In essence, 802.11ac is a supercharged version of 802.11n. 802.11ac is dozens of times faster, and delivers speeds ranging from 433 Mbps (megabits per second) up to several gigabits per second. To achieve that kind of throughput, 802.11ac works exclusively in the 5GHz band, uses plenty of bandwidth (80 or 160MHz), operates in up to eight spatial streams (MIMO), and employs a kind of technology called beamforming that sends signal directly to client devices.
If you’re currently using an 802.11n router — or an even older 802.11b/g model, like the perennial favorite Linksys WRT54G — and are thinking of upgrading to 802.11ac, here’s what you need to know.
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, 802.11n supported four spatial streams (4×4 MIMO) and a channel width of 40MHz. But 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 versus 4x40MHz — a huge difference that allows 802.11ac to squeeze vast amounts of data across the airwaves.
To boost throughput further, 802.11ac also introduces 256-QAM modulation (up from 64-QAM in 802.11n), which 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 measures 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 transmits 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 a device, or by modulating the amplitude and phase of the signals so that they destructively interfere with each other, leaving just a narrow, interference-free beam. The older 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 — so you can buy an 802.11ac router today, and it should work just fine with your older 802.11n and 802.11g Wi-Fi devices.
How fast is 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 much. The more important factors will be the transmission power and antenna quality of your devices.
And finally, the question everyone wants to know: Just how fast is Wi-Fi 802.11ac? As always, there are two answers: the theoretical max speed that can be achieved in the lab, and the practical maximum speed 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, for a 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.
In situations where you don’t need the maximum performance and reliability of wired gigabit Ethernet — still a good option for situations requiring the highest performance — 802.11ac is certainly compelling. 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 game console, set top box, or home theater PC. For all but the most demanding use cases, 802.11ac is a 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, chipset and device makers will need 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. Chipset and device manufacturers have plenty of work ahead to ensure advanced features, such as beamforming, comply with the standard and are inter-operable with other 802.11ac devices.