We consider the downlink of a wireless system withM-antenna base station and K single-antenna users. A limitedK regime. Unfortunately,K values,K), at the cost of moderate complexity increase.
an
feedback-based scheduling and precoding scenario is considered
that builds on the multiuser random beamforming (RBF). Such
a scheme was shown to yield the same capacity scaling, in terms
of multiplexing and multiuser diversity gain, as the optimal full
CSIT-based (channel state information at transmitter) precoding
scheme, in the large number of users
for more practically relevant (low to moderate)
RBF yields degraded performance. In this work, we investigate
solutions to this problem. We introduce a two-stage framework
that decouples the scheduling and beamforming problems. In our
scenario, RBF is exploited to identify good, spatially separable,
users in a first stage. In the second stage, the initial random
beams are refined based on the available feedback to offer
improved performance toward the selected users. Specifically, we
propose beam power control techniques that do not change the
direction of the second-stage beams, offering feedback reduction
and performance tradeoffs. The common feature of these schemes
is to restore robustness of RBF with respect to sparse network
settings (low
