# RIS-Assisted Fixed NOMA: Outage Probability Analysis and Transmit Power Optimization
## 2 Related Work  
[PERSON], [PERSON] et al. developed the hypersurface tile as a prototype of RIS to realize the software-controlled wireless environment [20]. [PERSON], [PERSON] et al. highlighted the recent research progress and key challenges in RIS-assisted communication [21]. [PERSON], [PERSON] et al. discussed the differences between RIS and other technologies, as well as the benefits and challenges of RIS-assisted communication [22]. [PERSON], [PERSON] et al. covered the issues related to RIS-assisted communication, the optimization of passive beamforming, channel estimation, and placement design [23]. [PERSON], [PERSON] et al. explored the myths and overstatements concerning the RIS that have been spread in the literature [7]. [PERSON], [PERSON] et al. investigated the impact of using RIS with multiple antenna BS and multiple users [3]. The transmit power and phase shifts are designed to be energy efficient such that individual link budgets of the UEs are guaranteed. Two computationally efficient approaches are explored in this article. The first technique uses fractional programming for optimal transmit power allocation and gradient descent to obtain RIS phase shift coefficients. The second approach optimizes RIS phase shifts using fractional programming. The suggested algorithms' performance is investigated in a realistic outdoor environment. When compared to typical multiple antenna AF relays, RIS-assisted resource allocation has a maximum energy efficiency improvement of 300%. [PERSON], [PERSON] et al. evaluated the RIS-assisted communication system under security risks [24]. The placement of RIS here is intended to increase the authorized user's secrecy probability of outage. The theoretical secrecy probability of outage expressions is constructed by considering the discrete phase shifts at RIS. It is established that increasing the RIS elements of a discrete phase shifter by 1.6 times yields a performance comparable to that of a continuous phase shifter. [PERSON], [PERSON] et al. highlighted the three important physical layer issues, such as acquiring channel state information (CSI), passive information transfer, and low-complexity design, when incorporating RIS into wireless networks [25]. Some of the prospective RIS research directions are also highlighted, such as PLS and edge intelligence. [PERSON], [PERSON] et al. maximized the weighted sum capacity of all UEs by jointly designing the beamforming at BS and phase shift angles at RIS [26]. On both perfect and poor CSI conditions, the suggested scheme was tested. This approach was shown to be effective, even when the channel uncertainty is less than 10%. [PERSON], [PERSON] et al. developed closed-form outage probability expressions for ordered NOMA uplink and downlink by examining generalized fading channels [27]. The authors took into account both statistical and instantaneous CSI-based ordering schemes. [PERSON], [PERSON] and [PERSON], M. proposed NOMA-assisted cooperative relaying for reliable communication [28]. At the first and second time slots of cooperative communication, the source and relay transmits a superimposed signal. The exact analytical closed-form outage probability formulas were developed considering Rayleigh fading channel and imperfect successive cancellation decoding. The suggested scheme's outage probability was assessed and compared to that of the traditional cooperative relaying-assisted NOMA. [PERSON], [PERSON] et al. jointly optimized the power assignment from the BS to UEs and the phase shift matrix of RIS to maximize the SINR of all the UEs [29]. [PERSON], [PERSON] et al. maximized the sum capacity by jointly optimizing the power allocation, phase shift matrix, user association, decoding order, and channel assignment [30]. [PERSON], [PERSON] et al. discussed the challenge of optimizing transmit power for a single input-single output (SISO) RIS-assisted NOMA system [31]. The theoretical performance of RIS-assisted orthogonal multiple access (OMA) and RIS-assisted NOMA was compared.