Reduce time to start channel sounding

[nikeub]

We have an application where response time is critical, and we are trying to minimize the time from advertising to an active channel sounding session.

What we have already optimized:

• Connection interval set to 7.5 ms
• Advertising interval reduced to 100 ms (can't go lower to remain within power constraints)
• Skip GATT discovery by hard-coding the GATT handles
• Bonding enabled to reduce secure connection setup time

This brings us down to around ~450 ms.

Now we are looking at what else we can do, and hope you can clarify what's possible.

• CS config/capabilities exchange takes ~100 ms.
  • Our understanding is that per BLE specification, this can be avoided by pre-storing a known configuration on both sides.
  • Does Noridc stack support or plan to support this?
• MTU exchange takes ~37 ms.
  • Default MTU size is 23 and we must increase it for faster data exchange between reflector and initiator.
  • Is there any way to hard-code the MTU size beforehand?
• CS security (bt_le_cs_security_enable) takes ~30 ms
  • Is there anything we can do to reduce this? E.g. piggy-backing on the existing secure connection, skipping DRBG?

[Simonr]

Hi

• Channel Sounding config/cap exchange: I'm not sure how much this would reduce the timing, but from ...\nrfxlib\softdevice_controller\include\sdc_hci_cmd_le.h The host may store a copy of the remote device's capabilities and write the remote capabilities in the local controller when it reconnects to the same remote device by using the HCI_LE_CS_Write_Cached_Remote_Supported_Capabilities command.
• As far as I know, I think this is per BLE specification, and the MTU exchange must be done. I'll have to double check that and get back to you though.
• I will also need to find out and get back to you whether this is a must or not, my initial guess is that it is required.

Best regards,

Simon