Broadband MC DS-CDMA using space-time and frequency-domain spreading

Multicarrier direct-sequence code-division multiple-access (MC DS-CDMA) using space-time spreading (STS) assisted transmit diversity and frequency-domain (F-domain) spreading is investigated in the context of broadband communications over frequency-selective Rayleigh fading channels. We consider the attainable capacity extension of broadband MC DS-CDMA by using time-frequency-domain (TF-domain) spreading. The BER performance of STS assisted broadband MC DS-CDMA using binary phase shift keying (BPSK) modulation and TF-domain spreading is investigated by simulation for a range of parameter values. Both the correlation based single-user detector and the decorrelating multiuser detector are considered. Our study shows that the number of users supported by the broadband MC DS-CDMA system is determined by the product of the T-domain spreading factor and the F-domain spreading factor, while it is independent of the frequency diversity order. Furthermore, when multiuser detection assisted F-domain spreading is considered, the broadband MC DS-CDMA system is capable of supporting a substantially increased number of users, while maintaining a similar bit error ratio (BER) performance to that of the broadband MC DS-CDMA system using no F-domain spreading.