1. HARQ Feedback Channel for 2bit HARQ feedback
IEEE Presentation Submission Template (Rev. 9)
Document Number:
C80216m-09/0672
Date Submitted:
Source:
Jinyoung Chun
Sukwoo Lee
Bin-Chul Ihm
LG Electronics
*<
Re:
Call for Comments on Amendment Working Document, IEEE m-09/0012
Target topic: UL PHY Control
Base Contribution:
None
Purpose:
Discussion and adoption for m AWD
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2. Contents UL HARQ feedback channel for 1bit feedback
Refer to C80216m-09_0386 (output of UL Ctrl DG).
The necessary of 2bit (or more) feedback
Proposed UL HARQ feedback channel for 2bit feedback
The comparison with other proposals
Proposed AWD text

3. UL HARQ feedback channel for 1bit feedback
The structure for 1bit feedback
There are 2 HARQ feedback channels in three HMTs, which is 2x2.
Orthogonal sequence
1-bit feedback
[ ]
ACK of channel 1
[ ]
NACK of channel 1
[ ]
ACK of channel 2
[ ]
NACK of channel 2

4. The necessary of multiple bit feedback
The usage scenario of multiple bit feedback for a MS
Multiple bits feedback for a DL burst
Multiple codeword (MCW): When a MS receives MCW bursts, the MS may transmit a HARQ feedback.
Multiple ACK/NACKs for multi-hop in Relay: Multiple NAK for multi-hop and single ACK is needed in Relay.
Multiple bits feedback for multiple DL bursts
Multiple ACK/NACKs in multicarrier: When a MS receives data to Primary Carrier and Secondary Carrier, the MS may transmit a HARQ feedback to a Carrier.
Asymmetric ratio of DL and UL subframe in TDD: When the ratio of DL subframes and UL subframes is asymmetric and a MS receives data in two or more DL subframes, the MS may transmit a HARQ feedback in a UL subframe.
Therefore we need to consider multiple bit feedback for a MS. Then how we can support it?

5. The structure for 2bit feedback
There are three options.
Option 1: two HARQ feedback channels separately
MS transmits two HARQ channels for 1bit feedback separately.
Option 2: two HARQ feedback channels jointly
MS transmits a signal made from two HARQ channels.
Option 3: one HARQ feedback channels
MS transmits a HARQ channel modulated to QPSK.
Orthogonal sequence
1-bit feedback
2-bit feedback
[Option 1]
[Option 2]
[Option 3]
[ ]
ACK of channel 1
ACK of 1st bit in channel 1
ACK/ACK in channel 1
[+1 -j j]
: ACK/ACK of channel 1
: ACK/NACK of channel 1
[ ]
NACK of channel 1
NACK of 1st bit in channel 1
ACK/NACK in channel 1
[+1 +j j] [ ]
: NACK/ACK of channel 1
: NACK/NACK of channel 1
[ ]
ACK of channel 2
ACK of 2nd bit in channel 1
NACK/ACK in channel 1
[+1 -j j]
: ACK/ACK of channel 2
: ACK/NACK of channel 2
[ ]
NACK of channel 2
NACK of 2nd bit in channel 1
NACK/NACK in channel 1
[+1 +j j]
[ ]
: NACK/ACK of channel 2
: NACK/NACK of channel 2

6. The structure for 2bit feedback
The comparison of the three schemes
Normally if we only transmits HARQ feedback channel (HFBCH) for 1-bit feedback, we can map DL burst and HFBCH to one-to-one. Therefore we don’t need any HFBCH indication.
In case of 2-bit feedback, option 1 and 2 need HFBCH indication because one or two HFBCHs can be allocated to a DL burst. But option 3 use the same resource with 1-bit feedback and we don’t need any HFBCH indication.
Option 1
Option 2
Option 3
MS power
½ power in each channel
1 power in a channel
Resource
2 HARQ feedback channels
1 HARQ feedback channels
Performance
Good
Better
DL control signaling overhead
Need indication for channel index
No need indication for channel index

7. Overhead comparison Assumption (Multiple codeword (MCW)) Overhead
Bandwidth
10MHz
DL/UL ratio
4:4
DL bursts per subframe 12
Total # of bursts in a frame 60
# DL burst with SCW
36 bursts
Max. # of bursts associated to a UL subframe for UL HFBCH 48
# DL burst with MCW
12 bursts
Option 1 & 2
Option 3
Notes
Required HFBCHs
60 = x12
48 =
Required UL PRUs
4 {=ceil(60/18)}
3 {=ceil(48/18)}
UL Overhead ratio
2.08 %
1.56 %
Required bits to indicate the index of HFBCH in DL MAP (bits)
6 {=ceil(log2(60) }
In case of option 3, the index of HFBCH follows the one of DL grant.
Required DL PRUs
8 {=ceil(6x60x2/96)}
DL Overhead ratio
3.13 %
0 %
Total Overhead ratio
2.61 %
0.78 %

8. Overhead comparison
Assumption (Asymmetric ratio of DL and UL subframe in TDD)
Overhead
Bandwidth
10MHz
DL/UL ratio
5:3
DL bursts per subframe 12
Total # of bursts in a frame 60
# user with 1 DL burst
42 users (42 bursts)
Max. # of bursts associated to a UL subframe for UL HFBCH 36
# user with 2 DL burst
9 users (18 bursts)
Option 1 & 2
Option 3
Notes
Required HFBCHs 60
Required UL PRUs
4 {=ceil(60/18)}
UL Overhead ratio (%)
2.78
Required bits to indicate the index of HFBCH in DL MAP (bits)
6 {=ceil(log2(60) }
In case of option 3, the index of HFBCH follows the one of DL grant.
Required DL PRUs
8 {=ceil(6x60x2/96)}
QPSK ¼ considered
DL Overhead ratio (%)
3.3
Total Overhead ratio (%)
3.13
1.04
8/9 8

9. Conclusion We prefer option 3 to transmit 2bit HARQ feedback.
There is a little performance loss but not critical.
Moreover, we maintain the same capacity with 1bit feedback and apply the same indexing rule with 1bit feedback without any indication overhead.

10. Proposed AWD text
Add the text below HARQ Feedback Control Channel in C80216m-09_0386 (UL Ctrl DG)