The Overlapped Carrier-Sense Multiple Access (OCSMA) Protocol

In wireless ad hoc networks with multi-hop routing, a node A may know the contents of a packet being transmitted by a neighbor B because A may have transmitted the packet to B in a previous interval. In networks not employing spread-spectrum multiple access (SSMA), a transmission by B will cause too much interference for A to receive a packet from another of its neighbors. However, if A has knowledge of the interfering packet, that information can be used to cancel the interference and allow receipt of a packet from another of A´s neighbors, provided that A can acquire the packet from B before starting to receive another packet. We consider the application of this approach in a network that uses a MAC protocol based on the IEEE 802.11 standard. We show how the 802.11 MAC protocol can be modified to allow for transmissions to be overlapped by taking advantage of noncausal knowledge of interfering signals. The resulting OCSMA protocol improves spatial reuse and end-to-end throughput in several scenarios.