1. A Multi-relay Cooperative Automatic Repeat Request Protocol in Wireless Networks Xin He and Frank Y. Li IEEE ICC 2010 Speaker: Huei-Rung Tsai

2. Outline  Introduction  Goals  System Model  MC-ARQ Protocol  Simulations  Conclusions

3. Outline  Introduction  Goals  System Model  MC-ARQ Protocol  Simulations  Conclusions

4. Introduction  Cooperative diversity has been studied during the past years  As a new trend, cooperative MAC design emerge recently  Existing cooperative MAC protocols  Require additional support from physical layer techniques  Code Division Multiple Access (CDMA)  Space-time coding  Based on CSMA/CA scheme  Cooperative retransmission implementation

5. Introduction_Related Work  Persistent Relay Carrier Sensing Multiple Access (PRCSMA)  Distributed cooperative automatic retransmission request schemes  All stations become active relays when meet certain criteria  All relays contend for channel access  Shortcoming  Long defer time  Long random back-off time  Low bandwidth efficiency

6. Goals  Proposes a Multi-relay Cooperative Automatic Repeat ReQuest protocol (MC-ARQ) MAC protocol  Cooperation on demand  Distributed relay selection scheme  Multiple relay cooperation

7. Outline  Introduction  Goals  System Model  MC-ARQ Protocol  Simulations  Conclusions

8. System Model  The network consists of  A source station S,  A destination station D  Several relay candidates R 1, R 2,..., R n  All nodes can hear each other

9. MC-ARQ Protocol  Multi-relay Selection Scheme  MC-ARQ Protocol Description  Case I: Direct Transmission Succeeds  Case II: Optimal-relay-channel Retransmission Succeeds  Case III: Multi-relay Cooperation Succeeds  Case VI: Cooperative Retransmission Fails

10. MC-ARQ Protocol  Multi-relay Selection Scheme  Nodes can decode the packets sent by S become relay candidates back-off time threshold SNR value received packet from D measured at R i

11. MC-ARQ Protocol  MC-ARQ Protocol Description  Case I: Direct Transmission Succeeds S D time DIFSbf SIFS DATA DIFS ACK DATA ACK Back-off DIFS SIFS CFC

12. MC-ARQ Protocol  MC-ARQ Protocol Description  Case II: Optimal-relay-channel Retransmission Succeeds time DIFSbfDATA S D RbRb RsRs SIFS CFC RiRi bf SIFS TbTb TsTs TiTi DATA SIFS ACK DIFS SIFSACK DATA ACK Back-off DIFS SIFS CFC

13. MC-ARQ Protocol  MC-ARQ Protocol Description  Case III: Multi-relay Cooperation Succeeds  Collision  Data corruption time S D RbRb RsRs RiRi TbTb TsTs TiTi T i -T b DATA ACK Back-off DIFS SIFS CFC T s -T b

14. MC-ARQ Protocol  MC-ARQ Protocol Description  Case VI: Cooperative Retransmission Fails

15. Outline  Introduction  Goals  System Model  MC-ARQ Protocol  Simulations  Conclusions

16. Simulations  Implement DCF, PRCSMA and MC-ARQ in Matlab  Simulation area =50 m × 50 m  Threshold SNR=2.0 dB  Retry limit=7  5 and 50 relay nodes are randomly distributed in the network

17. Simulations channel qualities

18. Simulations

21. Conclusions  Proposed a multi-relay cooperative retransmission MAC protocol which is based on DCF protocol and provides an efficient distributed relay selection scheme