| Nowadays the demand for high data rate in WLANs is becoming more and more urgent because of the explosive growth of wireless services. At the same time, the number of users in WLANs has become larger and larger. Multi-user Multiple Input Multiple Output(MU-MIMO), which aims to improve the performance of WLANs, is drawing more and more attention of researchers. Moreover, with the penetration of wireless networks into people's life, more and more types of traffic are emerging in an endless stream. Whether these types of traffic are supported by wireless networks is a significant aspect needed to be considered. In the above scenario, high Qo S(Quality of Service) and efficient operations at the MAC layer have become key requirements to improve the performance of networks.Considering the ever-increasing types of traffic in WLANs, this paper proposes a downlink MAC protocol for multi-user MIMO WLANs with differentiated traffic and adaptive CSI feedback. A modified CSMA/CA mechanism using new format of frame is adopted in the proposed protocol so that the throughput of the network is highly improved and the delay is decreased. The CSI information is exchanged between stations in an adaptive way by a key indication, successful ratio of packet delivery. A packet selection strategy which can guarantee a fairer Qo S is also included in the proposed protocol. The performance of the protocol is analyzed and the expressions of throughput, access delay and the probability of failed transmission of ACs are derived.Elaborate simulations are done using a MATLAB customized simulator. We examine several key indicators such as the saturated throughput, access delay, MAC queue status and fairness of transmission of ACs in the simulation. The effects of length of packets, variety of channel and number of users on the performance of network are completely considered. Simulation results show that the proposed protocol outperforms the common used protocol in terms of the above indicators. |
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