Performance of a cluster-based MAC protocol in multiuser MIMO wireless LANs

The IEEE 802.11n specifies MIMO techniques to enhance data rate in WLANs. However, using carrier sense multiple access with collision avoidance (CSMA/CA), it can support only point-to-point links. On the other hand, it is known that multiuser MIMO techniques significantly increase the spectral efficiency of a network. There are already some enhanced MIMO signal processing techniques available which enable concurrent multiuser transmissions by utilising multiuser interference cancellation techniques. Multiuser interference can also be cancelled in a distributed manner. To enhance IEEE 802.11n systems such that multiple users can transmit simultaneously, we propose a novel cluster-based CSMA/CA (CB-CSMA/CA) protocol. According to this protocol, nodes in a network are grouped in clusters such that the nodes which belong to the same cluster can transmit or receive simultaneously. In this paper, we explain the basics of the protocol and investigate throughput performance of the CB-CSMA/CA. We apply the CB-CSMA/CA to a multiuser zero-forcing relaying network, where several amplify-and-forward relays assist the communication between multiple source and destination pairs and perform distributed channel orthogonalisation. This cooperative network can be considered as a future application for next generation WLANs. As it is shown, the CB-CSMA/CA provides a significant throughput gain over point-to-point systems.