Ergodic Performance of Downlink Untrusted NOMA System With Imperfect SIC

In this letter, the ergodic performance of a non-orthogonal multiple access (NOMA) system with untrusted users and imperfect successive interference cancellation based decoding is manifested. Closed-form expressions of the ergodic rate and the ergodic secrecy rate of each user have been derived for all possible decoding orders. In addition, Taylor series expansion based approximation has been proposed to gain analytical insights and obtain optimal decoding order. Numerical simulations endorse the analytical findings, and highlight impact of various key parameters on the ergodic performance of the system.