  Non-Orthogonal Multiple Access (NOMA) is a multiplexing technique for future
wireless, which when combined with Multiple-Input Multiple-Output (MIMO)
unlocks higher capacities for systems where users have varying channel
strength. NOMA utilises the channel differences to increase the throughput,
while MIMO exploits the additional degrees of freedom (DoF) to enhance this.
This work analyses the secrecy capacity, demonstrating the robustness of a
combined MIMO-NOMA scheme at physical layer, when in the presence of a passive
eavesdropper. We present bounds on the eavesdropper performance and show
heuristically that, as the number of users and antennas increases, the
eavesdropper's SINR becomes small, regardless of how `lucky' they may be with
their channel.
