Radio resource management in wcdma

Radio Resource Management in WCDMA

Presentation by:

Naveen Jakhar, ITS

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Topics covered in this presentation:

What is a Radio Resource Unit ?

Why do we need RRM ?

Need of RRM in WCDMA ?

RRM algorithms Objectives

Different RRM functions : Handover, Power control, AdmissionControl, Code Management

Conclusion

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Radio Resource Unit:

A Radio Resource Unit (RRU) is the set of basic physical transmissionparameters necessary to support a signal waveform transporting enduser information

For example, in GSM, a radio resource unit is a 0.577 ms time slotperiod every 4.615 ms on a 200 KHz carrier in the 900 MHz, 1800MHz or 1900 MHz bands

In CDMA, a radio resource unit is defined by a carrier frequency, acode sequence and a power level

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Brief about UMTS and WCDMA:

Universal Mobile Telecommunications System (UMTS) is a 3G cellular

telecommunication system, successor of GSM

UMTS is designed to cope up with the growing demand of mobileand internet applications with required quality of service parameters

WCDMA is used for the radio interface of UMTS

Along with traditional telephony and data services offered by GSM,UMTS will offer more high speed services to mobile equipment users

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Radio Resource Management:

The delivery of multimedia services to the mobile user is one of thegoals of 3rd generation mobile communication system

In a multiservice scenario, each service may require that a differentamount of radio resource units are supported. Services with higherbit rates will, consequently, require more radio resource units

The use of several different services at the same time raises thedemands for mechanisms to guarantee Quality of Service (QoS) foreach application

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Why do we need Radio Resource Management?

The Cellular mobile communications are dynamic in nature

Dynamism arises from multiple dimensions: propagation conditions,traffic generation conditions, interference conditions

Thus, the dynamic network evolution calls for a dynamicmanagement of the radio resources, which is carried out by RRMmechanisms

Radio Resource and QoS management functionalities are veryimportant in the framework of WCDMA systems because the systemrelies on them to guarantee a certain target QoS, maintain theplanned coverage area and offer a high capacity, objectives whichtend to be contradictory

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Why do we need Radio Resource Management?

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Why do we need RRM in WCDMA ?

In WCDMA, users transmit at the same time and frequency by meansof different orthogonal spreading sequences

The maximum available capacity in case of WCDMA is tightlycoupled to the amount of interference in the air interface

Efficient management of radio resources may not involve animportant benefit for relatively low loads, but when the number ofusers in the system increases to a critical number, good radioresources management will be absolutely necessary

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The QoS parameters may be classified into two different levels:network-level (such as blocking probability, dropping probability) andconnection-level (such as bit error rate, maximum transmission rate)

One of the most important RRM tasks is to guarantee that everysingle connection achieves the target Eb/No that ensures the BERrequirement

The RRM functions need to adjust dynamically with : number ofsimultaneous users, Bit Rate and Power Level

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The number of users having a call in progress are defined as activeusers – camping users and transmitting users

Within a WCDMA cell, all users share the common bandwidth andeach new connection increases the interference level of otherconnections, affecting their quality expressed in terms of a certainEb/No

Capacity and coverage are closely related in WCDMA networks, andtherefore both must be considered simultaneously. The coverageproblem is directly related to the power availability, so the powerdemands deriving from the system load level should be in accordancewith the planned coverage

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Different RRM functions in WCDMA:

Open loop Power control

Closed loop: Inner loop Power control

Closed loop: Outer loop power control

Admission control

Code management

Handover

Congestion control and Cell breathing

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Admission Control:

Admission control decides the admission or rejection of requests forset-up and reconfiguration of radio bearers

The request should be admitted provided that the QoS requirementscan be met and that the QoS requirements of the already acceptedconnections are not affected by the new request acceptance

Admission control is particularly relevant in WCDMA because there isno hard limit on the maximum capacity

Admission control algorithms are executed separately for uplink anddownlink because of the different issues impacting on bothcommunication directions

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Admission Control:

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Admission Control:

WCDMA supports multimedia services, so admission controlalgorithms must take into consideration that the amount of radioresources needed for each connection request will vary

Similarly, the QoS requirements in terms of real time or non realtime transmission should also be considered in an efficient admissioncontrol algorithm

In addition to the connection set-up request, admission control mayalso be triggered by handover procedures, transport channel typeswitching

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How does Admission Control take place?

A transaction set-up request in UMTS is always triggered from the UEside, either because it is the UE itself that is initiating an interactionwith the network or because the UE is answering a paging message

Prior to the transaction set-up procedure, a signalling path from theUE towards the CN needs to be established, which in the case of theUTRAN is accomplished by means of an RRC connection and theRANAP (Radio Access Network Application Part) protocol, which takescare of the UTRAN-CN interactions

With the help of the RRC and RANAP protocol, a transaction set-uprequest message reaches the CN

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Therefore, it is always the CN that triggers a RAB establishment bymeans of the RAB assignment message sent from the CN to the SRNC

With the arrival of such a message, the Admission Control (AC)algorithm is executed

If the connection can be admitted, the SRNC establishes theresources in the radio and Iub interfaces by means of the RRC radiobearer establishment procedure

Similarly, the required connections are established in the Iuinterface. If the establishment procedure succeeds, a positiveresponse is given in the message RAB assignment response and theRAB is eventually set-up

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Power Control in WCDMA:

The Transmitter adapts the output power according to Path Loss

Mainly to solve the “Near-Far” problem

Goal is that all users should experience the same SIR

Open Loop Power control (Initially, No signaling):

UE uses PRACH (Pre-amble RACH) for access to NodeB, if receivesAICH – then no need for further open loop power control

If No AICH (Acquisition Indication Channel) received – then UEincreases its power in the steps of 1 dB and waits for getting the AICH

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Power Control ImplementationOpen-loop: (Initially)

• UE measure received BS power & read

BS transmit power – calculate initial

transmit power.

• access acknowledged??

• Increase UE power by 1dB

Inner-loop (Fast) Power Control:

• NodeB compares received UE – power

& power target value (SIR)

•Increase/decrease UE power,

1dB, 1500 times/sec

Outer-loop (Slow) Power Control:

• FER measured by NodeB

• RNC increases/decreases

power target value of the

Inner-loop (SIR), 1 time/sec

RNCCore

Network

During call

SIR – Symbol to interference Ratio

FER – Frame Error Rate

Closed loop Power Control in WCDMA:

Inner Loop Power Control also called Fast power control

This control takes place between UE and NodeB (continuously: 1500Hz or 1500 times/s, relative changes: 1 dB up or down)

The transmitted power in order to reach the receiver with therequired Eb/No target

Outer loop Power control also called slow power control

It takes place between NodeB and RNC

Outer loop power control is responsible for selecting a suitableEb/No target depending on the BLER (Block Error Rate) or BER (BitError Rate) requirement

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Congestion Control / Load Control:

Congestion control faces situations in which the QoS guarantees areat risk due to the evolution of system dynamics (mobility aspects,increase in interference, traffic variability, etc.)

Congestion situations in the radio interface are caused by excessiveinterference. Thus, congestion control algorithms need to monitor thenetwork status continuously in order to correct overload situationswhen they are present

The congestion control algorithm needs to exhibit a fast reactivityunder overload conditions in order to prevent degradation of thequality of the connections

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Congestion control is closely supported by Admission Control andHandover

RT Load – Real Time load

NRT – Non Real Time Load

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The congestion or load control (LC) algorithm will reside in the network side (RNC) and will be based on measurements acting as algorithm inputs (e.g. uplink cell load factor, downlink transmitted power, etc.)

When a congestion situation is triggered, congestion resolution actions are implemented with the aid of the RRC protocol

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Code Management:

The Code management is devoted to managing the downlink OVSF(Orthogonal Variable Spreading Factor) code tree used to allocatephysical channel orthogonality among different users

The advantage of the OVSF codes used in the UTRAN downlink isperfect orthogonality

However, the drawback is the limited number of available codes.Therefore, it is important to be able to allocate/reallocate thechannelization codes in the downlink with an efficient method, inorder to prevent ‘code blocking’

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Code Management:

‘Code blocking’ indicates the situation where a new call could beaccepted on the basis of interference analysis and also on the basis ofthe ‘spare capacity’ of the code tree

but, due to an inefficient code

assignment, this spare capacity is

not available for the new call

that must, therefore, be blocked

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Code Allocation Preventing Code Blocking:

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Handover in WCDMA:

In WCDMA more possibilities are open as long as the mobileterminal can be connected to more than one cell simultaneously duethe presence of Rake receivers in UE and NodeB

Handover involves three different steps: measurements, decisionand execution

Measurements may be of different categories: intra-frequency (onthe same UTRAN carrier), inter-frequency (on a different UTRANcarrier) or inter-RAT (on a radio access technology other than UTRAN)

Handover decisions are taken as a result of relative comparisons onCPICH measurements

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Types of Handover in CDMA:

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Handover Process in CDMA:

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Soft Handover - Changing active set in CDMA:

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Cell Breathing:

As the number of users increases the maximum allowed path loss for the reference user decreases

In some cases, the result is that the reference user’s path loss is higher than the maximum tolerable one. In such cases, the reference user would be in outage, so that it is not able to reach the cell site with enough power to achieve the target Eb/No

Therefore, it can be seen that the performance achieved depends on the cell load level or, equivalently, on the air interface interference level. This phenomenon is known as cell breathing, since it turns into a variable cell coverage

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Conclusion:

The various Radio Resource Management Functions which we have discussed helps in maintaining the desired QoS for user satisfaction

Radio Resource and QoS management functionalities are very important in the framework of WCDMA systems because the system relies on them to guarantee a certain target QoS, maintain the planned coverage area and offer a high capacity

The multimedia capabilities in the newer technologies like LTE and 4G are advancing day by day, so Radio Resource Management will keep playing an important role in helping optimising the networks.

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References:

3GPP 25.922 v6.0.1, ‘Radio resource management strategies (release 6)’

3rd Generation Partnership Project; Technical Specification Group Services and System Aspects General UMTS Architecture (3G TS 23.101 version 3.0.1). 2004

H. Holma, A. Toskala, WCDMA for UMTS, John Wiley & Sons Ltd, 2nd edition, 2000

http://www.rfwireless-world.com/

http://whytelecom.com/

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http://www.rfwireless-world.com/

http://whytelecom.com/

Thank YouInstant Telecommunication allows better and updated information

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Radio resource management in wcdma

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