Joint Precoding and On-Board Beamforming for Multiple gateway Multibeam Satellite Systems

This paper aims to design joint precoding and onboard
beamforming of a multiple gateway multibeam satellite
system, either in a hybrid space-ground mode, or in a totally
on-board one. In such an architecture, with employing high
throughput full frequency reuse pattern over both user and feeder
links, each gateway serves a cluster of adjacent beams such that
the adjacent clusters are served through a set of gateways that are
located at different geographical areas. However, such a system
brings in two challenges to overcome. First, the interference
in both user and feeder links is the bottleneck of the whole
system and applying interference mitigation techniques becomes
necessary. Second, as the data demand increases, the ground
and space segments should employ extensive bandwidth resources
in the feeder link accordingly. This entails embedding an extra
number of gateways aiming to support a fair balance between
the increasing demand and the corresponding required feeder
link resources. To solve these problems, this study investigates
the impact of employing a joint multiple gateway architecture
and on-board beamforming scheme. It is shown that by properly
designing the on-board beamforming scheme, the number of
gateways can be kept affordable even if the data demand
increases. Moreover, Zero Forcing (ZF) precoding techniques
are considered to cope with the interference in both user and
feeder links which embed in the following premises: (i) each
gateway constructs a part of block ZF precoding matrix, (ii) the
satellite and gateways perform the precoding scheme, and (iii)
a joint design of ZF precoding and on-board beamforming at
the payload of the satellite so that no signal processing scheme is
conceived at the gateways. The provided simulation results depict
the performance gain obtained by our proposed schemes.