Linear precoding in multibeam satellite under licensed shared access

Due to the scarcity of the spectrum, there is a current tendency to offer novel shared access licenses in order to increase the overall spectral efficiency. Under this context, license shared access (LSA) has appeared as an alternative to the exclusive license and license-exempt mechanisms, which so far have dominated the wireless communications. LSA provides shared access to a given set of users under certain conditions which must be optimized in order to foster the shared use of the spectrum, while maintaining certain restrictions on the generated interference. In this paper we consider a LSA system where both satellite and terrestrial wireless service providers share a given frequency band. Basically, the constraints in the LSA scenario reduce to the control of the received signal power within the coverage area. We focus on the precoding scheme in multi-beam satellite systems restricting the received power of the satellite user terminals to be under certain threshold. The objective is that the terrestrial wireless service provider observes the satellite signal power strength under a certain value, providing a peaceful coexistence between both services. Two traditional linear precoding techniques are properly modified in order to satisfy the receiver power constraints. The optimum precoder results to be zero forcing (ZF), in terms of maximum achievable sum-rate, nevertheless the so-called minimum mean square error (MMSE) exhibits better power efficiency than the ZF, in terms of bps/Hz unit power used at the transmitter.