LoRa Backscatter

TLDR

Current wireless technologies cannot provide reliable, long‑range, ultra‑low‑power, and inexpensive connectivity, and although backscatter is low‑power and cheap, it is traditionally limited to short ranges. This paper overturns that conventional wisdom by presenting the first wide‑area backscatter system. The authors deploy a single RF source and receiver in diverse settings—a multi‑floor house, a multi‑room office, and a one‑acre farm—while also building contact‑lens and epidermal‑patch prototypes, demonstrating that a LoRa backscatter IC can be fabricated for under a dime and consume only 9.25 µW. The system achieves 475 m backscatter between separate source and receiver, 2.8 km when co‑located, reliable coverage across a 3,328 ft² room, and the IC design confirms sub‑dime cost and 9.25 µW power consumption.

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.