Proposal for Downlink HARQ Scheme
Document Number: IEEE S802.16m-08/386
Date Submitted: 2008-05-12
Source:
Wang Junhu, Sun Changyin, Wang Wenhuan
Qu Hongyun, Fang HuiYing
ZTE Corporation
Du Yinggang, Wang Yingming
Huawei Technologies
Dong Xiaolu, Du Ying
CATR
*<http://standards.ieee.org/faqs/affiliationFAQ.html>
E-mail: wang.junhu@zte.com.cn
duyinggang@huawei.com
dongxiaolu@mail.ritt.com.cn
Venue:
IEEE 802.16m-08/016r1 –Call for Contributions on Project 802.16m System Description Document (SDD);
Proposed 802.16m Hybrid ARQ
Base Contributions:
IEEE C80216m-08/386
Purpose:
Adopt proposed text in base contribution into Project 802.16m SDD.
Notice:
This document does not represent the agreed views of the IEEE 802.16 Working Group or any of its subgroups. It represents only the views of the participants listed in
the “Source(s)” field above. It is offered as a basis for discussion. It is not binding on the contributor(s), who reserve(s) the right to add, amend or withdraw material
contained herein.
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1
HARQ Classification
According to the timing of retransmission:
•Synchronous HARQ: Predefined TTI, implicit signaling
•Asynchronous HARQ: Flexible scheduling, explicit signaling
According to retransmission formats:
•Adaptive HARQ :Transmission attributes (modulation, code
rate, resource block allocation, etc ) may not be changed, no
explicit signaling
•Non-adaptive HARQ: Transmission attributes may be
changed, explicit signaling
2
Design Considerations
• 1. Overhead of HARQ in TDD
Component
fields
related to HARQ
Asynchronous
Adaptive
Synchronous
Non-adaptive
Adaptive
Non-adaptive
Int. Tx
Re Tx
Int. Tx
Re Tx
Int. Tx
Re. Tx
Int Tx
Re Tx
Resource
allocation
12
12
12
0
12
12
12
0
Modulation and
coding scheme
5
5
5
0
5
5
5
0
HARQ process
number
3
3
3
3
0
0
0
0
Redundancy
version
2
2
0
0
2
2
0
0
New Data
indication
1
1
0
0
1
1
0
0
CID
16
16
16
16
16
16
16
0
Total (bits)
39
39
36
19
36
36
33
0
3
Design Considerations
• Overhead of HARQ in TDD (Cont.)
Assuming the number of HARQ processes in one radio frame is M,
the total transmission number is N, the overhead is illustrated in the
following table.
Asynchronous
adaptive HARQ
Asynchronous nonadaptive HARQ
Synchronous
adaptive HARQ
Synchronous nonadaptive HARQ
M, N
M*N*39
M*17+M*N*19
M*N*36
33*M
M=5, N=4
780
465
720
165
M=7,N=4
1092
651
1008
231
Overhead(bits)
4
Design Considerations
• 2. Delay of transmission in TDD
Additional delay for retransmission has to be considered,
which occurs when the radio channel is not immediately
available for the necessary UL or DL transmissions. The
process delay and frame alignment is supposed to be two
subframe length.
5
Proposed Downlink HARQ Scheme
•
Hybrid HARQ scheme in downlink for TDD system can acquire
trade-off benefit between asynchronous adaptive HARQ and
synchronous non-adaptive HARQ.
Asynchronous HARQ is the default configuration for downlink
subframes.
Synchronous non-adaptive HARQ is applied to some
subframes within the Maximum Allowable Synchronous HARQ
Region(MASHR).
•
•
–
–
synchronous HARQ subframes: Subframes within MASHR can
apply synchronous non-adaptive HARQ one radio frame as RTT
asynchronous subframes: apply asynchronous HARQ with
adaptive mode or non-adaptive mode
6
Proposed Downlink HARQ Scheme(cont’d)
• The assignment of synchronous HARQ subframes is
broadcast to all the MSs through Synchronous
HARQ Subframes Bitmap. MSs can share the same
synchronous subframes.
• The configuration of HARQ modes can be fixed or
semi-static.
7
SF0
• DL/UL=6:2
SF1
SF2
SF3
SF4
SF5
SF6
SF7
（a）
An application example
（b）
• Assuming one synchronous
subframe only contains one
HARQ process, the
retransmission number is
assumed to be 4, the
overhead saved by applying
synchronous non-adaptive
HARQ is 3*4*39=108bits.
• More HARQ processes
contanied in one subframe,
more overhead saved.
Synchronous HARQ process 1 RTT=8*TTI
（c）
Synchronous HARQ process 2 RTT=8*TTI
（d）
Synchronous HARQ process 3 RTT=8*TTI
（e）
Downlink
subframe
MASHR
Uplink
subframe
Downlink to
uplink switch
Uplink to
Downlink switch
Asynchronous HARQ
subframe
ACKNACK
Synchronous HARQ
subframe
8
SF0
• DL/UL=5:3
SF1
SF2
SF3
SF4
SF5
SF6
SF7
（a）
An application example
（b）
Synchronous HARQ process 1 RTT=8*TTI
（c）
Synchronous HARQ process2 RTT=8*TTI
（d）
Downlink
subframe
MASHR
Uplink
subframe
Downlink to
uplink switch
Uplink to
downlink switch
Asynchronous HARQ
subframe
ACKNACK
Synchronous HARQ
subframe
9
Proposed text to 802.16m SDD
Insert the following text:
X.Y HARQ
X.Y.1 DL HARQ
Downlink HARQ Scheme supports both asynchronous HARQ and synchronous
HARQ.
•
Asynchronous HARQ is the default configuration for downlink subframes;
•
Synchronous non-adaptive HARQ is applied to some subframes within the Maximum
Allowable Synchronous HARQ Region(MASHR). These subframes apply
synchronous non-adaptive HARQ with a RTT of one radio frame, which are called
synchronous HARQ subframes. And the other subframes in the downlink apply
asynchronous HARQ with adaptive mode or non-adaptive mode, which are called
asynchronous subframes.
•
The assignment of synchronous HARQ subframes is broadcast to all the MSs
through Synchronous HARQ Subframes Bitmap. MSs can share the same
synchronous subframes.
•
The configuration of HARQ modes can be fixed or semi-static.
10
Appendix :MASHR for different DL/UL ratio:
•
DL/UL=2:6
The two subframes in downlink are both configured to be synchronous
HARQ subframes.
SF0
SF1
SF2
SF3
SF4
SF5
SF6
SF7
An application example
Downlink
subframe
MASHR
Uplink
subframe
Downlink to
uplink switch
Uplink to
downlink switch
Asynchronous HARQ
subframe
Synchronous HARQ
ACKNACK
Synchronous HARQ
subframe
11
•
DL/UL=3:5
SF0
SF1
SF2
SF3
SF4
SF5
SF6
SF7
An application example
12
•
DL/UL=4:4
SF0
SF1
SF2
SF3
SF4
SF5
SF6
SF7
An application example
13
•
DL/UL=5:3
SF0
SF1
SF2
SF3
SF4
SF5
SF6
SF7
An application example
14
•
DL/UL=6:2
SF0
SF1
SF2
SF3
SF4
SF5
SF6
SF7
An application example
15