1. Chang-Yeong Oh and Tae-Jin Lee JOURNAL OF COMMUNICATIONS AND NETWORKS, VOL. 13, NO. 5, OCTOBER 2011 Cooperative MAC Protocol Using Active Relays for Multi-Rate WLANs

2. Outline Introduction Goals AR-CMAC protocol Simulation Conclusion

3. Introduction The cooperative communication approach effective uses of spatial diversity in wireless WLANs Improved throughput Delay performance Previous papers have not considered the helper’s transmission require.

4. Introduction Physical layer Virtual multiple-input multiple-output (MIMO) system MAC or network layer IEEE 802.11a/b/g support multi-rate transmissions Total network throughput is more influenced by the stations with lower rates in multi-rate WLANs.

5. Introduction IEEE 802.11a/b/g support multi-rate transmissions Different MAC service data unit size MSDU adaptation (DMA) Different initial contention window size adaptation (DICWA) 10 M 5 M (DMA) Enhance the utilization of channel time of the stations with higher rates (DICWA) higher rates lower rates 256  0 32  0 higher-rate stations will have more frequent chances to hold channel

6. Goals We propose a active relay-based cooperative MAC (AR-CMAC) protocol Consider the compensation mechanism for the Relay stations by providing extra transmission chances Solve the performance degradation problem Increase channel utilization

7. Network Model A multi-rate network model with IEEE 802.11b

8. Overview SourceActive Relay Destination, AP Data1 Data2 Data1Data2

9. AR-CMAC AR-CMAC supports three modes according to the transmission type of the source’s data (i) Direct Transmission (DT)-(a) (ii) Direct Transmission (DT)-(b) (iii) Cooperative Transmission (CT)

10. AR-CMAC Direct transmission (DT)-(a) mode If a source can transmit with the highest rate, its own data need not be transmitted with the help of a cooperative relay.

11. AR-CMAC Direct transmission (DT)-(b) mode The station does not have appropriate relays for cooperation.

12. AR-CMAC Cooperative transmission (CT) mode Candidate relays Must be within the effective transmission range from a source and a destination Have higher rates than that of the source.

13. AR-CMAC Cooperative transmission (CT) mode Data format rCTS format

14. AR-CMAC Cooperative transmission (CT) mode If W rCTS is too large, there may be waste of time If W rCTS is too small, intensive competition may cause collisions No candidate relays or collision of rCTSs, i.e., DT-(b) mode W rCTS

15. AR-CMAC Cases with No ACKs

16. AR-CMAC Hidden node problem SourceActive Relay Destination, AP Data1 Data2 Data1 Data2 ACK1 ACK2 Others

17. Simulation Simulation parameters

18. Simulation

22. Conclusion This paper proposed a new cooperative MAC protocol for multi-rate WLANs: AR-CMAC High-rate relay stations help to reduce the time required to send the data of low-rate source stations Better throughput performance Enhance the throughput of AR-CMAC by combining DMA and DICWA