Cell ID Detection and System Information Detection
i) Frequency Aquisition
ii) Primary Sync Signal Aquisition (Slot Timing Aquired, Secondary Sync Signal Scrambling Code Aquired)
iii) Secondary Sync Signal Aquisition (Frame timing Aquired, Cell Group ID sequence aquired)
iv) with PSS and SSS, Cell ID can be calculated
v) with Cell ID, Reference Signal Location is detected
vi) With the help of Reference Signal, PBCH (MIB) can be detected
vii) From MIB, SFN and System BW can be detected
viii) Decode PCFICH and detect how many symbols are allocated for PDCCH.
ix) Decode DCI for SIB1 from PDCCH
x) Decode SIB1 and get the scheduling information for other SIBs
xi) Decode SIBs (other than SIB1)
One of the most important step for testing/troubleshooting around the initial registration is to check whether UE successfully complete the time-sync (step i) and ii)), but it is very hard to check this step with any kind of equipment. One way to easily check whether UE succeeded in time-sync or not is to check from UE log whether UE successfuly decoded Cell ID or not. If UE successfully detected Cell ID, it means UE successfully completed the time-sync.
One of the common questions that I got from this page was "It is possible for a UE to decode MIB without detecting reference signal ?"..i.e.. "Is reference signal a mandatory precondition for MIB decoding ?".
I think theoretically UE can decode MIB without any help of Reference Signal since all the information which is needed for decoding MIB is predefined in 3GPP specification.
I also had an experience of testing a chipset at very early development stage. At that time, an equipment and the device is directly connected at base band I/Q signal. So we can assume the signal quality is almost ideal. The chipset were able to decode MIB without detecting Reference Signal. But in reality with RF, it would be very tricky to decode MIB properly without any help of reference signal detection before it. Usually UE try to detect/estimate reference signal and configure its Equalizer properly and then try to decode MIB.