After the mobile is switched ON, it has to synchronize itself with the network at the frame level and slot level. The UE then requires the information like PLMN ID, Tracking Area ID, Cell ID and the network capabilities for its network selection. The network broadcasts this information to help the UE's in their selection process. The LTE network broadcasts the network information in the form of MIBs and SIBs. Once the UE is synchronized with the network at the frame and slot level, it reads the broadcast information and selects a suitable cell.
The system information is very essential and the same is broadcasted by LTE eNB over BCCH logical channel. The System Information in LTE is of 2 kinds,
Master Information Block (MIB)
System Information Blocks (SIB)
The MIB is the first thing a UE looks for after it completes downlink synchronization. The MIB carries the most important information that is needed for a UE to acquire other information from the cell.
System Information Blocks are transmitted using BCCH mapped on DL-SCH which in turn mapped on PDSCH. System Information Blocks are composed of 11 other blocks where each block contains specific information which is required for the UE to perform cell selection, re-selection, handover etc. System information will be changed every BCCH modification period. Both in RRC_IDLE & RRC_CONNECTED a paging message containing “systemInfoModification” is used to inform the UE about system information change.
SIBs other than SystemInformationBlockType1 are carried in SystemInformation (SI) messages and mapping of SIBs to SI messages is flexibly configurable by schedulingInfoList included in SystemInformationBlockType1, with restrictions that: each SIB is contained only in a single SI message, and at most once in that message; only SIBs having the same scheduling requirement (periodicity) can be mapped to the same SI message;
Below is a summary about each System Information Block and the parameters contained in them.
System Information in LTE
Below are some examples shown about how a SIB will look like on a real live network. Click on the images to view it in expanded mode.