Peak-to-average power ratio analysis in multicode CDMA

This paper analyzes the peak-to-average power ratio (PAPR) problem in multicode-code division multiple access (MC-CDMA) systems. The statistical distribution of PAPR is derived and the achievable PAPR reduction for a given code rate is estimated. We show that the PAPR in MC-CDMA communications systems can be reduced by partial transmit sequence (PTS) and selected mapping (SLM) approaches. In PTS, the subblocks are multiplied by a set of phase factors that are optimized to minimize PAPR. In SLM, several independent data frames are generated and the data frame with the lowest PAPR is selected for transmission. We also show that the BER performance improves when the PAPR-reduced MC-CDMA signal is passed through a nonlinear amplifier. SLM reduces the error floor caused by amplifier nonlinearities and offers an SNR gain of 6 dB at 10/sup -5/ BER with an input back-off of 1 dB.