Performance Analysis of Uplink Index-Modulated NOMA for 6G Wireless Communications

In this letter, we mathematically analyze the bit-error rate (BER) performance of a generalized uplink index-modulated non-orthogonal multiple access (IM-NOMA) system consisting of a base station (BS) with multiple antennas and an arbitrary number of devices with different modulation schemes. We focus on the case that a single subcarrier is activated among ${S}$ ( $\ge2$ ) subcarriers according to index bits to reduce computational complexity. The optimal joint maximum-likelihood (JML) algorithm is assumed to be used for detecting a super-imposed symbol from multiple devices. The closed-form BER is shown to be matched well with simulation results. We also investigate the effect of channel estimation error on the BER. To the best of our knowledge, the mathematical characterization of BER of the generalized uplink IM-NOMA system with an arbitrary number of uplink devices with different modulation schemes and multiple receive antennas at the BS does not exist in the literature. Finally, we show that our analytical framework can be applied to analyze a cell-free massive MIMO NOMA system, which is expected to be one of the most promising techniques for 6G wireless communication systems.