Unified BER Analysis of Downlink NOMA with an Arbitrary Number of Users and Modulation Orders

This paper considers a downlink non-orthogonal multiple access (NOMA) communication system over general fading channels. Specifically, a new unified analytical expression is derived for the bit error rate (BER) evaluation of NOMA systems having an arbitrary number of users with an arbitrary order of M-ary quadrature amplitude modulation (MQAM) scheme. The preciseness of the newly derived expression for different number of users, modulation orders and fading channels is then validated through numerical and Monte-Carlo simulation results.