Exact Bit Error-Rate Analysis of Two-User NOMA Using QAM With Arbitrary Modulation Orders

This letter considers the exact bit error rate (BER) analysis of a two-user non-orthogonal multiple access (NOMA) system using square quadrature amplitude modulation (QAM). Unlike existing work, no constraints are imposed on the modulation order of the QAM symbols for any user. Closed-form expressions are derived for the BER of the successive interference cancellation (SIC) receiver in Raleigh fading channels. The analytical BER results corroborated by Mote Carlo simulation show that the power control becomes challenging for high order QAM. Moreover, the BER of each user is approximately independent of the modulation scheme used by the other user for certain power settings.