  While Reconfigurable Intelligent Surfaces (RISs) constitute one of the most
prominent enablers for the upcoming sixth Generation (6G) of wireless networks,
the design of efficient RIS phase profiles remains a notorious challenge when
large numbers of phase-quantized unit cells are involved, typically of a single
bit, as implemented by a vast majority of existing metasurface prototypes. In
this paper, we focus on the RIS phase configuration problem for the exemplary
case of the Signal-to-Noise Ratio (SNR) maximization for an RIS-enabled
single-input single-output system where the metasurface tunable elements admit
a phase difference of $\pi$ radians. We present a novel closed-form
configuration which serves as a lower bound guaranteeing at least half the SNR
of the ideal continuous (upper bound) SNR gain, and whose mean performance is
shown to be asymptotically optimal. The proposed sign alignment configuration
can be further used as initialization to standard discrete optimization
algorithms. A discussion on the reduced complexity hardware benefits via the
presented configuration is also included. Our numerical results demonstrate the
efficacy of the proposed RIS sign alignment scheme over iterative approaches as
well as the commonplace continuous phase quantization treatment.
