MIMO and TCP: A Case for Cross Layer Design

TCP has not fared well in wireless ad hoc networks. Even in a perfectly static network, there is the problem of throughput degradation due to the interference between flows, which becomes more severe as the nodes come close to each other. Moreover, when two or more TCP flows compete in the same collision domain, often one of the flows "Captures" the channel and blocks other flows, giving flows an unfair access to the channel. These problems have been traced in the 802.11 MAC protocol and the interaction between TCP and MAC protocol retransmission timeouts. Proposed solutions range from modifications in the 802.11 MAC protocols to the use of network layer selective drop strategies. However, none of these schemes offers full protection.