There are actually more Wi-Fi frequencies than you may think, and with all of the current and future Wi-Fi frequencies and technologies out there, things can get confusing. This blog will take a a high-level look at what’s out there and what’s coming up.

The Well-Known Frequencies — There are two dominant Wi-Fi frequencies used by 802.11a/b/g/n systems; 2.4 GHz and 5 GHz. Almost all modern Wi-Fi devices are made to operate in one or both of these frequencies.

Public Safety — The same basic OFDM technology used by 802.11a in 5 GHz is also used in a 4.9 GHz public safety band. This band is 50 MHz wide, is only available in some regulatory domains and requires a license. This band has specific, limited purposes, so you don’t see a lot of commercial interest or attention here.

802.11y — The FCC also opened up 50 MHz of bandwidth in a 3.6 GHz licensed band. OFDM is also used here. In the US, this band usage is not limited to certain technologies so the band will be shared, but does require a license. It seems that there aren’t many benefits to this frequency band, and the interference avoidance requirements represent a moderate R&D requirement without much ROI.

VHT <6 ghz=”” 802=”” 11ac=”” u=””> —  You may have heard about this PHY spec in development. It builds on 802.11n MIMO technology in 5 GHz and seeks to expand on the HT PHY with a few developments that are a natural next step. 802.11n gave us 40 MHz bonded channels. 802.11ac will give us 80 MHz channels and, likely, 160 MHz channels. 80 MHz bandwidth will get us past the gigabit rate threshold. MIMO will also be expanded to 8×8, but since client devices aren’t adopting that type of power hungry radio anytime in the near future (or ever), 8×8 will be used for MU-MIMO. MU-MIMO allows an AP to transmit simultaneous downlink frames to multiple users (MUs).

VHT 60 GHz (802.11ad) — This PHY opens up a fresh use case for Wi-Fi in the form of very high throughput at short range. At the 60 GHz frequency range, there are a lot of challenges getting the kind of range that would be useful to enterprises. We’ll see short-range, high bandwidth applications, but I’m still failing to see the exciting benefits that have been touted in the press.

White-Fi (802.11af) — There has also been some exciting buzz in the past several months about TV whitespace frequencies between 50 and 600 MHz. The benefits and limitations of this band are discussed in a number of good articles out there. Contiguous bandwidth is in short supply which is a big issue with this frequency, so we see a handful of 6 MHz-wide channels which will yield lower transmission rates than 802.11a/g. The merits of a low frequency are fairly well known; that is, despite the throughput-deficient bandwidth, the range/coverage is advantageous. The evident winner with this technology are rural broadband applications, where coverage is more important than bandwidth and high user density.

Least and last — 900 MHz. 900 MHz was a popular pre-802.11-Wi-Fi frequency way back in the 1990’s. It often gets lumped in with Wi-Fi frequencies because it is an unlicensed ISM band. You’ll still see some legacy technologies working their stuff there, and you might see a few modern, proprietary ones as well. This is a semi-popular broadband frequency with decent range and limited throughput. Many vendors use proprietary PtP and PtMP solutions here for wireless distribution, but they are not defined by 802.11, and they are not designed for client access. Shame on them.

Frequency Recap:

• 50-600 MHz TV Whitespace — Good range, low capacity.
• 900 MHz — Proprietary PtP and PtMP. Decent range, slow rates.
• 2.4 GHz — Well-known and used.
• 3.6 GHz — Little-used, licensed band.
• 4.9 GHz — Licensed public safety band.
• 5 GHz — Well-known and used, the future of Wi-Fi.
• 60 GHz — Short range, very high throughput.

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