Friday, 28 December 2012

The Fifth Generation of Wi-Fi

IEEE 802.11ac

The extraordinary growth in the number and type of WiFi devices, coupled with the increasing popularity of bandwidth intensive activities such as high definition video streaming, has created the demand for better performance with greater reach. 802.11ac, the next generation WiFi standard is designed to meet these needs.

Wireless LAN sites will see significant improvements in the number of clients supported by an access point (AP), a better experience for each client, and more available bandwidth for a higher number of parallel video streams. Even when the network is not fully loaded, users see a benefit: their file downloads and email sync happen at low-lag gigabit speeds. Also, device battery life is extended, since the device's Wi-Fi interface can wake up, exchange data with its AP, then revert to dozing that much more quickly.
802.11ac achieves its raw speed increase by pushing on three different dimensions:
• More channel bonding, increased from the maximum of 40 MHz in 802.11n, and now up to 80 or even 160 MHz (for 117% or 333% speed-ups, respectively)
• Denser modulation, now using 256 quadrature amplitude modulation (QAM), up from 802.11n's 64QAM (for a 33% speed burst at shorter, yet still usable, ranges)
• More multiple input, multiple output (MIMO). Whereas 802.11n stopped at four spatial streams, 802.11ac goes all the way to eight (for another 100% speed-up).
The design constraints and economics that kept 802.11n products at one, two, or three spatial streams haven't changed much for 802.11ac, so we can expect the same kind of product availability, with first-wave 802.11ac products built around 80 MHz and delivering up to 433 Mbps (low end), 867 Mbps (midtier), or 1300 Mbps (high end) at the physical layer. Second-generation products promise still more channel bonding and spatial streams, with plausible product configurations operating at up to 3.47 Gbps.

802.11ac is a 5 GHz-only technology, so dual-band APs and clients will continue to use 802.11n at 2.4 GHz. However, 802.11ac clients operate in the less crowded 5 GHz band.


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