This paper presents a novel Medium Access Control (MAC) protocol for 802.11 networks in which the nodes can adopt smart antenna systems. The presented protocol is designed to satisfy two fundamental requirements: the exploitation of adaptive arrays to increase the network throughput and the backward compatibility of the novel scheme with the 802.11 MAC layer. The developed solution allows the simultaneous coexistence of multiple communications, while maintaining, for the legacy nodes, the same throughput levels achievable in the 802.11 standard. The performance and the backward compatibility of the proposed MAC protocol are tested in multipath-fading environment and considering heterogeneous scenarios, including 802.11 legacy stations together with nodes implementing the novel scheme and equipped with different antenna systems.
