Huawei Hand Over

HandoverHuawei Wireless Training Department

ContentsSummary of Handover(HO)HO Algorithm FlowHO Data ConfigurationHO Signaling Flow

Summary of HO

Purpose of HOClassification of HOSummary of HO

Summary of HOPurpose of HOPurpose of HOTo keep moving MS continuous communicationTo improve network service performanceTo reduce the call drop rateTo reduce the congestion rate

Classification of HO: according to different HO triggering conditions 1.Emergency HOTA Emergency HO Bad quality(BQ) Emergency HO Rapid signal drop(RSD) Emergency HO Interference Emergency HO 2.Load HO3.Normal HOMargin HO Hierarchical HO PBGT HO4.Speed-sensitive HO (Fast moving HO)5.Over-layer/under-layer HO Summary of HOClassification of HO

Summary of HOClassification of HOClassification of HOsynchronization HOasynchronism HODifferenceIn the process of asynchronism HO,system transmit physical message to MS,but in the process of synchronization HO not the message

HO Algorithm FlowHO Algorithm FlowGeneral HO flowMeasurement report preprocessingPenalty processingBasic sequencing of cells and adjustment of network characteristicsHO judgement

General Flow of HO Algorithm

HO Algorithm FlowHO algorithm flowGeneral HO flowMeasurement report preprocessingPenalty processingBasic sequencing of cells and adjustment of network characteristicsHO judgment

Measurement Report Preprocessing

Measurement Report PreprocessingPeriod of measurement reportThe measurement report is sent to BTS in SACCH uplink1.The interval is 470ms/per time when MS is on SDCCH2.The interval is 480ms/time when MS is on TCH

Measurement Report PreprocessingMissing MR processingEvery time BSC receivesa measurement report, there will be a update to the basic sequencing of cells.As BTS may fail to receive the measurement report from MS, so before the sequencing updating, BSC needs to recover the missing measurement report according to Filter Data Table. If the missing MR amount is within the allowed range, then recover the missing MRs according to the algorithm.

How to recover a MR?


How to filter the measurement report?

Filter----Average several continuous MR.


HO Algorithm Flow General HO flow Measurement report preprocessing Penalty processing Basic sequencing of cells and adjustment of network characteristics HO judgment HO Algorithm Flow

Penalty ProcessingThere are altogether four types of penalty processing1. Penalty on the target cell when a HO fails.2. Penalty on the original serving cell when an emergency HO is performed.3. Penalty on the other non-layer4 cells after a fast moving HO is performed4. A second HO is prohibited within the penalty time after a over-layer/under-layer HO fails.

Penalty Processing1. Penalty on the target cell:Punish the target cell where a HO fails to avoid MS to select this cell again in another HO judgment and fail again.BTSHO failureBSCCell ACell DBSC gives corresponding signal level penalty on cell D

2. Penalty on the serving cell:Punish the original serving cell after TA\BQ HO, to avoid it to be handed over to the original cell again and cause ping-pang HO.BTSBQ HOBSCCell ACell DIn cases of HO from cell A to cell D due to poor quality, punishing the original serving cell (cell A)Penalty Processing

3. Give penalty to all non-layer4 neighbor cells after MS is handed over to a layer4 cell(Umbrella cell) by fast moving HO, to keep MS staying in the umbrella cell and avoid frequent HO.Penalty Processing

4. A second over-layer/under-layer HO is prohibited within the penalty time after an over-layer/under-layer HO failsPenalty ProcessingUnder-layerOver-layerNo second attempt after a failed HO!

HO Algorithm FlowGeneral HO flowMeasurement report preprocessingPenalty processingBasic sequencing of cells and adjustment of network characteristicsHO judgmentHO Algorithm Flow

Basic Sequencing of Cells and Adjustment of Network CharacteristicsBasic sequencing of cells and adjustment of network characteristics are major parts of the HO judgment. Sequencing is made by 16bits algorithm. The serving cell and the candidate neighbor cells will be listed in a cell list according to their 16bits value. The sequencing process includes:M ruleK rule 16bits sequencing

I. M judgment:According to the min downlink receiving power and the min receiving level offset of the reportedneighbor cell, judge whether the cell is qualified as a candidate neighbor cell to be put into the cell list for handover.M rule: only the cells with receiving signal level satisfy the following conditions can be put into the candidate cell list. For serving cell: RXLEV (o) >MSRXMIN(o) + MAX(0,Pa(o))For neighbour cell: RXLEV(n) > MSRXMIN(n)+ MAX(0,Pa(n)) + OFFSETBasic Sequencing of Cells and Adjustment of Network Characteristics

II. K rule:The cells surviving from M rule, including the serving cells and candidate neighbor cells, are sequenced according to their receiving signal level which is actually a part of 16bits rule.Basic Sequencing of Cells and Adjustment of Network Characteristics

Basic Sequencing of Cells and Adjustment of Network CharacteristicsIII. 16bits ruleBoth the serving cell and the neighbor cell have their own 16bits value. The smaller the value is, the higher the priority and the position is in the cell list.

The 1st-3rd bits: bit value is decided according to the cell signal level.The value result of 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 000.16910111213141512345678

Basic Sequencing of Cells and Adjustment of Network CharacteristicsThe 4th bit: bit value is decided by inter-cell HO hysteresis.The 4th bit of the serving cell is always 0,The receiving level of the neighbor cell > The receiving level of the serving cell + Inter-cell HO hysteresis, set to 0.The receiving level of the neighbor cell < The receiving level of the serving cell + Inter-cell HO hysteresis, set to 1.Note: In PBGT HO, if inter-cell hysteresis is larger than PBGT threshold, then inter-cell hysteresis will replace PBGT threshold.

Basic Sequencing of Cells and Adjustment of Network Characteristics before adding hysteresis after adding hysteresis function of hysteresis the neighbor cellthe neighbor cellthe serving cellthe serving cell

Basic Sequencing of Cells and Adjustment of Network CharacteristicsThe 5th-10th bits: bit value is decided according to their position in Huawei hierarchical network structure.When the signal level of the neighbor cell or the serving cell is lower than the hierarchical HO threshold(hysteresis), shield it and set all bits to 0).Huawei network 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 network.

Hierarchical network structure Basic Sequencing of Cells and Adjustment of Network Characteristics

Basic Sequencing of Cells and Adjustment of Network CharacteristicsThe 11th bit: bit value is decided by cell load

Serving cell: if Load>= Start threshold of load HO, set to 1, otherwise set to 0.

Neighbor cell: if Load>=receive threshold of load HO, set to 1, otherwise set to 0.

Refer to Load HO Data Table for the start threshold and receive threshold of load HO.

Basic Sequencing of Cells and Adjustment of Network CharacteristicsThe 12th and 13th bits: bit value is decided by co-BSC/MSC adjustmentServing cell: always 0Neighbor cell: if co-BSC/MSC with the serving cell, set 12/13 to 0, otherwise set to 1, 12th bit is for BSC, 13th bit is for MSC.

When the signal level from the neighbor cell or the serving cell is lower than the hierarchical HO threshold( including hysteresis) or co-BSC/MSC adjustment is not allowed, shield them and set 12/13 to 0.

Basic Sequencing of Cells and Adjustment of Network CharacteristicsThe 14th bit: Hierarchical HO threshold adjustment bit

Serving cell: The receiving level >= hierarchical HO threshold - hierarchical HO hysteresis, set to 0. Otherwise set to 1, and meanwhile, the 13th, 12th and 10th5th bits are set to 0

Neighbor cell: The receiving level >= hierarchical HO threshold + hierarchical HO hysteresis, set to 0. Otherwise set it to 1, and meanwhile, the 13th, 12th and 10th5th bits are set to 0

Basic Sequencing of Cells and Adjustment of Network CharacteristicsThe 15th bit: bit value is decided by cell type

No matter it is a serving cell or a neighbor cell:For an extension cell, set to 1.For a normal cell, set to 0.

The 16th bit: a reserved bit

HO Algorithm Flow General HO flow Measurement report preprocessing Penalty processing Basic sequencing of cells and adjustment of network characteristics HO judgmentHO Algorithm Flow

HO Judgment Order

HO JudgmentTypes of HO Judgment:

Emergency HO----TA, BQ, Interf. RSDLoad HONormal HO----margin HO, hierarchical HO and PBGT HOFast moving HOOver-layer/under-layer HO

Emergency HOTA HO:TA of the serving cell is bigger than emergency HO TA limitBQ HO:1. The average value of the uplink quality of the serving cell is bigger than the uplink quality limit of emergency HO2. The average value of the downlink quality of the serving cell within is bigger than the downlink quality limit of emergency HORequirements for the target cell (same for the two types of HO):Select the neighbor cells with highest position(lowest 16bits value) except the serving cell.

Emergency HORSD HO:Triggered upon detecting rapid signal drop during the call:Requirements for the target cell: the target cell is in the highest position in the cell list.

Emergency HOInterference HO: also classified as emergency HO, and triggered when the receiving level is bigger than a certain value but the receiving quality is worse than the quality threshold of interference HO.

Requirements for the target cell:1. The target cell is in the near front position, unrequested before the serving cell2. The signal level of the target cell should be bigger than the hierarchical HO threshold + the hierarchical HO hysteresisIf there is no candidate cell other than the serving cell in the cell list, and intra-cell HO is allowed, then start intra-cell HO. Otherwise, no HO is performed.

Load HOLoad HOTo trigger load HO, 3 pre-conditions should be satisfied at the same time:The system signaling flow is less than load HO flow level thresholdThe load of the cell needing HO is higher than load HO start thresholdThe load of the cell receiving HO is lower than load HO receive thresholdRequirements for the target cell: the receiving level should be bigger than the hierarchical HO threshold + hierarchical HO hysteresis. It should be in the highest position except the serving cell in the cell list.

Normal HOMargin HO:1. The serving cell receiving signal level is already lower than the margin HO threshold2. Within the margin HO statistics time, for example 5 seconds, the time in which the signal level of the serving cell lower than the margin HO threshold is longer than margin HO continuous time, for example 4 seconds3. The target cell ranks the highest in the cell list

margin threshold

Normal HOHierarchical HO:

1. hierarchical HO only exists between different layers or different priorities at the same layer, and there is no hierarchical HO between cells from the same layer and with the same priority.2. The triggering condition is that the signal level of the neighbor cell is higher than the hierarchical HO threshold + hysteresis, while there is no requirement for the level of the serving cell.3.The neighbor cell ranks higher than the serving cell and has higher priority than the serving cell 4. P/N judgment is satisfied, for example, within 5 seconds, the time that the cell is in the first position of the cell list is longer than 4 seconds.5. It can only choose one between margin HO and hierachical HO,it is first judging whether triggering margin HO then judging whether triggering hierachical HO.Attention: from low priorityhigh priority, emergency HO, margin HO and hierarchical HO are possible from high prioritylow priority, emergency HO and margin HO are possible, and hierarchical HO is not.

PBGT HOPBGT HO algorithm is based on path loss. PBGT HO algorithm looks for whether there is a neighbor cell with lower path loss and satisfying certain system requirements, and judges whether HO is necessary. PBGT HO brings the following advantages:Solution for problems of cross-cell coverage.Less times of dual band HO.More flexible method for traffic distribution control.Always offer users with the best service currently available. Reduce the overall network interference.Attention: the largest difference between it and other HO algorithms is----the triggering condition for PBGT is path loss instead of receiving power. To avoid Ping-pang HO, PBGT only happens between cells from the same layer and with the same priority.

PBGT HO

Triggering rule of PBGT HO:

The path loss of the neighbor cell is less than the serving cells by certain value which is called the PBGT HO threshold The neighbor cell ranks higher than the serving cell do in the cell listMeeting P/N rule in PBGT HO statistics time

Attention: PBGT is only available for TCH HO. PBGT HO

Fast Moving HOCriteria: Among the statistics cells, if the actual number of cells the MS past fast is equal to or more than fast moving cell actual number, then the MS will be handed over to the neighbor layer 4 cell.

Over-layer/Under-layer HOOver-layer/under-layer cell: able to realize tight frequency reuse in the under-layer subcell(inner circle) and wide coverage in the over-layer subcell(outer circle)

Over-layer/Under-layer HOOver-layer/under-layer cell: division of inner circle and outer circle is decided by MS downlink receiving level and TA value.

Summary of HOHO Algorithm FlowHO Data ConfigurationHO Signaling Flow

Major HO parameter configurationHO data lookup processHO Parameter Configuration1.[HO Control Data Table]2.[Cell Description Data Table]3.[Adjacent Cell Relation Table]4.[Penalty Data Table]5.[Emergency HO Data Table]6.[Load HO Data Table]7.[Normal HO Data Table]8.[Fast Moving HO Data Table]9.[Over-layer/under-layer HO Data Table]

1.[HO Control Data Table] -1

HO Parameter Configuration

Parameter name

Meaning

Value range

Recommended value

Allow common BSC/MSC adjustment

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

Allow penalty processing

It determines whether to punish the destination 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

Allow load handover

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 ratio, and improve network performance. It only applies in the same BSC or to cells at the same priority, with respect to TCH.

Yes, No

No

Allow fast moving micro cell handover algorithm

It determines whether to handle the fast moving MS with the algorithm. This algorithm enables fast moving MS handover to macro cell and lowers times of handover. 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

1.[HO Control Data Table] -2Major HO Parameter Configuration

Parameter name

Meaning

Value range

Recommended value

RXLEV drop HO algorithm allowed

It means whether RSD 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 algorithm 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. PBGT handover algorithm can effectively avoid co-frequency or adjacent frequency interference.

Yes, No

Yes

Post-HO PWR pred. Alg. allowed

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 in BSC).

Yes, No

Yes

Major HO Parameter Configuration 1.[HO Control Data Table] -3

Parameter name

Meaning

Value range

Recommended value

BTS meas. report pre-processing

It means whether to perform measurement report preprocessing on BTS. No means preprocessing on BSC, when 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 improvement 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 meas. report

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 level

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 over-layer/under-layer handover needing power compensation will be abnormal.

Yes, No

Yes


Parameter name

Meaning

Value range

Recommended value

Pre-processing meas. report frequency

It indicates the time interval at which a measurement report is preprocessed at BTS side and sent to BSC the Pre-processing measurement report. This parameter acts only when Measurement report pre-processing is open. 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 margin handover, inter-level handover, PBGT handover and over-layer/under-layer handover, it is necessary to shorten P/N judgment time, because P/N judgment time is correspondingly twice the number of measurement reports in the program, and when the measurement report frequency is lowered, the actual judgment time of BSC is lengthened.

Twice per second, Once per second

According to concrete conditions

2.[Cell Description Data Table] -1

Major HO Parameter Configuration

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 networking 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

Hierarchical handover threshold

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

0~63dB

25

hierarchical handover hysteresis

Works together with the hierarchical handover threshold.

0~63dB

3

Major HO Parameter Configuration 2.[Cell Description Data Table] -2

Parameter name

Meaning

Value range

Recommended value

Speed penalty value

It is valid when the fast moving handover algorithm is open. It is the signal level penalty value on the non-layer4 neighbor cells when MS moves fast and is handed over to layer4 cell. The parameter is only valid within the speed penalty time.

0~63dB

30

Speed penalty duration

It means that within this time, the penalty on the non-layer4 neighbor cells will be exerted after MS is handed over to layer4 cell by fast moving HO.

0~255 seconds

40

Min downlink power of handover candidate cell

This is the min signal level requirement for all candidate cells in M rule. Too low configuration may easily cause call drops, while too high a configuration might turn handover too hard to occur.

0~63db

15

3.[Adjacent Cell Relation Table] -1Major HO Parameter Configuration

Parameter name

Meaning

Value range

Recommended value

Adjacent cell ID

The index value of the adjacent cell. Case 1, if the adjacent cell module number is not the outer-BSC cell, then the adjacent cell ID value ranges 0~255. Case 2, if the adjacent cell module number is the outer-BSC cell, then the adjacent cell ID value ranges 0~799.

Min access level offset

This offset is based on Min downlink power 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 bigger than the sum of Min downlink power of handover candidate cell and Min. Access level offset.

0~63db

0

Major HO Parameter Configuration 3.[Adjacent Cell Relation Table] -2

Parameter name

Meaning

Value range

Recommended value

PBGT handover threshold

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 open, 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 and live network.

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

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

Inter-cell handover hysteresis

Handover hysteresis between an adjacent cell and the serving cell at the same layer. 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.

Major HO Parameter Configuration 4.[Penalty Data Table] -1

Parameter name

Meaning

Value range

Recommended value

HO failure cell strenth penalty

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

HO failure penalty duration

Penalty time on the corresponding target cell after handover failure

0~60 seconds

10

BQ HO strength penalty

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

BQ HO penalty duration

Penalty time for the original serving cell after BQ HO.

0~60 seconds

10

Major HO Parameter Configuration 4.[Penalty Data Table] -2

Parameter name

Meaning

Value range

Recommended value

TA HO strength penalty

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

TA HO penalty duration

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

0~60Seconds

10

Under-layer/over-layer HO penalty duration

After a under-layer/overlayer handover failure (big circle hands over to small circle or vice versa), within certain time (this parameter configuration value) under-layer/over-layer handover is forbidden for the same call.

0~16Seconds

10

Major HO Parameter Configuration 5.[Emergency HO Data Table] -1

Parameter name

Meaning

Value range

Recommended value

Emergency TA HO threshold

When TAthis value, emergency handover is triggered

0~63 bit period

63

Emergency HO DL qual. threshold

The downlink receiving quality threshold for BQ emergency handover. When frequency hopping or DTX is open, RQ becomes worse (normal phenomenon), this value should be set to 70. The adjustment should also base on the current network quality and handover statistics. When triggering emergency handover, the first to select is the inter-cell handover, the intra-cell handover is only triggered when there is no candidate cell and the intra-cell handover is allowed in the serving cell.

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

60

Emergency HO UL qual. threshold

The uplink receiving quality threshold for BQ emergency HO.

corresponding to BQ levels of 0~7

60


Parameter name

Meaning

Value range

Recommended value

Interf. HO UL quality threshold

Uplink receiving quality threshold in the serving cell for interference handover. When frequency hopping or DTX is open, 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

Interf. HO DL quality threshold

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

Interf. HO UL Rx PWR threshold

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 opens intra-cell handover, then start intra-cell HO. Otherwise select the second cell to perform intr-cell HO.

0~63db

25

Interf. HO DL Rx PWR threshold

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

0~63db

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

Major HO Parameter Configuration 6.[Load HO Data Table] -1

Parameter name

Meaning

Value range

Recommended value

Load HO flow level threshold

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 unexpected effect to the system.

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

10

Load HO start threshold

Load handover is triggered when the serving cell load is higher than the threshold, i.e. TCH occupied 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 HO Rx threshold

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

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

2

Major HO Parameter Configuration 6.[Load HO Data Table] -2

Parameter name

Meaning

Value range

Recommended value

Load handover bandwidth

This configuration is related to the margin 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

Graded load HO cycle

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

Graded load HO cycle

The whold load HO bandwidth will be divided into several subbands by this parameter.

1~63db

5

Major HO Parameter Configuration 7.[Normal HO Data Table] -1

Parameter name

Meaning

Value range

Recommended value

Margin HO uplink threshold

During the statistics time, if the time in which the uplink receiving level is lower than the value is higher than certain time called continuous time, margin handover will be performed. If PBGT handover is open, corresponding margin handover threshold will be set lower.

0~63db

25 (without PBGT handover, downtown), 15 (single station on outskirts), 15 (with PBGT handover, downtown)

Margin HO downlink threshold

Downlink consideration for margin HO.

63db

30 (without PBGT handover, downtown), 20 (single station on outskirts), 20 (with PBGT handover, downtown)


Parameter name

Meaning

Value range

Recommended value

Margin handover statistics 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

Margin handover continuous time

See the above.

1~16 seconds

4


Parameter name

Meaning

Value range

Recommended value

PBGT handover statistics time

Statistics time for PBGT HO signal level judgment.

1~16 seconds

5

PBGT handover continuous time

Continuous time for PBGT HO signal level judgment.

1~16 seconds

4


Parameter name

Meaning

Value range

Recommended value

Hierarchical handover statistics time

Statistics time for Hierarchical HO judgment

1~16 seconds

5

Hierarchical handover continuous time

Continuous time for Hierarchical HO judgment.

1~16 seconds

4

Major HO Parameter Configuration 8.[Fast Moving HO Data Table]

Parameter name

Meaning

Value range

Recommended value

Fast moving cell meas. number

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

Fast moving cell actual number

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

Fast moving time threshold

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

Major HO Parameter Configuration 9.[Over-layer/under-layer HO Data Table] -1

Parameter name

Meaning

Value range

Recommended value

U/O intensity difference

BTS transmitting Power difference between inner circle and outer circle may cause MS receiving signal intensity difference in inner circle and outer circle. The parameter indicates power compensation value for the inner circle, and it is usually antenna output power difference in dB between inner circle and outer circle. According to field measurement, multi-point measurement is necessary if the inner circle and outer circle use different antenna.

0~63db

Set according to actual conditions


Parameter name

Meaning

Value range

Recommended value

Rx level threshold

Rx level hysteresis, TA threshold and TA hysteresis land this threshold jointly define inner circle area and outer circle area. It must be bigger than margin handover threshold, and the recommended value is: margin handover threshold + signal intensity difference between inner circle and outer circle.

0~63db

25

Rx level hysteresis

Works with Rx threshold.

0~63db

5

TA threshold

It must be bigger than TA emergency handover threshold.

0~63 bit period, with 1 bit period corresponding to 0.55km

TA hysteresis

Works with TA threshold.

0~63 bit period


Parameter name

Meaning

Value range

Recommended value

U/O handover statistics time

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

0~16 seconds

5

U/O handover continuous time

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

0~16 seconds

4


Parameter name

Meaning

Value range

Recommended value

Assign optimum layer

In U/O cells, the following selection are available for TCH assignment: (1) The system judges according to the measurement report on SDCCH and assign to the best cell. (2) Select the outer circle first for TCH assignment. (3) Select the inner circle first for TCH assignment. (4) Do not give extra priority.

System optimization, over-layer subcell, under-layer subcell, no preferential

System optimization

Assign-optimum level threshold

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 outer or inner circle channel.

If SDCCH is in the outer circle: margin handover threshold + signal intensity difference between inner circle and outer circle + uplink and downlink balance allowance + SDCCH and TCH difference allowance. If SDCCH is in the inner circle: margin handover threshold + uplink and downlink balance allowance + SDCCH and TCH difference allowance, for the time being. 25 is recommended for the time being.

0~63dbm


Parameter name

Meaning

Value range

Recommended value

Intra-BSC intercell HO optimum algorithm

When the cell is configured into a U/O cell, there are two processing methods for incoming handover request in BSC: (1) No special processing for channel assignment. (2) Add BCCH signal level value of the target cell in inter-cell handover request message to BSC to make BSC allocate optimum channel for MS from inner cell or outer cell.

Yes, No

Yes

Incoming BSC HO optimum layer

If there is a incoming BSC HO, and the target cell is a U/O cell, then, this parameter will show which layer is prefered to provide service fro the MS.

Outer circle, inner circle, none

None

HO Data Configuration Major HO data configurationHO data lookup process

1.[HO Control Data Table]2.[Cell Description Data Table3.[Adjacent cell Relation Table]4.[Penalty Data Table]5.[Emergency HO Data Table]6.[Load HO Data Table]7.[Normal HO Data Table]8.[Fast Moving HO Data Table]9.[Over-layer/under-layer HO Data Table]

1.BA2 table defines BCCH carriers of all defined neighbor cells, and they are sent to MS by system message 5 on SACCH.2.MS reports BCCH carriers,BSICs and signal levels of the max. 6 neighbor cells which have highest signal levels out of all the defined neighbor cells, and of the serving cell to BSS (through measurement reports)3.After pre-processing of measurement reports, BSC ascertains module numbers, cell number and CGI of all neighbor cells through Adjacent cell Relation Table and Cell Description Data Table (or Outer Cell Description Data Table) by the aid of BCCH carrier and BSIC.4.BSC performs HO judgment processes such as basic sequencing of cells (completed in LAPD board),and it sends HO request messages carrying target cell CGI to MPU of BSC once finds suitable target.Then according to CGI, MPU ascertains the module number of the cell in Cell Module Information Table.5.MPU sends a HO request message to the module and counts Outgoing HO request one time. The process to Look for HO Data

Summary of HOHO Algorithm FlowHO Data ConfigurationHO Signaling Flow

HO Signaling FlowHO in BSCHO in MSCHO between MSCs

HO in BSCSignaling Flow

PrecautionsFor the asynchronous HO, if MS still could not access the new channel after the target cell sends PHY INFO up to max times, the target cell reports CONN FAIL IND to BSC, with the reason: HO access failure. After receiving the message, BSC starts the release flow for the new channel in the target cell . Attention: Max resending times of physical information*Radio link connection timer > Time interval of EST IND~HO DETECT (120~180ms), to make full use of the physical information in case the link is unstable.HO in BSC

Statistics counter pointsHO in BSC

MS BTS(Source) BSC BTS(Target) MSC

Measurement Report

Measurement Report

T09++

Handover algorithm judges outgoing handover request (incoming handover request reaches) T12++

Channel Activation

Channel Activation ACK

Handover Command (Old FACCH)

Handover Access (New FACCH)

Handover Complete (New FACCH) T10++ T13++

RF Channel Release

Handover Performed

Incoming handover request times in BSC

Outgoing handover request

times in BSC

Successful incoming handover times

In BSC

Successful outgoing handover times

In BSC

HO formulaHO success rate in BSC= *100% Times of success inter-cell HO in BSCTimes of inter-cell HO request in BSCWireless HO success rate in BSC Wireless HO success rate >= HO success rate HO in BSCTimes of success inter-cell HO in BSC *100% Times of inter-cell HO in BSC

HO in MSCHO Signaling FlowHO in BSCHO in MSCHO between MSCs

Signaling FlowHO in MSC

Channel Release FlowHO in MSC

Statistics counters of HO in MSCHO in MSC

MS BTS(Source) BSC MSC BSC BTS(Target)

Measurement Report

Measurement Report

Handover Required T17++

Handover Request T14++

Channel ACT

Channel ACT ACK

Handover Request ACK

Handover Command

Handover Access

Handover Detect

Handover Complete

Handover Complete T15++

Clear Command (HO successful) T18++

RF Channel Release

Clear Complete

Times of outgoing handover

request between BSCs

Times of incoming

handover request between BSCs

Times of successful

incoming handover between BSCs

Times of successful

outgoing handover between BSCs

HO formulaHO success rate in MSC= *100% Times of success outgoing BSC HOs + Times of success incoming BSC HOs Times of outgoing BSC HO requests+ Times of incoming BSC HO requestsWireless HO success rate in MSC*100%Times of success outgoing BSC HOs + Times of success incoming BSC HOsTimes of outgoing BSC HOs +Times of incoming BSC HOsHO in MSC

HO Between MSCsHO signaling flowHO in BSCHO in MSCHO between MSCs

HO Between MSCs~~~~MSMSBSS1MSCaMSCbBSS2VLRbRadio transmission signal measurement HO REQ.Perform HO(MAP)(Global target cell list)(Global target cell IDglobal service cell IDchannel type) HO REQUEST(PCM&Channel type)HO REQUEST ACKNOWLmarginIncl. New TCH and HONAllocation HO numberSend HO report (HON.)Radio channel ack.(MAP) Incl. New TCH and HON IAMACM HO COMMANDHO CMDHnadover MS to new channel via original BSSHO test HO DETECTHO finish HO COMPLETEBSS2 selects TCH to connect to PCM circuitMS enter target cellSend end signal Send end signal(MAP) CLEAR COMMANDRelease PCMDCLEAR COMPLETEANSRelease (TUP/ISUP)End signal(MAP)Disconnect MSCa and MSCbHO report MobileUmAEBAUm

HO Between MSCsSignaling flow Abnormal conditions

The following conditions will cause HO failure----

MSC-B fails to identify the target cellMSC-B does not allow HO to the indicated target cellThe target cell has no channel available in itVLR-B has no HO number availableHO error or unsuitable data

HO Between MSCsSubsequent HO Flow

HO Between MSCsSubsequent HO FlowHighwayMSC-AMSC-CMSC-BMSC-CSubsequent HO

HO Between MSCs

Statistics countersame as HO in MSC, statistics is made by BSCHO formula-- same as HO in MSC

1. There is no HO request information for HO in BSC, and all of the HO is analyzed and processed in BSC. Once the target cell as required is found in the BSC, Channel activation information is sent directly.2. When the target cell is not in the BSC, BSC reports CGI numbers of the serving cell and target cell, and HO cause to MSC through Ho-Required. When MSC finds that 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.3.When MSC finds that the target cell LAC does not belong to the MSC, it will query its REMOTLAC 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 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 receiving HO-Request acknowledgement, to execute the following procedure.Basic Flow of HO Signaling

Main differences:1. 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 message, it is handled inside BSC.2. Intra-BSC HO only sends HO-Performed to MSC upon completion of HO, and MSC is not involved before that time.But in the inter-BSC HO, MSC is involved ever since the HO request .HO in BSC and Inter-BSC HO

Thanks

****As an important radio link control method, handover can maintain the communication continuity of MS which moves across different cells and lower the call drop rate and provide better communication quality.

***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 neighboring cells. BTS--Responsible for monitoring of uplink receiving 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 judgement.MSC--Participate in the confirmation of destination cell in inter-BSC handover.**In connect mode, the system performs handover and power control judgment based on measurement reports. The measurement reports are reported to the network via uplink SACCH channel, including uplink MR and downlink MR.Downlink--In connection mode, MS reports regularly via uplink SACCH channel. The report includes the receiving signal level, receiving quality, TA, power control and whether DTX is used. At the same time, MS will perform pre-synchronization to neighboring cell defined by the system to obtain BCCH frequencies and BSICs, measure their receiving signal level and report the max. six neighbor cells with the highest receiving signal level.Uplink--The uplink measurement report measured by BTS, including the receiving level and receiving quality from the MS.Both parts are sent by BTS to BSC for further assessment at the same time.

*There are two values in the measurement report: FULL MR and SUB MR.FULL--Averaging 100 TCHs 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 bi-directional 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 connection mode.1. When associated with SDCCH, SACCH measurement period is 470ms, this is because there is an entire SACCH message block in 2 SDCCHs 51-multiframes.2. When associated with TCH, SACCH measurement period is 480ms, this is because there is an entire SACCH message block in 4 TCHs 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.

*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 report.

*Each measurement report has a serial number. If the serial numbers of received measurement report are not consecutive, there must be missing measurement report, and the system will make it 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, a more suitable method -- filter -- is employed. Use the last four measurement reports as shown in the diagram. Different filters are ready for uplink/downlink receiving level and receiving quality and TA.***When the handover to a target cell fails, a penalty will be given on the signal level of this target cell during a period called handover failure penalty time. That is, when sequencing the neighboring cells in the cell listl, the corresponding neighboring cell with a failed record within the penalty time will be penalized by cutting certain value on the reported signal level.

*1. In case of BQ emergency handover, the original serving cell will be penalized (called BQ HO signal level penalty) during BQ HO penalty time, avoiding MS to be handed back to the original serving cell again within certain time.2. It is the same for TA handover, i.e. the original serving cell is penalized (TA HO signal level penalty) during TA HO penalty time.

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

*Over-layer/under-layer HO failure means the failure of handover from the inner cell to the outer cell, or from the outer cell to the inner cell within one over-layer/under-layer cell.

***RXLEV(o), RXLEV(n)-- MS receiving signal level of the serving cell and the neighboring cell, MSRXMIN(o) and MSRXMIN(n)-- Lowest MS receiving signal level required by the serving cell and neighboring 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 is the maximum physical transmission power of MS.OFFSET--Minimum access level offsetMAX(0,Pa(o))--The current algorithm takes into consideration only the lowest receiving power threshold of downlink, not including uplink. 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.

Relevent parameters: Handover-cell description data tableLayer of the cellPriority level of the cell

******The handover algorithm starts a handover judgement every 0.5 second (a measurement report time). The judgement flow is described below:First judge whether the emergency handover switch is set to ON in the handover control data table. If not, emergency handover judgement will not be performed.If emergency handover judgement 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 judgement isdecided by the parameters of respective filters in the emergency handover data table. Then start load handover judgement.Then execute normal handover judgement: Start margin handover when it reaches the margin handover trigger threshold within the statistics time.Perform hierarchical HO judgement if margin 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 the threshold of Hierarchical handover.If hierarchical handover is not triggered, trigger PBGT handover when it reaches PBGT threshold (which can only be performed in the same layer and level).Then execute fast moving handover judgement. Once conditions are met, start handover and penalty.Finally execute over-layer/under-layer handover judgement. If conditions are met, start over-layer/under-layer handover.According to the aforementioned judgements, BSC sends the handover command.

**Related parameters: Handover-[Emergency handover data table]TA emergency handover Downlink quality restriction of emergency handover Uplink quality restriction of emergency handover

*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 receiving signal level in a period of time.

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

*Related parameters: Handover-[Emergency handover data table]Interference handover uplink quality thresholdInterference handover downlink quality thresholdInterference handover uplink signal level threshold(dBm)Interference handover downlink signal level threshold(dBm)

*A handover band is defined in load handover, in the range of margin handover threshold ~ margin handover threshold + load handover bandwidth. The handover band itself is divided into multiple equalized handover step sizes, MSs falling within the handover step sizes are handed over 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 receiving threshold), the handover stops. Load handover is an emergency measure 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 data table]Load handover system flow threshold (system flow level) Load handover start threshold (cell load level)Load handover receiving threshold (cell load level)Load handover bandwidth (dB)Load handover step size(dB) Load handover period (second)

*Related parameters: Handover - [Normal handover data table]Margin HO uplink threshold (dBm)Margin HO downlink threshold (dBm)Margin HO statistics time (second)Margin HO continuous time (second)

*Related parameters:1. Handover - [Cell description data table]Hierarchical handover threshold (dBm)Hierarchical handover hysteresis2. Handover - [Normal handover data table]Hierarchical handover statistics time (second)Hierarchical handover continuous time (second)

*In areas with densely distributed cells, the actual radio coverage range has become far larger than the distance between BTSs. 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 cross-cell coverage, 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 ) - RXLEV_DL - PWR_C_D ) - ( Min ( MS_TXPWR_MAX (n),P ) - RXLEV_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 nRXLEV_DLMS receiving power from the serving cellRXLEV_NCELL(n)MS receiving 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 power*P/N rule: P seconds in N-second measurement satisfies PBGT(n) > PGBT_Ho_Marginn).Note: In the program, P and N are processed as the corresponding number of MRs. 5 seconds corresponds to 10 MRs and 4 seconds corresponds to 8 MRs. After MR pre-processing switch is turned on, the report frequency of MRs will affect the PBGT HO.

Related parameters:1. Handover - [Adjacent cell relation table]PBGT handover threshold (dB) - i.e., PBGT_Ho_Margin (n) 2. Handover - [Normal handover data table]PBGT handover statistics time (second) - N in P/N judgementPBGT handover continuous time (second) - P in P/N judgement

*Related parameters: Handover - [Fast moving handover data table]Fast moving cells meas. number - the total number of cells for judging whether a MS is a fast moving MS or not.Fast moving cells actual number- Total N of actual cells that MS fast passes. That is, when N or more out of P cells that MS lately passes are fast passing ones, the fast moving micro cell handover algorithm will be started.Fast moving time threshold - 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.*Related parameters: Handover - [Over-layer/under-layer cell handover data table]Signal level difference between inner and outer cells (dB) - This parameter represents power compensation for the inner cell .Receiving level threshold (dBm) - This parameter is used to determine, together with the receiving level hysteresis, TA threshold, and TA hysteresis, the border between the inner cell and the outer cell, which must be larger than the margin handover threshold.Receiving level hysteresis (dB) - This parameter is used to determine, together with the receiving level threshold, TA threshold, and TA hysteresis, the border between the inner cell and the outer cell. TA threshold - One of the factors to determine the border between the inner cell and the outer cell. TA magnetic lag - One of the factors to determine the border between the inner cell and the outer cell. Over-layer/under-layer cell handover statistics time (second) - this kind of handover must also satisfy P/N judgement.Over-layer/under-layer cell handover continuous time (second).*An illustration of how to define the border between the inner cell and the outer cell.

**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 handover allowed is turned off, the 11th bit -- load adjustment bit-- in the 16bits still works. Therefore, the start threshold of load handover and receiving threshold of load handover in [Load handover data table] should still be set with much care.

*After the RSD emergency handover algorithm allowed for rapid drop is turned on, 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 turned on, the Transmit original measurement report should be set as Yes.

*Measurement report preprocessing: Indicate whether the measurement report interpolation, filtering and power control are executed at BTS side.*Transmit original measurement report: It works only when Measurement report preprocessing is turned on. In 15:1 configuration, it should be set as No when there are more than two SDCCH/8s, otherwise the link rate may be too low. If the RSD emergency handover algorithm allowed is turned on, it should be set as Yes, otherwise the BSC will not be able to judge whether MS has suffered from rapid signal drop.Transmit BS/MS power level: It works only when Measurement report preprocessing is turned on. Since the BTS will perform power control when the measurement report preprocessing is on, if the BS/MS power level is not reported to BSC, the BSC uplink/downlink average measurement results will be affected, and the handover that needs power compensation such as PBGT handover and over-layer/under-layer handover will be abnormal. Therefore, this parameter should be set as Yes as long as the measurement report preprocessing is turned on.*For example: When P/N is set as 5/4 seconds, it requires actually at least eight in the ten measurement reports to meet the requirements. When the frequency of report is once per second, BSC needs at least 10 seconds to confirm whether the trigger condition is satisfied. Normally, the measurement report is reported once per 480ms, i.e. twice per second, and it takes only five seconds to make judgment on 10 measurement reports. Therefore, when the frequency of report is once per second and P/N judgement is 5/4 seconds, the trigger time of handover is prolonged greatly. *This table describes various attributes of a cell, such as hierarchical priorities, hierarchical handover threshold, CGI, BCCH frequency band, BSIC and M rule parameter.Ensure the consistency of CGI in [Cell module information table], [BSC cell table] and MSC.Huawei BSC processes only capitalized CGIs, otherwise no handover will be performed. Huawei BSC can not acknowledge cells with the CI FFFF, so the CI value can not be set as FFFF, otherwise no handover will be performed.

*There is also an [External cell description data table], which is the description of external BSC neighbor cells.When modifying data from [Cell description data table] or [External cell description data table] on-line, no matter how many cells data has been modified, send all modules when resetting the entire table, otherwise the handover will be abnormal. When modifying data from [External cell description data table], set main cell information as Module No. and Parameter 1, that is, modify and set the external neighboring cell attributes via the serving cell command line data..

*The neighboring cells of all cells in the BSC are listed in this table, including respective PBGT handover thresholds, inter-cell handove 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 neighboring cells of a serving cell, for BSC will search for the target cell according to the BCCH frequency band and BSIC of a neighboring cell. If BSC can not identify the target cell, it will not send handover command. If BSC sends incorrect handover command, ratio of successful handover may be low.

*After modifying the BCCH frequency or BSIC of a cell, set it as the main cell of neighboring cells via [Cell adjacency relation table] setting . That is, to inform the neighbor cells of the modification.The larger value of PBGT threshold and inter-cell handover hysteresis will be the threshold condition of handover judgement. The 4th bit of 16bits queuing is the comparison bit of hierarchical cells in the same layer and hierarchy. If the handover hysteresis is larger than PBGT threshold value, the priorities are differentiated. If other judgement conditions of PBGT handover is satisfied, and if there is no handover of higher priority than that of PBGT handover judgement, PBGT handover will be triggered without judgement of whether PBGT threshold meets the standard.***In Huawei handover algorithm, in case of emergency handover (TA handover, BQ handover, interference handover and rapid signal drop handover), select the best cell according to the current cell sequencing rather than the PN sequencing result, in order to expedite system response.**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 lower 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 drop handover.

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

*PBGT handover should also satisfy P/N judgment.

*Hierarchical handover should also satisfy P/N judgment.

*This table is valid only when fast moving handover algorithm is turned on. It is usually unused, and is suggested to be applied in special places such as highway.*In addition to [Over-layer/under-layer handover data table], the following should also be configured for cells supporting over-layer/under-layer handover:1. Local office--[TRX configuration table]: Over-layer/under-layer cell attribute is the outer cell or inner cell.2. Handover-[Cell description data table]: Cell type is Over-layer/under-layer cell

*Inner cell range:Receiving level>=receiving level threshold + receiving level hysteresis and TA< TA threshold - TA hysteresisOuter cell range:Receiving level= TA threshold + TA hysteresisWhen TA threshold is 63 and TA hysteresis is 0, the inner cell border is determined completely by the receiving level parameter.When the receiving level threshold is 63 and receiving level hysteresis is 0, the inner cell border is determined completely by TA parameter.

*Over-layer/under-layer HO should satisfy P/N judgement*This is the feature of over-layer/under-layer handover, i.e. to assign outer cell or inner cell first when assigning voice channel.

*Precautions in incoming BSC HO priority layer configuration:1. BCCH TRX should be configured on the outer cell2. SDCCH should be configured on the outer cell3. 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 inner and outer cells will be disabled.

**Precautions:1. The module No., cell No. and CGI of all neighbor cells should be find before BSC performs basic cell sequencing2. In adjacent cell relation table: If there are cells with the same frequency and BSIC in neighboring cells, BSC will fail to identify the right target cell. As a result, the handover command may be incorrectly sent or not sent, thus the handover success rate will be affected.3. Cell sequencing and HO judgement 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 Out-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 Out-cell handover request.

***1. 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.2.For synchronous handover in BSC, i.e. When BTS1 and BTS2 belongs to the same BTS, there will be no PHY INFO message. MS reports SABM connection frame right after report of Handover Access message. 3. 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.

**Note: The key counter statistic points are as follows--1. Before BSC sends Channel-Activation to destination BTS, it counts one request time of incoming-cell handover in BSC and also one request time of outgoing-cell handover in BSC.2. After BSC sends HO-Command to MS, it counts one incoming-cell handover time in BSC and also one outgoing-cell handover time in BSC.3. After BSC receives HO-Complete from MS, it counts one success time of incoming-cell handover in BSC and one success time of outgoing-cell handover in BSC.

*Difference between Handover success rate in BSC and Wireless handover success rate in BSCAccording to the calculation formula, the numerators of two formulas are handover success times, and the denominators are different.According to the counter statistics point, handover request times>=handover times.Therefore, Handover success rate in BSC = Handover success rate between BSCs

*Handover performance measurement formulas of each cell are:

Inter-cell handover performance measurementInter-cell handover success rate=(Handover success times in BSC + Handover success times between BSCs)/(Handover request times in BSC + Handover request times between BSCs)

Inter-cell wireless handover success rate=(Handover success times in BSC + Handover success times between BSCs)/(Handover times in BSC + Handover times between BSCs)

**1. After receiving HO-Required from BSC-A (the message includes CGIs of serving cell and target cell), if MSC-A finds out that the LAC of the target cell does not belong to local MSC, it will query the REMOTLAC table (including LAC and routing address of neighboring MSCs). Then it will send Prepare-HO message to MSC-B according to the routing address. The message includes the CGI of the target cell and the instruction whether to allocate handover number or not. 2. If it is required to allocate handover number according to the Prepare-HO message received, MSC-B will request local VLR for the allocation. If VLR has handover number, it will sent the number to MSC-B via Send-HO-Report. If it is not required to allocate handover number, perform the next step directly.3. After creating SCCP link with BSC-B, MSC-B sends HO-Request message to BSC-B. Then BSC-B activates the channel in the target cell, and sends HO-Request-ACK message to MSC-B after receiving channel activating confirmation. According to the message, MSC-B sends Prepare-HO-ACK message to MSC-A.4. MSC-A creates route with MSC-B according to the handover number, and sends IAI message to MSC-B, which enables MSC-B to identify which voice channel is reserved for MS. MSC-B will respond ACM to MSC-A.5. MSC-A will send HO command to MS after receiving ACM, and MS will perform handover access on new channel. If the access succeeds, BTS-B will send a UA frame, and MSC-A will send Clear-Complete message to MSC-B.6. MSC-B informs MSC-A to release the original channel via Send-End-Signal. After receiving Clear-Complete from BSC-A, MSC-A will send (Send-End-Signal-Confirmation) message to MSC-B. Thus finishing the inter-MSC handover flow. 7. In any time after MSC-B sends ACM to MSC-A, the former can sends Release-HO-Report to VLR-B to release the handover number.

**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 flow, 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 laocation 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 flow, during a continuous conversation through several MSCs, the first MSC created in a conversation must make all other MSCs as the neighboring ones, otherwise the handover may fail.

*Note: If there is no available handover number 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.

***

Huawei Hand Over

Documents

tabq ho

process of asynchronism

process of synchronization

missing measurement

cause pingpang ho

original cell

target cell

penalty time