Constrained Priority Countdown Freezing - A Collision Memory Avoidance Algorithm

Collision memory in IEEE 802.11 Distributed Coordination Function (DCF) has been detected. The collision memory can increase the physical collision rate and this effect is inherent to any DCF type of countdown. In this paper, we introduce a collision memory avoidance algorithm, called Constrained Priority Countdown Freezing (CPCF). The CPCF can completely or partially remove collision memory depending on how many priority freezing steps are allowed. Since DCF’s well known countdown decreases the contention overhead, but increases collision memory effect, the solution is to find the compromise between the two, in order to achieve good performance in both low and high load network conditions. The CPCF achieves this by limiting the countdown process, and thus reducing the collision memory, while still producing significant countdown effect.