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Stanford researchers look forward to battery-free WiFi IoT devices

Researchers at Stanford University claim they have brought a self-supporting Internet of Things network based on WiFi closer to reality.

The technology, called backscattering, has been a topic of academic interest for several years, and works by harvesting electromagnetic energy from the air to power IoT devices, avoiding the challenge of monitoring and maintaining many millions of battery-powered end points.

Stanford has produced a prototype called HitchHike, which works with standard WiFi without any changes required. The researchers say their worst case is that they will be able to prolong the battery life of a WiFi device to 10 years – something which can currently be achieved using low power protocols like ZigBee, but not with WLANs. In the best case, they would do without batteries altogether, except if back-up were needed.

“HitchHike is the first self-sufficient WiFi system that enables data transmission using just micro-watts of energy, almost zero,” said Pengyu Zhang, a member of the team, in a statement from Stanford.

The underlying technology, backscattering, is the basis of various similar projects round the world. It involves creating new signals from gathered, ambient radio waves, such as those emanating from TV. Those signals are ingested and converted into new signals and the energy from the collected radio waves powers the newly created ones.

In Stanford’s prototype, the processor and radio piggyback on incoming WiFi signals and “translates those incoming signals to its own messages and retransmits its own data on a different WiFi channel”. This approach to backscatter reuses 802.11b WiFi via ‘codeword translation’, a technique to embed the IoT information in standard, existing 802.11b packets, allowing any receiver to decode it, so that no special hardware is required – unlike some other backscatter systems.

“A backscatter system that can be deployed using commodity WiFi radios on access points, smartphones, watches and tablets, does not exist,” Stanford claims in its statement.

The HitchHike prototype is about the size of a postage stamp and uses a coin battery. It has a functioning range of 50 meters and data rate of 300Kbps. The next aim is to shrink the unit to the size of a “grain of rice”.

“HitchHike consumes 10,000 times less current than WiFi radios. It can operate for years on a simple coin battery,” the scientists claim.

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