  Multi-user (MU) diversity yields sum-rate gains by scheduling a user for
transmission at times when its channel is near its peak. The only information
required at the base station (BS) for scheduling is the users' signal-to-noise
ratios (SNR)s. MU diversity gains are limited in environments with
line-of-sight (LoS) channel components and/or spatial correlation. To remedy
this, previous works have proposed opportunistic beamforming (OBF) using
multiple antennas at the BS to transmit the same signal, modulated by
time-varying gains, to the best user at each time slot. In this paper, we
propose reconfigurable surface (RS)-assisted OBF to increase the range of
channel fluctuations in a single-antenna broadcast channel (BC), where
opportunistic scheduling (OS) strategy achieves the sum-rate capacity. The RS
is abstracted as an array of passive reflecting elements, and is dumb in the
sense that it only induces random phase shifts onto the impinging
electromagnetic waves, without requiring any channel state information. We
develop the sum-rate scaling laws under Rayleigh, Rician and correlated
Rayleigh fading and show that RS-assisted OBF with only a single-antenna BS
outperforms multi-antenna BS-assisted OBF. We also extend our results to OFDMA
systems and the multi-antenna BC.
