Hi,
Both SR-DVB and OpenBTS wrote their own code from scratch,
even though major parts of the computation could have been handled by
GNU Radio processing blocks. Why?
OpenBTS makes uses of inband signaling to maintain strict TX/RX sync,
AFAIK this is not supported in the standard blocks.
They also tweak the way the RFX are tuned, trying to put the TX carrier
inside a notch of the RX IF filter (at least that's what the docs says).
Not using the standard libs for tuning is however quite annoying because
when you deviate from the standard 2*RFX setup (like 1 RFX or a
RFX+DBSRX or WBX), you have to change a lot of code :(