Multi-user beamforming for sum-rate maximization in frequency-selective MIMO MC-CDMA systems

In this paper we propose novel time domain beamforming techniques for nulling multi-user interference in frequency-selective multiple-input multiple-output (MIMO) multi-carrier code division multiple access (MC-CDMA) systems. First a multi-path multi-carrier decorrelator (MMD) receiver is derived, which transforms a frequency selective MIMO MC-CDMA system to an equivalent flat fading multi-user MIMO system of appropriate dimension. Based on the MMD receiver, we propose a joint path and antenna selection based block diagonalization scheme to cancel the multiuser interference. Further, a successive constrained eigenbeamforming (SCEB) algorithm is developed which maximizes the signal to interference-plus-noise ratio (SINR) at each user. The proposed SCEB beamforming technique can support a higher number of users compared to block diagonalization techniques making it ideal to increase the spectral efficiency of the system.