Handover Analysis

Handover analysis

ObjectivesObjectives

How to configure the handover

parameters

How to do at handover

optimization

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

Course ContentsCourse Contents

Chapter 1Introduction

Chapter 2 handover principle

Chapter 3 SHO Optimization

Chapter4 Inter-RAT Optimization

IntroductionIntroduction

In WCDMA system, there are soft handover, Intra frequent

hard handover, Inter frequent hard handover, Inter system

handover. Handover is the most important part of mobile

manage. It plays very important role in RNO of WCDMA

system .

Chapter 2 Handover principle Chapter 2 Handover principle

2.1 Intra-frequency measurement2.1 Intra-frequency measurement

2.2 Hard handover measurement2.2 Hard handover measurement

2.3 Handover algorithms review

2.4 Handover parameters review

Intra-frequency measurementIntra-frequency measurementIntra-frequency measurementIntra-frequency measurement

Event 1A: A primary pilot channel enters the reporting range

When the measurement values satisfy the following formulas, the UE deems that a primary pilot channel has ent

ered the reporting range,the trig condition for Ec/Io:

MNew is the measurement result of the cell that has entered the reporting range

CIOnew is the cell individual offset which is configured for neighbor cells of servicing cell

Mi is the measurement result of the cells in the active set

NA is the number of cells in the current active set

MBest is the measurement result of the best cell in the current active set

W is the weight factor

R is the reporting range. With the signal strength as an example, R equals to the signal strength of the best cell

in the current active set minus a value

H1a is the hysteresis value of event 1A

)2/(log.10).1(.10.log10 11

abest

N

iinewnew HRMWMLogWCIOM

A


Event 1B: A primary pilot channel leaves the reporting range

When the following formulas are satisfied, the UE deems that a primary pilot channel has left th

e reporting range .trig condition for Ec/Io:

MOld is the measurement result of the cell that has left the reporting range

CIOold is the cell individual offset which is configured for neighbor cells of servicing cell

Mi is the measurement result of the cell in the active set

NA is the number of cells in the current active set

MBest is the measurement result of the best cell in the current active set

W is the weighted factor

R is the reporting range

H1b is the hysteresis value of event 1B

)2/(log.10).1(.10.log10 11

bbest

N

iioldold HRMWMLogWCIOM

A


Event 1C: The primary pilot channel in a non active set is better than the primary pilot

channel in an active set

When the following formulas are satisfied, a non-active set cell replaces an old active set cell a

nd becomes an active set cell.trig condition for Ec/Io:

MNew is the measurement result Ec/Io of the cell not included in the active set.

CIONew is the individual cell offset for the cell becoming better than the cell in the active set if

an individual cell offset is stored for that cell. Otherwise it is equal to 0.

MInAS is the measurement result Ec/Io of the cell in the active set with the lowest measureme

nt result.

CIOInAS is the individual cell offset for the cell in the active set that is becoming worse than th

e new cell

H1c is the hysteresis parameter for the event 1C, which is Hystfor1C.

2/.10.log10 1cInASInASnewnew HCIOLogMWInASCIOM


Event 1D: The best cell changes

When the following formulas are satisfied, the best cell will be changed .tri

g condition for Ec/Io:

MNotBest is the measurement result Ec/Io of a cell not stored in "best cell".

MBest is the measurement result Ec/Io of the cell stored in "best cell".

H1d is the hysteresis parameter for the event 1D, which is Hystfor1D

2/log.10log10 1DbestNotBest HMM






Hard handover measurementHard handover measurementHard handover measurementHard handover measurement

Event 2D: The estimated quality value of the used frequency is lower than a certain threshol

d. Event 2D can be used to enable the compressed mode to perform inter-frequency measure

ment.

Qcarrierj is the logarithmic form of the estimated quality value of frequency j

Mcarrier j is the estimated quality value of frequency j

Mi j is the measurement result of cell i with the frequency of j in the virtual active set

NA j is the number of cells with the frequency of j in the virtual active set

MBest j is the measurement result of the best cell with the frequency of j in the virtual ac

tive set

Wj is the weight factor

H is the hysteresis value

,2/10)1(10101

HLogMWMLogWLogMQ jBestj

N

ijijjcarrierjcarrier

jA

Hard handover measurementHard handover measurementHard handover measurementHard handover measurement

Event 2F: The estimated quality value of the used frequency is higher than a certain threshol

d. Event 2F can be used to disable the compressed mode to stop inter-frequency measuremen

t .

Qcarrierj is the logarithmic form of the estimated quality value of frequency j

Mcarrier j is the estimated quality value of frequency j

Mi j is the measurement result of cell i with the frequency of j in the virtual active set

NA j is the number of cells with the frequency of j in the virtual active set

MBest j is the measurement result of the best cell with the frequency of j in the virtual ac

tive set

Wj is the weight factor

H is the hysteresis value

,2/10)1(10101

HLogMWMLogWLogMQ jBestj

N

ijijjcarrierjcarrier

jA






Handover Algorithms reviewHandover Algorithms review

Soft Handover Algorithms review

Inter-RAT Handover Algorithms review

Handover algorithms review: SHOHandover algorithms review: SHO

When event 1A report is received, if the active set is not full, t

hen links are sequenced and added in the order of good qualit

y to poor quality (CPICH Ec/No) (in case that multiple cells rep

ort event 1A), until the active set is full; if the active set is alrea

dy full, no processing will be made.

When event 1B is received, if there are more than one links in

the active set, then the braches are sequenced and removed i

n the order of poor quality to good quality (CPICH Ec/No) (in c

ase that multiple cells report event 1B), until only one link is lef

t; if there is only one in the active set, no processing will be m

ade.

Handover algorithms review: SHOHandover algorithms review: SHO

In case of event 1C, the UE will report the replacing and

replaced cells in the event trigger list. If the active set is not

full, then the triggered cell link will be added; if the active set is

already full at this moment and the replaced cell is not the

best cell in the active set, then this cell link will be removed.

In case of event 1D, if the triggered cell is an active set cell,

then it will be marked as the best cell and measurement

control is updated; if the triggered cell doe not belong to the

active set, then this cell link will be added (if the active set is

full, one of the non-best cell will be removed before this link is

added) and marked as the best cell, with measurement

control updated.

Handover algorithms review: Inter-RATHandover algorithms review: Inter-RAT

Inter-system handover is enabled only in cells located at the

verge of WCDMA FDD system coverage.

For inter-system handover, CPICH RSCP is used as the

physical measurement quantity and events 2D and 2F are

used to decide enabling or disabling the compressed mode.

For inter-system handover, three compressed mode style

sequences are used for concurrent measurement of GSM

RSSI, BASIC identification and BASIC reconfirm, and the

configuration of parameters is oriented to the cell type.

Handover algorithms review: Inter-RATHandover algorithms review: Inter-RAT

Periodic measurement reports are used for inter-system hand

over, and the RNC decides whether to implement hard hando

ver according to the measurement reports.

Handover Evaluation, while the compressed mode is started

and this following formulas is satisfied, Inter-system handover

will be implemented. .

Mother_RAT + CIO Tother_RAT + H/2 Mother_RAT is the estimated quality value RSSI of inter-system frequency

Tother_RAT is the GSM RAT measurement init_threshold, the minimum sign

al Rxlev requirement for GSM cell as a handover target cell.

CIO is Cell individual offset , the measurement signal Rxlev offset for GSM cel

l

H is the hysteresis for GSM RSSI threshold.






Handover parameters review-SHOHandover parameters review-SHO

Report range (SHO relative threshold )

Intra-frequency measurement filter coefficient

Time to Trigger

Hysteresis

CIO (cell individual offset)


Report range (SHO relative threshold )

The relative threshold parameters for soft handover include

IntraRelThdFor1A (relative threshold for event 1A) and

IntraRelThdFor1B (relative threshold for event 1B) .

The parameters determine the size of the soft handover area

and the soft handover subscriber proportion. If report range is

too larger, monitor cell adds to active set cell very easily, soft

handover area is too larger and the forward capacity will be

waste serious; if the 1A and 1B report range is too small,

monitor cell is difficult to join to active cell and SHO can’t

implement smoothly, and handover success rate may be low


Intra-frequency measurement filter coefficient

The filter is configured at Layer 3 intra-frequency measurem

ent report. This parameter used to smooth the influence of sh

adow fading and some fast fading burrs.

The bigger the filter coefficient is, the stronger the smoothing

capability of the burr will be, but the lower the signal tracing ca

pacity will be. If if this parameter is too small, unnecessary sof

t handover and ping pong handover will influence the system;

if the filter is too bigger, soft handover can’t implement in time

and the call will always dropped in handover area .


Time to Trigger

The effect of the time-to-trigger is that the report is triggered

only after the conditions for the event have existed for the spe

cified time-to-trigger

Mobile stations moving at different speeds respond differently

to the time-to-trigger value. The call drop rate is more sensitiv

e to the time-to-trigger value when the mobile station is in hig

h-speed movement, while it is less sensitive when the mobile

station is in low-speed movement, and ping-pong handover a

nd mis-handover are suppressed to a certain extent


Hysteresis parameter related to SHO

To limit the amount of event-triggered reports.

The bigger the hysteresis is, the stronger the signal fluctuation

resistance capability will be, and the better the ping pong effec

t will be suppressed; however, the response speed of the han

dover algorithm on signal changes will be decreased. Therefo

re, the radio environment (slow fading characteristics), the act

ual handover distance and the user moving speed should be f

ully considered for the setting of this parameter.


CIO (Cell Individual Offset )

This offset mechanism provides the network with an efficient t

ool to change the reporting of an individual primary CPICH .

The bigger this parameter is, the more easily soft handover wi

ll occur, and the more UEs will be in the soft handover state, b

ut the more forward resources will be occupied; the smaller thi

s parameter is, the more difficultly soft handover will occur, wh

ich will be likely to affect the receiving quality .

Handover parameters review-HHOHandover parameters review-HHO

compressed mode enable /disable threshold (2D/2F

Event threshold )

GSM RSSI threshold

filter coefficient

Time to Trigger

Hysteresis

CIO (cell individual offset)


2D/2F Event threshold

UE will start compressed mode and measure GSM signal as

a handover target cell when the value of RSCP is below the

setting. UE will stop compressed mode l when the value of

WCDMA cell RSCP is higher than the setting.

if the compressed mode is expected to start as early as

possible, set the 2D event threshold to a relatively big value;

otherwise, set it to a relatively small value. To control the ping

pong effect of the compressed mode start/stop, increase

appropriately the difference between the thresholds for 2D

event and 2F .


filter coefficient

The hysteresis for GSM RSSI threshold and the setting of whi

ch can reduce the probability of mis-decision caused by signal

jitter .


Time to Trigger

If the inter-RAT quality always satisfies the inter-RAT

handover decision condition within the time specified by this

parameter, the network will start the inter-RAT handover

process

In high-speed cells, as mobile stations usually move fast, they

pass through the handover area very quickly. In addition, as

the shadow fading variance in a high-speed cell is small and

signal jitter after filtered by mobile stations is relatively small,

this parameter can be set to 2000ms or lower for high-speed

cells.


Hysteresis

The hysteresis for GSM RSSI threshold and the setting of whi

ch can reduce the probability of mis-decision caused by signal

jitter.


CIO

The measurement signal Rxlev offset for GSM cell .

The bigger this parameter is, the higher the handover priority

of the GSM cells will be .






Soft Handover OptimizationSoft Handover Optimization

SHO Optimization Target

Drive Routes

Optimization Solution

Optimization Analysis approach


SHO Optimization Target

In the early phase of the network, from KPI target, soft

handover success rate for event 1A&1B&1C should be larger

than 95%, and the call drop rate should be smaller than 5%.


Drive Routes

In the early phase of the network, because KPI result don’t

change in evidence prior and post optimization, GPS drive

test is very important .It is essential to use identical drive

routes prior and post any optimization changes in order to

accurately quantify the impact of such changes.


Optimization Solution

Many handover problems can be resolved through adjusting t

he soft handover parameters, such as:

1A & 1B report range

time to trigger

intra-frequceny measurement filter coefficient

CIO

hysteresis

Soft Handover Optimization: Optimization Analysis approach


Small handover area

The active set quality decreases quickly but the good quality

monitor cell can’t add to active set in time.

This issue may be RNP problem but sometime this can’t be

resolved at RF optimization stage and also could be due to

soft handover configuration problem .

Enlarge 1A &1B&CIO report range to make the UE monitor

cell easily add to active set;

Short 1A time to trig to make the measurement report in time,

also can optimize the intra-frequency measurement

coefficient;


CIO Handover optimization example

After setting 3dB CIO of 506 and 505 cell, we can see

that the drop calls between 505 and 506 decreased.

(Left picture is before optimization)



Ping-Pong handover

The active set cell change frequently between the same cells.

This issue may be RF problem, and also cell soft handover

configuration problem.

Cells with many Ping-Pong handover may be causing call

dropped and poorer cell capacity.

This can enlarge intra-frequency measurement coefficient and

time to trigger.


Ping-Pong handover example

The ping-pong handover of 505 cell and 506 cell

can be seen.






Inter-RAT OptimizationInter-RAT Optimization

Presently, the main purpose of inter-RAT handover is to exten

d the signal coverage range, so that the UEs at the verge of

WCDMA coverage can implement handover to the GSM syste

m without communication interruption.

The configuration GSM neighbor list of WCDMA cells is very i

mportant and always make wrong. At the same time, the para

meters optimization is very important.

The optimization solution is parameters configuration such as:

2D & 2F Event threshold, GSM RSSI threshold, Inter-RAT han

dover trigger time, intra-frequceny measurement filter coefficie

nt, CIO and Hysteresis.

Documents

Handover Analysis