In this thesis, we explore physical layer cooperative communication in order to design network layer routing algorithms that are energy efficient. We assume each node in the network is equipped with a single omnidirectional antenna and that multiple nodes are able to coordinate their transmissions in order to take advantage of spatial diversity to save energy. Specifically, we consider cooperative diversity at physical layer and multi-hop routing at network layer, and formulate minimum energy

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... uting as a joint optimization of the transmission power at the physical layer and the link selection at the network layer. We study wireless networks with both static and time-varying channels. Based on the optimal algorithms described throughout the thesis, we develop heuristic cooperative routing algorithms that find suboptimal routes, which are computationally simpler. Simulation results are also presented, which investigate the performance of optimal and heuristic routing algorithms in terms of energy efficiency and throughput.