MAC Protocols for Cooperative Diversity in Wireless LANs and Wireless Sensor Networks

In this paper, we present a survey of cooperative diversity-enabled Medium Access Control (MAC) protocols for Wireless LANs (WLANs) and Wireless Sensor Networks (WSNs). Cooperative diversity has emerged as a promising technique to combat fading and improve reliability in a wireless environment. In cooperative diversity protocols, neighboring nodes act as virtual multiple-input-multiple-output (VMIMO) systems, where they cooperate with the transmitter-receiver pair to deliver multiple copies of a packet to the receiver via independent fading channels. These multiple copies of the same packet can be combined at the receiver to recover the original packet, thus improving reliability by exploiting spatial diversity in the wireless channel. MAC protocols play an important part in realizing this concept by effectively coordinating transmissions between source, partner and destination nodes. Cooperative MAC protocols can also collect channel state information (CSI) between neighboring nodes and provide this information to the routing layer, where it can be exploited for partner selection. For this reason, the research community has proposed a large number of cooperative MAC protocols to realize this concept. We present an overview of these protocols and discuss their handshaking schemes, medium access schemes, results, strengths, and any observed shortcomings.