Effect of Random Assigning of Initial Contention Window Value on Performance of Persistent Relay CSMA with and without Binary Exponential Backoff Algorithm

Based on IEEE 802.11 Distributed Coordination Function (DCF), Persistent Relay Carrier Sense Multiple Access (PRCSMA) was proposed for cooperative transmission with two or more relay nodes. We propose random assigning of the initial Contention Window (CW) value of each relay node at the beginning of cooperation phase in PRCSMA and evaluate its performance with and without binary exponential baskoff (BEB) algorithm. Each relay node independently and randomly selects its initial CW value among a predefined set of integers, while in the original PRCSMA, a relay node fixes its CW value to a common given integer. Numerical results obtained from computer simulation reveal that the proposed protocol can improve the performance of the original PRCSMA. The proposed protocol makes it possible to reduce the possibility of frame collisions among relay nodes and successfully reduce the duration of cooperation. Also, the results demonstrate that the BEB algorithm is inefficient for PRCSMA, since it introduces redundant idle slots and more collision slots before the first success of frame transmission