Ensuring communication for Public Safety Users (PSUs) in all events, and specifically in disaster situations, is one of the main challenges of Cellular Networks (CNs). Various types of communications, such as in-band and outband communications, can be used to integrate the Public Safety Network (PSN) into the CN. In this paper, we focus on in-band overlay Device-to-Device (D2D) communication, which effectively reduces the interference caused by Cellular Users (CUs), and ensures the availability of Resource Blocks (RBs) for PSUs at any time and for different events. Furthermore, by using a Non-Orthogonal Multiple Access (NOMA) based system and the Particle Swarm Optimization (PSO) algorithm, the user throughput and the resource wastage problem are improved. Our goal is to provide the necessary resources to PSUs and, at the same time, to maximize the use of these resources. Compared to the traditional Orthogonal Frequency-Division Multiple Access (OFDMA) system, the simulation results show the efficiency of our proposed PSO-based NOMA system in terms of average user throughput and user sum-throughput, and also show that the relation between throughput and fairness among users is a requirement-dependent tradeoff, where we can achieve optimal fairness by decreasing the total throughput.