I. OverviewWBS (wide band speech) popular is Bluetooth broadband call, call data frequency 16K, using MSBC codec (chip in the implementation)
Compared with NBS (narrow band speech), NBS is popular in terms of narrowband calls, call data frequency 8K, using CSVD codec (implemented in chip)
NBS is the default
Two. ImplementTo implement a WBS, it is generally more complex
To be carried out in two phases:
1.profile layer (HFP at COMMAND)
2.control bluetooth chip (e.g. CSR through Bccmd)
Three. Profile Layer implementation:Steps:
1.First, in the initialization procedure, the HF shall send the AT+BRSF=<HF supported features>
command to the both notify the AG on the supported features in the HF, as well as to
Retrieve the supported features in the AG using the +BRSF result code.
2.Secondly, in the initialization procedure, if the HF supports the CODEC negotiation feature, it
Shall check if the AT+BRSF command response from the AG have indicated that it supports the
CODEC negotiation feature. If both the HF and AG do support the CODEC negotiation feature
Then the HF shall send the AT+BAC=<HF available codecs> command to the AG to notify the
AG of the available codecs in the HF.
HF Feature:
AG Feature:
3. When calling, AG will send it over +bcs=id
We reply At+bcs=id
Four. Flowchart:
Example:
This accepted SCO connection, equivalent to the profile level started the WBS
Through the aerial packet analysis, it turns out that coding is really msbc.
This is usually the time to switch the Mic,pcm_in,pcm_out,speaker to 16K.
But now the question is, why is it all a murmur after switching to 16K?
Answer to the announcement:
HFP profile level just notifies the cell phone to make a WBS call, but local chip does not know, and will not parse the HFP level at command
So we should have some mechanism to tell chip some news, such as CSR needs bccmd inform, each chip vendor has its own strategy
Due to the complexity of the process of informing the chip, the following article introduces (take CSR example)
Bluetooth broadband call (wide band speech) WBS Anatomy (i)--profile layer
