handover

Handover

Gurpreet Singh Kalsi21-May-2009

2 | Presentation Title | Month 2006 All Rights Reserved © Alcatel-Lucent 2006, #####

Contents Objective & Classification of Handover Type of Handover Handover Preparation Conditions of Handover Call Flow for different types of Handover Parameter used in the Handover Analysis of Handover Failure


Objective

What is the purpose of HO? Call continuity Call quality Others...


Emergency HO• Timing advance (TA) Emergency HO• Bad quality (BQ) Emergency HO • Rx_Level_Drop Emergency HO• Interference emergency HO

load HO Normal HO

• Edge HO• Layer HO• Power budget (PBGT) HO

Fast moving MS HO (Speed-sensitive HO ) Concentric cell HO

Handover Classification

The handover procedure consists of handover trigger, handover preparation and decision, and handover execution.


Types of Handoffs

HO can be divided into synchronous HO and asynchronous HO based on Timing Advance (TA) Asynchronous handover-Source and target cell belong the different BTS Synchronous handover-Source and target cell belong the Same BTS


Measurement Report

The downlink MR is sent to BTS in SACCH uplink The interval is 480ms/per time when MS is on TCH The interval is 470ms/per time when MS is on SDCCH


Penalty Processing

There are overall four types of penalty 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 IUO cell HO attempt is prohibited within the penalty time

after an IUO cell HO fails.

Penaltyallowed

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 BSCYes, No Yes

Different Penalty timer for different type of HO are defined at cell level.


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.

Cell A

BTSHO failure

BSC

Cell BParameter

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 attempt to

that cell again. This value is only valid within the penalty time for handover failure.

0 ~ 63 dB30

Penalty time after HO fail

Penalty time on the corresponding target cell after seconds handover failure 0 ~ 60 s 10


BTSBQ& TA HO

BSC

Cell A

Cell B

Penalty on the Source Cell Punish the original serving cell when an emergency HO ( due to BQ and TA)

occurs.


Back? No way!Back? No way!

Umbrella

Micro cell

Penalty on Non-umbrella Layer

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.


Underlaid

Overlaid Do not attempt

again after a failed HO!

Penalty on Overlaid/Underlaid Cell

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


Basic Ranking and Secondary RankingProcedure of Ranking

Basic 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 rule

• K rule

• 16bits ranking


M 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) >MS_RX_MIN(o) + MAX(0,Pa(o))

For Neighbor cell

RX_LEV (n) > MS_RX_MIN(n)+ MAX(0,Pa(n))+ OFFSET

• MS_RX_MIN(o) and MS_RX_MIN(n)-- Minimum MS received signal level required by the serving cell and neighbor cell.

• Pa(0) : MS_TXPWR_MAX(0) – P• Pa(n) : MS_TXPWR_MAX(n) – P• MS_TXPWR_MAX( ) : The appointed MS transmitting power by the BSS. • P : MS maximum transmitting power

This factor is normally zero, but included for

Lower end mobiles


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

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.

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.

16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1


The 4th Bit: Determined by HO Hysteresis 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.

16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1

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 andtraffic between

two adjacent cells.

0 ~ 63 dB

It is around 4 in the densely populated

downtown, andaround 8 on the

outskirts.


The 5th—10th 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 < 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.

16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1

Layer HO

Thresh.

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 and load handover. Then such level should be higher than layer handover threshold + layerhandover hysteresis. The layer handover threshold

should be set >= Edge handover threshold + Inter cell handover hysteresis.

0 ~ 63

(-110~-47dBm) 25

Layer HO

hysteresisWorks together with the Layer handover threshold. 0 ~ 63 dB 3


Hierarchical Cell Structure

GSM900 Cell（ Lay 3 ）

Micro Cell（ Lay 1 ）

（ high ）

Umbrella Cell

（ Lay 4 ）（ low ）

GSM 900

GSM1800 GSM1800GSM1800

GSM 900

GSM900GSM900

GSM1800

GSM1800

GSM1800 Cell

（ Lay 2 ）

GSM 900

GSM900GSM900

GSM1800

GSM1800


The 11th Bit: Determined by Load 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. Less congested cell.

Refer to Load HO Table for the load HO threshold and load req. on candidate cell.

>>>>> 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.

16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1


The 12th/13th Bit: Determined by Co-BSC/MSC

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.

16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1

Co BSC/MSCAdj.

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


The 14th Bit: Determined by Layer HO

The 14th bit: Layer HO threshold adjustment bit

Serving cell criterion

• Receive level >= layer HO threshold - layer HO hysteresis , bit 14th is set to 0.

• If the above criterion is not met, then bit 14th is set to 1. At the same time, bit 13th, 12th and 10th—5th bits are turned off.

16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1


The 14th Bit: Determined by Layer HO Neighbor cell criterion

• RXLEV >=layer HO threshold + layer HO hysteresis0.

• If the above criterion is not met 1.

• At the same time, bit 13th, 12th and 10th—5th bits are turned off.

Note >>>>The layer HO threshold and hierarchical hysteresis correspond to the value of that individual cell’s value.

16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1


The 15th Bit: Determined by Cell Type

The 15th bit: bit value is decided by cell type.

Serving cell or Neighbor cell criterion

• When cell type is extension cell 1.

• When cell type is normal cell 0.

16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1


The 16th Bit: Determined by MNC HO Strategy

The 16th bit: bit value is decided by MNC HO strategy.

Serving cell: is always set to 0.

Neighbor cell criterion

• If the inter MNC HO is supported then bit 16 is set to 1 otherwise it is 0.

• When handover in same MNC is on priority, then bit 16 for Neighboring cell is set as 1 otherwise 0.

16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1


Condition of Handover

Emergency HO

• TA HO

• BQ HO

• Interference HO

• Rx_Level_Drop HO

Load HO

Normal HO

• Edge HO, layer cell HO and PBGT HO

Fast moving HO

Overlaid/Underlaid HO


TA HO

Triggering condition

• The actual TA > TA HO Thrsh.

Target cell selection

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

Limitation

• The target cell cannot serve as serving cell.

• If the TA threshold of Co-site neighbor cell < TA threshold of serving cell, a handover to cell is not allowed.

• After TA handover is successful, penalty is performed on originating cell.

Parameter

TA threshold is the parameter which distinguish the boundary between underlay and overlay cell. HO between concentric cell will not trigger if TA threshold of neighbor cell within the BTS is < the server Cell.


Bad Quality HO Triggering condition

• UL receiving quality >=UL receiving quality thrsh. of the service cell.

• OR DL receiving quality >=DL receiving quality thrsh. of the service cell.

Target cell selection

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

Limitation

• Handover to the neighboring cell with the highest priority. If there is no neighboring cell, handover to the service cell, and the channel at different TRX is preference.

• After BQ handover is successful, penalty is performed on originating cell

Parameter


Rx_Level_Drop HO Triggering condition

• Triggered upon detecting rapid level drop during MS busy mode Target cell selection

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

Restriction

• The service cell cannot be the Target cell.

Parameter


Interference HO Triggering condition

• UL receiving quality>=Service cell UL receiving quality Thrsh. AND UL receiving level>=Service cell UL receiving level Thrsh.

• OR DL receiving quality>=Service cell DL receiving quality Thrsh. AND DL receiving level>=Service cell DL receiving level Thrsh.

target cell selection

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

Limitation

• The service cell that is not in the penalty time for intra-cell handover. • The neighboring cell with the receiving level higher than the inter layer HO

Thrsh.


Interference Handover

Lev_Thr

Rx_Qual

RX_Lev

Qual_Thr

InterferenceOrigin

Serving Cell Neighboring Cell

Handover Triggering Zone


Load HO Triggering condition

• The load HO switch of the service cell is enabled.

• The system signaling flow is not larger than the Load HO system flow Thrsh.

• The service cell traffic is larger than the Load HO Thrsh.

• The DL receiving level is in the load HO zones.


• The service cell cannot be the target cell.

• The traffic of the neighboring cell must be lower than its load HO receiving thrsh.

• The neighboring cell with the receiving level higher than the inter layer HO Thrsh.

Restriction

• It is not available with SDCCH.

• Load HO just occur within the same BSC.

Parameter - 1Parameter- 2


Load Handover

Handover triggering zone

Load HO Thr

Time

Traffic of Serving Cell

Receiving Threshold

Traffic of Neighboring Cell

Congested CellCongested Cell

Congested Cell


Cell A Cell B

Normal HO border

CONF_HO_RXLEV

CONF_HO_RXLEV+CLS_Ramp

CONF_HO_RXLEV+CLS_Offset

Load HO zone

Load HO

As load HO may trigger more HOs, consider the CPU load (system flow level) before triggering it. In addition, load is taken by step, that is, the edge HO thrsh. raises according to certain step and period and stops after without the Load HO Zone.

Load HO bandwidth Edge HO threshold

Load HO step level


Edge HO


• The DL receiving level < Edge HO DL RX_LEV Thrsh.

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

• Satisfying P/N rule.



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


Edge Handover

HandoverTriggering

P/N


P: Watch Time = 5 sc N: Valid Time = 4 Sec

RX_LEV Thr

Time

RX_Lev

It means that within P seconds

Condition for PBGT HO meet for

N Second


Layer HO


• The layer of the target cell is lower than that of the service cell.

• The DL level of the target cell is higher than the inter layer HO thrsh.

• Satisfying P/N rule.

• target cell selection




Layer HO

GSM900 Cell

(Lay 3)

GSM1800 Cell

（ Lay 2 ）

GSM 900

GSM1800GSM1800

GSM 900

GSM 900

GSM1800

GSM1800


PBGT HO


• The layer and level of the target cell are the same as those of the service cell.

• The DL level must be the result of the following formula.

• Target cell selection



• Restriction

• It is not available with SDCCH.


PBGT = ((msTxPwrMax- msTxPwrMax(n)) - (AV_RXLEV_DL_HO-AV_RXLEV_NCELL(n)) - (btsTxPwrMax - BTS_TXPWR)

PBGT = ((33dBm-33dBm)-(-90 - -80)-(42dBm-42dBm) = 10 dB

10 dB > 5 dB OK !!!!

Equations 1 and 2 are used

AV_RXLEV_DL_HO = -90 dBmmsTxPwrMax = 33 dBm (= 2W)btsTxPwrMax = 42 dBm (= 16 W)BTS_TX_PWR = 42 dBm = (16 W)hoMarginPBGT(n) = 6 dB

Serving Cell: Best Adjacent Cell:

AV_RXLEV_NCELL(n) = -80 dBmrxLevMinCell(n) = -99 dBmmsTxPwrMax(n) = 33 dBm (= 2W)btsTxPwrMax = 42 dBm (= 16 W)

Power Budget Handover


PBGT HO

Watch Time / Valid Time


PBGT HO Thr

Time

Patch Loss (dB)

126dB 119dB

5

126-119=7dB>5dB

HandoverTriggering

P: Watch Time = 5 sc N: Valid Time = 4 Sec

It means that within P seconds

Condition for PBGT HO meet for

N Second


Fast-Moving HO

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.

• Target Cell Selection

Number of layer where target cell is located must be => 4. Target cell is umberlla cell.

RX level of target cell is => inter layer HO thre + Inter layer HO hysteresis.


MS Fast-Moving Handover

Handover Triggering

Time Thr

Umbrella Cell

Time

P/NP: Watch CellsN: Valid Cells

1 1 2 3

Micro Cell

Cells Number


Overlaid / Underlaid Cell

Assume: 6TRX in one cell, two CDUs and one SCU are adopted

Where can we configure BCCH CH, CDU or SCU?

SCU

CDU

CDU

Antenna

TRXTRXTRXTRX

TRX

TRX

Antenna


How to Allocate SDCCH/TCH?

SDCCH

• SDCCH are always allocated in Underlaid

• Layer is allocated according the transmission delay of access burst

TCH

• The receiving level

• TA

• They are included in MR of SDCCH on uplink reported by BTS


Factor of Handover between Overlaid/Underlaid

Normal Overlaid/Underlaid

• Receiving level

• Time Advance

• Quality

Enhanced Overlaid/Underlaid

• Receiving level

• Time Advance

• Quality

• Traffic Load of Underlaid


underlaid

overlaid

Normal Overlaid/Underlaid HO

Division of underlaid and overlaid is decided by MS downlink receive level ,TA value and quality.


Normal Overlaid/Underlaid HO Criterion for HO from overlaid(OL) to underlaid(UL):

• TA value => TA threshold + TA hysteresis OR

• RX_LEV <= RX_LEV threshold － RX_LEV hysteresis OR

• Qua. =>Qua. threshold

• Satisfying P/N rule

Criterion for HO from underlaid to overlaid:

• TA value =< TA threshold － TA hysteresis AND

• RX_LEV >=RX_LEV threshold + RX_LEV hysteresis AND

• Qua. =<Qua. threshold


ULOL

ULOL


Enhance Overlaid/Underlaid HO

Division of underlaid and overlaid is decided by MS downlink receive level, quality, TA value and traffic Load of Underlaid (optional).


Enhance Overlaid/Underlaid HO Criterion for HO from overlaid to underlaid:

• TA value => TA threshold + TA hysteresis OR

• RX_LEV <= O to U level OR

• Qua. =>Qua. threshold


Criterion for HO from underlaid to overlaid:

• TA value =< TA threshold － TA hysteresis AND

• RX_LEV >= U to O level AND

• Qua. =<Qua. Threshold

• If the “U to O HO traffic threshold” is checked, just in the condition that underlaid load is more than this threshold, U to O handover based on previous conditions can be triggered


ULOL

ULOL


Handover Signaling Flow


GSM Handoffs

Types of handoffs

• Intra-Cell : Handoff between sectors of same cell

• Inter-Cell Intra-BSC: if old and new BTSs are attached to same base station MSC is not involved

• Inter-BSC: if old and new BTSs are attached to different base stations but within same MSC

• Inter-MSC: if MSCs are changed


Intra Cell HandoverMSC BTSBSC MS

RR(SACCH)

RR(FACCH)

L2-SABM

L2-UI

ASSIGN COM

MEAS REPMEAS REP

CHAN ACTIV

CHAN ACT ACK

<ASSIGN CMD> ASSIGN CMD

RR(New FACCH)

Assign Comp

EST IND

RF CHA REL

(old TCH)

HO PERFOMED(DT1)(Cause: intra_cell)

<ASSIGN COM>

RF CHA REL ACK

Old channel local end release

RR(FACCH)

RR(FACCH)

Start -T3107

Stop T3107


Inter- Cell Intra-BSC Handover Procedure

CH Actvn

CH Actvn Ack

MS BTS (Target)BTS (server) BSC MSC

Handover CommandHandover Command

Handover Access

Handover Detect

Phys Info

Handover Complete

Handover Complete

Channel Release

Channel Release ACK

HO PERFORMED

Measurement Report Measurement ResultSACCH

FACCHStart T3103

Start T3124

Stop T3124

Stop T3103

SABMStart T3105StopT3105UA Con. Est

This Massage is

Missing in syn

Handover. In that

MS directly send

The SABM after

Handover access


Inter BSC HO Signaling Process

Attempted incoming inter BSC inter cell handovers

MS BTS 1 BTS 2BSC1 BSC2MSC

(original) (Target)

Measurement ReportMeasurement Report

Handover RequiredHandover Request

Channel_ActiveChannel_Active_ACK

Handover_Request_ACKHandover Command

Handover Access

Handover Detect

Handover CompleteHandover Complete

Clear Command (HO Successful)

RF Channel ReleaseClear Complete

Successful outgoing interBSC inter cell handovers

incoming interBSC inter cell handovers outgong interBSC inter cell handovers

Successful incoming inter BSC handovers

Start Timer

T 7Stop Timer

T 7 & start T 8

t3103

Stop T 8/ T3103

Start 3124Stop 3124


Inter MSC Handover

Indicate theRouting btwMSC a & MSCb


Layer -3 Analysis for Inter Cell handoverSynch Channel Information


Layer -3 Analysis for Inter Cell handoverSystem Information Type-5


Layer -3 Analysis for Inter Cell handoverSystem Information Type-6


Layer -3 Analysis for Inter Cell handoverMeasurement Report Massage


Layer -3 Analysis for Inter Cell handoverHandover Command

Target sector


Layer -3 Analysis for Inter Cell handoverHandover Access

Please note that the HANDOVER ACCESS is send by the access burst. It is the only time when the access burst is used on the DCH. It only contains the 8-bit HO reference number obtained from the handover command. Since this reference number is known to the target cell, the target cell can check whether the access request is from the expected MS with this number.


Layer -3 Analysis for Inter Cell handoverHandover Complete


Layer -3 Analysis for Inter Cell handoverAfter Handover


Few Important Timers for Handover

T3103 - In inter- and intra-BSS handover, the BSC determines the time for keeping TCH both in handover-originated cell and target cell. When the time receives handover completion (intra-BSC) or clearing (inter-BSC) message, T3103 stops. The recommended value is 5s. T3105 - When sending physical information, the network starts T3105. If the timer expires before receiving any correct frames from MS, the network resends physical information and restarts the T3105. The maximum repeated times is Ny1. T3105 ranges from 0 to 255, with unit of 10ms. Ny * T3105 > T3124 + delta T3124 - T3124 is used in occupation process in asynchronous handover. It is the time for MS to receive the physical information send by network side. When the MS sends the HANDOVER ACCESS message on the primary DCCH, T3124 starts. When the MS receives a PHYSICAL INFORMATION message, the MS stops T3124, stops sending access burst, activates the PCH in sending and receiving mode, and connects to the channel if necessary.


Major HO Parameters Configuration

Major HO parameter configuration 1.[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


Parameter

nameMeaning Value

rangeRecommend

value

Co BSC/MSC

Adj.

It means whether the 12 and 13 bits acts in the 16bit order. “Yes” means handover in the same BSC/MSC is preferred. “No” means that the 12 and 13 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 Yes

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 on ly 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 area (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

Handover Control Table


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 y (this parameter acts

when intra BSC handover occurs

Yes, No Yes



Parameter

nameMeaning Value range

Recommended

value

MR.

reprocessing

“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


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 rep ort 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

nameMeaning

Value range

Recommended

value

Sent Freq. of

Preprocessed

MR.

It indicates the time interval at which a measurement report is preprocessed at B TS side and sent to BSC the preprocessed measurement report. This parameter acts only when “Measurement t report preprocessing” 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 nee ding 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



Parameter

nameMeaning

Value

range

Recommended

value

Layer of the

cell

Huawei hierarchical network structure is divided into 4 layers. 16 Thepriorities 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 layers layer, Micro layer is the major 1800 layer, Pico is the 900 and 1800 micro cell layer. The smaller layer value, the higher priority.

1 ~ 4M900 : layer 3

M1800:Laye 2

Cell priority

Each layer may have 16 priorities, used to control the handover

priority between cells at the same layer. Usually priorities of priorities

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 1

Layer HO

Thresh.

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 and load handover. Then such level should be higher than layer handover threshold + layerhandover hysteresis. The layer handover threshold should be set >= Edge handover threshold + Inter cell handover hysteresis.

0 ~ 63

(-110~-47dBm) 25

Layer HO

hysteresisWorks together with the Layer handover threshold. 0 ~ 63

dB 3

Cell Description Table


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~ 63 dB 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 s 40

Min DL level 0n

Candidate Cell

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

0 ~ 63 15

Cell Description Table


Parameter


Recommended

value

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 dB 0

PBGT HO

Thresh.

It means that PBGT handover is performed when the

difference between the target cell downlink path loss and the corresponding to 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)”, “Intercell 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 ~ 63 dB

It is around 4 in the

densely populated

downtown, and

around 8 on the

outskirts.

Adjacent Cell Relation Table


Normal Handover Table

Parameter

nameMeaning

Value range

Recommended value

Edge HO UL

RX_LEV Thresh.

During the statistics time, if the time in which the uplink receiving level is lower than the value is longer than certain time called continuous time, edge handover will be performed. If PBGT handover is enabled, Corresponding edge handover threshold will be set Lower

0 ~ 63

25 (without PBGT

handover, downtown),

15 (single station on

outskirts), 15 (with

PBGT handover,

downtown)

Edge HO DL

RX_LEV Thresh.Downlink consideration for edge HO 0 ~ 63

30 (without PBGT

handover, downtown),

20 (single station on

outskirts), 20 (with

PBGT handover,

downtown)



Parameter


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 s 5

Edge valid

timeSee the above. 1 ~16 4



Parameter


Recommended

value

Layer HO

watch timestatistics time for Layer HO judgment 1 ~ 16 s 5

Layer HO

valid timeContinuous time for Layer HO judgment 1 ~ 16 s 4

PBGT watch

time Statistics time for PBGT HO signal level judgment. 1 ~ 16 s 5

PBGT valid

time

Continuous time for PBGT HO signal level judgment. 1 ~ 16 s4



Parameter

nameMeaning

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 Thresh.

The time threshold (2r/v) determined by the cell radius

(r) and moving speed (v). If the time in which MS seconds passes the cell is smaller than the threshold, then MS is judged to quickly pass the cell.

1 ~ 225 15


Common Concentric Data

Parameter name Meaning Value range Recommended

value

Assign optimum layer

In 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 preferential

System optimization

Assign-optimum level Thresh.

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



Parameter

NameMeaning

Value

range

Recommended

value

Pref. subcell

in HO of

intra-BSC

When the cell is configured into a Overlaid/Underlaid,

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 underlaid or overlaid

Yes, No Yes

Incoming-

to-BSC HO

optimum

layer

If there is a incoming BSC HO, and the target cell is a

Overlaid/Underlaid, then, this parameter will show

which layer is preferred to provide service for the MS.

overlaid ,

underlaid ,

none

None



Parameter name Meaning Value range Recommended value

RX_QUAL Thresh.

In case of Qua. Is worse than this value, MS handover from overlay to underlay 0 ~ 70 60

UO HO watch time P/N judgment statistics time for U/O HO judgment. 0 ~ 16 s 5

UO HO valid time

P/N judgment continuous time for U/O HO judgment. 0 ~ 16 s 4

TA thresh. Of Assignment Pref.

TA is more than this value, TCH in underlay will be allocated

0 ~ 63 According concrete condition

TA Thresh. Of IMM-Assign Pref.

TA is more than this value, SDCCH in underlay will be allocated

0 ~ 63 According concrete condition

TA Prefer Of IMM-Assign Allowed

TA attend allocation of SDCCH or not Yes, NoAccording concrete

condition



Parameter

nameMeaning Value range Recommended value

TA Thresh.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

UO HO watch

timeP/N judgment statistics time for U/O HO judgment. 0 ~ 16 s 5

UO HO valid

time

P/N judgment continuous time for U/O HO

judgment.0 ~ 16 s 4


Normal Concentric Data

Parameter name Meaning Value range Recommended

value

RX_LEV Thresh

Rx level hysteresis, Receiving Quality Thrsh.,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 ~ 63 25

RX_LEV hysteresis Works with Rx threshold. 0 ~ 63 5

UO signal intensity

difference

Transmitting Power at antenna difference between underlaid and overlaid may cause MS receiving signal intensity difference in underlaid and overlaid . The parameter usually 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 ~ 63 dB Set according to actual conditions


Enhance IUO Data

Parameter name

MeaningValue range

Recommended value

Enhance IUO Allowed

Enable function of Enhance IUO or not Yes, No

Set according to actual conditions

UtoO Traffic HO Allowed

Enable traffic to be one condition of HO or not Yes, No

Set according to actual conditions

OtoU HO Received

Level Thresh.

In case of receiving level in overlay is less than this value, HO occurs from overlay to underlay

0 ~ 6325

UtoO HO Received

Level Thresh.

In case of receiving level in underlay is more than this value, and traffic in underlay is more than Traffic Thresh. Of Underlay, HO occurs from underlay to overlay

0 ~ 6335


Concentric Cell Handover Table

Parameter name Meaning Value range

Recommended

value

Traffic Thresh. Of Underlay

If the traffic in underlay is over this value, MS will handover from under to overlay

0 ~ 100 %80

Underlay HO Step Period

If there are some handover requests from under to overlay at the same time, system will handover the call with level firstly. This value determine period per step

1 ~ 255 s 5

Underlay HO Step Level

It is the step that handover band decreases, used to control the grade by grade handover band from underlay to overlay with “underlay HO step level”

1 ~ 63 dB 5

Penalty Time of UtoO HO

To prevent ping-pong handover, the call can’t be handed over back within penalty time when a call is handed over from underlay to overlay

1 ~ 255 s 10


Handover Failure Cause

Late Handover – Handover margin (like Rx level-Rx Qual etc )need to define properly.

Ping-Pong Handover – A proper Hysteresis is used to prevent the Ping Pong effect. This can be caused by fading.

Unnecessary Handover – more number of handovers, higher risk of facing quality problem and even in call drop.

Missing neighbor – Best server is not in there in neighbor list. BCCH MissingSame BCCH & BSIC combination one way neighbor handover Neighbor cell in other BSC- need to define correct CGI,BCCHNO,BSIC. Congestion on other cell.


Q&A

Thanks You

handover

Documents