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New Wi-Fi coming in waves, but surf at your own risk

David Callisch, VP of marketing, Ruckus Wireless | June 24, 2013
802.11ac promises to deliver the next big step in performance, but without better RF controls performance boosts will be limited.

This vendor-written tech primer has been edited by Network World to eliminate product promotion, but readers should note it will likely favor the submitter's approach.

802.11ac is all the rage, and rightfully so. It represents another fundamental change in the innovation of the Wi-Fi 802.11 protocol that promises to boost wireless LAN speeds into the gigabit world.

802.11ac gets this big leap in Wi-Fi performance using wider channels, more efficient modulation (the way in which bits are carried within RF waves), and multiple user connections (so-called multi-user MIMO). And it will come in waves. Literally. However, Wave 2 requires new silicon chips that are different from Wave 1 devices, meaning a hardware upgrade will be required.

Also, beware that not all 802.11sc access points will be created equal. Many using the Broadcom chip will suffer from some limitations, such as the inability to support more than 50 encrypted clients. And without an onboard CPU in the Broadcom chip, all Wi-Fi functions will have to be processed by the AP's host CPU. This is far less efficient because the offloading prevents the AP CPU from using low-power states.

As always, don't actually believe that you'll get any of the gigabit speeds that vendors are promising anytime soon because most of these features are dependent on how well Wi-Fi access points can manage the RF spectrum. The vast majority of enterprise APs today still use basic omni-directional antenna designs that have no control over RF signals. 

802.11ac

Steps forward
The single best benefit of 802.11ac is it operates within the channel-rich 5GHz band -- offering 500MHz of bandwidth from 25 non-overlapping channels (compared to 83.5MHz of bandwidth within the 2.4GHz band using three non-overlapping channels).

Wider channels are also compatible with 20MHz or 40MHz 802.11a and 11n devices. 802.11ac uses an enhanced version of protection mechanisms (RTS/CTS) to dynamically determine whether all or only some (such as the primary 20MHz, 40MHz or 80MHz) of the wider channel is available for transmission.

Finally, a fundamental priority for the IEEE is to maintain backward compatibility with previous 802.11 protocols. As a 5GHz-only technology, 802.11ac supports both 802.11a and 11n frame formats and protection mechanisms and is fully backward compatible with both.

So we're all good, right? Not so fast.

Spectral efficiency: the key to faster 802.11ac
What vendors won't tell you about 802.11ac is that spectral efficiency can easily be reduced in a Wi-Fi network whenever multiple APs are using wider channels.

Spectral efficiency relates to the information rate that can be transmitted over a given bandwidth in a specific communication system. It is a measure of how efficiently a limited spectrum is utilized by the physical layer protocol.

 

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