Guide of CDMA1X Handoff Planning-20010816-B-1.00.doc

Documentation Center, Wireless Network Planning Dept

Documentation Center, Wireless Network Planning Section, Huawei Technologies Co., Ltd.

File No.

Product Version

Confidentiality level

1.0

Internal publicity

Product Name:

Total Pages: 19

Guide of CDMA 1X Handoff Planning

(V1.0 for internal use only)

Prepared by:

Li Zhongdong

Date:

2001/08/18

Reviewed by:

Technical Support Team

Date:

yyyy/mm/dd

Reviewed by:

Date:

yyyy/mm/dd

Approved by:

Date:

yyyy/mm/dd

Huawei Technologies Co., Ltd.

All Rights Reserved

Revision Record

Date

Revision version

Description

Author

2001/05/11

1.00

Completed the first draft.

Li Chenfei

2001/08/16

1.00

Revised the contents of handoff type.

Li Zhongdong

Table of Content

1 Basic Conception of CDMA Handoff2

1.1 Handoff Principle2

1.2 Explanation of CDMA 1X Handoff Terms and Major Parameters2

1.2.1 Terms Explanation2

1.2.2 Explanations of Major Parameter3

2 Handoff Procedures4

2.1 Brief Flow of Handoff4

2.2 Handoff Measurement5

2.2.1 Handoff Measurement Method5

2.2.2 Pilot Search5

2.2.3 PSMM5

2.2.4 Hard Handoff Measurement6

2.3 Soft Handoff Signal Flow6

2.3.1 Soft Handoff Flow6

2.3.2 Hard Handoff Flow7

2.3.3 Handoff Procedure of Data Service Status7

2.4 Causes of Handoff Failure and Rollback after Handoff Failure8

3 Handoff Planning8

3.1 Intra-frequency Handoff8

3.1.1 Soft/Softer Handoff8

3.1.2 Intra-frequency Hard Handoff9

3.2 Inter-frequency Handoff10

3.2.1 MS Assisted Hard Handoff10

3.2.2 Pseudo Pilot Hard Handoff10

3.2.3 Handdown Hard Handoff11

3.2.4 Direct Hard Handoff12

3.2.5 Load Balance13

3.3 Examples13

3.3.1 Pseudo pilot13

3.3.2 Direct Hard Handoff13

3.3.3 HANDDOWN Handoff14

3.4 Search Window14

4 Setting of Handoff Parameters15

5 Planning of Neighbor cell15

Table of Figure Description

Figure 3-1 Hard handoff algorithms based on pilot beacon11

Figure 3-2 Hard handoff algorithms based on HANDDOWN12

Figure 3-3 Algorithms based on direct hard handoff12

Figure 3-4 Use pseudo pilot hard handoff method to realize intra-frequency inter-BSC handoff13

Figure 3-5 Use direct hard handoff method to realize intra-frequency inter-BSC handoff14

Figure 3-6 Use HANDDOWN hard handoff to realize inter-frequency inter-BSC handoff14

Guide of CDMA 1X Handoff Planning

Key words: CDMA 1X, Handoff, measurement, and planning

Abstract: the document gives the brief introduction to CDMA 1X handoff algorithms and basic flow for the reader to understand the handoff parameters configuration in case of network planning.

List of abbreviations:

List of reference files:

List of Reference Files

Name

Author

No.

Release date

Consulting places or sources

Publish unit (fill the column if the file is not released by Huawei)

User's Manual of CDMA2000 BSC Handoff Requirements Spec 1

Chen Faping

CDMA2000 BSC Data Configuration (ALG 0227)

Wu Yong

is20005

Training Slides for CDMA2000 BSC Handoff Algorithms 1.1

Wu Yong

CDMA handoff is not only related to network quality (such as conversation quality, dropped call performance), but also related to coverage, capacity, and interference. The document describes and analyzes the problems about CDMA 1X handoff procedure and handoff planning in terms of network planning. For the details of handoff algorithms and flow, refer to the protocols, technical manual or instructions.

1 Basic Conception of CDMA Handoff

1.1 Handoff Principle

The meaning of handoff: when the MS is close to the edge of the original service cell and is moving to another service cell, the link between the original base station and the MS will be replaced by the new link between the new base station and the MS. Handoff belongs to mobility management; handoff, service resources management, power control, and channel management constitute RRM sub system. In CDMA1X, handoff algorithms and parameters configuration will greatly influence system capacity, load control and conversation quality.

The status of MS can be divided into two big categories: idle status and conversation status. Handoff, from the angle of broad sense, is shifted from one communication connection to another communication connection. In CDMA 1X includes idle handoff and conversation handoff. The document will only give the description of the handoff of conversation status.

1.2 Explanation of CDMA 1X Handoff Terms and Major Parameters

1.2.1 Terms Explanation

Soft handoff

This is the inter-pilot handoff of different base stations in the intra-frequency. Can keep connection with multiple base stations at the same time to get multi-path diversity.

Softer handoff

This is the inter-pilot handoff of different sectors in the same base station and in the intra-frequency. Actually, it is inter-pilot handoff in the same channel board. The difference of soft handoff and softer handoff: softer handoff occurs in the same BTS and the diversity signal performs max gain ratio combination in BTS; soft handoff occurs between two BTSs and the diversity signal performs selection combination at BSC.

Hard handoff

Include two cases: intra-frequency and inter-frequency. Usually, it is inter-BTS handoff in case of different frequencies, different MSCs and different frame offset.

Pilot set

It is the set of the pilots corresponding to the service frequencies of current MS. That is, they have the same CDMA frequency but phase (PN offset) is different. Pilot set can be divided into active set, candidate set, neighbor set, and remnant pilot set.

Active set

It is the set of the pilots corresponding to the service channels in which the MS keeps connection.

Candidate set

When the pilot signal is strong enough, the MS can be successfully demodulated and can access at any time.

Neighbor set

It is the set of the pilots that are currently not in active set or candidate set but may enter candidate set.

Remnant set: refer to the set of all of the remaining pilots.

Pilot pollution

There are many effective pilots in the coverage scope. Probably, PSMM reports four pilots, and the strength >= T_add or PSMM reports five pilots and the strength >=T_Drop.

1.2.2 Explanations of Major Parameter

T_ADD: pilot measurement threshold

When Ec/Io>T_ADD, the MS sends pilot strength measurement message and add the pilot to candidate set from neighbor set.

T_DROP: pilot DROP threshold

When the pilot Ec/Io is lower than T_Drop, it will trigger counter TT_Drop.

If the pilot Ec/Io is more than T_Drop, the counter stops; when the counter is full, the pilot is wiped off from active set or candidate set to neighbor set.

TT_DROP: Active or Candidate Set drop timer

If the pilot decrease time in pilot set and candidate set is more than TT_DROP counter, the pilot is wiped off to neighbor set.

If candidate set is full and a new pilot meets the requirements of T_ADD and needs to be added, the pilot that is the closest to TT_DROP threshold will be wiped off.

In this procedure, the MS only sends power strength measurement message to pilot cell which is in active set, and the pilot in candidate set will be directly wiped off to the neighbor set, so the MS need not send power strength measurement message.

TComp: active vs. candidate Comparison threshold

When Ec/Io>T_add, the pilot is added to candidate set and PSMM is sent; if Ec/Io>Active Ec/Io + TComp, the MS sends the additional PSMM.

2 Handoff Procedures

2.1 Brief Flow of Handoff

When the MS triggers the handoff in the conversation, the flow is as follow:

C

o

n

v

e

r

s

a

t

i

o

n

s

t

a

t

u

s

A

p

i

l

o

t

s

t

r

e

n

g

t

h

>

r

e

p

o

r

t

t

h

r

e

s

h

o

l

d

Y

e

s

N

o

R

e

p

o

r

t

B

S

C

t

o

p

e

r

f

o

r

m

h

a

n

d

o

f

f

P

e

r

f

o

r

m

s

o

f

t

h

a

n

d

o

f

f

o

r

s

o

f

t

e

r

h

a

n

d

o

f

f

?

Y

e

s

T

r

i

g

g

e

r

s

o

f

t

h

a

n

d

o

f

f

/

s

o

f

t

e

r

h

a

n

d

o

f

f

P

e

r

f

o

r

m

M

A

H

H

O

Y

e

s

T

r

i

g

g

e

r

M

A

H

H

O

P

e

r

f

o

r

m

h

a

r

d

h

a

n

d

o

f

f

(

e

.

g

,

p

i

l

o

t

b

e

a

c

o

n

)

Y

e

s

T

r

i

g

g

e

r

h

a

r

d

h

a

n

d

o

f

f

1) When the pilot signal is more than T_ADD, the MS reports PSMM, and add the pilot to candidate set.

2) BS: Extended Handoff Direction Message.

3) MS: add the pilot to active set, and send Handoff Completion Message.

4) MS: when pilot signal is lower than T_DROP, start HO DROP counting.

5) MS: counter is time up, send PSMM.

6) BS: send Extend Handoff Direction Message

7) MS: throw the pilot from active set into neighbor set, and send Completion Message.

In IS95A, the threshold is static (T-ADD, T-DROP) when the pilot is added in the active set. In IS95B and CDMA2000, the threshold is dynamic when the pilot is added into the active set. In different cells or different noise environments, the absolute threshold for adding or deleting the cell pilot of Active Set is related to the strongest and weakest signal strength in the active set. If the pilot signal strength in the current Active Set is large, the requirement for the pilots to enter the active set will be high. If pilot signal strength in Active Set is weak, the requirement for the pilot to move out of the active set will be lower relatively.

Typical Handoff procedure: measurement control(measurement report(handoff judgment(handoff execute(new measurement control.

In measurement control phase, the network notifies the MS of the parameters to perform measurement via sending measurement control message. In measurement report phase, the MS sends PSMM to the network. In handoff judgment phase, the network judges the handoff according to measurement report. In handoff execute phase, the MS and network follows signaling flow and makes response according to the signaling.

2.2 Handoff Measurement

2.2.1 Handoff Measurement Method

The MS searches pilot signal in the current CDMA frequency distribution to detect the existence of CDMA channel and measure the strength: when MS finds a pilot signal has enough strength (>T_Add) without relating to the forward service channel that allocates the pilot (that is, it is not in active set or candidate set), the MS will send a PSMM (pilot signal measurement message) to BTS.

2.2.2 Pilot Search

BTS is set with search window (PN offset range). In the window, MS searches the available direction signal multi-path component. For the pilot signal in active set and candidate set, each pilot signal's search windows dimensions is corresponding to the PN of SRCH_WIN_ASr (for the table, please refer to IS20005). The MS locates the center of the search window of each pilot signal of active set and candidate set at the place close to the multi-path component pilot signal that arrives earliest.

In neighbor set, search dimensions and search methods are determined together by the parameters such as SRCH_WIN_NGHBR_INCLS, SRCH_WIN_NGHBRS, SRCH_OFFSET_INCLS and SRCH_OFFSET_NGHBRS. For details, refer to protocol IS20005 and other documents of search windows.

8) If SRCH_OFFSET_INCLs is equal to 0, the search window offset for each pilot in the Neighbor Set shall be zero PN chip. The mobile station should center the search window for each pilot in the Neighbor Set around the pilots PN sequence offset plus the corresponding search window offset, using timing defined by the mobile stations time reference (see TIA/EIA/IS-2000-2).

9) If SEARCH_PRIORITY_INCLs is equal to 1, the mobile station should use SEARCH_PRIORITYs for the corresponding pilot to schedule its neighbor search.

10) If ADD_PILOT_REC_INCL of the corresponding pilot NGHBR_REC is equal to 1, the MS will use the information containing in NGHBR_PILOT_REC to search the pilot signal in neighbor set.

Search window dimension of each pilot signal in remnant set is also corresponding to PN number of SRCH_WIN_RS. The mobile station should center the search window for each pilot in the remnant Set around the pilot's PN sequence offset, using timing defined by the mobile station's time reference. The MS will only search the remnant set pilot signal whose direction signal PN serial offset is equal to the multiple integer of PILOT_INCS.

2.2.3 PSMM

The report in PSMM (Pilot Strength Measurement Message) is the status of (N pilots phases, Ec/Io and each pilots signal handoff) divided by timer.

2.2.4 Hard Handoff Measurement

In hard handoff, we can use pilot search control message to perform one-step search or cyclic search; BSC is subject to the actual situation. Inter-frequency search will influence the voice quality, so it is not preferred. Generally, cyclic search is needed in case of inter-frequency handoff; otherwise, one-time search is preferred.

After BS sends MS candidate frequency search control message, MS starts to search. If the requirements can be met, the MS will report it.

2.3 Soft Handoff Signal Flow

2.3.1 Soft Handoff Flow

MS

BSC

psmm

soft handoff required

extended ho direction

msg

soft handoff complete

Add to active set

handoff complete

Msg

psmm




msg

Get rid of the relevant pilot

Allocate service

channel resources

Set up service channel connection

Release service channel resources

Release radio resources

TT_Drop time up

MS

BSC

psmm



msg


Add to active set

handoff complete

Msg

psmm




msg

Get rid of the relevant pilot

Allocate service

channel resources

Set up service channel connection

Release service channel resources

Release radio resources

TT_Drop time up

( Notes:

When the MS has multiple soft handoff tributaries, only one main control service call performs call connection.

2.3.2 Hard Handoff Flow

MS

BSC



handoff complete

Msg

Allocate service channel resources

Set up the service channel connection

Candidate

freq search

req

msg

candidate

freq search response

msg

Candidate

Freq Search Control

Msg

At the frequency, start pilot search

Return the original configuration frequency

Candidate

FreqSearch

Report

Msg

General

HoDirection

Msg.

At the new

frequecy

, attempt to handoff to the new pilot set

Use cyclic search or one

-

step search

MS

BSC



handoff complete

Msg



Candidate

freq search

req msg

candidate freq search response

msg

Candidate Freq Search Control

Msg



Candidate

FreqSearch

Report

Msg

General

HoDirection

Msg.

At the new

frequecy



-

step search

Here only one procedure of inter-frequency hard handoff is described. For inter-BSC hard handoff or other hard handoff, refer to protocol IS20005.

2.3.3 Handoff Procedure of Data Service Status

The call soft handoff of data service is the same as that of the voice service.

The data service subscriber generally possesses one DCCH (or FCH), and 1~2 supplemental channels (or 1~6 supplemental code channel). No matter it is one or multiple channels, one call always operates as one whole unit to perform soft handoff judgment. After performing soft handoff, the processing on DCCH and FCH is different from the processing on supplemental (code) channel.

The rate of supplemental channel is high. If supplemental channel and fundamental channel keep the same handoff tributaries, this will decrease the system forward capacity. The supplemental channel of data service is effective only in certain part of time and will not be kept always, so supplemental service channel will not set up soft handoff tributary.

For the data service, hard handoff will not support Supplemental Channel. The needed service processing will be completed according to the flow. Firstly, disconnect supplemental channel; then perform allocation after handoff.

2.4 Causes of Handoff Failure and Rollback after Handoff Failure

Causes of handoff failure include:

11) Target cell pilot coverage is not consistent with service channel coverage, and service channel signal strength in handoff is not strong enough.

12) Signal quality of target cell is not high;

13) Handoff timeout

14) Target cell resources is not available

15) Maintenance interference causes the failure

16) The cell doesn't exist;

17) Voice coder rates are not matched;

18) Terrestrial resource is not available

19) Equipment or interface fault

20) Failure in case of recovering to the previous channel

21) Others

After the handoff fails, recover to the configuration status before attempting to the handoff, and send candidate frequency measurement report or pilot strength measurement message. The MS will switch off the relevant counter in handoff attempt.

The transmitting of reverse supplemental channel may not be recovered.

3 Handoff Planning

The key point of handoff planning is to select the proper handoff band zone and to avoid selecting handoff band at the dense traffic area. Well plan the handoff bandwidth to assure the proper soft handoff proportion. Generally, soft handoff (not including softer handoff) should be controlled under 40%. For different networking, select the proper handoff strategy to determine the proper handoff parameters and neighbor relations.

The handoff algorithms can be divided into intra-frequency handoff and inter-frequency handoff according to the standard that whether the frequency of source cell and target cell is the same. In addition, load balance belongs to load controlled and triggered handoff algorithms.

3.1 Intra-frequency Handoff

3.1.1 Soft/Softer Handoff

The handoff in the intra-frequency from the same manufacturer belongs to soft/softer handoff. For the uplink, soft/softer handoff can provide the gain to lower down the MS transmitting power and improve the reverse coverage. For the downlink, too many soft/softer handoff tributaries will occupy too many WALSH code resources, power resources and channel board CE.

Major parameters: T_Add, T_Drop, intra-frequency neighbor relation, and search window

Application guideline:

22) Properly prepare cell layout and coverage planning, properly set sector frequency's pilot power distribution, and avoid pilot pollution and coverage blind spot. Refer to power distribution part of "Guide of Parameters Configuration Spec in CDMA 1X Network Planning".

23) T_Add, and T_Drop, is generally configured as: T_Add = -14dB, T_Drop = -16dB, or T_Add = -13, T_Drop = -15dB. If the whole network Ec/Io is high, increase this group of parameters, or use the dynamic threshold.

24) Maximum tributaries number is limited as 3. Set it in BSC module handoff parameter table.

25) Soft handoff and signaling flow in the same manufacturer, inter-BSC, and intra-BSC modules is much more complicated than the intra-module soft handoff. So the planning should be subject to the traffic distribution. Meanwhile, perform BSC coverage area division and module coverage areas division. Plan the lower traffic to be at the edge, and reduce inter-BSC and intra-BSC inter-module soft handoff. (this is also applicable for hard handoff).

26) If the vendors are cooperative and the cooperation partner can provide standard A3/A7 interface, inter-BSC soft handoff can be carried out.

27) IS95 MS neighbor set has maximum 20 PNs. IS2000 MS neighbor set has maximum 40. Note the number of neighbor pilots in case of configuring neighbor pilot. Configure the really needed neighbor relation and get rid of the unnecessary ones to avoid that the really needed neighbor pilots are located out of the MS neighbor set. In the later version, neighbor set can be configured with the division of priorities, and the really useful neighbor pilot can be remained.

3.1.2 Intra-frequency Hard Handoff

It is impossible to add two BSC sector frequencies to the active set at the same time if there is no soft handoff channel between BSCs. In this case, intra-frequency hard handoff algorithms is provided to judge the pilot to handoff to the target BSC in the method of hard handoff in case that the condition is mature.

Before the intra-frequency hard handoff, the intra-frequency pilots that are not added to soft handoff active set are the interference to current service cell. After intra-frequency hard handoff, the original service cell is out of active set, so its signals are also the interference to the current demodulation. Meanwhile, intra-frequency hard handoff is also different from the diversity gain that can provide soft handoff. Be careful in case of using intra-frequency hard handoff.

Major parameters of intra-frequency hard handoff are included in intra-frequency hard handoff parameter (HHOSAMEFREQPARA). The major parameters: intra-frequency hard handoff relative threshold. In most of the cases, the relative threshold will trigger the intra-frequency hard handoff. That is, another pilot's strength is stronger than the previous pilot, and this relative threshold will perform intra-frequency hard handoff.


When there is no inter-BSC soft handoff path, two BSCs are in the intra-frequency, so the edge can only perform intra-frequency hard handoff. The performance of intra-frequency hard handoff is poor, so inter-BSC soft handoff of the same vendor is usually adopted as much as possible. For different vendors, we can consider to use inter-frequency hard handoff to replace the intra-frequency hard handoff. If the intra-frequency hard handoff is really used, please note the following:

28) Be careful to plan the handoff band and avoid heavy traffic area. The handoff band zone should be at the area in which the traffic is not dense.

29) Be careful to set intra-frequency hard handoff trigger threshold. The relative threshold is used. When the target cell pilot strength is higher than one relative threshold of the previous cell, the intra-frequency hard handoff occurs.

3.2 Inter-frequency Handoff

Huawei provides multiple hard handoff algorithms: MS assisted hard handoff, pseudo pilot hard handoff, Handdown hard handoff, direct hard handoff, etc. In the actual applications, one or more methods will be used.

3.2.1 MS Assisted Hard Handoff

When IS95B and IS2000 MS are in conversation, BSC may control it to change to other frequency to search the available inter-frequency neighbor pilot. According to the MS reported inter-frequency measurement report, MSC will judge to perform one hard handoff at the proper time.

Major parameters:

30) Hard handoff trigger threshold. Currently, it shares soft handoff T_ADD. Additional parameter will be used for the configuration in the future.

31) Candidate frequency T_ADD has the lowest requirement on target cell pilot strength.

32) Search the relevant parameters: candidate frequency search control parameter, pilot measurement request parameter.

33) Neighbor relations (inter-frequency neighbor relation table)


34) Hard handoff is firstly disconnected and then is connected, and one time handoff procedure needs more time than soft handoff. Be sure to guarantee the success ratio of hard handoff.

35) Hard handoff trigger threshold should not be too lower. Soft handoff T_Add should be set as -14dB, and -13dB. For hard handoff trigger threshold, when the original cell pilot decreases to -9dB and -10dB, hard handoff is triggered. At the same time, the pilot strength of target cell should at least reach -9dB, and -10dB.

36) The MS inter-frequency search will spend some time, so it is necessary to control the MS to perform the search in advance. That is, when the original cell pilot strength are about -6dB, and -7dB, start to send inter-frequency search request to MS. When the original cell pilot strength is lower than hard handoff trigger threshold, BSC has acquired the effective inter-frequency search report and can send hard handoff request immediately.

37) IS95B and IS2000 MSs can perform inter-frequency measurement. If IS95 and IS95A in the cell also need hard handoff, it is necessary to use the method that MS is not needed for inter-frequency search, such as, pseudo pilot.

3.2.2 Pseudo Pilot Hard Handoff

In the following diagram, Cell 1 has four frequencies and each one is with service; Cell 2 has four frequencies, and F3 is configured as pseudo pilot, and only pilot, sync and paging channels are configured and service channel is not configured, and no service exists. When the MS of F3 in Cell moves towards Cell 2 and detects pilot signal of F3 in Cell 2, it will trigger hard handoff of real frequency toward Cell 2. In the procedure of pseudo pilot hard handoff, it is unnecessary for MS to perform inter-frequency search.

Major parameters:

38) Pseudo pilot hard handoff on-off (pilot handoff algorithms configuration table)

39) Trigger threshold (Pseudo pilot hard handoff parameter table)

40) Target pilot (Pseudo pilot hard handoff target table)

F1

F0

F0

F0

F1

F2

F2

F3

Cell 1

Cell 2

Cell 3

PilotBeacon

F3

PilotBeacon

F2

PilotBeacon

F1

F1

F0

F0

F0

F1

F2

F2

F3

Cell 1

Cell 2

Cell 3

PilotBeacon

F3

PilotBeacon

F2

PilotBeacon

F1

Figure 3-1 Hard handoff algorithms based on pilot beacon


Success ratio of pseudo pilot hard handoff can reach 95%. We should clearly learn about pseudo pilot and its corresponding real pilot's coverage range.

In idle status, pilot power of pseudo pilot is the same as that of real pilot. So, in the same place, the MS received Ec/Io are equivalent. But Ec/Io distribution of real pilot is influenced by the load. When the load exists, Ec/Io of real pilot will decrease. So pseudo pilot hard handoff parameter should be set according to 50% load.

3.2.3 Handdown Hard Handoff

Handdown hard handoff controls the MS to handoff from one frequency of the sector to another frequency without undergoing inter-frequency search. The trigger conditions include the original cell pilot strength and RTD.

Major parameters:

41) HANDDOWN hard handoff on-off (pilot handoff algorithms configuration table)

42) Trigger threshold and target pilot (HANDDOWN hard handoff parameters table)

F1

F1

(

B)

F2

(

A)

Figure 3-2 Hard handoff algorithms based on HANDDOWN

The problem of handdown hard handoff: the original pilot and target pilot are in the same sector, but their coverage is different greatly because different bands have different interference or the two pilot loads are different. So we should assure that the handoff occurs in the reliable area from angle of setting trigger conditions. After hard handoff is over, it is still in coverage scope of the corresponding pilot.

3.2.4 Direct Hard Handoff

When the original cell pilot strength threshold and RTD threshold can directly meet the trigger condition of hard handoff, the pilot will be directly handoff to the neighbor sector frequency.

Major parameters:

43) Direct hard handoff on-off (pilot handoff algorithms configuration table)

44) Trigger threshold and target pilot (direct hard handoff parameter table)

F2

F1

(

B)

Figure 3-3 Algorithms based on direct hard handoff

The target cell of direct hard handoff belongs to another base station, and is designated in data configuration, and it is unique. The network designer and planner should learn about this. For the long and narrow area, such as expressway, metro, etc., direct hard handoff can be used.

3.2.5 Load Balance

When multiple frequencies exist in the sector, load balance algorithms will automatically handoff partial traffic to the pilot whose traffic is relatively lower in case that one load is heavy and another load is light.

3.3 Examples

The following examples respectively adopt the algorithms such as pseudo pilot, direct hard handoff and HANDDOWN.

3.3.1 Pseudo pilot

Two BSCs adopt basic frequency283 frequency, and are respectively from different vendors. So inter-BSC soft handoff cannot be used. Use transition inter-frequency frequency method to realize inter-BSC handoff. Assume transition inter-frequency frequency is 201. It is shown in the following figure. When the MS is through the edge, it will undergo two pseudo pilot hard handoff.

Regarding hardware, add three frequencies.

PB2

83

283

283

PB201

PB201

201

(

2)

(

2)

IS95

or

IS2000 MS

Figure 3-4 Use pseudo pilot hard handoff method to realize intra-frequency inter-BSC handoff

3.3.2 Direct Hard Handoff

Two BSCs adopt basic frequency --283 frequency, and are respectively from different vendors. So inter-BSC soft handoff cannot be used. Use transition inter-frequency frequency method to realize inter-BSC handoff. Assume transition inter-frequency frequency is 201. It is shown in the following figure. When the MS is through the edge, it will undergo two direct hard handoffs.

Regarding hardware, add one frequency.

283

283

201

(

2)

(1)

IS95

or

IS2000 MS

283

283

201

(

2)

(1)

IS95

or

IS2000 MS

Figure 3-5 Use direct hard handoff method to realize intra-frequency inter-BSC handoff

3.3.3 HANDDOWN Handoff

Two BSCs are from different vendors, and the frequencies are respectively 283 and 201. Use HANDDOWN hard handoff to realize inter-BSC handoff. It is shown in the following diagram.

283

283

283

201

201

IS95

/IS2000

MS

201

Figure 3-6 Use HANDDOWN hard handoff to realize inter-frequency inter-BSC handoff

3.4 Search Window

Strategy of search window: the best signal should be in the search window; if the search window is too narrow, the important pilot signal will lose and interference comes into being; if the search window is too wide, the search window efficiency will lower down and the conversation quality will lower down.

The MS has three search windows, respectively used for search active set (including candidate set), neighbor set and remnant set. The setting strategies for the three widows are different. Active set (including candidate set) window recommends to be 4-7 (14-40 chips), and this is determined by delay extension of propagation environment, and the typical delay extension in urban area is 7ms, and is 2ms in suburban area, and the big cellar delay extension is larger than the small cellar. Neighbor set window recommendation is 7-13 (40-226 chips), and this is determined by delay extension of propagation environment and difference of relevant MS reference pilot cell distances; remnant set window is recommended to be 7-13. It is 0 (4 chips) after the optimization is over

The time of each chip is 813.8ns, and the propagation length is 244m.

4 Setting of Handoff Parameters

For detailed data configuration, refer to "Guide of Data Configuration Spec for CDMA 1X BSS Network Planning".

5 Planning of Neighbor cell

In CDMA, the definition in neighbor cell list may be the handoff candidate target cell. Compared with GSM, neighbor cell planning differs greatly. The proper neighbor cell is helpful for searching the corresponding pilot set to acquire handoff gain. For each pilot, the system supported neighbor cell's length is 40 (for 2000 MS) or 20 (for 95 MS).

When 2 or 3 soft handoff tributaries exist, the combined neighbor cell list comes into being: combine neighbor cell list and get rid of the repeated ones according to the update active set, and cut them until only 20 neighbor cells remain. This is the dynamic neighbor cell list.

In CDMA system, the setting principle for the possible neighbor cell is to set them as many as possible, because the pilot signal that cannot enter soft handoff tributary will be interference for the MS at the edge of cell. Planning cell service scope is one of the important tasks in CDMA so that too many neighbor cells or over-strong signal at the edge can be avoided.

45) The missed cell will cause pilot interference.

46) Too many cells will reduce the system processing capability; max number of static neighbor cells in data configuration is 20.

47) During handoff, the dynamic neighbor cell table will only be combined as "20". So the important neighbor cell should be listed at the front in case of configuration.

48) If the pilot is more than T_Add and cannot be added to active set, this is called pilot pollution and will cause interference. Configure the effective neighbor cell.

02-10-29 2002-10-28All rights reserved Page 14 of 15

_1097308220.doc
MS

BSC



handoff complete

Msg



Candidate freq search

req msg


msg


Msg



Candidate

FreqSearch

Report

Msg

General

HoDirection

Msg.

At the new

frequecy



-

step search

MS

BSC



handoff complete

Msg



Candidate freq search

req msg


msg


Msg



Candidate

FreqSearch

Report

Msg

General

HoDirection

Msg.

At the new

frequecy



-

step search

Documents

Guide of CDMA1X Handoff Planning-20010816-B-1.00.doc