<i>BAAS</i>: Backscatter as a Sensor for Ultra-Low-Power Context Recognition

Abstract

Context recognition has attracted attention for various daily life applications. Many existing approaches use micro-electromechanical systems (MEMS) sensors which require additional silicon chips to process and transmit the sensor data. The energy consumption of such components is relatively large, requiring maintenance for charging or replacing batteries. In this paper, we propose BAAS: a novel concept using Backscatter As A Sensor. BAAS recognizes contexts using a frequency shift backscatter tag with ultra-low power consumption. The key components of the backscatter tag are an oscillator and a motion switch. The state of the motion switch changes according to the movement of humans or the change of the situation of things. While the motion switch is on, the energy is supplied to the oscillator, and the frequency of the backscattered signal shifts according to the oscillation frequency of the oscillator. Context recognition is achieved by observing the existence and absence of the frequency shift. To demonstrate the feasibility of context recognition using the backscatter tag, we have implemented a prototype and evaluated its performance. Our results show that we can detect the frequency shift by BAAS within 3 m, backscattering BLE signal from an exciter implemented by a commodity device.

Daily Living Activity Recognition with Frequency-Shift WiFi Backscatter Tags

“…However, when off, it is absorbed and not reflected, making the amplitude of the reflected wave zero. Thus, the backscatter tag modulates the amplitude of the external carrier wave via the antenna [ 32 ].…”

“…The frequency-shift backscatter tags used in this study are designed to be extremely simple, thereby consuming very low power. According to Nakagawa et al., the total power consumption of the primary components of the backscatter tag, the RF switch, and oscillator, is 11 A, with power consumption on the order of W. Therefore, the backscatter tag is expected to operate for approximately two years without sleep mode when powered by a CR2032 coin cell (225 mAh), and semi-permanent operation is anticipated with the application of energy harvesting technology [ 32 ].…”

“…We employ the frequency-shift WiFi backscatter tag developed by Nakagawa et al. [ 32 ], referred to herein as the “backscatter tag” or simply the “tag”. Unlike existing methods that often involve transmitting sensor data or functioning as relay devices, the frequency-shift backscatter tag is designed solely for sensing using the tag.…”

“…In this paper, we aim to investigate the feasibility of backscatter communication for recognizing ADLs in homes, leveraging its benefits of low installation and maintenance costs and low privacy exposure while addressing the limitations of existing methods. We employ the frequency-shift WiFi backscatter tag developed by Nakagawa et al [32], referred to herein as the "backscatter tag" or simply the "tag". Unlike existing methods that often involve transmitting sensor data or functioning as relay devices, the frequency-shift backscatter tag is designed solely for sensing using the tag.…”