LTE System Information: Part 1

Expert Opinion

Expert Opinion
Short LTE articles and opinions by our team of Subject Matter Experts (SMEs)

LTE System Information: Part 1

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LTE system information is one of the key aspects of the air interface. It consists of the Master Information Block (MIB) and a number of System Information Blocks (SIBs). The MIB is broadcast on the Physical Broadcast Channel (PBCH), while SIBs are sent on the Physical Downlink Shared Channel (PDSCH) through Radio Resource Control (RRC) messages. SIB1 is carried by "SystemInformationBlockType 1" message. SIB2 and other SIBs are carried by "SystemInformation (SI)" message. An SI message can contain one or several SIBs.

1.       The MIB is the first thing a UE looks for after it achieves downlink synchronization. The MIB carries the most essential information that is needed for the UE to acquire other information from the cell. It includes:

  • The downlink channel bandwidth
  • The PHICH configuration. The Physical Hybrid ARQ Indicator Channel carries the HARQ ACKs and NACKs for uplink transmissions
  • The SFN (System Frame Number) which helps with synchronization and acts as a timing reference
  • The eNB transmit antenna configuration specifying the number of transmit antennas at eNB such as 1, 2, or 4, which is carried by CRC mask for PBCH

2.       SIB1 is carried in a SystemInformationBlockType1 message. It includes information related to UE cell access and defines the schedules of other SIBs, such as:

  • The PLMN Identities of the network
  • The tracking area code (TAC) and cell ID
  • The cell barring status, to indicate if a UE may camp on the cell or not
  • q-RxLevMin, which indicates the minimum required Rx Level in the cell to fulfill the cell selection criteria
  • The transmissions times and periodicities of other SIBs

3.       SIB2 contains radio resource configuration information common for all UEs, including:

  • The uplink carrier frequency and the uplink channel bandwidth (in terms of the number of Resource Blocks, for example n25, n50)
  • The Random Access Channel (RACH) configuration, which helps a UE start the random access procedure, such as preamble information, transmit time in terms of frame and subframe number (prach-ConfigInfo), and powerRampingParameters which indicates the initial Tx power and ramping step.
  • The paging configuration, such as the paging cycle
  • The uplink power control configuration, such as P0-NominalPUSCH/PUCCH
  • The Sounding Reference Signal configuration
  • The Physical Uplink Control Channel (PUCCH) configuration to support the transmission of ACK/NACK, scheduling requests, and CQI reports
  • The Physical Uplink Shared Channel (PUSCH) configuration, such as hopping

4.       SIB3 contains information common for intra-frequency, inter-frequency, and/or inter-RAT cell reselection. This information does not necessarily apply to all scenarios; please refer to 3GPP TS 36.304 for the details. The basic parameters include:

  • s-IntraSearch: the threshold for starting intra-frequency measurement. When s-ServingCell (i.e., cell selection criterion for serving cell) is higher than s-IntraSearch, the UE may choose not to perform measurement in order to save battery life.
  • s-NonIntraSearch: the threshold for starting inter-frequency and IRAT measurements
  • q-RxLevMin: the minimum required Rx level in the cell
  • Cell reselection priority: the absolute frequency priority for E-UTRAN or UTRAN or GERAN or CDMA2000 HRPD or CDMA2000 1xRTT
  • q-Hyst: the hysteresis value used for calculating the cell-ranking criteria for the serving cell, based on RSRP.
  • t-ReselectionEUTRA: the cell reselection timer value for EUTRA. t-ReselectionEUTRA and q-Hyst can be configured to trigger cell reselection sooner or later.

5.       SIB4 contains the intra-frequency neighboring cell information for Intra-LTE intra-frequency cell reselection, such as neighbor cell list, black cell list, and Physical Cell Identities (PCIs) for Closed Subscriber Group (CSG).  CSG can be used to support Home eNBs.

6.       SIB5 contains the neighbor cell related information for Intra-LTE inter-frequency cell-reselection, such as neighbor cell list, carrier frequency, cell reselection priority, threshold used by the UE when reselecting a higher/lower priority frequency than the current serving frequency, etc.

 (Note that 3GPP states that LTE neighbor cell search is feasible without providing an explicit neighbor list. Since the UE can do blind detection of neighbor cells in LTE, the broadcast of LTE neighbor cells is optional.)

  • well written article and very informative. Found a complete list of functionalities of SIB 2