Adaptation Techniques in WirelessPacket Data Services

Speaker: Chih-Wei WangAdvisor: Li-Chun Wang

Abstract

Cellular systems are designed to achieve 90-95percent coverage for voice users— SINR is over design target over 90-95 percent of the cell area

For packet data service, larger SINR can be used toprovide higher data rates— reducing coding or spreading and/or increasing constellation density

Cellular spectral efficiency can be increased

Motivation

— Explosive growth of internet and dramatic increase in demand for increasing capacity

• Basic and enhanced voice services (audio conferencing, voice mail)• Low-data-rate services (messaging, email, fax)• Medium-data-rate services (file transfer, internet access, 64-144 kb/s)• High-data-rate services (high speed packet and circuit-based network access)• Multimedia services

System orstandard

Method of rateadaptation

Method ofindicating format

Channel qualityfeedback

Peak datarate

CDMA IS-95BM supplementalcode channelseach at 8 or 14 kb/s

Supplementalchannel assignmentmessage (SCAM)

Supplementalchannel requestmessage, pilotstrengthmeasurementmessage

64 kb/s

Cdma2000

Variable-ratesupplemental codechannel—variablespreading andcoding

SCAM, alsoconsidering blind ratedetection

Supplementalchannel requestmessage, pilotstrengthmeasurementmessage, powercontrol bits (800 Hz)

614.4 kb/sper Walshcode, codeaggregationto obtain2048 kb/s

UMTSWidebandCDMA(WCDMA)

Variable-rate trafficchannel—variablespreading andcoding

Transport formatcombination indicator(TFCI) identifiesformat of each frame

Measurement report: Pilot strength SINR BER, BLER

2048 kb/s(6 Walshcodes)

A summary of rate adaptation for packet data servicesin second- and third-generation cellular standards

System orstandard

Method of rateadaptation

Method ofindicating format

Channel qualityfeedback

Peak datarate

GPRSTime slotaggregation,adaptive coding

Separately codedfield “stealing bits”

Measurement reportsin ARQ Statusmessage: Signal and

interference Bit error rate Signal variance

160 kb/s

TDMA 136+(GPRS-136)

Time slotaggregation,adaptivemodulation andincrementalredundancy

Separately codeddata field type (DFT)

Channel qualityfeedback (CQF) In uplink ARQ

Status messag In downlink

packet channelfeedback

44.4 kb/s

EGPRS

Time slotaggregation,adaptive coding,adaptivemodulation,incrementalredundancy

Separately codedfield “stealing bits”

Measurement reportsin ARQ Statusmessage: Signal and

interference Bit error rate Fading rate

473.6 kb/s

(cont’d)

Rate adaptation in CDMA

achieved through a combination of variable spreading, coding, and code aggregation.

How to achieve higher data rates?

IS-95B CDMA— Walsh code aggregation

WCDMA and cdma2000 — Combination of variable spreading and coding

Rate adaptation in TDMA

slot-by-slot data rate adaptation—adaptive coding and modulationsymbol rate and block size—unchanged

How to achieve higher data rates?Time slot aggregation:GPRS-136 —(1-3 time slots/20 ms)EGPRS —(1-8 time slots/GSM frame)

higher throughput—incremental redundancy transmission

Channel quality estimation

CDMA— Pilot strength measurements are used to estimate the SINR at the receiver

IS-95B and cdma2000 —Pilot strength measurement message (PSMM)Supplemental channel request message (SCRM)

WCDMA —additionally include block error rate, BER, received power, path loss, downlink SINR measurements

Channel quality estimation (cont’d)

TDMA— • Frame error rate• Mean and standard deviation of symbol error rate (SER) or BER• Average SINR

GPRS and EGPRS — Measurement reports are included in supervisory ARQ status messages

Packet Data over CDMAIS-95 Revision B

Higher data rate is provided through code aggregation — up to 8 codes maybe assignedfor the duration of a burst

Fundamental code channel (FCH): 9.6 kb/sSupplemental code channels (SCHs): 9.6 kb/s each

Data rate controlled by base station, assigned to mobile station through supplemental channel assignment message (SCAM)

Packet Data over CDMAIS-95 Revision B (cont’d)

Channel quality feedback is indicated to the transmitter through pilot strength measurements

provided by the mobile in pilot strength measurement messages and in the supplemental channel request message (SCRM) on the uplink

Packet Data over CDMAcdma2000

— Providing several medium access control (MAC) layer enhancements To minimize access and setup delays, for fast accessand setups with efficient air interference

Physical layer provides a single SCH with variablespreading gain

Packet Data over CDMAcdma2000 (cont’d)

Other physical layer enhancements— turbo coding, a reverse link pilot for coherent detection, fast forward link power control, forward link dedicated pilots for operation with narrow-band antennas

Packet Data over CDMAWideband CDMA (WCDMA)

Similar set of physical layer enhancements as cdma2000

Supports data rates up to 2.048 Mb/s in 5 MHz BWthrough variable spreading and code puncturingfrom a rate 1/3 base channel code

A continuum of data rates is achieved by usingrate matching

Packet Data over CDMAWideband CDMA (WCDMA) (cont’d)

Burst Allocation and Management in CDMA

Data rate adaptation for packet data service in CDMA cellular systems requires dynamic bandwidth management and burst allocation

Higher Data Rates through Code Aggregation

Code aggregation may be used to provide even higher data rates to users with favorable SINRs, orto the same user requiring services with multipleQoS requirements

Packet Data over TDMA

GSM — General Packet Radio Service (GPRS)IS-136 TDMA — GPRS-136

GPRS-136 — TDMA packet data standard Based on GPRS 30 kHz for the physical layer allows for connection to the ANSI-41 network

Enhanced Data Rates for GSM Evolution (EDGE)

Packet Data over TDMA (cont’d)

EDGE — enhanced circuit-switched data (ECSD) EGPRS

ECSD — enhancement for circuit-mode dataEGPRS — enhancement for packet-mode data

How to achieve variable data rates?

Adaptive coding, adaptive modulation, incrementalredundancy

Packet Data over TDMAGPRS-136

To achieve higher throughput— adaptive modulation and incremental redundancy

Incremental redundancy— each RLP segment is coded into D data blocks and D parity blocks

Packet Data over TDMAGPRS-136 (cont’d)

Adaptive modulation— modulation is switched between 4-, 8-, and 16-level modulation as a function of the SINR

Packet Data over TDMAGPRS

Using adaptive coding with Gaussian minimum shift keying (GMSK) modulationbut no incremental redundancy

As in GPRS-136, operation on multiple time slots isused to achieve higher data rates

Packet Data over TDMAEGPRS

9 modulation schemes, MCS-1to 9, are defined— 4 code rate with GMSK and 5 code rates with 8-PSK modulation

3 RLC block sizes are defined for the nine modulation and coding formats— providing plenty of flexibility for block-by-blockrate adaptation

Summary

Channel quality feedback mechanisms have been defined to carry out rate adaptation. Further workis needed to obtain fast and accurate channel quality measurements

Resource management that permits ideal exploitation of these adaptation schemes as a function of SINR is still an open area of research

Summary (cont’d)

CDMA has features that permit efficient sharing ofthe available resource

• Use of pilot strength measurements for efficient power and interference management

• Low overhead dedicated or common control channels with discontinuous transmission

Summary (cont’d)

TDMA has features that permit achieving high datarates

• Incremental redundancy with separately protected headers• Dynamic adaptation between different coding and modulation schemes• Proposed channel quality metric based on Euclidean distance• Aggressive reuse schemes for achieving the highest spectral efficiency