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8/12/2019 CDMA huawei

1/76

RG000012

CDMA 1X Load Control &

Channel Management Algorithm

ISSUE 1.0

RG000012

CDMA 1X Load Control &

Channel Management Algorithm

ISSUE 1.0

Course Development Room,

Wireless Product


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Course ObjectiveCourse Objective

Learn the purpose of the CDMA

1X load control

Master the means of the CDMA

1X system load control

Learn the structure of the

channel management moduleMaster the contents of the

channel management

Master the algorithm of channel

assignment


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Contents of CourseContents of Course

Chapter 1 CDMA 1X Load Control

Chapter 2 CDMA 1X Channel

Management


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Chapter 1 CDMA 1X Load ControlChapter 1 CDMA 1X Load Control

Purpose of Load ControlPurpose of Load Control

Means of Load Control

Admission Control


Load Balancing


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Purpose of Load ControlPurpose of Load Control

The CDMA 1X is an interference-restricted system whose capacity

depends on the interference it suffers

To guarantee the quality of service of the subscribers in the system, it

is necessary to control the load of the system so as to avoid the

overload and intensified interference from causing the system crash.


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Purpose of Load Control

Means of Load ControlMeans of Load Control

Admission ControlAdmission Control


Load Balancing


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Purpose of Admission Control and Trigger

Condition

Purpose of Admission Control and Trigger

Condition

Purpose

Control the access of subscribers to the cell so as toControl the access of subscribers to the cell so as to

guarantee the running quality and resource utilization of theguarantee the running quality and resource utilization of the

systemsystem.

Trigger ConditionTrigger Condition

11The system will perform the admission control when theThe system will perform the admission control when the

MS establishes a new call in a new cell or in the case of theMS establishes a new call in a new cell or in the case of the

handoffhandoff

22The system will perform the admission control when aThe system will perform the admission control when a

new service is added during an established callnew service is added during an established call


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Principle of Admission ControlPrinciple of Admission Control

Predict the load change that the admission of the call access

request may bring to the system according to the current loadof the system and the call access requests.

Judge whether the system can run normally with the new load.

The call access request is admitted if the changed load of the

system does not exceed the restricted load that allows the

system to run normally.

Otherwise, the access request is refused

Admission control algorithmAdmission control algorithm ------ an algorithm based onan algorithm based on

load predictionload prediction


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Method of Admission ControlMethod of Admission Control

Predict the system load after the call access according to the

transmission rate that the channel assignment requestrequires .

The load of the forward channel is the ratio of the current

transmitting power to the maximal power of the BS, which canbe obtained from the load control module .

The load of the reverse channel is obtained from the empirical

formula according to the RSSI reported by the BS after themeasurement.


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Classification of Admission ControlClassification of Admission Control

Set the admission thresholds for the data service and voice

service, respectively. The admission threshold for the data

service is lower than that for the voice service.

If an emergency call or high priority call can not access the

system, then the connection of the user EXEC can be

released forcedly so that the emergency call or high priority

call can access the system.

Restrict the admission of the data service according to the

settings of the traffic model of the cell.

The admission threshold for the common voice call is lower

than the soft handoff threshold for the voice call.


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Purpose of Load Control


Admission Control

Means of Load ControlMeans of Load Control

Load BalancingLoad Balancing


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Purpose and Precondition of Load BalancingPurpose and Precondition of Load Balancing

Purpose: Guarantee the load balancing in the system, including:

Load balancing between different carriers

Load balancing between intra-frequency cells.

Precondition:

The load of some carriers is so heavy that the communication

quality is badly affected

Some resources are in the idle state and not fully utilized.


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Classification of Load Balancing AlgorithmClassification of Load Balancing Algorithm

Load balancing (handoff) between carriers

Cell breath

Both the two load-balancing methods are based on the

load measurement.

The load balancing between carriers is prior to the cell

breath.


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Load Balancing between CarriersLoad Balancing between Carriers

Load balancing algorithm between carriers:

The load balancing between carriers refers to the load

balancing between different carriers in the same region

(mainly referring to the same sector). The algorithm is to

guarantee that the subscribers on the carrier with a heavy

load in the coverage of the same sector can be handed over

to other carriers with a sufficient residual capacity


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Cell BreathCell Breath

When the loads of the adjacent cells are different, the cell with

a heavy load will reduce the transmitting power so that the

subscribers at the border of this cell would be handed over to

other adjacent cells to realize the load control.

Cell Breath dynamically assigns the cell load so as to improve the

network coverage and increase the system capacity.

load controlmainly relies oncell breath and

handoff


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SummarySummary

Master the purpose of the load control

Master the means of load control

Master the differences between the cell breath and the load

balancing


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Contents of CourseContents of Course

Chapter 1 CDMA 1X Load Control

Chapter 2 CDMA 1X Channel

Management


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Chapter 2 CDMA 1X Channel ManagementChapter 2 CDMA 1X Channel Management

Structure of Channel ManagementStructure of Channel Management

ModuleModule

Contents of Channel Management

Radio Channel Assignment

Channel Assignment Algorithm


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Diagram of CDMA 1X Channel Management

Modules

Diagram of CDMA 1X Channel Management

Modules

Wireless

Resource table

Channel

Configuration

Channel

distribution

Channel

release

State

Maintenance

CCM

Test

interface

OSDB

Test

model

BIM OAM


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Relationship between Cell, Sector, Carrier and

Channel Element

Relationship between Cell, Sector, Carrier and

Channel Element

The relevant logic resource of the radio channel includes the

channel element pool, sector and cell.

TRX

TRX

TRX

TRX

TRX

TRX

CE Pool 1

ARFCN m

ARFCN1

CE Pool m

Sector1 Sector2

TRX

TRX

TRX

Sector n

CEs

CEs

CEs


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Logical Unit of Radio ChannelLogical Unit of Radio Channel

Channel1ARFCN1 CE Pool1Sector1Cell1

Cell2

Channel1-nARFCN2 CE Pool2

Channel1-nARFCN1 CE Pool1Sector2

Channel n

Channel2

Channel1ARFCN2 CE Pool2

Channel n

Channel2


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Structure of ChannelStructure of Channel

Management ModuleManagement Module

Contents of Channel

Management




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Contents of Channel ManagementContents of Channel Management

Configuration

Assignment

Release

Maintenance of State


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Configuration of Radio ChannelConfiguration of Radio Channel

Concept: It refers to the configuration of the forward common

channel information. The forward channel of the CDMAsystem includes the forward common channel and forward

traffic channel.

The system distinguishes forward common channels from

forward traffic channels via different Walsh codes.


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Code Resource of Forward Common ChannelCode Resource of Forward Common Channel

It refers to the specific code resource channel number

stipulated in the protocol of the forward common channels.

Except the Walsh resource occupied by the common channels,the rest of one CDMA channel can be freely assigned to the

MS as traffic channels. The assignment of the fixed code

resource of forward common channels is shown in the table.

Channel Name Walsh Code

Forward Pilot Channel W(640)

Forward Synchronous

Channel

W(6432)

Forward Paging Channel W(641)W(647)


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Structure of Channel

Management Module

Contents of ChannelContents of Channel

ManagementManagement




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Radio Channel AssignmentRadio Channel Assignment

Basic Concept and Principle

Contents

Reasons

Flow Chat

General Principle


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Concept and Principle of Radio Channel AssignmentConcept and Principle of Radio Channel Assignment

Concept: When the BS and a specific MS expect to establish

the point-to-point connection on a CDMA channel, the BSCwill assign the corresponding traffic channel resource to

transfer the service & signaling data.

Principle: According to the service type and bit raterequirement, the channel assignment submodule will decide

whether to assign channels and what channels to assign, and

determine parameters of the transmission rate and radio

configuration, with reference to the current resource state.


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Contents of AssignmentContents of Assignment

Channel Type

Radio Configuration, RC

Frame Duration

Coding Scheme

Frame Offset

Code Resource


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Channel TypeChannel Type

Basic TypeFCH, SCH.

Each MS can possess one FCH, two forward SCH (F-SCH) and two

reverse SCH (F-SCH) at most on a specific CDMA channel. During the initial establishment of a call, whether voice service or

data service, only the FCH is assigned to transfer signaling and data.

For the packet data service, SCH can be assigned to transfer data on

the basis of the established FCH when high-speed operations are

required.

The assignment of the forward and reverse FCH is symmetrical. The

forward and reverse SCH for the packet data service is asymmetrical,

where the forward SCH is used for the forward packet data service

and the reverse SCH for the reverse packet data service, and they

are assigned as required.


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Radio ConfigurationRadio Configuration

It refers to the working mode of a series of forward or reverse

channels, including the encoding & decoding types, the

modulation & demodulation mechanism. Each RC supports a

set of data rates that differ in the parameters, modulation

characteristics and spreading rates of the physical channel.

BSC assigns the RC to channels according to the rate set of the

service:

IS-95 only assign RC1 or RC2

CDMA 1X --- assign RC3 ~ RC5 to forward channels and RC3 or

RC4 to reverse channels. RC1/RC2 is compatible.

RC1~RC2IS-95A/B

RC3~RC4CDMA 1X 1X

RC5~RC6CDMA 1X 3x


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Forward Channel RC (Radio Configuration)Forward Channel RC (Radio Configuration)

RadioConfiguration

SpreadingRate

Max Data Rate*(kbps)

Effective FECCode Rate

OTDAl lowed

FEC Encoding Modulation

1** 1 9.6 1/2 No Conv BPSK

2** 1 14.4 3/4 No Conv BPSK

3 1 153.6 1/4 Yes Conv and Turbo QPSK





8 3 460.8 1/4 or 1/3 Yes Conv and Turbo QPSK

9 3 1036.8 1/2or 1/3 Yes Conv and Turbo QPSK


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Reverse Channel RC (Radio Configuration)Reverse Channel RC (Radio Configuration)

Radio

Configuration

Spreading

Rate

Max Data Rate*

(kbps)

Effective FEC

Code Rate

OTD

Al low ed FEC Encoding Modulation

1** 1 9.6 1/3 No Conv 64-ary ortho

2** 1 14.4 1/2 No Conv 64-ary ortho

3 1 153.6 1/4 Yes Conv or Turbo BPSK

(307.2) (1/2)

4 1 230.4 3.8 Yes Conv or Turbo BPSK


(614.4) (1/3)


(1036.8) (1/2)


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Frame Duration (Time Span of Interweaver)Frame Duration (Time Span of Interweaver)

FCH can support 5ms frame and 20ms frame SCH can support 20ms frame, 40ms frame and 80ms frame

Since the current MS can only support the 20ms frame, the

BSC only considers the 20ms frame when assigning channels.


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Frame OffsetFrame Offset

There are altogether 16 frame offsets available to each CDMA

channels.

The BSC lets all the branches on the channel evenly distributed

on each frame offset when assigning the frame offsets.

For the same call, keep each soft handoff branch to have thesame frame offset.


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Code ResourceCode Resource

The radio channel assignment module determines the QOF

(quasi-orthogonal function) index and Walsh code of each

forward channel.

IS-95A/B adopts the fixed-length 64-bit Walsh code while theSCH in the CDMA system adopts the variable-length Walsh code.

The Walsh code length of F-FCH is fixed (RC3 and RC5 are 64,

and RC4 is 128), and the Walsh code length of F-SCH decreases

as the channel rate increases.

The BSC guarantees that the Walsh codes assigned to the SCH

of different rates are always mutually orthogonal when

assigning the code resource. If the BSC assigns a 4-bit Walsh

code with all 0s (0000), it wi ll never assign two 8-bit Walsh

codes (00000000 and 00001111) any longer.


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Reason for Radio Channel AssignmentReason for Radio Channel Assignment

Normal call

Hard handoff Soft handoff/softer handoff

SCH assignment


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Normal CallNormal Call

When the MS originates a call request to the BS or the BS

originates a paging request to the MS to establish a call, the

radio channel resource will be applied.

From one CDMA channel, the BSC assigns the channel

resource that corresponds to the Service Option and can meet

the MS capability according to the Service Option carried in

the request message as well as the MS processing capability.


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Hard HandoffHard Handoff

When the BS requires a hard handoff of the MS to hand overto another frequency, the resource assignment will be

required on another CDMA channel.

The parameters of the channel type and frame offset of thereassigned channel source can completely be different from

those of the channel resource on the original branch. The

BSC will treat the resource like a new call when it assigns the

channel resource.


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SCH (Data Service)SCH (Data Service)

If the service is the packet data service, only FCH will be

assigned during the call establishment.

When there is heavy data traffic to be transferred, the

MS may apply for the R-SCH for the uplink data, while

the BS may apply for F-SCH for the downlink data.

The BSC will assign the SCH with a certain bit rate and

duration according to the Service Option, the capability

that the MS supports SCH and the load of the system.


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Reason for Radio Channel AssignmentReason for Radio Channel Assignment

Call

Origination

Termination

Handoff

Hard Handoff Intra BSC soft handoff

Inter BSC soft handoff

Procedure of Data Service

(DS)

DS call originated by MS

DS call originated by BSC

DS call originated by the

MS is activated

DS call originated at the

network side is activated

Burst service process in

the active state

C C


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Classification of Radio Channel AssignmentClassification of Radio Channel Assignment

Requirement of

ChannelAssignment

PCH

Assign

Handoff

CH

Assign

Burst CH

of Data

Assign

i f i C A i


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Block Diagram of Radio Channel AssignmentBlock Diagram of Radio Channel Assignment

ChannelRequest

DecidetransmissionRate

Success?

Changerate

Can ratebe changedAdmission?

Can Parabe changed

Assign Coderesource

Fail andreturn

Decide CHparameter

No

ChangeParameter

SuccessAnd return

Fail andreturn

Yes

Yes

Yes

Yes

No

No

No

P i i l f Ch l A i C ll Ch lP i i l f Ch l A i t C ll Ch l


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Principle of Channel Assignment --- Call ChannelPrinciple of Channel Assignment --- Call Channel

Available State will be high priority

To Data Service , first priority of channel is DCCH that meets the

requirement and has the least resource waste

If higher requirement , reduce the data rate of data users with

lower priori ty.

Lower rate channel can be accepted if full channel can not be

afforded

For the burst data service, centralize the existing supplemental

channel resource to assign SCCH/SCH to a subscriber.

SCH , a code as long as possible will be assigned according tothe requested traffic rate so as to save the code resource

For high service, DCCH is tried to be specialized in transmitting

signaling

Principle of Channel Assignment --- HandoffPrinciple of Channel Assignment --- Handoff


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Principle of Channel Assignment Handoff

Channel

p g

Channel

Besides the Service Option and the MS capability, there are Cell

Identifier List (Target) and IS-95 Channel Identity or IS-2000

Channel Identity in the hard handoff message. When channels

are assigned, the channel type and parameters in Channel

Identity will be more considered than the principle and method

of channel assignment.

For the channel assignment of the inter-BS soft handoff, pleaserefer to the fields of channel type and service configuration

record in the A7-Handoff Request message.

In the case of the intra-BSC soft handoff, the type and

parameters of the channel can be determined with reference to

other soft handoff branches.

Ch l R lCh l R l


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Channel ReleaseChannel Release

Reason of Channel releaseReason of Channel release

Clear callClear call

Clear original branch after a hard handoffClear original branch after a hard handoff

Clear soft handoff branchClear soft handoff branch

Normal Release ProcessNormal Release Process


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Normal Release ProcessNormal Release Process

MS BTS BSC MSC

Abis-Bts Release

Release OrderRelease Order

Release Order

Clear Command

Release Order

Abis-Remove

Abis-Remove Ack

Abis-Bts Release Ack

Clear Complete

Process of Clearing Soft Handoff Branch betweenProcess of Clearing Soft Handoff Branch between


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g

BSBS

Channel State MaintenanceChannel State Maintenance


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Three states of maintenance channel of radio channelThree states of maintenance channel of radio channel

management module:management module:

Operational StateOperational State

Administrative StateAdministrative State

Usage StateUsage State



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It indicates whether the resource has been physically installed

and started to operate, and whether it is available. Including:

Disabled: When a resource does not exist any longer, the

operational state is set as Disabled.

Enabled: When a resource is physically installed, the

operational state is set as Enabled.



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It indicates the usage of the enabled or disabled resource,

including:

Blocked: If the resource is shut down and no subscriber uses it,

the administrative state is Blocked.

Unblocked: When the resource is completely allowed to be used,

the resource is in the Unblocked state.

Shuttingdown: If some subscribers still use the resource after it

is shut down, the administrative state is Shuttingdown.



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It indicates whether the resource is being used at a specific

point and whether there is any extra capacity to provide for

other subscribers, including: Idle: When a resource is not used by any subscriber, the usage

state is Idle.

Active: When some subscriber is using the resource and it stillhas enough capacity to support other subscribers (the current

system load is less than the admission threshold), then the

usage state is Active.

Busy: If the resource does not have enough capacity to support

other subscribers (the current system load is greater than or

equal to the admission threshold), then the usage state is Busy.



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available block

Unavailable

Receiving

Unavailable

clear all calls

Receiving

Available Allow

assignment

Receiving

Block Stop

assignment

SummarySummary


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SummarySummary

Contents of radio channel assignment

Classification of radio channel state

Chapter 2 Channel ManagementChapter 2 Channel Management


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Chapter 2 Channel ManagementC apte C a e a age e t

Structure of Channel

Management Module

Contents of Channel

Management


Channel Assignment AlgorithmChannel Assignment Algorithm

Channel Assignment AlgorithmChannel Assignment Algorithm


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g gg g

Admission control algorithm based on the load

prediction

Code resource assignment algorithm

Dynamic rate adjustment algorithm

Improved frame offset algorithm

Admission Control Algorithm Based on Load

Prediction

Admission Control Algorithm Based on Load

Prediction


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PredictionPrediction

Brief introduction of algorithm:

At the time of channel assignment, first predict the effect of

the access on the whole system according to the

characteristics of the channel to be assigned, and then decide

whether to admit the access or not.

Algorithm characteristics:

The algorithm can more effectively make use of the system

capacity and better satisfy the requirements of different

service types and subscribers with different priority levels.

Purpose of Admission ControlPurpose of Admission Control


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pp

To maintain the forward and reverse load of the system in a

safe state, it is necessary to first make an admission

judgement before the channel assignment. If the latest

assignment brings the unstability of load or even a system

crash, then the channel assignment request will be refused.

Only when the access of a new call does not bring the

deterioration of the system interference, will channels be

assigned to the new call.

Principle of Admission ControlPrinciple of Admission Control


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p

Predict the system load after the access according to the

transmission rate required by the channel assignment request.

Set admission thresholds for the data service and voice service,

respectively.

If an emergency call or high priority subscriber can not access the

system, then the connection of the user EXEC can be released

forcedly so that the emergency call or high priority subscriber can

access the system.

Set admission thresholds for the data service and voice service,

respectively.

Restrict the admission of the data service according to the settings of

the traffic model of the cell.

Code Resource Assignment AlgorithmCode Resource Assignment Algorithm


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Brief introduct ion of algorithm:

Adopt the featured code resource

assignment algorithm to rationally

assign the required forward code.


Integrate the characteristics of

mult iple service types.

Make use of the code resource to the

greatest extent so as to guarantee the

balance between the capacity and the

performance of the system.

Code Resource AssignmentCode Resource Assignment


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The codes required to be fixedly assigned in the protocol are

assigned as required.

Channel in forward link can bedistinguished by Walsh Functionor quasi-orthogonal function

By default, the index of the QOFis 00. if Walsh code resourcedeficient, will be non-zero. QOFof Channel W (64, 0) can onlybe 00.

IS95 (RC1, RC2), length of Walshcode is fixed as 64.

IS2000 (RC>=3), length of Walshcode can vary within [4, 128].

The structure of Walsh code canbe obtained from the HADAMARDmatrix.

Brief Introduction of Rate Adjustment AlgorithmBrief Introduction of Rate Adjustment Algorithm


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When the load of a pilot exceeds the rate change load

threshold, trigger the low bit rate change.


When the load ratio of the system is high, via the rate change,the rate of the data service whose delay requirement is not ver

high in the cell can be reduced so as to optimize the resource

assignment and improve the system capacity.

Process of Rate Adjustment AlgorithmProcess of Rate Adjustment Algorithm


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When the load of a pilotexceeds the rate changeload threshold, trigger

the low bit rate change.`

Decrease the transmissionrate of the data service whosedelay requirement is not veryhigh in this cell and reduce the

bandwidth assignment.

When the loadrecovers normal,the changed rate

will recover.

Purpose of Rate Adjustment AlgorithmPurpose of Rate Adjustment Algorithm


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Make full use of the finite data service bandwidth of the air

interface.

Avoid the impact of the high-speed data traffic channel on the

load of the whole system.

How to meet such grand demand

with limited air interface

Make full use of the finite data bandwidthMake full use of the finite data bandwidth


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The BSC firstly assigns a fundamental channel (FCH) to each data service subscriber.

Then the BSC assigns a data buffer to each data service subscriber on the data service

processing board.

When the data size in the buffer is less than the SCH assignment threshold, only the

FCH (9.6kbps) is used. Only when the data size exceeds the SCH assignment threshold,

will the SCH (9.6 ~ 153.6kbps) be assigned so as to avoid unnecessary resource waste.

The value of the SCH assignment threshold is determined by the signaling delay from the

SCH assignment to the SCH establishment.

FCH

SCH

t

t

t1 t2 t1:deciding assign SCH

t2SCH setting up

t: Delay of SCH setting up

t

Rate Adjustment Algorithm SCH AssignmentRate Adjustment Algorithm SCH Assignment


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Dynamically assign the bit rate of the

SCH according to the data flow in the

buffer of each subscriber.

Determine the duration of the SCH

according to the total data size in the

buffer of each subscriber and the bit rate

of the assigned SCH, and dynamically

assign the duration-limited SCH.

It is the most economical

data rate and duration together meet

the through exactly.

Data Suffer

Data from PSDN

FCH +

9.619.238.476.8 or

153.6kbpsSCH

Significance of Rate Adjustment AlgorithmSignificance of Rate Adjustment Algorithm


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The data service is usually discontinuous, so the rate

adjustment algorithm can

make better use of the air interface resource;

save the transmitting power;

enable multiple subscribers to share the radio resources.

SCH of User1

t

SCH of User2

t

ProblemProblem


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How to avoid the impact of high-speed data

traffic channel on the load of the whole

system?

SolutionSolution


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Restrict the highest bit rate that can be assigned to the SCH according to the

pilot strength reported by the MS so as to guarantee the stability of the

system.

Predict the system load after different bit rates are assigned to the SCH so as

to carry out the admission control. If the system load does not permit, make

another judgement after reducing the bit rate by half. Thus the subscribers

request will not easily be refused, and meanwhile, with the system resource

permitted, the requirements of the subscribers, to the greatest extent, can be

met, so as to improve the bandwidth of the system.

BTS

Improved Frame Offset Assignment AlgorithmImproved Frame Offset Assignment Algorithm


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For the frame offset assignment, make all the calls in one BS

evenly distributed on each frame offset and integrate the

frame offset distribution of the adjacent BS.


This algorithm can more effectively make use of the frame-

offset resource, and improve the call connection rate and

handoff success ratio, compared with the traditional algorithm.

SummarySummary


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Differences and characteristics of several channel assignment

algorithms

Sum-up of the ChapterSum-up of the Chapter


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This chapter mainly introduces the structure of the

radio channel management module, contents of radio

channel assignment and reasons thereof, states of

channels, and assignment algorithms.

ReferencesReferences


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Guide to CDMA 1X Admission & Load Control

CDMA BTS Controller Technical Manual (Radio Channel

Management Part)


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