Understanding gigabit Wireless LAN: 802.11ac and 802.11ad

Just when enterprises are getting comfortable with 802.11n technology, enter gigabit wireless LAN standards 802.11ad and 802.11ac, which could produce draft products in a year.

With 802.11n deployment well under way, enterprises are beginning to eye gigabit wireless LAN.

IEEE standards 802.11ac and 802.11ad (still in working group) both aim to provide gigabit speed wireless LAN in different channels. 802.11ac is chartered to deliver throughput at frequencies under 6 GHz—or the 2.4 and 5 GHz bands (and perhaps 900 MHz too), lending itself to easier migration from 802.11n. Meanwhile, 802.11ad will employ the same underlying technologies over the unlicensed 60 GHz band at a much shorter-range transmission.

The truth about the 802.11ac and throughput

It was just last year that vendors touted next-generation products that increased data rates to 802.11n's 600 Mpbs from 802.11a/g's 54 Mbps. By the end of 2012, In-Stat expects to see products based on draft 802.11ac top 1 Gbps. And that's just the beginning of the potential. By the time the IEEE finalizes 802.11ac and its shorter-range sibling 802.11ad, max data rates will reach 7 Gbps—another order of magnitude.

But these max rates have to be taken in perspective. In the real world, 802.11a/g throughput maxed out around 30 Mbps, declining with distance between AP and station. Similarly, real world 802.11n throughput stops well short of 300 Mbps for today's 3x3 MIMO APs using 40 MHz channels.

802.11ac APs will likely start with 4x4 MIMO (multiple input, multiple output) antennas, according to Aerohive Networks director of product management Matthew Gast. Due to coding and error correction improvements, 4x4 MIMO 802.11ac will have a max data rate of 867 Mbps when using the same channel width and number of streams. Thus, by the end of next year, APs based on 802.11ac draft will double your throughput.

But 802.11ac won't stop there. According to Gast, the initial draft (0.1) distributed for letter ballot in January does not depend upon fundamentally new technologies. "We're applying what we already have to make wireless work faster," he said.

"As we have gained experience with how Wi-Fi performs, we find we don't need as many redundant bits, and we use more aggressive modulation— 256 QAM versus 64 QAM—which gets you roughly 25 Mbps. There's an option for more streams—up to eight versus four—and wider channels, in addition to 40 and 20, 80 and 160. By packing more bits into each stream and being more efficient, 8x8 MIMO using 160 MHz channels gets that monster peak data rate of 7 Gbps."

However, few enterprise wireless LANs are likely to use 160 MHz channels with 802.11ac, because doing so in the 5 GHz band would leave just two non-overlapping channels—the same reason that 40 MHz channels are rarely used by 802.11n in the 2.4 GHz band.

"If you want the fastest data rate at peak, you want to use the widest channel you can," said Gast. "If you want best total throughput—many stations sharing an AP, doing about the same thing—then you want to use narrower channels." Network engineers should thus expect to devote time to spectrum and capacity planning when deploying 802.11ac.

Where does the 802.11ad standard play?

Functioning in the unlicensed 60 GHz band, 802.11ad will likely be a shorter-range, super-speed technology.

"Range is inversely proportional to frequency. Increasing frequency by a factor of 10 reduces range by a significant amount. So 802.11ad is shaping up to be more of a personal area range, and will probably be used in some ways that you'd use Bluetooth today, but with higher data rates," explained Gast.

In short, network engineers should plan for 802.11ac as an evolution of 802.11n–increasing speed and capacity for today's enterprise wireless LANs. But they should be looking at 802.11ad for different applications—primarily short-distance, peer-to-peer connectivity. One potential use for 802.11d's short, fat pipes will be offload and backhaul.

Multitasking MIMO and beamforming

Perhaps the most interesting technological advance included in the 802.11ac draft is multiuser MIMO (MU-MIMO).

With 802.11n, vendors learned how to use transmit beamforming—or the ability to focus RF energy in a given direction to improve delivery to individual stations. With 802.11ac, they'll have a chance to learn how to implement MU-MIMO—the ability to transmit beamforming to stations that lie in different directions simultaneously using the same channel. For example, an eight-antenna AP might be able to use 4x4 MIMO to two physically separated stations at once, eking out twice the capacity from a single 40—or 80 or 160—MHz wide channel.

"MU-MIMO leverages the fundamental of [Ethernet] switching by reducing contention. It's likely to work better in the downstream direction because APs will need to keep track of stations and be aware of [spatial] overlap," said Gast. "It's easier to think this stuff up than to build it, so I'm anxiously awaiting to see chipsets that can do this."

Read part two of this series to learn about considerations in gigabit wireless LAN planning.

About the author: Lisa A. Phifer is president of Core Competence Inc. She has been involved in the design, implementation and evaluation of data communications, internetworking, security and network management products for more than 20 years and has advised companies large and small regarding security needs, product assessment and the use of emerging technologies and best practices.

This was first published in May 2011

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