Wednesday, August 20, 2014

802.11ac Receiver Sensitivity

Following my previous post regarding typical SNR to MCS rate mappings for Wi-Fi clients, an interesting discussion was held on Twitter regarding the effects of increased channel width on the ability of a client to decode frames at any given SNR. Long story short, wider channels increase the noise power captured by the receiving radio which reduces its SNR. For every doubling of channel width, you require 3dB better signal to achieve the same MCS rate.

George Ou created a chart showing the relative range of each MCS rate based at various channel widths:

Following up on his work, I thought it would be useful to provide some context around these coverage ranges by referencing it against a typical noise floor of -93 dBm found in many environments. Using this noise floor and the SNR to MCS rate mapping table, combined with the relative coverage ranges (based on RF signal propagation using the inverse square law) we can visualize what data rates a typical 802.11ac radio will experience at various RSSI and SNR signal levels for each channel width.

Note - these receiver sensitivities are not absolute. Wi-Fi radios vary. But this chart is a good approximation for many radios and provides a generic reference for you to visualize and understand this effect.

802.11ac Receiver Sensitivity (Down to -91 dBm)

Update: as requested by various folks, here is a zoomed-in version of the same chart so that the higher data rates are easier to distinguish.

802.11ac Receiver Sensitivity (Down to -82 dBm)

Thanks to George Ou for his work on the initial chart!



  1. That's really useful, thanks Andrew.

  2. on the subject of ACI, I came across Ubiquiti's blurb for AirPrism today, claiming to zap up to 30dB of ACI. I'm a bit sceptical (of marketing, by default) , but if it works in practice this feature would definitely be an advantage when deploying wide channels.