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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
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Outline Introduction Goals AR-CMAC protocol Simulation Conclusion
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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.
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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.
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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
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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
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Network Model A multi-rate network model with IEEE 802.11b
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Overview SourceActive Relay Destination, AP Data1 Data2 Data1Data2
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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)
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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.
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AR-CMAC Direct transmission (DT)-(b) mode The station does not have appropriate relays for cooperation.
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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.
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AR-CMAC Cooperative transmission (CT) mode Data format rCTS format
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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
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AR-CMAC Cases with No ACKs
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AR-CMAC Hidden node problem SourceActive Relay Destination, AP Data1 Data2 Data1 Data2 ACK1 ACK2 Others
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Simulation Simulation parameters
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Simulation
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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
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