  Sixth generation (6G) mobile networks may include new passive technologies,
such as ambient backscatter communication or the use of reconfigurable
intelligent surfaces, to avoid the emission of waves and the corresponding
energy consumption. On the one hand, a reconfigurable intelligent surface
improves the network performance by adding electronically controlled reflected
paths in the radio propagation channel. On the other hand, in an ambient
backscatter system, a device, named tag, communicates towards a reader by
backscattering the waves of an ambient source (such as a TV tower). However,
the tag's backscattered signal is weak and strongly interfered by the direct
signal from the ambient source. In this paper, we propose a new reconfigurable
intelligent surface assisted ambient backscatter system. The proposed surface
allows to control the reflection of an incident wave coming from the exact
source location towards the tag and reader locations (creating hot spots at
their locations), thanks to passive reflected beams from a predefined codebook.
A common phase-shift can also be applied to the beam. Thanks to these features,
we demonstrate experimentally that the performance of ambient backscatter
communications can be significantly improved.
