802.11ac : Next Evolution of WiFi

What is 802.11ac?

 802.11ac is the next evolution of WiFi.

First there was 802.11b which provided up to 11 mbps data rates per radio in the 2.4 GHz spectrum.

 The next evolution was 802.11a which provided up to 54 mbps data rates per radio in the 5 GHz spectrum. 802.11g came out shortly after enabling 54 mbps per radio in the 2.4 GHz spectrum.

 802.11n was ratified in 2009. The 802.11n spec allows for data rates up to 600 mbps per radio and the current generation of 802.11n allows for up to 450 mbps per radio.

 802.11ac builds on 11n and enable wireless speeds over a gigabit per second in 5 GHz.

Is it true that 802.11ac will only work in the 5 GHz band?

Maybe. The spec, as written, only applies to the 5 GHz band. The wide channels provide the majority of speed improvements to 802.11ac and there isn’t enough room in the 2.4 GHz band to accommodate the larger channels. Some aspects of 802.11ac including additional spatial streams and 256-QAM are likely to make it into the 2.4 GHz radios at some point.

Will there be phases to 802.11ac support like there were to 11n?

Yes. Early 802.11ac products are expected to support up to 4 spatial streams, 80 MHz channel widths and the 256-QAM. Later 802.11ac products will enable the full potential of the standard by supporting downlink multi-user MIMO and 160 MHz channels.

How does 802.11ad compare to AC? Is this the same?

802.11ad uses the 60 GHz spaces to push wireless traffic up to 7 gpbs over short distances. Signals will not travel nearly as far in the 60 GHz space as they do in the 2.4 and 5 GHz spaces used by 802.11a/b/g/n/ac. 802.11ad will likely be a replacement for shorter cables like HDMI, USB, etc. It will enable wireless laptop docks, wirelessly pushing video to HDTVs, etc.

How does 802.11ac gain its speed?

The 802.11ac protocol has a number of enhancements that will be implemented in multiple phases.

 Wider Channel Widths
o 80 MHz channels (contiguous)
o 160 MHz channels (contiguous or two non-contiguous 80 MHz slices)

 256-QAM (Quadrature amplitude modulation)
o Provides a 33% increase in throughput over the 64-QAM used in 11n

 Downlink Multi-user MIMO
o Allows 1 AP to transmit unique data to multiple stations simultaneously
Up to 8 spatial streams
o Compared to a maximum of 4 spatial streams in 11n
o Up to 8 spatial streams in both single-user and multi-user modes
o No more than 4 spatial streams per station in multi-user mode

 Other Enhancements
o Single sounding & feedback format for beam forming (as opposed to multiple, incompatible formats in 11n)
o Coexistence mechanisms
o Independent virtual carrier sense in sub-channels

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