ECS: An enhanced carrier sensing mechanism for wireless ad hoc networks

In wireless ad-hoc networks, whenever a node overhears a frame, the node should defer its transmission to prevent the interference with the ongoing transmission. The exact duration value by which the node should defer is contained in the frame. However, due to the wireless transmission errors and due to the fact that the carrier sensing range is normally greater than the transmission range, a frame overheard by a node may not always be interpretable and thus the node cannot get the precise duration value by which the node should defer. Therefore, an important issue is that whenever a node detects an erroneous frame, how long the node should defer for. In the current IEEE 802.11 standards, the node will always defer the transmission by a fixed duration (represented by EIFS). We show that this duration is sometimes smaller and sometimes larger than the desired period by which the transmission should be deferred, and it leads to substantial unfairness and throughput degradation. We propose an enhanced carrier sensing (ECS) scheme, which distinguishes among the type of the erroneous frames based on their lengths and defers the transmission accordingly. Simulation results show that the ECS improves the fairness as well as the throughput substantially. To the best of our knowledge, this is the first work that focuses on the carrier sensing mechanism to improve the performance of IEEE 802.11.