Reducing The Peak-To-Average Power Ratio By Optimizing Phase Of Subcarriers In Ofdm System Using Pso-Ga Algorithm

Orthogonal Frequency Division Multiplexing (OFDM) techniques have received a great deal of attention due to its high data rate transmission capability with high bandwidth efficiency in coping with multipath fading and have been successfully applied to WLAN. One of the shortcomings of OFDM system is the high PAPR, because of the high PAPR, OFDM signals are vulnerable to non-linear distortion when passing amplifier, resulting in the destruction of orthogonality among subcarriers, thus affecting the overall system efficiency. The thesis aim at contructing a phase sequence, by setting the phase of the subcarriers according to the phase sequence, we can reduce PAPR as soon as possible.The principle and crucial technique of OFDM is introduced at the beginning. After that, we probe into how to choose the parameters of OFDM system and show its merits and drawbacks.Then, we analyze the reason and influence of high RAPR in OFDM systems. Based on analyzing the previous works on reducing PAPR home and abroad, we simulate several methods for reducing PAPR, and a new phasing scheme using Genetic Algorithm (GA) to achieve the lower PAPR of OFDM system is introduced in this paper. After that, we analyze how GA parameters affect the PAPR.A new phasing scheme using Particle Swarm Optimization (PSO) to achieve the lower PAPR of OFDM symbols is presented in this paper based on the slow convergence of GA and sensitivity to the initial population. The new phasing scheme uses PSO to optimize the phases of the subcarriers to minimize the PAPR of OFDM symbols. Compared to other phase sequence, such as Newman,S.Narahashi and T.Nojima (S.N T.N) phase sequence, the PSO optimized sequence can achieve the lower PAPR, simulation results show that PSO converge very quickly, but the derived PAPR using PSO is bigger than GA when the subcarriers is large enough.Hence, we implement a new algorithm combining two algorithm using the quick convergence characteristics of the good performance of PSO when subcarriers is large enough, simulation results prove that the new algorithm is more effective and efficient than PSO and GA, but complexity of the proposed algorithm is slightly larger than GA.