  Non-orthogonal multiple access (NOMA) is very promising for future wireless
systems thanks to its spectral efficiency. In NOMA schemes, the effect of
imperfect successive interference canceler (SIC) has dominant effect on the
error performances. In addition to this imperfect SIC effect, the error
performance will get worse with the channel estimation errors just as in all
wireless communications systems. However, all literature has been devoted to
analyze error performance of NOMA systems with the perfect channel state
information (CSI) at the receivers which is very strict/unreasonable
assumption. In this paper, we analyze error performance of NOMA systems with
imperfect SIC and channel estimation errors, much more practical scenario. We
derive exact bit error probabilities (BEPs) in closed-forms. All theoretical
analysis is validated via computer simulations. Then, we discuss optimum power
allocation for user fairness in terms of error performance of users and propose
a novel power allocation scheme which achieves maximum user fairness.
