Novel Comb Spectrum CDMA System Using Perfect Gaussian Integer Sequences

Multi-carrier code division multiple access (MC- CDMA) systems experience serious multiple access interference in uplink transmission since the orthogonality among codes is destroyed by the frequency-selective fading channels. The comb- spectrum (CS) CDMA system was proposed to overcome this drawback by orthogonally assigning subcarriers to various users. However, the CS-CDMA system has three main drawbacks: 1) the numbers of nonzero elements of various frequency-domain CS codes are different, 2) the nonzero elements of the frequency-domain CS codes have unequal magnitude, and 3) the computational complexity of the transmitter and receiver is extremely high. This study proposes a novel CS-CDMA system, wherein the perfect Gaussian integer sequences are adopted as the frequency-domain CS codes. The proposed CS-CDMA system inherits all the advantages of the traditional CS-CDMA system, and all three drawbacks are overcome. Simulation experiments demonstrate that the improvements of the proposed scheme for quadrature phase-shift keying and 16-quadrature amplitude modulation are approximately 7.5 dB and 4.5 dB, respectively.