Performance comparison of CSMA/CA Advanced Infrared (AIr) and a new point-to-multipoint optical MAC protocol

Point-to-multipoint communication is the most common topology used in applications providing Internet service through access points. Optical communication is sensitive to shadowing and cannot efficiently use reliable carrier sensing in point-to-multipoint communication, causing serious problems since shadowed terminals behave like hidden terminals and cause collisions. Advanced Infrared (AIr) is the standard MAC protocol for wireless infrared LANs and is able to support point-to-multipoint communication even though it is not specifically designed for such communication. AIr also suffers from performance degradation as number of users varies. This paper demonstrates that the standard protocol is unable to simultaneously provide high channel use efficiency and low level access delay. The contribution of this paper is the introduction of a protocol specifically designed for point-to-multipoint communication without carrier sensing. An analytical model for performance evaluation of the proposed protocol is derived in terms of throughput and access delay. The proposed protocol is compared with AIr MAC layer in terms of delay and normalized throughput. Simulations verify both the analytical model and improved performance.