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WiFi Backscatter

posted by chromas on Saturday April 21 2018, @11:24PM   Printer-friendly

Arthur T Knackerbracket has found the following story:

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.

From the PDF:

[W]e seek to design RF-powered devices that communicate directly with commodity Wi-Fi devices. A positive answer would pave the way for a rapid and simple deployment of the RF-powered Internet of Things by letting these devices connect to existing mobile phones and Wi-Fi APs. It would also expand the functionality of Wi-Fi networks in a new direction: from providing connectivity to existing Wi-Fi clients to a whole new class of battery-free devices.

Achieving this capability, however, is challenging since conventional low-power Wi-Fi transceivers require much more power than is available from ambient RF signals. Thus, it is not feasible for RF-powered devices to literally speak the Wi-Fi protocol. Conversely, since existing Wi-Fi devices are specifically designed to receive Wi-Fi signals, it is unclear how they would decode other kinds of signals from RF-powered devices.

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  • (Score: 2) by c0lo on Sunday April 22 2018, @10:12PM (1 child)

    by c0lo (156) Subscriber Badge on Sunday April 22 2018, @10:12PM (#670504) Journal

    their relative power levels vs data rates.

    The do so in the linked PDF, at least in what they achieved with their antenna/cicuit

    We use off-the-shelf Wi-Fi devices including Intel Wi-Fi cards, Linksys Routers, and our organization’s Wi-Fi infrastructure, and achieve communication rates of up to 1 kbps and ranges of up to 2.1 meters.
    ...

    • The Wi-Fi devices can reliably decode information on the uplink at distances of up to 65 cm and 30 cm using CSI and RSSI information respectively. This is achieved at bit rates ranging from 100 bps to 1 kbps. The uplink range can be increased to more than 2.1 meters by performing coding at the Wi-Fi device.
    • The uplink can operate using only the ambient Wi-Fi transmissions in the network. Specifically, the Wi-Fi device can use RSSI information extracted from all the packets transmitted by the AP in our organization to achieve uplink bit rates between 100 bps and 200 bps, depending on the network load.
    • The prototype can detect Wi-Fi packets as short as 50 μs at distances of up to 2.2 meters; this translates to a bit rate of 20 kbps on the downlink. The downlink range can be further extended to about 3 meters by reducing the bit rate to 5 kbps.
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  • (Score: 2) by leftover on Monday April 23 2018, @02:59AM

    by leftover (2448) on Monday April 23 2018, @02:59AM (#670586)

    Thanks for this. The numbers are in line with what I expected. Trying to stretch the range in real-world conditions becomes troublesome. Omnidirectional antennas get slaughtered by multipath distortion with as few as one data channel. The longest-range system I worked with, for identifying railroad cars as they passed by, had to use a focused beam of non-trivial power. (Not knocking birds out of the sky like military air-search radar but too high for people to be close.) The grid-dip signal was just a static number. My bottom line is still that it does not support use for general Internet access. Round-the-clock energy collection and daily short report from a sensor, sure in cities. By the time you get far enough out to see green spaces the RF noise really drops. I don't think most people are aware just how feeble our RF links can be. Receiver technology has made astonishing gains over the past few decades, allowing transmit power to drop by orders of magnitude.

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