PAPR reduction and performance analysis of modulation techniques in OFDM for WLAN applications

Abstract

Orthogonal Frequency Division Multiplexing (OFDM) is a multi-carrier multiplexing technique used in many applications such as Wireless Local Area Network (WLAN), Digital Audio Broadcasting Terrestrial (DAB-T) and Long Term Evolution (LTE). It provides high efficiency and low data loss in multipath environment hence there is a need for suitable modulation technique. Different modulation techniques in OFDM give different Bit Error Rate (BER) performance and spectral efficiency. Moreover Even after modulation the output of Inverse Fast Fourier Transform (IFFT) gives large Peak Amplitude Power Ratio (PAPR) which poses a problem in amplifier efficiency and complexity in analog to digital converters. This paper aims at finding a suitable modulation scheme and efficient technique to reduce PAPR in OFDM, based on BER and bandwidth. Algorithms are implemented using MATLAB for different modulation schemes over AWGN, Rayleigh and Rician channel for WLAN application with 52 subcarriers. Random bits are generated such that there are 16 symbols, each symbol having 52 bits. In AWGN for 3db SNR 64-QAM gives BER of 0.23 and to achieve same BER, 64-PSK requires 25db SNR. Rician channel gives better performance compared to Rayleigh, where BER is 0.2965 for Rayleigh and 0.2714 for Rician thereby reducing it by 0.02. Using wavelet transform PAPR is reduced to 62% of that using FFT.