Reconfigurable Intelligent Surface-Assisted Ambient Backscatter Communications – Experimental Assessment

Abstract

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 has two features: it controls 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. The surface also applies a common phase-shift to the beam. We demonstrate experimentally that by tuning the beam and the phase-shift of the reconfigurable intelligent surface, we can improve significantly the performance of ambient backscatter communications.

Exploring Reconfigurable Intelligent Surfaces for 6G: State-of-the-Art and the Road Ahead

“…12, the RIS-assisted backscatter system achieves high spectrum efficiency for smaller distance between the transmitter and RIS. Furthermore, the authors in [82] experimentally demonstrated the improvement in the performance of backscatter communications with the aid of RIS.…”

Communication Models for Reconfigurable Intelligent Surfaces: From Surface Electromagnetics to Wireless Networks Optimization

“…1. Other applications include the design of multi-stream multi-antenna transmitters with a single radio frequency chain (often called holographic surfaces and holographic MIMO) [24] and reconfigurable ambient backscatterers [25]. In general terms, an RIS is a candidate future wireless technology for controlling and shaping the electromagnetic waves in a dynamic and goal-oriented way, possibly turning the wireless environment into a service, and for realizing new transceiver designs and network elements at a lower complexity and power consumption.…”

“…The analytical formulation in (25) is not only analytically convenient, as it will be apparent next, but it has a useful physical interpretation. The function Φ(r Rx , r, r Tx ) corresponds to the phase shift that needs to be applied by the RIS, based on the geometrical optics approximation, in order to steer (reradiate) an electromagnetic wave the impinges upon S from the direction identified by k i (r Tx ) towards the direction identified by k r (r Rx ) [2].…”

“…As mentioned, ( 36) and ( 37) are applicable under the assumption that the inequality constraint in ( 29) is satisfied, i.e., the surface reflection coefficient is slowly varying, at the wavelength scale, along the surface S. We note, in addition, that the reflected electric field and the reflected magnetic field are related as for a plane wave that propagates towards the direction θ r (r Rx ). This is due to the assumption of plane wave for the incident electromagnetic wave and to the definition of field reflection coefficient in (25), which result in the term cos θ r (r Rx ) in (37). In general, based on (31), this latter term depends on the specific expression of the function g(y, z) according to (25).…”

“…This is due to the assumption of plane wave for the incident electromagnetic wave and to the definition of field reflection coefficient in (25), which result in the term cos θ r (r Rx ) in (37). In general, based on (31), this latter term depends on the specific expression of the function g(y, z) according to (25).…”