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. (C) 2015 Elsevier GmbH. All rights reserved.