Symbol Vector Interleaving for Chase-Combining HARQ
Document Number:
IEEE S802.16m-08/629
Date Submitted:
2008-07-07
Source:
Yakun Sun, Jungwon Lee
Marvell Semiconductor Inc.
E-mail:
yakunsun@marvell.com
*<http://standards.ieee.org/faqs/affiliationFAQ.html>
Venue:
IEEE 802.16m-08/016 – Call for Contributions on Project 802.16m System Description Document (SDD). Specifically, HARQ PHY.
Base Contribution:
IEEE C802.16m-08/629
Purpose:
To be discussed and adopted by TGm for use in 802.16m SDD
Notice:
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contained herein.
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Introduction
• Chase combining (CC) is a low-complexity and
effective HARQ scheme.
– Allows low complexity symbol-level combining, which is
optimal for MIMO HARQ.
• Time-varying symbol vector to subcarrier and
antenna mapping is effective for slow-varying
channels
– Exploits frequency selectivity and spatial diversity, and
hence improves chase combining performance.
– Support optimal symbol-level combining for CC
– No extra signaling
Symbol Level Combining
• Bit level combining sums up LLR’s of corresponding
bits over transmissions
– Suboptimal for MIMO transmissions
• Symbol level combining is optimal for MIMO HARQ
– x: transmitted signal (symbol vector)
– Hi, yi, ni : MIMO channel, received signal and noise of the ith transmission
 y1   H1 
 n1 
 
x 
  

 
 yN   H N 
 nN 
Performance of Symbol Level Combining
MIMO, QPSK-1/2, L=60 bytes, VA-120 km/h, High correlation
0
BLER
10
•
•
-1
10
•
•
1 transmission, ZF
2 transmissions, CC, ZF-SLC
2 transmissions, CC, ZF-BLC
-2
10
1
2
3
4
5
SNR [dB]
• 2dB gain using SLC
6
7
8
ITU VA-120km/h
2x2 MIMO, High
correlation
STBC (Matrix-A)
QPSK, rate-1/2
Frequency-Domain Symbol Vector Interleaver
• Reorder symbol-vector-to-subcarrier mapping across transmissions.
– Symbol deinterleaver at the receiver, followed by the optimal symbollevel combining.
– Exploit frequency selectivity.
– With sufficient frequency selectivity, symbol level interleaving realizes
the same level of diversity as bit level interleaving.
• Symbol vector interleaver at different resolutions
– Across RU’s
– RU shifting
Encoder
+
Bit
Interleaver
Modulation
Sym Vector
Interleaver
(sym vec-tosubcarrier
mapping)
SpaceTime
Coding
IFFT
MIMO
Channels
Decoder
Symbol
Level
Combining
Symbol
deinterleaver
FFT
Performance of Frequency Symbol Level Interleaving
10MHz, PB-3km/h, High corr, Matrix B, AMC, HARQ 2-frame interval
0
10
•
•
•
•
•
•
-1
BLER
10
ITU PedB-3km/h
2x2 MIMO, High correlation
SM (Matrix-B)
16QAM, rate-3/4
Localized allocation (AMC)
Retx every two 5ms frames
-2
10
No HARQ
BLC, 2 trans
SLC, 2 trans
SLC sym arrange, 2 logic bands
SLC, band rotation
-3
10
6
8
10
12
14
16
18
SNR (dB)
20
22
24
26
• 2dB gain by symbol level interleaving
Spatial Symbol Vector Interleaver
• Time-varying symbol vector to antenna mapping ,
in addition to frequency domain interleaving.
– Different space-time coding schemes across
transmissions.
• Example:
– Switching symbols across transmit antennas
– Soft packet combining: 1st Tx [s1 s2]T; 2nd Tx [-s2* s1*]T
Encoder
+
Bit
Interleaver
Modulation
Freq
Symbol
Interleaver
SpaceTime
Coding
(timevarying)
IFFT
MIMO
Channels
Decoder
Symbol
Level
Combining
Symbol
deinterleaver
FFT
Performance of Spatial Symbol Level Interleaving
10MHz, PB-3km/h, High corr, Matrix B, AMC, HARQ 2-frame interval
0
10
-1
•
•
•
•
•
•
BLER
10
-2
10
No HARQ
BLC, 2 trans
SLC, 2 trans
SLC, HARQ STBC
-3
10
6
8
10
12
14
16
18
SNR (dB)
20
22
24
26
• 4dB gain by using HARQ-STBC
ITU PedB-3km/h
2x2 MIMO, High correlation
SM (Matrix-B)
16QAM, rate-3/4
Localized allocation (AMC)
Retx every two 5ms frames
Conclusions
• Symbol level combining outperforms bit level combining.
• With sufficient space-frequency selectivity, symbol level
interleaving can realize the same diversity as bit level
interleaving.
• Propose: symbol level interleaver so that the benefit of the
symbol level combining at the receiver can be maximized.
Text
• “Symbol to subcarrier and antenna mapping
will be reordered from transmission to
transmission.”