LE audio: Simultaneous Broadcast Sink and Broadcast Source

[droid]

Hello,

Is it possible to configure an nRF5340 to be both a Broadcast Sink and a Broadcast Source, but with the condition that only frames received by the Broadcast Sink are sent ("relayed") to the Broadcast Source?

So long as the data stream is compressed, there should be sufficient bandwidth, but can the SD Controller support this configuration?

A simple test with NCS 3.2.0 and SD Controller received and sent data, however the received stream was unstable (100ms or so gaps in data received from Controller after some minutes followed by bursts of invalid frames).

Thank you,

Carl

[Maria Gilje]

Hi Carl, 

It is possible for the SoftDecive Controller to support both a broadcaster and a receiver role, but I'm not quite sure if it is feasible to do so simultaneously. Could you please explain a bit more about your usecase? Is it necessary for the device to have the roles simultaneously or could it switch between them? Would it be an option for it to be a broadcast source and a unicast server? 

Best regards,

Maria

[droid]

Hello Maria,

The use case is an important one: Range Extension. The Broadcast Receiver can use the co-located Broadcast Source to re-transmit ("relay") received audio to other Broadcast Sinks, which may be located farther away from the original Broadcast Source. This procedure can be repeated multiple times, and/or with multiple Broadcast Sinks at each stage to further extend the range. As encoded frames are not decoded or re-encoded, this can also be quite efficient.

Examples:

- Original Broadcaster is located in a large building with many interior walls, and broadcast audio cannot be directly received at throughout building. Broadcast Sink(s) co-located with Broadcast Source(s) ("relays") can be placed at one or more interior points within building to re-transmit audio so that the distance from any Broadcast Source ("relay") to any Broadcast Sink is within transmission range.

- Original Broadcaster is located outdoors e.g. in an urban environment with many buildings which block RF signals. Broadcast Sink(s) co-located with Broadcast Source(s) ("relays") can be placed at corners, enabling audio reception "around" buildings.

In order for the above to work, nRF5340s would need to function simultaneously in Broadcast Sink and Broadcast Source roles. The change in roles would need to be supported in real-time without reboot or re-configuration.

This is a Broadcast-only application, so Unicast cannot be used.

It is interesting that this configuration does function correctly (for some tens of minutes) before failing. It is possible there are packet collisions (since timing of received packets is controlled by remote Broadcast Source and not local Broadcast Sink) but perhaps these need not be fatal. There may be other reasons as well. Perhaps some changes in audio stream definition (bandwidth, latency, retransmit count, etc.) and/or SD Controller configuration could be used to improve the results. We appreciate any insight or suggestions you may be able to provide.

Thank you,

Carl

[Simonr]

Sorry about the late reply, Maria will be back on Thursday to follow-up on this ticket.

Thank you for your patience,

Simon

[Maria Gilje]

Hi Carl, 

Thank you for describing your usecase more. I agree that your application is important and we will do what we can to help you towards an application which works as you expect it to. In our documentation for the SoftDevice Controller it is described that the controller supports scanning and advertising simultaneously. You would need to fine tune the parameters for a smooth sound experience though. I recommend that you check out the following documentation: 

Broadcast isochronous channels timing from the SoftDevice Controller scheduling documentation

LE isochronous channels

In the Broadcast isochronous channels timing section, there is also a parameter selection visualization which can help to optimize your parameters to allow for enough time for scanning while also broadcasting. 

Using a professional sniffer can also be helpful while trying to fine tune parameters, as collisions will be visible there. We have a professional sniffer available and can run test applications on our side if you provide the firmware for us to test. 

Best regards,

Maria

[droid]

Hello Maria,

Thank you for the offer. I will try to create a simple example using NCS samples that reproduces the issue.