In satellite communications (SATCOM) downlinks, physical layer security (PLS) is challenging to achieve due to their broadcasting nature and line-of-sight channel characteristics. This work investigates the potentials and benefits of a multiple-reflector (MR) antenna scheme in geostationary satellite systems for key-less PLS. Multiple antennas on a satellite essentially unlock the space domain as a further physical resource besides time, frequency and polarization. The exploitation of the spatial degree of freedom enables multiuser multiple-input multiple-output (MU-MIMO) as a convenient signaling strategy for SATCOM providers. In an MU-MIMO system, the receivers do not need to be synchronized and the interference is utilized for eavesdropping protection. In this work, an overview and fundamentals on PLS and the most common secrecy metrics is provided and their suitability for geostationary SATCOM is discussed. Two precoding algorithms to secure the downlinks of multiple users against multiple eavesdroppers are developed. Their optimization objective and constraints are chosen to perfectly fit the scenario of a geostationary satellite providing secure fixed satellite service. Zero-forcing precoding will be used as a performance reference and demonstrates how much capacity must be sacrificed for security. The goal of the precoding algorithms for security is to generate a channel condition such that the legitimate users receives the signal in higher quality than all eavesdroppers and, thus, fulfilling the requirement of key-less PLS. The utilization of artificial noise is included for improved security performance. Since both precoding algorithms are complicated to solve in the direct form, a reformulation to a convex form is provided to be solvable in polynomial time with off-the-shelf numerical programs. Numerical simulations demonstrate the effectiveness of the precodings and that a MR antenna design provides a significantly higher secrecy performance when compared to a single-reflector design due to the additional degrees of freedom, exhibited by the signal phases.     «

In satellite communications (SATCOM) downlinks, physical layer security (PLS) is challenging to achieve due to their broadcasting nature and line-of-sight channel characteristics. This work investigates the potentials and benefits of a multiple-reflector (MR) antenna scheme in geostationary satellite systems for key-less PLS. Multiple antennas on a satellite essentially unlock the space domain as a further physical resource besides time, frequency and polarization. The exploitation of the spatia...     »