criterion: Receive level >=layer HO threshold + layer HO hysteresis, bit 14th is set to 0. At the same time, bit 13th, 12th and 10th5th bits are set to 0If the above criterion is not met, then bit 14th is set to 1.Example : 20+5 = 25 ( -85 dBm )note :The layer HO threshold and hierarchical hysteresis correspond to the value of that individual cells value.Usual situation : When the neighbor cells are of the same layer, each of the neighbor cells layer HO threshold value will be the same. Same concept goes for the layer HO hysteresis. This can maintain the entire hierarchical layers of the cell.

The 15th bit: Bit value is decided by cell typeServing cell or Neighbor cells:When cell type is extension cell 1.When cell type is normal cell 0.The 16th bit: Reserved bitBasic Ranking and Secondary Ranking

General HO processMeasurement report preprocessingPenalty processingBasic ranking and secondary ranking HO judgment

HO Algorithm process

HO Algorithm

Types of HOTypes of HO :Emergency HOTA & BQ HO, interference HO, Rx_Level_Drop HOLoad HONormal HOEdge HO, layer cell HO and PBGT HOFast moving HOOverlaid/underlaid HO

Emergency HOTA HO criterion :TA of the serving cell > TA Thrsh.BQ HO criterion :The average value of the uplink quality of the serving cell > UL Qual. Thrsh.The average value of the downlink quality of the serving cell > DL Qual. Thrsh.Requirements on the target cell (same as the above two types of HO):Select the first cell in the neighbor cell list i.e. lowest 16bits value.

Emergency HORx_Level_Drop HO:Due to downlink signal level dropTriggered upon detecting rapid level drop during MS busy mode. Requirements for the target cell: The target cell is the first cell in the neighbor cell list.

Emergency HOInterference HO (DL&UL) : When the receiving level > receiving threshold level. But Receiving quality < threshold of quality interference.Requirements for the target cell:The target cell is in the cell list.

Cell Load HOCell Load HO Criterions :System load of BSC < Permissible load of HO thresholdLoad of serving cell > Load HO thresholdRequirements for the target cellLoad of target cell < Load HO threshold

Normal HOEdge HO Criterion:In N seconds, when there are P seconds that neighbor cells DL or MSs UL signal level is lower than the Edge HO threshold. Then the criterion is met and Edge HO occurs. This method utilizes the P/N rule. Requirements for the target cell:The target cell should be ranked in front of the serving cell.

Normal HOLayer HO criterions:Serving cell : No requirement.Target cell : Layer of the target cell is lower than the serving cell.Receive level of the target cell > layer cell threshold + layer cell hysteresis.Target cell should be ranked in front of the serving cell. The priority of target cell should be higher than the serving cells.

PBGT HO Criterions :Target cells path loss is smaller than the serving cells path loss by the PBGT threshold value. Satisfying the P/N rule. Target cell should be ranked in front of the serving cell. Note :PBGT HO can only occur between same-priority cell. If the system permits PBGT HO for the cell, PBGT HO can occur in either inter-BSC or inter-MSC. PBGT HO

Fast-Moving HOWhen the serving cell is micro cell :When the MS has traveled through P numbers of cell, and there are Q (=

Overlaid/Underlaid HOOverlaid/underlaid : Division of underlaid and overlaid is decided by MS downlink receive level and TA value.underlaidoverlaid

Overlaid/Underlaid HOCriterion for HO from overlaid to underlaid:TA value => TA threshold + TA hysteresis Or RX_LEV

QuestionCan you list the function of each bit in 16bit ranking?What is the period of measurement report?

Major HO Parameters ConfigurationMajor HO parameter configuration1.[Handover Control Table]2.[Cell Description Table]3.[Adjacent Cell Relation Table]4.[Penalty Table]5.[Emergency Handover Table]6.[Load Handover Table]7.[Normal Handover Table]8.[Fast-Moving Handover Table]9.[Concentric Cell Handover Table]HO data lookup process

Major HO Parameters Configuration [Handover Control Table] -1

Parameter name

Meaning

Value range

Recommended value

Co-BSC/MSC Adj.

It means whether the 12th and 13th bits acts in the 16bit order. Yes means handover in the same BSC/MSC is preferred. No means that the 12th and 13th bits are shielded and set to 0.

Yes, No

Yes

Penalty allowed

It determines whether to punish the target cell of handover failure, or the original served cell of handover upon too big TA or bad quality. The penalty measures can apply to cells in or out of the same BSC.

Yes, No

No

Load HO allowed

It determines whether to perform the handover to share traffic load. Load sharing can lower the channel assignment failure ratio caused by cell congestion, so as to make evener allocation of the service in respective cells, and lower the cell congestion rate, and improve network performance. It only applies in the same BSC or cells at the same level.

Yes, No

No

MS Fast moving HO allowed

It determines whether to handle the fast moving MS with the algorithm. It is only recommended in special areas (such as a highway), to lower CPU load. This algorithm should only be used in suitable conditions, and usually it is not applied.

Yes, No

No

Major HO Parameters Configuration[Handover Control Table] -2

Parameter name

Meaning

Value range

Recommended value

RX_Level_Drop HO allowed

It means whether RX_Level_Drop emergency handover algorithm is allowed, handover the MS which receiving signal level is dropping quickly in advance to avoid potential call drop. This algorithm should be applied in suitable conditions, and usually it is not used. To apply the handover algorithm, BSC must have original measurement report.

Yes, No

No

PBGT HO allowed

It means whether PBGT handover algorithm is allowed. PBGT handover algorithm currently is processed on LAPD board. To avoid Ping-pang handover, PBGT handover is only performed between cells at the same layer and with the same priority, and meanwhile it is only triggered on TCH.

Yes, No

Yes

MS power prediction after HO

It means after a handover whether MS is to use proper predicted transmitting power to access the new channel. This can reduce system interference and improve service quality (this parameter acts when intra BSC handover occurs).

Yes, No

Yes

[Handover control table] -3Major HO Parameters Configuration

Parameter name

Meaning

Value range

Recommended value

MR. Preprocessing

Yes means perform measurement report preprocessing on BTS; No means preprocessing on BSC, then the two parameters of Send original measurement report and Send BS/MS power level do not act. Yes means decreasing of Abis interface signaling and BSC load, and improving of network response time performance. The switch determines where to perform power control. When it is set to Yes, power control is performed at BTS side. When it is set to No, power control is performed at BSC side. When setting this parameter, first be clear whether BTS supports the power control algorithm to set or not.

Yes, No

Yes


Parameter name

Meaning

Value range

Recommended value

Transfer original MR.

It means whether to send the original measurement report to BSC after measurement report preprocessing on BTS. When it is set to Yes, BTS sends not only processed measurement report but also original measurement report to BSC.

Yes, No

No

Transfer BS/MS power class

It means whether to send BS/MS power level from BTS to BSC. This function is used to view the effect of power control on BTS. Meanwhile, when preprocessing is available, if BS/MS power level is not reported, the uplink and downlink balance measurements will be affected, and handover types such as PBGT handover and overlaid/underlaid handover needing power compensation will be abnormal.

Yes, No

Yes


Parameter name

Meaning

Value range

Recommended value

Sent Freq. of preprocessed MR.

It indicates the time interval at which a measurement report is preprocessed at BTS side and sent to BSC the Preprocessed measurement report. This parameter acts only when Measurement report pre-processing is enabled. For 15:1 link configuration, the report frequency should be as low as once per second due to limited link resource. At this time, for handover needing P/N judgment such as edge handover, layer handover, PBGT handover and overlaid/underlaid handover,

Twice per second, Once per second

According to concrete conditions

Major HO Parameters Configuration[Cell Description Table] -1

Parameter name

Meaning

Value range

Recommended value

Layer of the cell

Huwei hierarchical network structure is divided into 4 layers. 16 priorities can be set for each layer, which provides enough room of network planning for the operator to adapt to various complex network environment. Normally, Macro layer is the major 900 layer, Micro layer is the major 1800 layer, Pico is the 900 and 1800 micro cell layer. The smaller layer value, the higher priority.

The 1st~4th layers

M900: the 3rd layer

M1800: the 2nd layer

Cell priority

Each layer may have 16 priorities, used to control the handover priority between cells at the same layer. Usually priorities of cells at the same layer are set the same. For cells at the same layer, the smaller the priority value, the higher the priority.

1~16 priorities

1

Layer HO Thrsh.

It affects the value of the 14th bit in the 16bit ranking, and it is also the level requirement on the target cell for interference handover, layer handover and load handover. Then such level should be higher than layer handover threshold + layer handover hysteresis. The layer handover threshold should be set >= Edge handover threshold + Inter-cell handover hysteresis.

0~63

25

Layer HO hysteresis

Works together with the Layer handover threshold.

0~63dB

3

Major HO Parameters Configuration[Cell Description Table] -2

Parameter name

Meaning

Value range

Recommended value

Penalty on MS Fasting moving HO

It is valid when the fast moving handover algorithm is enabled. It is the signal level penalty value on the other neighbor cells when MS moves fast and is handed over to umbrella cell. The parameter is only valid within the penalty time.

0~63dB

30

Penalty Time on MS Fasting moving HO

It means that within this time, the penalty on the other neighbor cells will be exerted after MS is handed over to umbrella cell by fast moving HO.

0~255 seconds

40

Min DL level 0n candidate cell

This is the min signal level requirement for the cell itself to be a candidate cell. Too low configuration may easily cause call drops, while too high a configuration might turn handover too hard to occur.

0~63

15

Major HO Parameters Configuration[Adjacent Cell Relation Table] -1

Parameter name

Meaning

Value range

Recommended value

Ncell ID

Neighbor cell ID index.

0~255 for internal cell;

0~799 for external cell

Min access level offset

This offset is based on Min downlink level of handover candidate cell. Different offsets can be defined for different adjacent cells, and to enter the candidate cell list, the corresponding adjacent cell receiving signal level must be higher than the sum of Min downlink level of handover candidate cell and Min. Access level offset.

0~63

0

[Adjacent Cell Relation Table] -2Major HO Parameters Configuration

Parameter name

Meaning

Value range

Recommended value

PBGT HO Thrsh.

It means that PBGT handover is performed when the difference between the target cell downlink path loss and the serving cell downlink path loss is bigger than PBGT handover threshold. When PBGT handover is enabled, and Inter-cell handover hysteresis > PBGT handover threshold (corresponding dB value), Inter-cell handover hysteresis takes place of PBGT handover threshold to act. . PBGT handover threshold also needs to be adjusted according to handover performance statistics result.

0~127,corresponding to --64~63dB

It is around 68 in the densely populated downtown, and around 72 on the outskirts.

Inter-cell HO hysteresis

Handover hysteresis between an adjacent cell and the serving cell. It is set to reduce Ping-pang HO. The hysteresis value also needs to be adjusted according to the handover performance statistics result and live network. Flexible configuration of the value can effectively lead handover and traffic between two adjacent cells.

0~63db

It is around 4 in the densely populated downtown, and around 8 on the outskirts.

[Penalty Table] -1Major HO Parameters Configuration

Parameter name

Meaning

Value range

Recommended value

Penalty level after HO fail

The signal level value in dB, to punish the target cell which has caused a HO failure due to problems such as congestion , to prevent MS from a handover re-attempt to that cell again. This value is only valid within the penalty time for handover failure.

0~63dB

30

Penalty time after HO fail

Penalty time on the corresponding target cell after handover failure

0~60 seconds

10

Penalty level after BQ HO fail

The signal level penalty value for the original serving cell, to avoid Ping-pang handover after emergency handover upon bad quality. It is only valid within the penalty time for BQ HO.

0~63dB

63

Penalty time after BQ HO fail

Penalty time for the original serving cell after BQ HO.

0~60 seconds

10

[Penalty Table] -2Major HO Parameters Configuration

Parameter name

Meaning

Value range

Recommended value

Penalty level after TA HO fail

The signal strength penalty value for the original serving cell, to avoid Ping-pang handover after TA emergency handover. It is only valid within the penalty time for ta handover.

0~63dB

63

Penalty time after TA HO fail

Penalty time for the original serving cell after TA emergency handover.

0~60Seconds

10

Penalty time after IUO HO fail

After an overlaid/underlaid handover failure (big circle hands over to small circle or vice versa), within certain time (this parameter configuration value) overlaid/underlaid handover is forbidden for the same call.

0~16Seconds

10

[Emergency Handover Table] -1Major HO Parameters Configuration


Parameter name

Meaning

Value range

Recommended value

UL Qual.Thrsh. for interf. HO

Uplink receiving quality threshold in the serving cell for interference handover. When frequency hopping or DTX is enbaled, RQ becomes worse (normal phenomenon), this value should be set to 60. The adjustment should also base on the current network quality and handover statistics. When triggering interference handover. If the serving cell is in the first position and intra-cell handover is permitted, perform intra-cell handover. Otherwise select the second candidate cell to perform inter-cell handover.

corresponding to BQ levels of 0~7

50, interference quality threshold must be better than the emergency quality threshold

DL Qual. Thrsh. For interf HO.

Downlink receiving quality threshold in the serving cell for interference handover.

0~70, corresponding to BQ levels of 0~7

50


Parameter name

Meaning

Value range

Recommended value

UL RX_LEV Thrsh. for interf.HO

Min uplink receiving power threshold from the serving cell required for interf. HO, when interference handover is triggered if the uplink quality is worse than quality threshold and at this time the uplink signal level is higher than the signal threshold. When triggering interference handover, If the serving cell is in the first position in the cell list, and intra-cell handover permitted, then start intra-cell HO. Otherwise select the second cell to perform inter-cell HO.

0~63

25

DL RX_LEV Thrsh. for interf HO.

Min downlink receiving power threshold from the serving cell required for interf. HO.

0~63

30


Parameter name

Meaning

Value range

Recommended value

Filter parameters A1~A8

Used for configuration of filter for rapid signal drop judgment, and together with filter parameter B, they are 9 parameters for a filter. The corresponding formula is (in the program, A1~A8 is configuration value minus 10 and B is the negative configuration value):

C1(nt)=A1C(nt)+A2C(nt-t)+A3C(nt2t)++A8C(nt-7t)

Where, C (nt) is the receiving signal level in the uplink measurement report of the serving cell sent at the time of nt. If C1 (nt) < B, and C (nt) is below the edge handover threshold, then the signal level is considered to be of rapid drop.

0~20

10

Filter parameter B

Used for configuration of filter for rapid signal drop judgment. Please refer to the explanation for A1~A8 of filter.

0~255

0

[Load Handover Table] -1Major HO Parameters Configuration

Parameter name

Meaning

Value range

Recommended value

System flux Thrsh. for load HO

The pre-condition for load HO is that the system flow (signaling flow) is lower the threshold. This value can not be set too high because load handover upon max threshold may cause serious effect to the system.

0, 8~11 system flow levels, corresponding to 0, 70, 80, 90 and 95.

10

Load HO Thrsh

Load handover is triggered when the serving cell load is higher than the threshold, TCH seized in the cell has reaching the corresponding percentage.

0~7 cell load levels, corresponding to 0, 50, 60, 70, 75, 80, 85, 90

5

Load Req. on candidate cell

The Load threshold for the target cells that can accept MS from serving cell in load HO, i.e. when the TCH under Idle mode in the neighbor cell is lower than the corresponding percentage, the cell refuses to accept MS from serving cell handed over due to the load reason.

0~7, corresponding to 0, 50, 60, 70, 75, 80, 85, 90

2

[Load Handover Table] -2Major HO Parameters Configuration

Parameter name

Meaning

Value range

Recommended value

Load HO bandwidth

This configuration is related to the edge handover threshold. Load handover is only allowed when the MS receiving level from the serving cell is within the range of margin handover threshold, margin handover threshold + load handover bandwidth.

0~63db

25

Load HO step period

When a cell is up to conditions for load handover, all calls within the serving cell will send handover request at the same time, this will cause abrupt increase on processor load, and under certain conditions this will cause the target cell congestion and result in call drops. Thereby, step by step load handover algorithm is used to control handover. The cycle is the time needed for handovers of each step.

1~60 seconds

10

Load HO step level

The whole load HO bandwidth will be divided into several sub-bands by this parameter.

1~63db

5

[Normal Handover Table] -1Major HO Parameters Configuration


Parameter name

Meaning

Value range

Recommended value

Edge HO watch time

It means that within the time statistics, if the time in which the signal level is lower than threshold is higher than the continuous time, then margin HO is to be triggered.

1~16 seconds

5

Edge valid time

See the above.

1~16 seconds

4


Parameter name

Meaning

Value range

Recommended value

PBGT watch time

Statistics time for PBGT HO signal level judgment.

1~16 seconds

5

PBGT valid time

Continuous time for PBGT HO signal level judgment.

1~16 seconds

4


Parameter name

Meaning

Value range

Recommended value

Layer HO watch time

Statistics time for Layer HO judgment

1~16 seconds

5

Layer HO valid time

Continuous time for Layer HO judgment.

1~16 seconds

4

[Fast-Moving Handover Table]Major HO Parameters Configuration

Parameter name

Meaning

Value range

Recommended value

MS Fast-moving watch cells

The cell sum P for judge whether MS is fast moving. The value, if too large, may cause abrupt increase of system flow, while too small value may cause inaccurate judgment for fast moving MS.

1~10

3

MS Fast-moving valid cells

The cell sum N by which MS actually quickly passes. If within P cells that MS continuously past, the number of cells by which the MS is judged to pass quickly is equal to or more than N, then the MS will be judged as a fast moving MS.

1~10

2

MS Fast-moving time Thrsh.

The time threshold (2r/v) determined by the cell radius (r) and moving speed (v). If the time in which MS passes the cell is smaller than the threshold, then MS is judged to quickly pass the cell.

0~255 seconds

15

[Concentric Cell Handover Table] -1Major HO Parameters Configuration

Parameter nameMeaningValue rangeRecommended valueUO signal intensity differenceBTS transmitting Power difference between underlaid and overlaid may cause MS receiving signal intensity difference in underlaid and overlaid . The parameter uaually indicates the antenna EIRP difference in dB between underlaid cell and overlaid cell. According to field measurement, multi-point measurement is necessary if the underlaid and overlaid use different antenna.0~63dbSet according to actual conditions


Parameter nameMeaningValue rangeRecommended valueRX_LEV ThrshRx level hysteresis, TA threshold and TA hysteresis jointly define underlaid area and overlaid area. It must be bigger than edge handover threshold, and the recommended value is: edge handover threshold + signal intensity difference between underlaid and overlaid .0~6325RX_LEV hysteresisWorks with Rx threshold.0~635TA Thrsh.It must be bigger than TA emergency handover threshold.0~63 bit period, with 1 bit period corresponding to 0.55km TA hysteresisWorks with TA threshold.0~63 bit period


Parameter name

Meaning

Value range

Recommended value

UO HO watch time

P/N judgment statistics time for U/O HO judgment.

0~16 seconds

5

UO HO valid time

P/N judgment continuous time for U/O HO judgment.

0~16 seconds

4


Parameter nameMeaningValue rangeRecommended valueAssign optimum layerIn Overlaid/Underlaid, the following selection are available for TCH assignment: (1) The system judges according to the measurement report on SDCCH and assign to the best sub-cell. (2) Select the overlaid first for TCH assignment. (3) Select the underlaid first for TCH assignment. (4) Do not give extra priority.System optimization, overlaid , underlaid , no preferentialSystem optimizationAssign-optimum level Thrsh.If system optimization is selected, estimate (interpolate, filter) current SDCCH level value through uplink measurement value in the former SDCCH measurement report, and compare with Assign-optimum Level threshold, so as to assign overlaid or underlaid channel.If SDCCH is in the overlaid : edge handover threshold + signal intensity difference between underlaid and overlaid + uplink and downlink balance allowance + SDCCH and TCH difference allowance. If SDCCH is in the underlaid : edge handover threshold + uplink and downlink balance allowance + SDCCH and TCH difference allowance. 0~63

HO Parameters ConfigurationHO data lookup processBA2 table defines BCCH frequencies of all neighbor cells. It is sent to MS by system message 5, system message 5-bis and system message 5ter on SACCH channel.MS reports the serving cell and BCCH, BSIC and signal levels of 6 strongest neighbor cells to BSS. This is done through SACCH.MR pre-process is done in BTS. Module number, cell number and CGI of all neighbor cells are derived from Adjacent cell Relation Table, and Cell Description Table (or External Cell Description Table) through BCCH and BSIC in the MR.

HO data lookup process BSC performs HO judgment process, such as basic rank of cells (completed in LAPD board). When BSC finds suitable target, It sends HO request messages containing the target CGI to MPU of BSC. According to CGI, MPU derive the module number of the cell from Cell Module Information Table.MPU sends a HO command message to the target module and step up the inter-cell/ intra-cell HO request counter by one.Summary of BSC HO

HO Signaling processIntra BSC HandoverIntra MSC HandoverInter MSC Handover

Intra-BSC Handover Signaling process

Intra-BSC Handover Signaling processAttentionIn asynchronous HO, if MS could not reach the new TCH channel after the target cell has sent PHY INFO up to max times, the target cell reports CONN FAIL IND to BSC with the reason: HO access failure. After the above message is received, BSC release the assigned TCH channel in the target cell .Max resend times of physical information*Radio link connection timer > Time interval between EST IND and HO DETECT (120~180ms). This is to make sure that the physical information reach MS.

Intra-BSC Handover Signaling process

Handover formula definitionInternal inter cell radio handover success rate =(Successful incoming internal inter cell handovers + Successful outgoing internal inter cell handovers) / (Incoming internal inter cell handovers + Outgoing internal inter cell handovers )Internal inter cell handover success rate =(Successful incoming internal inter cell handovers + Successful outgoing internal inter cell handovers) / (Attempted incoming internal inter cell handovers + Attempted outgoing internal inter cell handovers)Internal inter cell radio handover success rate >= Internal inter cell handover success rate

Measurement Points of Intra BSC Handover

Signaling intra MSCIntra-MSC HO Signaling process

Intra-MSC HO Signaling processChannel Release process

Signaling process between MSCMeasurement Points of Inter-BSC Handover

Inter-MSC HO Signaling processSignaling process Abnormal conditionsThe following conditions will cause HO failureMSC-B fails to identify the target cell.MSC-B does not allow HO to the indicated target cell.The target cell has no channel available.VLR-B has no HO number available.HO error or unsuitable data.

Inter MSC HOSubsequent HO process

Inter MSC HOSubsequent HO processSubsequent HOHighwayMSC-AMSC-CMSC-BMSC-C

Inter MSC HO Signaling processStatistics countersame as Intra MSC HO, Statistics is handled by BSCHO formula-- same as Intra MSC HO

Basic process of HO Signaling processThere is no HO request information for intra-BSC HO, and all of the HO are analyzed and processed in BSC. Once the target cell as required is found in the BSC, Channel activation information is sent to it directly.When the target cell is not in the same BSC, BSC reports CGI numbers of the serving cell and target cell, and HO cause to MSC through Ho-Required. When MSC finds the LAC of the target cell is in the MSC, it sends Ho-Request to the BSC of the target cell, and the target BSC activates the target cell channel to complete the following procedure.When MSC finds that the target cell LAC does not belong to the MSC, it will query its LAI and GCI Table (including LAC and router address of the adjacent MSC), and send Prepare-HO message to the target MSC-B according to the router address. The message includes CGI of the target cell and indication whether or not to allocate HO number, etc. According to the message, the target MSC-B sends HO-Request message to the target BSC-B after demanding HO number (unless it is not required in the indication) from VLR-B, and sends Prepare-HO acknowledgement to serving MSC after received HO-Request acknowledgement, to execute the next procedure.

Intra-BSC HO and Inter-BSC HOMajor differences:Inter BSC HO transfers HO-REQ message through MSC, with CGI of the serving cell and target cell carried in the message.Intra BSC HO does not have any CGI in any messages, it is handled inside BSC.Intra BSC HO only sends HO-Performed to MSC upon completion of HO, and MSC is not involved before that time.In inter BSC HO, MSC is involved since the HO request .

QuestionWhat is the content of PHY INFO? When will the system send this message to MS?Why Internal inter cell radio handover success rate >= Internal inter cell handover success 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.

All the network element will be involved in the HO process, including BTS, BSC and MSC.MS--Responsible for measurement report of the serving cell and neighbor cells. BTS--Responsible for monitoring of uplink received level and quality of each served MS, and monitoring of the interference level on its idle traffic channel.BSC--Processing the measurement report and making handover judgment.MSC--Participating in the confirmation of target cell in inter-BSC handover.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.

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.

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.The SACCH measurement report period varies with the channel occupied by MS in dedicated mode.When associated with SDCCH, SACCH measurement period is 470ms, this is because there is an entire SACCH message block in 2 SDCCH 51-multiframes.When associated with TCH, SACCH measurement period is 480ms, this is because there is an entire SACCH message block in 4 TCH 26-multiframesA 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.

MR Interpolation:The continuity of measurement report is judged by measurement result number. First-order interpolation is employed in the interpolation algorithm for missing measurement report, i.e., to calculate the missing values (linear) between the measurement values at both ends of the missing measurement reports.

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.

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.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.

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.

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.

HW-Overlaid/underlaid HO failure means the failure of handover from the Underlaid to the Overlaid, or from the Overlaid to the Underlaid.RX_LEV(o), RX_LEV(n)-- MS received signal level of the serving cell and the neighbor cell, MSRXMIN(o) and MSRXMIN(n)-- Lowest MS received signal level required by the serving cell and neighbor cell.Pa(o)=MS_TXPWR_MAX(o) P;Pa(n)=MS_TXPWR_MAX(n) P;P =MAX_POWER_OF_MS ;MS_TXPWR_MAX(n)-- Maximum transmission power of mobile phone allowed.MAX_POWER_OF_MS -- Maximum physical transmission power of MS.OFFSET--Minimum access level offsetMAX(0,Pa(o))--The current algorithm takes into consideration only the lowest received power threshold of downlink, uplink is not included. For the uplink: If the physical maximum power of MS exceeds the maximum transmission level required by BSS, then Pa is 0.Otherwise, a compensation value will be added.

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.Relevant parameters: Handover [Cell Description Table]Layer of the cellLevel priority

The handover algorithm starts a handover decision every 0.5 second (one measurement report time). The judgment process is described below:First judge whether the emergency handover switch is set to ON in the handover control data table. If not, emergency handover judgment will not be performed.If emergency handover judgment has been enabled, make judgment on TA, BQ and interference and rapid signal level drop of MS and BTS in the current serving cell. The criteria for rapid signal level drop judgment is decided by the parameters of respective filters in the emergency handover data table. Then start load handover judgment.Then execute normal handover judgment: Start edge handover when it reaches the edge handover trigger threshold within the statistics time.Perform hierarchical HO judgment if edge handover is not triggered. That is, within the statistics time, trigger handover when signal level from a neighbor cell with different layers (low) or priorities (low) has reached layer handover threshold. If layer handover is not triggered, trigger PBGT handover when it reaches PBGT threshold (which can only be performed in the same layer and priority).Then execute fast moving handover judgment. Once conditions are met, start handover and penalty.Finally execute overlaid/underlaid handover judgment. If conditions are met, start overlaid/underlaid handover.According to the aforementioned judgments, BSC sends the handover command.Related parameters: Handover-[emergency handover table]TA Thrsh. DL Qual. Thrsh. UL Qual. Thrsh.

This indicates the falling tendency of signal level. Formula:value=K6*MR6+K5*MR5+K4*MR4+K3*MR3+K2*MR2+K1*MR1Since K1=-K6K2=-K5K3=-K4, so: value=K6*(MR6-MR1)+K5*(M5-MR2)+K4*(MR4-MR3). This formula emphasizes the changing tendency of received signal level in a period of time.

Related parameters: Handover-[Emergency handover table]Filter parameters A1~A8Filter parameter B

Related parameters: Handover-[Emergency handover table]UL Qual. Thrsh. for interf. HO (dBm)DL Qual. Thrsh. for interf. HO (dBm)UL RX_LEV Thrsh. for interf. HO (dBm)DL RX_LEV Thrsh. for interf. HO (dBm)

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 cellLoad handover bandwidth (dB)Load HO step level (dB) Load HO step period (second)Related parameters: Handover - [Normal handover data table]Edge HO UL RX_LEV Thrsh. Edge HO DL RX_LEV Thrsh. Edge HO watch time (second)Edge HO valid time (second)

In areas with densely distributed cells, the actual radio coverage range has become far larger than the distance between BTS. If MS keeps 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 Company develops PBGT handover algorithm that is 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 its necessary to perform handover.PGBT calculation is described as below:PBGT(n) = ( Min ( MS_TXPWR_MAX,P ) - RX_LEV_DL - PWR_C_D ) - ( Min ( MS_TXPWR_MAX (n),P ) - RX_LEV_NCELL(n) )Meanings of respective parameters are as follows:MS_TXPWR_MAX Max MS transmission power allowed by the serving cellMS_TXPWR_MAX (n) Max MS transmission power allowed by the adjacent cell nRX_LEV_DLMS received power from the serving cellRX_LEV_NCELL(n)MS received power from the adjacent cell nPWR_C_DDifference between the downlink transmission power of the serving cell without power control and the actual downlink transmission power of the serving cellP: MS physical Max. transmission powerRelated parameters: Handover - [Fast-moving handover table]MS Fast-moving watch cells - The total number of cells for judging whether a MS is fast moving or not.MS Fast-moving valid cells - Total N of actual cells that MS fast passes. That is, when N equal to or more than Q cells that MS lately passes are fast passing ones, the fast moving micro cell handover algorithm will be started.MS Fast-moving time Thrsh. - Time threshold (2r/v) specified according to the cell radius (r) and the moving speed (v). If the time used by MS to pass this cell is less than this threshold, it means that MS passes the cell quickly.An illustration of how to define the border between the underlaid and the overlaid.

Related parameters: Handover - [Concentric cell handover table]UO Signal intensity difference (dB) - This parameter represents power compensation for the underlaid .RX_LEV Thrsh. (dBm) - This parameter is used to determine, together with the received level hysteresis, TA threshold, and TA hysteresis, the border between the underlaid and overlaid, which must be larger than the margin handover threshold.RX_LEV hysteresis (dBm) - This parameter is used to determine, together with the received level threshold, TA threshold, and TA hysteresis, the border between the underlaid and the overlaid. TA Thrsh. - One of the factors to determine the border between the underlaid and the overlaid. TA hysteresis- One of the factors to determine the border between the underlaid and the overlaid . UO HO watch time (second) - This kind of handover must satisfy P/N rule.UO HO valid time (second).This section introduces the main handover parameter configuration and the lookup process of handover data in the program.

This table describes mainly the handover algorithm, interval of repeated handover, and switches of various handovers.After the Load HO allowed is disable, the 11th bit -- load adjustment bit-- in the 16bits still works. Therefore, the Load HO Thrsh. and Load Req. on candidate cell in [Load handover table] should still be set with much care.

After the RX_Level_Drop HO allowed is enable, BSC can only make a quick judgment on whether it is rapid signal drop with the help of the original measurement report. Therefore, after the Measurement report preprocessing is enable, the Transfer original measurement report should be set to Yes.

Measurement report preprocessing: Indicates whether the measurement report interpolation, filtering and power control are executed at BTS side.Transfer original MR: It works only when Measurement report preprocessing is turned on. In 15:1 configuration, it should be set to No when there are more than two SDCCH/8, otherwise the link rate may be too low. If the Rx_Level_Drop emergency handover algorithm allowed is enable, it should be set to Yes, otherwise the BSC will not be able to judge whether MS has suffered from rapid signal level drop.Transfer BS/MS power class: It works only when Measurement report preprocessing is enable. If the BS/MS power level is not reported to BSC, the BSC uplink/downlink average measurement results will be affected.This table describes various attributes of a cell, such as layer priorities, layer handover threshold, CGI, BCCH frequency, BSIC and M rule parameter.Ensure the consistency of CGI in [Cell module information table], [BSC cell table] and one of the tables including CGI in MSC.Huawei BSC can not acknowledge cells with the CI FFFF, so the CI value can not be set to FFFF, otherwise no handover will be performed.

There is also an [External cell description table], which is the description of external BSC neighbor cells.When modifying data from [Cell description table] or [External cell description table] online, no matter how many cells data has been modified, send all modules when resetting the entire table, otherwise the handover will be abnormal. The neighbor cells of all cells in the BSC are listed in this table, including respective PBGT handover threshold, inter-cell handover hysteresis and minimum level offset.The module No. and cell No. should be correct, otherwise BSC will send incorrect handover command and thus lead to handover failure.The neighbor cell can not be missed out, otherwise BSC can not find it and thus can not send the handover command.There should not be cells with the same BCCH frequency and BSIC in all neighbor cells of one serving cell, BSC will search for the target cell according to the BCCH frequency and BSIC of a neighbor cell. If BSC can not identify the target cell, it will not send handover command. If BSC sends incorrect handover command, rate of successful handover may be low.

As shown in data configuration, there is not only quality threshold requirement, but also level threshold requirement for interference handover. Only when the level value is higher than a certain threshold, and the quality is worse than a certain threshold, it is regarded as interference. This is the difference between interference handover and BQ handover.

The two parameters are both for judging Rapid signal level drop handover.

After MR preprocessing switch is turned on, the reporting frequency of MR will affect the handover speed.

PBGT handover should satisfy P/N judgment.

Hierarchical handover should satisfy P/N judgment.

This table is valid only when MS Fast-moving HO allowed is turned on. It is usually unused, and is suggested to be applied in special places such as highway.In addition to [Concentric Cell Handover Table], the following should also be configured for cells supporting overlaid/underlaid handover:1. Local office--[Carrier configuration table]: Overlaid/underlaid property is the overlaid or underlaid .2. Handover-[Cell description table]: Cell type is normal cell/concentric cell

Overlaid range:Receiving level>=receiving level threshold + receiving level hysteresis and TA< TA threshold - TA hysteresisUnderlaid range:Receiving level= TA threshold + TA hysteresisWhen TA threshold is 63 and TA hysteresis is 0, the underlaid border is determined completely by the receiving level parameter.When the receiving level threshold is 63 and receiving level hysteresis is 0, the underlaid border is determined completely by TA parameter.

Overlaid/underlaid HO should satisfy P/N rule.This is the feature of overlaid/underlaid handover, i.e. to assign overlaid or underlaid first when assigning voice channel.

Precautions in Incoming to BSC HO optimum layer configuration:1. BCCH TRX should be configured on the underlaid 2. SDCCH should be configured on the underlaid 3. If the receiving level threshold and receiving level hysteresis, or TA threshold and TA hysteresis are configured as 63 and 63, the handover between the underlaid and overlaid will be disabled.

Precautions:1. The module No., cell No. and CGI of all neighbor cells should be found before BSC performs basic cell ranking2. In adjacent cell relation table: If there are cells with the same frequency and BSIC in neighbor cells, BSC will fail to identify the right target cell. As a result, the handover command may be sent incorrectly, thus the handover successful rate will be affected.3. Cell ranking and HO judgment are performed in LAPD board. The handover request message is sent via MPU, therefore the connection between LAPD and MPU is Cell module information table, with CGI as index.4. Once there is no CGI find in the Cell module information table, MPU may regard the target cell as an outer BSC cell. It will send HO-Request to MSC, and count it as an Outgoing-BSC handover request.5. In case of incorrect module No. in Cell module information table, the handover request will be sent to wrong modules and the handover will fail. However, BSC will still count it as an inter-cell handover request.

After receiving the SABM frame reported by MS, BTS will report Establish_IND to BSC, and respond UA frame to MS hereafter. Not until the UA frame is received, MS will send HO-Complete message to the network. SABM and UA, corresponding to each other, are link creation frames of Layer 2 of Um interface. In poor radio environment (weak signal or interference), the network can not receive the SABM frame sent by MS, or MS can not receive UA frame. Either condition will lead to handover failure, and the failure cause value is radio link failure.For synchronous handover in BSC, i.e. When BTS1 and BTS2 is the same BTS, there will be no PHY INFO message. MS reports SABM connection frame right after report of Handover Access message. After receiving the HO-Complete message, BSC will send first HO-Performed message to MSC, and will release the radio channel resource of old BTS. The old BTS1 will respond RF-Channel-ACK to BSC.

The above process include the counter for incoming of target cell and outgoing of original cell.The measurement points of key counter are as follows: 1. Before sending "Channel-Activation" to the target BTS, BSC measures "Request times of in-cell handover in BSC" The number of times of request intra-BSC incoming cell handover and "Request times of out-cell handover in BSC" The number of times of request intra-BSC outgoing cell handover.2. After sending "HO-Command" to MS, BSC measures "Request times of in-cell handover in BSC" The number of times of request intra-BSC incoming cell handover and "Request times of out-cell handover in BSC". The number of times of request intra-BSC outgoing cell handover.3. After receiving "HO-Complete" from MS, BSC measures "Success times of in-cell handover in BSC" The number of times of successful intra-BSC incoming cell handover and "Success times of out-cell handover in BSC". The number of times of successful intra-BSC outgoing cell handover.

Difference between "Internal inter cell handover success rate " and "Cell radio handover success rate " :As viewed from formulas, both numerators are success times of handover, while the denominators are different. While viewed from the measurement points of the counter, Attempted inter cell handovers >= inter cell handovers, so intra BSC handover success rate = inter BSC inter cell handover success rate.

Note: This release is originated from the network side. For the release is originated actively by MS, the signaling process is the same except the three transparent transmission direction mentioned above is reversed.

Note: Signaling process of A interface and Abis interface of inter MSC handover is the same as that of intra MSC handover, only the signaling between two MSC is particular for the inter-MSC handover. As shown in above figure the signaling with "MAP" is of the MAP layer, and signaling of A and Abis interfaces are omitted. After receiving "HO-REQUIRED" of BSC-A (the request message includes CGI of the original cell and target cell), if MSC-A finds that LAC of the target cell doesnt belong to this MSC, MSC-A will query the "REMOT LAC Table (including the LAC and route of the adjacent MSC), and send "Prepare-HO" message to MSC-B according to the route. CGI of the target cell and the indicator of whether to allocate the handover number are included in this Prepare-HO message. According to the received "Prepare-HO" message, if the handover number needs allocating, MSC-B will request the local VLR to allocate the handover number. If VLR has the free handover number, the handover number will be sent to MSC-B through "Send-HO-Report". If no handover number is needed, proceed to the next step.After SCCP link between MSC-B and BSC-B is established, MSC-B sends "HO-REQUEST" to BSC-B. After that, BSC-B activates the target cells channel, and returns "HO-REQUEST ACK" to MSC-B after receiving the channel activation acknowledgement. According to this message, MSC-B sends "Prepare-HO ACK" to MSC-A. MSC-A establishes the route to MSC-B according to the handover number, and sends "Initialize-Address" (IAI) to MSC-B to help the latter to identify which voice channel is reserved for MS. While MSC-B returns "Address-Complete" (ACM) to MSC-A.

After receiving the ACM message, MSC-A sends "HO-Command" to MS. After that MS handover access is performed in the new channel. If its successful, UA frame from BTS-B will be received, and "HO-Complete" will be sent to MSC-B. MSC-B sends "Send-End-Signal" to notify MSC-A to release the original channel. After receiving "Clear-Complete" from BSC-A, MSC-A returns "Sent-End-Signal ACK" to MSC-B, thus finishing the inter MSC handover process.

Description:1. When MSC-B receives handover request for a second time, it will first view whether its CGI belongs to local MSC. If yes, it executes internal MSC handover process, and inform MSC-A after the handover.2. If not, it will not send handover request directly to MSC-B, but send Perform-Subs-HO message to MSC-A, and this message contains MSC-B identification.3. MSC-A finds out in Location cell table that CGI belongs to MSC-B, and then sends Perform-HO message to MSC-B.4. MSC-B applies a new handover number from VLR-B and activates the channel resource. It informs MSC-A Wireless-Channel-ACK, and create a route between MSC-A and MSC-B via IAI and ACM.5. MSC-A returns Subs-HO-ACK message to MSC-B, and MSC-B sends HO-COMD to MS. MS will inform MSC-B after successful access.6.MSC-B sends end signal to MSC-A, and MSC-A sends this signal to MSC-B. MSC-B sends clear command to BSC-B to release the original channel, then remove the physical signal between MSC-A and MSC-B.7. MSC-A sends end signal to MSC-B, and the latter will inform VLR-B to release the handover number.

Exception: If the second handover is back to MSC-A, no handover number is needed. MSC-A will find its BSC to send handover request directly.Note: According to the subsequent handover process, during a continuous conversation through several MSCs, the first MSC created in a conversation must make all other MSCs as the neighbor ones, otherwise the handover may fail.

Note: If there is no handover number available for destination MSC-B, it will return HO-Request-Refuse message to the source MSC-A. There will be no statistics in the destination BSC, but one out-BSC handover request time and one Out-BSC handover failure.

omf010002 handover issue1.5

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