003 wcdma radio resource management

WCDMA Radio Resource Management

Huawei Technologies Co., Ltd. All rights reserved

WCDMA Radio Resource Management Confidentiality level: Customer

Mexico Training Center Confidential information of Huawei. Page 2/42



Revision Record

Date Version Change description Author

03-06-2007 1A Victor Toledo



Table of Contents 1 Introduction to RRM .............................................................................................................11

Procedure of Radio Resource Mnagement.......................................................................9 2 Channel Configuration ..........................................................................................................10

QoS Mapping...................................................................................................................11 RB and RLC Parameter Configuration ...........................................................................12 MAC Parameter configuration..........................................................................................12 PHY Parameter Configuration .........................................................................................13 Dynamic Channel Configuration .....................................................................................14 DCCC: Dynamic Channel Configuration Control ............................................................15

3 Power Control ........................................................................................................................17 Open loop Power Control for DPCH ...............................................................................19 Open loop Power Control for PRACH.............................................................................20 Uplink Closed Loop Power Control ................................................................................21 Downlink Power Control ..................................................................................................23

4 Mobility Management ............................................................................................................24 UE Working modes and states........................................................................................24 Idle Mode.........................................................................................................................24 Connected mode Cell_DCH............................................................................................25 Connected mode Cell_FACH...........................................................................................26 Connected mode Cell_PCH.............................................................................................27 Connected mode URA PCH.............................................................................................28 UE States switching ........................................................................................................29 Hard Handover ................................................................................................................30 Soft Handover .................................................................................................................30 The baisc Concept of Soft Hoandover ............................................................................31 The baisc Concept of Measurement ...............................................................................33 Compressed mode ..........................................................................................................36

5 AMR Mode Control ................................................................................................................38 AMR Coding ...................................................................................................................38 Features of AMR Speech ................................................................................................39



Objectives

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

Describe the procedure of radio resource management.

Explain the basis of power control.

Explain the different RRC states of the UE.



Introduction to RRM

In WCDMA system, radio resource includes frequency, code and power, and WCDMA is also a self-interfered system. For guaranteeing QoS (Quality of Service) of all users, we should define rules to allocate just enough resources to every users. These rules are called Radio Resource Management Algorithms.

Expect to confirm the QoS, RRM also can enhance system coverage, or increase system capacity.

RRM: Radio Resource Management

RRM is responsible for supplying optimum coverage, offering the maximum planned capacity, guaranteeing the required quality of service (QoS) and ensuring efficient use of physical and transport resources.

Power is the ultimate radio resource. The best way to utilize the radio resource is to control the power consumption strictly.

Increasing the transmission power of a certain user can improve his QoS.

However, due to the self-interference, the increasing power would result in more interference on other users and consequently reduce the receiving QoS.

Procedure of RRM

Usually, RRM algorithm will be designed in RRC layer of UTRAN.

RRC layer will send the control parameters to Layer 2 (in RNC), Layer 1 (in NodeB) or UE through Measurement control message.

Layer 2, Layer 1 or UE will execute measurement procedure, then send measurement result to RRC Layer through measurement report.

According to the measurement report and actual resource, RRC Layer will make decision to allocate the radio resources.

Through signaling, RRC Layer will send this decision to Layer 2, Layer 1 or UE to execute it.



Fundamental procedure of radio resource management Measurement control measurement

UE, NodeB, RNC Measurement report Judgment Execution

Channel Configuration

Fundamental Channel Configuration

Fundamental channel configuration is to map the RAB QoS features requested by CN into the corresponding parameters and configuration mode on each AS layer.

QoS CN requested includes traffic classes, data rate demand, quality demand (BLER) and time delay.

For different traffic class, the QoS requirement is different. For conversational service (like voice), the time delay cannot be too long, usually, it should be less than 40ms; but BLER can be up to 1%. For background service (like E_mail), the time delay can be longer, but BLUR must be lower.

For different service, the data rate is also different. For voice service, 12.2Kbps is enough, but for VP service, 64Kbps is minimum requirement.

Objective: mapping the RAB QoS features requested to distribute appropriate channel

QoS requested by CN Traffic Classes

Conversational Streaming Interactive Background

Rate demand Quality demand (BLER) Time delay



QoS Mapping

Figure 1.- QoS Mapping.

The QoS which CN requested will be sent to UTRAN in RAB Assignment Request message of Iu interface.

UTRAN will distribute one or several RBs (Radio Bearer) for this service first.

Then RLC layer will choose transport mode according to the feature of this service.

MAC layer implement the mapping from logical channels to transport channels, and configure the parameters for different kinds of transport channels.

Of course, all of the data should be transmitted through physical channels.



RB and RLC Parameter Configuration

UTRAN will distribute one or several RBs (Radio Bearer) for this service first. Usually, for voice service, 2 or 3 RB is needed (depended on voice coding algorithm); for VP (Video Phone) and data service, just one RB is needed.

RLC layer will choose transport mode according to the feature of this service. For voice service, transparent mode will be chosen, means RLC layer will do nothing for the voice data, so the data can pass through quickly with no time delay; for BE (best Effort) service, like interactive service and background service, their BLER demand are very high and time delay can be longer, so acknowledged mode will be chosen.

RB parameters RB number

RLC parameters Different RLC transfer modes

transparent mode (TM) Unacknowledged mode (UM) Acknowledged mode (AM)

Different logic channel parameters

MAC Parameter Configuration

MAC layer implements the mapping from logical channels to transport channels, and configure the parameters for different kinds of transport channels.

For voice service and high speed data service, dedicated transport channel will be distributed; for signaling and low speed data service (like Short Message), common transport channel (RACH/FACH) will be distributed.

MAC-c implements the mapping from common logical channels to common transport channels, MAC-d implements the mapping from dedicated logical channels to dedicated transport channels.

MAC layer also configures the priority of services and TFCS (Transport Format Combination Set).



MAC parameters The mapping/multiplexing relation between logic channel and transport

channel Different types and parameters of transport channel

Dedicated channel Common channel

Different configurations of MAC entity MAC-d/MAC-c

Priority configuration of MAC sub layer TFCS configuration

PHY Parameter Configuration

Channel Coding scheme: for voice service, convolutional code will be selected; for high speed data service, Turbo coding is demanded, for some unimportant data, maybe no channel coding is needed.

Interleaving length: Interleaving length is longer, BLER is lower, but time delay is longer.

Rate matching attribute: different data rate must be matched to one of the following data rate: 960K, 480K, 240K, 120K, 60K, 30K, 15K, 7.5K

Spreading factor (SF): different services use different spreading factor. For example, voice service: 128, VP: 32.

Power offset: different kinds of physical channel will be distributed to different power.

Other physical channel parameters, such as TD (Transmission Diversity) mode: STTD, TSTD or FBTD.

PHY parameters Mapping relation from transport channel to physical channel Channel Coding scheme

Convolutional code Turbo code Non



Interleaving length Rate matching attribute Spreading factor (SF) Power offset Other physical channel parameters, such as diversity mode, etc.

Dynamic Channel Configuration

Figure 2.- Dynamic Channel Configuration.

While receiving data come from RLC Buffer, MAC layer will check the data saved in buffer.

If the data saved in buffer is more than the threshold we had defined, MAC layer will send 4A event to RRC layer;

if the data saved in buffer is less than the threshold we had defined, MAC layer will send 4B event to RRC layer;



DCCC: Dynamic Channel Configuration Control

BE services usually mean interactive service and background service. For BE services, time delay can be longer, but BLER must be lower, so RLC

uses acknowledged mode (AM), thus all data should be buffered in RLC Buffer.

Object of DCCC: Best Effort (BE) service Features of BE service

rate of service source changes largely Less demand on time delay More demand on bit error rate

Decision of DCCC

Measurement report on traffic volume of RLC Buffer

Decide whether to change the bandwidth used by UE dynamically based on the measurement result.

Consider whether there is limitation on air interface during the decision of reconfiguration.

4A event means the bandwidth distributed to the service is not enough, so RRC layer will increase the channel resource for the service;

4B event means the bandwidth distributed to the service is more than the demand of the service, so RRC layer will decrease the channel bandwidth.

The system also should consider whether there is limitation on air interface during the decision of reconfiguration. This is done by measuring the transmitting power of UE in both downlink and uplink.

If the channel bandwidth should be changed, Reconfigure Procedure will be executed.



Figure 3.- Effect of DCCC.

The objectives of DCCC are: Meeting bandwidth requirement of users to the greatest degree; Making best usage of resource on air interface Saving downlink channel code (OVSF code) resource



Power Control

Near-far effect in CDMA

Figure 4.- Near Far Effect in WCDMA.

In terms of power management, the QoS of a subscriber can be improved by increasing the transmit power of the subscriber; however, such improvement may result in deteriorating other subscribers receiving quality due to the self-interference feature of the CDMA system.

The worst thing is Near-far effect. Near-far effect occurs in the uplink. If all the subscribers in the cell transmit signals to the BS with the same power, then the signals of the MS near the BS are strong while the signals of the MS far from the BS are weak. In such a case, the weak signals will be masked by the strong signals.

Therefore, on the basis of ensuring QoS for subscribers, how to effectively control power, how to reduce the transmit power as much as possible, and how to reduce the system interference and increase the system capacity are the key to WCDMA technologies.



Classification of Power Control

Uplink power control Open loop power control Closed loop power control

Inner loop power control Outer loop power control

Downlink power control Open loop power control Closed loop power control

Inner loop power control Outer loop power control

In the WCDMA system, power control may be divided into open loop power control and closed loop power control.

The objective of open loop power control is to provide the estimates of the initial transmit power.

The objective of closed loop power control is to rapidly adjust the power in the uplink/downlink during the communication period.

The inner loop power control is to converge the received SIR to the target SIR by controlling the transmit power of physical channels.

The outer loop control mechanism is to dynamically adjust the SIR target value of the inner loop control, so as to ensure that the communication quality always meets the requirements.



Open Loop Power Control for DPCH

Figure 5.- Open Loop Power Control for DCH.

In the WCDMA system, the open loop power control is adopted in both the uplink and downlink.

It estimates the path loss and the interference level according to the measurement result, so as to calculate the process of initial transmit power.

Through open loop power control, WCDMA system can lessen the time of power convergence, and reduce the impact on system load.



Open Loop Power Control for PRACH

Figure 6.- Open loop Power Control for PRACH.

Open-loop power control is used to decide the initial power of PRACH preamble according to the path loss.

Primary CPICH DL TX power: the CPICH transmission power, UE can get it from SI (System Information).

CPICH_RSCP: the CPICH received power.

UL interference: uplink interference, NodeB will test it, and send it to UE through SI.

Constant Value: it can be configured during radio network optimization, sent to UE through SI.

But In the WCDMA-FDD system, the fast fading conditions in the uplink and downlink are absolutely irrelevant because the frequency spacing between the uplink and the downlink is large. Therefore, the path loss estimates obtained through the open loop power control according to the downlink signals are inaccurate for the uplink. The method to solve this problem is to introduce the fast closed loop power control mechanism.



Uplink Closed Loop Power Control

Figure 7yt Figure 7.- Uplink Closed Loop Power Control.

The inner loop power control happens between NodeB and UE. It is to converge the received SIR to the target SIR by controlling the transmission power of physical channels.

If estimated SIR is larger than SIRtar, it means the signal which NodeB received is too good, so NodeB will set TPC=0, command UE to decrease the transmission power;

If estimated SIR is smaller than SIRtar, it means the signal which NodeB received is not enough, so NodeB will set TPC=1, command UE to increase the transmission power.



BLER--SIR

Figure 8.- BLER and SIR Relations.

The radio channels are complex, so the power control based only on the SIR value cannot reflect the real quality of the links. For instance, based on the same BLER, the requirements of static subscribers, low speed subscribers (3 km/H) and high speed subscribers (50 km/H) for SIR are different. The communication quality is finally measured with FER/BLER/BER, so it is necessary to dynamically adjust the SIR target value according to the actual FER/BLER value.

Uplink Closed Loop Power Control

Figure 9.- Uplink Closed Loop Power Control.



The uplink outer loop control happens between RNC and NodeB. It is to dynamically adjust the SIR target value of the inner loop control, so as to ensure that the communication quality always meets the requirements.

If estimated BLER is larger than BLERtar, it means the signal quality is worse, so RNC will increase SIRtar to make the power of UE increased;

If estimated BLER is smaller than BLERtar, it means the signal quality is too good, so RNC will decrease SIRtar to make the power of UE decreased;

If estimated BLER is equal to BLERtar, it means the signal quality is just enough, so SIRtar neednt to be changed.

Downlink Power Control

Figure 10. - Downlink Power Control.

The downlink power control is similar with the uplink power control.

The only difference is that the downlink outer loop power control happens between UE L3 and UE physical layer.



Mobility Management

UE Working Modes and states

Idle mode Connected mode

Cell_DCH Cell_FACH Cell_PCH URA_PCH

The UE may operate in one of two basic modes: Idle mode and connected mode. After being switched on, the UE operates in the idle mode and is identified by a non-access stratum identification such as IMSI, TMSI or P-TMSI. The UTRAN does not save the information of the UE operating in the idle mode. It can only page all the UEs in a cell or all the UEs at one paging time slot.

After establishing an RRC connection, the UE shifts from the idle mode to the connected mode: CELL_FACH or CELL_DCH state. The connected mode of UE is also called the RRC state of UE. It reflects the level of the UE connection and the transport channel that can be used by the UE. When the RRC connection is released, the UE shifts from the connected mode to the idle mode.

Idle Mode

The UE has no relation to UTRAN, only to 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 establish an RRC connection; it can do this by initially

accessing the network on the control channel of the cell on which it is camped.

UE can receive "paging" message from PCH.

The idle mode tasks can be subdivided 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.

Connected Mode Cell_DCH

In active state. Communicating via its dedicated channels. UTRAN knows the cell in which UE is located.

The CELL_DCH state features the following:

A dedicated physical channel is allocated to the UE in both the uplink and the downlink.

RNC knows the cell where the UE camps on according the current active set of the UE.

The UE enters the CELL_DCH state in one of the following two ways:

1. In the idle mode, the UE sets up the RRC connection on the dedicated channel, thus shifting from the idle mode to the CELL_DCH state.

2. In the CELL_FACH state, the UE uses the common transport channel and then is converted to the dedicated transport channel, thus shifting from the CELL_FACH state to the CELL_DCH state.



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 relative information. UTRAN knows the cell in which UE is located.

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.

The CELL_FACH state features the following:

No dedicated transport channel is allocated to the UE.

The UE continuously monitors a downlink FACH channel.

A default uplink common channel (for example, RACH) or an uplink shared transport channel is allocated to the UE for the UE to use at any time during the access procedure.

UTRAN knows the cell in which UE is located.

The UE performs the following operations in the CELL_FACH state:

Monitors an FACH.

Monitors the BCH channel of the current serving cell to decode the system messages.

Transmits uplink control signaling and small data packets on the RACH.

Initiates a cell update procedure when the cell becomes another UTRA cell.



Connected Mode Cell_PCH

No data to be transmitted or received. DRX (discontinuous reception) monitor PICH, to receive its paging. Lower the power consumption of UE. UTRAN knows the cell in which UE is located. UTRAN has to update cell information of UE when UE roams to

another cell.

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 UTRAN update UE information only after UE which is in URA_PCH state has roamed to other URA.

The CELL_PCH state features the following:

No dedicated channel is allocated to the UE.

The DRX technology is adopted for the UE to monitor the information transmitted on the PCH channel at a specific paging time slot.

UTRAN knows the cell or URA in which UE is located.

The UE performs the following operations in the CELL_PCH state:

Monitors the paging time slot based on the DRX period and receives the paging messages transmitted on the PCH.


Initiates the cell update procedure when the cell changes.

The UE shifts to the CELL_FACH state in one of the following two ways: By paging from the UTRAN and by any uplink access.



Connected Mode URA_PCH

No data to be transmitted or received. DRX monitor PICH. UTRAN only knows the URA in which UE is located. UTRAN updates UE information only after UE has roamed to other

URA (UE report own new URA by URA update procedure). A better way to lower the resource occupancy.

The URA_PCH state features the following:

No dedicated channel is allocated to the UE.

The DRX technology is adopted for the UE to monitor the information transmitted on the PCH channel at a specific paging time slot.

No uplink activity is allowed.

UTRAN knows the UAR in which UE is located.

The UE performs the following operations in the URA_PCH state:

Monitors the paging time slot based on the DRX period and receives the paging messages transmitted on the PCH.


Initiates the URA update procedure when the URA changes.

No resource is allocated for data transport in the URA_PCH state. Therefore, if the UE has the data transport requirement, it needs to first shift to the CELL_FACH state.



UE states switching

Figure 11. - UE Switching States.

This is the UE states figure. These states are significant only for UTRAN and UE. They are transparent to CN. Lets focus on the switch between the states.



Hard handover

Figure 12. - Hard Handover.

Features of hard handover:

HHO causes a temporary disconnection for RT radio access bearer and is lossless for NRT bearers.

The UE must either be equipped with a second receiver or support compressed mode to execute inter-system/inter-system measurement.

Figure 13. - Soft Handover.



Features of soft handover

Seamless handover with no disconnection of the radio access bearer.

To enable a sufficient reception level for maintaining communications by combining the received signal at symbol level from multiple cells in case the UE moves to the cell boundary areas.

The macro diversity gain achieved by combining the received signal in the NodeB (softer handover) or in the RNC (soft handover) improves the uplink signal quality and thus decrease the required transmission power of the UE.

For soft handover, selection combination in uplink completes in RNC. For softer handover, maximum ratio combination in uplink completes in NodeB.

The Basic Concept of SHO

Active Set Including all cells currently participating in a SHO connection of a UE.

Monitored Set Including all cells being continuously monitored by the UE and which

are not current included in its active set. Detected set

Including the cells the UE has detected but are neither in the active set nor in the monitored set.

Cells that the UE is monitoring (e.g. for handover measurements) are grouped in the UE into three different categories:

1.Cells, which belong to the active set. User information is sent from all these cells. The cells in the active set are involved in soft handover or softer handover.

2.Cells, which are not included in the active set, but are monitored according to a neighbor list assigned by the UTRAN belong to the monitored set.

3.Cells detected by the UE, which are neither included in the active set nor in the monitored set belong to the detected set. Reporting of measurements of the detected set is only required for intra-frequency measurements made by UEs in CELL_DCH state.



Three Steps of Handover

Figure 14.- The steps of Handover.

Measurement

Measurement control. Measurement execution and the result processing. The measurement report. Mainly accomplished by UE.

Decision

Based on Measurement. The application and distribution of resource. Mainly accomplished by RRM in RNC.

Execution

The process of signaling. Support the failure drawback. Measurement control refresh.



The Basic Concepts of Measurement

The measurement values of Handover

Intra-frequency and inter-frequency: CPICH RSCPCPICH Ec/N0Path loss.

Inter-frequencyCPICH RSCPCPICH Ec/N0. Inter-systemGSM Carrier RSSI BSIC Identification BSIC

Reconfirmation.

The reporting methods of measurement

Periodic reporting. Event reporting.

The events of reporting

Intra-frequency events1A, 1B, 1C, 1D, 1F. Inter-frequency events 2D, 2F, 2B, 2C. Inter-system events 3A, 3C. Others6G, 6F.

Reporting Criterion

Reporting Criterion Decision formula: for example, 1A event : 1.Path Loss

2.Other measurement quantity

Relative threshold, Absolute threshold, Hysteresis, Time to trigger, CIO.



Event triggered handover for addition of a radio link is described by the above formula.

MNew is the measurement result of the cell entering the reporting range.

CIONew is the individual cell offset for the cell entering the reporting range if an individual cell offset is stored for that cell. Otherwise it is equal to 0.

Mi is a measurement result of a cell not forbidden to affect reporting range in the active set.

NA is the number of cells not forbidden to affect reporting range in the current active set.

MBest is the measurement result of the cell not forbidden to affect reporting range in the active set with the lowest measurement result, not taking into account any cell individual offset.

MBest is the measurement result of the cell not forbidden to affect reporting range in the active set with the highest measurement result, not taking into account any cell individual offset.

W is a parameter sent from UTRAN to UE. The default value for W=0. R1a is the reporting range constant. H1a is the hysteresis parameter for the event 1a.



Soft Handover

Figure 15. - Events 1A and 1B.

The default value of W is zero. That means when a cell, not in the Active set, enters Reporting Range1A+Hystersis 1A/2 (from the strongest cell in Active set), and the measured value remain exceed Reporting Range1A+Hystersis 1A/2 at least a time equal to time to Trigger (Time to Trigger 1A), event 1A will happen .(see above figure). The UE deliver Measurement Report (1A) to SRNC.

Application of Hard Handover in 3G Intra-frequency hard handover

When inter-RNC SHO cant be executed or is not allowed.

Inter-frequency hard handover Needed in certain areas due to network planning. Load balance between frequencies.

Inter-RAT handover 2G-3G smooth evolution. The finite coverage range of initial phase of 3G.

Intra-frequency hard handover includes two instances:

1. Handover between two RNCs without Iur interface. 2. Code tree reconstruction.



Compressed Mode

Figure 16. - Illustration of compressed mode.

Intra-frequency neighbors can be measured simultaneously with normal transmission by UE using a RAKE receiver.

But inter-frequency or inter-system neighbors measurements require the UE measuring on a different frequency, this has either to be done with multiple receivers in the UE or in the compressed mode (CM). CM is to stop the normal transmission and reception for a certain period of time, enable the UE to measure on the other frequency.

The basic methods of the compressed mode technology is: When sending some frames (the data sent per 10ms is a frame), the Node B speeds up to send the data that are previously sent in 10ms in less than 10ms, so that the UE can use the time saved to conduct inter-frequency measurement. The mode and time for increasing the transmit rate is controlled by the RNC.

Classification of Compressed Mode

Downlink compressed mode To create time for UEs measurement and synchronization. 2 optional schemes -- SF/2,higher layer scheduling.



Uplink compressed mode

To avoid the interference on its own downlink measurement and synchronization when UE is measuring certain target frequency or RAT.

2 optional schemes -- SF/2, higher layer scheduling.

Halve the SF: in several frame, the system just use SF/2. (for example, voice service, changing SF from 128 to 64).

Puncturing: cancel some symbols which are not very important.

Higher layer scheduling: pause data transmission, it will cause time delay, usually used in data service.

SRNS(C) Relocation

Figure 17. - Relocation of SRNS during a call.

Advantage of SRNS relocation Reducing data flow on Iur interface. Improving the systems adaptability. Reducing the time delay.

Problem of SRNS Relocation: a large amount of signaling is needed to interact.



The RNC relocation refers to that the SRNC of the UE changes from one RNC to another RNC. It is divided into two cases based on the UE location at the time of relocation: Static relocation and associated relocation.

Static relocation

The precondition for the static relocation is that the UE accesses the network from one and only one DRNC. Since the relocation procedure does not require the UEs participation, it is also called the UE Not Involved relocation. Static relocation usually happens after soft handover.

Associated relocation

Associated relocation refers to that the UE accesses the target RNC from the SRNC via hard handover, and the Iu interface changes at the same time. Since the relocation procedure requires the UEs participation, it is also called the UE Involved relocation. Static relocation usually happens during hard handover.

AMR Mode Control

AMR Coding

WCDMA system uses Adaptive Multi-Rate (AMR) speech code, which is linear prediction coding.



The AMR speech codec produces a certain number of bits depending on the mode used. The speech encoder outputs are put in order according to their subjective importance. This bit ordering can be utilized for error protection purposes.

In fact, after the bits have been ordered according to a predefined table, they are further divided into three indicative classes, still according to their subjective importance. Therefore, the AMR codec delivers three classes of bits, each containing a different number of bits depending on the rate of the coder. They are Class A, Class B and Class C.

On the radio interface, one dedicated transport channel can be established per class of bits, i.e. DCH A for Class A bits, DCH B for Class B bits and DCH C for Class C bits. Thus, each class can be subject to a different error protection scheme.

Class A contains the bits most sensitive to errors and any error in these bits would result in a corrupted speech frame which needs error correction for proper decoding. It may be the only class protected by a CRC.

Classes B and C contain bits where increasing error rates gradually reduce the speech quality, but the decoding of an erroneous frame can be done without significantly degrading the quality. Class B bits are more sensitive to errors than Class C bits.

SID: Silence Indicator

Features of AMR speech: MOS-CIR

Figure 18.- Effect of AMR on speech quality.



Features of AMR speech:

At a certain load level (which corresponds with SIR of UE), the Mean Opinion Score (MOS) which the users experience does not increase linearly with the speech rate which UE uses. That is, at a certain load level, the most appropriate AMR speech rate used to acquire the highest MOS does not refer to the highest rate, but an appropriate middle rate.

The limitation of UEs maximum transmitting power restricts the coverage of uplink AMR speech. To increase the uplink coverage of AMR speech, uplink rate should be reduced without worsening the UEs speech quality.

AMR Mode Control

AMR mode control is to weigh the load level, and:

Reduce AMR speech rate on heavy load condition, thus reduce the system load and improve speech quality relatively.

Increase AMR speech rate on light load condition, thus improve QoS.

Reducing of AMR speech rate can widen the uplink coverage effectively.

The AMR speech mode control can be done in every 20ms.

The AMR codec offers the possibility to adapt the coding scheme to the radio channel conditions. The most robust codec mode is selected in bad propagation conditions. The codec mode providing the highest source rate is selected in good propagation conditions.

During an AMR communication, the receiver measures the radio link quality and must return to the transmitter either the quality measurements or the actual codec mode the transmitter should use during the next frame. That change needs to be done as fast as possible in order to follow better the evolution of the channels quality.

In uplink, the UTRAN explicitly indicates to the UE the codec mode it should use. However, in downlink, the mobile has to send quality measurements to UTRAN that will deduce the appropriate mode to use, using an algorithm. The AMR control algorithms are located in the RNC, and they will have a major impact on voice quality and system capacity.



In each transmitted speech frame, the AMR codec has to indicate the mode it is currently using as well as the quality/mode-to-use information. In the network, the Codec Mode Indication must also be sent to the Transcoder Units so that the correct source decoding is selected.

The rate adaptation scheme is based on thresholds. For each mode, lower and upper thresholds are defined. These bands may overlap from one mode to another. The decision to change rate is made on the network side.

In theory, the codec mode can be changed every speech frame (20 ms). In practice, the codec mode should be adapted at a lower rate.

003 wcdma radio resource management

Documents

open loop power control

downlink power control

connected mode cell

mobility management

rlc parameter configuration

mac parameter configuration

phy parameter configuration

connected mode ura pch