Preemptive toplogy control solutions consist of designing WSN layouts that optimise coverage, WSN lifetime and/or economic gain in number of WSN nodes used. By revealing optimal ways of connecting sensors through resolution of an optimal placement problem, layout optimisation studies such as those provided in [11-14] and [15] may also reduce energy consumption. While [11, 12] are based on a heuristic solution using multi-objective evolutionary optimisation, the placement problem in [13] is formulated as an non-linear optimisation problem solved using a self-incremental algorithm that adds nodes one-at-a-time into the network in the most efficient identified way.

In [14], the optimal placement of static sensors in a network is used to help an agent navigate in an area by us
A Media Access Control (MAC) protocol is designed for coordinating access to shared channel(s) among multiple users in order to avoid collisions and achieve efficient use of the medium. It has been shown that the IEEE 802.11 MAC [1], although widely adopted, suffers low throughput performance in the multi-hop wireless network environment [2�C4]. In the IEEE 802.11 MAC, the nodes around a transmitter and the target receiver are regarded as potentially interfering nodes. The virtual carrier sensing mechanism is used to prevent these nodes from initiating their transmissions. However, there are scenarios that some of the neighboring nodes’ transmissions will not cause collision with, and will not be interfered by the ongoing transmission, but are still forbidden to transmit.

Such nodes are termed ��exposed terminals�� and in such situations the channel spectrum is not efficiently utilized. It has attracted considerable interest to solve or alleviate the exposed terminal problem, since the IEEE 802.11 MAC is becoming the most popular MAC protocol for single- and multi-hop wireless networks.There have been considerable research efforts on this aspect. For example, MAC protocols requiring additional Drug_discovery hardware or PHY capacities are shown to be helpful [5, 6]. In addition, there have been proposals on tuning the carrier sensing range [7�C9], controlling the transmit power [10�C12], and modifying the behavior of the IEEE 802.11 MAC [13�C15]. However, these studies are conducted assuming deterministic wireless propagation models, such as the free-space propagation model or the two-ray ground reflection model [16].

In these models, path loss is determined by the distance between the transmitter and receiver deterministically. However, due to obstacles, multi-path propagation, and mobility, randomness such as shadowing or fading exists in most wireless networks and should be considered in MAC protocol design.In a wireless network environment, factors such as reflection, diffraction, and scattering affect the propagation of radio waves.