Sum Rate and Energy Efficiency Maximization in a Cognitive Radio Network with a Successive Relay Primary User

In this paper, we propose a cognitive radio network which consists of a number of secondary users and one primary user. The primary user utilized a successive relay performance. The successive relaying technique creates a full duplex relay performance by two half duplex relays, which improves spectral efficiency. In the presence of secondary users, we use successive relay technique in the primary user to ensure its acceptable performance. Also, the sum rate of secondary users is increased. The challenges of this network are inter-relay interference and inter user interference. The interference alignment method is utilized to eliminate the interferences in the successive relay technique and in the cognitive radio network. Besides, the minimum transmitted power of the primary user is derived to guarantee its quality of service requirement. Two power allocations algorithms are proposed to maximize the sum rate of secondary users and the energy efficiency of the network. In both power allocations algorithms, satisfying the quality of service of the primary user is considered. The closed-form solutions of these algorithms are studied. The fractional programing approach was employed to solve the energy efficiency optimization in two steps.