Study of Error Performance of Rotated PSK Modulation over Rayleigh Fading Channel

In this paper, we study the modulation diversity obtained by rotating the signal constellation and incorporating bit interleaving. We derive here the closed form expressions for the average bit error rate (ABER) of rotated PSK modulation over frequency non-selective slowly Rayleigh fading channel using moment generating function (MGF) based approach. Numerical results are obtained to compare the performance of conventional and rotated modulation schemes. The results show the improved performance of rotated scheme over conventional method. We also find the optimum rotation angle for rotated PSK scheme and discuss the results. I. Introduction Fading causes significant degradation of the performance of wireless digital communication systems. One way to reduce the effect of fading is to apply diversity techniques on the communication systems. Diversity can be implemented as space, time, frequency, code and modulation [1-11]. In recent years, modulation diversity obtained by applying a certain rotation to the signal constellation, is attracting much interest to the researchers [12]. Rotation diversity employs an interleaver/ de-interleaver pair to have in-phase and quadrature components of the received signals affected by independent channel fading coefficients. These fading coefficients called channel state information (CSI) are assumed to be known at the receiver. The idea of rotating signal constellation to have good performance on Gaussian and Rayleigh fading channels was presented in [2, 10]. In this paper the authors derive the closed form expression for pair-wise error probabilities for rotated phase shift keying (PSK) on a frequency non selective Rayleigh fading channel and obtain optimum rotation angles. The derivation of error probability is based on moment generating function (MGF). The rest of the paper is organized as follows: in section II the system model is described. The performance analysis and error probability are presented in section III. Section IV presents the numerical results and discussions. Finally, conclusion is drawn in section V.