NRF52 master + Bluez and BLE HCI_USB (ideas for a project)

[caveman]

Hello,

I'm doing some research for a product my company wants to develop. It will be a BLE central that needs to connect with ~ 30 BLE peripherals.
The peripherals will send aprox. 3200 bytes/second each, using notifications and the central will forward the data to a computer, where Linux and other software will run
(we need to use Linux and cannot change that)

We already have a peripheral running and sending data. It was tested with different centrals (linux bluez, android and nrf52 dongle) and the result is good.

For the central we're thinking about: A) Linux (Bluez) or B) another nrf52 dealing with all the BLE communication and sending data to the PC using USB.

I prefer the Bluez way but (I know this is not a bluez/Linux list, but maybe people have experience with this):

- we need to know how many connections the BLE controller can support and we're not able to find this information for laptops/desktops. Is there a way to discover this?

- if we cannot connect 30 devices we could add more controllers using USB ports, but the problem is the same. Trial and error is dangerous

- we could use Nordic dongles with Zephyr + BLE HCI_USB


So my questions are:

1.  can a nrf52 central support this data rate + USB communication?
2.  is there a way to know how many connections a BLE controller supports?
3.  how many peripherals Zephyr + BLE HCI_USB can support?
4.  maybe there's a better solution using Zephyr? We never worked with Zephyr but we're open to learn.

Any suggestions/ideas are greatly appreciated!

Thank you!
 

[mtsunstrum]

If you need to connect to 30 peripherals simultaneously ... then there is no single BLE solution (whether Nordic, BlueZ, etc ...) that can sustain that constant throughput nor maintain 30 simultaneous connections.

At that sustained throughput, you might be able to sustain possibly 4 to 8 peripherals per Central BLE ... assuming ideal conditions.

[caveman]

thank you for the answer mtsunstrum!

I got more clear requirements and the data throughput is lower than the initial estimate (I updated the question with the correct number), but the question remains the same.

How did you find the 4/8 peripherals? You did some tests or there are ways to calculate/estimate it?

I keep digging and found this,

but how to know which throughput can be achieved with the 20 connections supported by nrf52?

thank you

[mtsunstrum]

Yes, if you have lower per peripheral throughput needs (3200 bytes/sec), then likely you can have more peripherals. 

My guess is at that (new) throughput is that you might hit 6-8 simultaneous connections, under the most ideal scenarios ... but I have not done the math on this.

See https://devzone.nordicsemi.com/nordic/nordic-blog/b/blog/posts/throughput-and-long-range-demo

Keep in mind that these tests above are done between one Central, one Peripheral. Having multiple peripheral connections will slow down the overall throughput.

[caveman]

Any help from Nordic here, please?

[Håkon Alseth]

Hi,

 

We haven't done testing wrt. throughput in the scenario where you're running 20 concurrent roles. 

I would recommend that you try this out and see if it meets your requirements.

You could try to reach out to the zephyr community to hear if they have more information related to your question.

 

As mtsunstrum mentions, getting 3.2kByte/s (~25kBit/s) in a 30-to-1 network is highly unlikely, so you might have to distribute this out over more than one central.

 

Kind regards,

Håkon