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How 802.11ac Improves Upon 802.11n

In the next few blog posts, we’ll be discussing 802.11ac and how it will help the wireless industry at large. To help set the foundation for blogs to come, we’re going to be discussing our favorite highlights of 802.11ac.

For the most part, 802.11ac is really a “lessons learned” from 802.11n. Below we break down the essential ways that 802.11ac has improved upon 802.11n and how it results in an amazing improvement in aggregate WLAN capacity.

More, and More Efficient, MIMO (Multiple Input Multiple Output)
802.11n has become the de facto wireless standard – and many people have moved to this new standard and are already seeing huge benefits. 802.11ac takes many of the new technologies introduced with 802.11n, including MIMO, and drives them even further.

In 802.11n, the maximum number of MIMO streams is four. Addition of MIMO streams creates a linear increase in overall throughput, and with 802.11ac the maximum number of MIMO streams is increased to eight. So with no other improvements (even though there ARE many more), 802.11ac would double the overall available throughput.

Along with an increase in the number of streams, 802.11ac also introduces higher encoding rates when converting digital traffic for RF modulation. This higher encoding rate results in an overall throughput improvement of over 40%, which is realized for each individual data stream.

As you can see, we’re already on our way to some significant improvements!

Smarter Channel Bonding
Channel bonding was also first introduced in 802.11n. In essence channel bonding creates new, data only channels that are wider than the existing 802.11 channel definitions. Specifically, a single 802.11 channel is approximately 20MHz wide. Channel bonding “steals” some space from adjacent channels and increases the overall channel width to, in the case of 802.11n, 40MHz. This effectively doubles the throughput for the data packets. All management packets are still sent using the standard 20MHz bandwidth and on standard channels to accommodate backward compatibility.

802.11ac increases the number of channels that can be bonded, creating even wider channels that can handle even greater throughput. Channel widths of 80MHz, and optionally 160MHz, have been added. Channel bonding is a bit of a double-edged sword, because although users benefit from the increased throughput, the number of channels available for use effectively decreases. This is often not an issue in consumer environments, where WLANs typically consist of a single AP and very little overlap with other adjacent WLANs (like your neighbor’s). In fact, this is an ideal case for greater channel bonding since only one channel is usually in use anyway, so why not maximize the bandwidth of that channel to take advantage of as much spectrum, and as much throughput, as you can? Channel bonding in enterprise environments can be a bit more tricky. 802.11ac tries to deal with this by limiting operation to only the 5GHz band, where the original channel allocation is wider, and more overall spectrum is available. But there can still be issues, and we’ll likely cover this in more detail in a future blog post.

So, if you’re keeping track, additional channel bonding in 802.11ac doubles or quadruples the maximum data throughput, offering yet another significant improvement!

Multi-User MIMO
Earlier we described how 802.11ac uses eight spatial streams, while 802.11n only uses four. But this is not the only MIMO improvement in 802.11ac.

Multi-User MIMO (or MU-MIMO) allows multiple stations to transmit or receive the exact same data simultaneously. For example, if you’re hosting a Super Bowl party and you want to have the game displayed on all your video screens (say two HDTV monitors and an iPad that can be moved around the house), 802.11ac can distribute this video stream simultaneously to all these devices. Without 802.11ac, even for an identical data stream, the wireless protocol required you to send the data stream to each device separately, and serially, thereby limiting the effective throughput for each individual device. In our Super Bowl example, and without 802.11ac, this means each device would actually see an effective throughput less than one third of the available throughput since the data would be sent three times, once for each individual device.

The tally of increased performance continues to grow by leaps and bounds, with MU-MIMO providing significant improvements in effective WLAN throughput.

Additional Updates
Additional improvements, including more efficient and effective use of beam forming (another optional feature) and other layer 1 and 2 changes, round out the list of substantial improvements. So, when the accounting is all done, the aggregate capacity of the WLAN grows from 600Mbps with an all-out implementation of 802.11n to 6.93Gbps with an all-out implementation of 802.11ac, better than a 10x improvement!

Stay tuned in the coming weeks as we translate these technical improvements into the real-world improvements we all hope to take advantage of as 802.11ac begins to roll out. First up will be improvements for mobile, battery-operated devices, including those we’ve become dependent on, like iPhones and Droids.

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