System information acquisition

• UE read system information in RRC Idle mode to acquire the parameter necessary to complete cell selection and cell reselection. System message also provide the parameter necessary to access the network and detect paging messages.
• Paging message can be used  to inform  the UE that there has been a change to the system information and so trigger the UE to require the system information. Paging message are also used to alert UE of Earthquake and Tsunami warning system notification.
• There are two parts in SI static part and dynamic part. Static part is called as MIB and is transmitted using BCH and carried by PBCH once every 40ms.
• Dynamic part is called as SIB and is mapped on RRC SI messages(SI-1,2,3,4,5,6,7,8,9,10,11) over DL-SCH and transmitted using PDSCH at periodic intervals. SI-1 transmitted every 80ms, SI-2 every 160ms and SI-3 every 320 ms
• System information is broadcast using Master Information Block (MIB) and series of System Information Block (SIB).Logical, transport and physical channel used to transfer the MIB and SIB.

RRC Message                                              Logical Channel                     Transport Channel            Physical Channel

Master Information Block                               BCCH                                                     BCH                                   PBCH

System Information Block  1                          BCCH                                                     DL-SCH                            PDSCH

System Information   (all SIB,                        BCCH                                                     DL-SCH                            PDSCH

SIB 2, SIB 3…………)

• MIB is the only system information transferred using the BCH and PBCH. SIBS are transferred using DL-SCH and PDSCH.
• SIB-1 has its RRC message whereas SIB-2 to SIB-13 are encapsulated within the more general system Information RRC message.
• The set of Resource Element used by the MIB on the PBCH is standardised by 3GPP so does not require any additional signalling, i.e. the PBCH occupies the central 72 subcarriers within the first4 OFDM symbols of the second slot of radio frame. The same allocation is made for both FDD and TDD.
• The set of Resource Element used by the SIB on the PDSCH is not standardized by 3GPP so requires addition signalling to inform the UE of where to look. The PDCCH is used to provide the additional signalling.
• The PDCCH includes CRC which is scrambled by the System Information RNTI (SI-RNTI) if it includes resource allocation information relevant to the SIB. The SI-RNTI has been standardised to have a single fixed value of 0xffff.
• Downlink Control Information (DCI) format 1A and 1C can be used to signal PDSCH resource allocation  for the SIB , i.e. DCI format 1A and DCI format 1C can have their CRC scrambled by the SI-RNTI.
• The eNodeB is responsible for scheduling the Resource Blocks used to transfer the SIB. The MIB and SIB1 are broadcast at a rate which is specified by 3GPP.The rate at which SIB2 to SIB 11are broadcast is implementation dependent.
• UE start by reading MIB and the provide sufficient information to read SIB1 and SIB1 provide scheduling information for the remaining SIB.
• Read Master Information Block ------>Allow UE to Read System Information Block -1 ---> Read SIB -1 then allowed the ----------->UE to read all remaining SIB.

• MIB– defines the most essential physical layer information of the cell required to receive further system information.
• SIB1– contains information relevant when evaluating if a UE is allowed to access a cell and defines the scheduling of other system information blocks.
• SIB2 – Contains common and shared channel information.
• SIB3 – Contains cell re-selection information.
• SIB4 – contains information about the serving neighboring frequencies and intra-frequency neighboring cells relevant for cell re-selection, covering both E UTRA and other RATs.
• SIB5 – contains information about other E UTRA frequencies and inter-frequency neighboring cells relevant for cell reselection.
• SIB6 – contains information about UTRA frequencies and UTRA neighboring cells relevant for cell re-selection.
• SIB7 – contains information about GERAN frequencies and GERAN neighboring cells relevant for cell re-selection/handover.
• SIB8 – contains information about CDMA2000 frequencies and CDMA2000 neighboring cells relevant for cell re-selection/handover.
• SIB9 – contains a home eNB identifier (HNBID)
• SIB10 – contains an ETWS primary notification
• SIB11 – contains an ETWS secondary notification