| In IEEE802.11n, MIMO based adaptive beamforming is introduced to enhance signal quality. However, if the space presents a line-of-sight (LOS) and the antennas are near enough, radio frequency beamforming (RF-BF) technology is more suitable to be used. Based on traditional IEEE802.11 MAC protocol, the main work of this thesis is to reaearch how to support joint beamforming based SDMA algorithm in downlink.At the beginning, the basic architecture of IEEE802.11 is introduced, and DCF mechanism which based on CSMA/CA+BEB and the impact of amart antenna techenology to the existing MAC access mechanism are analyzed.Secondly, the enhanced techenologies of physical layer and improved measures of throughput at MAC layer of 802.11n are anylyzed.Finally, basing on DCF and refering to the the existing MAC protocols which support SDMA, a joint beamforming (MIMO-BF+RF-BF) based downlink SDMA algorithm is proposed. The algorithm resolves several key problems in achieving SDMA, such as grouping, obtaining user information, reserving channel and parral uplink signals checking. After that, Simulations and performance analysis of throughput with burst frame mechnism and aggragation frame mechenism are applied in the proposed algorithm, are done. The simulation results show that the proposed SDMA algorithm has evident advantage in improving the system throughput. |
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