Ground based and onboard based beamforming for hybrid terrestrial-satellite mobile system

Adaptive beamforming in terrestrial networks is viable due to relaxed complexity constraints. In case of satellite payload, adaptive beamforming is currently not cost effective due to higher onboard complexity requirements, power consumption issues and associated costs. In our earlier proposed Hybrid Terrestrial-Satellite Mobile System (HTSMS) incorporating frequency reuse, Onboard Based Beam-Forming (OBBF) is employed to mitigate Co-Channel Interference (CCI) for a Orthogonal Frequency Division Multiple Access (OFDM) system. The less complex solution is to opt for Ground Based Beam-Forming (GBBF) saving valuable onboard resources. Despite the benefits of GBBF, high feeder link bandwidth is required to support uplink and downlink transmissions. Moreover with GBBF, the satellite payload complexity is a sensitive function of the feed signals transmitted through gateway uplinks and downlinks. Furthermore, performance of GBBF is highly sensitive to the gateway calibration system which must compensate instabilities induced due to payload/gateway component changes over temperature and life as well as propagation amplitude and phase dispersion effects. Hence the choice of beamforming not only depends on complexity but also on performance. In this paper we employ ground based and onboard based beamforming solutions for a Bit Interleaved Coded Modulation-OFDM (BICM-OFDM) in our proposed HTSMS. We also propose a semi static hybrid space/ground beamforming and show that it is a far less complex solution compared to onboard adaptive beamforming. We then investigate the applicability of onboard and ground based approaches and quantify their performance advantages for the HTSMS case in AWGN channel scenario.