The Effect of Exerting Adequate Persistence in Collision Avoidance Protocols

Many medium-access control (MAC) protocols based on a collision-avoidance handshake between the sender and the receiver have been proposed for wireless networks. To date, however, the analysis of these protocols has assumed non-persistent strategies in sending control packets for collision avoidance. The persistent strategies discussed in the past for CSMA and CSMA/CD provide performance improvements over non-persistent access only at small traffic loads. We present and analyze a limited persistence approach to the transmission of collision-avoidance control packets. With limited persistence, a node senses the channel before sending collision-avoidance control packets. If the channel is sensed busy, the node persists sensing for an amount of time proportional to the transmission time of a control packet. The node can transmit its control packet if the channel is idle within its persistence waiting time and the channel is known to be available for transmissions; otherwise, the node backs off for a random amount of time and tries sending its control packet at the end of that time. We analyze the effect of limited persistence in sourceinitiated and receiver-initiated collision avoidance protocols by comparing their throughput with and without persistence; the analysis shows that limited persistence makes collision-avoidance protocols more efficient.