Cooperative WLAN Protocols for Multimedia Communication

The IEEE 802.11n specifies MIMO techniques to enhance data rate in WLANs. However, it can support only MIMO point-to-point links. On the other hand, it is known that multiuser MIMO techniques can significantly increase the spectral efficiency of networks. In this thesis, to realise MIMO spatial multiplexing gain in networks with single-antenna stations and to enhance network performance, cooperative protocols are considered with respect to both PHY and MAC layers. In order to utilise cooperative signalling in WLANs, the MAC protocol has to be modified. The existing CSMA/CA-based MAC avoids any interference and supports only point-to-point links. To enhance IEEE 802.11n system in a way that multiple users can transmit simultaneously, a novel cluster-based CSMA/CA has been proposed in this work. Our study has shown that the CB-CSMA/CA can significantly improve throughput and reduce delay in different types of infrastructure or ad hoc networks with single-hop or two-hop links. Furthermore, we have shown that throughput of CB-CSMA/CA can further be improved by taking cross-layer parameters into account, when forming the clusters or defining the backoff models.