Applying opportunistic medium access and multiuser MIMO techniques in multi-channel multi-radio WLANs

Opportunistic medium access (i.e., multiuser diversity) and MIMO techniques (i.e., multiple-antenna techniques) are two effective ways to achieve a substantial throughput gain in a multiuser wireless system. In this paper, we propose a medium access control (MAC) protocol with opportunistic medium access and multiuser MIMO techniques (MAC-OMA/MM) in Multi-channel Multi-radio Wireless Local Area Networks (WLANs) to explore the utility of the joint design of these two techniques for the challenging MAC design. Specifically, in addition to utilizing multiple channels simultaneously and assigning multiple radio transceivers dynamically, multiuser MIMO technique is applied on each frequency channel to enhance the data rates. The key ideas of MAC-OMA/MM can be summarized as follows. By utilizing ATIM (Ad-hoc Traffic Indication Message) windows as in IEEE 802.11 power saving mechanism (PSM), user selection and channel negotiation are conducted between the access point (AP) and multiple users via ATIM messages on a common channel. Multiuser diversity are employed to opportunistically schedule among multiple candidate users to optimize data transmission in each negotiation. During data exchange, on each frequency channel, the AP is capable to communicate with two distinct users simultaneously both for the downlink and uplink data transmissions with the help of multiuser MIMO technique, which creates an extra dimension in spatial domain to further leverage the effect of multiuser diversity and multi-channel gains. Another contribution of this paper is to provide an analytical model to characterize the impact of our protocol on the system throughput and energy efficiency performance. Extensive simulations have been conducted and the results demonstrate that our protocol outperforms existing multi-channel MAC protocols with only minimal additional overhead and minor enhancements to the IEEE 802.11 PSM.