Performance Analysis of Uplink Non-Orthogonal Multiple Access in the Presence of Co-Channel Interference

In sixth generation (6 G) networks, a massive number of users and devices must be connected, necessitating flexible resource allocation. In this context, non-orthogonal multiple access (NOMA) has been proposed as a promising technique to enable mass connectivity. This study presents a performance analysis for the impact of co-channel interference (CCI) on uplink NOMA networks. More specifically, it is considered that CCI is introduced by randomly deployed terminals within the cellular coverage area, affecting the reception of the base station (BS) in the uplink. In this network, fading conditions follow the Rayleigh distribution and two cases are examined for the CCI statistics, i.e. independent and identically distributed, and independent but not identically distributed. A thorough performance analysis is conducted to derive the outage probability, ergodic rate, error probability, achievable sum-rate, and throughput expressions, highlighting the adverse effects of CCI on the uplink NOMA network. Furthermore, an asymptotic analysis is provided, shedding light on the derived analytical results. Towards improving the performance of uplink NOMA, power allocation is formulated as an optimization problem, and solved to derive the power allocation coefficient of the users. Our analytical and asymptotic derivations are verified through Monte-Carlo-based computer simulations and it is revealed that the proposed power allocation method achieves significant performance gains, facilitating uplink NOMA.