Fetching RSSI values while synced on a BIS

[Ran531]

Hello,

We are trying to assess signal quality while synced to a BIS and we would like to use the RSSI values. RSSI values do show up when scanning and at least in the Auracast sample, scanning stops once we sync on the PA. Also, RSSI from advertisement values do not represent the actual LE Audio stream RSSI?

I know about the HCI command to read RSSI, but it requires a connection handle which I don't have? Does that even make sense in a broadcast scenario? If it does where can I find the relevant connection handle for the BIS or BIG if synced on more than one channel?

[Priyanka]

Hi,

For BIS broadcast audio, there is no regular BLE connection, so HCI command to read RSSI is not the right API to use. That API is mainly for normal connected BLE links.

You could maybe use the RSSI from the periodic advertising packets as an estimate of the broadcaster’s signal strength. This can tell roughly how strong the broadcaster is nearby. However, for the actual audio quality, RSSI alone is not enough. The better thing to monitor is whether BIS/ISO audio packets are being received correctly, lost, or received with errors.

-Priyanka

[matthewtap]

No, a BIS/BIG sync is not an ACL connection, so there is no connection handle available for the standard HCI Read RSSI command. The RSSI obtained while scanning or synchronized to a periodic advertiser reflects advertising/PA packets, not necessarily the actual BIS audio stream. In most current BLE Audio implementations (including Nordic's), per-BIS RSSI is not exposed to the application, so there is generally no direct way to read RSSI for a BIS stream.