A new contention based adaptive MAC protocol based on the renewal access protocol

Efficient sharing of the network spectrum is required to meet the exponentially growing demand of wireless communications, and the role of the MAC protocols has been becoming more important. In this regard, a novel MAC protocol called the Renewal Access Protocol (RAP) was recently proposed. It was shown that the RAP achieves optimal throughput, high short-term fairness, and near-optimal delay performances when the number of nodes in the network is known to all nodes. However, it is not easy for a node to know the number of nodes in the network and the number of nodes is time varying. So we propose an adaptive version of the RAP called the Adaptive Renewal Access Protocol (A-RAP) in this paper. A node equipped with the A-RAP estimates the number of nodes utilizing two dimensional Backoff Selection State (BSS), the Estimated Number of Nodes (ENN) and phase, based on its transmission results. For an efficient design of the A-RAP, we analyze the performance of the A-RAP and carefully determine two key parameters, the adjustment probabilities and the numbers of phases. Numerical and simulation results are provided to verify that the proposed A-RAP achieves good throughput and short-term fairness as the RAP. The results also show that the A-RAP achieves better short-term fairness than other MAC protocols proposed in the open literature.