Collision avoidance and resolution multiple access (CARMA)

Abstract

The collision avoidance and resolution multiple access (CARMA) protocol is presented and analyzed. CARMA uses a collision avoidance handshake in which the sender and receiver exchange a request to send (RTS) and a clear to send (CTS) before the sender transmits any data. CARMA is based on carrier sensing, together with collision resolution based on a deterministic tree-splitting algorithm. For analytical purposes, an upper bound is derived for the average number of steps required to resolve collisions of RTSs using the tree-splitting algorithm. This bound is then applied to the computation of the average channel utilization in a fully connected network with a large number of stations. Under light-load conditions, CARMA achieves the same average throughput as multiple access protocols based on RTS/CTS exchange and carrier sensing. It is also shown that, as the arrival rate of RTSs increases, the throughput achieved by CARMA is close to the maximum throughput that any protocol based on collision avoidance (i.e., RTS/CTS exchange) can achieve if the control packets used to acquire the floor are much smaller than the data packet trains sent by the stations. Simulation results validate the simplifying approximations made in the analytical model. Our analysis results indicate that collision resolution makes floor acquisition multiple access much more effective.