A new code allocation algorithm for multirate CI/MC-CDMA system

Abstract

This paper introduces an efficient code allocation algorithm for multirate carrier interferometry/multicarrier code division multiple access (CI/CM-CDMA) system through simultaneous support of high and low data rate transmission. High priority users are assigned all subcarriers to transmit at high data rate, while low data rate users are gradually increased through alternate allocation of odd-even subcarriers. The cross-correlation between different code pattern is reduced through phase shift of even (odd) CI code using odd (even) sub-carriers by an amount of π/2 and odd (even) CI code using odd (even) sub-carriers by −π/2, all measured with respect to orthogonal CI codes assigned to support high data rate transmission. This algorithm ensures addition of extra users with improved bit error rate (BER) performance by reducing of multiple access interference (MAI). Simulation results show that new code allocation scheme allows more users at a low signal-to-noise ratio (SNR) compared to scheme proposed in [9]. Simulation results also show that new code allocation reduces PAPR by 1.9 dB for 3N system compared to fixed allocation [9].