Beamforming schemes for hybrid satellite-terrestrial cooperative networks

This paper studies the relay beamforming (BF) schemes for a hybrid satellite-terrestrial cooperative network (HSTCN), where a cognitive base station (CBS) with multi-antenna is used not only as a relay to assist the signal transmission between a satellite and a terrestrial primary user (PU), but also as a base station to transmit signals to multiple secondary users (SUs). Our goal is to minimize the total transmit power, while guaranteeing the quality-of-service (QoS) of all users. Specifically, by supposing that the channel state information (CSI) of both the uplink and downlink are perfectly known at the relay, we first present a non-robust BF method. Then, note that downlink CSI often contains errors, we propose two approaches based on worst-case criterion, namely, lowest bound robust BF scheme (LB-RBF) and tight bound robust BF scheme (TB-RBF), each of which relaxes the constraints and converts the complex problem to a convex optimization problem so that it can be solved by using standard numerical optimization packages. Finally, computer simulations are provided to demonstrate the performance of the three BF algorithms.