There’s an increase in articles on the web lately about the ‘new wifi standard’, 802.11ac. It seems Asus has released a router supporting the standard, together with a PCI and a USB Wireless NIC supporting it. But while Asus tries to market it as the first in its kind, the actual winner here is Buffalo, who launched the first 802.11ac capable router in May. Meanwhile, other vendors like Aruba and Netgear have started giving some basic information about the standard on their page.

But, they all seem to forget one thing: the 802.11ac standard isn’t finalized yet. The standard will be finalized around 2013 it seems. In that regards, it’s the 802.11n story all over again, where ‘pre-802.11n’ and ‘802.11n-draft’ routers flooded the market long before the actual standard. That means there’s no guarantee pre-draft access points will work with the final standard. Granted, there’s a high chance they will, but it’s still not 100% sure.

So what’s the all the fuss about? Bandwidth of course, as it is the most significant improvement over the existing standards. Let’s check the theoretical specifications:

Frequency
802.11ac is 5 Ghz only. Where 802.11b and g used 2.4 Ghz, and 802.11n could use both 2.4 Ghz and 5 Ghz, it’s only 5 Ghz for the ac-standard, just like 802.11a. This should mean less interference from household equipment (a microwave uses the 2.4 Ghz frequency), but the 5 Ghz frequency cannot penetrate concrete walls as well as 2.4 Ghz. If you immediately think of this as a downside, remember that less penetration also means less noise from neighboring networks.

Channel width
Up until the 802.11n standard, channels were 20 Mhz wide. The 802.11n standard changed that and also allowed for 40 Mhz channels on the 5 Ghz frequency. 802.11ac abandons 20 and 40 Mhz altogether and uses 80 Mhz channels by default, with 160 Mhz as an option. Needless to say, broader channels mean more throughput, as modulation techniques can be improved: the wider the channel, the less error-prone it is.

Spatial streams
Quite a complex technology, but simply explained it allows for different antennas to communicate over the same frequency, each one in its own spatial stream. 802.11n allowed four spatial streams, 802.11ac allows for eight, which means up to eight antennas can be used.

Actual bandwidth gain
So yes, what is the actual bandwidth gain? Well, the increased channel width and improved technology by itself allow for 433 Mbps throughput in one stream, on a standard 80 Mhz channel. 160 Mhz doubles this to 867 Mbps per stream. Note that I’m talking about streams, and 802.11ac allows up to eight streams, so this translates to a theoretical maximum bandwidth of 6.93 Gbps. Impressive for a wireless technology! However, in real world scenarios receivers will most likely have three antennas, so three streams, and handheld devices like cell phones just one. If, just like with 802.11n, only the standard channel width is used, thats 1.3 Gbps for most devices, and 433 Mbps for handheld devices. Since it’s wireless, half duplex, a realistic value would be half of this, meaning around 500 Mbps actual throughput for computers with a decent wireless NIC, and about 200 Mbps for a handheld device. Still, great values, and you can expect a full 4.3 gigabyte DVD to be copied over in raw format in under 90 seconds at 500 Mbps.

What are your thoughts? Do you see any practical applications with this? I certainly do!

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