LoRea

Abstract

There is the long-standing assumption that radio communication in the range of hundreds of meters needs to consume mWs of power at the transmitting device. In this paper, we demonstrate that this is not necessarily the case for some devices equipped with backscatter radios. We present LoRea an architecture consisting of a tag, a reader and multiple carrier generators that overcomes the power, cost and range limitations of existing systems such as Computational Radio Frequency Identification (CRFID). LoRea achieves this by: First, generating narrow-band backscatter transmissions that improve receiver sensitivity. Second, mitigating self-interference without the complex designs employed on RFID readers by keeping carrier signal and backscattered signal apart in frequency. Finally, decoupling carrier generation from the reader and using devices such as WiFi routers and sensor nodes as a source of the carrier signal. An off-the-shelf implementation of LoRea costs 70 USD, a drastic reduction in price considering commercial RFID readers cost 2000 USD. LoRea's range scales with the carrier strength, and proximity to the carrier source and achieves a maximum range of 3.4 km when the tag is located at 1 m distance from a 28 dBm carrier source while consuming 70 µW at the tag. When the tag is equidistant from the carrier source and the receiver, we can communicate upto 75 m, a significant improvement over existing RFID readers.

TunnelScatter

“…Sensor tags eliminate batteries by operating on energy that is harvested from ambient sources such as light [71] or wireless signals [45,62]. It is, however, challenging to transmit on minuscule and intermittent energy using conventional wireless transmission mechanisms [26,31,60,70].…”

“…Backscatter communication overcomes this limitation by enabling wireless transmissions at tens of µWs of power [26,31,60,60,70]. Consequently, backscatter has emerged as the mechanism of choice to enable battery-free sensor tags.…”

“…Although the underlying concept of backscatter communication has been known for decades, it is recently that backscatter systems have made significant progress. Recent systems are able to generate commodity wireless transmissions such as WiFi [31], ZigBee [26], BLE [18] and LoRa [60], or achieve a large (km) communication range [49,60,70]. These advances in backscatter systems have also enabled novel applications [26,44,60,61,71] such as battery-free cameras.…”

“…Despite this success, limitations that hinder practical deployments remain; backscatter systems require the presence of a strong strong ambient carrier signal (ACS). This requires the tag to be located in close proximity (1 m) of a strong ACS emitter (> 500 mW) to achieve the highest and often practical range [31,49,70]. Even backscatter systems that leverage ambient signals instead of a dedicated ACS emitter encounter this problem.…”

“…Based upon this concept, we design a long-range mode we call amplified backscatter transmissions (ABT). This mode encodes sensor readings using frequency shift keying (FSK), and shows orders of magnitude improvement in communication range as compared to LoRea [70], when backscattering a weak ACS. However, when the ACS is strong, we observe that the reflection amplifier performs poorly compared to a conventional backscatter tag.…”