Large code set for PAPR reduction of OFDM signals and capacity increasing in MC-CDMA system

An interest to increase the capacity of multicarrier system such as multi-carrier code division multiple access (MC-CDMA) is attracting many studies to develop spreading code for a higher user capacity. In this paper, we proposes a new large spreading code set that is capable of increasing the capacity of MC-CDMA more than twice, offering better performance due to its uniform low cross correlations and high autocorrelation properties and has an additional advantage to reduce peak power of the orthogonal frequency division multiplexing (OFDM) transmit signals. By the proposed code, peak-to-average power ratio (PAPR) of OFDM system can be reduced up to the PAPR level of single carrier system (for some roll-of-factor values). Our proposed code with code length of N, has large code number of K=2N+1 for supporting 2N+1 users, while the conventional spreading codes is up to K=N+M, where M≥N. The capacity of 2N+1 means that 2N+1 users or data symbols are able to be transmitted over only N subcarriers. Our results confirms that the proposed code outperforms current famous pseudo-orthogonal carrier interferometry (POCI) code with gain of 3dB at bit-error-rate (BER) level of 10⁻⁶ in additive white Gaussian noise (AWGN) channel and gain of more than 4dB in multipath fading channel.