Combined phase and code optimization for PAPR reduction in M-ary CI/MC-CDMA system

Abstract

This paper proposes a high capacity M-ary modulation based carrier interferometry/multicarrier code division multiple access (CI/MC-CDMA) system with reduced peak-to-average power ratio (PAPR). The new method simultaneously supports high and low data rate transmission. The implementation is done by allocating all sub-carriers to the users who transmit high data rate and alternate odd and even subcarriers are assigned to the other sets of users transmitting at low data rate. The usage of alternate sub-carriers suggests to split CI codes in odd and even parts leading to an increase in capacity. PAPR reduction is achieved through the combined use of (1) phase shift of subcarriers, odd CI code using odd sub-carriers by an amount of −π/2M, odd CI using even sub-carriers by an amount of −π/2M −π/2, even CI code using odd sub-carriers by −π/2M −π, and even CI code using even subcarriers by −π/2M −3π/2, all measured with respect to orthogonal codes supporting high data rate transmission and (2) left and right cyclic shift of the code pattern by an amount of one to three chips. Trellis coding is then applied for further improvement in PAPR values. Complementary cumulative distribution function (CCDF) for PAPR values are reported for different values of M through extensive simulation results.