System Information Block Type 4 or with abbreviated version SIB4 contains neighboring cell related information and relevant only for intra-frequency cell re-selection. The message includes cells with specific re-selection parameters as well as blacklisted cells, Physical Cell Identities (PCI) for CSG. CSG can be used to support Home eNBs (Femto Cell). SIB4 is transmitted from the network to UE through BCCH -> DL-SCH -> PDSCH channels.
Here the list of carried information from the network to UE through SIB4:
Intra Freq Neigh Cell List: contains LTE cell neighbor list with specific parameters.
Phys Cell Id: indicates the physical cell ID of the intra-frequency neighbor cell.
q-Offset Cell: offset for the intra-frequency neighboring cell, which is used in evaluation for cell reselections. A larger value of this parameter results in a lower probability of cell reselections. If this parameter is not set to dB0, it is delivered in SIB4.
Intra Freq Black Cell List: consists of the parameters related to a blacklisted intra-frequency cell.
Phys Cell Id: starting physical cell ID of the intra-frequency blacklisted cell.
Phys Cell Id Range: physical cell ID range of the intra-frequency blacklisted cell.
CSG Phys Cell Id Range: Set of physical cell identities reserved for CSG cells. The received csg-PhysCellIdRange applies if less than 24 hours has elapsed since it was received and the UE is camped on a cell of the same primary PLMN where this field was received.
*Note: CSG (Closed Subscriber Group) is a group of users who are allowed for a specific cell (usually Femto cell). A CSG cell has restrictions on UE access. It broadcasts a specific CSG ID in the SIB and only those UEs of the group can access the CSG cell.
SIB4 carried information:
Example for SIB4, taken from drive-test tool:
systemInformation
criticalExtensions
systemInformation_r8
sib_TypeAndInfo
SystemInformation_r8_IEs_0_of_type
sib4
intraFreqNeighCellList
IntraFreqNeighCellInfo
physCellId = 0
q-OffsetCell = dB4
IntraFreqNeighCellInfo
physCellId = 1
q-OffsetCell = dB4
IntraFreqNeighCellInfo
physCellId = 2
q-OffsetCell = dB10
intraFreqBlackCellList
csg_PhysCellIdRange
nonCriticalExtension