Novel MC-CDMA system using fourier duals of sparse perfect Gaussian integer sequences

Abstract

Serious multiple access interference (MAI) exists in uplink transmission of a multi-carrier code division multiple access (MC-CDMA) system in frequency-selective fading channels because orthogonality among codes cannot be restored. A novel MC-CDMA system is proposed in this paper to avoid MAI by employing Fourier duals of sparse perfect Gaussian integer sequences (SPGISs) as frequency-domain spreading codes. The SPGISs are obtained by linearly combining four base sequences or their cyclic-shift equivalents using nonzero Gaussian integer coefficients of equal magnitudes. The number of nonzero elements of SPGISs is 16 at most. The Fourier dual is the fast Fourier transform (FFT) of a SPGIS. Thus, when the Fourier duals of SPGISs are employed as frequency-domain spreading codes, the corresponding time-domain spreading codes are SPGISs. Furthermore, the modulated symbols of users should be properly allocated and the receiver architecture should be redesigned to avoid MAI. The computational complexity of the proposed MC-CDMA system is much lower than that of the traditional MC-CDMA system at the transmitter. Simulation results demonstrate both the bit error rate and peak-to-average power ratio performance of the proposed MC-CDMA system outperform those of the orthogonal frequency division multiple access, single-carrier frequency division multiple access, and the traditional MC-CDMA systems.