“Turbo Soft Combining Hybrid ARQ Techniques: Theory and Application to 3G Wireless Networks”

Laboratorio di Elaborazione Numerica dei Segnali e Telematica 1/25COST 289 6th MCM, Barcelona October 28-29 2004

“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 TelecommunicationsUniversity of Florence

Via di S. Marta, 3I-50139 Florence, ITALY

E-mail: {fantacci,chiti}@lenst.det.unifi.it


Outlinei. Introduction

1. Soft combining principle

• Soft Input Combining

• Soft Output Combining

2. Theoretical analysis

• AWGN

• Multipath fading channel

3. Application to UMTS systems

4. Conclusions


i. Introduction

Soft Combining techniques

Service ClassesUMTS/HSDPA

• Conversational

• Streaming

• Interactive

• Background

IPvx

• Elastic

• Stream 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]PHY

MAC

LLC


• 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).

i. Introduction

Soft Combining techniques

Reliable packet communications


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

Traditional approaches comparison

Soft Combining techniquesi. 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/reception process (e.g. Chase Combining)

• Type III

transport formats are dynamically updated to cope with the signal quality variations (e.g. Incremental Redundancy)

Soft Combining techniquesi. Introduction

Acknowledgement Driven (PHY+MAC+LLC)

Soft Combining (MAC+LLC)


Functional block diagram

BufferReceiver Decoder

LOGIC

Soft Combining techniques1. Soft combining principle

Despreading

Descrambling

Rake Demodulator

DE

MU

X

BCJR BCJR


• 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

Soft Input 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

Soft Output Combining H-ARQ



0,0

0,5

1,0

1,5

2,0

2,5

-2 0 2 4 6 8 10 12 14 16 18 20

SNR [dB]

Rel

ativ

e G

ain

Gain

OUT IN

1G• : input combining

1G• : output combining


• Coding gain: 2

2

IN

OUTG

under Gaussian output approximations

(except for interdiction and saturation regions)


Coder

Layer II - LLC

Buffer

New Frame

Previous Frame

Logic

Pack

CRC adder PackCRC

PackCRC Redundancy

ACK/NACK

Modulator

Layer II - MAC

Layer I -PHY

Transmitter protocol stack



Decoder

Layer II - LLC

Buffer

Previous OUTPUT

Previous INPUT

Logic

Pack

CRC checkPackCRC

PackCRC Redundancy

Demodulator

Layer II - MAC

Layer I -PHY

Receiver protocol stack

ACK/NACK

ACK/NACK



• BER

AWGN channel

2

12, 2min

min22

1

22

K

jj

k

j

kkb z

z

H

H

j

jjP 2

kSNR

k eH

1

1,

k

iioutin nnxky

1

1

2

2

,

12k

iiin

bkOUT

G

REkSNR

innxky 2, 2 in

bkIN

REkSNR



kGk

ii

1

1

1 SOC outperforms SIC

Soft Combining techniques2. Theoretical analysis


• FER

AWGN channel

RTTGl

llR

f

CRCf

1

1

1

1,,

1

1k

iifkf

k

PPkG

• Average needed retransmissions

• Throughput

flkbkf PP ,, 11 fl frame length



• BERk

Multipath fading channel

2

12, 2min

min22

1

22

K

jj

k

j

kkb z

z

H

H

j

jjP 2

kSNR

k eH

2, 2 in

bkkIN k

RESNR


1

1

2,

12k

iiin

bkkOUT

Gk

RESNR


k

i

L

l l

lk

l

i

ep1 1

joint pdf of kL fading coefficients (1 kL)



• BER


kkkk

OUT

INbkb ddpSNRPPk

11,

,

1

• FER

k

k

ii

l

kk

OUT

INbkf ddpSNRPPk

f

11

1,

, 111



Goodputmultiplicative increase/multiplicative decrease SLW congestion control


n

i

nK

ifn

PPBB

1,0 2

12

nKP


Prob that current block has been transmitted K times at time n

Timeout value is equal to K(RTT)

0B Initial SLW size


• UMTS uplink (3GPP complain);

• Bit rate: 30 kb/s – 120 kb/s;

• Turbo coder/decoder:

– (1,15/13)8 ;

– R=1/2;

– MAP-BCJR.

• Interleaver (3GPP complain);

• ETSI urban channel (6 paths).

Operative assumptions

Soft Combining techniques3. Application to UMTS systems


Frame Error Rate

H-ARQ type II vs H-ARQ type I

1,0E-03

1,0E-02

1,0E-01

1,0E+00

0 1 2 3 4 5 6 7 8

SNR [dB]

FE

R

H-ARQ

SOC

SIC

Better FER (QoS) or reduced power wasting (lesser electromagnetic pollution)



Throughput


5,0E-02

1,0E-01

1,5E-01

2,0E-01

2,5E-01

3,0E-01

3,5E-01

4,0E-01

4,5E-01

5,0E-01

0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0

FER

Th

rou

gh

pu

t

H-ARQ

SOC

SIC

Better FER (QoS) or better throughput or reduced delay



Cell capacity (64 nominal users)


1,0E-04

1,0E-03

1,0E-02

1,0E-01

1,0E+00

6 8 10 12 14 16 18 20

Additional users

BE

R SIC

SOC

Capacity increasing up to 20 oversaturated users ()



Goodput


1,0E-02

1,1E-01

2,1E-01

3,1E-01

4,1E-01

0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 4,0 4,5 5,0 5,5 6,0

SNR [dB]

No

rma

lize

d G

oo

dp

ut

H-ARQ

SOC

SIC

Reduced power or higher effective bandwidth



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)


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.

PublicationsJournal papers

Conference papers1. 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.


“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 TelecommunicationsUniversity of Florence

Via di S. Marta, 3I-50139 Florence, ITALY

E-mail: {fantacci,chiti}@lenst.det.unifi.it

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“Turbo Soft Combining Hybrid ARQ Techniques: Theory and Application to 3G Wireless Networks”