An OFDM-CDMA scheme using orthogonal code multiplexing and its parallel interference cancellation receiver

We propose a novel orthogonal frequency division multiplexing/code division multiple access (OFDM-CDMA) scheme that can support effectively multiple users with variable transmission rates over frequency-selective fading channels. It uses orthogonal code multiplexing (OCM) to support variable rate transmission and pseudonoise (PN) code scrambling for user separation. Each modulation symbol is spread over all the effective subcarriers using a distinct orthogonal multiplexing code to exploit frequency diversity fully. In multiple access environments, the use of interference suppression techniques is strongly required to maximize resource utilization. Hence, we use a parallel interference cancellation (PIC) receiver in terms of its complexity and performance. In addition, we set the reference value for the signal-to-interference-plus-noise ratio (SINR), which can give the maximum channel capacity through the use of the PIC receiver. Through simulation results in both additive white Gaussian noise (AWGN) and multipath fading channels, we analyze the performance and capacity of the proposed system according to channel environments.