2.4 GHz networking is five feet under with 802.11ac

Matthew Gast

This post originally ran on the Aerohive blog where Matthew Gast has his own author blog.

In many ways, spectrum is the wellspring of the Wi-Fi industry. At the time I started working with wireless LANs over a decade ago, most products were built on either the original 2 Mbps 802.11 direct sequence specification, or if you were well-connected (both to a network and to a source that would give you products!), the blazing fast 11 Mbps offered by 802.11b. At the time, 802.11a was emerging, and the value proposition was simple: more spectrum supports more devices.

802.11 began life in the US in the ISM bands, and essentially staked its future on the slim 83 MHz band available around 2.4 GHz. To put 83 MHz in perspective, check out the NTIA’s spectrum allocation chart – it’s tough to see the tiny ISM bands. Back in 2004, 802.11a devices were few and far between.

It’s amazing what the tsunami of mobile internet devices will do for you. Building high-density networks is the order of the day for Wi-Fi infrastructure vendors. Whether it’s a conference room, auditorium, school room with 30 students on iPads, or a temporary meeting site, there are just too many devices crammed into the room to get decent speeds out of a mere 83 MHz.

When the 802.11ac task group was chartered, they were given a wide scope: Develop a gigabit wireless LAN standard using spectrum below 6 GHz. The charter offered the option of building a standard that would use both the existing 2.4 GHz spectrum and the multiple 5 GHz options.

In the end, the task group decided to produce a specification that operated only in the 5 GHz bands. The current 802.11ac drafts are spectrum-hungry. Significant portions of the speed gain come from using wider channels; 802.11ac includes options for both 80 MHz and 160 MHz channels, compared to the 20 MHz and 40 MHz channels we know and love today in 802.11n. Using an 80 MHz channel in the crowded 2.4 GHz band is simply a non-starter. There are so many 2.4 GHz devices in any spot that 802.11ac would be deployed that the odds of being able to see the whole band clear and transmit on it are even lower than the odds of winning the lottery.

As a result, 802.11n is likely to be the capstone technology in the 2.4 GHz band. 802.11n is as good as it gets for 2.4 GHz. New standards will bring higher speeds, but the new standards won’t come to 2.4 GHz. The first wave of 802.11ac products will still be dual-band – it’s just that it will be a dual-radio device with 802.11n (2.4 GHz) and 802.11ac (5 GHz).

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