What is 802.11ac WiFi, and how much faster than 802.11n is it?

If you’re looking for faster WiFi performance, you want 802.11ac — it’s as simple as that. In essence, 802.11ac is a supercharged version of 802.11n (the current WiFi standard that your smartphone and laptop probably use), offering link speeds ranging from 433 megabits-per-second (Mbps), all the way through to several gigabits per second. To achieve speeds that are dozens of times faster than 802.11n, 802.11ac works exclusively in the 5GHz band, uses a ton of bandwidth (80 or 160MHz), operates in up to eight spatial streams (MIMO), and employs a kind of technology called beamforming. For more details on what 802.11ac is, and how it will eventually replace wired gigabit Ethernet networking at home and in the office, read on.

How 802.11ac works

Years ago, 802.11n introduced some exciting technologies that brought massive speed boosts over 802.11b and g. 802.11ac does something similar compared with 802.11n. For example, whereas 802.11n had support for four spatial streams (4×4 MIMO) and a channel width of 40MHz, 802.11ac can utilize eight spatial streams and has channels up to 80MHz wide — which can then be combined to make 160MHz channels. Even if everything else remained the same (and it doesn’t), this means 802.11ac has 8x160MHz of spectral bandwidth to play with, vs. 4x40MHz — a huge difference that allows it to squeeze vast amounts of data across the airwaves.

WiFi 802.11acTo boost throughput further, 802.11ac also introduces 256-QAM modulation (up from 64-QAM in 802.11n), which basically squeezes 256 different signals over the same frequency by shifting and twisting each into a slightly different phase. In theory, that quadruples the spectral efficiency of 802.11ac over 802.11n. Spectral efficiency is a measure of how well a given wireless protocol or multiplexing technique uses the bandwidth available to it. In the 5GHz band, where channels are fairly wide (20MHz+), spectral efficiency isn’t so important. In cellular bands, though, channels are often only 5MHz wide, which makes spectral efficiency very important.

802.11ac also introduces standardized beamforming (802.11n had it, but it wasn’t standardized, which made interoperability an issue). Beamforming is essentially transmitting radio signals in such a way that they’re directed at a specific device. This can increase overall throughput and make it more consistent, as well as reduce power consumption. Beamforming can be done with smart antennae that physically move to track the device, or by modulating the amplitude and phase of the signals so that they destructively interfere with each other, leaving just a narrow, not-interfered-with beam. 802.11n uses this second method, which can be implemented by both routers and mobile devices. Finally, 802.11ac, like 802.11 versions before it, is fully backwards compatible with 802.11n and 802.11g  so you can buy an 802.11ac router today, and it should work just fine with your older WiFi devices.

The range of 802.11ac

In theory, on the 5GHz band and using beamforming, 802.11ac should have the same or better range than 802.11n (without beamforming). The 5GHz band, thanks to less penetration power, doesn’t have quite the same range as 2.4GHz (802.11b/g). But that’s the trade-off we have to make: There simply isn’t enough spectral bandwidth in the massively overused 2.4GHz band to allow for 802.11ac’s gigabit-level speeds. As long as your router is well-positioned, or you have multiple routers, it shouldn’t matter a huge amount. As always, the more important factor will likely be the transmission power of your devices, and the quality of their antennae.

How fast is 802.11ac?

And finally, the question everyone wants to know: Just how fast is WiFi 802.11ac? As always, there are two answers: the theoretical max speed that can be achieved in the lab, and the practical maximum speed that you’ll most likely receive at home in the real world, surrounded by lots of signal-attenuating obstacles.

The theoretical max speed of 802.11ac is eight 160MHz 256-QAM channels, each of which are capable of 866.7Mbps  a grand total of 6,933Mbps, or just shy of 7Gbps. That’s a transfer rate of 900 megabytes per second  more than you can squeeze down a SATA 3 link. In the real world, thanks to channel contention, you probably won’t get more than two or three 160MHz channels, so the max speed comes down to somewhere between 1.7Gbps and 2.5Gbps. Compare this with 802.11n’s max theoretical speed, which is 600Mbps.

Top-performing routers today (April 2015) include the D-Link AC3200 Ultra Wi-Fi Router (DIR-890L/R), the Linksys Smart Wi-Fi Router AC 1900 (WRT1900AC), and the Trendnet AC1750 Dual-Band Wireless Router (TEW-812DRU), as our sister site PCMag reports. With these routers, you can certainly expect some impressive speeds from 802.11ac, but it still won’t replace your wired Gigabit Ethernet network just yet.

In Anandtech’s 2013 testing, they paired a WD MyNet AC1300 802.11ac router (up to three streams), paired with a range of 802.11ac devices that supported either one or two streams. The fastest data rate was achieved by a laptop with an Intel 7260 802.11ac wireless adapter, which used two streams to reach 364 megabits per second  over a distance of just five feet (1.5m) At 20 feet (6m) and through a wall, the same laptop was the fastest  but this time maxing out at 140Mbps. The listed max speed for the Intel 7260 is 867Mbps (2x433Mbps streams).

In situations where you don’t need the maximum performance and reliability of wired GigE, though, 802.11ac is very compelling indeed. Instead of cluttering up your living room by running an Ethernet cable to the home theater PC under your TV, 802.11ac now has enough bandwidth to wirelessly stream the highest-definition content to your HTPC. For all but the most demanding use cases, 802.11ac is a very viable alternative to Ethernet.

The future of 802.11ac

802.11ac will only get faster, too. As we mentioned earlier, the theoretical max speed of 802.11ac is just shy of 7Gbps  and while you’ll never hit that in a real-world scenario, we wouldn’t be surprised to see link speeds of 2Gbps or more in the next few years. At 2Gbps, you’ll get a transfer rate of 256MB/sec, and suddenly Ethernet serves less and less purpose if that happens. To reach such speeds, though, chipset and device makers will have to suss out how to implement four or more 802.11ac streams, both in terms of software and hardware.

We imagine Broadcom, Qualcomm, MediaTek, Marvell, and Intel are already well on their way to implementing four- and eight-stream 802.11ac solutions for integration in the latest routers, access points, and mobile devices  but until the 802.11ac spec is finalized, second-wave chipsets and devices are unlikely to emerge. A lot of work will be have to done by the chipset and device makers to ensure that advanced features, such as beamforming, comply with the standard and are interoperable with other 802.11ac devices.