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20 MHz, 40 MHz, 80 MHz and more…

May 2, 2016


We are surrounded by waves: radar, radio, mobile telephone, Wi-Fi etc., all occupying an established man-made order and based on invisible highways known as frequency bands.

Wi-Fi technology, on the whole, uses 2.4 and 5 GHz bands, a small part of the electromagnetic spectrum divided into a series of channels, over which information flows (like traffic on a freeway). Channel distribution is regulated by legal standards (set up by the USA, Europe, Japan, etc.) to guarantee interoperability between devices emitting waves and prevent interference with others.

802.11n technology and its limitations

The most widely-known Wi-Fi technology is 802.11n. Products using this technology can operate over both bands using 20MHz wide channels.

Channel width is very significant. The greater the width, the better the information transfer rate and, as a result, the faster the connections. However, having a wider channel has its drawbacks: it means increased radio frequency space occupation within a band.

802.11n offers the possibility of operating at a higher speed through channel bonding: joining two 20MHz bands to make one of 40.

This option is easy to accomplish in a 5GHz band, where there are many channels and little operating equipment (although new devices are beginning to ‘colonize’ this area), yet extremely difficult in 2.4GHz.  There are only 13 20MHz channels in 2.4GHz, which quickly become congested due to many devices that, in turn, generate interferences. Thus, it’s practically impossible to connect to 40MHz channels in that frequency band.

As expected, it was merely a matter of waiting for new generation technologies, such as 802.11ac, to evolve and improve channel width with the prospect of far better features.

And so it did, with 802.11ac being the first.  This technology, operating over 5GHz only, is able to use 20, 40, 80 and so on…up to 160MHz channels!

5GHz, however, is limited in space. Only n channels can fit, depending on their width. In Europe, for example, there are 20-25 20MHz channels, 8-12 40MHz and only 1-2 160MHz.  In other words, the same problem rears its head.

So is 802.11ac the answer?

What first drew our attention to this was the new 802.11ac wave 2 Access Points, which offer radio performance of up to 3.5 Gbps, 4 flows and 160MHz channels. Unfortunately, this tends to be restricted to laboratory conditions.

This is because, with so few 160MHz channels available, APs interfere with each other and degrade the signal. So much so, in fact, that network designers have opted for narrower channels: 80MHz, up to 40 in high density areas, to offer users quality connections.

In the end, despite appearing to be the ideal solution for wireless offices and allowing for quality multimedia content distribution, 802.11ac and 802.11n face similar problems. Published transfer rates are never achieved in real life situations (offices) and any improvement to them would need case by case analysis and research on radio distribution.

However, 802.11ac not only has wider channels, it also offers significant technical innovations in just its basic version (wave 1).  These include QAM256 modulation, which triples the bandwidth being offered to customers so far and improves MIMO technologies significantly. So far an Access Point could be a Single User MIMO 3×3, or even a 4×4, without tapping into its full potential as there are few terminals on the market that support this.  The second version, 802.11ac Wave 2, is a Multiuser MIMO: for the first time an Access Point can simultaneously serve different traffic flows to different users (an AP MIMO 4×4 can speak to two portable MIMO 2×2 at the same time), and considerably improve net transfer rate to various terminals.

In short, 802.11ac offers users tangible improvements, despite channel difficulties. This solution is here to stay as it provides wireless connectivity services with a quality and performance, which, up until now, was only achieved through cable.

It’s along this technological path Teldat’s putting in considerable time and effort. Not only have we got 802.11ac products already on the market, but are also working in parallel to offer our customers the most competitive solutions as these evolve.

Tags: 802.11n

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