  Among various promising candidate technologies for the sixth-generation (6G)
wireless communications, recent advances in microwave metasurfaces have sparked
a new research area of reconfigurable intelligent surfaces (RISs). By
controllably reprogramming the wireless propagation channel, RISs are
envisioned to achieve low-cost wireless capacity boosting, coverage extension,
and enhanced energy efficiency. To reprogram the channel, each meta-atom on RIS
needs an external control signal, which is usually generated by base station
(BS). However, BS-controlled RISs require complicated control cables, which
hamper their massive deployments. Here, we eliminate the need for BS control by
proposing a self-controlled RIS (SC-RIS), which is inspired by the optical
holography principle. Different from the existing BS-controlled RISs, each
meta-atom of SC-RIS is integrated with an additional power detector for
holographic recording. By applying the classical Fourier-transform processing
to the measured hologram, SC-RIS is capable of retrieving the user's channel
state information required for beamforming, thus enabling autonomous RIS
beamforming without control cables. Owing to this WiFi-like plug-and-play
capability without the BS control, SC-RISs are expected to enable easy and
massive deployments in the future 6G systems.
