Successive Optimization Transmission for High and Low SNR Stations in Wireless LAN Systems

Multiuser (MU) - multiple input multiple output (MIMO) techniques are attractive for increasing the downlink spectrum efficiency while requiring few antennas at each user station (STA). As practical precoding methods for multi-user MIMO systems, block diagonalization (BD) and successive optimization (SO) algorithms have been investigated using the metric of channel capacity. However, the throughput of SO algorithms has not been evaluated for wireless LAN systems. This paper focuses on the two-STA scenario where a close STA lies in the very near field of the access point (AP) while the distant STA lies farther from the AP; it proposes MU-MIMO transmission based on an SO algorithm that uses only the channel state information (CSI) of the close STA. The proposed method determines the transmission weight for the distant STA so as to nullify the close STA and reduces the inter-user interference at the distant STA by decreasing the transmission power for the close STA. Thus, the distant STA does not have to implement the CSI feedback function. Simulations compare zero forcing (ZF), BD, and proposed SO algorithms and confirm the conditions wherein the proposed method outperforms single user MIMO and multiuser MIMO based on ZF and BD algorithms.