# Multiple-Intelligent Reflective Surfaces (Multi-IRSs)-Based NOMA System  
[PERSON]  
1 Middle Technical University (MTU), Baquha Technical Institute, Baghdad 10001, Iraq1  
differences in their channel gains. At the destination, all users apply successive interference cancellation (SIC) so that each one can decode its respective data message [1; 2; 3]. Nevertheless, the achievable spectral efficiency (SE) and energy efficiency (EE) of existing wireless networks could be enhanced further by deploying software-controlled reflecting surfaces known as intelligent reflective surfaces (IRSs). As can be seen in Figure 1, the IRS surface is formed by a large number of passive reflecting elements, where each element is capable of changing the phase shift of the incident signal to be reflected towards the receiving destination [17; 18]. Lately, a combination of NOMA empowered with IRS has emerged as a promising and cost effective solution to boost both SE and EE, as well as to increase the probability of successful reception in wireless networks. This is possible as the IRS modifies the propagation environment in such a way that strengthens the received signal by the users, as shown in Figure 1, particularly in situations where those environments are characterized by obstacles and/or have a weak direct path between the source and the destination [19]. A number of literature works have already presented the IRS and have examined its prospects and applicability, and this paper is an effort in the same direction. The IRS potential allows its integration with several existing technologies such as the single-input, single-output (SISO) system, MIMO system, NOMA, and others. For example, the authors of [20] addressed the performance gain of combining IRS and a millimeter-wave (mmWave) communication system through optimizing the phases of the transmitted signals. The authors of [21] addressed the performance of IRS as compared to the with classic decode-and-forward technique with no NOMA being taken into consideration. The authors concluded that for IRS to overcome the DF relaying performance, it requires large meta-surfaces and considerably high rates. Hence, such results form one of the reasons that encourage a study of the combination of NOMA with IRS to avoid using high rates and wide meta-surfaces. In addition, works such as ref. [17] investigated minimizing the transmission power of IRS-NOMA via joint optimization of the IRS-phase shift matrix and the transmission beam-former of the BS. Moreover, [22] considered optimizing the overall sum rate of IRS-NOMA through jointly optimizing the beam-forming at the BS and the IRS under the constraints of the decoding rate of the SIC, as well as the IRS reflecting elements. The authors in [23] presented an IRS-assisted downlink NOMA system and showed that the cooperation between IRS and NOMA can enhance the cell edge user's experience. The authors in [24] addressed the effects of two phase shifting designs on the performance of IRS-NOMA in terms of complexity and reception reliability. The potential of IRS is even investigated in satellite networks [25; 26; 27; 28]; for instance, the authors in [25]  
Figure 1: An illustration of the modeled IRS-assisted system. studied the application of IRS units to tackle the path loss results from the long transmission distances. The authors proved that IRS-assisted satellites can offer several thousand fold of the achievable rates for IoT networks in both uplink and downlink. In this paper, one motivating idea behind adopting multiple IRSs is the outcomes that could be obtained, such as reducing the required numbers of the serving BS, and hence reducing the consumed transmission power and improving the energy efficiency. Moreover, having less BSs means less interference problems, which also nullify the need for interference cancellation techniques.