Diapositiva 1

1
Turbo Soft Combining Hybrid ARQ Techniques
Theory and Application to 3G Wireless Networks
Romano Fantacci Full Professor Francesco Chiti
Ph.D. Department of Electronics and
Telecommunications University of Florence Via di
S. Marta, 3 I-50139 Florence, ITALY E-mail
fantacci,chiti_at_lenst.det.unifi.it
2
Outline

• Introduction
• Soft combining principle
• Soft Input Combining
• Soft Output Combining
• Theoretical analysis
• AWGN
• Multipath fading channel
• Application to UMTS systems
• Conclusions

3
Service Classes
Soft Combining techniques
i. Introduction

• IPvx
• Elastic
• Stream

• UMTS/HSDPA
• Conversational
• Streaming
• Interactive
• Background

• DiffServ
• Expedited Forward
• Assured Forward
• Best Effort

Traffic class Traffic attributes
Priority integer
Bit rate (max., guar.) bps
PDU Size Byte
Residual Error Ratio
Transfer delay s
Delivery order integer
4
Reliable packet communications
Soft Combining techniques
i. Introduction

• Automatic Repeat reQuest (ARQ) protocols
• Erroneous packets detection by means of a CRC
• Packet retransmission through dedicated signals
  (ACK/NACK)
• Stop and Wait (SW),
• Go Back N (GBN),
• Selective Repeat (SR).
• Forward Error Correction (FEC) techniques
• Erroneous packet correction by means of a
  suitable channel code (convolutional codes turbo
  codes).

5
Traditional approaches comparison
Soft Combining techniques
i. Introduction
FEC techniques ARQ protocols
MAC Layer duty LLC Layer duty
Heavy decoding Light Decoding
Without control signaling With onerous control signaling
Throughput limited by added redundancies Throughput limited by number of needed retransmissions
service outage prone Stall prone
Well suited for fixed wireless nws Conceived for wired nws
6
Soft Combining techniques
i. Introduction

• Hybrid ARQ (H-ARQ) approaches
• Type I
• channel coding and retransmission mechanism are
  merely integrated within the same scheme
• Type II
• traditional approaches are harmonized and jointly
  optimized by keeping trace of transmission/recepti
  on process (e.g. Chase Combining)
• Type III
• transport formats are dynamically updated to cope
  with the signal quality variations (e.g.
  Incremental Redundancy)

7
Soft Combining techniques
1. Soft combining principle
Functional block diagram
8
Soft Input Combining H-ARQ
Soft Combining techniques
1. Soft combining principle

• Packet replicas are combined via a soft metric,
  maximizing the Euclidean distance among symbols
• Combination schemes follow a diversity technique
• Maximum Ratio Combining (MRC)
• Equal Gain Combining (EGC)
• Weighted Gain Combining (WGC).
• Diversity gain is advantageously considered

9
Soft Combining techniques
1. Soft combining principle
Soft Output Combining H-ARQ

• Last packet replica is combined via a soft metric
  to the decoding process outputs, maximizing the
  Euclidean distance among codewords
• Suitable for SISO decoder (turbo principle)
• Combination schemes follow a diversity technique
• Maximum Ratio Combining (MRC)
• Equal Gain Combining (EGC)
• Weighted Gain Combining (WGC).
• Diversity gain and decoding gain are considered

10
Soft Combining techniques
1. Soft combining principle
11
Soft Combining techniques
1. Soft combining principle
Transmitter protocol stack
Layer II - LLC
Pack
New Frame
Previous Frame
Logic
Buffer
Layer II - MAC
Layer I -PHY
12
Soft Combining techniques
1. Soft combining principle
Receiver protocol stack
Layer II - LLC
Pack
Layer II - MAC
Layer I -PHY
13
Soft Combining techniques
2. Theoretical analysis
AWGN channel

• BER

• Soft Input Combining

• Soft Output Combining

14
Soft Combining techniques
2. Theoretical analysis
AWGN channel

• FER

• Average needed retransmissions

• Throughput

15
Soft Combining techniques
2. Theoretical analysis
Multipath fading channel

• BER??k

joint pdf of kL fading coefficients (?1? ?kL)
16
Soft Combining techniques
2. Theoretical analysis
Multipath fading channel

• BER

• FER

17
Soft Combining techniques
2. Theoretical analysis
Multipath fading channel

• Goodput
• multiplicative increase/multiplicative decrease
  SLW congestion control

Initial SLW size
Prob that current block has been transmitted K
times at time n
Timeout value is equal to K?(RTT)
18
Soft Combining techniques
3. Application to UMTS systems
Operative assumptions

• UMTS uplink (3GPP complain)
• Bit rate 30 kb/s 120 kb/s
• Turbo coder/decoder
• (1,15/13)8
• R1/2
• MAP-BCJR.
• Interleaver (3GPP complain)
• ETSI urban channel (6 paths).

19
Soft Combining techniques
3. Application to UMTS systems
Frame Error Rate
Better FER (QoS) or reduced power wasting (lesser
electromagnetic pollution)
20
Soft Combining techniques
3. Application to UMTS systems
Throughput
Better FER (QoS) or better throughput or reduced
delay
21
Soft Combining techniques
3. Application to UMTS systems
Cell capacity (64 nominal users)
Capacity increasing up to 20 oversaturated users
(??????)
22
Soft Combining techniques
3. Application to UMTS systems
Goodput
Reduced power or higher effective bandwidth
23
Conclusions

• QoS oriented services within wireless networks
• Cross-layer adaptive protocols design for
  reliable applications
• Soft Combining techniques (H-ARQ type II)
• Analytical performance evaluation
• Application to 3G public systems (UMTS)

24
Journal papers
Publications

1. F. Chiti, R. Fantacci, F. Versaci Turbo Soft
   Combining Hybrid ARQ Techniques Theory and
   Application to 3G Wireless Networks, Annals of
   Telecommunications Special Issue on Turbo Codes,
   January 2005.
2. F. Chiti, R. Fantacci, F. Versaci An Efficient
   Turbo Soft Combining Hybrid ARQ Techniques for
   Application in Wireless Communication Systems,
   IEEE Trans. on Comm., submitted for publication.
3. F. Chiti, R. Fantacci A Soft Combining Hybrid
   ARQ Technique applied to Throughput Maximization
   within 3G Satellite IP Networks, IEEE Trans. on
   Vehic. Tech., submitted for publication.

Conference papers

1. F. Chiti, R. Fantacci, T. Pecorella, F. Versaci
   Soft Combining Hybrid ARQ Techniques Application
   to Packet Communications within 3G Wireless
   Networks, in Proc. of IEEE WCNC 2003.
2. F. Chiti, R. Fantacci, T. Pecorella, F. Versaci
   Soft Combining Hybrid ARQ Techniques Application
   to 3G Wireless Networks, in Proc. of IEEE ICC
   2003.
3. F. Chiti, R. Fantacci, G. Mennuti, D. Tarchi
   Dynamic SIR based Admission Control Algorithm
   for 3G Wireless Networks, in Proc. of IEEE ICC
   2003.
4. F. Chiti, R. Fantacci, F. Versaci Turbo Soft
   Combining Hybrid ARQ Techniques Theory and
   Application to 3G Wireless Networks, in Proc. of
   IEEE ISTC 2003.

25
Turbo Soft Combining Hybrid ARQ Techniques
Theory and Application to 3G Wireless Networks
Romano Fantacci Full Professor Francesco Chiti
Ph.D. Department of Electronics and
Telecommunications University of Florence Via di
S. Marta, 3 I-50139 Florence, ITALY E-mail
fantacci,chiti_at_lenst.det.unifi.it