Cooperative communications is a new communication paradigm in which different terminals in the wireless network share their

antennas and resources for distributed transmission and processing.

Recent studies have shown that cooperative communications can yield

significant performance improvement due to spatial diversity gains.

The theory of cooperative communications is however still immature

to fully understand its broader impacts on the design of future

wireless networks.

This thesis contributes to the advancement of cooperative communications by developing and analyzing cooperation protocols at different

network levels, with the

goal to provide significant improvements in signal reliability,

coverage area, network throughput, and energy efficiency with

respect to other existing alternatives.

We first propose a family of cooperative protocols for multi-node

cooperative communications. We demonstrate that full diversity gains

is achieved, which yields a significant improvement in the error

performance. Based on the derived symbol-error-rate expressions, we

characterize the optimal power allocation strategy among the relays

and the source to further improve the performance of the system.

We develop distributed relay assignment protocols, and analyze their

outage performance. We derive lower bounds on any relay-assignment

scheme to benchmark the performance of our proposed schemes. We

study the impact of our proposed protocols on increasing the

coverage area of cellular networks without increasing the transmit

power or adding extra base-stations.

We demonstrate that the gains promised by cooperation can be

leveraged to the multiple-access layer. We propose the deployment of

cognitive relays to utilize the periods of silence of the terminals

to enable cooperation. This alleviates the spectral inefficiency

problems inherent in conventional cooperation protocols. Our results

reveal significant improvements in the maximum stable throughput

region and delay performance of the network.

Finally, an analytical framework for studying the energy efficiency

of cooperation in wireless networks is presented. This framework

considers the overhead in the processing and receiving powers

introduced by cooperation. The results characterize the regions

where cooperation is more energy efficient than direct transmission.

The results also provide guidelines for the design of power

allocation strategies, relay-assignment algorithms and the selection

of the optimal number of relays to help the source.