802.11ac will be faster, but how much faster really?

Network World - Six months from now, enterprise IT groups will be facing a big change for their Wi-Fi networks: the shift to 802.11ac, which promises wireless data rates that start at 433Mbps.

But what's on paper and what happens in the real world are two different things.

RESEARCH: Resources for 802.11ac 'Gigabit' Wi-Fi

The 11ac overview

The IEEE 802.11ac standard builds on some of the technologies introduced in 802.11n, makes mandatory some 11n options, leverages several ways to dramatically boost Wi-Fi throughput, and works solely in the under-used 5GHz band.

Yet at least one of the most important features, dubbed multi-user MIMO, which will let an access point 11ac radio talk to as many as four clients simultaneously, won't be available until 2014, with the second-generation 11ac chipsets. Today's access point can only talk to one connected client at a time.

With the current draft of the new standard considered stable, some consumer-grade routers and adapters already are available, or have been announced. Cisco, in an unusual move, announced in May that it will introduce in the first quarter of 2013 an 802.11ac radio module that will snap into its popular enterprise access point, the Aironet 3600. Other WLAN vendors and device makers are expected to introduce enterprise-class products starting in that same period.

The 11ac radios are backward compatible with 802.11n and 11a radios in the 5GHz bands; and new two-radio access points will likely have the single-band 11ac radio and a dual-band 11n radio to handle legacy clients.

But there are a lot of variables, and together, they add up to a wide range of performance possibilities for end users and the network.

Why is 11ac so much faster?

Vendors say a single data stream 11ac radio, which is what most 11ac-equipped mobile devices will have, will yield maximum data rate of 433Mbps using an 80MHz-wide channel, compared to 150Mbps for single-stream 11n with a 40MHz channel.

The new Wi-Fi does several things to be faster.

First, the first-generation 11ac chips will support 20MHz, 40MHz and 80MHz channel widths, compared to 20MHz and 40MHz for 11n. The wider channel is like a fatter pipe: You can push more through it in the same amount of time.

Second, there's a new modulation scheme, called 256 QAM, which essentially lets 11ac pack more information into the radio signal. "Inside a given finite 'space,' the whole process [of 256 QAM] lets you get more data transmitted, with an improved possibility that you send a '1' and receive a '1' on other end," says Dino Bekis, senior director of wireless connectivity at Broadcom.

Third, beamforming will be standard feature in 11ac instead of the rarely implemented option in 11n. Today, some vendors such as Ruckus use specially designed antennas with multiple components that can be used in different combinations to create an optimal signal for each associated client.