Robust Secure Beamforming for Integrated Satellite Terrestrial Relay Networks Coexisting with Cognitive Terrestrial User

This paper investigates the robust beamforming (BF) schemes for an integrated satellite terrestrial relay network coexisting with a cognitive terrestrial user. Owing to the unavailable line-of-sight (LOS) between satellite and intended terminal, a multi-antenna base station (BS) is used to be a relay. By assuming that only the imperfect channel state information (CSI) is available, we propose two schemes based on loose robust BF and tight robust BF schemes, respectively. Due to the non-convexity and mathematically intractability of the initial optimization problem, we develop a reformulation and transformation approach. Finally, the validity and effectiveness of the proposed schemes are confirmed.