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802.11ac Promises Better Coverage, but Won’t Hit Advertised Speeds

Apple’s towering revisions to the AirPort Extreme Base Station and the Time Capsule tout the speed bump that will come from its inclusion of the 802.11ac standard, the latest in wireless local area networking. Instead of (up to) 450 Mbps with 802.11n, your data will zip around at (up to) 1.3 Gbps*†ª⚔! (Note the parenthetical, asterisk, footnote, clarification, and proviso — it’s not that simple.)

Now, it is true that 802.11ac can offer higher speeds than 802.11n, and Apple’s implementation is technically capable of 1.3 Gbps. But as Apple notes at the bottom of the page, “Actual speeds will be lower.” I’ll say. In practice, I would wager that most home users and some business users will see only modest improvement in net throughput across their networks.

What 802.11ac should achieve, however, is far better coverage. Those who moved from 802.11g (a 2003-era standard) to 802.11n (released widely in 2007) remember what a difference that was. Dead spots in your home and office were suddenly lit up. Areas in which you had slow data rates but a good signal were now able to communicate at several times the previous data rate.

Apple doesn’t ignore range and coverage, but that’s really the benefit of 802.11ac for most users, not speed. Let’s dig into Apple’s claims.

Closed Course with Professional Drivers -- I object to Apple’s chart because it’s exceedingly misleading about average, typical performance, and sets expectations far too high. It’s as if Toyota advertised that its consumer sedans could travel at “up to 150 miles per hour!†” (“†Closed course with professional drivers on a sunny day with new tires on a flat straightaway.”) Most drivers will be lucky to average 15 to 30 mph in the city.

When Apple says that its implementation of 802.11ac can achieve up to 1.3 Gbps — and other manufacturers with beefier radio systems already say up to 1.7 Gbps — the reality is that a lot of conditions have to be met to achieve that raw data rate. And, as you well know from decades of network-technology advertising, dear reader, a “raw” data rate (often incorrectly called “theoretical”) is the maximum number of bits that can pass over a network. That includes all the network overhead as well as actual data carried in packets and frames. The net throughput is often 30 to 60 percent lower.

The key improvements in 802.11ac that give it the potential for higher data rates are:

  • 5 GHz only. 802.11ac works only in the higher-frequency 5 GHz band, which, in the countries where that spectrum is available, has many fewer problems with interference. The United States has 23 non-overlapping channels in 5 GHz, but Apple supports only 8 of those. All “802.11ac” base stations and adapters, like in the new MacBook Air models, are really multiple layers of Wi-Fi standards. They can fall back to 802.11n (in 2.4 GHz and 5 GHz), 802.11a (in 5 GHz), and 802.11g (in 2.4 GHz) if necessary to make a connection.

  • Support for super-wide channels. While 802.11b, g, and a allow only for channels that are 20 MHz wide, which max out at a raw rate of about 54 Mbps in those standards, 802.11n allows for channels that are up to 40 MHz wide in 5 GHz and hit about 150 Mbps. (Most base stations won’t try to find and bond two adjacent channels in 2.4 GHz; Apple’s base stations don’t.) With 802.11ac, however, base stations can combine multiple adjacent channels into super-wide channels that are either 80 MHz or 160 MHz wide, and thus have much higher raw data rates!

  • More efficient encoding. 802.11ac’s 80 MHz and 160 MHz channels not only provide more raw spectrum, but also use a more efficient way to pack bits into the radio waves because of that extra frequency space. About 33 percent more data can be squeezed into 80 MHz or 160 MHz on top of the doubling or quadrupling of data by the channel width. That’s 433 Mbps and 866 Mbps in the highest-speed configuration! (There are some technical choices that could reduce those rates, but Apple and most others are going for the gusto.)

  • Multiple spatial streams. 802.11n introduced MIMO (multiple input, multiple output) radio systems to Wi-Fi networks. MIMO can send and receive different streams of data, each at the maximum channel bandwidth, as they follow a different path through space, reflecting off and traveling through objects. This is called spatial multiplexing. Apple’s current 802.11n equipment in laptops, desktops, and pre-2013 AirPort Extreme and Time Capsule base stations (and the current AirPort Express) can handle up to three streams. Some corporate gear can handle four streams. 802.11ac bumps that up to a maximum of eight streams, although we will likely see that many streams only in expensive business equipment for quite some time. (Apple took years to go from two to three streams in its consumer 802.11n gear, while corporate hardware has four.)

If you do the math for Apple’s current 802.11n systems, you get an ideal case of 75 Mbps times two (two 20 MHz channels) times three spatial streams or 450 Mbps — that’s when using the 5 GHz band. With 802.11ac, Apple increases that: using 80 MHz (the biggest channel Apple opted for) with the improved encoding calculates out to 433 Mbps times three streams for roughly 1.3 Gbps. (Some companies that sell to corporations are already using four streams, which gets you that higher 1.7 Gbps advertised top rate.)

But we’ll rarely see that data rate.

Play Nice -- With all Wi-Fi standards, the technology tries to play nice with other networks and potential nearby interferers. Networks slow down when there’s other traffic nearby on the same or adjacent channels, unless the signals can clearly be discriminated from one another. MIMO helps with this, because the multiple antennas allow overlapping signals to be teased out. (Some people argue there’s no such thing as interference, but merely a limit to how effectively a receiver can tease out an incoming signal.)

802.11n had to go a step further. With 40 MHz channels, the chance of stepping on other networks is higher because of the increased radio space. 802.11n is designed to make devices and base stations listen for signals outside of a core 20 MHz channel, such as networks in adjacent businesses, houses, or apartments. If none are detected, the whole 40 MHz channel is used; otherwise, devices stick with the regular 20 MHz channel. Users don’t notice whether a narrower or wider channel is in use, although they might notice the variation in throughput.

802.11ac starts with a disadvantage for its 80 MHz and 160 MHz channels: there are simply not enough of them available without restrictions in most countries to allow multiple networks in the same general vicinity to rely on channels that aren’t already in use. In the United States, only two 80 MHz channels (four contiguous 20 MHz channels) are available: channels 36 to 48 as one chunk and 149 to 161 as another. Europe has even fewer clear channels, with likely just one consistent 80 MHz chunk possible. (Channel numbers are in increments of 5 MHz, so channel 36 comprises 36–39 as a total of 20 MHz, and so forth. Yes, it is confusing!)

Europe and the United States have additional 5 GHz channels that can be used, but with a strict requirement that base stations on these channels (15 more 20 MHz channels in the United States!) must listen for telltale signs of weather-sensing radar used by governments. If detected, the base station has to tell clients that it is switching to another channel and then immediately move to that channel. Manufacturers have told me for years that the detection mechanism suffers from many false positives, and is thus triggered frequently where no radar installations exist! It’s hard to use these channels reliably and introduces complexity in networking software. As a result, Apple has never included these channels as options in its base stations, and most consumer gear avoids it as well. (Meru Networks, an enterprise wireless network hardware maker, has a chart with more detail.)

For the channels in which checking for radar isn’t required, 802.11ac is much cleverer than 802.11n about backing off when it senses there’s traffic on any of the narrow channels it might be combining into one of its wide ones. So it’s quite efficient about using up to 80 MHz (in 20 MHz to 40 MHz swaths) as available for each chunk of data sent. If there are no other networks nearby, or those that exist are mostly quiet, an 802.11ac network can get great throughput. But in places with active networks, throughput drops significantly.

This problem might not exist forever. Future 802.11ac gear could combine 20 MHz or 40 MHz channels that aren’t directly adjacent from different parts of the 5 GHz band.

With Laser-Like Focus -- Don’t let the speed discussion get you down, because 802.11ac does have three distinct advantages: better coverage, better performance at greater distances, and multiple-device simultaneous transmissions.

Let’s take these one at time:

  • Coverage improves. 802.11ac fully implements a feature touted for 802.11n called “beamforming.” With 802.11n, the industry never quite got its act together, and very few devices actually shipped with this option correctly enabled. What beamforming does is use different amounts of power on each antenna to “steer” a wireless signal directly to a device. It’s a way to put some english — just like spin on a billiards ball — on the signal and twist and turn it to hit the receiving device dead on. Beamforming is why Apple now has two separate sets of antennas for these new base stations: the 5 GHz band needs a separate set to form beams uniquely.

  • Better performance at distance. Because of beamforming and the raw increases in speed, even if you can’t get the top raw rate close up, you’re much more likely to get a quite high rate — much higher than with 802.11n — when you’re dozens to even hundreds of feet away from a base station.

  • Multi-user… what did he say? Called MU-MIMO, for multi-user MIMO, this option lets a base station target more than one receiver simultaneously, each with a unique stream of data. This is nifty, because a lot of mobile devices have only single-stream support in 802.11n, and are likely to retain that in 802.11ac. When sending or receiving data, an iPhone on a network now slows everything else on the network down even though it can only receive one-third of the network traffic that a MacBook Pro can. With 802.11ac, the iPhone could be served at its full speed while one or two other devices maintain a full-stream connection at the same time.

These three new features require new 802.11ac radios in all the gear you want to use, which will disappoint those who hoped for some backward-compatible improvements. Unlike the shift from 802.11g to 802.11n — where 802.11g devices saw improvements merely by talking to an 802.11n-capable base station — you won’t see these improvements without new adapters. It worked with 802.11n because its benefits came from more-sensitive receivers, multiple antennas, and more-directed and -powerful transmitters, even without beamforming. 802.11ac uses essentially the same basic technology as 802.11n in that regard and thus requires that all devices have new chips and radios to take advantage of the improvements.

(For a vastly more detailed and technical discussion, Cisco has a very nice explanation from last year.)

Eventually, 802.11ac Will Be the New Normal -- Just as 802.11n gradually made its way first into base stations, then into desktop and laptop computers, and finally into tablets and then smartphones, 802.11ac will follow the same progression as chips get smaller, require less energy, and become cheaper.

For most of us, 802.11ac isn’t a must-have feature, especially when homes and offices that really need throughput already have cheap gigabit Ethernet everywhere. However, as 802.11ac becomes commonplace, we’ll slowly see improvements in speed and more significant ones in coverage.

We might finally reach a point where, instead of the three 802.11n base stations I need to cover my modest main floor and basement home and office (riddled as it is with signal-blocking older building materials), a single 802.11ac base station could handle the whole shack.


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Comments about 802.11ac Promises Better Coverage, but Won’t Hit Advertised Speeds
(Comments are closed.)

Jess Have  2013-06-13 13:58
Very informative as usual!

Just got my new 3 TB TC ac yesterday and it works very well. As noted by you, the range is a lot better than the previous TC
David P  2013-06-15 18:20
This article is so infuriating its not even funny.

802.11AC is nothing but complete market hype.

802.11ac draft (in its current form) offers absolutely no increase in actual distance itself over 802.11n.

NONE. period.

The only thing new here is the additional spatial streams with beam forming that has been around for years now. Its already available in routers available from both ruckuswireless and even in some netgear routers.

You WILL get better data rates with 802.11ac at further ranges but it will NOT give you more range itself.

Stay with 802.11n until atleast 802.11r (r as in romeo) is fully ratified. Anything else is just a waste of money.

At least 802.11R will offer fast roaming which will allow cellular like handoff times between AP's until 802.16 comes along in about 3 years. It's not for another few years until we see actual increases in range using technology that is incredibly expensive for consumers and SMB's in current form.
Glenn Fleishman  An apple icon for a TidBITS Staffer 2013-06-15 18:34
What is fascinating about your comment is that I do not, in fact, state that 802.11ac will offer greater distance.

I say it will offer "better coverage, better performance at greater distances" which are two entirely different matters

Better coverage doesn't mean greater distance; it means removing dead zones (as noted in the article) in existing areas coveraged. Better performance at greater distances is not "greater distance": is that the farther you are from the base station, where you would in 802.11n get a slower data rate you could now get a faster one.

The issue of coverage will come from beamforming. As you note, while "beamforming has been around for years now" it is, in fact, in almost no popularly shipping 802.11n gear. So for most users, they will be switching from regular but useful 802.11n to beamformed 802.11ac, as beamforming is being sold as a competitive feature and should be widely available.

The issue of greater speed at the same distance comes from both beamforming (as noted above, not in wide use), and the flexibility of 802.11ac in how it handles moving from 20 MHz to 40 MHz to 80 MHz and back across very short stretches of data.

I find it very peculiar you're finding fault with a subject on which I agree with you: 802.11ac won't, per se, increase range at all. It will improve performance and coverage in the same area.
David P  2013-06-23 17:48
Glen, why don't you do an article on some of the new tech that EMB's are using in corporate offices that will be available to consumers down the line? Like for instance microwave based Wifi and mag polarity based antenna.
Glenn Fleishman  An apple icon for a TidBITS Staffer 2013-06-23 18:16
Way beyond my ability to test and cover.
Jerry Walz  2013-06-13 14:03
But as of now only the new AirBook incorporates the protocol
Troy Payne  2013-06-13 15:08
Will all 802.11ac gear need to be so... large? The new AEBS and TC are huge compared to the old models. Is there any chance of them shrinking over the next few years?
Glenn Fleishman  An apple icon for a TidBITS Staffer 2013-06-13 15:19
There's 3.5 vertical inches of empty air in the AirPort Extreme Base Station. It could be close to a 3.5-inch cube except that Apple made both it and the Time Capsule the same dimensions to reduce manufacturing costs. The Time Capsule uses the space for a hard drive.
Tonya Engst  An apple icon for a TidBITS Staffer 2013-06-13 16:06
TidBITS staffers have been making jokes amongst ourselves about what you could hide in the unused space in a new AirPort Extreme. We've had some, um, creative, ideas!
M. Perry  2013-06-13 16:47
I wonder if the beam forming could be user programmed to offer more security and less interference with neighbors. It'd need the software to be able to tell the beam not to form in certain directions. Don't go west, for instance, for a WiFi on the west side of the house.
Glenn Fleishman  An apple icon for a TidBITS Staffer 2013-06-14 16:06
Security through obscurity never works with a public signal. WPA2 does. Beamforming isn't precise enough to provide an actual solution, but it will reduce crosstalk among nearby networks by focusing power.
Jim Rea  2013-06-13 17:40
You mention that currently, an iPhone on a network slows down the entire network. Is that only when the iPhone is doing something on WiFi, or is it's mere presence in the area enough to cause the slowdown?
Glenn Fleishman  An apple icon for a TidBITS Staffer 2013-06-13 18:01
Its presence (newer models) doesn't cause a slowdown. Rather, when it's sending and receiving data, it occupies 100% of the network's capacity during its thin slices of data transfer, while it only needs one stream (33%).

802.11ac will allow targeting a single stream to single-stream devices, thus freeing up this capacity for other devices.
HellfireHD  2013-06-14 14:50
"...a single 802.11ac base station could handle the whole shack."

So far that has not been my experience with AC. There are as many dead spots as ever and only modest speed improvements.
Glenn Fleishman  An apple icon for a TidBITS Staffer 2013-06-15 16:41
It's going to vary by equipment and home.
Joseph Yarak  2013-06-14 16:01
Very good and informative article. But I think it is not completely true that 802.11ac improves the range coverage. It does offer the same coverage as 802.11n as beamforming is also part of 11n standard. Manufacturers opted to turn the option off. Quantenna has been shipping chipsets with beamforming for more than three years now.
Great explanation for MU-MIMO benefits and we have seen Quantenna just introducing chipset that supports this feature in its QSR1000 family.
Glenn Fleishman  An apple icon for a TidBITS Staffer 2013-06-14 16:04
Yes, beamforming is available in 802.11n, but wasn't required and was implemented only on a limited number of devices. Thus 802.11ac, with beamforming as a requirement, will improve coverage over most 802.11n base stations.
Joseph Yarak  2013-06-14 16:14
As in 802.11n, beamforming in 802.11ac is an optional feature. However I agree that it is required to get great coverage.
Glenn Fleishman  An apple icon for a TidBITS Staffer 2013-06-14 16:35
It's optional? I'm sorry I misunderstood that. In my reading, it seems as though manufacturers are treating it as mandatory. I wonder if the Wi-Fi certification will require or brand it?
Joseph Yarak  2013-06-17 16:54
Beamforming is optional in both 802.11n and 802.11ac.
It’s also not part of the mandatory certification tests for WFA. The WFA 11n certification program does not have a test for BF. The WFA 11ac program which will launch shortly only has an optional test for BF. This means products can be (and will be) 11ac certified without supporting BF. Note that the WFA test for BF will only verify that a STA correctly indicates BF capabilities, not the performance of BF itself.
Jerry Walz  2013-06-18 04:42
Only the new MacBook Air handles 802.11ac. Any adaptors available for other Macs?
Konrad  2013-06-20 17:31
My 13" Air [upgraded ram and processor] arrived on the 14th and my Airport TC 2TB arrived on the 19th. Today I used wireless to execute initial backup of appx. 95 GB to TC via TM. Timed this at two hours and two minutes including cleanup. Air sat two feet from TC. I don't know how this translates into speed numbers but my March 2008 MBP [2.5 processor and 7200 rpm HD] and 500GB TC were a lot slower, so as a consumer I'm very happy with the new 'ac' products from Apple.