Spatial Filtering for Underlay Cognitive SatComs

Herein, we study an underlay beamforming technique for the
coexistence scenario of satellite and terrestrial networks with the satel-
lite return link as primary and the terrestrial uplink as secondary. Since
satellite terminals are unique in that they always point towards the geo-
stationary satellite, interference received by the terrestrial Base Station
(BS) is concentrated in a specific angular sector. The priori knowledge
that all the geostationary satellite terminals are facing south for the
European coverage can be used in designing a beamformer at the ter-
restrial BS. Based on this concept, we propose a receive beamformer at
the BS to maximize the Signal to Interference plus Noise Ratio (SINR)
towards the desired user and to mitigate the interference coming from
the interfering satellite terminals. The performances of Minimum Vari-
ance Distortionless (MVDR) and Linear Constrained Minimum Variance
(LCMV) beamformers are compared for our considered scenario. It is
shown that LCMV beamformer is better suited in rejecting interference
even in case of Direction of Arrival (DoA) uncertainty of interfering satel-
lite terminals as long as DoA range of the interfering sector is known to
the beamformer. Furthermore, it is noted that MVDR beamformer is
suitable for a large number of interferers.