1. HARQ Feedback Joint Coding
IEEE Presentation Submission Template (Rev. 9)
Document Number:
IEEE S802.16m-09/0046
Date Submitted:
Source:
Zheng Yan-Xiu, Yu-Chuan Fang, Chang-Lan Tsai, Chung-Lien Ho, Hsi-Min Hsiao, Ren-Jr Chen, Richard Li,
ITRI
Venue:
IEEE Session #59, San Diego.
Base Contribution: N/A
Re: m-08/052, Call for Comments on m SDD (802.16m-08/003r6), Section UL HARQ Feedback
Purpose: To be discussed and approval by IEEE m TG
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2. Motivation
HARQ feedback introduces significant overhead in uplink control channel due to 1-bit information feedback
The HARQ feedback highly influences system coverage and occupies large radio resource
Concurrent HARQ feedbacks would occur for some scenarios
Multi-carrier introduces parallel and concurrent HARQ feedback channels from different carriers
Multiple streams MIMO transmission needs multiple HARQ feedbacks for multiple streams
TDD mode makes multiple HARQ feedbacks aggregated on the same subframe
In IEEE m, two or three bits HARQ feedback would occur within one subframe due to TDD mode,
Coding or information aggregation on these multiple feedbacks improves feedback reliability or enlarge HARQ feedback channel capacity

3. Examples of Concurrent HARQ Feedback
Multi-Carrier
TDD Mode
Multiple Streams MIMO

4. Mapping Concept
Mapping multiple HARQ feedbacks on a sequence or a composite sequence
The composite sequences can be linear combination of sequences for 1-bit feedback
Since more than one feedbacks are transmitted by one sequence, power can be aggregated
Power gain or coding gain can be acquired

5. Existing Design No. orthogonal Sequence 1 1 1 1 1 1 1 1 1 1 1 1 1 2 3 4 5 6 7 8 9 10 11 12
IEEE C80216m-08_1057r2
12 orthogonal sequences
6 for ACK and 6 for NACK
6 independent HARQ channels for 6 users
Distribute the code three 2x6 or 6x2 resource tile
Non-coherent detection is used to detect code sequence

6. Example of 2-bit Concurrent HARQ Feedbacks
12 orthogonal sequences with length 12 for HARQ feedback channel
Two HARQ channel feedbacks from a user
Three users share this HARQ feedback channel
Conventional design
6 for ACK and 6 for NACK
Each user chooses two from ACK sequences and two from NACK sequences
Two sequences are transmitted by one user
New design
3 for ACK-ACK; 3 for ACK-NACK; 3 for NACK-NACK; 3 for NACK-ACK
One sequence are transmitted by one user
Channel Bandwidth
10MHz
Over-sampling Factor
28/25
FFT Size
1024
Cyclic prefix (CP) ratio
1/8
Channel condition
PB3, VA120, VA350
The number of antennas
Tx:1, Rx:2
Modulation
BPSK
FMT size
6x2
Block size
6x6
Receiver
HARQ FB: non-coherent detection, MLD

7. Example of Nine-State HARQ feedback
No.
orthogonal Sequence S1 S2 S3 S4 S5 S6 S7 S8 S9
S10
S11
S12
12 sequences
2 HARQ feedback channel
3 states per channel: ACK, NACK and DROP
Choose S1, S2, S3 and S4 as a subset
Construct sequences C1~C9 by
Mapping of C1~C9 is shown as following table
Code C1 C2 C3 C4 C5 C6 C7 C8 C9
Channel 1
ACK
NACK
DROP
Channel 2

8. Performance of Nine State Joint Coding
Similar performance is achieved to provide extra information “DROP”
Channel Bandwidth
10MHz
Over-sampling Factor
28/25
FFT Size
1024
Cyclic prefix (CP) ratio
1/8
Channel condition
PB3, VA120, VA350
The number of antennas
Tx:1, Rx:2
Modulation
BPSK
FMT size
6x2
Block size
6x6
Receiver
HARQ FB: non-coherent detection, MLD

9. Example of 2-bit Concurrent HARQ Feedbacks
Three distributed 6x2 resource tiles
Non-coherent detection
12 orthogonal sequences with length 12 for HARQ feedback channel
Two HARQ channel feedbacks from a user
Three users share this HARQ feedback channel
Conventional design
6 for ACK and 6 for NACK
Each user chooses two from ACK sequences and two from NACK sequences
Two sequences are transmitted
New design
3 for ACK-ACK;
3 for ACK-NACK;
3 for NACK-NACK
3 for NACK-ACK
Each transmit one of these sequences to represent 2-bit HARQ feedbacks
Only one sequence is transmitted and power gain is acquired

10. Conclusion
Mapping multiple HARQ feedbacks on one sequence provides performance gain.
The sequence can be constructed by choosing 1-bit feedback or composite 1-bit feedbacks with normalized power.
More information can be transmitted with similar performance, e.g. tri-state feedback.
Multicarrier, TDD mode and multiple streams MIMO are highly recommended to adopt this feedback to enhance link reliability or capacity.

11. SDD TEXT Proposal 11.13.2.6 HARQ feedback
A basic ACK/NAK channel to transmit 1-bit feedback is supported.
1-bit feedback compatible joint coded HARQ feedback will be supported to enhance feedback channel reliability or increase the capacity for concurrent feedback scenarios, e.g. multi-carrier, TDD mode, multiple streams MIMO. Mapping multiple feedbacks by 1-bit feedback or composite 1-bit feedbacks with normalized power will be used.
An enhanced ACK/NAK control channel with some additional information is FFS.