  Non-orthogonal multiple access (NOMA) can improve the spectral efficiency by
exploiting the power domain and successive interference cancellation (SIC), and
it can be applied to various transmission schemes including random access that
plays a crucial role in the Internet of Things (IoT) to support connectivity
for a number of devices with sparse activity. In this paper, we formulate a
game when NOMA is applied to ALOHA to decide the transmission probability. We
consider a payoff function based on an energy-efficiency metric and drive the
mixed strategy Nash equilibrium (NE).
