The rapidly increasing demands in the area of wireless communications have encouraged the researchers to modify the existing techniques, propose new diversity techniques, and evaluate the system performance of these techniques under different channel impairment scenarios. This book considers various communication system models and derives expressions for several performance metrics under different channel conditions. This book is partitioned mainly into four parts. The first part analyzes the performance of wireless communication systems under small-scale multipath fading without diversity techniques considering one of the most generalized fading models. The second part considers the space diversity techniques to mitigate the fading effect, and derives different performance metrics. While the third part considers the cooperative communication systems, as virtual antennas, to enhance the transmission quality. Finally, the last part of this book deals with the security issues in wireless communication systems proposing an encryption algorithm.