Esp-idf: Faster Wifi station connect improvement - avoid 100ms passive scan (IDFGH-78)

Created on 11 Sep 2017 · 13Comments · Source: espressif/esp-idf

Hello,

As recommended by ESP_Sprite on esp32.com forum I am opening an issue on this here:

How would it be possible to setup wifi station mode so that ESP32 connects to AP immediately after receiving good Probe Response?

My tests are showing that after esp_wifi_connect() is invoked (sta.channel in config is set to channel the AP is in) the ESP32 actually does so called "active scan" by sending Probe Request frame and receives a good "Probe Response".

But the problem is that ESP32 even after receiving good Probe Response is still waiting for the per channel scan timeout (100ms) before attempting to actually connect.

I can understand the logic behind this behaviour of course - there might be other APs with same SSID, with better signal that might respond later.

But it would be greatly appreciated if it would be possible to have a "hinted" connect mode - just like channel "hint" in struct wifi_sta_config_t - connect to first responding AP (or connect to AP with specific MAC address avoiding scanning / Probe Request / Response stuff altogether).

This would save about 100ms of PHY RF active time in most cases when the AP you are connecting to is the same as previous time -
which is a great deal of power saving in our battery powered application.

Gatis

Source

gatispei

Most helpful comment

@jack0c @liuzfesp We are still interested in the feature, thanks for the update!

gatispei on 16 Jan 2018

👍3

All 13 comments

Just to illustrate the issue I am attaching an oscilloscope screenshot. The graph shows current drawn over time in a typical esp32 boot in our application.

On x axis is time - 100ms per division, on y axis is amperes 100mA per division (actually volts but I am using a special device that converts mA to mV.

As you can see the passive scan time contributes a big part of the overall current consumption of the device in a typical boot.

2017-09-17 15 16 59

Please advise on how it would be possible to implement the above feature. Thank you.

gatispei on 17 Sep 2017

Thanks @gatispei, we will put it into our optimization list. Now some optimizations are already done (but merge into IDF master yet), and more optimized options for scan will be supported in release 3.0.

liuzfesp on 18 Sep 2017

Great, sounds good! Are there any time estimates for v3.0 release?

gatispei on 18 Sep 2017

Is there any progress?

kimata on 22 Nov 2017

@gatispei @kimata We are still considering about this. Will add a flag(temporary names 'Stop on first match') in scan. But we have no time to merge this into idf3.0, which was feature freezed. It will be added into idf3.1. The good news is, after scanning refactoring in idf3.0, it will be easy to do this.