  The use of software controlled passive Reconfigurable Intelligent Surface
(RIS) in wireless communications has attracted many researchers in recent
years. RIS has a certain degree of control over the scattering and reflection
characteristics of the electromagnetic waves, compared to the conventional
communications in which the received signal is degraded due to the
uncontrollable scattering of the transmitted signal and its interaction with
the objects in propagating medium. Further, in RIS assisted communications, the
phases of the multiple incoming signals can be controlled to enable
constructive addition of multiple signals from different channel paths to
improve Signal to Noise Ratio (SNR). On the other hand, Non-Orthogonal Multiple
Access (NOMA) provides massive connectivity and low latency. The power domain
variant NOMA uses superposition coded symbols with different powers for
different user symbols. In this paper, a novel RIS assisted downlink NOMA
system is proposed by combining the merits of both RIS and NOMA to improve the
reliability of the system. Analytical expressions are derived for the Bit Error
Rate (BER) performance of the proposed RIS assisted power domain NOMA system.
The BER performance of the proposed system is analyzed using the numerical
simulation results. It is observed that the proposed system has better
performance than the conventional NOMA system.
