Connect the Dots: IEEE 802.11ax WLAN Standard to Connect Many IoT Dots

Create: 04/14/2017 - 15:22

Watch this space. Literally. It’s been discussed for four years already, but the IEEE 802.11ax wireless LAN (WLAN) standard is finally starting to gel, and it’s going to greatly impact IoT deployments.

It sounds counterintuitive, given that so much of the discussion of IoT connectivity revolves around wireless interfaces such as Bluetooth, LoRa, Narrowband-IoT, Sigfox and ZigBee,  just to mention a few. Still, Wi-Fi is the dominant interface for wirelessly connecting devices to the Internet.

The reasons are many, of course. It’s natively IP addressable, it has long range, supports multiple users, has greater bandwidth, it’s power consumption can be scaled down for battery-driven applications, and it’s pervasive in homes, industry, the enterprise and municipalities.

In fact, it’s the pervasiveness and popularity of Wi-Fi, whether in the 2.45- or 5-GHz band, that sent the IEEE 802.11 group back to the drawing board in 2013. The problem was, and still is, the ability of Wi-Fi to scale with users in high-density environments such as airports, stadiums or downtown. Twenty years of WLANs, and this is still an issue: who would have thought it?

This density problem, which results from a combination of interference at the physical layer (PHY) and user coordination issues at the media access control (MAC) layer, has been tackled in stages. For example, when IEEE 802.11g was announced for the 2.45-GHz band, the group introduced the use of orthogonal frequency division multiplexing (OFDM).

ofdm ofdma 802.11ax

For 802.11ax, the IEEE is borrowing from cellular technology and is using OFDMA for greater user density and better quality of service. (Image source: Hussein Al-Sanabani, Sakarya University)

Instead of encoding data on a single wideband signal using high-order modulation, OFDM encodes it across multiple narrow bands, using lower-order modulation. This requires more complex processing but reduces interference.

OFDM addressed issues such as narrowband and multipath interference, so it was the default scheme used when the IEEE added 5-GHz operation to the specification with 802.11a. This took Wi-

Fi out of the noisy 2.45-GHz band and gave it even more spectrum in the 5-GHz band, along with OFDM. Data rates went up (good for video) and interference went down. Alas, so too did range, as for a given RF output power and data rate at the antenna, physical range decreases as the operating frequency increases.

However, the ensuing addition and refinement of multiple input, multiple output (MIMO) antenna arrays and beamforming has mitigated the impact of the higher-band operation. Despite these additions, and their many iterations, the density problem still looms because the number of users continues to increase. With the emergence of the IoT, density will be increasing a lot more quickly as connected devices start to come online at a rate that may eclipse the number of users. That’s why 802.11ax is so important for IoT solutions providers.

One eye on the future: 802.11ax

The prime directive of 802.11ax is to cater to current and future WLAN density issues. To this end, it is drawing from what has been learned from cellular networks, that orthogonal frequency, multiple access (OFDMA) is even better than OFDM.

With OFDM, a user or an IoT device occupies all the OFDM subcarriers for the duration of a data transfer. Even though 802.11ac is fast, at up to 1 Gbit/s for multiple stations, this still causes bottlenecks. Instead, OFDMA allocates certain blocks of frequencies and time slots to each user, and it can control this allocation, dynamically.

This adds complexity on the hardware side, and potentially greater power consumption for the access point (AP), but user and IoT device gets greater quality of service (QoS). It bears repeating that the provider can control this QoS.

The IEEE group is adding many other features, and it is hard at work developing the future of WLANs, including power control and higher orders of modulation for increased data rates.

However, when it emerges in 2018, as expected, it will change the face of the wireless industry. So much so, that IHS Markit expects 116,000 802.11ax-enabled devices in 2019, increasing to 58 million devices in 2021, and that it will become the most popular Wi-Fi standard in the next decade.

For IoT solution providers, it means getting prepared to exercise greater control over a device’s use of the airwaves. Soon you’ll be able to provide some level of assurance that an IoT device will connect and provide the required data, when it needs to, vs. when it’s allowed to.

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Patrick Mannion
Patrick Mannion is an independent writer and content consultant who has been working in, studying, and writing about engineering and technology for over 25 years.

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