Proposal for Downlink HARQ Scheme Document Number: IEEE S802.16m-08/386 Date Submitted: 2008-05-12 Source: Wang Junhu, Sun Changyin, Wang Wenhuan E-mail: wang.junhu@zte.com.cn Qu Hongyun, Fang HuiYing ZTE Corporation Du Yinggang, Wang Yingming duyinggang@huawei.com Huawei Technologies Dong Xiaolu, Du Ying dongxiaolu@mail.ritt.com.cn CATR *<http://standards.ieee.org/faqs/affiliationFAQ.html> Venue: IEEE 802.16m-08/016r1 –Call for Contributions on Project 802.16m System Description Document (SDD); Proposed 802.16m Hybrid ARQ Base Contributions: IEEE C80216m-08/386 Purpose: Adopt proposed text in base contribution into Project 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. 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: <http://standards.ieee.org/guides/bylaws/sect6-7.html#6> and <http://standards.ieee.org/guides/opman/sect6.html#6.3>. Further information is located at <http://standards.ieee.org/board/pat/pat-material.html> and <http://standards.ieee.org/board/pat >.

HARQ Classification According to the timing of retransmission: Synchronous HARQ: Predefined TTI, implicit signaling Asynchronous HARQ: Flexible scheduling, explicit signaling According to retransmission formats: Adaptive HARQ :Transmission attributes (modulation, code rate, resource block allocation, etc ) may not be changed, no explicit signaling Non-adaptive HARQ: Transmission attributes may be changed, explicit signaling

Design Considerations 1. Overhead of HARQ in TDD Component fields related to HARQ Asynchronous Synchronous Adaptive Non-adaptive Int. Tx Re Tx Re. Tx Int Tx Resource allocation 12 Modulation and coding scheme 5 HARQ process number 3 Redundancy version 2 New Data indication 1 CID 16 Total (bits) 39 36 19 33

Design Considerations Overhead of HARQ in TDD (Cont.) Assuming the number of HARQ processes in one radio frame is M, the total transmission number is N, the overhead is illustrated in the following table. Asynchronous adaptive HARQ Asynchronous non-adaptive HARQ Synchronous adaptive HARQ Synchronous non-adaptive HARQ M, N M*N*39 M*17+M*N*19 M*N*36 33*M M=5, N=4 780 465 720 165 M=7,N=4 1092 651 1008 231 Overhead(bits)

Design Considerations 2. Delay of transmission in TDD Additional delay for retransmission has to be considered, which occurs when the radio channel is not immediately available for the necessary UL or DL transmissions. The process delay and frame alignment is supposed to be two subframe length.

Proposed Downlink HARQ Scheme Hybrid HARQ scheme in downlink for TDD system can acquire trade-off benefit between asynchronous adaptive HARQ and synchronous non-adaptive HARQ. Asynchronous HARQ is the default configuration for downlink subframes. Synchronous non-adaptive HARQ is applied to some subframes within the Maximum Allowable Synchronous HARQ Region(MASHR). synchronous HARQ subframes: Subframes within MASHR can apply synchronous non-adaptive HARQ one radio frame as RTT asynchronous subframes: apply asynchronous HARQ with adaptive mode or non-adaptive mode

Proposed Downlink HARQ Scheme(cont’d) The assignment of synchronous HARQ subframes is broadcast to all the MSs through Synchronous HARQ Subframes Bitmap. MSs can share the same synchronous subframes. The configuration of HARQ modes can be fixed or semi-static.

DL/UL=6:2 Assuming one synchronous subframe only contains one HARQ process, the retransmission number is assumed to be 4, the overhead saved by applying synchronous non-adaptive HARQ is 3*4*39=108bits. More HARQ processes contanied in one subframe, more overhead saved.

DL/UL=5:3

Proposed text to 802.16m SDD Insert the following text: X.Y HARQ X.Y.1 DL HARQ Downlink HARQ Scheme supports both asynchronous HARQ and synchronous HARQ. Asynchronous HARQ is the default configuration for downlink subframes; Synchronous non-adaptive HARQ is applied to some subframes within the Maximum Allowable Synchronous HARQ Region(MASHR). These subframes apply synchronous non-adaptive HARQ with a RTT of one radio frame, which are called synchronous HARQ subframes. And the other subframes in the downlink apply asynchronous HARQ with adaptive mode or non-adaptive mode, which are called asynchronous subframes. The assignment of synchronous HARQ subframes is broadcast to all the MSs through Synchronous HARQ Subframes Bitmap. MSs can share the same synchronous subframes. The configuration of HARQ modes can be fixed or semi-static.

Appendix :MASHR for different DL/UL ratio: The two subframes in downlink are both configured to be synchronous HARQ subframes.

DL/UL=3:5

DL/UL=4:4

DL/UL=5:3

DL/UL=6:2