Research On The Peak-to-Average Power Ratio For Wireless Communication Systems Using OFDM

Orthogonal Frequency Division Multiplexing (OFDM) is an effective transmission scheme to cope with many impairments, such as cochannel interference, serve multipath fading and impulsive parasitic noise. However, a major drawback of OFDM signals is their high Peak-to-Average Power Ratio (PAPR), which makes the intermodulation distortion occurs due to the nonlinearity of the high power amplifier. The distortion severely deteriorates the performance of the OFDM systems. So, how to effectively reduce the PAPR of input OFDM signal of the amplifier is the important issue, which needs to be addressed in OFDM systems. According the problems mentioned above, this dissertation focuses on the reducing the PAPR algorithms design for OFDM systems.This dissertation formulates the PAPR problem for OFDM and proposes three new methods for PAPR reduction. These methods prevent distortions by reducing the PAPR on the discrete-time signals prior to any nonlinear device such a DAC or a power amplifier.First, in the dissertation, the structure reduces the PAPR by applying a new nonlinear companding transform scheme. By exploiting statistical distribution of transmitted OFDM signals, the proposed nonlinear companding transform scheme effectively reduces the PAPR by compressing the peak signals and expanding the small signals, while maintaining the average power unchanged by properly choosing the transform parameters. The fact that the proposed companding scheme is described by a single valued function based on error function allows to be transformed before amplification and to be restored the signals at the receiver. The proposed companding scheme can be applicable with any modulation format and subcarriers. The simulation results confirm that the suggested companding exhibits a good ability to reduce PAPR and a good BER performance with a Solid State Power Amplifier (SSPA) and in an Additive White Gaussian Noise (AWGN) channel.Secondly, we present a low-complexity reducing the PAPR scheme for OFDM systems termed Complement Block Coding (CBC). The CBC scheme is based on utilizing the complement bits that are added to the original information bits, which can avoid the subcarriers produce the same phase shift or the alternative phase shift. CBC can effectively reduce the PAPR of OFDM systems with arbitrary frame size N and the coding rate R ≤ (N-k)/N, where k is a positive integer and k ≤ N. The performance results, which obtained with CBC are given and compared with that of some well-known schemes, show that at the same coding rate 3/4, the CBC can achieve almost the same performance as these well-known schemes, but that the same performance can be obtained with higher coding rate by using CBC. The simulation results show that the CBC can provide error detection and correction error. We also propose a Modified Complement Block Coding (MCBC) scheme based on the CBC and subblock. And last we show the idea of the CBC combined error correction coding.Finally, some new phasing schemes are proposed to reduce the PAPR for OFDM signals. The first technique named the Phase Recursive Optimizing Method (PROM) gives a new quadratic polynomial to obtain the phase angle of each subcarrier. It is very interesting that PROM is effective for reducing the PAPR with less calculated quantities and explicit side information. Based on the PROM, we propose the Seriate Phase Recursive Optimizing Method (SPROM) for reducing the continuous time PAPR in OFDM systems. The third proposed scheme named Simulated Annealing Phase Optimization Calculating (SA_POC) uses the simulated annealing algorithm to optimize the optimization phase angle of each subcarrier. Some previous published schemes have focused on obtaining a minimization of the PAPR by using a mathematical approximation for the envelop of the OFDM signals, which resulted in good solution, but does not approach the lowest PAPR possible. SA_POC performs a global searching algorithm to find the lowest PAPR phase sequences, and SA_POC does not depend on the values of the initial solutions and can s...