3 wcdma radio resource management issue 2.00

7/31/2019 3 WCDMA Radio Resource Management ISSUE 2.00

1/57

WCDMA RRM

Confidential Information of Huawei. No Spreading Without Permission

N-0

www.huawei.com

Copyright 2009 Huawei Technologies Co., Ltd. All rights reserved.

WCDMA Radio

Resource Management


2/57

WCDMA RRM


N-1

Page1Copyright 2009 Huawei Technologies Co., Ltd. All rights reserved.

Objectives

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

Describe the Purpose of the RRM

Know the RRM principles:

Channel configuration

Power control

Handover

Load control


3/57

WCDMA RRM


N-2


Contents

1. RRM Overview

2. Channel Configuration

3. Power Control

4. Handover

5. Load Control


4/57

WCDMA RRM


N-3


Why RRM is needed?

To guarantee the QoS of different types of services

To guarantee the network performance satisfy the network

planning requirement

To increase network capacity

The Radio resources are limited, to utilize the radio resources reasonably can greatlyimprove the network performance and increase the network capacity.

By RRM algorithms, the coverage of the network and QoS of the services will beguaranteed and meanwhile the network capacity is maximum.


5/57

WCDMA RRM


N-4


WCDMA RRM Algorithms


Power control

Handover

Load control

In order to guarantee the service QoS, the CN QoS requirement must be mapped intosome RAN parameters, so as to let RAN resource support the service .So we need channelconfiguration.

For CDMA system ,to guarantee the service data error rate with the minimum TX power isvery important, which can effectively increase the network coverage and capacity. So weneed power control

To satisfy the UE mobility, handover is need .

After the network is loaded, to ensure the stability of the network and the QoS of most ofthe services ,load control must be used.


6/57

WCDMA RRM


N-5


The Cooperation of WCDMA RRM

Algorithms

Initial ChannelConfiguration

Load Control-AdmissionControl

CN

RNC

Iu QoS Mapping

Initial Rate

Radio BearerAllocation

RAB Assignment(QoS)

In the service setup stage, CN will send the QoS requirement to RNC by RAB Assignmentmessage. The QoS requirement include maximum bit rate"," guaranteed bit rate, timedelay allowed"," user priority, and so on.

Based on the initial rate, RNC perform Admission Control to avoid bad impact to thesystem.

After succeed the admission, RNC will allocate channels for the user and configure thechannel parameters ,such as time interval of the data processing, size of the data block,block error rate, and so on.


7/57

WCDMA RRM


N-6


The Cooperation of WCDMA RRM

Algorithms (Cont.)

Channel Setup

Call service

UE ActivityChanges

Go Across Cells

Call Over

Load Control--

CongestionControl

Power Control

Closed Loop

Power Control

Open Loop

Dynamic Channel

configuration

Handover

In channel initial setup stage, to avoid interference, the initial power of the channels mustbe calculated carefully, which is called Open Loop Power Control.

After the initial stage, in the whole service duration ,the power of transmitter must becontrolled in real time, which is called Closed Loop Power Control.

During a PS service, the activities of the user may change largely, so RNC will monitor theactivity of each user, based on which the channel is dynamically reconfigured, so as tomatch the actual service requirement.

If the user moves across a cell coverage area, RNC must reconfigure the physical channelsfor the UE, to maintain the service continuously, that is function of handover .

Channel configuration, power control, and handover are all user oriented RRM algorithms.Load control is cell oriented algorithm.

After the network startup, RNC will monitor the load level of all the cells. When a cell iscongested or overloaded, load control will be trigged to avoid load increase and recoverthe cell to normal state.


8/57

WCDMA RRM


N-7


Contents

1. RRM Overview


3. Power control

4. Handover

5. Load control


9/57

WCDMA RRM


N-8


Radio Bears Provided by WRAN

To guarantee the QoS of different types of services, in RNC,

many kinds of Radio Bearers are pre-defined:

Conversational 12.2/28.8/32/56/64

Streaming 8/12/32/64/128k

Interactive 8/16/32/64/128/384/2048/7200/14400k

Background 8/16/32/64/128/384/2048/7200/14400k

Since the variety of the service QoS required, RAN must provide different Radio Bearers fordifferent service.

Different types of Radio Bearers are configured with different transition time intervals,different transmission block sizes, different number of transmission blocks, differentchannel coding rates, different spreading factors to realize different rates and time delayfor conversational ,streaming, interactive and background services.


10/57

WCDMA RRM


N-9


Initial Channel Configuration

The initial channel configurations for CS and PS are different:

For CS services, service rates can not be negotiated

For PS services ,RNC can firstly decide the initial bit rate and

maximum bit rate (MBR).

The initial bit rate is based on the configuration

The maximum bit rate is based on:

UE capability

CN assignment

For a CS service ,RNC will allocate the service rate based on the CN assignment directly.

For a PS service ,the initial rate is not the maximum bit rate ,RNC will choose a lower rate

for the accessing service. This initial rate is based on the RNC configuration.


11/57

WCDMA RRM


N-10


Dynamic Channel Configuration

Dynamic channel configuration:

Adjust radio bearer based on user activity

Objective of Dynamic channel configuration

BE services (interactive and background services)

Target of Dynamic channel configuration

To utilize the radio resources with high efficiency

For BE services ,the activity changes largely, if a fixed rate is allocated, it will waste theradio resources.

RNC will monitor the activity of each user, and dynamically reallocate the service rate, soas to satisfy the service requirement with minimum resources.


12/57

WCDMA RRM


N-11


Dynamic Channel Configuration Algorithms

Dynamic Channel Configuration Algorithms include:

Rate Reallocation Algorithm

UE State Translating Algorithm

PS Service Always Online Algorithm

Rate Reallocation Algorithm work in uplink and downlink independently .

When uplink is inactive ,RNC reconfigure uplink channel

When downlink is inactive ,RNC reconfigure downlink channel Rate Reallocation affect R99 BE services and HSUPA services. (HSDPA resource

reallocation is handled by fast scheduling)


UE State Translating Algorithm affects uplink and downlink both, so only whenboth uplink and downlink are inactive, RNC will trigger UE translating to commonchannel states, or even release the common channel .

PS service always online Algorithm

For PS services, if both uplink and downlink are inactive and last for a certainduration, RNC requires CN to release the IU connection ,after that , RNC will then

release the RRC connection. But the PDP context is always reserved .when the userwant to activate the service, it is no need to request the PDP again. So for PSservice users ,they feel they are always online.


13/57

WCDMA RRM


N-12



MAC-d

RLC buffer

ThresholdRLC

DCH1

RLC

DCH2

Channelconfiguration

Channelconfiguration

RRC

UE traffic


RNC will monitor the RLC buffer volume in uplink and downlink.

In downlink, RNC takes internal measurement;

In uplink, RNC request UE report the RLC buffer volume. RNC will compare the measurement result with the configured threshold , then

reconfigure the channel in MAC layer.


14/57

WCDMA RRM


N-13


UE Working Modes and States

Idle Mode

Connected Mode

Cell_DCH

Cell_FACH

Cell_PCH

URA_PCH

UE enters connected mode after the RRC connection is established. The UE leaves the

connected mode and returns to idle mode after the RRC connection is released

Based on the UE mobility and activity, RNC controls the UE states in connected mode.


15/57

WCDMA RRM


N-14


Idle Mode

The UE has no relation with UTRAN, only with CN. For data

transfer, a signalling connection has to be established.

UE camps on a cell

It enables the UE to receive system information from the PLMN

UE can receive paging message from the PICH of a cell

The idle mode tasks can be divided into three processes:

PLMN selection and reselection

Cell selection and reselection

Location registration

When a UE is switched on, a public land mobile network (PLMN) is selected and the UE

searches for a suitable cell of this PLMN to camp on.

The NAS shall provide a list of equivalent PLMNs, if available, that the AS shall use for cell

selection and cell reselection.

The UE searches for a suitable cell of the chosen PLMN and chooses that cell to provide

available services, and tunes to its control channel. This choosing is known as "camping on

the cell". The UE will, if necessary, then register its presence, by means of a NAS

registration procedure, in the registration area of the chosen cell.

If the UE finds a more suitable cell, it reselects onto that cell and camps on it. If the new

cell is in a different registration area, location registration is performed.


16/57

WCDMA RRM


N-15


Connected Mode

When UE is in connected mode, there is an RRC connection

between UE and UTRAN.

The UE position can be known on different levels:

Cell level

UTRAN Registration Area (URA) level

Dedicated transport channels (DCH)

Common transport channels (RACH / FACH)

In connected mode ,the level of UE connection to UTRAN is determined by the quality ofservice requirements of the active radio bearers and the characteristics of the traffic onthose bearers.

The Uu interface is designed to support a large number of UEs using packet data servicesby providing flexible means to utilize statistical multiplexing. Due to limitations, such as airinterface capacity, UE power consumption and network availability, the dedicatedresources cannot be allocated to all of the packet service users at all times.

The UE state in the connected mode defines the level of activity associated to the UE. Thekey parameters of each state are the required activity and resources within the state andthe required signaling prior to the data transmission. The state of the UE shall at least bedependent on the application requirement and the period of inactivity.

Assuming that there exists an RRC connection, there are two basic families of RRCconnection mobility procedures, URA updating and handover. Different families of RRC

connection mobility procedures are used in different levels of UE connection (cell level andURA level):

URA update is a family of procedures that updates the UTRAN registration area ofa UE when an RRC connection exists and the position of the UE is known on URAlevel in the UTRAN;

Handover and cell update is a family of procedures that adds or removes one orseveral radio links between one UE and UTRAN when an RRC connection exists andthe position of the UE is known on cell level in the UTRAN.


17/57

WCDMA RRM


N-16


Connected Mode

Cell-DCH

In active state

Communicating via its dedicated channels

UTRAN knows which cell UE stays in

If there is huge data to be transmitted, it must allocate dedicated channel. Thus UE will be

in Cell-DCH. UE in Cell-DCH state is communicating via DCH (downlink and uplink) with

UTRAN.


18/57

WCDMA RRM


N-17


Connected Mode

Cell-FACH

In active state

Few data to be transmitted both in uplink and in downlink. There

is no need to allocate dedicated channel for this UE

Downlink uses FACH and uplink uses RACH

UE needs to monitor the FACH for its information

UTRAN knows which cell the UE stays in

If there is only few data to be transmitted, there is no need to allocate dedicated channel.

Thus UE will be in Cell-FACH. UE in Cell-FACH state is communicating via FACH (downlink)

and RACH (uplink) with UTRAN. UE need to monitor the FACH for its relative informationbecause FACH is shared for all users in the cell.


19/57

WCDMA RRM


N-18


Connected Mode

Cell-PCH

No data to be transmitted or received

Monitor PICH, to receive its paging

UTRAN knows which cell the UE stays in

UTRAN has to update cell information of UE when UE roams to

another cell

Lower the power consumption of UE

If UE has no data to be transmitted or received, UE will be in Cell-PCH or URA-PCH. In

these two states, UE needs to monitor PICH, to receive its paging. UTRAN knows which

cell or URA UE is now in. The difference between Cell-PCH and URA-PCH is that UTRANupdate UE information only after UE which is in URA-PCH state has roamed to other URA.

UTRAN have to update cell information of UE when UE roams to another cell. UE migrates

to cell-FACH state to complete the cell update. If there is also no data to be transmitted or

received, UE is back to CELL-PCH state after cell update. If the cell update times in a fixed

time reach a preset value, UTRAN will let UE migrate to URA-PCH. URA is an area of

several cells.


20/57

WCDMA RRM


N-19


Connected Mode

URA-PCH

No data to be transmitted or received

Monitor PICH, to receive its paging

UTRAN only knows which URA (which consists of multiple cells)

that UE stays

UTRAN updates UE information only after UE has roamed to other

URA

A better way to reduce the resource occupancy and signalingtransmission

Similar with the CELL-PCH state, UE in URA-PCH states should migrate to CELL-FACH state

to complete the URA update when it roams to other URA.


21/57

WCDMA RRM


N-20



CELL_DCHCELL_DCH CELL_FACHCELL_FACH

CELL_PCHCELL_PCHURA_PCHURA_PCH

IDLEIDLE

RRC Connection


Similar with Rate Reallocation Algorithm, in Rate Reallocation Algorithm ,RNC will monitorthe activity of the service in uplink and downlink both:

If the activity in uplink and downlink are both decreased, RNC will translate the UEfrom CELL_DCH to CELL_FACH states, then to CELL_PCH/URA_PCH states.

UE in CELL_PCH and URA_PCH states will be translated back to CELL_FACH statesafter paging or when the UE need to upload some data.

UE in CELL_FACH state will be translated to CELL_DCH state if the activity in uplinkor downlink increases.


22/57

WCDMA RRM


N-21


PS Service Always Online Algorithm

RRC IU

PDP Context

UE RAN CN-PS

PS service always online Algorithm

After the service setup, if RNC detect there is no traffic in uplink and downlink, RNC willrequest CN release the service bearer , then CN will trigger bearer release signalingprocedure to release IU interface ,then RNC release RRC connection .

After this procedure, the UE is actually in idle mode, all the resources are released. Butlogically the PDP context is maintained, so the user feels online as well.

When the user want to trigger some new traffic transition, UE just need to reestablish theservice bearer .


23/57

WCDMA RRM


N-22


Contents

1. RRM Overview


3. Power Control

4. Handover

5. Load Control


24/57

WCDMA RRM


N-23


Near Far Effect

Signal from UEb issubmerged in signalfrom UEa

A B

Near Far Effect is one of the difficulties of any CDMA system.

In radio network, different UEs are differently far away from the NodeB, so the path losses

are different as well. In uplink , if all UEs transmit signal with same power level, the signals received by the

NodeB are very different, the difference can be up to 70 dB.

So the signal from the farther UEs are easily submerged. The UEs near to the NodeB willblock the whole cell.

By power control , the transmitting power of UEs are balanced, and then, by processinggain, more UE signals can be decoded ,so the capacity is increased.


25/57

WCDMA RRM


N-24


Purposes of Power Control

Purposes of uplink power control

Overcome near-far effect, decrease intra-frequency

interference ,then increase uplink capacity

Save UE transmitting power

Purposes of downlink power control

Save the cell power resource, increase downlink capacity

Decrease inter-cell interference

Principle of power control

Just enough

In WCDMA, Power control is needed in uplink and downlink both :

In uplink, by controlling the UE transmitting power ,the interference from each UE is

minimum, so the system capacity is increased. In downlink ,by controlling the dedicated channel power for each UE to make the power

occupied by each UE is minimum, the cell capacity is improved and the inter-cellinterference is well controlled.


26/57

WCDMA RRM


N-25


Categories of Power Control

Open loop power control

Uplink Open loop power control

Downlink Open loop power control

Closed loop power control

Uplink closed loop power control

Downlink closed loop power control

WCDMA power control is channel oriented. The transmitting power of each channel iscontrolled by two steps:

Open loop power control Closed loop power control

Open loop power control works at the initial setup stage of a radio link, it will calculate aproper initial transmitting power

Closed loop power control works after the radio link setup stage, it will dynamically adjustthe transmitting power in real time.


27/57

WCDMA RRM


N-26


Categories of Power Control (Cont.)

WCDMA channel power control

SCH

PICH

AICH

PRACH

SCCPCH

PCCPCH

DPCCH

DPDCH

No Power ControlClosed LoopOpen LoopChannels


28/57

WCDMA RRM


N-27


Application Scenario of Open Loop Power Control

5. Downlink Synchronization

UE Node BServing

RNC

DCH -FP

Allocate RNTISelect L1 and L2parameters

RRCRRC

NBAPNBAP3. Radio Link Setup Response

NBAPNBAP2. Radio Link Setup Request

RRCRRC7. CCCH: RRC Connection Set up

Start RXdescription

Start TXdescription

4. ALCAP Iub Data Transport Bearer Setup

RRCRRC9. DCCH: RRC Connection Setup Complete

6. Uplink Synchronization

NBAPNBAP8. Radio Link Restore Indication

DCH -FP

DCH - FP

DCH - FP

1. CCCH: RRC Connection Request

DownlinkDPCH openloop power

control

Uplink DPCHopen loop power

control

PRACH open looppower control

Open loop power control works only at the initial setup stage of radio link


29/57

WCDMA RRM


N-28


Significance of closed loop power control

Calculation result of open loop power control is not accurate

After radio link initial setup, the radio channels change dynamically

Closed Loop Power Control

The open loop power control is just a simple evaluation by the transmitter, the calculationresult is not very accurate.

After the initial access stage, because of the channel fading, mobility of the user, in orderto guarantee the QoS, the power must be dynamically adjusted.

In order to save power, decrease the interference ,after the initial access stage, the realtime closed loop power control is necessary.


30/57

WCDMA RRM


N-29



Principle of closed inner loop power control

Measure the received signal SIR,

compare it with SIR target

Measure the received signal SIR,compare it with SIR target

Closed loop power control is realized by two parts. It works in uplink and downlinkindependently.

closed inner loop power control In uplink, NodeB will measure the received signal SIR from UE, and compare it with

a target value. If the measured value is higher than target, NodeB will control theUE to decrease the transmitting power, otherwise, increase. In downlink, themechanism is similar ,UE will measure the received signal SIR from NodeBdedicated channel, and compare it with a target value. If the measured value ishigh than target, UE will control the NodeB to decrease the transmitting power onthe dedicated channel, otherwise, increase.

The frequency of closed loop power control is 1500Hz.


31/57

WCDMA RRM


N-30



Relation between SIR and QoS

SIR

BLER

Different curvecoresponding todifferent radio

channel

The index of QoS is BLER (block error rate), but not SIR.

SIR is measured in physical layer. BLER is monitored in MAC layer.

For a fixed SIR, in different channel condition, for different service, the BLER will bedifferent.

In order to guarantee the BLER of the service, the SIR target value must be dynamicallyadjusted, which is called outer loop power control.

Outer loop power control and inner loop power control work together to guarantee theQoS.


32/57

WCDMA RRM


N-31



Principle of closed outer loop power control

NodeB UE

Measure the SIR andcompare with the SIRtarget, then adjust theUE transmitting power

Inner loopOuter loop

RNC

Measure the BLERand compare withthe BLER target, thenadjust the SIR target

BLER target

In uplink, RNC will measure the BLER of the user data from NodeB ,then compare it willBLER target value configured .If the measured value is higher than target value, RNC willcontrol the NodeB to increase the SIR target, otherwise decrease.

In downlink ,the principle is the same, but the control is realized inside the UE.

The frequency of outer loop power control is configurable.


33/57

WCDMA RRM


N-32


Contents

1. RRM Overview


3. Power Control

4. Handover

5. Load Control


34/57

WCDMA RRM


N-33


Purposes of Handover

Why a mobile system need handover?

Mobility of the user

Balance the load

Hierarchical cell structure

Handover is the basic function of a mobile system, by handover , the radio link betweenthe UE and a cell is switched to another cell, so the service is continuously maintained.

In WCDMA system, handover can realize some other target, for instance :to balance cellload, to realize hierarchical cell structure, so as to improve the network utilization, andoptimize network performance


35/57

WCDMA RRM


N-34


Categories of Handover

Handover in WCDMA include:

Intra-UMTS handover

Intra-frequency handover

Inter-frequency handover

Inter-system handover

Handover in WCDMA system include

Intra-UMTS handover

Intra-frequency handover

Intra-frequency hard handover

Intra-frequency soft handover

Inter-frequency handover

Coverage-based Inter-frequency handover

QoS-based Inter-frequency handover

Load-based Inter-frequency handover

Speed-Based Inter-frequency handover UMTS-to-GSM Handover

Coverage-based UMTS-to-GSM handover

QoS-based UMTS-to-GSM handover

Load-based UMTS-to-GSM handover

Service-based UMTS-to-GSM handover


36/57

WCDMA RRM


N-35


Intra-Frequency Soft Handover

Soft handover:

UE maintains radio links with several cells

Soft handover could be:

Intra NodeB soft handover, called softer handover

Softer handover is a special case of soft handover

Inter NodeB soft handover

Inter-RNC soft handover

In WCDMA ,most of the handover are soft handover, it will last for a duration. In softhandover state, UE connects will several cells

During soft handover, the UE radio links with different cells may be from one NodeB,different NodeB under one RNC, even NodeBs under different RNC. (Of course, theprecondition of inter-RNC soft handover is IUR interface is configured)

During soft handover, if the UE radio links are from the same NodeB, the signals ondifferent radio links are combined in uplink in NodeB, this is called softer handover.


37/57

WCDMA RRM


N-36


Characters of Intra-frequency soft Handover

Its a feature of WCDMA system, It only applicable between intra-

frequency cells.

There is no gap during the handover, so ,less call drop

More recourses needed

Intra-Frequency Soft Handover (Cont.)

During soft handover ,UE has several radio links ,so the service quality is better duringhandover.

Since WCDMA UE normally can only support one frequency transmitting and reception,the frequency of several radio links must be the same, so it only applicable between intra-frequency cells.

During the soft handover ,each radio link occupies cell OVSF code resource, cell powerresource, baseband process resource, so too much soft handover will occupy morenetwork radio resources ,decrease the utilization of the radio network.


38/57

WCDMA RRM


N-37


Intra-Frequency Soft Handover (Cont.)

Combination of signal in soft handover

Maximum ratio combination in

NodeB

Selective combination in

RNC

Uplink signals

Maximum ratio combination in

UE

Maximum ratio

combination in UE

Downlink signals

Do not occupy additionaltransmission resource

Occupy additionaltransmission resource

IUB transmissionresource occupied

Softer handoverSofter handoverNormal soft handoverNormal soft handover

During the soft handover, the signals from several radio links are combined in uplink anddownlink.

For normal soft handover, the uplink signals are combined in RNC by selective combination,that is, RNC select a better signal.

For softer handover, the uplink signals are combined in NodeB by maximum ratiocombination, that is, NodeB will take rake combination ,so the combination gain is better.

Softer handover does not occupy additional transmission resource.


39/57

WCDMA RRM


N-38


Intra-Frequency Hard Handover

Hard handover

During the handover, RNC will firstly switch off the radio link with

the old cell, and then setup the radio link with the new cell

The application scenario of Intra-frequency hard Handover

Inter-RNC intra-frequency handover with out IUR interface

High bit rate R99 BE service

Although in most of the conditions, intra-frequency handovers are soft handovers, but issome special scenario, intra-frequency hard handover is still needed to ensure the userservice mobility.

During the hard handover, RNC will firstly switch off the radio link with the old cell, andthen set up the radio link with the new cell.

Compare with soft handover, hard handover occupy less resources

The intra-frequency handover is used in the following scenarios:

Inter-RNC intra-frequency handover without IUR interface or IUR interface iscongested

User service is high data rate R99 BE service, in this case ,in order to avoidoccupying more resources, RNC do not allowed soft handover, only take Intra-frequency hard Handover.


40/57

WCDMA RRM


N-39


Inter-Frequency Handover

Inter-frequency Handover

UE handover from one carrier to another carrier

Inter-frequency handover must be hard handover

Inter-frequency handover could be triggered by the following

causes:

Coverage based

QoS based

Load based

Speed based

When UE need to handover to another carrier, inter-frequency is needed. It must be hardhandover, that is, RNC will firstly switch off the radio link with the old cell, and then setup the radio link with the new cell

Inter-frequency handover could be triggered by different causes, and the handoverprocedure will be some different with each other:

Coverage-based handover: When UE move to the border of the cell. UE will detect the current cell turn bad; Compressed mode is triggered by the UE measurement report, then UE start to

measure inter-frequency neighbors By the measurement reports, UE reports the measure results to RNC , RNC decides

to trigger handover. QoS-based handover:

When the uplink UE TX power or NodeB down TX power is approaching the limit,there is very probability of call drop.

In this case ,UE will report this condition to RNC, compressed mode is triggered bythe UE measurement report, then UE start to measure inter-frequency neighbors

By the measurement reports, UE reports the measure results to RNC , RNC decidesto trigger handover.

Load-based handover:

When cell load exceed a threshold ,RNC will trigger some actions to try todecrease the cell load, one of which is inter-frequency handover.

RNC sort all the cell users based on priorities, low priority users will be chosen to

handover to inter-frequency cell.


41/57

WCDMA RRM


N-40

Speed-based handover:

This handover is only used in Hierarchical cell structure.

If the UE moving speed is high, RNC will handover the UE to a macro cell to avoidfrequent handover.

If the UE moving speed is low, RNC will handover the UE to a micro cell to makethe UE has a better service quality.


42/57

WCDMA RRM


N-41


Compressed Mode

Why does WCDMA need compressed mode?

WCDMA UE normally has only one RF receiver

WCDMA UE need to measure inter-frequency neighbor for

handover

WCDMA UE has only one RF receiver, so the UE can only decoding signal from one carrier,in normal state, the UE can not measure the inter-frequency neighbors or inter-RATneighbors. But the precondition of RNC triggering handover is the measurement results ofthe target cells . So in order to enable the inter-frequency and inter-RAT handover,WCDMA must introduce compressed mode.

Compressed mode is a special working mode of the UE, it is triggered by RNC ,RNCreconfigures the uplink and downlink physical channels to start and stop compressedmode.

Compressed mode could be realized by two ways: SF/2 and high layer scheduling.


43/57

WCDMA RRM


N-42


Compressed Mode

Disadvantage of compressed mode

Compressed affects PS service throughput

Compressed affects network performance

For high bit rate PS service, compressed mode is realized by high layer scheduling, so thethroughput of the service is affected during the compressed mode period

For low bit rate service, compressed mode is realized by SF/2, it will decrease theprocessing gain, so the uplink and downlink physical channel power must be increased tomaintain the QoS , it will increase the downlink power load and uplink interference. so thecoverage and capacity may be affected.


44/57

WCDMA RRM


N-43


Inter-RAT Handover

Inter-RAT Handover

UE handover from WCDMA cell to GSM cell

Inter-RAT handover must be hard handover

Inter-RAT handover could be triggered by the following causes:

Coverage based

QoS based

Load based

Service based

When UE need to handover to GSM cell, inter-RAT is needed. It must be hard handover,that is, RNC will firstly switch off the radio link with the old cell, and then set up the radiolink with the GSM cell

Inter-RAT handover could be triggered by different causes, and the handover procedurewill be some different with each other:

Coverage-based handover:

When UE move to the border of the cell. UE will detect the current cell turn bad;

Compressed mode is triggered by the UE measurement report, then UE start tomeasure inter-RAT neighbors;


QoS-based handover:

When the uplink UE tx power or NodeB down TX power is approaching the limit,there is very probability of call drop.

In this case ,UE will report this condition to RNC by the measurement report, thencompressed mode is triggered, and UE start to measure inter-RAT neighbors


Load-based handover:

When cell load exceed a threshold ,RNC will trigger some actions to try to decreasethe cell load, one of which is inter-RAT handover.

RNC sort all the cell users based on priorities, low priority users will be chosen to

handover to GSM cell.


45/57

WCDMA RRM


N-44

Service based handover:

Based on operator strategy and characters of WCDMA and GSM, Services can bespited ,GSM cells carry voice service, WCDMA cells carry PS service .

After service access to WCDMA cell, if the service is more suitable to be carried on

GSM ,RNC will trigger service handover to GSM.


46/57

WCDMA RRM


N-45


Contents

1. RRM Overview


3. Power control

4. Handover

5. Load Control


47/57

WCDMA RRM


N-46


What is load?

Load: Occupancy of the capacity

WCDMA capacity include :

Hard capacity

Downlink OVSF code of a cell

IUB transmission resources of a NodeB

Baseband process resources of NodeB (CE)

Soft capacity

Power resource (uplink cell interference raise, downlink cell transmitting

power)

WCDMA network load is defined by following factors:

Downlink OVSF code of a cell

IUB transmission resources of a NodeB Baseband process resources of NodeB (CE)

uplink cell interference raise

downlink cell transmitting power

For a service, the caused interference and occupied power is not fixed, it is related to theuser mobility, user distribution and radio channel quality. So a cell power resource is calledsoft capacity.


48/57

WCDMA RRM


N-47


Keep the system stable

Guarantee the network coverage and service QoS ,

maximize the system capacity

Distinguish the users and services with different priorities

Purposes of Load Control

By a series of algorithms, RNC will try to keep the system stable, maximum the systemcapacity, and provide services with different qualities based on priorities


49/57

WCDMA RRM


N-48


Load Control Algorithms

Load control algorithms include:

PUC: (Potential User Control)

CAC: (Call Admission Control)

IAC : ( Intelligent Admission Control)

LDR: (Load Reshuffling)

OLC: (Overload Control)

Huawei load control algorithms include:

PUC: (Potential User Control)

CAC: (Call Admission Control) IAC : ( Intelligent Admission Control)

LDR: (Load Reshuffling)

OLC: (Overload Control)

If the network load is high, the UEs in idle mode with be affected by the PUC (PotentialUser Control) on cell selection and reselection;

Call Admission Control and Intelligent Admission Control will affect UE access procedure;

If the cell is congested, the ongoing services will be affected by Load Reshuffling actionsand Overload Control actions.


50/57

WCDMA RRM


N-49


Load Control Algorithms (Cont.)

No Loadcontrol

PUC startsLDR starts

CAC and IAC:

Traffic

Cell load

OLC starts

Icons for different load levels

Different algorithms start at different load level.

With the increase of the cell load , the PUC will firstly start to execute to affect the idle

mode UEs. Then the LDR starts, to affect some ongoing service . If the load of the cell is still increasing , CAC will reject some access to try to avoid the

overload. But processed by IAC, some service can access after DRD , rate renegotiation,preemption ,queuing

At last , the OLC will be triggered to forcibly release some service or forcibly decrease therate of some service. Of course , it will negatively affecting user experience.


51/57

WCDMA RRM


N-50


Potential User Control

Target of PUC

To avoid the UEs camp on the high load cell

Principle of PUC

To update the inter-frequency cell selection and reselection

parameters periodically according to cell load

Target UE of PUC algorithm:

Idle mode UEs CELL-FACH state UEsCELL-PCH state UEsURA-PCH state UEs

The target of PUC is to balance the potential users between different carriers

Based on cell load , RNC updates the inter-frequency cell selection and reselection

parameters by system information periodically, so as to trigger the UE cell reselect to inter-frequency neighbors with light load.


52/57

WCDMA RRM


N-51


Call Admission Control

After access a new service, the cell load will increase. By CAC,

RNC judges if the cell has enough resources to accept each new

service.

Call Admission Control will affect following procedures:

RRC connection setup procedure

RAB assignment procedure

Handover procedure

Service rate reconfiguration

For each access procedure, RNC will check the load of all kinds of resources. In CallAdmission Control ,RNC will check :

Downlink OVSF code of a cell IUB transmission resources of a NodeB




After passing the admission for all the resources, RNC accepts the new service.


53/57

WCDMA RRM


N-52


Intelligent Admission Control

When the cell load is high, CAC will reject new accesses ,the

access KPI will be very bad

IAC will try to save these rejected accesses as much as possible,

IAC algorithm include:

Rate negotiation

Directly retry

Queuing

Preemption

The disadvantage of CAC is obviously:

It is not flexible for PS BE service.

It does not consider the user and service priorities It does not consider the available resources of neighbor cells

By Intelligent Admission Control, RNC could save some access failure and consider thepriorities of the users and services.

Intelligent Admission Control algorithm include:

Rate negotiation

For BE services, the initial bit rate could be lower, so as to increase theaccess probability.

Directly retry

RNC always select a most suitable cell to accept the service. If access failed,RNC will select other inter-frequency neighbor cells or inter-RAT neighborcells to try to accept the service. So the UE has several changes to accessthe network.

Queuing

After service access failure, RNC does not reject the service immediately.RNC will let the UE wait in a queue for a certain period, then try to acceptthe service periodically. By queuing, the access failure caused byinstantaneous congestion could be avoided.

Preemption

After a high priority service access failure, RNC will release some lowpriority services and accept the high priority service.


54/57

WCDMA RRM


N-53


Load Reshuffling

When the cell load is high, CAC will reject new accesses . So LDR

will adjust the ongoing services by some actions to decrease the

cell load

LDR actions include:

Inter-frequency/inter-RAT handover

Service rate reduction

Code reshuffling

When the cell load is high than load admission threshold, CAC will reject new accesses .LDR will adjust the ongoing services to decrease the cell load in advance.

The triggers of LDR include: Downlink OVSF code of a cell

IUB transmission resources of a NodeB




LDR will trigger some actions ,include:

Inter-frequency/inter-RAT handover some low priority users to neighbor cell.

Trigger some low priority service rate reduction

Code reshuffling


55/57

WCDMA RRM


N-54


Overload Control

When the cell load approaching the limit ,the network is not

stable

The overload control algorithm will try to recover the cell load

back to normal state by some actions, include:

Fast TF (transmission format) control

Switching BE services to common channel

Releaseing some RABs

The overload control actions are effective and fast

When the cell load approaching the limit ,the network is not stable, some services couldnot be maintained because of lack of power resource.

The idea of OLC is similar with LDR. OLC algorithm will trigger some actions to decreasethe cell load effectively. The difference is trigger threshold for OLC is much higher ,andeffect is more obvious and fast. It will affect the service quality greatly as well.

Triggers of OLC are uplink cell interference raise and downlink cell transmitting power. OLC actions include

Select some low priority service to limit the TF (transmission format), that is fast TFcontrol.

Switching low priority BE services to common channel

Releaseing some low priority RABs


56/57

WCDMA RRM


N-55


Summary

In this course ,we discussed following RRM principles:


Power control

Handover

Load control


57/57

WCDMA RRM N-56

Thank youwww.huawei.com

3 wcdma radio resource management issue 2.00

Documents