Wi-Fi Frequencies: An Overview

Wi-Fi Frequencies: An Overview

By CWNP On 11/16/2010 - 12 Comments

All of the current and future Wi-Fi frequencies and technologies are getting confusing. There are actually more than you might think. Let’s take a high-level look at what’s out there and what’s coming up.

The Well-Known Frequencies — We all know about the 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, requires a license, and is only available in some regulatory domains. By definition, there are specific, limited purposes for this band, 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 used here as well. In the US, this band requires a license, but usage is not limited to certain technologies, so the band will be shared. In my estimation, 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=""> — By now, you’ve probably 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 (or should I say channel). 80 MHz bandwidth will get us past the gigabit rate threshold. MIMO will also be expanded to 8x8, but since client devices aren’t adopting that type of power hungry radio anytime in the near future (or ever), 8x8 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. I haven’t yet read any of the protocol details about this PHY, but I do know that 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) — The TV whitespace frequencies between 50 and 600 MHz have also created some exciting buzz in the past several months. There are a number of good articles out there discussing the limitations and benefits of this band. The big issue with this frequency is that contiguous bandwidth is in short supply, 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. Rural broadband applications are the evident winner with this technology where coverage is more important than bandwidth and high user density. Come soon, please. I love living in the boonies, but Internet access here is lame.

Least and last — I guess I should also mention 900 MHz. Way back in the 1990s, 900 MHz was a popular pre-802.11-Wi-Fi frequency. 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.

Tagged with: Wi-Fi frequencies, public safety, 4.9 GHz, 802.11y, 3.6 GHz, 802.11ac, 802.11ad, 802.11af, 60 GHz, White-Fi, TV White space, VHT

Blog Disclaimer: The opinions expressed within these blog posts are solely the author’s and do not reflect the opinions and beliefs of the Certitrek, CWNP or its affiliates.