  In this paper, the impact of imperfect channel state information (CSI) on a
downlink coordinated multipoint (CoMP) transmission system with non-orthogonal
multiple access (NOMA) is investigated since perfect knowledge of a channel can
not be guaranteed in practice. Furthermore, the channel estimation error is
applied to estimate the channel information wherein its priori of variance is
assumed to be known. The impact of the number of coordinated base stations
(BSs) on downlink CoMP NOMA is investigated. Users are classified into one of
two groups according to their position within the cell, namely cell-center user
(CCU) and cell-edge user (CEU). In this paper, ergodic capacity and sum
capacity for both CCU and CEU are derived as closed form. In addition, various
experiments are conducted with different parameters such as SNR, error
variance, and power allocation to show their impact on the CoMP method. The
results show that CoMP NOMA outperforms the CoMP orthogonal multiple access
(OMA) wherein the condition of the channel impacts the performance of CoMP NOMA
less. It is worth noting that a higher number of coordinated BSs enhances the
total capacity of CoMP NOMA. Finally, the performance analysis is validated due
to the close accordance between the analytical and simulation results.
