Hybrid ARQ Operation for IEEE 802.16m
IEEE 802.16 Presentation Submission Template (Rev. 9)
Document Number:
IEEE C802.16m-08/454r1
Date Submitted:
2008-05-08
Source:
Sungkyung Kim, Kwangjae Lim, Sungcheol Chang,
Seokheon Cho, Jungim Kim, Chulsik Yoon
ETRI
161 Gajeong-dong Yusong-gu Daejeon, Korea
Voice: +82-42-860-6448
E-mail: {cyrano, kjlim, scchang, csyoon}@etri.re.kr
*<http://standards.ieee.org/faqs/affiliationFAQ.html>
Venue:
EEE 802.16 Session #55, Macau, China
Base Contribution:
N/A
Purpose:
To discuss and adopt the proposed text in the next revision of the 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
Contents
•
•
•
•
•
HARQ Mode
HARQ Signaling
HARQ Operation
HARQ in Persistent Allocation
HARQ Support for Fast MAC PDU retransmission
2
HARQ Mode
•
•
Comparison among the HARQ Operation
Synchronous
Asynchronous
Asynchronous
Modes Synchronous
non-adaptive
adaptive
non-adaptive
adaptive
Retransmission timing
fixed
fixed
Not-fixed
Not-fixed
Retransmission format
fixed
dynamic
fixed
Dynamic
Required retransmission
signaling
Implicit
signaling
Explicit
signaling
Explicit
signaling
Explicit
signaling
MAP overhead
low
high
high
high
flexibility
low
medium
medium
high
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.
3
HARQ Signaling
• For new transmission of an HARQ burst
[The Example for HARQ signaling]
– 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 nonadaptive mode
– No signaling
• For HARQ mode change
Synchronous
HARQ interval
Tx Side
Rx Side
HARQ CH ID(x), toggle bit(0), SPID(IR case), MCS,
allocated resource region
New HARQ burst (1)
HARQ signaling for
new transmission
HARQ Feedback Delay
HARQ Feedback (NAK)
Retx. HARQ burst (1)
HARQ Feedback Delay
Synchronous
HARQ interval
HARQ Feedback (NAK)
Asynchronous mode indication
HARQ signaling for
change of HARQ mode
HARQ CH ID(x), toggle bit(0), SPID(IR case), MCS,
allocated resource region
HARQ signaling for
asynchronous retransmssion
– Asynchronous mode indication
• For retransmission in asynchronous
adaptive mode
–
–
–
–
HARQ CH ID (or interlace ID)
Toggle bit
SPID in IR case
MCS and radio resource
Retx. HARQ burst (1)
HARQ Feedback Delay
HARQ Feedback (ACK)
HARQ CH ID(x), toggle bit(1), SPID(IR case), MCS,
allocated resource region
New HARQ burst (2)
HARQ signaling for
new transmission
4
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
Asynchronous Mode
Synchronous Mode
New
transmission
Synchronous HARQ subframe (N+M*X)={0,8,16..}
Allocation info. for
asynchronous retransmission
Asynchronous
mode indication
DL
X-subframes
0
UL
1
2
HARQ FD
delay
HARQ FD delay
Synchronous
non-adaptive
Y(0)=5
subframe
Y(3)=3
– The Example of FDD
New
transmission
[DL]
Synchronous HARQ subframe (N+M*X)={0,8,16..}
Asynchronous
mode indication
Allocation info. for
asynchronous retransmission
UL HARQ Feedback Channel
0
1
HARQ FD
delay
[UL]
Asynchronous Mode
Synchronous Mode
Y(0)=3
X subframes
2
HARQ FD
delay
HARQ FD
delay
Y(0)=3
Synchronous
non-adaptive
Y(3)=3
5
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)
Synchronous Mode
New transmission
asynchronous
Synchronous HARQ subframe (N+M*X)={5,13,21,..}
Asynchronous mode indication & allocation info. for
asynchronous retransmission
DL
0
1
2
X subframes
HARQ FD delay
Y(5)=6
MAP
HARQ Feedback
UL
NAK indication
UL HARQ burst
Synchronous
non-adaptive
NAK indication
ACK indication
• DL HARQ ACK/NAK Feedback
CRC included
Feedback error cases
Resource allocation and
multiplexing for FB bits
Physical DL Feedback channel
DL HARQ Feedback IE in MAP
No
Yes
• ACK to NAK error: possible
collision due to synchronous
retransmission
• NAK to ACK error: data loss &
resource waste
Semi-static
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
Flexible (MAP IE)
6
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.
Persistent Allocation Period
N+1 frame
N+2 frame
N frame
Asynchronous retransmission (HARQ CH
ID, toggle bit(0), SPID(IR case), MCS,
radio resource)
Asynchronous retransmission (HARQ CH
ID, toggle bit(0), SPID(IR case), MCS,
radio resource)
PA (HARQ CH IDs)
N+3 frame
N+4 frame
1
0
NAK
N+5 frame
N+6 frame
0
N+7 frame
1
ACK
ACK
NAK
[ Downlink PA with HARQ Operation]
Asynchronous retransmission (HARQ CH
ID, toggle bit(0), SPID(IR case), MCS,
radio resource)
Persistent allocation
(HARQ CH IDs)
N frame
N+1 frame
Persistent Allocation Period
N+3 frame
N+2 frame
1
0
N+5 frame
0
1
2
NAK
NAK
N+4 frame
Synchronous
retransmission
The number of synchronous retransmissions = 1
Asynchronous
retransmission
ACK
[ Uplink PA with HARQ Operation]
NAK
Synchronous
retransmission
N+6 frame
N+7 frame
ACK
7
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
N frame
N+1 frame
1
0
RX
failure
NAK
HARQ TX side: Notification
of Maximum retransmission
failure to ARQ module
NAK
...
RX
failure
NAK
Maximum retransmission: 2
MAP
HARQ burst
Feedback error
(NACK à ACK)
N+2 frame
2
RX
failure
New transmission
(HARQ CH ID: X, toggle bit:1)
UL HARQ Feedback Channel
HARQ Feedback Message
0
RX
failure
New transmission
(HARQ CH ID: X, toggle bit:0)
Fast Retransmission
0
NAK
Detection of allocation
for other MS (MAP IE).
New transmission
(HARQ CH ID: X, toggle bit:0)
...
HARQ CH ID,
subframe index
HARQ RX side: Generation of an
HARQ feedback message
8
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
9
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 nonadaptive 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.
10