An Adaptive MAC Protocol for Wireless LANs Under Error-Prone Environment

The impact of conditional collision probability (p\-cl) on saturation throughput of 802.11 DCF (distributed coordination function) under error-prone channel is investigated through mathematical modeling. The study shows that under a certain network configuration in the basic CSMA/CA mode there exists an optimal p\-cl to maximize the throughput, and the optimal p\-cl is approximately independent of the number of active nodes, the bit error rate and the length of the packet payload (100—4000B). Based on the stated results, combining contention window and frame length adjustment methods, a channel adaptive protocol is proposed to enhance the performance of 802.11 DCF in case of error-prone environment. The contention window adjustment method adjusts the initial contention window to make p\-cl reach its optimum; moreover, the frame length adjustment scheme determines the optimal frame length according to channel condition. The analytical model is implemented based on NS-2 to evaluate the performance of the proposed protocol and the impact of channel condition. The results show that, as compared with legacy 802.11 DCF, the proposed protocol not only significantly improves the throughput in error-prone conditions, but also achieves the self-adapt character with the variation of channel condition and the node number.