Diversity considerations for MC-CDMA systems in mobile communications

In this paper, the diversity gain achievable with MC-CDMA (multi-carrier CDMA) transmission in mobile communications is investigated. It is shown that only a certain amount of diversity is available depending on the transmission bandwidth and the transmission channel. For example, a diversity of about D=7 can be achieved for a typical mobile radio application. As a consequence, a modified MC-CDMA transmission scheme is investigated which allows the use of short spreading sequences, e.g. L=8 chips, without losing diversity. Due to the short spreading sequences maximum likelihood multi-user detection can be applied at the receiver with acceptable effort. This detection strategy achieves a bit error rate of about 1.0×10^-3 in a system with maximum number of simultaneously transmitting users at a signal-to-noise ratio of 12 dB whereas for a simple detector applying equal-gain-combining the bit error rate is about 3.0×10^-2