  In downlink, a base station (BS) with multiple transmit antennas applies
zeroforcing beamforming to transmit to single-antenna mobile users in a cell.
We propose the schemes that optimize transmit power and the number of bits for
channel direction information (CDI) for all users to achieve the max-min
signal-to-interference plus noise ratio (SINR) fairness. The optimal allocation
can be obtained by a geometric program for both non-orthogonal multiple access
(NOMA) and orthogonal multiple access (OMA). For NOMA, 2 users with highly
correlated channels are paired and share the same transmit beamforming. In some
small total-CDI rate regimes, we show that NOMA can outperform OMA by as much
as 3 dB. The performance gain over OMA increases when the
correlation-coefficient threshold for user pairing is set higher. To reduce
computational complexity, we propose to allocate transmit power and CDI rate to
groups of multiple users instead of individual users. The user grouping scheme
is based on K-means over the user SINR. We also propose a progressive filling
scheme that performs close to the optimum, but can reduce the computation time
by almost 3 orders of magnitude in some numerical examples.
