What you need to know about 802.11ac Wi-Fi

Yardena Arar

The Wave 2 update for the relatively new 802.11ac Wi-Fi standard promises even faster and more efficient networks.

Here’s what to expect — and why you might want to wait a bit before purchasing that new 802.11ac router.

The move to the newest Wi-Fi standard — 802.11ac — has been under way for a couple of years now. As with each new generation of Wi-Fi, 802.11ac offers faster connections for all devices that support it. But the newest technology built into 802.11ac should give wireless networks a significant speed boost — especially in today’s typical networking environment of multiple smartphones, tablets, set-top boxes, laptops, printers, and other devices — all competing for time on the router.

Enhanced versions of new Wi-Fi standards are relatively common phenomena. You might recall all those Turbo-G and pre-802.11n products that appeared during the long 802.11n incubation period. But the improvements were always proprietary; typically, the devices that could actually use the enhancements all had to come from the same vendor.

That shouldn’t be the case for the upcoming 802.11ac Wave 2 products. Wave 2 isn’t a proprietary enhancement developed by one Wi-Fi vendor; instead, it’s a set of optional components in the final 802.11ac specifications, ratified by the IEEE standards organization just this past January (more info).

With every new amendment of the 802.11 standard, products are typically released long before the IEEE gives its final blessing. That’s partially the case with 802.11ac: products based on the new Wi-Fi standard have been shipping for more than two years. But those products are based on the mandatory component of the 802.11ac standard (sometimes referred to as Wave 1). Wave 2, again, is a set of optional features, and those products are still to come.

Whereas the IEEE develops and ratifies Wi-Fi standards, an industry trade group — the Wi-Fi Alliance — uses certification programs to promote device interoperability. Essentially, it polices how vendors implement the standards. The Wi-Fi Alliance is already certifying the first generation of 802.11ac devices, and it’s now working on amending that certification program to add Wave 2 features. However, they haven’t disclosed exactly which Wave 2 enhancements will be added to the certification program or when they expect to begin certifying using the amended specs. That said, the Wi-Fi Alliance program should ensure that all certified 802.11ac devices work together — but Wave 2 products should work somewhat faster (more on that below).

Defining the new enhanced 802.11ac standard

The timeline for new Wi-Fi products has always been confusing. In theory, the IEEE would ratify a new standard and Wi-Fi vendors would then produce devices based on that standard. But in most cases, it’s quite the opposite; products based on a new Wi-Fi standard are often out long before the IEEE publishes the standard. The vendors build their devices based on the draft version of a new standard. (That was certainly the case for the now common 802.11n and 802.11ac.) Any changes a vendor might need to make once the standard is final can often be handled via firmware updates.

That seemingly skewed timeline might explain the two “waves” of 802.11ac technology. To ensure interoperability, the manufacturers of Wave 1 devices (nearly all 802.11ac products currently sold) stuck with the standard’s mandatory component as defined in the 802.11ac draft specifications. They left the implementation of the optional component for a second generation of 802.11ac devices.

The mandatory component focuses on channel width; typically, a wider channel gives faster Wi-Fi throughput. 802.11ac requires support for 80MHz channels — versus 802.11n’s maximum 40MHz. The maximum speed of current 802.11ac-certified gear is 1.3 gigabits per second (Gbps). (802.11n delivers up to 600 megabits per second.)

Also, 802.11ac works only on the (for now) less-crowded 5GHz band; the 802.11n spec covers operations on both 5GHz and 2.4GHz bands, but most early “n” routers and adapters supported only the now oversaturated 2.4GHz band, and many of those products are still in use. (The 5GHz band offers more non-overlapping channels, which reduces overcrowding in places with many Wi-Fi devices, and also allows for the wider channel bandwidths required by 802.11ac.)

By default, 802.11ac is backward-compatible with any 802.11n device using the 5GHz spectrum. But because there are still millions of 2.4GHz-only “n” devices in use, most current 802.11ac routers also include 2.4GHz “n” radios for full backward-compatibility. In other words, 802.11ac won’t be the reason why you suddenly lose Wi-Fi at the local coffee shop.

Wave 2 products, expected out next year, will add the standard’s optional component. One of the optional features is support for 160MHz channels through channel bonding. Wave 2 devices will also support between four and eight spatial streams, whereas devices using only the mandatory component support only up to three spatial streams. (Spatial streaming is a multiplexing technique that increases channel bandwidth by using multiple signals over the same channel. Each stream must be sent by a separate antenna, so a device that supports eight spatial streams needs eight antennas [Technopedia definition].)

Wave 1 (and 802.11n) specs provide for single-user MIMO (multiple input-multiple output; more info), but Wave 2 supports multiple-user MIMO (MU-MIMO).

Related to spatial streaming, MIMO improves Wi-Fi throughput by sending and receiving radio signals over multiple antennas. But unlike full spatial streaming, MIMO doesn’t increase overall bandwidth. It does, however, improve network efficiency when there are several active Wi-Fi devices on a network.

In 802.11n and 802.11ac Wave 1, a MIMO transmitter (e.g., a router) can service multiple Wi-Fi devices only one at a time, in sequence. MU-MIMO technology can stream to multiple clients simultaneously.

Combined, Wave 2’s enhancements can — in theory — deliver impressive speeds of up to 7Gbps. Real-world speeds are, of course, likely to be significantly slower. The bulk of those Wave 2 enhancements will work only between devices that fully support 802.11ac’s optional component specs. But on a mixed network of Wave 2 and non–Wave 2 devices, the entire network — again, in theory — should not drop down to the slowest device.

For now, consider 802.11ac — especially Wave 2 — as future-proofing. It’s predicted that most Wi-Fi devices shipped in 2015 will have to support some level of 802.11ac. Undoubtedly, price will determine what optional enhancements you get in your next “ac” device. (For a good overview of the 802.11ac standard, see the Motorola white paper [PDF], “What you need to know about 802.11ac.”)

Waiting in the wings: 802.11ax Wi-Fi

Even further down the road, better network efficiency will be the goal of the next-generation Wi-Fi standard, which the IEEE has already named 802.11ax. It’s interesting to note that before the IEEE formally named the 802.11n, 802.11ac, and 802.11ax standards, the teams working on them were known as “the high-speed WLAN,” “the very high-speed WLAN,” and the “high-efficiency WLAN” study groups. Note that there’s nothing about speed in that last name (for 802.11ax).

A couple of months ago, Chinese vendor Huawei made a little news splash by demonstrating what it described as 802.11ax technology (more info). But in truth, the standard is still a work in progress. In fact, it’s unlikely 802.11ax will be ratified much before the end of the decade, although (as usual) products based on the draft spec will likely appear a year or so earlier.

That said, the reported focus of 802.11ax is on making smarter antennas, which in turn will improve Wi-Fi performance when multiple devices are placing heavy demands on the network simultaneously. That might not seem like a big deal, but the number of Wi-Fi devices connected to the Internet is exploding, and antennas are a bottleneck. Do you want to know how many devices your home or small-business Wi-Fi network is supporting? Take a look at your router’s DHCP client table — you might be surprised.

In the near term, Wi-Fi device vendors will continue to add their own “enhancements” to both “n” and “ac” devices. For example, in a demo at Broadcom’s Sunnyvale offices, a router based on the company’s 5GHz Xstream technology delivered nearly twice the bandwidth of a conventional 802.11ac router — to an assortment of both 802.11ac and 802.11n devices. In Broadcom’s view, Xstream’s support for legacy devices offers a distinct advantage over Wave 2 technology.

If you’re looking for a high-end 802.11ac router now, NETGEAR has just released its U.S. $300 Nighthawk X6 AC3200 Tri-Band WiFi Router (more info). It might be one of the first models to support dual 1.3Gbps bands. ASUS will reportedly have a competing model (also based on Broadcom’s XStream technology) out soon. You can also find numerous dual-band (802.11n and 802.11ac Wave 1) models starting at about $100.

Given the new standard’s optional features, knowing exactly what you’re getting in a new 802.11ac router might take some careful reading. But whatever route you take, be sure that the router supports your older 2.4GHz devices — in other words, that it’s certified for 802.11n on the 2.4GHz band, regardless of which 802.11ac flavor it supports for 5GHz operations.



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All Windows Secrets articles posted on 2014-07-24:

Yardena Arar

About Yardena Arar

Yardena Arar has written about technology for the New York Times, the Canadian Press, the Associated Press, and the Los Angeles Daily News. She was an editor at PC World magazine from 1996 to 2009, and is now a PC World contributing editor.