  Non-orthogonal multiple access (NOMA) is one of the key technologies to serve
in ultra-dense networks with massive connections which is crucial for Internet
of Things (IoT) applications. Besides, NOMA provides better spectral efficiency
compared to orthogonal multiple access (OMA) schemes. However, in NOMA,
successive interference canceler (SIC) should be implemented for interference
mitigation and mostly in the literature, perfect SIC is assumed for NOMA
involved systems. Unfortunately, this is not the case for practical scenarios
and this imperfect SIC effect limits the performance of NOMA involved systems.
In addition, it causes unfairness between users. In this paper, we introduce
reversed decode-forward relaying NOMA (R-DFNOMA) to improve user fairness
compared to conventional DFNOMA (C-DFNOMA) which is widely analyzed in
literature. In the analysis, we define imperfect SIC effect dependant to
channel fading and with this imperfect SIC, we derive exact expressions for
ergodic capacity (EC) and outage probability (OP). Moreover, we evaluate bit
error performance of proposed R-DFNOMA and derive bit error probability (BEP)
in closed-form which has not been also studied well in literature. Then, we
define user fairness index in terms of all key performance indicators (KPIs)
(i.e., EC, OP and BEP). Based on extensive simulations, all derived expressions
are validated, and it is proved that proposed R-DFNOMA provides better user
fairness than C-DFNOMA in terms of all KPIs. Finally, we discuss the effect of
power allocations at the both source and relay on the performance metrics and
user fairness
