RSSI accuracy

[Stanislav Silnitskiy]

Hello!

As per documentation, RSSI is measured during the time, when particular packet is being received. In particular, nRF51822 Product Specification v3.1 states RSSIperiod as 8.8 us at minimum. Does it mean, that it can differ for packets with different length?

If so, does it mean, that overall accuracy of RSSI can be improved, implementing a sophisticated filter over greater number of RSSI samples for shorter packets, compared to averaging for longer packets, as it is implemented in hardware?

[Kenneth]

The RSSI measurement is done one time for each packet received, there is a radio short 'ADDRESS_RSSISTART' that can be enabled to do one RSSI sample after each radio address match.

[Stanislav Silnitskiy]

Hi Kenneth! Yes, I saw it in docs and I like the concept of SHORTS. I wonder, is the length of time, when RSSI collected can vary depending on the packet length and is this appropriate field to play with, improving RSSI accuracy (overall, of course)? My vision is to receive more RSSI samples per second and filter them somehow. It is crucial in building positioning system, so every percent of improvement is important.

[Kenneth]

The length of time doesn't vary depending on packet lenght no, the radio simply take one single sample of the receive signal strength each time the RSSISTART task is triggered. You are free to trigger the task as frequently as you like, though you would like to wait for the RSSIEND event to read out the actual RSSISAMPLE before next RSSISTART task.

[Stanislav Silnitskiy]

So, theoretically, how many samples it is possible to grab while receiving standard BLE packet?

[Kenneth]

I guess it depends on the packet, but presuming an empty packet in BLE, that will be 40bit (40us) including 3byte CRC after the address match. So maybe you can do 2-3 sampling in best case during that time.