Bryce Kellogg

Wi-fi backscatter: internet connectivity for RF-powered devices

RF-powered computers are small devices that compute and communicate using only the power that they harvest from RF signals. While existing technologies have harvested power from ambient RF sources (e.g., TV broadcasts), they require a dedicated gateway (like an RFID reader) for Internet connectivity. We present Wi-Fi Backscatter, a novel communication system that bridges RF-powered devices with the Internet. Specifically, we show that it is possible to reuse existing Wi-Fi infrastructure to provide Internet connectivity to RF-powered devices. To show Wi-Fi Backscatters feasibility, we build a hardware prototype and demonstrate the first communication link between an RF-powered device and commodity Wi-Fi devices. We use off-the-shelf Wi-Fi devices including Intel Wi-Fi cards, Linksys Routers, and our organizations Wi-Fi infrastructure, and achieve communication rates of up to 1 kbps and ranges of up to 2.1 meters. We believe that this new capability can pave the way for the rapid deployment and adoption of RF-powered devices and achieve ubiquitous connectivity via nearby mobile devices that are Wi-Fi enabled.

Wi-Fi backscatter

RF-powered computers are small devices that compute and communicate using only the power that they harvest from RF signals. While existing technologies have harvested power from ambient RF sources (e.g., TV broadcasts), they require a dedicated gateway (like an RFID reader) for Internet connectivity. We present Wi-Fi Backscatter, a novel communication system that bridges RF-powered devices with the Internet. Specifically, we show that it is possible to reuse existing Wi-Fi infrastructure to provide Internet connectivity to RF-powered devices. To show Wi-Fi Backscatters feasibility, we build a hardware prototype and demonstrate the first communication link between an RF-powered device and commodity Wi-Fi devices. We use off-the-shelf Wi-Fi devices including Intel Wi-Fi cards, Linksys Routers, and our organizations Wi-Fi infrastructure, and achieve communication rates of up to 1 kbps and ranges of up to 2.1 meters. We believe that this new capability can pave the way for the rapid deployment and adoption of RF-powered devices and achieve ubiquitous connectivity via nearby mobile devices that are Wi-Fi enabled.

Powering the next billion devices with wi-fi

We present the first power over Wi-Fi system that delivers power to low-power sensors and devices and works with existing Wi-Fi chipsets. Specifically, we show that a ubiquitous part of wireless communication infrastructure, the Wi-Fi router, can provide far field wireless power without significantly compromising the networks communication performance. Building on our design, we prototype battery-free temperature and camera sensors that we power with Wi-Fi at ranges of 20 and 17 feet respectively. We also demonstrate the ability to wirelessly trickle-charge nickel---metal hydride and lithium-ion coin-cell batteries at distances of up to 28 feet. We deploy our system in six homes in a metropolitan area and show that it can successfully deliver power via Wi-Fi under real-world network conditions without significantly degrading network performance.

Battery-Free Cellphone

We present the first battery-free cellphone design that consumes only a few micro-watts of power. Our design can sense speech, actuate the earphones, and switch between uplink and downlink communications, all in real time. Our system optimizes transmission and reception of speech while simultaneously harvesting power which enables the battery-free cellphone to operate continuously. The battery-free device prototype is built using commercial-off-the-shelf components on a printed circuit board. It can operate on power that is harvested from RF signals transmitted by a basestation 31 feet (9.4 m) away. Further, using power harvested from ambient light with tiny photodiodes, we show that our device can communicate with a basestation that is 50 feet (15.2 m) away. Finally, we perform the first Skype call using a battery-free phone over a cellular network, via our custom bridged basestation. This we believe is a major leap in the capability of battery-free devices and a step towards a fully functional battery-free cellphone.

LoRa Backscatter: Enabling The Vision of Ubiquitous Connectivity

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 &mgr;W of power, which is more than 1000x lower power than LoRa radio chipsets.

PASSIVE WI-FI: Bringing Low Power to Wi-Fi Transmissions

Wi-Fi has traditionally been considered a power-consuming communication system and has not been widely adopted in the sensor network and Internet of Things (IoT) space. We introduce Passive Wi-Fi that demonstrates that one can generate 802.11b transmissions using backscatter communication, while consuming 3-4 orders of magnitude lower power than existing Wi-Fi chipsets. Passive Wi-Fi transmissions can be decoded on any Wi-Fi device including routers, mobile phones and tablets. Our experimental evaluation shows that passive Wi-Fi transmissions can be decoded on off-the-shelf smartphones and Wi-Fi chipsets over distances of up to 100 feet. We also design a passive Wi-Fi IC that shows that 1 and 11 Mbps transmissions consume 14.5 and 59.2 ?W respectively. This translates to 10000x lower power than existing Wi-Fi chipsets and 1000x lower power than Bluetooth LE and ZigBee.

Passive wi-fi and interscatter

The ubiquity of Wi-Fi has been a boon to pervasive connectivity of devices; We have Wi-Fi in our homes, schools, offices, and even factories. However, Wi-Fi has long been underutilized in the IoT space in favor of other wireless protocols such as Zigbee or BLE. This results in less than optimal deployment solutions that do not fully take advantage of the enormous existing installation base of Wi-Fi. One of the main reasons for the lack of use of Wi-Fi in IoT is the incredible power consumtion of Wi-Fi radios. While transmitting, a Wi-Fi radio can consume 100s of mW of power, much too much for a simple batter limited IoT device. With Passive Wi-Fi we show how Wi-Fi connectivity can be achieved for 10,000x lower power than traditional Wi-Fi and 1,000x lower power than BLE or Zigbee by synthesizing Wi-Fi packets using only reflections. This opens up the possibility of using Wi-Fi everywhere, even on the most power constrained of IoT devices. Additionally, with Interscatter we demonstrate how to use reflections to transform BLE transmissions into Wi-Fi packets. This can allow phones, smartwatches, or other BLE devices to interrogate low power backscatter devices with no hardware modifications, and brings backscatter into the personal area network space. These technologies have the potential to make backscatter a first class citizen in IoT wireless communication by allowing them to communicate with existing ecosystems and current consumer devices.