Three-Minute Tech: IEEE 802.11ac
The first thing you need to know about IEEE 802.11ac—the latest wireless networking standard—is that the standard isn’t actually finished. Today’s 802.11ac routers are based on a second draft. Early 802.11n hardware was likewise based on a draft IEEE standard, but those products were certified to assure consumers they would be compatible. Although this first generation of 802.11ac routers isn’t certified in the same way, no compatibility problems have surfaced to date, so it’s unlikely you’ll encounter problems if you buy one now.
The second thing you need to know is that no manufacturer is selling an 802.11ac USB Wi-Fi adapter today, so your existing laptop computer won’t benefit from the speed boost the new technology promises to deliver. The new 802.11ac routers are backward compatible with the older 802.11n standard, however, so you’ll still be able to connect your existing wireless gear to the new routers, but you won’t gain any performance boost (unless you’re upgrading from a very old router).
The real reason to buy an 802.11ac router today is to stream high-definition video to and from the devices in your entertainment center: your Blu-ray player, smart TV, media-streaming box, or home theater PC. To do that, you’ll need to buy an 802.11ac ethernet bridge in addition to an 802.11ac router (or you could buy two routers and configure one of them as a bridge). The bridge will establish a wireless connection to your 802.11ac network, and you’ll hardwire your various devices to the bridge. Buffalo Technology is the only manufacturer offering a purpose-built 802.11ac ethernet bridge today: Their model WLI-H4-D1300 is street-priced at $180 (this happens to be the same price as their new 802.11ac router, model number WZR-D1800H). Netgear recommends that consumers buy two of their model number R6300 802.11ac routers (street-priced at $200 each) and configure one as an ethernet bridge.
Now that we’ve established the usage model for 802.11ac, we’ll explain what makes this wireless networking technology so freakin’ fast.
It’s All About Throughput
Wireless networks can use either the 2.4GHz frequency band (where they must compete with devices such as baby monitors, microwave ovens, and Bluetooth headsets), or the much less crowded 5GHz frequency band. Both frequency bands are divided into a series of channels that provide 20MHz of bandwidth each, but there are fewer channels within the 2.4GHz frequency band. There are many more channels, and with less channel overlap, on the 5GHz frequency band.
An 802.11n router can bond two channels on the 2.4GHz band and two channels on the 5GHz band to produce one channel on each band that’s 40MHz wide. 802.11ac routers also support channel bonding, but these routers are capable of bonding four channels to produce a single channel on the 5GHz band that’s 80MHz wide.
Both types of routers use radios and antenna arrays to transmit and receive data in spatial streams over these channels. The number of radios and antennas in the router determine how many spatial streams the router can support, and the method used to encode the data—combined with the channel’s bandwidth—determine how much data can fit inside each spatial stream. Today’s high-end 802.11n routers support up to three spatial streams. When using a bonded 40MHz channel, they deliver throughput up to 450 megabits per second (150 mbps per spatial stream).
The 802.11ac standard provides a more robust encoding scheme that packs much more data into the same space. A three spatial-stream 802.11ac router using a bonded 80MHz channel can deliver throughput up to 1.3 gigabits per second (433 mbps per spatial stream). Note: each of these throughput figures is a theoretical maximum that doesn’t take into account factors such as protocol overhead, so real-world throughput will be anywhere from one third to one half less.
Signals carried on the 5GHz frequency band don’t travel as far as signals carried on the 2.4GHz frequency band. So an 802.11ac router will deliver roughly the same range as an 802.11n router operating on the 5GHz band, but less range than an 802.11n router operating on the 2.4GHz band. An 802.11ac router, however, should provide higher throughput—more megabits per second—at most distances compared to an 802.11n router, thanks to the improved data encoding and channel-bonding features of the 802.11ac standard.
There is a caveat, however: Manufacturers of 802.11ac routers will likely adhere to the same “good neighbor” policy that was developed for 802.11n routers. This policy is intended to prevent two or more wireless routers operating in the same vicinity from interfering with each other by utilizing the same channels or monopolizing channels. The typical 802.11n router, for example, won’t engage channel bonding at all on the 2.4GHz band if it detects another router operating nearby, because there are so few channels available in that spectrum. While the 5GHz band has many more channels to choose from, an 802.11ac router operating in crowded airspace might not find enough free channels to form the single 80MHz channel that would enable it to deliver its highest throughput.
The Future of 802.11ac
Future 802.11ac routers promise to deliver even higher throughput and better range. One of the most interesting new developments will come with the implementation of “beamforming,” one of several optional features of the 802.11ac standard. Today’s wireless routers and clients transmit and receive in an omnidirectional fashion; signals emanate from the devices in concentric rings, much like the ripples that develop when you throw a stone into a pond. Beamforming describes a process by which the router and the client actively exchange information to determine the optimal path by which their signals should travel. Instead of broadcasting everywhere, the router and client focus and concentrate their signals.
Beamforming was an optional element of the 802.11n standard, too, but it was never widely implemented because the IEEE never defined how it was to be implemented. Although the 802.11ac standard does spell out how beamforming is to be performed, the technology isn’t present in any of the first generation of 802.11ac routers now on the market.
Should You Buy One?
Recall what we said at the opening: 802.11ac is a work in progress, and the IEEE won’t publish the final standard until sometime in 2013. If you’re an early adopter who needs better performance right now, and you can afford either two routers or a router and a media bridge, go for it. If you’re worried about getting burned should the IEEE suddenly change direction—however unlikely that might be—wait for the dust to settle.
[Updated 7/9 to make changes throughout to clarify and simplify.]