  This letter puts forth an analytical approach to evaluate the outage
probability of power-based NOMA on the uplink of a 5G cell, the outage being
defined as the event where the receiver fails to successfully decode all the
simultaneously received signals. In the examined scenario, Successive
Interference Cancellation (SIC) is considered and an arbitrary number of
superimposed signals is present. For the Rayleigh fading case, the outage
probability is provided in closed-form, clearly outlining its dependency on the
signal-to-noise ratio of the users that are simultaneously transmitting, as
well as on their distance from the receiver.
