With the growth of wireless networks such as sensor networks and mesh
networks, the challenges of sustaining higher data rates and coverage, coupled
with requirement for high quality of services, need to be addressed. The use
of spatial diversity proves to be an attractive option due to its ability to
significantly enhance network performance without additional bandwidth
or transmission power. This thesis proposes the use of cooperative wireless
relays to improvise spatial diversity in wireless sensor networks and wireless
mesh networks. Cooperation in this context implies that the signals are
exchanged between relays for optimal performance. The network gains
realised using the proposed cooperative relays for signal forwarding are
significantly large, advocating the utilisation of cooperation amongst relays.
The work begins with proposing a minimum mean square error (MMSE)
based relaying strategy that provides improvement in bit error rate. A simplified
algorithm has been developed to calculate the roots of a polynomial equation.
Following this work, a novel signal forwarding technique based on convex
optimisation techniques is proposed which attains specific quality of services
for end users with minimal transmission power at the relays. Quantisation
of signals passed between relays has been considered in the optimisation
framework. Finally, a reduced complexity scheme together with a more
realistic algorithm incorporating per relay node power constraints is proposed.
This optimisation framework is extended to a cognitive radio environment
where relays in a secondary network forward signals without causing harmful
interferences to primary network users.
A Doctoral Thesis. Submitted in partial fulfillment of the requirements for the award of Doctor of Philosophy of Loughborough University.