New Spreading Codes for MC-CDMA and OFDM Systems

Recently, there is an interest to increase capacity of multicarrier code division multiplexing (MC-CDMA) and orthogonal frequency division multiplexing (OFDM) by using spreading codes. Some spreading codes only support up to K = N+M, where M le N. In this paper, we propose a new spreading code with low cross correlation and high autocorrelation while capable of supporting K = 2N+1 users. It means that 2N+1 users or data symbols are able to be transmitted over only N subcarriers. The numerical results show that our proposed code outperforms current Pseudo- Orthogonal Carrier Interferometry (POCI) code with gain of 3dB in additive white Gaussian noise (AWGN) channel and more than 4dB in multipath fading channel at bit-error-rate (BER) level of 10-5. By the proposed code, peak-to-average power ratio (PAPR) problem as a typical problem in multicarrier system is also able to be reduced up to the PAPR level of single carrier system (with roll-of-factor=0.10).