Relay Selection and Power Control to Maximize Energy Efficiency in Two-Way Relay Network with Network Coding and Non-Orthogonal Multiple Access

Non-othogonal multiple access (NOMA), as a promising technology, increases spectral efficiency and system capacity by allocating a resource block to multiple users. Network coding (NC) has the advantages of data compression and high spectral efficiency and plays an important role in two-way relay networks. However, conventional two-way relay networks suffer from transmission power limitations due to the use of mrthogonal multiple access (OMA). The performance of this type of network depends on the selected relay and the transmission power. In this paper, considering the need for secure communications and also the energy limitation in military communications, a method is proposed for relay selection and transmission power control to maximize energy efficiency in two-way relay networks with network coding and power control taking into account the limits of the maximum transmission power and the minimum acceptable spectral efficiency. To solve this problem, it is converted into two sub-problems and first, for each candidate relay, the transmission power is calculated to maximize the energy efficiency. Finally, the relay candidate with the maximum energy efficiency is selected as the final relay. The performance of the proposed model is evaluated in terms of spectral efficiency, energy efficiency, and the possibility of disconnection in different transmitted signal-to-noise ratios (SNR). Also, the effect of the number of candidate relays and the minimum acceptable spectral efficiency on the system efficiency has been investigated. The results show that network coding in NOMA communications increases the spectral efficiency and energy efficiency and reduces the outage possibility.