Energy Detection Mode for 1Mbit/2Mbit

[JulianKaroliny]

Dear people of DevZone,

I set up a TDMA-based sensor network using the NRF52840 without the BLE-Softdevice or any API functions (message transmission and reception all by hand with NRF registers).

Everything works fine and now I wanted to extend the network with the capability to measure the RSSI/signal level of each timeslot in my TDMA-superframes (without receiving messages e.g. also interferences ).
The NRF52840 (and 52833) support Energy Detection (ED) that comes with the IEEE 802.15.4 operation modes of the SoC. I start the ED mode every timeslot and the result looks promising.

But now my question:
I do not use the 802.15.4 mode and also not the corresponding bitrate of 250 kbps.
I use the Ble_1Mbit and Ble_2Mbit mode and cannot find anything in the datasheets if these modes  support the ED at all and if the result I get is valid/trustable? I also observed that by going from Ble_1Mbit to Ble_2Mbit the measured ED is varying more and it also shows way more interference (high ED value in timeslots I am not using). Which again raises my question if the ED is supported in the 1Mbit/2Mbit mode at all?

I hope you can help me with my ED questions or suggest me another way to measure the (average/max) RSSI/signal level over a certain time period (~1ms) without receiving messages.

Br
Julian

[Simonr]

Hi Julian

The BLE 1Mbit and 2Mbit modes do not support Energy detection in the same way it is available in the IEEE 802.15.4 operation modes of the SoC, and we have no such examples in the SDK. One thing you might find useful is the QoS channel survey which is an unofficial example by one of my colleagues explained in his blog found here. Alternatively, you can do a more basic approach where you measure the received RSSI level against a set threshold (I.E. -100dBm) where the device will only proceed if the RSSI level is higher than that.

Best regards,

Simon

[JulianKaroliny]

Hello Simon,

First, thank you for your reply.

I understand that Energy Detection is not supported in the SoftDecive and there is no example in the SDK, but what exactly happens when I start the ED mode (NRF_RADIO->TASKS_EDSTART = 1 ) and wait for the interrupt. Does it trigger a longer RSSIsample period or something completely different what is particularly for the 802.15.4 mode?
Although I am in the 1Mbit mode the result seems promising as I already wrote, so it would be interesting if the ED mode simply averages the RSSI over the descrived 128us period (nRF52840 PSv1.1 Page 319)? (though, for the 2Mbit mode the result is less promising)

The link you posted I already found on my google search and at first look, it completely relies on the SoftDevice which I am not using.

Mhh the problem for the raw RSSI sampling is that the sampling period (nRF52840 PS_v1.1 Page 359) is 0.25us ( which I cannot change in my opinion), which may be a little bit too short to continuously catch every RSSIEND interrupt and average on my own :-/

Thank you for your help and BR
Julian