The book is intended for the readers having backgounds in principles of electronic communication systems. The book consists of six chapters starting with introduction about wireless communication system. Various fading effects in signal transmission are explained. To mitigate the effects of fading, various diversity techniques, namely, frequency, space, time, polarization and modulation are discussed. A case study by using modulation diversity is thoroughly investigated in Rayleigh and Ricean fading environments. Modulation diversity in PSK scheme is obtained by rotating the signal constellation and incorporating bit interleaving. We derive here the expressions for the average bit error rate (ABER) of rotated PSK modulation over frequency non-selective slowly fading Rayleigh and Ricean channels using moment generating function (MGF) based approach. Numerical results are obtained and compared with conventional (un-rotated) modulation schemes. We also studied the dependence of bit error rate on signal-to-noise ratio, fading parameters and the angle of rotation.