Polarization Conversion-Based Ambient Backscatter System

Jari Lietzen,Aleksi Liljemark,Riku Jantti,Ville Viikari,Ruifeng Duan

doi:10.1109/access.2020.3042018

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.

Highlights

B ACKSCATTERING radio waves from an object has been a subject of active study since the development of radar technologies back in the 1930’s, and the use of backscattered radio for communications since Harry Stockman’s work in 1948 [1]
Backscatter Communication (BC) technology has been widely used in radio frequency identification (RFID) communication systems, where a reader device generates an unmodulated carrier signal, a passive tag absorbs the energy of this signal and sends back the modulated signal to the reader
In many practical ambient backscatter communication (AmBC) deployments, the received power from the direct signal path is several orders of magnitude larger than that of the desired signal component of the AmBC system [14]. This imposes a challenge to the backscatter receiver design that needs to have a large dynamic range in order not to lose the backscatter message into the quantization noise of the analog-to-digital converter (ADC) or distortion products due to receiver amplifier saturation [15], [16]

Summary

INTRODUCTION

B ACKSCATTERING radio waves from an object has been a subject of active study since the development of radar technologies back in the 1930’s, and the use of backscattered radio for communications since Harry Stockman’s work in 1948 [1]. One technique for minimizing the effect of the strong ambient RF signal is to shift the radio frequency on which the backscatter communication system operates away from the one of the ambient RF signal This approach has been utilized to co-exist with WiFi in [11], [23] and with LoRA [24]. The authors in [28] propose a polarization-based reconfigurable (PR) antenna design to improve the backscatter modulated signal path over the direct signal path. 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 is exploited at the dual-polarized receiver to cancel the direct path and reflected components.

SYSTEM CONCEPT

FREQUENCY SENSITIVITY ANALYSIS

PERFORMANCE EVALUATION

CONCLUSION