Linear transmit-receive beamforming design for MIMO relay broadcast channels

This paper studies the relay broadcast channel with one source, one decode-and-forward half-duplex relay, and two destinations, with one of them receiving data directly from the source and the other being cooperatively served by the source and the relay. Such scenario models a situation that may arise in practice in the downlink channel of a single cell in cellular systems. We derive the achievable sum rate of the proposed scheme in the form of a non-convex optimization problem that is hard to solve. Thus, we propose a low-complexity, suboptimal solution that employs a linear transmit-receive beamforming scheme based on block diagonalization and interference alignment with resource allocation. The numerical results confirm that the proposed scheme achieves a higher rate than that of the reference schemes in a symmetric scenario, with the channel between source and one of the destinations being relatively poor.