  We provide in this paper a comprehensive solution to the design, performance
analysis, and optimization of a multi-antenna non-orthogonal multiple access
(NOMA) system for multiuser downlink communications under a general limited
channel state information (CSI) feedback framework for frequency division
duplex mode. We design a general framework including user clustering, joint
power and bits allocation, CSI quantization and feedback, signal superposition
coding, transmit beamforming, and successive interference cancellation at
receivers. Then, we conduct a mathematically strict performance analysis of the
considered system, and obtain a closed-form lower bound on the ergodic rate of
each user in terms of transmit power, CSI quantization accuracy and channel
conditions. For exploiting the potentials of multiple-antenna techniques in
NOMA systems, we jointly optimize two key parameters, i.e., transmit power and
the number of feedback bits allocated to each user, and propose low-complexity
closed-form solutions. Moreover, through asymptotic analysis, we reveal the
interactions between the main system parameters and their impacts on the joint
power and feedback bits allocation result, and hence show some guidelines on
the system design. Finally, numerical results validate the correctness of our
theoretical analysis and demonstrate the advantages of the proposed algorithms
over the most related state of the art.
