# Modeling of NOMA-MIMO-Based Power Domain for 5G Network under Selective Rayleigh Fading Channels
## 1 Introduction  
Due to the compelling multimedia applications and the popularity of smart mobile devices, wireless communication has developed at a breakneck pace over the last decade [1, 2]. Non-orthogonal multiple access (NOMA) has been offered as a possible strategy for achieving mass accessibility with keeping spectral efficiency [3, 4]. NOMA achieves multiple access by modifying the power level of overlay user signals at the transmitter and receiving the signal using successive interference cancellation (SIC) in receivers, with noise-limitinguser rates for better channels and bandwidth-limiting user rates for bad channels [5; 6; 7; 8]. SIC is implemented at the power user level because NOMA is sequential interference cancellation, allowing the powerful user to detect and discard messages from users with weaker channel conditions. Data from users with better channel conditions is considered interference by the weaker user [9]. In the NOMA downlink (DL) system, multiple users share the same time, coding, and frequency resources due to the multiplexing of the power field. The base station (BS) sends an overlay signal to each user, which includes a signal for all users [10]. Because users no longer have to wait for an orthogonal resource block to become available, NOMA can accomplish huge connections while drastically lowering transmission delay [11]. As a result, NOMA with SIC is a promising multiple-access approach in the next-generation communication system [12]. NOMA is a wireless technology that can meet the demands of today's wireless environment [13]. The analysis of different access technologies is still in its early phases [14]. The main leading research group is working on determining the spectrum's efficiency because all features are constantly generated [15; 16]. In uplink (UL) NOMA, a group of users simultaneously sends their signals to their associated BS [17; 18]. Intra-cluster interference, as a result, impacts a user's received signal, which is determined statically by other users' channel data [19]. To reduce interference, the BS could use SIC to decode signals. Separate message signals with an adequate power variance must arrive at the receiver BS to correctly utilize the SIC technique. This is commonly handled in the DL by employing different scales at the transmitter. Furthermore, such values are superfluous because the UL channel gains already offer enough separation between the received signals. The standard UL transmits power control, which is supposed to balance the received signal levels of users, is not recommended for UL NOMA transmissions because it may reduce channel distinctness [20; 21; 22; 23; 24]. Using several antennas in both the transmitter and receiver can considerably increase the capacity of a radio communication channel. That is, many separate channels can be managed in the same bandwidth using multiple-input multiple-output (MIMO) technology with these antennas, but only if the propagation environment is sufficiently rich [25; 26]. Although the use of MIMO techniques adds another dimension to enhance efficiency, research into combining MIMO and NOMA has recently a lot of interest [26; 27]. The additive white Gaussian noise (AWGN) and Rayleigh fading channels were investigated for the accurate expression of the BER rate generated in a closed form for BPSK modulation in the perfect and deficient SIC states for the DL NOMA network. However, it did not include parameters that influence the BER, such as distance and power location coefficients in [28]. Three power assignment strategies are proposed to improve NOMA SE by optimizing the given power to each NOMA in [29; 30]. The impact of interference on users of the energy allocation process, nevertheless, has not been investigated or examined.