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Passive Wi-Fi – the key to the smart city puzzle?

The difficulty when creating something new is that there is no template to follow, writes Narayan Menon, the CTO of XCellAir. No flat pack manual that takes you through the trickier parts step by step.

In many ways, when you look at how the Internet of Things (IoT) is growing and expanding, it’s like trying to solve a puzzle without the full picture on the box cover. Those involved in building smart cities have an idea of what the end product will look like, but no single definitive vision. One of the best examples of this trial and error approach to solve the riddle is trying to decide what the train tracks connecting the things should look like.

At present, it’s generally accepted that there are many access technology contenders to help stitch IoT together. Because of the complexity of the challenges faced in connecting things, there is no one-size-fits-all answer. No one picture on the box to aim towards. Instead, there are multiple ways to get there. One option may solve the challenge of dealing with a diversity of applications, but fall short when considering access requirements and energy consumption.

A case in point would be cellular connectivity, which offers mobility, high reliability and high data rates. Yet, it may not fit the bill when taking into account cost and physical limitations. For less frequent, lower data connections, Wireless Personal Access Network (WPAN) technologies may offer a better option. ZigBee, Bluetooth, Z-Wave, amongst others, are good examples of the various other routes to take.

What does sit comfortably between the two is Wi-Fi. It won’t break the bank to install, while having a demonstrable record of performing well indoors, especially as more smart devices such as fridges and heating devices are installed. Gateways are going to play a strong role in IoT, acting as the internet-facing conduits on behalf of more constrained sensor devices. Wi-Fi is very much entrenched in this regards – the Wi-Fi router is everyone’s home gateway today. However, Wi-Fi does require a significant power source that may not be available for devices such as smart meters that require low data capacity and power.

This may not always be the case. Researchers at the University of Washington have been working on passive Wi-Fi that enables lightweight sensor devices to house only baseband operations. A separate radio device, plugged into a power outlet, generates the analogue RF signal, then 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.

These sensor devices effectively become radio frequency identification (RFID) tags. That means the power consumption is driven down and becomes less of a burden on the property owner to keep the green light on all the time. In fact, based on the current research, Passive Wi-Fi will consume 10,000 times less power than standard Wi-Fi. Even compared with Bluetooth Low Energy, Passive Wi-Fi will consume 1,000 times less power. What makes it a very exciting technology is the fact it will not compromise on data rates and will operate on a par with other members of the Wi-Fi family.

It’s too early to completely determine the use cases for Passive Wi-Fi, but it’s likely to be a natural fit for indoor applications, where power outlets are available for the radio device to plug into. Automotive applications will also be able to make use of the technology, as power sources are not an issue. It may not fit quite so well within healthcare or fitness devices, which involve sensors wrapped around a human body in motion.

On paper, this all sounds promising and of course the prospect of a low-energy way of connecting devices really is a step in the right direction. However, if we back Passive Wi-Fi as an access channel for IoT, we must take into account that this means many more devices using unlicensed spectrum in our homes and offices. Creating more of these unmanaged access points could leave people and organizations open to abuse. On top of that, assuming the technology is a success, we will see bottlenecks – the same capacity crunch that worries mobile operators is inevitably the consequence. The whole point of IoT is the interconnectivity of things – many things, including sensors in places we can’t yet imagine. The data traffic they generate, albeit in very small packets, will be enormous in volume. The technology supporting IoT needs to be as robust – if not more so – than we have come to expect with mature mobile and fixed line networks, otherwise the entire premise fails.

As with the rest of the smart cities conundrum, it’s impossible to chart a secure route without knowing the end destination. What we can know for sure is that taking small incremental steps along the way is likely to be the course of least resistance. When introducing the new technologies that will make up smart cities, detailed analysis, scenario planning, and proof of concepts should be looked into before mass adoption takes place. For a new technology such as Passive Wi-Fi, taking the time to do this due diligence will help to maximise the value of the technology, prevent a capacity crunch, and ensure what is finally brought to the market is fit for purpose. Standardisation is critical as well – Passive Wi-Fi will need to go through the Wi-Fi standards development process to ensure device and access point compatibility. While we may not have the full picture on the box to solve the puzzle, the use of trial and error to understand what the final picture looks like will be the best way of achieving success.