Performance analysis of cooperative NOMA system for defense application with relay selection in a hostile environment

In the current scenario, where all the services have become online, the demand for increased capacity, low symbol error rate (SER), better data rate, and low latency with high quality of services has been expected from the service providers. Non-orthogonal multiple access (NOMA) is the key enabling technology by which all the above requirements could be achieved. In this work, the physical layer security of a cooperative NOMA system has been improved. The present approach of the decode-and-forward (DF) method consists of one base station (BS), N relays, and two users. Here, a two-stage relay method has been proposed, and analytical results are generated to show that this two-stage relay scheme has been found to achieve the lowest outage probability among all possible relay schemes with the highest attainable diversity gain. In a high signal-to-noise ratio (SNR), the asymptotic and closed-form expressions for outage probability have been obtained. The outage probability for N relays is also computed, which shows that the outage probability decreases as the number of relays get increased. Meanwhile, the Monte-Carlo simulation shows that cooperative NOMA with the proposed two-stage relay technique outperforms cooperative NOMA using the traditional max-min approach.