In this paper, we propose a novel asynchronous Media Access Control (MAC) protocol, Opportunistic MAC (OMAC), for Multiple Input Multiple Output (MIMO) ad-hoc networks. The proposed solution is based on closed loop minimal feedback antenna selection diversity scheme and optimum receive combining. The use of antenna selection diversity contributes to a reduction in the feedback information and the effective interference produced. To utilize the spatial degrees of freedom offered by MIMO, we propose the use of a novel rank based metric to obtain interference information as well as to enable multiple simultaneous transmissions and to make MAC decisions. The rank of the interference matrix, (R{sub}I) is used as a metric. We present the performance of the proposed solution from the throughput perspective for a single hop ad-hoc wireless network. Through analysis and simulation, we found that the proposed protocol significantly outperforms 802.11 MIMO and it obtained as high spatial degree of freedom utilization as 85%.
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