802.11ac Wi-Fi Part 1: Building Blocks
January 27, 2014
With the 802.11ac standard, Wi-Fi has finally matured to the point that it can meet or beat the user experience of Ethernet, making wireless the LAN of choice. Wireless LAN products that use the very high-throughput protocols of 802.11ac to reach gigabit speeds have been gaining ground since the Wi-Fi Alliance launched its Wi-Fi Certified ac program last June. The December publication of the final standard will throw open the floodgates.
In a series of articles, I'll examine the 11ac standard, its benefits, how it's incorporated into products, and enterprise 11ac adoption strategies.
The 802.11ac standard builds on lessons learned from 802.11n, tweaking technologies to get more from multiple input, multiple output (MIMO) wireless devices operating in the 5-GHz radio frequency (RF) band. The major enhancements in the 11ac standard include:
Cleaner airspace: 11ac leaves the 2.4-GHz band to legacy Wi-Fi products, pulling the industry into the wider, less-congested 5-GHz band, improving capacity and performance for all.
Wider channels: 11ac not only mandates support for 40-MHz-wide channels that double data rates, but ups the ante by adding 80- and 160-MHz options needed to reach multi-gigabit speeds.
Tighter modulation: 11ac quadruples data packed into each RF transmission using 256-bit quadrature amplitude modulation (256 QAM) to boost throughput between nearby devices.
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Supporting more streams: 11ac increases the maximum number of spatial streams from four to eight, potentially doubling per-user rates and total capacity, depending on the number of antennas.
Standard beamforming: 11ac standardizes the beamforming concept introduced by 11n, using interoperable per-client transmission optimization to better overcome RF interference.
Supporting more users: Like 11n, 11ac supports single-user (SU) MIMO, where each Wi-Fi access point (AP) can utilize up to four spatial streams to talk to one client at a time. But 11ac also introduces a revolutionary new multiple-user (MU) MIMO option, in which each AP divvies available spatial streams to talk to up to four clients simultaneously, theoretically quadrupling user density.
These enhancements are best viewed as building blocks. Stack them all together, under the best possible circumstances, and 11ac could hit a new top speed of 6.93 Gbps. That’s a fifteen-fold gain over 11n’s 3 x 3 450 Mbps.
In practice, Wi-Fi Certified ac products currently max out at around 1.3 Gbps -- a roughly threefold improvement over 11n, which can satisfy many enterprise customers. In my next article, I'll look at the 802.11ac certified products available today, as well as what's expected in 802.11ac Wave 2 products.