Orthogonal multiple access; non-orthogonal multiple access; user Pair; device-to-device pair; eavesdropper; Optimal power allocation; outage probability; secrecy outage probability; ergodic secrecy capacity; non-zero secrecy capacity; system throughput; effective secrecy throughput; energy harvesting; simultaneous wireless in formation and power transfer; energy efficiency; spectral efficiency(Topical Term)