  Multibeam satellite systems have been employed to provide interactive
broadband services to geographical areas under-served by terrestrial
infrastructure. In this context, this paper studies joint multiuser linear
precoding design in the forward link of fixed multibeam satellite systems. We
provide a generic optimization framework for linear precoding design to handle
any objective functions of data rate with general linear and nonlinear power
constraints. To achieve this, an iterative algorithm which optimizes the
precoding vectors and power allocation alternatingly is proposed and most
importantly, the proposed algorithm is proved to always converge. The proposed
optimization algorithm is also applicable to nonlinear dirty paper coding. In
addition, the aforementioned problems and algorithms are extended to the case
that each terminal has multiple co-polarization or dual-polarization antennas.
Simulation results demonstrate substantial performance improvement of the
proposed schemes over conventional multibeam satellite systems, zero-forcing
and regularized zero-forcing precoding schemes in terms of meeting the traffic
demand. The performance of the proposed linear precoding scheme is also shown
to be very close to the dirty paper coding.
