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Wi-Fi’s Not-So-Passive Approach for IoT

Posted by Narayan Menon on 11 April 2016

Although there has been a buzz around the Internet of Things (IoT) for a few years now, Wi-Fi has been around for much longer. And even though it is older, Wi-Fi seems to have been inherently well designed to support IoT – at least certain vertical segments and their associated applications. From the beginning Wi-Fi has been designed for reasonably low cost and lightweight operation, plug-n-play interoperability and ease of deployment. Essentially it has been designed with connectivity as its primary goal.

Wi-Fi is essentially internet-like in spirit – connectionless and best-effort to a large degree – and therefore seems naturally aligned to meet the needs of IoT. What’s more, even the most evolved Wi-Fi products can be purchased from a retail outlet and installed by the user with minimum fuss.

It’s a widely accepted fact that there will be many access technology contenders for IoT. But you’re not going to find a one-size-fits-all solution given the diversity of applications and access requirements. Cellular is going to play a role for applications that need mobility, high reliability (Quality of Service) and high data rates. Wireless Personal Access Network (WPAN) technologies are being touted for sensor-based applications where very low cost, small real estate and battery lives extending to years are paramount. ZigBee, Bluetooth, Z-Wave and several other technologies compete in this segment.

Wi-Fi fits naturally into the middle segment, where cost, flexibility and power are not “all-consuming” issues. In fact, Wi-Fi works very well for home appliances that are power-tethered. Refrigerators, washing machines and other appliances are already being shipped out with Wi-Fi in them.

Where today’s Wi-Fi tends to struggle slightly is in the low-end sensor segment. Wi-Fi is a power hog, and battery life in the Wi-Fi world is typically counted in hours – not in months or years. But Wi-Fi hasn’t been sitting around idly – incarnations are being proposed that, if commercially viable, should help Wi-Fi compete in the WPAN space.

Passive Wi-Fi is one such development. Researchers at the University of Washington revealed prototypes of this technology in early 2016. Passive Wi-Fi enables lightweight sensor devices to house only baseband operation. A separate radio device, plugged into a power outlet, generates the analog RF signal. A sensor device piggybacks onto this RF signal, modulates it with its data, and reflects the signal back out for Wi-Fi devices to pick up.

Essentially the sensor devices behave a bit like passive RFID tags. They avoid having to house power-hungry RF functionality, and are therefore able to reduce power consumption by orders of magnitude. The promise of Passive Wi-Fi is that it will consume 10,000 times less power than standard Wi-Fi. Compared to a technology like Bluetooth Low Energy, it seeks to soak up 1,000 times less power, while promising data rates similar to some of today’s Wi-Fi variants.

Passive Wi-Fi is far from being commercial though. The technology needs to be validated for technical and commercial viability, and has to go through a standardization cycle before it can get into products. How compatible Passive Wi-Fi devices will be with legacy Wi-Fi access points, routers and clients also remains to be seen.

HaLow is another such flavor being developed by the Wi-Fi community, based on the 80211.ah standard. By operating in a lower frequency band (900 MHz), HaLow offers longer-range operation than regular Wi-Fi, penetrates walls better, consumes less power and provides longer battery life, albeit at lower data rates. The Wi-Fi Alliance will likely start certifying HaLow products sometime in 2018, after which HaLow might start making its way into Wi-Fi routers – and eventually, perhaps wristwatches, coffee makers and the like.

By way of being an 802.11 standard, HaLow promises compatibility and interoperability between devices, routers and access points. It’s likely that future Wi-Fi routers will support tri-band operation – in the 900MHz band, as well as the traditional 2.4 and 5 GHz bands.

Of course, all this doesn’t mean Wi-Fi will corner the sensor market – not by any means. The likes of Bluetooth Low Energy and ZigBee aren’t going to sit still, and they will make their own improvements by the time the likes of HaLow and Passive Wi-Fi become product-ready. Whether these Wi-Fi variants become successful in the IoT sphere will depend partly on their speed of standardization and commercialization. The fact that Wi-Fi has been ubiquitous for a while and gives devices ready access to the internet should help, of course.

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