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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
Laboratorio di Elaborazione Numerica dei Segnali e Telematica 2/25COST 289 6th MCM, Barcelona October 28-29 2004
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
Laboratorio di Elaborazione Numerica dei Segnali e Telematica 3/25COST 289 6th MCM, Barcelona October 28-29 2004
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
Laboratorio di Elaborazione Numerica dei Segnali e Telematica 4/25COST 289 6th MCM, Barcelona October 28-29 2004
• 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
Laboratorio di Elaborazione Numerica dei Segnali e Telematica 5/25COST 289 6th MCM, Barcelona October 28-29 2004
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
Laboratorio di Elaborazione Numerica dei Segnali e Telematica 6/25COST 289 6th MCM, Barcelona October 28-29 2004
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)
Laboratorio di Elaborazione Numerica dei Segnali e Telematica 7/25COST 289 6th MCM, Barcelona October 28-29 2004
Functional block diagram
BufferReceiver Decoder
LOGIC
Soft Combining techniques1. Soft combining principle
Despreading
Descrambling
Rake Demodulator
DE
MU
X
BCJR BCJR
Laboratorio di Elaborazione Numerica dei Segnali e Telematica 8/25COST 289 6th MCM, Barcelona October 28-29 2004
• 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
Soft Combining techniques1. Soft combining principle
Laboratorio di Elaborazione Numerica dei Segnali e Telematica 9/25COST 289 6th MCM, Barcelona October 28-29 2004
• 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
Soft Combining techniques1. Soft combining principle
Laboratorio di Elaborazione Numerica dei Segnali e Telematica 10/25COST 289 6th MCM, Barcelona October 28-29 2004
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
Soft Combining techniques1. Soft combining principle
• Coding gain: 2
2
IN
OUTG
under Gaussian output approximations
(except for interdiction and saturation regions)
Laboratorio di Elaborazione Numerica dei Segnali e Telematica 11/25COST 289 6th MCM, Barcelona October 28-29 2004
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
Soft Combining techniques1. Soft combining principle
Laboratorio di Elaborazione Numerica dei Segnali e Telematica 12/25COST 289 6th MCM, Barcelona October 28-29 2004
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
Soft Combining techniques1. Soft combining principle
Laboratorio di Elaborazione Numerica dei Segnali e Telematica 13/25COST 289 6th MCM, Barcelona October 28-29 2004
• 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
• Soft Input Combining
• Soft Output Combining
kGk
ii
1
1
1 SOC outperforms SIC
Soft Combining techniques2. Theoretical analysis
Laboratorio di Elaborazione Numerica dei Segnali e Telematica 14/25COST 289 6th MCM, Barcelona October 28-29 2004
• 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
Soft Combining techniques2. Theoretical analysis
Laboratorio di Elaborazione Numerica dei Segnali e Telematica 15/25COST 289 6th MCM, Barcelona October 28-29 2004
• 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
• Soft Input Combining
1
1
2,
12k
iiin
bkkOUT
Gk
RESNR
• Soft Output Combining
k
i
L
l l
lk
l
i
ep1 1
joint pdf of kL fading coefficients (1 kL)
Soft Combining techniques2. Theoretical analysis
Laboratorio di Elaborazione Numerica dei Segnali e Telematica 16/25COST 289 6th MCM, Barcelona October 28-29 2004
• BER
Multipath fading channel
kkkk
OUT
INbkb ddpSNRPPk
11,
,
1
• FER
k
k
ii
l
kk
OUT
INbkf ddpSNRPPk
f
11
1,
, 111
Soft Combining techniques2. Theoretical analysis
Laboratorio di Elaborazione Numerica dei Segnali e Telematica 17/25COST 289 6th MCM, Barcelona October 28-29 2004
Goodputmultiplicative increase/multiplicative decrease SLW congestion control
Multipath fading channel
n
i
nK
ifn
PPBB
1,0 2
12
nKP
Soft Combining techniques2. Theoretical analysis
Prob that current block has been transmitted K times at time n
Timeout value is equal to K(RTT)
0B Initial SLW size
Laboratorio di Elaborazione Numerica dei Segnali e Telematica 18/25COST 289 6th MCM, Barcelona October 28-29 2004
• 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
Laboratorio di Elaborazione Numerica dei Segnali e Telematica 19/25COST 289 6th MCM, Barcelona October 28-29 2004
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)
Soft Combining techniques3. Application to UMTS systems
Laboratorio di Elaborazione Numerica dei Segnali e Telematica 20/25COST 289 6th MCM, Barcelona October 28-29 2004
Throughput
H-ARQ type II vs H-ARQ type I
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
Soft Combining techniques3. Application to UMTS systems
Laboratorio di Elaborazione Numerica dei Segnali e Telematica 21/25COST 289 6th MCM, Barcelona October 28-29 2004
Cell capacity (64 nominal users)
H-ARQ type II vs H-ARQ type I
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 ()
Soft Combining techniques3. Application to UMTS systems
Laboratorio di Elaborazione Numerica dei Segnali e Telematica 22/25COST 289 6th MCM, Barcelona October 28-29 2004
Goodput
H-ARQ type II vs H-ARQ type I
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
Soft Combining techniques3. Application to UMTS systems
Laboratorio di Elaborazione Numerica dei Segnali e Telematica 23/25COST 289 6th MCM, Barcelona October 28-29 2004
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)
Laboratorio di Elaborazione Numerica dei Segnali e Telematica 24/25COST 289 6th MCM, Barcelona October 28-29 2004
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.
Laboratorio di Elaborazione Numerica dei Segnali e Telematica 25/25COST 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
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