Research On MU-MIMO Beamforming In New Generation WLAN

As the standard of the new generation wireless local area network (WLAN), IEEE 802.11ac applies the technology of multi-user multiple-input multiple-output (MU-MIMO) firstly, and uses the technology of beamforming for precoding to suppress the interference between users, making more users can communicate in the same time and frequency resources. However, restricted by the number of base station antennas, the system supports limited users, thus needing user selection algorithm to choose users for beamforming. This paper goes in-depth research on user selection algorithms when the number of users in the system more than the number of users the base station supported based on multi-user beamforming algorithm.This paper first studies the MIMO diversity and multiplexing technology in wireless local area network, analyzes the scheme of Alamouti space-time coding and contrast several system detection methods of V-BLAST; Next study the characteristic of the MIMO channel in WLAN and introduce the TGac channel of 802.11ac; Meanwhile analyze the system capacity of single user and multi-user MIMO.Then, the paper studies the beamforming technology of single user and multi-user in 802.11ac. For example analyze the singular value decomposition(SVD) beamforming algorithm of single user in detail and study zero-forcing(ZF) beamforming、block diagonalization(BD) beamforming and zero forcing dirty paper coding(ZFDPC) of multi-user. And give the simulation of their performance.Finally, the paper goes further study on MIMO user selection algorithms in 802.11ac. Firstly, study multi-user selection algorithms in MIMO, such as semi-orthogonal user selection、minimum of the frobenius norm of the pseudo-inverse、proportional fair scheduling and greedy user selection; Then, research a greedy user selection with low complexity based on the serial zero forced beamforming(SZF-LcGUS), which use channel correlation to reduce the complexity of the algorithm and guarantee the system throughput at the same time. But it can not ensure equity. Based on this situation the paper proposes an improved Greedy User Selection with equity which combing proportional fair scheduling and SZF-LcGUS Simulation result show that the improved algorithm not only can achieve higher throughput, but also can guarantee the equity between users.