Medium access control protocol to address hidden terminals in MU-MIMO WLANs

We exploit the Degrees of Freedom (DoF) resulting from the deployment of multiple antennas, both at the Access Points (APs) and the clients, to address the Hidden Terminal problem in Multi User (MU) Multiple Input Multiple Output (MIMO) Wireless Local Area Networks (WLANs). This approach permits concurrent transmissions and is able to maintain a constant gain in network throughput in a Hidden Terminal scenario. We treat concurrent transmissions as an integral part of our design, so we adopt and extend the traditional Point Coordination Function (PCF) to manage them. Specifically, contention free period of the traditional PCF is used in uplink and downlink. In addition, based on DoF at APs, our MAC decides the Transmission Opportunity (TXOP) of APs/Transmitters in contrast to many traditional approaches. Besides, our MAC runs a concurrent algorithm at APs which forms an important part for the calculation of precoding vectors (based on the Zeroforcing) in the Physical Layer (PHY). Additionally, a seamless channel sounding process is designed to support the ZF precoding at the PHY which has 98.67μs signaling overhead, lower than IEEE802.11ac. Simulation studies in a typical 6-antenna AP and client scenario show that our MAC provides a remarkable constant network throughput gain of 4-5 times in comparison to traditional RTS/CTS, and a lower signaling overhead than IEEE802.11ac. Besides, our simple fairness algorithm provides a fair share in the throughput among APs, with the Jain Fairness Index greater than 90%.