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Adaptation Techniques in Wireless Packet Data Services Speaker: Chih-Wei Wang Advisor: Li-Chun Wang.
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Transcript of Adaptation Techniques in Wireless Packet Data Services Speaker: Chih-Wei Wang Advisor: Li-Chun Wang.
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