Performance analysis of multi carrier CDMA modulation system peak to average power ratio reduction techniques

Abstract

In a single carrier system, a deep noise of fading can cause the entire link to fail but within a multi-carrier system, only a small percentage of the subcarriers will be affected. The Multi-Carrier-Code Division Multiple Access modulation (MC-CDMA) system minimizes multipath effects such as Inter symbol Interference (ISI) and Inter Carrier Interference (ICI) thereby increasing the system capacity to accommodate a higher number of users. The MC-CDMA system is a very attractive technique beyond 4th and 5th generation networks for high data rate transmission over multipath fading channels. High Peak to Average Power Ratio (PAPR) of the transmitted signal is a major problem in the MC-CDMA system. It deteriorates the system performance due to large number of subcarriers and also reduces power amplifier efficiency, the battery life and resolution. Several methods are proposed for the PAPR reduction in the literature such as and#956;-law, Exponential and Linear Non Symmetrical Transform (LNST) companding techniques. These techniques are implemented for the OFDM system over AWGN channel only. A-Law generates distortion at the small signals and and#956;-law companding technique enlarges only small signals so that average power increases and causes spectral side-lobe generation. The exponential companding technique significantly reduces the PAPR but it results in increased latency and complexity. The LNST companding technique offers more bandwidth. In this research work, a few methods are proposed to reduce the PAPR, system complexity, processing delay, distortion, noise, interference and improve the BER performance and quality of the channel. The existing and proposed methods are implemented for the MC-CDMA system over AWGN, Rayleigh fading and Stanford University Interim (SUI) fading channels. newline