The Wi-Fi industry has ambitions to make Wi-Fi the dominant wireless technology for the Internet of Things (IoT). While its current incarnation lacks two key features for this emerging market, Wi-Fi would be attractive option for a number of reasons. It is more IP-friendly than any of the alternative wireless technologies, supports higher rates, and the chip industry backs it with high volumes and low prices. If new versions of Wi-Fi for IoT maintain commonality with current MAC and PHY designs and familiar interfaces allowing easy integration into devices, they should be attractive to IoT developers.
We can somewhat narrowly define IoT as head-less, often battery-powered devices that need building-wide connectivity to report data and receive control from the “cloud.” The two requirements where Wi-Fi falls short in IoT are range and power consumption. When compared with the alternative IoT wireless technologies, Zigbee, Z-wave, and Bluetooth Low Energy (BLE), a battery-powered Wi-Fi sensor lasts months, not years; attempts to make very-low-power chips using 802.11b/a/g/n/ac have had marginal commercial success. Also, a single Wi-Fi access point cannot reliably cover all locations in all modern houses and commercial buildings due to multiple floors, thick walls, basements, and the other Wi-Fi-unfriendly features. When an installer cannot rely on Wi-Fi coverage throughout a building or business, we cannot claim a full solution for IoT.
Four initiatives seek to remedy these shortcomings. All are progressing through the standards process, and some are years from shipping. But they are worth following because the Wi-Fi industry has shown success in reaching technical agreement on standards, then building and shipping products based on new certifications.
The first Wi-Fi initiative is “extended-range” 802.11ah. This improves range by moving to a lower frequency, the 900 MHz band, and narrow 1 MHz RF channels. Narrower channels and protocol changes reduce chip power requirements. It should be possible to get a range of twice 802.11n (at 2.4 GHz): a reliable 40+ meters range at 150 kbps (single stream) or, with a more complex dual-stream chip, multi-Mbps at 80+ meters. The 900 MHz band, while allowed for license-exempt use in the U.S., is not harmonized globally, but the better propagation characteristics (over 2.4 GHz or 5 GHz) are important for increased range.
This looks promising, but in addition to spectrum, the timescale is a potential risk. While 802.11ah is already an IEEE standard, the Wi-Fi Alliance will take a while to conduct interoperability tests and develop an industry certification – it’s a frustratingly deliberate process, but we have not found a better way – and by the time the technology is ready to ship, there’s a risk the market may have moved on. But by most measures, this is the Wi-Fi industry’s flagship entry for mainstream IoT applications, with the range of Zigbee (which uses multi-hop mesh to compensate for shorter hops) and battery life surpassing BLE.
Meanwhile, another initiative, the “Connected Home,” proposes a stop-gap approach to bridge 802.11ah’s timescale and backwards-compatibility challenges. An intermediate proxy server in the home would communicate with the current Wi-Fi access point, answering on behalf of end-devices that in turn connect to it, while allowing those devices to sleep for much longer intervals. This approach offers a short-term path to lower-power consumption. Connected Home doesn’t really extend range, but should make Wi-Fi IoT devices in the home more viable while working with existing access points.
A more recent idea presented to the IEEE proposes extending Wi-Fi to provide equivalent functionality to Zigbee indoors and over short distances outdoors. Designed for the 2.4 GHz band, it is closer to existing Wi-Fi than 802.11ah. Range improvements come from narrower RF channels and lower rates, rather than lower frequencies. It should be implemented with a simple low-rate addition to existing chip designs, much easier for the chip and module designers to implement and hopefully included in all new 2.4 GHz Wi-Fi chips in the same way that higher rates were added in the past.
Meanwhile, we must not forget the UHF bands, where propagation is even more favorable than at 900 MHz. “White space” rests on a spectrum-sharing arrangement, where Wi-Fi access points re-designed for the 450 to 700 MHz TV bands use sensing and a geographical database of incumbents to discover and occupy locally unused spectrum. IoT is not a primary target for this technology, but it’s well-suited to wide-area sensor and control networks.
We sometimes forget that Wi-Fi’s success is largely due to a single application, Internet connectivity for mobile phones, tablets, and PCs. This has provided such a rich market for Wi-Fi that there has been little need to branch out. But IoT is one of several new opportunities for short- and medium-range wireless technologies and the industry is – at last – determined to offer a viable alternative to Zigbee and BLE.
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