  Reconfigurable intelligent surfaces (RIS) are a key enabler of various new
applications in 6G smart radio environments. By utilizing an RIS prototype
system, this paper aims to enhance self-interference (SI) cancellation for
in-band full-duplex (FD) communication systems. SI suppression is a crucial
requirement for FD communication as the SI severely limits the performance of a
node by shadowing the received signal from a distant node with its own transmit
signal. To this end, we propose to assist SI cancellation by exploiting an RIS
to form a suitable cancellation signal in the analog domain. Building upon a
256-element RIS prototype, we present results of RIS-assisted SI cancellation
from a practical testbed. Given an initial analog isolation of 44 dB provided
by the antenna design, we are able to cancel the leaked signal by an additional
59 dB in the narrowband case, resulting in an overall SI suppression of 103 dB
without additional digital cancellation. The presented case study shows
promising performance to build an FD communication system on this foundation.
