The UE first looks for the primary synchronization signal (PSS) which is transmitted in the last OFDM symbol of the first time slot of the first subframe (subframe 0) in a radio frame.
This enables the UE to acquire the slot boundary independently from the chosen cyclic prefix selected for this cell. Based on the downlink frame structure ( FDD).
The primary synchronization signal is transmitted twice per radio frame, so it is repeated in subframe 5 (in time slot 11). This enables the UE to get time synchronized on a 5 ms basis, which was selected to simplify the required inter-frequency and inter-RAT measurements.