Medium Access Control for Wireless Sensor Networks with Directional Antennas

This thesis explores Medium Access Control (MAC) protocol design for wireless sensor networks (WSNs) with directional antennas. In particular, this work focuses on ways of realistically improving the network performance and quality of service (QoS) with directional antennas. MAC protocols play a vital role in making effective use of a multi-access channel as they govern the achievable channel utilisation efficiency and QoS. Conventional MAC protocols incorporating different multiple channel access techniques were designed for wireless sensor nodes equipped with omni-directional antennas. In order to exploit the potential benefits of directional antennas, modifications and novel designs are required to provide the enhanced performance. Significant advances in the effectiveness of directional MAC (DMAC) protocols are described, with the enhancements to the channel utilisation shown. These DMAC protocols are able to offer good throughput performance but only with a number of simplifying assumptions and they are limited by the directional antenna pattern. The performance of the DMAC protocols proposed in this thesis are mathematically analysed and evaluated via simulation models with different scenarios. These involve WSNs with various number of sensor nodes, and in some cases with mobile sensor nodes with different speeds, all sharing a single frequency channel. While in most instances, DMAC protocols assume idealised directional antenna patterns, this thesis presents a novel directional hub MAC protocol that employs realistic directional antennas and power control strategy in order to deliver significantly enhanced performance. An analytical technique is introduced to evaluate the performance of DMAC protocols incorporating a hub node with multiple directional antennas, which is used in combination with simulation to investigate the effects of antenna pattern overlap. While the results show that directional antennas with a suitable MAC protocol can provide enhanced performance, the antenna overlap ratio has a significant impact on the potential improvements. Furthermore, a hybrid DMAC protocol is proposed. It combines realistic directional antennas and adapted multiple channel access techniques in order to significantly improve the performance and QoS, and thus, increase their adaptability in channelling WSN environments.