LC15: BTS does not send L2 fill frame
We have noticed that the LC15 BTS does not send L2 fill frame in case there is nothing to transmit.
This leads to bad RXQUAL repored by MS during signaling in TCH channel. Please refer to GSM 05.08, section 8.3
"On any TCH this subset of TDMA frames is always used for transmission during DTX. For speech, when
no signalling or speech is to be transmitted these TDMA frames are occupied by the SID (Silence
Descriptor) speech frame, see TS GSM 06.12 and TSM GSM 06.31 for detailed specification of the SID
frame and its transmission requirements. In other cases when no information is required to be transmitted,
e.g. on data channels, the L2 fill frame (see GSM 04.06 section 18.104.22.168) shall be transmitted as a FACCH
in the TDMA frame subset always to be transmitted.
On the SDCCH and on the half rate speech traffic channel in signalling only mode DTX is not allowed. In
these cases and during signalling on the TCH when DTX is not used, the same L2 fill frame shall be
transmitted in case there is nothing else to transmit."