Improving the MAC layer performance in ad hoc networks of nodes with heterogeneous transmit power capabilities

The performance of the IEEE 802.11 MAC protocol has been shown to degrade considerably in an ad hoc network with nodes that transmit at heterogeneous power levels. The main cause of this degradation is the potential inability of the high power nodes to hear the RTS/CTS exchanges between nodes when at least one node involved in the communication is a low power node. The propagation of the CTS message beyond the one-hop neighborhood of two communicating low power nodes was considered in our prior work in an attempt to alleviate this effect. However, this resulted in an excessive overhead and further degraded the performance at the MAC layer. In this paper we consider two techniques to reduce the overhead incurred due to the aforementioned propagation of the CTS message: (a) the use of an intelligent broadcast scheme and (b) the reservation of bandwidth for the sequential transmission of multiple data packets with a single RTS/CTS exchange (and propagation as needed). These techniques require changes only at the MAC layer. We find, by means of extensive simulations, that these techniques provide a significant improvement over the legacy IEEE 802.11 MAC protocol in the considered power heterogeneous ad hoc network. The overall throughput improves by as much as 12 % and the throughput of the low power nodes improves by up to 14 % as compared to the IEEE 802.11 MAC protocol. Furthermore, the schemes find applicability even in homogeneous networks as they reduce the number of false link failures that arise when the IEEE 802.11 MAC protocol is used, by about 20 %. We conclude that the proposed schemes together offer a simple yet effective and viable means of performing medium access control in power heterogeneous ad hoc networks.

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