Reserch Of Downlink Key Methods Based On802.11AC

Continuous development of wireless communication technology makes people feel the convenience of wireless communication, but the demand for big-data applications also increased. Wireless LAN, as a key way of wireless communication, also has a great mission ahead.The next generation WLAN standard802.11ac developed adding enhancements for PHY and MAC layers, the major approach to increase the network throughput is using the downlink multi-user MIMO technology, which allow multiple frames to be transmitted from the AP to different receivers simultaneously via multiple spatial streams. However, the traditional single-user MAC access scheme is not DL-MU-MIMO capable. Therefore,802.11ac Working Group brought out the concept of TXOP sharing. Some scholars improved the acknowledgment mechanism, as well as backoff procedures and retransmission protocol in order to achieve a more fair performance for the new multi-user frame type.When the network is saturated, the access categories’own data is huge, it will affect the of QoS performance if the access category choose to transmit other AC’s packets rather than its own. Therefore, how to achieve a multi-user transmission in the same access category is more considerable. This paper presents a dual competition mechanism by dividing the access categories’queue based on destination station, so that we can mitigate the hidden node problem by setting per-station weight, and also introduce a threshold feedback mechanism. Then we can select users in good channel condition in the secondary competition process to send multi-user data frames. Theoretical analysis and simulation results have proved that the proper selection of system parameters can increase the throughput performance of this multi-user MAC protocol dramatically.