1. Optional retransmission schemes for E-MBS Document Number: IEEE S802.16m-08/1138 Date Submitted: 2008-9-15 Source: Ji LI, Yonggang WANG, Zhongji HU, Bijun ZHANG, Hongwei YANGVoice: +86 21 50554550 Ext 9692 Alcatel Lucent Shanghai Bell Co., Ltd. E-mail: ji.a.li@alcatel-sbell.com.cnji.a.li@alcatel-sbell.com.cn hongwei.yang@alcatel-sbell.com.cn Venue: IEEE 802.16m-08/033: Call for Contributions and Comments on Project 802.16m System Description Document (SDD) Contributions on topic: PHY aspects of enhanced MBS Base Contribution: IEEE C802.16m-08/1138 Purpose: For 802.16m discussion, adoption into the SDD and eventual adoption for standardization 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 IEEEs name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEEs 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. Introduction Three optional retransmission schemes on EMBS can be considered –Scheme 1: when at least one MS requests a packet retransmission, retransmit this packet. –Scheme 2: when at least α MSs request a packet retransmission, retransmit this packet. –Scheme 3: when at least two MSs request two different packet retransmission, retransmit these two or more packets together via network coding

3. Network coding aided EMBS retransmission For scheme 1, 4 packets (P3, P4, P5 and P7) need to be retransmitted. For scheme 2, only P5 is retransmitted when α equals to 2. PER gets worse compared to scheme 1, but save more retransmission resource For scheme 3, randomly pair two packets for retransmission via network coding, namely and. PER is similar to scheme 1, but save much more retransmission resource. At the receiver side, network decoding is performed first, and then perform e.g. Chase combining.

4. Simulation results More overhead Less overhead Larger PER Less PER Performance gain from network coding aided scheme does not depend on MBS group size when the size is more than 30 For the case that network coding aided scheme achieves the same receive PER ratio as scheme 1 (benchmark), redundancy factor is about 1.5, then the retransmission packet ratio can be reduced by about 25%

5. Summary of the proposed solution Advantages of three proposed retransmission schemes: –Scheme 1: the most simple retransmission scheme. The conventional scheme on unicast can be adapted easily. However the retransmission rate is high under large EMBS group, and thus leads to too much retransmission overhead. –Scheme 2: also very simple to realize. Some of retransmission resource can be saved. However some MSs performance will be sacrificed. –Scheme 3: 25% retransmission resource can be saved. Suggest to adopt the text proposal in base contributions.

6. Text proposal Refer to the base contribution