Design and development of MAC and routing protocols for cognitive radio based wireless mesh networks

Abstract

Wireless Mesh Networks (WMNs) are communications networks made up of radio nodes organized in a mesh topology. It is envisaged that WMNs can provide broadband wireless access and replace traditional wired based communications infrastructure in the near future. Correspondingly, WMNs are also expected to support delay sensitive and/or high bandwidth real-time streaming multimedia applications such as VoIP and video conferencing. However, Quality-of-Service (QoS) provisioning in WMNs is very challenging due to various factors. These include physical layer factors such as fading or attenuation of a transmitted signal over the wireless medium which results in a loss of signal power at the receiver. Other factors include the dynamical changing of topology, capacity limitations, link variability and multi-hop communications. On the network layer, many existing dynamic routing protocols select paths based on only one criteria (shortest hops, delay etc), which do not take into account topology, interference or traffic pattern. This causes the traffic to flow through nodes that experience high interference and thus increases the occurrences of dropped packets and retransmissions. Despite ongoing research efforts, one key limitation to the performance of the WMNs is the interfering nature of wireless transmissions which degrades the network capacity. This is made worse, especially for the case of devices operating in the unlicensed spectrum where it is becoming increasingly crowded due to the proliferation of diverse wireless communication systems. The overcrowding of the unlicensed spectrum aggravates the interference issues which further reduces the performances of wireless devices. The interference is further exacerbated in WMNs where traffic takes multiple hops to reach the destination.