Improving the efficiency and fairness of time-spread multiple-access (TSMA) using adaptive p-persistency

Because of partially connected dynamic network topology and the hidden terminal problems in multihop packet radio network, contention among stations is not homogenous and any scheduling decision made at a station will have impact on its neighbors. In this paper, we discuss how to calculate the channel access probability, p, dynamically in wireless medium using a distributed approach. The goal of the proposed scheduling algorithm is to provide a simple and effective solution for the fairness problem without sacrificing the system throughput. In the proposed scheduling algorithm, link access probabilities can be calculated at each node by monitoring the collisions in the previous frames withoug using a centralized coordinator. Each host estimates traffic intensity for each transmission slot and uses the estimated traffic intensity value and the number of collisions-free slots to calculate the channel access probability. Our simulation results show that the fairness problem can be very severe with the original TSMA algorithm when the load of the channel is high, and our new scheduling algorithm can achieve far better fairness. The proposed algorithm improves not only the fairness but also the system throughput by reducing the number of collisions.