nrf5340 audio:BIS audio bad frame

[Reskyllr]

We have an nrf5340audio application and are doing BIS broadcast audio testing.
However, when there are any obstructions in the middle, a large number of bad frames will appear, and the audio listening quality will be very difficult to receive.
There is no problem in open scenes, but obviously there are many obstructions in actual scenes.
Do you have any suggestions for solving this problem, or is there a more suitable PLC algorithm? Because the transmission is streaming, I cannot write the PLC algorithm through subsequent data.

[Karl Ylvisaker]

Hello,

Could you elaborate or describe the environment that the devices will be working with?
If there are many dense obstacles between the transmitter and receiver there is of course no way to guarantee that a packet will make its way across, but there are at least some changes we can do to increase its likelihood.

Which audio bitrate are you streaming, and what is the number of retransmissions you are using?
In general the first thing you could try is to increase the TX power of the broadcaster, as well as increasing the number of retransmissions - keep in mind that both of these changes will increase your device power consumption.

Best regards,
Karl

[Reskyllr]

I've set CONFIG_BT_AUDIO_RETRANSMITS=4, but that didn't improve anything.
Bad frames still appear very frequently, and the effect is good when there is no obstruction.
Any other suggestions, I did the same test using nrf5340 audio dk and the official le audio demo, the results are the same, very bad when there are obstructions.

[Reskyllr]

Hi,Karl,

If there is occlusion at a very close distance, a lot of bad frames will appear.

CONFIG_BT_CTRL_TX_PWR_ANTENNA has been set, there is no difference in the result.

Adding PA will make our module larger, which is bad. We have tried it.

[Karl Ylvisaker]

Hello,

Reskyllr said:

If there is occlusion at a very close distance, a lot of bad frames will appear.

If you could please elaborate on what kind of occlusion you are referring to here, and if you could quantify what you mean when you say 'very close distance' that would be very helpful for my understanding of your issue.

Reskyllr said:

CONFIG_BT_CTRL_TX_PWR_ANTENNA has been set, there is no difference in the result.

Could you check that the RSSI is increased as expected following this change, either by using the nRF Connect application for Desktop to check the RSSI of the extended advertisements, or to use the nRF Sniffer to verify this?

Reskyllr said:

Adding PA will make our module larger, which is bad. We have tried it.

I understand, thank you for clarifying.

Best regards,
Karl

[Reskyllr]

Occlusion is simple, such as the human body or even a display screen, and bad frames will appear.

For RSSI, already confirmed, it works fine.

[Karl Ylvisaker]

In general the human body is a very good blocker for RF signals due to its density, and a display screen could have a full metal frame or backing which would serve as an effective blocker as well - especially so if the devices are located right next to the display screen, or far away on either side.

I am glad to read that you already confirmed the RSSI to increase following the TX Power adjustment.

Could you confirm whether or not you are working on a custom board, or on a nRF5340 Audio DK? In the case of a custom board, have any review been done by us on the schematic and layout of the board?

Best regards,
Karl

[Reskyllr]

Hi Karl,

Yes, it's a custom build, but that doesn't matter.
Because I also own the nrf5340 audio DK, the problem still exists when using it, even if I burn the original nrf demo.
In other words, the current official DK and demo also have the same problem. Have you done any relevant tests? The BIS is very bad when there is occlusion.

Thank you for your attention. I hope I can pay attention to it to analyze whether it is a hardware problem or a software problem.

Best regards,
Reskyllr

[Karl Ylvisaker]

Hello again Reskyllr,

Thank you for your patience with this - I have reported this as a BIS range issue to the LE Audio developers.

To aid the debugging of the issue, could you possibly conduct the same test as you have done now with CIS, to see if that makes any difference in the glitching in the audio?

For good measure we can also perform a schematic and layout review for you, to see if there could be any optimizations or improvements in the RF circuitry. If you would like this, please open another Private DevZone ticket to request the review :) 

Best regards,
Karl