Does eNodeB broadcast the signals at periodic intervals or at particular time or when a particular criteria is met?

Question

When does eNodeB comes to know that UE wants to do an IRAT handover in the live network?
Or, eNodeB always sends the measurement gap config info in the RRC connection reconfiguration message which has the measconfig IE?

Without knowing the measurement gap configuration, how does the UE perform inter frequency measurements?
Is it something like, the NodeB sends the meas gap config info to UE after succesful attach?Because UE needs to measure other frequency cells both during idle mode and connected mode.
Please clarify.

Answer 1

Information is broadcasted in two forms, one is known as Master Information Block (MIB) and the other one is known as System Information Block (SIB). Master Information Block is broadcasted in every radio frame (10 ms long) at sub frame zero but a new MIB can be broadcasted from the radio frame for which SFN%4 = 0 satisfies.
Similarly, System Information blocks are broadcasted with the periodicity of 20 ms and new SIB information can be broadcasted from the radio frame for which SFN%8 = 0 condition satisfies.

One more important thing needs to remember that one MIB is transmitted using one BCH transport block and periodicity of one BCH transport block is 40ms i.e. 4 frame. BCH information is divided into 4 parts and each part is transmitted in subframe 0 of each radio frame.