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

[damien5606]

Thank you for your answer Martin, Q1) yes, each Central connect every time to the same peripheral. Q2) No, sometime it changes, an other link can be faster. Q3) I mean that the connection speed of each link is steady, the only thing that can make it faster is the "end of communication" of an other link and the only think that make it slower is a new communication. Q4) https://ibb.co/gLmWSm https://ibb.co/mR69DR

I put the devices side by side following this order : From the left C1,C2,C3,C4,C5 (see attached picture) and at the peripheral location from the left P1,P2,P3,P4,P5.

Note: this is a test in my office (board 1m from each other :1) 33,53Kbps. 2) 28,9Kbps. 3) 27Kbps 4)29,6Kbps 5)25,26Kbps

When I connect only one link I reach 40Kbps.

[damien5606]

Hi Martin, I'd be really grateful if you can give me any updates on this case. Thank you, -Damien

[MartinBL]

Hi Damien. I'm still looking into it.

1. Would it be possible for you to provide some statistics? Could you e.g. run 10+ tests and provide the results in a table of some sort?
2. Do you make sure to start all the tests on the 5 links at the same time? If you e.g. start one of the links significantly later than the others I would assume it will avoid interference from the other devices at the end of the test and achieve a higher average throughput.
3. You are transferring 1MB of data in each test right? How long does each test take?

[damien5606]

1. I'd have difficulties to run test again in the near future
2. I use serial communication to my computer & putty to run those test, so there're a few seconds between I type "run" on each of my terminals but I every times run the tests in this order link 5 then link4 then 3 then 2 then 1.
3. from the test I did in my office, the results were: link1) 250.146seconds, link2) 290.205 seconds, link3) 308.410 seconds, link 4) 282.760 seconds, link 5) 332.64 seconds.

If I understand well how Bluetooth work, there're 37 communication channels, and on my test, it looks like all the links are using the same one, I thought the frequency hoping would avoid that, or maybe there're an issue with the throughput_example_connecting_on_long_range I'm using

[MartinBL]

Hi,

I have talked with the Softdevice team and we don't think there is anything wrong with the hopping algorithm itself.

1. However it could be interesting if you tried to use an individual channel map on all centrals. For example, configure link 1 to use channel 0-5-10-15-20-25-30-35, link two to use channel 1-6-11-16-21-26-31-36, and so on.

2. The second thing I would like to ask is whether it is possible for you to use fewer centrals? It is possible to have more than 5 concurrent links, so unless your use case prohibits it, you can e.g. have three centrals with 16, 17, and 17 links each.

3. You say that "it looks like all the links are using the same one". What are you basing this on? Do you have any other reason to believe this than the varying throughputs?