2G HO

Prsentation PowerPoint

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 HOClassification by ReasonClassification by SynchronizationAsynchronous handover: source and target cell belong the different BTS Synchronous handover: source and target cell belong the same BTS M.R.preprocessingPenalty processingCell rankingHO judgmentTA emergency HOBQ emergency HORSD emergency HOInterf. emergency HOLoad Sharing HOEdge HOLayer HOPBGT HOProcessing programOM forced HODirected retryOverlaid/underlaid HOFast moving MS HO11General process of HO AlgorithmAll 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.3Period of measurement report The downlink MR is sent to BTS in SACCH uplink The interval is 480ms/per time when MS is on TCHThe interval is 470ms/per time when MS is on SDCCH 12TCH12TCH1SACCH1 Idle480ms4 TCH multi-frames There 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 ProcessingCell RankingM Rule

Cell RankingK RuleRanking 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 serving cell and candidate neighbor cells are ranked in descending order according to the receiving level.

Both 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.

Cell Ranking16 bits RuleThe 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. The value for the cell with the 2nd strongest signal level is 001.

16151413121110987654321The 4th bit: determined by HO hysteresisThe 4th bit: Inter-cell HO hysteresis bit to reduce the "Ping-Pong" handovers.

16151413121110987654321Note: 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.

The 5th10th bit: determined by Layer 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.16151413121110987654321Layer (0-3)Prio (0-15)Prio (0-63) Hierarchical cell structure

The 11th bit: determined by load

The 11th bit: The bit value is decided by cell-load-sharing criterion.This bit is affected by 14th bit.The 11th bit: bit value is decided by cell-load-sharing criterion. And this bitwill be turned off when the system load is higher than System FluxThreshold for Load HO or Load HO Allowed is set to NOService cell: if cell load >= Load HO Threshold, bit 11th is set to 1.Otherwise, set to 0Neighboring cell: if cell load >= Load Rep. on Candidate Cell, bit 11th is setto 1. Otherwise, set to 0

[Load HO Allowed] Value Range: Yes, No Default Value: No Description: This parameter indicates whether a traffic load-sharing handover is allowed. Load-sharing helps toreduce cell congestion, improve the success rate of assignment, and balance the traffic load among cells. Loadsharingfunctions only within the same BSC or in cells of the same layer. It applies to only TCH. If loadhandover is frequently required, TRX configuration and network planning should be properly adjusted. Remarks: In areas with tight frequency reuse, extra interference may occur if Load HO Allowed is set to Yes.[System Flux Threshold for Load HO] Value Range: 0~11 Default Value: 10 Description: System Flux Threshold for Load HO is obtained based on message load, CPU load, and so on.The system flow level is the current flow control level of the system. 0~11:It is the system flux control level when the alarm module send out alarms information. Level11 is the highest and level 0 is the lowest. A load handover is allowed only when the system flow is lower than this threshold. Otherwise,unexpected situations may occur. Therefore, this parameter must be set properly. Flow control threshold for the CPU to start to discard the channel access messages and pagingmessages: 80% Flow control threshold for the CPU to discard all the channel access messages and paging messages:100% CPU usage smaller than 80% corresponds to level 0. CPU usage equal to or greater than CPU flowcontrol threshold 80% corresponds to level 2. An increase of 5% means an increase of 2 levels. Level 10 is the highest. The level value can be 0, 2, 4, 6, 8, and 10.[Load HO Threshold] Value Range: 0~100(%) Default Value: 85 Description: When the load handover is switched on, it is recommended that the Load HOThreshold is set to 85.The cell load refers to TCH usage. When the cell load exceeds thevalue of Load HO Threshold, the BSC starts the load handover. That is, the BSC starts theload handover after the TCH in the cell are proportionally occupied. Remarks: Even if the Load HO Allowed is set to Yes, the Load HO Threshold and LoadReq. on Candidate Cell affect the queuing of the candidate cell handover. Therefore, whenthe cell is overloaded, the handovers such as PBGT cannot be performed if this parameteris not properly set.[Load Req. on Candidate Cell] Value Range: 0~100(%) Default Value: 75 Description: If the cell load is lower than the value of this parameter, the cell accepts usersthat are handed over to the cell due to their cell load. If the cell load is not lower than thevalue of this parameter, the cell refuses the users. Remarks: The same as that of Load HO Threshold13 The 12th/13th bit: determined by co-BSC/MSC

Whether to adjust the candidate cell queue to give priority to intra-BSC/MSC handover The 14th bit: determined by Layer HO16151413121110987654321The 14th bit: Layer HO threshold adjustment bitServing cell criterionReceive 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 ) The 14th bit: determined by Layer HO16151413121110987654321

serving cell = Inter-layer HO threshold - Inter-layer HO Hysteresis. Inter-layer HO threshold of the neighboring cell = Inter-layer HO threshold + Adjacent Cell Inter-layer HO Hysteresis - 64.

[Inter-layer HO Threshold]Handover threshold during the handovers between cells on different layers or of different priorities. This value is used to suppress inter-layer ping-pong handovers. Value Range: 0~63(-110 dBm to -47 dBm)Default Value: 25Description: In BSC handover algorithm, the M criterion is used to rank the handovercandidate cells. The M criterion includes 16 bits. This parameter is one bit of the 16 bits andit affects the rank of a candidate cell. When the downlink level of a cell is lower than thisthreshold, the cell takes low priority as far as comprehensive sequence is concerned.Remarks: Make sure that the receive level of the destination cell is higher than this thresholdin inter-layer handover or load handover. Otherwise, the MS may be handed from a cell withheavy load and high level (high priority cell) to a cell with light load and low level (lowpriority cell), thus leading to call drops.[Inter-layer HO Hysteresis]Value Range: 0~63Unit: dBDefault Value: 3Description: This parameter indicates the hysteresis of an inter-layer or inter-priorityhandover. It is used to avoid inter-layer ping-pong handovers. Actual Inter-layer HOThreshold of a serving cell = Inter-layer HO Threshold C Inter-layer HO hysteresis ActualInter-layer HO Threshold of a neighboring cell = Inter-layer HO Threshold + Inter-layer HOhysteresis16 The 15th bit: determined by Cell Type16151413121110987654321The 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 bit

General HO Process

No DL MR HOTriggering condition No DL information in current MR Stored UL Rx_Qual Value Number >= Rx_Qual Filter Length UL Rx_Qual >= No DL MR HO UL Rx_Qual Threshold Number of Lost DL MR < Cons. No DL MR HO Allowed LimitObject cell selection Prefer neighboring cell If choose the service cell, it cannot in the penalty time for intra-cell handover.19TA (Time Advance) HO

Triggering condition The actual TA >= TA ThresholdObject cell selection The cell must be of the highest priority in the candidate cell sequence and meet the following restrictions.Restriction The service cell cannot be the object cell. HO is not allowed when TA Threshold of the neighboring cell with the same BTS is equal or smaller than that of the service cell.20Interference HO

BQ (Bad Quality) HO

BQ HO Margin : If (downlink level of the neighbor cell after filtering - downlink level of the serving cell (after power control compensation)) > ((Inter-cell HO Hysteresis - 64) - BQ HO Margin + 64), the BQ handover to the neighbor cell is triggered.23Enhanced Dual Band HOLoad HO

Triggering ConditionsIf LoadHoEn is set to Yes, the triggering conditions of load handover are as follows:l The CPU usage of the system is less than or equal to SYSFLOWLEV.l The current load of the serving cell is greater than or equal to TRIGTHRES.Target Cell SelectionThe conditions for selecting the target cell are as follows:l Filtered RX level after handover penalty HOTHRES + INTELEVHOHYST - 64l The serving cell cannot be selected as the target cell.l If the target cell and the serving cell are in the same BSC, a load handover is performed when the current load of the target cell is lower than LoadAccThres.l If the target cell and the serving cell are not in the same BSC, a load handover is performed when the load of the target cell is lower than LoadAccThres and OutBscLoadHoEn is set to Yes.

25Edge HO

MS Fast-Moving Handover

Layer HO

PBGT HO

In algo 1 urgency bad quality HO will trigger intracell HO if there is no strong neighbour cell. This leads to high number of intracell ho at low signal strength -> leads to more drops and quality degradation.

Furthermore HO algo2 allows different UL and DL Rxlev and Rxqual offsets for interference HO (another type of intracell HO). This huge advantage, because UL and DL receive levels are different because of different TX power and sensitivity levels in MS and BTS. That improves intracell HO performance further.