tree 60863ebe6cbf0654479935bb9c266b6ff4af3cd7
parent 6cc5301e4cccba1021f168b4083bc44760b9db6d
author Andreas Eversberg <jolly@eversberg.eu> 1700841141 +0100
committer laforge <laforge@osmocom.org> 1701102452 +0000

coding: gsm0503_tch_{afs,ahs}_encode(): add ability to emit BFI

Similar to Change ID Iade3310e16b906efb6892d28f474a0d15204e861, add
BFI support to TCH AFS and TCH AHS encoder.

Every BTS needs to have some graceful handling for the scenario
where it is time to send out a speech frame on TCH DL, but there is
no frame to be sent. One possible solution is to transmit dummy
FACCH, but this option is unattractive for TCH/AHS where FACCH
displaces two speech frames rather than one. A more elegant solution
is to emit a speech frame with inverted CRC6, causing the MS receiver
to declare a BFI condition to trigger substitution and muting procedure.
Setting all u(k) bits to 0 is one way to produce such an inverted-CRC
speech frame (normal TCH FR/HR CRC6 for an all-zeros frame would be
111111). This patch adds the abiliy to gsm0503_tch_{afs,ahs}_encode()
functions, indicated by payload length of 0.

See §6.2 of 3GPP TS 26.191 for substitution and muting procedure.

Related: OS#6049
Change-Id: I82ce2adf995a4b42d1f378c5819f88d773b9104a