Digital beamforming technique in MC- CDMA for interference suppression

Orthogonal Frequency Division Multiplexing (OFDM) has recently gained a lot of attention and is a potential candidate for Fourth Generation (4G) wireless systems because it promises data rates up to 10 Mbps. A variation of OFDM is the Multi-Carrier CDMA (MC-CDMA) where the individual data symbols are spread using a spreading code in the frequency domain. Often times in cellular and military environments the desired signal can be buried below interference. In such conditions, the processing gain associated with the spreading cannot provide the needed interference suppression. This paper investigates multiantenna receivers for MC-CDMA systems. Frequency domain beamforming and time domain beamforming are studied in this paper through simulations. Time variations in the channel can disrupt the orthogonality between subcarriers. Minimum Mean Square Error (MMSE) detection coupled with MMSE beamforming is proposed for time varying channels. The simulation results show significant performance improvement for the proposed MC-CDMA systems in the presence of interference.