Frequency Offset Calibration

[ABH]

I wonder if Espressif could elaborate on how the "frequency offset calibration" works?
I searched the documentation, but could not find any detailed explanation.
As the word "calibration" is consistently used (and not "compensation") I assume that it really is a calibration that is done and the frequency offset is really tracked.

A frequency offset calibration can only be done if there is a frequency reference available and for obvious reasons the only reference that can be used is a received RF signal. So, when there is no signal received then no calibration can be done! My question is then, what kind of received signal is required for the frequency offset tracking to work:

1. The signal from a client connected to the ESP8266 AP?

2. The signal from an AP that the ESP8266 connected to as client?

3. The beacon signals from other AP's that can be received by the ESP8266 during a scan?

In our application we need the ESP8266 to work as an AP in the full temperature range up to 120 degC and only very seldom will there be a client that connects to the ESP8266 AP. There might however be beacons from other AP's that the ESP8266 can receive, and so it could be beneficial if the ESP8266 would track its frequency offset relative to these beacons.
If it is so, that AP beacons received during a scan are used for frequency tracking, how often will this scan (and frequency offset calibration) then occur?

Thanks in advance!

[pratik]

Complying will full temperature range will require proper matching and calibration. The crystal would be the first thing of importance here. Make sure you use a good quality one from certified vendor like DigiKey or Mouser.
For help with RF calibration, please contact support at
http://espressif.com/en/company/contact/after-sale-questions