  Joint user selection (US) and vector precoding (US-VP) is proposed for
multiuser multiple-input multiple-output (MU-MIMO) downlink. The main
difference between joint US-VP and conventional US is that US depends on data
symbols for joint US-VP, whereas conventional US is independent of data
symbols. The replica method is used to analyze the performance of joint US-VP
in the large-system limit, where the numbers of transmit antennas, users, and
selected users tend to infinity while their ratios are kept constant. The
analysis under the assumptions of replica symmetry (RS) and 1-step replica
symmetry breaking (1RSB) implies that optimal data-independent US provides
nothing but the same performance as random US in the large-system limit,
whereas data-independent US is capacity-achieving as only the number of users
tends to infinity. It is shown that joint US-VP can provide a substantial
reduction of the energy penalty in the large-system limit. Consequently, joint
US-VP outperforms separate US-VP in terms of the achievable sum rate, which
consists of a combination of vector precoding (VP) and data-independent US. In
particular, data-dependent US can be applied to general modulation, and
implemented with a greedy algorithm.
