A downlink and uplink collision mitigation scheme for multi-user MIMO-based WLANs through relaying

Collision mitigation is one of main research issues to improve the system performance in wireless local area networks (WLANs). Our previous study showed that our proposed multi-user multiple-input multiple-output (MIMO)-based collision mitigation scheme is very efficient for uplink throughput performance. However, for infrastructure-based WLANs, there still exists a downlink and uplink collision problem, since the multi-user MIMO-based collision mitigation scheme only can partially resolve uplink collisions. In order to mitigate this kind of collision, in this paper, we propose a relay-assisted downlink and uplink collision mitigation scheme and analyze the corresponding performance. Moreover, when it comes to the coexistence of the uplink and downlink traffic in WLANs, due to a random access nature of the WLAN systems, the access point (AP) may have less channel access opportunities than stations(STAs). Thus, we need to take into account a downlink and uplink throughput balancing problem. Numerical results show that the proposed scheme yields better throughput performance than the conventional multi-user MIMO-based collision mitigation scheme, especially when we consider the uplink and downink throughput balancing.