I'm testing PHY coding (for long range), I'm pretty surprise from what I get when I scan the RSSI of bluetooth channels (with Nordic app).
This is my set up:
M1 is the central, S1 is the peripheral sending 1ko/s. (with uart exemple)
I use softdevice 140 V5 alpha.2
M3 is the RSSI scanner connected to "Nordic app RSSI Viewer" Here are the results I get for phy= 1mbps (Short Range) and for phy=125kbps (coded-Long Range):
Can you explain me why the long Range mode trash all Bluetooth channels ? this is one link (S1-M1) so my data received is what I expected (1ko/s) but when I use 10 links, the data rate drops dramatically.
It seems like we still have some issues with the coded PHY. Here are two relevant cases:
We don't know what it is yet, but we are looking into it. Just a few simple questions to get us started:
Thank you for your answer Martin,
To my mind it comes from the hardware side (since the results look different when I change the nrf52840pdk version).
Thank you for your help,
Are you using the same connection intervals (CI) in both of those tests? I have done some tests myself and when I use coded phy and 400ms CI the RSSI viewer looks like your top most picture. If I use coded phy and 7.5ms CI it looks more like the image at the bottom. This is probably because the channel selection algorithm is designed to change channel between each connection events. Since you have turned on "Channel Scan Repeat" in the RSSI viewer you will get sort of an average view over the last couple of connection events, which manifests itself as the "ripple" in the RSSI plot.
Yes, I'm using the same CI on those tests. MSEC_TO_UNITS(10, UNIT_1_25_MS)
for uart_app. (For all the tests I've done with those pictures)
When PHY is coded (bottom picture), the data is staying 8x longer in the air that's might be why I see a RSSI stronger signal (than the short range, top picture).
But I've an other project, base on the nrf52832 chip with a 5kBytes/s data rate (at PHY 1Mbps) with the same CI, So I guess It should corresponds to 625Bytes/s in coded phy if you compare on-air time and It's not that far from the 1000Bytes/s data rate from the bottom picture. And I don't see any RSSI activities like the one I see here on long range.
I understand that my RSSI viewer set-up do kind of an averaging and maybe there's only one active channel at a the same time so the boards shouldn't disturb each others.