Long range coexistence

[damien5606]

Hello,

We'd like to connect 50 bluetooth 5 devices (nRF52840) to a Receiver (made of multiple centrals nRF52840) with a long range (PHY 250kbps, conn interval 50ms, no dle, ATT_MTU 23)

As I understood there're 37 bluetooth channels + 3 for advertising. If I assume that a nRF52840 central can be connected at 5 nRF52840 peripheral at the same time (I guess on the same bluetooth channel), I would need 10 nrf52840 centrals in my receiver to connect all my devices. So I'd use 10 channels.

Do you think they will interfere with eachother (knowing we'll work with long distance signal so very weak ones) or the space between the channel is big enough ?

Thank you a lot,

-Damien

[endnode]

You mean that by operating 5 independent links at the same time and measuring the throughput on them leads to various values from 10 to 30kbps? And how these values vary in time on each link? Are they steady for seconds/minutes or they fluctuate randomly on each of them?

[damien5606]

Yes (for you first question). Usually when a connection is fast (on this example the link 4) it stays fast during all the exchange. When I do my tests, I use the throughput_example_connecting_on_long_range provided with the S140 V6, so when It sent the 1024KByte, the central disconnect, and I can notice that when the fastest links (link 4, link1, link5 here) disconnect, the data rate of the remaining slow connection increase a lot.

[endnode]

This is interesting however I cannot help further. You can either wait if some Nordic support person will pick this up or (because we have diverted from original question) submit new query with specifically all these details (maybe some more inputs like screenshots from metering app or photos of your set-up would help). Alternatively ask through MyPage portal (closed support ticketing system) on main Nordic web page.

[MartinBL]

Hi Damien,

I have a few questions regarding your test setup.

Q1: Are the devices always connected in the same configuration? Like this:

Peripheral 1 <-- Link 1 --> Central 1
Peripheral 2 <-- Link 2 --> Central 2
Peripheral 3 <-- Link 3 --> Central 3
...
...

Or is it random which devices connect from test to test?

Q2: You mention further up that e.g. link 2 is 11 kbps and link 4 is 28 kbps. Is link 4 consistently performing better than link 2 in every test?

Q3: You say that usually when a connection starts fast, it stays fast. This implies that sometimes it happens that the speed drops during a test?

Q4: Do you mind uploading a picture of your test setup?

End part 1/2

[MartinBL]

Start part 2/2:

Maybe e.g. P1 and C1 coincidentally have better or worse radio performance than e.g. P2 and C2. Or maybe it depends on P1 and C1 positions relative to P2 and C2? Maybe you have the devices mounted in a rack and that the devices in the middle consistently perform worse than the devices at the ends?

If one link consistently performs better than the others that would be really strange, unless the issue is caused by poor antennas or positioning of the devices. Because, as @endnode mentions, BLE utilizes frequency hopping mechanisms, meaning that each link hops between radio channels in a pseudo random pattern. In the long run this should even out any issues with interference between your devices or other radio sources in the vicinity.