  The physical layer security of uplink non-orthogonal multiple access (NOMA)
is analyzed. A stochastic geometry approach is applied to analyze the coverage
probability and the effective secrecy throughput (EST) of the kth NOMA user,
where a fixed or an adaptive transmission rate can be used. A protected zone
around the legitimate terminals to establish an eavesdropper-exclusion area. We
assume that the channel state information associated with eavesdroppers is not
available at the base station. We consider that the base station is equipped
with multiple antennas. The impact of imperfect successive interference
cancellation is also taken into account in this work. Our analysis allows an
easy selection of the wiretap code rates that maximizes the EST. Additionally,
our framework also allows an optimum selection of other system parameters like
the transmit power or the eavesdropper-exclusion radius.
