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I am developing an industrial hardware that communicates via BLE 5.0. The design is this: multiple devices: (10, 20 devices) communicates with an high bitrate (around 20 bytes every 50 ms, so around 150 3.2 kbps). Sometimes is also the central that communicates, but it is mostly peripheral vs. central.

I am developing this architecture with CC2564 trasmitters (https://www.ti.com/lit/ds/symlink/cc2564.pdf?ts=1616973324278&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FCC2564).

Now, I have the next choices:

  1. pairing all devices, before the transmission
  2. connect via BLE connection, without pairing, and manage data trasmission using carachteristic read or write.
  3. not connecting devices, but transmit messages using advertisement system.

The question is: what approach would you use to avoid collapsing data, increase the range and the reliability of the trasmission, that is crucial, and avoid losing data, or, even worst, the connection?

Do you see any possible problems that I should know or intrinsic limit of bluetooth for this kind of application?

Thank you for your suggestions.

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  • \$\begingroup\$ sounds like you want something that's not bluetooth? \$\endgroup\$ – Marcus Müller Mar 28 at 23:22
  • \$\begingroup\$ @MarcusMüller why not? But if there is something more suitable, I am opened to any proposal. AFAIK, bluetooth 5.0 supports unlimited connections ( stackoverflow.com/questions/48418427/… ). \$\endgroup\$ – max_s Mar 28 at 23:30
  • \$\begingroup\$ yeah, but BLE is basically uncoordinated. You're heading into a situation where you get more collisions than data across! \$\endgroup\$ – Marcus Müller Mar 28 at 23:38
  • \$\begingroup\$ @MarcusMüller that's the point. As you can see the bitrate is quite low. If there are some system of automatic subdivision in different channels, this could not be true. What technology do you suggest? Anyway, I think about a crowded area: there are hundreds of bluetooth devices advertising and bluetooth still working. I know that the use case is quite particular, that's why I am asking. \$\endgroup\$ – max_s Mar 28 at 23:44
  • \$\begingroup\$ let's talk less about bitrate, and more about duty cycle. each of your 20 devices is actively transmitting how much % of the time? \$\endgroup\$ – Marcus Müller Mar 29 at 0:01
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I feel you are trying to overstress the BLE architecture. An attribute send each 50ms from 20 nodes would need a central with a connection interval of 2.5ms. Too bad that the minimum is 7.5ms (exactly six 1.25ms ticks)

I think you should review your bandwidth need and maybe use another kind of protocol.

This of course if the master actually support 20 connected nodes. When transmitting data in the advertising protocol (i.e. as a beacon) the limit goes up to 20ms but it's quite possibile that some conflict would happen: the idea is that even if one advert is jumbled the next one will more or less arrive correctly (but of course the air will saturate)

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  • \$\begingroup\$ What commercial protocol do you suggest to use? \$\endgroup\$ – max_s Mar 29 at 21:19

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