Harmonic Suppression in Frequency Shifted Backscatter Communications

Yuan Ding,Ricardo Correia,Nuno Borges Carvalho,George Goussetis,Romwald Lihakanga

doi:10.1109/ojcoms.2020.3011520

Abstract

This paper provides a comprehensive study of the harmonics generated by a frequency shifted backscatter communication system. The suppression and the manipulability of different harmonics are of importance to avoid detrimental inter-user interference when a number of backscattering nodes (and perhaps also other active wireless users) operate simultaneously in a network. In this paper the harmonics generated by a widely adopted open-short backscatter tag architecture is firstly presented. Then the ideal backscatter system which generates no unwanted harmonics is discussed, which inspires various harmonic suppression strategies. In particular, practical constraints of the backscatter tag hardware capabilities are applied, e.g., the number of discrete reflection coefficients that can be synthesized, and the dimension of the reflection coefficients (real-valued or complex-valued). Furthermore, the dual-transistor based IQ backscatter modulator is found useful to suppress all mirror harmonics and any specified higher order harmonics. The applicability of these proposed harmonic suppression approaches are demonstrated by an exemplar backscatter network consisting of multiple nodes performing binary frequency shifted keying (2FSK) modulated backscatter communications simultaneously.

Highlights

M ASSIVE machine-type communications (MTC), as one of three important pillars to the ever-evolving 5G and beyond, have been gaining momentum to become an indispensable part of our everyday life [1]
HARMONICS IN CONVENTIONAL FREQUENCY SHIFTED BACKSCATTER SYSTEMS Amplitude shifted keying (ASK) modulation is adopted in the commercial Ultra High Frequency (UHF) Radio-frequency identification (RFID) systems, wherein a sophisticated reader is required to extract the weak backscatter signals out of the strong carrier waves that occupy a same frequency band
It is the first time that the harmonics in the frequency shifted backscatter communications have been systematically investigated

Summary

INTRODUCTION

M ASSIVE machine-type communications (MTC), as one of three important pillars to the ever-evolving 5G and beyond, have been gaining momentum to become an indispensable part of our everyday life [1]. Communication technologies that reside in the ultra-lowpower regime, say three orders lower down to tens of μW, which in turn can be supported by harvested wireless power This target can only be reached if the current active radio transmissions are replaced with the passive backscatter transmissions [4], removing the needs of powerhungry radio frequency (RF) carrier synthesizers and power amplifiers. As a consequence, when harmonics of one user fall into frequency bands allocated to other users that are required to operate simultaneously, the link performance of other users can be greatly compromised This issue was first raised in [26], where a series of four discrete complex impedances was used to cancel out the first mirror harmonic. DING et al.: HARMONIC SUPPRESSION IN FREQUENCY SHIFTED BACKSCATTER COMMUNICATIONS

HARMONICS IN CONVENTIONAL FREQUENCY SHIFTED BACKSCATTER SYSTEMS

MIRROR HARMONIC SUPPRESSION WITH ORTHOGONAL LOADS

EXEMPLAR SYSTEMS

CONCLUSION