Hello Everyone,
For some time now I'm figuring out the best way to perform timer synchronization with µs-accuracy (+- 20 µ) between several BLE nodes in a star network with one Central and multiple Peripherals.
In our current project we are using four BLE nodes equiped with the nRF52840 chip and the latest nRF Connect SDK version (2.6). We have one Central node, which is the time reference and three Peripheral nodes which will synchronize their clocks to the Central device, so that we can synchronize data acquisition. The peripheral nodes will acquire signals and send the data to the Central device, so that we need some bandwith for data and cannot afford to much packet overhead for synchronization.
There's a 8 year old post form Nordic on how to synchronize timer with proprietary radio packets (Link), which will be send when the BLE link layer has nothing to do. However this approach is not fesable for us because of various reasons.
With BLE 5.x it seems to be possible to use Isochronous Channels with LE Audio, which apparently can also be used for BLE time synchronization, according to this example code from Nordic (Link). Unfortunately I didn't really get the concept of the Isochronous Channels: According to this Webinar (Link) the Isochronous Channels are a parallel communication channel to the BLE service used in LE Audio, but it's not mentioned how this is done in detail.
I have multiple questions now:
- How is this done on the BLE link layer then? Is data transmission on the Isochronous Channels only performed, when there's no other packet transfer?
- Would this LE Audio approach of time synchronization als work in our setup, where we have to transmit sensor data alongside with synchronization / time data?
- Is there any other standardized time synchronization BLE service to date?
- What's the best way to perform time synchronization over BLE?
Thanks for helping me out.
Best Regards,
Dominik