Transfer Speeds at 100m with 15 devices

Hey,

I am having trouble validating this idea through research. I was hoping someone could give me some ballpark feedback.

The setup:

- 15 NRF52832 devices on custom PCB (30mmx50mm)

- All around 100m away outside with little to no obstacles in the way

- I need to stream data from each device. This means that the Bluetooth transfer speed needs to be faster than the combined data collection speed.

- Each device collects at 24kbps. So there is a combined 360kbps of data. 

I imagine that I need to connect to each device individually and receive data. Then cycle through to the next device. 

The connection parameters would be:

- BLE 5.0

- PHY: 2M

- TX power: 4dB

- connection interval 7.5ms

- data packet length extension on

- connection event length extension on

I can calculate theoretical transfer speeds using the nordic online power profiler. However, it's hard to get data at long distances. Also, I am not sure if I can cycle through the 15 devices fast enough?

Can I achieve this transfer rate (360kbps) at 100m? If not, what distance should be OK?

Parents Reply
  • Hi,

    In the case of option 2, would there be significant interference due to multiple connections streaming at the same time?

    Of course there will be collisions, as you have no way to synchronize modules - you can either divide frequency range with channel map, or ensure data rate that will cover probability of lost packets. I think one board and 15 slaves with the same connection interval is much more predictable solution. To maximize throughput, set up your connection interval to maximum allowed latency for your system, configure event length to a fixed value near 1/20 of connection interval, and do not set MTU to very high values (long packets have higher probability to be corrupted). To increase distance, you have an option to add PA/LNA to central device.

    BTW, is BLE a requirement for your project? You could achieve your goal with a simple custom protocol (a start frame from central then 15 frames from devices) even at 500Kbit Coded PHY.

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