1. HARQ Operational Modes for 802.16m Document Number: S80216m-08/322 Date Submitted: 2008-05-08 Source: Yih-Shen Chen, Kelvin Chou, I-Kang Fu, and Paul Cheng Voice: +886-3-5670766 E-mail:yihshen.chen@mediatek.com, IK.Fu@mediatek.com,yihshen.chen@mediatek.comIK.Fu@mediatek.com Paul.Cheng@mediatek.com MediaTek Inc. Venue: IEEE session #55, Macau Base Contribution: C80216m-08/322. Purpose: To be discussed and adopted by TGm for the P802.16m 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. Release: The contributor grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEE’s name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEE’s sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. The contributor also acknowledges and accepts that this contribution may be made public by IEEE 802.16. Patent Policy: The contributor is familiar with the IEEE-SA Patent Policy and Procedures: and.http://standards.ieee.org/guides/bylaws/sect6-7.html#6http://standards.ieee.org/guides/opman/sect6.html#6.3 Further information is located at and.http://standards.ieee.org/board/pat/pat-material.htmlhttp://standards.ieee.org/board/pat

2. 2 HARQ Operation Candidates Synchronous operation: a retransmission occurs at a fixed delay after an initial transmission if no ACK is received by the transmitter. Adaptive operation: the transmission attributes (e.g.: MCS, packet length, location and etc) may be changed during a retransmission. Three possible candidates to be discussed –Asynchronous adaptive HARQ –Synchronous adaptive HARQ –Synchronous non-adaptive HARQ

3. 3 Comparison for HARQ Modes Asynchronous adaptive HARQ Synchronous adaptive HARQ Synchronous non-adaptive HARQ Advantage- Multi-user diversity gain - Link-adaptation gain - Frequency diversity gain - Priority-based scheduling - High flexibility on bandwidth management - Link adaptation gain - Frequency diversity gain - Easy scheduling - Moderate flexibility on bandwidth management -Less signaling overhead - Easy scheduling Disadvantage- Large signaling overhead - Lost-of-MAP issue - Large signaling overhead - Restricted scheduling - No multi-user diversity gain - No link adaptation gain - No frequency diversity gain - Less flexibility on bandwidth management

4. 4 Discussions for DL HARQ Operation Mode For DL transmission, all the three schemes are possible candidates, depending on services –Asynchronous adaptive mode: BE, nrtPS –Synchronous adaptive: UGS, rtPS –Synchronous non-adaptive: UGS Since BS has to schedule the transmission of multiple services/connections over DL frame/subframe, we propose –asynchronous adaptive HARQ as the basic operational mode –synchronous HARQ as supplementary mode

5. 5 Lost-of-MAP Issue for Asynchronous Adaptive DL-HARQ (1/2) When DL-MAP is lost, the DL HARQ transmission status in the BS side is unknown because MS has no idea whether a DL_HARQ_IE is assigned –soft buffer overflow: new HARQ burst is received while occupied soft buffer is not released

6. 6 Lost-of-MAP Issue for Asynchronous Adaptive DL-HARQ (2/2) Suggestion: add a parameter “maximum scheduling delay” to each DL HARQ process –flat or per-connection

7. 7 Discussions for UL HARQ Operation Mode For UL transmission, synchronous HARQ schemes are preferable –The other-cell UL interference varies in time, and there are some leakage on the UL scheduling gain Synchronous hybrid mode is proposed, which combine of adaptive and non-adaptive operations –When transmission bandwidth is congested, some HARQ transmissions may be suspended for a fixed duration –When an HARQ burst is not correctly decoded, a retransmission may be adaptively assigned by Changing RU allocation to exploit the frequency diversity gain Changing the RU size to exploit the benefit of adaptive MCS

8. 8 Synchronous Hybrid UL HARQ Mode For initial transmission, BS allocates a set of transmission parameters For retransmission, the parameters may be dynamically changed if signaled The parameters are deemed unchanged if no UL_HARQ_IE is received at the transmission instance

9. 9 HARQ Acknowledgement In DL-HARQ, MS feedbacks ACK/NACK in an explicit and synchronous fashion –A feedback channel is required –Synchronous ACK offset (N) should be chosen to meet SRD requirement Data transmission latency is within 10ms In UL-HARQ, BS may –explicitly sends the ACK/NACK, or –allocates a new initial transmission with implicit AI_SN toggling

10. 10 Data Multiplexing in HARQ Packets from multiple connections can be multiplexed onto a single HARQ burst –The data multiplexing may be per-QoS basis Packets from data connection and signaling connection are not suitable to be multiplexed onto the same HARQ burst –Dedicate HARQ processes for BCH data and MAC management messages are preferable

11. 11 Text Proposal 10.x Hybrid-ARQ (HARQ) 10.x.1 Comparing of HARQ operational modes 10.x.2 Choices of DL HARQ operation 10.x.3 Choices of UL HARQ operation 10.x.4 Acknowledgement feedback for HARQ 10.x.5 Data multiplexing over HARQ