Development of Collision Alleviating DCF Protocol with Efficient Backoff Algorithm for Wireless Ad hoc Networks

Ad hoc networks have been proposed for emergency communication wherein the required infrastructure is unavailable. However, a major concern in Ad hoc networks is collisions. Even in infrastructure based wireless networks, when the number of contending nodes is high, more number of frame collisions occur which leads to drastic reduction in network performance. In all IEEE 802.11 based wireless and Ad hoc networks, the backoff algorithm dynamically controls the contention window of the nodes experiencing collisions. Even though several algorithms such as Binary Exponential Backoff, Double Increment Double Decrement backoff, Exponential Increase Exponential Decrease backoff, Hybrid Backoff, Binary Negative Exponential Backoff etc. have been proposed in the literature to enhance the performance of IEEE 802.11 Distributed Coordination Function (DCF) protocol, most of them have not been developed for real- traffic scenarios. Also the packet collision rate is high using these algorithms. So, in this paper, a new Contention Window based Multiplicative Increase Decrease Backoff (CWMIDB) algorithm is proposed for the DCF protocol to alleviate the number of collisions. Furthermore, the packet transmission procedure of the DCF protocol is modified to avoid channel capture effect and this is represented with a Markov chain model. A simple mathematical model is developed for transmission probability considering the non-saturated traffic and channel errors. Results show that the proposed CWMIDB algorithm provides superior quality-of-service parameters over existing backoff algorithms.