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Living In A Dual-Band Wi-Fi World

By Craig Mathias in · Technology · June 21, 2017
If the next hottest thing in Wi-Fi spectrum is 5 GHz, why is there still so much talk about planning around 2.4 GHz devices? After all, the latest Wi-Fi standard, 802.11ac, is 5 GHz-only and new 5 GHz devices continually stream into the market. The fact is, many 802.11ac access points are dual 5 AND 2.4 GHz radio, and 2.4 GHz devices are still heavily in use - and will be for the foreseeable future. We keep talking about 2.4 GHz … because 2.4 GHz isn’t going anywhere any time soon. This blog series will explain the role of 2.4 GHz in a dual-band world, starting with some historical context for spectrum.

Optimizing our use of available spectrum is at the heart of essentially all elements of modern life. Spectrum is the highway all that wireless runs on.

There’s only one electromagnetic spectrum, covering a vast range of frequencies (regulated frequencies in the US stretch from 9 KHz to 300 GHz). But most of this is useless for WLAN-class communications, and much of this spectrum is already allocated to a correspondingly-vast array of long-standing wireless services.Many 802.11ac access points are dual 5 AND 2.4 GHz radio, and 2.4 GHz devices are still heavily in use - and will be for the foreseeable future.

As such, we’re left with only relatively small chunks of spectrum – 26 MHz and 900 MHz, the above-noted 83.5 MHz and 2.4 GHz, around 500 MHz at 5 GHz (the rules here are complex), and a few more I’ll get to later.

The key trends of recent years – more users with more devices and more apps, including those requiring time-bounded communications – show no signs of deceleration.

Maximizing the use of spectrum, then, is key. Essential. Way more important than almost any other element of wireless. You get the point –spectrum is limited, so make the most of it.

With so much spectrum available at 5 GHz and with the latest and greatest 802.11ac standard operating only in this spectrum, 2.4 GHz must be obsolete, right?

The answer is no, but first I’ll provide a little historical perspective to this position that I’m sure is beyond the awareness of many current practitioners.

Some Wi-Fi history

Let’s go back to 1999 and IEEE 802.11a – the first standard to specify the use of 5 GHz spectrum, in this case the unlicensed ISM band from 5.725-5.875 GHz.

You may not remember this key development in the history of Wi-Fi, even if you’re otherwise old enough to otherwise do so because – well, .11a was a serious flop, this despite the fact that building radios that could operate at those frequencies required major advances in semiconductor technologies that today underlay way more than just Wi-Fi.

Bottom line: 802.11a worked; it just didn’t sell.

And why was that? Because of a half-truth that 5 GHz yielded much less range than 2.4 GHz.

Why half-truth? Because, at face value, such is in fact true: 5 GHz signals in general do not propagate as far as 2.4 GHz signals at any given transmit power. Now the whole truth: At any given range, over which 802.11a could provide sufficient range, it always outperformed Wi-Fi operating at 2.4 GHz, as typified in 802.11g (which appeared a few years later and is essentially the same technology as .11a but operating at 2.4 GHz).

And why was that effective performance better? Easy: because it was rare to find any other traffic or signals of any form in those bands in essentially every location. Farpoint Group immediately adopted .11a, and we couldn’t have been happier (until .11n, anyway).

The irony here is that range was ultimately recognized as the last thing to optimize for (in most cases, anyway); as adoption of Wi-Fi zoomed, capacity provisioned via dense deployments of APs – less range between endpoints – was clearly the right direction to go, and remains such today.

Again, few got this at the time.

Fast-forward to today

5 GHz is, for many, the only spectrum that matters. Despite the irony, it’s easy to see why: Thanks to the U-NII bands, there’s a lot more spectrum available at 5 GHz than there is at 2.4 GHz – about five times as much.

To be fair, there are other allocations of spectrum which could be used for Wi-Fi – the unlicensed PCS bands, the TV White Spaces, other ISM bands, the new CBRS spectrum, and, the mother lode, 60 GHz with its 7 GHz of spectrum (again, U.S. allocation) that’s home to hard-to-find 802.11ad products but which promises fast and very-high-capacity services over the next few years, albeit with even more-limited range.

But 2.4 GHz, even with all this, will remain important. And, next time, we’ll discuss why.

Craig Mathias (@farpoint1)

Craig J. Mathias is a Principal with Farpoint Group, an advisory firm specializing in wireless networking and mobile IT. Founded in 1991, Farpoint Group works with technology developers, manufacturers, carriers and operators, enterprises, and the financial community. Craig is an internationally-recognized industry and technology analyst, consultant, conference and event speaker, and author. He currently writes columns for Boundless, Connected Futures, CIO.com, and various sites at TechTarget. Craig holds an Sc.B. degree in Computer Science from Brown University, and is a member of the Society of Sigma Xi and the IEEE.

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