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.

[Karl Ylvisaker]

Hello Reskyllr,

Reskyllr said:

In an open environment, the effective range can reach more than 50m.
However, with just one monitor separated, bad frames started to appear.

Could you please provide more detail of the test environment when you are placing obstacles in the line of sight between the devices? Are you still operating at 50m, and what kind of obstacles is it that you are placing?
In general I would expect packet drops for connections at 50m without line of sight, or if you are placing very dense obstacles(such as humans or concrete walls) between the two devices.

You can use the CONFIG_BT_CTRL_TX_PWR_ANTENNA kconfig to configure the TX power at compile time. The maximum TX power of the nRF5340 is +3 dBm. Please give this a try, and see if it makes any difference for your tests.

If a larger range is critical to your application, could it be an option to include a Front End Module (FEM), like the nRF21540, in your design?

Best regards,
Karl

[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