[gr-gsm] gr-gsm uplink loop

Hi, I am trying to develop a mobile loop (uplink) for the receiver in receiver_impl.cc. gr-gsm currently synchronizes, finds the start of a burst, using FCHH and SCHH signals. These are all downlink signals. There is no provision for synchronizing to uplink signals. I was wondering if there were any uplink bursts that the receiver could synchronize to. I can try to synchronize with autocorrelation of the training sequence, but I was wondering whether there are any better options out there. Any help would be appreciated. TIA Nikos