On the Performance of Non-Orthogonal Multiple Access Systems with Imperfect Successive Interference Cancellation

Non-orthogonal multiple access (NOMA) technique has sparked a growing research interest due to its ability to enhance the overall spectral efficiency of wireless systems. In this paper, we investigate the pairwise error probability (PEP) performance of conventional NOMA systems, where an exact closed form expression for the PEP is derived for different users, to give some insight about the reliability of the far and near users. Through the derivation of PEP expressions, we demonstrate that the maximum achievable diversity order is proportional to the user's order. The obtained error probability expressions are used to formulate an optimization problem that minimizes the overall bit error rate (BER) under power and error rate threshold constrains. The derived analytical results, corroborated by Monte Carlo simulations, are presented to show the diversity order and error rate performance of each individual user.