Transmission Techniques for Downlink Multi-Antenna MC-CDMA Systems in a Beyond-3G Context
Résumé
The combination of multiple antennas and multi-carrier code division multiple-access (MC-CDMA) is a strong candidate for the downlink of the next generation mobile communications. The study of such systems in scenarios that model real-life transmissions is an additional step towards an optimized achievement. We consider a realistic MIMO channel with two or four transmit antennas and up to two receive antennas, and channel state information (CSI) mismatches. Depending on the mobile terminal (MT) class, its number of antennas or complexity allowed, different data-rates are proposed with turbo-coding and asymptotic spectral efficiencies from 1 to 4.5 bit/s/Hz, using three algorithms developed within the European IST-MATRICE project. These algorithms can be classified according to the degree of CSI at base-station (BS): i ) Transmit space-frequency prefiltering based on constrained zero-forcing algorithm, with complete CSI at BS; ii) Transmit beamforming based on spatial correlation matrix estimation from partial CSI at BS; iii ) Orthogonal space-time block coding based on Alamouti scheme, without CSI at BS. All presented schemes require a reasonable complexity at MT, and are compatible with a single-antenna receiver. A choice between these algorithms is proposed in order to significantly improve the performance of MC-CDMA and to cover the different environments considered for the next generation cellular systems. For Beyond-3G, we propose prefiltering for indoor and pedestrian microcell environments, beamforming for suburban macrocells including highspeed train, and space-time coding for urban conditions with moderate to high speeds.