Performance of Selective DF-Based Multiple Relayed NOMA System With Imperfect CSI and SIC Errors

The next-generation networks are supposed to handle the large number of connections required for fifth-generation (5G) and beyond applications. Cooperative multi-relay communication with the downlink non-orthogonal multiple access (DL-NOMA) technique has the capability to provide increased energy and spectral efficiency (SE) by enabling such large connections. It promotes green communication by efficiently serving multiple users through a common resource and improving the system's diversity without compromising the existing infrastructure. This paper investigates the performance of a multi-relay cooperative NOMA system to support 5G and beyond scenarios with practical impairments. The base station communicates with the NOMA end users using cooperative selective decode-and-forward (DF) based ${K}$ multiple relays and direct links. The asymptotic closed-form expression of the symbol error rate (SER) is derived for the NOMA users with imperfect channel state information (CSI) and successive interference cancellation (SIC) errors. The analysis is carried out for the generalized modulation pair, i.e., BPSK-BPSK, QPSK-BPSK and QPSK-QPSK, for NOMA end users. The efficacy of channel estimation error (CEE), power allocation coefficient and diversity order for the aforesaid system is also demonstrated. Finally, the theoretical analysis is endorsed by the Monte Carlo simulations.