A Class of Non-Linear Signal Processing Scheme for PMEPR Reduction in MC-CDMA Systems

The main feature of the next-generation wireless systems will be the convergence of multi-media services such as speech, audio, video, image, and data. This implies that a future wireless terminal, by guaranteeing high speed data, will be able to connect to   different networks in order to support various services: switched traffic, IP data packets, and broadband streaming services such as video. Multicarrier code-division multiple-access (MC-CDMA) scheme is the promising candidate for future broadband wireless systems, as it provides higher flexibility, transmission rates and spectral efficiency. It combines an orthogonal frequency division multiplexing (OFDM) modulation with a code-division multiple-access (CDMA) scheme and hence exploits the advantages of   OFDM as well as CDMA.

A well-known, major drawback of conventional orthogonal frequency-division multiplexing (OFDM) transmission schemes is their strong envelope fluctuation and high peak-to-mean envelope power ratio (PMEPR), leading to power amplification difficulties. That is the OFDM signal which is the superposition of large number of modulated subcarriers, usually exhibits a high instantaneous peak value with respect to average value leading to envelope fluctuations. This is cited as a major drawback in OFDM scheme. This drawback is found in MC-CDMA too.  As MC-CDMA signals have high envelope fluctuations and a high peak-to-mean envelope power ratio (PMEPR), which leads to amplification difficulties.

In order to avoid the out-of-band  radiation levels which are inherent to nonlinear distortion, power amplifiers for OFDM transmission are required to have linear characteristics and/or a significant input back off  has to be adopted. Therefore, reduced power efficiency is the price to pay for a high bandwidth efficiency. A class of low-complexity signal-processing schemes for reduced PMEPR, spectrally efficient MC-CDMA transmission was proposed.