Passive WiFi: A New Way to Connect

Will Passive WiFi be the next big thing?
Until now, WiFi has been considered “a power-consuming communication system and has not been widely adopting in the sensor network and IoT space.” In other words WiFi swallows energy by the buckets. As more and more gadgets rely on a WiFi connection, the energy consumption is impacting global power, and of course the battery life of your device. Researchers are looking at ways of avoiding the energy-draining WiFi with hopes of more efficient options.
What is Passive WiFi?
The paper published by Kellogg et al from the University of Washington focuses on Passive WiFi, which is 3-4 orders of magnitude lower in power than existing chipsets. They continue to integrate passive WiFi with regular WiFi devices, such as routers, mobile phones and tablets. These passive WiFi transmissions can be decoded.
Kellogg et al note that until now a lot of research has been done regarding WiFi backscatter. This “creates an additional narrowband data stream to ride on top of existing Wi-Fi signals.” The drawbacks of the backscatter are the low data rates and complex hardware that is incompatible with any WiFi devices. Kellogg et al have a novel way of approaching the problem: “instead
of backscattering existing Wi-Fi signals to send an additional data stream, we use backscatter communication to directly generate Wi-Fi transmissions that can be decoded on any of the billions of existing devices with a Wi-Fi chipset.”
The Solution:
How does this work? A regular WiFi device consists of a digital baseband and an analog RF. The digital baseband’s power has been scaled down drastically using Moore’s law. However, no such work has been done for the analog portion, aka the power consumer. The technique is based on devices only having a digital baseband component. The analog function is practically delegated to one plugged-in device, with this device creating the continuous wave RF signal. The baseband processor on a passive device reflects the RF signal in WiFi packets which are then decoded in any WiFi receiving device. The energy required for such a system is 10,000 times less than that of a regular WiFi device.
This method requires almost no energy and maintains 11 megabits per second of transfer speeds: “That’s 11 times faster than Bluetooth, even while remaining 1,000 times more energy efficient than Bluetooth Low Energy” according to Wired’s article on Passive WiFi.
Are there other more efficient WiFi methods?
This is not the only alternative method suggested. At the end of 2015, Harald Hass of Edinburgh University presented a “LiFi” system which enabled internet data to be streamed via LED lights.
LiFi or Light Enabled WiFi was first demonstrated by Hass by literally “beaming a movie over the air to a laptop using only an LED lamp.”
At the Royal Institution’s Faraday Lecture Hall, Hass performed the demonstration to a TEDSalon. “Using a standard LED light to transmit video as fluctuating light signals, and a domestic solar cell to receive the light signals.” Haas used an offline laptop to show footage of rolling clouds on a monitor. He said the signal could be “transmitted at up to 50MB per second”, faster than most home broadband systems, and would help provide internet connectivity to areas that are currently off the grid. “We expect to go to market with this in two or three years,” he told the audience at a TEDSalon where he presented the technology.”
This is a great example of Visible Light Communication (VLC). VLC uses light that is visible to our human eye – a visible light at a wavelength between 780-375nm. It is also part of optical wireless communication technology. Typically fluorescent lamps, or LEDs, are used and data transmissions to up to 1-2 kilometres were demonstrated, with devices equipped with photodiodes receive the light signals. Ordinary mobile phone cameras can act in the same way.
VLC dates back to the 1880s when Bell invented the photophone, “which transmitted speech on modulated sunlight over several hundred meters. This pre-dates the transmission of speech by radio.” Since 2003, research in VLC has resumed at Nakagawa Laboratory, Penn State University and Siemens and Heinrich Hertz Institut Berlin. In 2015, Phillips together with Carrefour deployed location based services to their shoppers’ smartphones.
The future:
All signs are pointing towards more and more interaction and personalised experiences via information transmission. Lowering our power consumption is of the essence if we don’t want a cataclysmic event wiping out all gadgets. The ideas of passive WiFi and light based inventions could be the start of something we will desperately need.