Polarization Conversion-Based Ambient Backscatter System

Abstract

In Ambient Backscatter Communications (AmBC), a backscatter device communicates by modulating the ambient radio frequency (RF) signal impinging at its antenna. In many cases, the system setup is bi-static such that the receiver and the ambient signal source are separated in space. This configuration suffers from the direct path interference problem. The direct signal component can be several orders of magnitude stronger than the scattered one. This imposes a challenge for the receiver that needs to have high dynamic range in order not to lose the scattered signal component to the quantization noise. In this paper, we propose a novel AmBC system concept, in which a polarization conversion between the direct and scattered path is introduced at the backscatter device and exploited at the dual polarization based receiver antenna to mitigate the direct path interference. The proposed system is agnostic to the ambient signal source characteristics as long as it uses linearly polarized antennas. The backscatter device changes the polarization from linear to circular. The receiver antenna is a circularly polarized patch antenna with a 180°-hybrid to obtain the difference between the left-and right-hand polarized fields. Ideally, this receiver antenna and 180°-hybrid combination would completely remove linearly polarized direct path and reflected components. In this paper, we propose a robust design that can mitigate the direct path signal power more than 25 dB despite nonidealities in the antenna manufacturing. INDEX TERMS Polarization conversion, ambient backscatter communication.

Secret Key Generation Between Ambient Backscatter Devices

“…We proposed a method based on polarization conversion in [41] to significantly reduce the ambient signal level at the receiver, thus making it easier for the receiver to recover the backscattered signal. Under ideal circumstances the proposed method completely removes the ambient signal, and a 25 dB attenuation at 2.4 GHz was confirmed by measurements.…”

“…The use of circular polarization also helps the alignment of the sensors, as the rotational angle between the backscatter device and the receiver is no longer an issue. An additional advantage is that the reflections originating from the ambient transmitter are also suppressed by the same attenuation as the direct path signal [41].…”

“…The backscatter receiver connected to the circular polarized antenna listens other sensors. We assume a polarization conversion method as in [41] to better mitigate the suppression of the ambient signal at the receiver.…”

Directional amplitude backscatter modulation with suppressed Doppler based on rotating resonant loop

“…any scattering structure in which there is no loading point or port) 2 and loaded scatterers 3 . The latter, called “variable-damping modulation” in 1 , is mainly realized by load-modulated antennas 4 , and it has been widely employed in classical UHF Radio Frequency IDentification (RFID) 5 and Ambient Backscattering Communication (AmBC) 6 where a modulating electronic component modifies the magnitude and phase 7 , or polarization 8 , 9 of the reflection from the antenna during time. Usually, in this type, the energy required for the modulation is harvested from the incident electromagnetic wave, or the built-in battery, to power up the electronic component.…”

Bendable ultra‐high frequency radio‐frequency identification tag antenna for retail garments using nonuniform meandered lines

“…Typically, the RFID system consists of a reader and a tag comprising a chip and an antenna. The tag chip is powered through the antenna by signals originating from the reader and sends back the chip unique code information using the back‐scattering principle 8‐12 . Several design approaches have already been discussed for impedance matching and size reduction of RFID tags, which include T‐Matching, 13‐15 inductively coupled loop, 16 and meander line antennas.…”