1. Hybrid ARQ Operation for IEEE 802.16m
IEEE Presentation Submission Template (Rev. 9)
Document Number:
IEEE C802.16m-08/454r1
Date Submitted:
Source:
Sungkyung Kim, Kwangjae Lim, Sungcheol Chang, Voice:
Seokheon Cho, Jungim Kim, Chulsik Yoon {cyrano, kjlim, scchang,
ETRI
161 Gajeong-dong Yusong-gu Daejeon, Korea
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Venue:
EEE Session #55, Macau, China
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Purpose:
To discuss and adopt the proposed text in the next revision of the m SDD
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2. Contents HARQ Mode HARQ Signaling HARQ Operation
HARQ in Persistent Allocation
HARQ Support for Fast MAC PDU retransmission

3. HARQ Mode Comparison among the HARQ Operation Modes
We propose the synchronous non-adaptive HARQ mode as a default mechanism by reason of low MAP overhead. Also, HARQ mode can be changed to the asynchronous adaptive scheme in order to get the scheduling gain or/and to support the flexibility of resource allocation.
Synchronous non-adaptive
Synchronous adaptive
Asynchronous non-adaptive
Asynchronous adaptive
Retransmission timing
fixed
Not-fixed
Retransmission format
dynamic
Dynamic
Required retransmission signaling
Implicit signaling
Explicit signaling
MAP overhead
low
high
flexibility
medium

4. HARQ Signaling For new transmission of an HARQ burst
HARQ CH ID (or implicit HARQ interlace ID)
Toggle bit for new packet indication
SPID in IR case
MCS and radio resource
For retransmission in synchronous non-adaptive mode
No signaling
For HARQ mode change
Asynchronous mode indication
For retransmission in asynchronous adaptive mode
HARQ CH ID (or interlace ID)
Toggle bit
[The Example for HARQ signaling]

5. DL HARQ Operation DL HARQ timing for synchronous mode
HARQ feedback delay and retransmission delay should be defined in specification
HARQ feedback delay and retransmission delay are dependent on the subframe position in a frame, legacy subframe position in a frame, duplex scheme, DL/UL ratio, TX/RX processing time, etc.
The Example of TDD (5:3)
Synchronous HARQ retransmission : N+M*X (N: subframe index of new transmission. M: the number of retransmission trials. X: synchronous HARQ interval)
Synchronous HARQ feedback: Y([N+M*X]%8) defined
The Example of FDD

6. UL HARQ Operation UL HARQ timing for synchronous mode
HARQ feedback delay and retransmission delay should be defined in specification
HARQ feedback delay and retransmission delay are dependent on the subframe position in a frame, legacy subframe position in a frame, duplex scheme, DL/UL ratio, TX/RX processing time, etc.
The Example of TDD (5:3)
DL HARQ ACK/NAK Feedback
Physical DL Feedback channel
DL HARQ Feedback IE in MAP
CRC included No
Yes
Feedback error cases
ACK to NAK error: possible collision due to synchronous retransmission
NAK to ACK error: data loss & resource waste
No uplink collisions in synchronous retransmissions (because MS should not transmit its UL HARQ burst when it fails to decode the MAP)
Resource waste in uplink frame
Resource allocation and multiplexing for FB bits
Semi-static
Flexible (MAP IE)

7. HARQ in Persistent Allocation
Persistent Allocation for the first HARQ transmission
MCS, Radio resource, Period,
HARQ CH IDs
Dynamic Allocation by Asynchronous HARQ signaling for HARQ retransmission
MCS, Radio resource,
HARQ CH ID (or interlace ID), Toggle bit, SPID in IR case
Additional synchronous retransmission for an MS with low link budget in UL case
Additional synchronous retransmission may be defined as part of PA.
After N (=1, 2, …) synchronous retransmissions, asynchronous retransmission may be issued.

8. HARQ Support for Fast MAC PDU Retransmission
Purpose
When some packets are lost due to HARQ failure
NAK feedback after the maximum retransmission trials
NAK-to-ACK feedback error
To reduce the long ARQ retransmission delay for ARQ connections
To fast retransmit a MAC message before the response timeout
Operation
At HARQ TX side: Internal notification of HARQ failure to the corresponding connection when BS/MS receives NAK feedback after the maximum retransmission trials
At HARQ RX side: HARQ failure signaling to the TX side by using MAC signaling (sub)header or message when BS/MS detects the NAK-to-ACK feedback error

9. Proposed Text (1) X.x. Hybrid ARQ Operations X.x.1 Basic Principles
The HARQ scheme is basically a stop-and-wait protocol and supports multiple HARQ channels.
Synchronous non-adaptive HARQ mode is used as a default scheme on both downlink HARQ and uplink HARQ in order to reduce downlink control overhead. Moreover, on purpose to enhance the scheduling gain and to support the flexibility of resource allocation, HARQ retransmission mode can be switched to asynchronous adaptive HARQ mode. To support optional asynchronous adaptive HARQ mode per HARQ burst, explicit signaling or implicit signaling is needed.
For the HARQ operations the following parameters are considered:
- HARQ type (CC, IR, CC-IR, etc.)
- HARQ mode (synchronous non-adaptive, asynchronous adaptive)
- HARQ CH ID
- Toggle bit (new burst indication)
- SPID (Redundancy version of IR)
- MCS or Shortened adaptive HARQ transmission format
- Allocated resource region
동작 위주로 필요한 필드 언급하고..

10. Proposed Text (2)
For downlink HARQ operations, uplink HARQ feedback information (ACK/NAK) shall be transmitted through a physical uplink feedback channel.
X.x.2 HARQ Operation in Persistent Allocation
For Persistent Allocation, HARQ CH ID or interlace ID shall be implicitly signaled each new transmission. HARQ operation for Persistent Allocation is based on the asynchronous adaptive retransmission scheme on both downlink and uplink transmissions. However, synchronous non-adaptive retransmissions can be used for a MS with low link budget in uplink transmission. In this case, after N synchronous retransmissions, HARQ mode is automatically changed to the asynchronous adaptive HARQ scheme in uplink persistent allocation. (N=0, 1, 2, ..).
Xx3 HARQ support for fast MAC PDU retransmission
Owing to the errors of the physical HARQ feedback channel and failure of maximum retransmission, data loss and resource waste can be generated on both downlink and uplink transmissions. To recover data loss and to reduce retransmission delay, HARQ feedback information can be used by the TX side and RX side in transmissions of MAC management message with response timeout as well as ARQ transmissions. When a HARQ burst isn’t delivered any more owing to excess of the maximum retransmission, HARQ TX module will report this event to its ARQ module.
If HARQ RX module detects a NAK to ACK feedback error, it can deliver a HARQ feedback message or a signaling (sub)Header to the TX side.