NOMA Power Allocation for Minimizing System Outage under Rayleigh Fading Channel

With the proliferation of the delay sensitive applications and services in cellular networks, the outage probability becomes an important metric that should be minimized to support the low latency requirement of the 5G network. In this paper, the analytical model is proposed to calculate the system outage probability as a closed form expression under the Rayleigh fading channel for the NOMA downlink system. We utilize the model to obtain the optimum power allocation that minimizes the system outage probability as a closed form expression. The accuracy of the proposed analytical model and optimum power allocation is validated by the Monte Carlo simulations. The numerical results show that the outage probability depends on the power allocation and the outage probability of OMA with the fractional power allocation is lower than NOMA with the optimum power allocation. The results indicate that the trade-off between the outage and spectral efficiency in NOMA should be carefully controlled to meet higher throughput and lower latency objectives of 5G.