Optimal Polynomial Backoff for IEEE 802.11 DCF

In the IEEE 802.11 protocol, the binary exponential backoff (BEB) function is implemented to handle retransmissions of packets to detect or avoid network congestion. In the recent related works, different backoff functions such as the Cubic backoff, which is a polynomial backoff (PB) function, have been shown to have better performance than the BEB function. However, it is unknown whether the Cubic backoff function achieves the maximum performance among all candidate PB functions with higher exponents. This paper aims to find the optimal PB function with the highest saturation throughput for both the Basic access and the RTS/CTS access mechanisms under various saturation conditions. We developed an analytical model based on the Markov chain model to calculate the saturation throughput for any PB function with any exponent for both access mechanisms. The results obtained using the analytical model were validated through simulations using the Network Simulator tool. Using this framework, we compared and analyzed 16 PB functions for both access mechanisms, which led to quite interesting results. They indicate that the PB with an exponent of 6 is the most optimal for the Basic access. In contrast, the PB with an exponent value of either 1 or 3 is the most optimal for the RTS/CTS access, which is dependent on the number of stations. In general, the results demonstrate that it is advantageous to choose a PB function that typically increases rapidly for the Basic access, whereas a PB function that typically increases slowly is more beneficial for the RTS/CTS access.