MCA-BEB algorithm to improve fairness in multiple access for optical wireless LAN

Abstract

Wireless communications cannot know the state of medium. Thus, the retransmission strategy is the very important and medium access control is critical issue in wireless communications. CSMA/CA uses the well-known BEB algorithm for retransmission. Capture effect exists in the conventional BEB algorithm as a problem; the pre-emptive terminal has a higher likelihood to send its data successively. This induces the wasteful attempts and delays. Most of all, capture effect doesn``t give the multiple access fair opportunity. In this thesis, we propose a MCA-BEB(Modified Capture Avoidance Binary Exponential Backoff) algorithm to improve multiple access fairness for Optical Wireless LAN. Conventional backoff algorithm used for multiple access in wired and wireless LAN doesn``t give the fair opportunity to transmit data. MCA-BEB algorithm, which can improve the fairness of multiple access, uses "Attempt History Variable". AHV is the sum of last success attempts and each terminal``s attempting history with different weighting factors. This eliminates wasteful attempts and lowers the likelihood that pre-emptive terminal sends its data successively. Simulation results reveal that MCA-BEB algorithm improves fairness of multiple access 120% ~ 200% compared with conventional BEB algorithm.