Relaying strategies are studied for two different purposes in wireless communication systems, namely cooperative diversity relaying for mitigating signal power fluctuation due to multipath fading, and two-hop relaying for alleviating signal attenuation due to path loss.;Cooperative diversity relaying is a viable strategy to gain transmit spatial diversity with single antenna transceivers. A union bound analysis is derived for the error performance of signal superposition coded cooperative diversity schemes. The numerical results show excellent agreement with computer simulations. The power allocation between the locally generated signal and the relay signal is optimized so as to minimize the error bound, circumventing the time-consuming Monte Carlo simulation adopted in literature.;A novel network coded cooperative diversity scheme is also proposed to make efficient use of the resources associated with the links between cooperating partners and those to the message destination. The main idea is to interpret---and thus decode---the network coded codeword differently at the cooperative partner and the destination. It is shown via simulation that the newly proposed scheme provides substantial coding gain over other cooperative diversity techniques, including those based on time multiplexing and signal (Euclidean space) superposition. Generalizations of network coded cooperative diversity are also considered for the adoption of graph-based LDGM codes and the case with three partner nodes.;Two hop relaying is studied as a possible method of range extension and throughput enhancement for a fixed wireless base station. Contrary to the majority of the work in this area, we consider mobile relays that are randomly placed and move in a nondeterministic manner. A queueing process model is used to capture the movements of the mobile relays that can provide feasible two-hop routing. Meaningful metrics are calculated and interpreted, providing insights into the potential benefits of mobile relays.
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