| The revolutionary concept of space-time coding introduced in the last decade has demonstrated that the deployment of multiple antennas at the transmitter allows for simultaneous increase in throughput and reliability because of the additional degrees of freedom offered by the spatial dimension of the wireless channel. However, the use of antenna arrays is not practical for deployment in some practical scenarios, e.g., sensor networks, due to space and power limitations. Cooperative diversity, which is also known as user cooperation, is a novel transmission paradigm which has been recently introduced to overcome these limitations by pooling together the resources of neighboring nodes. This technique exploits the broadcast nature of wireless transmission and creates a virtual (distributed) antenna array through cooperating nodes to realize spatial diversity advantages.; Cooperative diversity has recently garnered much attention, and fundamental results on the performance of cooperative networks in the presence of Rayleigh, Rician and Nakagami fading channels have been already documented. In this thesis, we consider log-normal fading channels which represent a realistic model for indoor wireless environments and wireless optical links. We present a comprehensive framework for the error rate performance of cooperative diversity over log-normal channels. Our performance analysis builds upon the derivation of pairwiser error probability and a union bound on the bit error rate (BER). Relying on the derived BER expressions, we further formulate power allocation rules for optimum performance in log-normal fading channels. We consider various cooperation protocols which effectively cover distributed MIMO (multi-input-multi-output), SIMO (single-input-multi-output) and MISO (multi-input-single-output) configurations. The proposed protocols with optimal power allocation demonstrate significant performance gains over their original versions which assume equal sharing of overall transmit power between broadcasting and relay phases and equal sharing of available power in the relaying phase between relay-to-destination and source-to-destination links. Performance gains up to 4dB at a target BER of 10-3 are observed depending on the relay geometry, deployed protocol, and fading channel strength. |
