Physical Layer Security with Unknown Eavesdroppers in Beyond-5G MU-MIMO SATCOM

In multiuser multiple-input multiple-output (MUMIMO) systems for beyond-5G, many user groups are served by the same transmitter in a time-based scheduling. Considering all unscheduled users as eavesdroppers puts a high complexity on algorithms to achieve physical layer security (PLS). Moreover, due to the Line-of-Sight channel properties, PLS is even more challenging to achieve in satellite communication (SATCOM) downlinks. In multibeam MU-MIMO satellite systems, which will be part of beyond-5G networks, the spatial degrees of freedom can be used for both throughput and secrecy improvements. We extend a user-fairness zero-forcing algorithm with artificial noise to achieve secure precoding even if the channel state information of the eavesdroppers is unknown. We define the secrecy outage probability for Line-of-Sight MU-MIMO SATCOM channels and analyze how it can be reduced by the aforementioned algorithm. Moreover, we introduce a trade-off between a high system throughput and a low secrecy outage probability for the cost-effectiveness considerations of PLS.