LTE Radio Resource Control (RRC) System Information


System Information is divided into MasterInformationBlock and a number of SystemInformationBlocks. UE needs to locate and read the system information before establishing any connection to the E-UTRA. SystemInformationBlockType1 and all SI messages are transmitted on DL-SCH.

UE shall apply the system information acquisition procedure:

  • upon selecting and upon reselecting,
  • after handover completion,
  • after entering E-EUTRA from other RAT,
  • upon return from out of coverage,
  • upon receiving a notification that the system information is changed,
  • upon receiving an indication about the presence of an ETWS notification,
  • upon receiving a request from CDMA2000 upper layer and
  • upon receiving maximum validity duration.

System Information Required by UE

The System Information required by an UE depends on the RRC state of the UE.

RRC Idle

In RRC Idle state the following system information are required:

  • MasterInformationBlock
  • SystemInformationBlockType1
  • SystemInformationBlockType2 through SystemInformationBlocakType8 depending on the type of RATs supported by UE

RRC Connected

In RRC Connected state the following system information are required:

  • MasterInformationBlock
  • SystemInformationBlockType1
  • SyetmInformationBlockType 2
  • SystemInformationType8 depending on support of CDMA2000

MasterInformationBlock

The MIB includes a limited number of most essential and most frequently transmitted parameters that are required to acquire other information from the cell. MIB uses a fixed schedule with a periodicity of 40 ms and repetitions made within 40 ms. The first transmission of MIB is scheduled at subframe #0 of radio frame for which SFN mod 4 = 0, and repetition are scheduled at subframe #0 for all other radio frames.
MasterInformationBlock contains the following information elements:

Downlink Bandwidth (dl-Bandwidth)
It represents the transmission bandwidth configuration in downlink.

Channel bandwidth BWChannel [MHz] 1.4 3 5 10 15 20
Transmission bandwidth configuration N-RB 6 15 25 50 75 100

PHICH-Config
The PHICH carries the hybrid-ARQ ACK/NAK.

System Frame Number (systemFrameNumber)
systemFrameNumber defines the 8 most significant bits in SFN.

SystemInformationBlockType1

SystemInformationBlockType1 are carried in SystemInformation(SI) message. The SystemInformationBlockType1 uses a fixed schedule with periodicity of 80 ms and repetition made within 80 ms. The first transmission of SystemInformationBlockType1 is schedule in subframe #5 of radio frames for which SFN mod8 = 0, and repetition are schedule in all radio frames for which SFN mod2 = 0.

SystemInformationBlockType1 configures the SI-window length and transmission periodicity for the SI messages.
Important parameters in SystemInformationBlockType1

PLMN-IdentityList
The List of PLMN identities. The first listed PLMN identity is the primary PLMN identity.

Tracking Area Code
The common tracking area code for all listed PLMN

CellBarred information
Cell is barred or not.

IntraFrequencyReselection
This is used to control reselection when highest ranked cell is barred or treated as barred by UE.

sib-MappingInfo
List of SIBs mapped to the SystemInformation message. There is no mapping information of SIB2, it is always present in the first system information message listed in the schedulingInformationList.

SystemInformationBlockType2

SystemInformationBlockType2 contains common and shared channel information.

The important parameters present in SystemInformationBlockType2 are:

  • Access barring information
  • Radio resource configuration of common channels
  • UE times and constants

SystemInformationBlockType3

The IE SystemInformationBlockType3 contains cell re-selection information common for intra-frequency, inter-frequency and/ or inter-RAT cell re-selection. Speed dependent reselection parameters are also included for control of UE cell reselection depending on UE speed.

SystemInformationBlockType4

The IE SystemInformationBlockType4 contains neighbouring cell related information relevant only for intra-frequency cell re-selection. The IE includes cells with specific re-selection parameters as well as blacklisted cells.

SystemInformationBlockType5

The IE SystemInformationBlockType5 contains information relevant only for inter-frequency cell re-selection i.e. information about other E-UTRA frequencies and inter-frequency neighbouring cells relevant for cell re-selection.

SystemInformationBlockType6

The IE SystemInformationBlockType6 contains information relevant only for inter-RAT cell re-selection i.e. information about UTRA frequencies and UTRA neighbouring cells relevant for cell re-selection.

SystemInformationBlockType7

The IE SystemInformationBlockType7 contains information relevant only for inter-RAT cell re-selection i.e. information about GERAN frequencies relevant for cell re-selection. The IE includes cell re-selection parameters for each frequency.

SystemInformationBlockType8

The IE SystemInformationBlockType8 contains information relevant only for inter-RAT cell re-selection i.e. information about CDMA2000 frequencies and CDMA2000 neighbouring cells relevant for cell re-selection. The IE includes cell re-selection parameters common for a frequency as well as cell specific re-selection parameters.

SystemInformationBlockType9

The IE SystemInformationBlockType9 contains a home eNB name (HNB Name).

SystemInformationBlockType10

The IE SystemInformationBlockType10 contains an ETWS (Earthquake and Tsunami Warning System) primary notification.

SystemInformationBlockType11

The IE SystemInformationBlockType11 contains an ETWS (Earthquake and Tsunami Warning System) secondary notification.

System Information Modification

Changes in system information occur only at certain radio frames. The modification period boundaries are defined by SFN values. The paging message is used to inform UEs in RRC_IDLE and in RRC_CONNECTED state about system information change.

SystemInformationBlockType1 contains value tag, systemInfoValueTag, that indicates is if a change has occurred in the SI messages. UE also check systemInforValueTag, upon return from out of coverage, to verify if the system information messages are still valid.

UE considers stored system information to be invalid after 3 hours from the moment it was successfully confirmed as valid.

Reference