Joint user pairing, frequency allocation, and beamforming for MIMO SC-FDMA transmission with QoS requirements

In this paper, we consider joint user pairing and frequency allocation with beamforming (BF) assuming per user Quality of Service (QoS) requirements. A single-carrier frequency-division multiple-access (SC-FDMA) transmission employing a zero-forcing (ZF) detector at the receiver is assumed. The BF filter coefficients are jointly optimized with the user pairing and frequency allocation of the users. The transmit power savings achievable by combining BF with user pairing and frequency allocation are compared to these of a constant power allocation over all subcarriers. To this end, BF filter coefficient optimization and constant power allocation are briefly revisited and novel BF filter solutions for single-input multiple-output (SIMO) and single-input single-output (SISO) transmission, respectively, are derived for SC-FDMA. Numerical results show that the transmit power can be significantly reduced with BF for suboptimum algorithms, but for optimal joint user pairing and frequency allocation the gain of BF compared to constant power allocation is negligible.