High Data-Rate Communication in Near-Field RFID and Wireless Power Using Higher Order Modulation

We present the theory of high-order modulation for near-field RF identification (RFID) and wireless power transfer (WPT) systems. We show that while related, the design of RFID and WPT systems differ. The theory and calculation of load modulated quadrature amplitude modulation (QAM) and phase shift keying (PSK) is presented. We then present two experimental prototypes. The first demonstrates a 16-QAM RFID link achieving 480 kb/s at a 2.38-MHz carrier (>19.8 fractional bandwidth), significantly higher than the 1% fractional bandwidth of traditional RFID systems. The second experimental prototype demonstrates 4-PSK for WPT applications achieving a data rate 256 kb/s at a 2.38-MHz carrier (a 10.7% fractional bandwidth) with an average efficiency reduction of only 4%.

I. Introduction

Near-Field systems, such as RF identification (RFID) and near-field wireless power transfer (NF-WPT), have become important technologies owing to their ability to eliminate direct contact between objects [1], [2]. RFID systems have become ubiquitous in enabling keyless entry, identification, and asset tracking, as well as innovative uses in biological applications [3]. NF-WPT has become mainstream in cellular phone chargers, as well as in medical devices [4]. These near-field technologies operate in the magnetoquasi-static regime, where the magnetic field plays the dominant role, and are therefore compatible with environments containing small metallic objects as well as humans—making such technologies ideal for a multitude of applications.