Cooperative Noma Via Bilayer Factor Graphs

In this paper we propose the cooperative non-orthogonal multiple access by constructing the bilayer factor graph. The users at the source transmit their symbols by superimposing on a number of resource elements. If the NOMA transmission is not successful at the destination, the relay assists by decoding and forwarding. The superposition structures on the two links construct a bilayer factor graph. The information from the relay helps to distinguish the constellation overlapping and improve the distance property. Optimizations are carried out to maximize the sum rate of the transmission by using the genetic algorithm. Numerical results in terms of transmission rate and symbol error rate are provided, which illustrate the superiority of the bilayer factor graph in the cooperative NOMA system.