11ac's First Wave: What to Expect

The emerging 802.11ac standard promises significant performance enhancements over the current 11n standard, including an eye-popping 7-Gbps maximum throughput. But as vendors begin to roll out pre- or draft-standard products, what performance can you realistically expect? You'll get increases in rate over range, individual throughput and aggregate capacity, but don't bank on 7 Gbps any time soon.

11ac is a grab-bag of incremental refinements that largely build on lessons learned from 11n to eke more out of the same technologies. Like 11n, 11ac uses wider channels to increase throughput. 11n combined 20 MHz-wide channels into 40 MHz pipes. Early draft 11ac products will pick up where 11n left off by combining 40 MHz-wide channels into 80 MHz pipes.

Eventually, final 11ac products will offer the option of 160 MHz channels, although it's not clear whether enterprises will choose to use big chunks of spectrum this way.

11ac also boosts data rates by packing four times the number of bits into each transmission. The standard increases Quadrature Amplitude Modulation (QAM) symbol density from 11n's 64 QAM to 11ac's 256 QAM. But there's a catch: 256 QAM can only be used over short distances--perhaps 20 feet in early draft 11ac products. Otherwise, 11ac products will drop back to 64 QAM.

Like 11n, 11ac uses multiple-input multiple-output (MIMO) and simultaneous streams to boost max data rates and aggregate capacity. But where 11n APs could support up to four transmit and four receive streams (4x4), 11ac APs will double up to 8x8. However, most vendors expect early draft 11ac APs will stay with 4x4, focusing instead on other 11ac tweaks.

For more on vendor plans for 11ac, and how to prepare for the new standard, see the report "Is Your WLAN Ready for 802.11ac?" Registration is required.

Shifting Into High Gear

In addition to the above improvements, 11ac deviates from 11n in two significant ways. First, 11ac abandons the overcrowded 2.4 GHz band and will operate only in cleaner 5 GHz airspace. Second, 11ac introduces a new technique dubbed multiuser (MU) MIMO that will use beam-forming to simultaneously transmit/receive independent streams, letting a single AP communicate with up to four clients at once.

Reducing interference and competition by moving to the 5 GHz band can increase data rates, even without tossing in 256 QAM or extra antennas. And 5 GHz is a necessity to use 80 or 160 GHz channel widths. So expect to see these benefits emerge in new 11ac products this year--including single-stream smartphones that will enjoy better battery life by transmitting faster, for shorter periods.

However, MU-MIMO won't appear until the second wave of 11ac products in 2014-2015. Until that happens, Gigabit Wi-Fi can't hit that monster 7-Gbps data rate promised by the standard. In the meantime, expect to see Wi-Fi-certified draft 11ac single-stream clients reaching 433 Mbps and APs transmitting up to 1.3 Gbps. These rates still blow away the best of today's 11n products. If you set your expectations appropriately, you won't be disappointed.

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Lisa Phifer is president of Core Competence, a consulting firm focused on enterprise adoption of emerging network and security technologies. Lisa has been involved in the design, implementation and evaluation of networking, security and management products for 30 years.