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]

Hi Martin, Thank you again for this answer, I did some tests at my office (6 tests for 2links, 6 tests for 3links) link text I did not put the result for one link because it's always between 39,5 and 40,5kbps so the speed is ok. Note: For the 3 links setup, at some point (after the test n°4) I thought it could come from the serial link, so I plugged 2 links to my computer, and one link to an other computer (without changing the boards location or placing some object between the links), the results are even worse.

1. Ok, I'll try this option
2. I'd like to receive (notification only) from 50 devices (sending 0,5KBytes/s each) in long range mode, so I planned to use 10 centrals, each one connected to 5 peripherals, I'm not sure if I understand the end of your N°2.
3. I'm basing it by the fact that when a link stop communicating, the other increase their speed.

Regards, -Damien

[MartinBL]

Still looking into this. Here is a relevant case: devzone.nordicsemi.com/.../

[MartinBL]

Hi

I have done some testing on my own and I am not able to reproduce your problem. I used:

• SDK: 14.0.0
• Example: \examples\ble_central_and_peripheral\experimental\ble_app_att_mtu_throughput with S140 v6.0.0-6.alpha patch. Here is the example hex file that I used.
• Softdevice: s140_nrf52840_6.0.0-6.alpha_softdevice.hex

Throughput test parameters:

• MTU [bytes] 23
• CI [ms] 50
• DLE yes
• Conn evt ext yes
• Phy coded (S8)
• Data transfered per test 256kB

Kit versions:

• Link 1: 0.9.0 & 0.9.0
• Link 2: 0.9.2 & 0.9.0
• Link 3: 0.9.0 & 0.9.0

I did the tests in the office after working hours, so the probability of significant interference from other BLE devices were low (but there is wifi of course). I manually started each measurement using a serial terminals, but all links usually started the throughput tests within seconds from each other. I.e. most of the time, they transferred data at the same time. I transferred 256Kb per test, which typically took 50 seconds to complete.

I have 6 kits which I have configured as 3 peripherals and 3 centrals, all connected in pairs (3 sepparate links). I did 20 tests with the kits placed in various positions. The first three tests were with all of the kits laying on at my desk, and the fourth with two of the kits in a separate room (“long range test”). Four setups with 5 tests in each. All three links transferred data at the same time. I also tried several tests with only a single link transmitting at the time to compare. As you can see below, the speeds are about the same in all tests when the kits are at my desk. When I moved two of them away, their respective throughputs naturally went down, but the important thing to notice is that they performed consistently. I am not able to reproduce what you report regarding links that changes performance significantly from test to test.

Here are the results:

Here is the spreadsheet I made.

And here are the test setups:

1. Does this make sense to you?
2. Have I forgotten something of importance?
3. What kit versions are you using?

---

EDIT 11.12.17

I did some more tests today:

Same software and link parameters as yesterday, but I reduced the TX power to -30 dBm to simulate long range, and used 10 kits to make 5 links. I am still not able to find anything out of the ordinary. There were some variations from link to link, but each link performed fairly consistent between all tests:

[damien5606]

First thank you a lot for all those efforts to try to solve my case.

1. Yes that make sense but I don't have the same results, maybe It'd be different with more than 3 links and further ?
2. I don't think so
3. I'm using a mix with 0.91, 0.92 and 0.93

I did a test with the uart exemple phy coded, 1kBytes/s 10 links (CI 12.5ms, ATT_MTU payload 23, dle off, phy coded), I tried at my office everything was fine (every central was receiving 1kB/s) then I went to a football field, I set up 10 centrals at one point: link text 70m from the peripherals https://ibb.co/mprQKb when I use only 2-3 links, everything is fine but when I use 10 links I see huge data rate variation (see at the bottom left : https://ibb.co/nvTi5G) (SD140 V0.5.2) and I observe similar behavior with SD 140 V0.6.

Here is my main.c : www.dropbox.com/.../AAC-knx-D7AeQZhgq-TCrgMRa

[damien5606]

2. Actually It'd be interesting to see the results with the 3 peripherals side by side in one room, and the 3 centrals in an other room side by side.