Before answering the exact question, let's go back little at once UE is switched on. When UE is switched on, it feels there are numerous signal around itself with different frequencies. So, it is now confused, with which signal he has to go with? Which is its right signal? So it starts scanning the radio signals which it supports. UE supports some specific bands. Bands contain a range of frequencies like band 7. Band: 7 Uplink Freq: 2500 - 2570 MHz Downlink Freq: 2620 - 2690MHz So it scans the frequencies which is supported by UE, and read PSS. To know more about how to read PSS and SSS, go to PSS signals and SSS signals . So, Between UE is turned on and UE starts receiving and sending data it needs to synchronize with it's supported frequencies. This is done by PSS and SSS. Now, Where is PSS transmitted? PSS is transmitted in the last symbol of 0th and 10th slot in a frame. It gets repeated in each 5 msec time interval. [ Click here for the above image
As per 3GPP spec, 36.331 (RRC Protocol Spec), RRC Connection Reestablishment initiates after these conditions occur : 1. Upon detection of RLF (Radio Link Failure) 2. After Handover failure 3. Integrity check failure indication received from lower layers. 4. RRC connection Reconfiguration Failure. 5. Mobility from E-UTRA failure.