WiFi Goes Gigabit-802.11ac

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The Interop trade show wrapped up recently in New York City and featured an excellent lineup of sessions on wireless and mobility. The topic of effective strategies for dealing with BYOD clearly topped the list (and popped up in virtually every session I attended), but there was also a lot of talk about developments on the Wi-Fi front.

The one session on Wi-Fi that stood out was "Wi-Fi: Gigabit Performance (and a lot more!)." It provided an overview of the emerging 8023.11ac and ad radio links, along with other interesting developments. The CEO of the Wi-Fi Alliance, Edgar Figueroa moderated the panel.  It featured the Director for Standards and Business Development at Realtek, Sean Coffey talking about 802.11ac. The Marketing VP at Wilocity, Mark Grodzinksy discussed developments with 802.11ad. We'll look at 802.11ac in this TechNote and 802.11ad in the next.

What Network Managers Need to Know

Lisa Phifer of Core Competence wrote about 802.11ac and ad back in March, but Sean Coffey of Realtek got into the details at Interop. The new standard will be the follow-on to 802.11n and will operate exclusively in the 5 GHz band delivering data rates into the gigabit range. At the raw bit level, 802.11ac will support data rates from 6.5 Mbps to 866.7 Mbps on a single stream using a combination of wider bandwidth channels and more efficient coding mechanisms.

Where 802.11n could run on 20 MHz or 40 MHz channels, 802.11ac can be deployed on 20-, 40-, 80-, and 160-MHz channels. Bigger channels translate into more potential bits per second, but it also means there will be fewer channels available. That's something network managers will have to take into account in their planning.

To pack more bits into the available radio spectrum, 802.11ac also uses a more efficient coding system. Like 802.11a, g, and n, 802.11ac uses OFDM signal encoding. However, where 802.11a, g, and n maxed out at 64-QAM (six-bits per symbol), the 802.11ac defines modulation up to 256-QAM (eight-bits per symbol), a 33% increase in efficiency. As we try to send more bits per cycle of radio bandwidth, the probability of error increases. So some of those bits are used to provide forward error correction to improve the reliability of the transmission.

More On MIMO

802.11ac also adds important enhancements to the multiple input-multiple output (MIMO) capability. MIMO allows a transmitter to send multiple simultaneous data streams over the same radio channel and it was first included in the 802.11n standard. However, where 80.11n can send up to four-streams (most existing products use a max of two or three), 802.11ac can go to eight-streams. Eight streams at 866.7 Mbps adds up to a total maximum data rate of 6.934 Gbps versus a maximum of 600 Mbps for 802.11n. In other words, we're looking at a 10x increase in capacity.

The high capacity per stream will be very important to devices like smartphones. The downside of running multiple data streams is that it calls for multiple radios. That means more power draw. To conserve battery, devices like smartphones generally use a single stream, but now that stream will be able to carry a data rate of 866.7 Mbps versus 150 Mbps in 802.11n.

The other key feature in 802.11ac is multi-user MIMO capability. In the 802.11n MIMO implementation, all the streams are used to communicate between the access point and a single device. With multi-user MIMO, different MIMO streams could be directed to different users. This could provide a real boost in an environment where the access point has multiple radios, but the devices are single stream. The access point could now be communicating with multiple users simultaneously, greatly increasing the total network throughput.

While the standard has not yet been finalized, chipsets for 802.11ac are already going into production and we can expect to see enterprise products rolling out early next year. While users are typically reluctant to purchase "pre-standard" implementations, the Wi-Fi Alliance's track record in ensuring compliance with the eventual standard is without blemish, so we fully expect that the lack of an official standard will not deter sales.  That's the scenario we saw with 802.11n.

Conclusion

Interoperability has been a challenge in many parts of our industry, but the Wi-Fi Alliance has managed to get all of the key vendors working out of the same playbook, which is a big reason Wi-Fi continues to flourish. Mr. Figueroa's statistics are pretty impressive. 1.2 billion Wi-Fi devices were shipped in 2011 and the technology has seen 10% year-over-year growth every year since 2001,

Suffice it to say that Wi-Fi is not going away any time soon, and the work of the Wi-Fi Alliance in ensuring multi-vendor interoperability has been one of the keys to its enormous success.

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