802.11ac Wi-Fi – Planning for better channel bonding and more

July 15, 2013 Extreme Marketing Team

802.11ac is the next generation of Wi-Fi – the fifth to be specific – and it is expected to be over three times faster than 802.11n – in theory, over 10 times faster. The theoretical maximum speed of 802.11n is 600Mbps while 801.11ac boasts about 6.93 Gbps, although in reality it will be much less and very close to the speed of 802.11n with the first generation (wave-1) of access points and clients.

Today 802.11ac is a draft specification, with final 802.11 Working Group approval and publication scheduled for late 2013 / early 2014.  However, there are already several APs and client devices out there.  Client devices include Apple’s latest MacBook Air, Samsung Galaxy S4, and the HTC One.

So what is new in 802.11ac and why is it so much faster? Here is a Summary

  • Operating only in the 5GHz band. In the US, 5.0 GHz offers 24 non-overlapping channels, which means less noise, and the ability to design networks with higher capacity.

  • Wider channel bonding (80MHz & optional 160MHz) which means more capacity in the band but in enterprise networks you should keep the channels at 40MHz so that adjacent APs are assigned non-overlapping channels in the spectrum to avoid interference. (note: 160 MHz is not supported in wave-1 of 11ac)

  • Denser amplitude modulation with 256 QAM (Quadrature Amplitude Modulation), providing 4 times denser than 802.11n which has 64 QAM.  This gives higher throughput when you are closer to the access point (within 10 ft.)

  • Multi-User MIMO, which allows an AP to transmit to multiple clients simultaneously. This is a big deal especially for streaming videos to multiple devices. Prior to 11ac, data streams from the APs are transmitted to each of its devices separately, and serially, thereby limiting the effective throughput for each individual device. (Note: not available in wave-1)

  • Up to 8 Spatial streams which doubles the number of spatial streams used in 802.11n (note: in wave-1 only 3 spatial streams are supported)

  • Beam forming: detects where devices are and intensifies the signal in their direction(s) to focus RF energy for better signal strength, rather than broadcast wireless signal equally in all directions

Today with wave-1 of 11ac, the two biggest benefits are:

  1. The move towards 5 GHz — and since 802.11ac is backwards compatible with 802.11n in this band, it means they can coexist

  2. The other benefit is that client devices should consume less power due to faster speed/less time and also less power requirement by the 11ac chipsets.

As the list above shows, there are other nice improvements in 11ac such as channel bonding. However, the use of channel bonding should be done wisely. In an enterprise Wi-Fi network where multiple APs are used, adjacent APs are assigned non-overlapping channels in the spectrum to avoid interference. In the 2.4 GHz spectrum (in 802.11n) there are 3 non-overlapping 20 MHz channels, while the 5 GHz spectrum offers 24 non-overlapping 20 MHz channels (for US channel allocation). However, these non-overlapping channels drop down to 11, 5, and 2 channels when doing channel bonding for 40 MHz, 80 MHz and 160 MHz, respectively. This means if used unnecessarily bonding channels (above 40 MHz) can be counterproductive especially in a mixed 11n and 11ac environment.

Want to learn more about optimal channel utilization and simplifying the migration to 802.11ac, join us for a free July 31 webinar as we talk about this and other 801.11 factors.


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