Particle swarm optimisation with embedded/ cascaded parallel update for cooperative transmit beamforming in multiuser multiple-input multiple-output systems

The authors present a cooperative transmit beamforming (CTBF) technique for the uplink of multiuser multiple-input multiple-output (MIMO) systems. To maximise MIMO channel capacity, the proposed technique embeds a parallel update (PU) mechanism into the particle swarm optimisation (PSO) scheme to concurrently search and refine each user´s CTBF weights at every iteration in the PSO, thus named the embedded PU/PSO. Moreover, a reduced complexity and yet effective scheme is also proposed, which cascades the conventional PSO with the PU mechanism, thus called the cascaded PU/PSO. Simulation results demonstrate that the proposed CTBF schemes overcome the bit-error-rate floor phenomenon problem at higher signal-to-noise ratios, which appears in the existing works, at the expense of moderately higher complexity if the cascaded PU/PSO is used.