Advanced CDMA transmission concepts for 3G and 4G mobile radio communications

CDMA techniques are widely used in 3G mobile radio systems, and this can be also expected for the fourth generation of mobile radio communications. CDMA offers the advantages of frequency diversity, interferer diversity and flexibility. Unfortunately, these advantages go along with the problem of signal separation typical of CDMA, which hampers spectral efficiency and capacity. In the paper some possibilities to mitigate this problem and to thus enhance CDMA performance are shown. These possibilities include CDMA signal separation based on the turbo principle, the application of multi-element antennas at the base stations in combination with nonlinear signal processing, and an alternative to conventional cellular structures exploiting the spatial separation of the mobile terminals.