10-CRNP Handoff Algorithm

8/22/2019 10-CRNP Handoff Algorithm

http://slidepdf.com/reader/full/10-crnp-handoff-algorithm 1/52

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ORG000004 CDMA1X Handoff Algorithm

Issue 3.0



Internal Use

Introduction

In CDMA system Handoff has close

relationship with network quality

(conversation quality, call-drop

performance, etc.).

It also effects the system coverage,

capacity and interference.



Internal Use

Chapter 1 Basic Concept of CDMA Handoff

Chapter 2 Handoff in CDMA

Chapter 3 Here is Handoff



Internal Use

What is handoff?

When an MS moves from one sector/cell to the service area of

other sector/cell, it disconnects itself from the old sector/cell andmakes connection with the new sector/cell. The sector/cell from

which it disconnects is called “source” and the sector/cell with

which it is being connected is called “target”. In CDMA system,

there are three kinds of handoffs, these are:

1: Hard handoff

2: Soft handoff

3: Softer handoff



Internal Use

Why need handoff?

To ensure continuous conversation.

In wireless communications, during HO

process, there is a high probability of call drop,

which directly effects the system performance（

90% of radio call drop occurs during handoff).Proper handoff algorithm can reduce system call

drop and increase network capacity.



Internal Use

Handoff types in CDMA

Hard handoff Break-make

Soft handoff

Make-break

Softer handoff

Make-break


http://slidepdf.com/reader/full/10-crnp-handoff-algorithm 7/52Internal Use

Soft handoff

Soft handoff branches are selected by BSC.

Better frame selected

in CFMR (BSC)

Abis Link

BTS BBTS A

Pilot A Pilot B



Softer handoff

Softer handoff: Signal of different branches are combined in BTS.

CFMR in BSC

BTS



Handoff in CDMA

In CDMA network, a user need to switch within

Same frequency

Different frequency

Soft handoff is possible only within the same

frequency i.e. intra-frequency handoff

Hard handoff is required for inter-frequency handoffs Softer handoff is possible only within the same

frequency and BTS



Handoff in CDMA

Not all the intra-frequency handoffs are soft handoff For example, if the frequencies of the target pilot and the

current pilot are the same, but:

Belonging to the different BSCs

Soft handoff path unavailable between two BSCs Frame offset unavailable for destination pilot

Different SID/NID

then hard handoff is required.



The pilot set, carries the active pilots. An active pilot is a pilotwhose paging or traffic channels are actually being monitoredor used.

The pilot set, not in the active set but

potential to be demodulated

The pilot set, not included in the

active set or the candidate set but

being possible to be added in the

candidate set

Other pilot sets

Active Set

Candidate

Set

Neighbor

Set

Remaining

Set

What are the pilot sets?



Internal Use

Handoff parameters

T_ADD:

Threshold for new pilot to be added in

active or candidate set.

Range: 0~63 (unit: -0.5db)

Recommended value: 28 (-14dB)

T_DROP:

Threshold for serving pilot to be removed

from active or candidate set

Range: 0~63 (unit: -0.5dB),

Recommended value :32 (-16dB)

Active Set

CandidateSet

Neighbor

Set

>T_ADD<T_DROP

>T_ADD <T_DROP



Internal Use

T_TDROP:

It is a timer, which triggers when the Ec/Io drops below

T_DROP. If this timer expires and Ec/Io is still below T_DROP,

the pilot is moved from Active set to the Candidate set or

Neighbor set. In other words, it is an Active or Candidate Set

drop timer.

Range: 2~5

Recommended value: 3

Handoff parameters



Internal Use

T_COMP:

Active versus candidate pilot strength comparison threshold

Range: 0~15 (unit: 0.5dB)

Recommended value: 5 (2.5dB)

Note: We need to choose appropriate value of T_COMP because low value

causes much signaling and high value will increase the pilot interference.

Handoff parameters



Internal Use

Pilot P1

Pilot P2

Pilot P0

t0

T_COMP×0.5dB

t1 t2

T_ADD

Pilot strength

P0-Strengh of Pilot P0 in Candidate Set.

P1,P2-Stength of Pilot P1,P2 in Active Set.

t0-Pilot strength Measurement Message Sent, P0>T_ADD

t1-Pilot strength Measurement Message Sent, P0>P1+T_COMP*0.5dB

t2 -Pilot strength Measurement Message Sent, P0>P2+T_COMP*0.5dB

Handoff parameters



Internal Use

Handoff Completion Message

Extended Handoff Direction Message

Mobile Station Acknowledgment Order

Base Station Acknowledgment Order

Pilot Strength Measurement Message

Base Station Acknowledgment Order

Selector arranges channel elements/Walsh codes in requested sector

Handset verifies which assigned PNs it can now hear.

Neighbor List Update Message

Mobile Station Acknowledgment Order

12

3

4

Ec/Io better than T_ADD then sends a PSMM to BS

Once the HO is completed, the BS sends new neighbor list message.

Handoff flows



Internal Use

Time

Ec /Io

Sector

A Sector

B

T_TDROP

T_ADD

T_DROP

Soft Handoff Region

T_ADD & T_DROP is the standards used to add or drop a pilot.

T_TDROP is a timer.

1 2 3 4 5

Soft handoff procedure



Internal Use

The purpose of SRCH-WIN set by MS is to

capture the multi-path components, which

arrived before or after the current signal.

Based on experience, the SRCH-WIN

should be set wide enough so that it can

capture the signal, which has the maximumtime delay due to multi-path.

How to find pilot?



Internal Use

Types of search window

Currently an MS uses three kinds of search windows, these are:

SRCH-WIN-A， used for searching the pilots in the active

set and the candidate set

SRCH-WIN-N ， used for searching the pilots in the

neighbor set

SRCH-WIN-R ， used for searching the pilots in the remain

set

The MS fixes the width of the search window according to

the system message. An MS can search the multi-path

components of the available pilot signals within the setting.



Internal Use

Pilot searching

SRCH-WIN-AThe MS can utilize this search window to search the pilots in the active

set and the candidate set based on the PN code. For pilots in the active

set and candidate set, the MS fixes the center of the search window first,

based on the multi-path signal of the pilot reaches earliest.

SRCH-WIN-A

The earliest arrived pilot

PILOT PHASE



Internal Use

Pilot searching

SRCH-WIN-N

Used to monitor neighbor set , the size of this window is larger than SRCH-WIN-A. The distance is measured in term of chips (1

chip approximately covers 244m).

PN4 { {

n chip offset with delayed signal necessaryPN16

{

n chip offset because of the search center of active set

{

Expected window



Internal Use

Pilot searching

SRCH-WIN-R

Used to track the remaining pilots. Typically it should be equal or

larger than SRCH-WIN-N at the start of the project. After

optimization, this window is set to zero.



Internal Use

PILOT SEARCHER VIEWED IN SEQUENCE: Typical Elapsed Time = 4 seconds

A A A C N

R

A A A C A A A C A A A C A A A C A A A C A A A CN N N N N N

A A A C N A A A C A A A C A A A C A A A C A A A C A A A CN N N N N

A A A CN A A A C A A A C A A A C A A A C A A A C A A A CN N N N N N

N A A A C A A A C A A A CN N N R A A A C N A A A C A A A C A A AN N

C A A A C A A A CN N N

R

A A A C N A A A C A A A C A A AN N C A A AN

C A A A CN N Only 3 of 112 remaining set pi lots h ave been c hecked thu s far!

CURRENT PILOT SET CONTENTS A A A

CN N N N N N N N N N N N

R R R R R R R R R R R R





R R R R R R R R R R R RR R R R R R R R R R R R



R R R R

3

112

112

A

N

R

R

R

R

R

R

R

NN

N

N

N

NN N

A

A

The Pilot Searcher’s Measurement Process



Internal Use

Delay budget and size of search window

SRCH_WIN_A Width of

SRCH_WIN_A

(chips)

Delay budget

（ms）

Availab

-le PN 0 4 T< 1.64 512

1 6 1.64<T<2.45 512

2 8 2.45<T< 3.27 512

3 10 3.27<T< 4.09 512

4 14 4.09<T< 5.72 512

5 20 5.72<T< 8.17 5126 28 8.17<T<11.44 512

7 40 11.44<T< 16.34 512

8 60 16.34<T<24.51 512

9 80 24.51<T< 32.68 512

10 100 32.68<T< 40.85 512

11 130 40.85<T< 53.11 512

12 160 53.11<T< 65.36 256

13 226 65.36<T< 92.32 256

14 320 92.32<T< 130.72 170

15 452 130.72<T<184.42 128



Internal Use

Question

Whether data service supports soft handoff?

Consideration the fact, high power may affect the

system, whether soft handoff can be performed

after reducing the rate?



Internal Use






Internal Use

CDMA handoff analogy

The objectives of handoff are:

Reduce call-drop rate to guarantee QoS Reduce interference to increase network capacity Balance the distribution of traffic load of the network and

reduce the congestion of the hot spots



Internal Use

Types of handoffs

In a CDMA network following handoff can occur: Intra-frequency handoff

Soft handoff/softer handoff

Hard handoff

Inter-frequency handoff

MS assisted hard handoff

Pseudo pilot hard handoff

Handdown hard handoff

Direct hard handoff



Internal Use

Optimize the soft handoff by

Reasonable coverage planning and BTS layout Reasonable setting of T_ADD, T_DROP, T_TDROP

Optimize the maximum branches in active handoff

Reasonable planning of handoff region

Reasonable setting of neighbor and neighbor priority

Useful command:

MOD HO

MOD BSCHO



Internal Use

This slide is kept blank intentionally.



Internal Use




Internal Use

Intra-frequency Hard Handoff

In some cases, soft/softer handoff cannot be realized even the

frequencies of the pilots are the same. For example:

Inter-BSC handoff without A3/A7 connection

Handoff between different frame offsets on the same pilot

In such cases, hard handoff is applied to ensure the uninterrupted

communication.

I f H d H d ff b



Internal Use

Intra-frequency Hard Handoff by

Reasonable planning of handoff region Reasonable setting of same-frequency HHO service carrier

threshold, same-frequency HHO target carrier threshold, and same-

frequency HHO relative threshold

Useful command:

MOD HHOSF

MS i t d H d H d ff



Internal Use

MS assisted Hard Handoff

MS-assisted hard handoff is occurred when:

MS measures the current pilot strength is below than the

threshold value. And the target pilot cannot allocate the same

frame offset. Then MS sends PSMM to BS, to trigger the hard

handoff. BS receives abundant FER over forward or reverse link. It

means the quality of link is poor. If there is neighbor inter-

frequency pilot reported by the MS, which meets the setting

conditions of the system, then the system will trigger hard

handoff.

MS i t d H d H d ff



Internal Use

MS assisted Hard Handoff

CFSRPM(Report)

CFSCNM

(Search Order)

F1 (serving)

F2 (candidate)

GHDM

(HHO)

CFSRQM

(Search Parameters)

CFSRSM(Acceptance)

CFSRQM: Candidate Frequency Search Request

CFSRSM: Candidate Frequency Search Response

CFSCNM: Candidate Frequency Search Order

CFSRPM: Candidate Frequency Search Report

O ti i MS A i t t H d H d ff b



Internal Use

Optimize MS Assistant Hard Handoff by

The following parameters would be optimized: MS assisted HHO service carrier threshold

MS assisted HHO target carrier threshold

MS assisted HHO relative threshold

MS assisted HHO start search threshold

MS assisted HHO stop search thresholdUseful command:

MOD HHOMA



Internal Use


P d Pil t H d H d ff



Internal Use

Pseudo Pilot Hard Handoff

O ti i th P d Pil t H d H d ff b



Internal Use

Optimize the Pseudo Pilot Hard Handoff by

The following parameters would be optimized:Pseudo pilot hard HO T_ADD

Pseudo pilot hard HO absolute threshold

Pseudo pilot hard HO relative threshold

Useful command:

MOD HHOBPLT

ADD BCDMACHTRG

RMV BCDMACHTRG

LST BCDMACHTRG

H d D H d H d ff



Internal Use

Hand Down Hard Handoff

Once serving BTS is offering frequency (F1) different to the target BTS (F0),

and serving BTS also can handle calls on F1. Then MS will observe Hand

down handoff.

Optimize Hand Down Hard Handoff by



Internal Use

Optimize Hand Down Hard Handoff by

The following parameters would be optimized:Handdown hard HO Ec/Io intensity absolute threshold

Handdown hard HO max. loop delay threshold

Useful command:

MOD HNDDWN

ADD HNDDWNTRG

RMV HNDDWNTRG

LST HNDDWNTRG

MOD HNDDWNTRG

Direct Hard Handoff



Internal Use

Direct Hard Handoff

It is applicable to the sectors with simple network structure, but different frequencies;

Optimize Direct Hard Handoff



Internal Use

Optimize Direct Hard Handoff

The following parameters would be optimized:Direct hard HO Ec/Io strength absolute threshold

Direct hard HO maximum loop delay threshold

Useful command:

MOD DRCT

ADD DRCTTRG

RMV DRCTTRG

LST DRCTTRG

MOD DRCTTRG



Internal Use




The Call is Already Established



Internal Use

The Call is Already Established

E c / I o

All PN Offsets

0PN

0

-20

Rake Fingers

3

Reference PN

Active Pilot

168 500220

Mobile Rake RX

Srch PN??? W0

F1 PN168 W61

F2 PN168 W61

F3 PN168 W61F3 PN220 W20

Mobile Requests the Handoff!



Internal Use

Mobile Requests the Handoff!

PILOT STRENGTH MEASUREMENT MESSAGE(PSMM)

BASE STATION ACKNOWLEDGMENT

Just prior to this message, this particular

mobile already was in handoff with PN 168

and 220.

This PSMM reports PN 500 has increased

above T_Add, and the mobile wants to use

it too.

The base station acknowledgesreceiving the PSMM.

Ok! Handoff is Accepted



Internal Use

Ok! Handoff is Accepted

HANDOFF DIRECTION MESSAGE

The base station sends a Handoff

Direction Message authorizing the

mobile to begin soft handoff with all three

requested PNs. The pre-existing link on

PN 168 will continue to use Walsh code

61, PN220 will continue to use Walsh

Code 20, and the new link on PN500 willuse Walsh code 50.

The mobile acknowledges it has received

the Handoff Direction Message.

MOBILE STATION ACKNOWLEDGMENT

Handoff is Done!



Internal Use

Handoff is Done!

The mobile searcher quickly re-checksall three PNs. It still hears their pilots!

The mobile sends a Handoff Completion

Message, confirming it still wants to go

ahead with the handoff.

BASE STATION ACKNOWLEDGMENT

HANDOFF COMPLETION MESSAGE

The base station confirms it has

received the mobile’s Handoff

Completion message, and will

continue with all of the links

active.

Time to Update Neighbor List



Internal Use

Time to Update Neighbor List

MOBILE STATION ACKNOWLEDGMENT

NEIGHBOR LIST UPDATE MESSAGE

In response to the mobile’s Handoff

Completion Message, the base station

assembles a new composite neighbor

list including all the neighbors of each of

the three active pilots.

This is necessary since the mobile

could be traveling toward any one of these pilots and may need to request

soft handoff with any of them soon.

The mobile confirms receiving the

Neighbor List Update Message. It isalready checking the neighbor list and

will do so continuously from now on.

The handoff is fully established.

Oops!!!



Internal Use

Oops!!!

E c / I o

All PN Offsets

0 512PN

0

-20

T_ADD

Rake Fingers

Reference PN

Active Set

168 500220

3T_DROP

Mobile Rake RX

Srch PN??? W0

F1 PN168 W61

F2 PN500 W50

F3 PN220 W20

BSC soft handoff flow



Internal Use

BSC soft handoff flow

MS BTS_D

Pilot StrengthMeas. Msg Abis-IS-2000FCHRvs(Pilot Strength)

Abis-BTSSetup

Abis-Connect

Abis-Connect Ack

Abis-BTSSetupAck Abis-IS-2000FCHFwd(ForwardFra)

ForwardTrafficFrame Abis-IS-2000FCHRvs(Idle)

Abis-IS-2000FCHFwd(EHDM)

MSAckOrder Abis-IS-2000FCHRvs(MSAck)

Handoff CompletionMsg Abis-IS-2000FCHRvs(HCM)

Abis-IS-2000FCHFwd(BaseAck)BaseAckOrder

BaseAckOrder

BTS_S

Abis-IS-2000FCHFwd(BaseAck)

Handoff DirectionMessage

Hard handoff flow



Hard handoff flow

MS Source BS MSC Time

a

b

c

d

e

f

g

Handoff Required

Handoff Request

Handoff Command

Handoff Direction Message

MS Ack Order

Target BS

Null forward traffic channel frames

Handoff Request Ack

Handoff Commenced h

j

i

k

l

m

n

Reverse Traffic Channel Frames or Traffic Channel Preamble

Handoff Completion Message

Clear Command

Clear Complete

BS Ack Order

Handoff Complete

x

Documents

10-CRNP Handoff Algorithm