LoRa Backscatter

Abstract

The vision of embedding connectivity into billions of everyday objects runs into the reality of existing communication technologies -- there is no existing wireless technology that can provide reliable and long-range communication at tens of microwatts of power as well as cost less than a dime. While backscatter is low-power and low-cost, it is known to be limited to short ranges. This paper overturns this conventional wisdom about backscatter and presents the first wide-area backscatter system. Our design can successfully backscatter from any location between an RF source and receiver, separated by 475 m, while being compatible with commodity LoRa hardware. Further, when our backscatter device is co-located with the RF source, the receiver can be as far as 2.8 km away. We deploy our system in a 4,800 ft2 (446 m2) house spread across three floors, a 13,024 ft2 (1210 m2) office area covering 41 rooms, as well as a one-acre (4046 m2) vegetable farm and show that we can achieve reliable coverage, using only a single RF source and receiver. We also build a contact lens prototype as well as a flexible epidermal patch device attached to the human skin. We show that these devices can reliably backscatter data across a 3,328 ft2 (309 m2) room. Finally, we present a design sketch of a LoRa backscatter IC that shows that it costs less than a dime at scale and consumes only 9.25 μW of power, which is more than 1000x lower power than LoRa radio chipsets.

A compact and low-power wireless receiver for implanted medical backscatter

“…To reduce uncertainty such as multipath and fading, testing approaches similar to [2] are used where programmable attenuators are placed between RF signal source and the receiver's SMA input. The amount of attenuation is swept and the bit error rate is counted in a daughter board.…”

“…Some of the papers are designed for so-called "Wake-up Receivers", that usually has no transmitter and the purpose is to detect wake-up signal and wake up the main receiver, such as [9] and [11]. This paper is the first low power chip that includes receiver and transmitter but has similar power consumption as the receiver-only counterparts Board level implementations of backscatters [2], [3] successfully demonstrated the concept of zeropower transmitter, however, that board is quite large (>3 cm à 3 cm) and power hungry as a medical implanted device. The ultra-low sensitivity receivers in [10] is obtained at the cost of large power consumption (4500 nW) and is also not suitable for implanted medical devices.…”

“…Backscatters, such as those demonstrated in [2] and [3], have been implemented at board levels with various wireless protocols such as Lora, Bluetooth and even Wi-Fi.…”

“…The key benefit of a passive backscatter system is that the transmitter is a scatter to reflect incoming wireless waves and effectively consumes zero power. The focus of this paper will be on the receiver chain since the transmitter is covered in detail in [2]. The details and measurements of the synthesizer will be covered in a separate paper.…”

Challenge

“…Their use of simple protocols and unlicensed bands allowed them to take a first-to-market approach, and their ability to transmit at ranges over a kilometer while drawing only a few hundred milliwatts enables exciting new applications. Numerous research results further improve their performance-backscatter drastically reduces the power needed for for LoRa edge devices [15,40,51,56], and coherent combining improves network range and throughput [9].…”