SIB2 in LTE

SIB-2: an IMPORTANT SIB

• The IE SystemInformationBlockType2 contains radio resource configuration information that is common for all UEs.
• It carries Common and shared channel configuration, RACH related configuration, Timers, UL Power controls.
• Without this SIB UE cannot initiate ATTACH procedure.
• SIB2 is not specifically included in the scheduling information in SIB1 but it is always mapped to the SI message that corresponds to the first entry in the list of SI messages in schedulingInfoList in SIB1

Signalling radio bearer: N/A
RLC-Mode: TM
Logical channel: BCCH
Direction: E‑UTRAN to UE  

Important contents of SystemInformationBlockType2
rach_ConfigCommon
radioResourceConfigCommon
  numberOfRA_Preambles
    preamblesGroupAConfig_exist
    powerRampingParameters
    powerRampingStep
    preambleInitialReceivedTargetPower
    ra_SupervisionInfo
    preambleTransMax
    ra_ResponseWindowSize
  mac_ContentionResolutionTimer
  maxHARQ_Msg3Tx 4
bcch_Config
pcch_Config
prach_Config
pdsch_ConfigCommon
pusch_ConfigCommon
pucch_ConfigCommon
soundingRS_UL_ConfigCommon
uplinkPowerControlCommon
ue_TimersAndConstants
freqInfo
timeAlignmentTimerCommon   

Field Descriptions:

ac-BarringInfo	Access Class Barring configuration
radioResourceConfig	used to specify common radio resource configurations in the system information and in the mobility control information
numberOfRA_Preambles	Number of non-dedicated random access preambles
preamblesGroupAConfig_exist	Provides the configuration for preamble grouping. If the field is not signalled, the size of the random access preambles group A is equal to numberOfRA-Preambles
powerRampingParameters
powerRampingStep	Power ramping factor
preambleInitialReceivedTargetPower	Initial preamble power
ra_SupervisionInfo
preambleTransMax	Maximum number of preamble transmission
ra_ResponseWindowSize	Duration of the RA response window. Value in subframes. Value sf2 corresponds to 2 subframes
mac_ContentionResolutionTimer	Timer for contention resolution. Value in subframes. Value sf8 corresponds to 8 subframes
maxHARQ_Msg3Tx 4	Maximum number of Msg3 HARQ transmissions, used for contention based random access
bcch_Config
modificationPeriodCoeff	Actual modification period, expressed in number of radio frames= modificationPeriodCoeff * defaultPagingCycle. n2 corresponds to value 2
pcch_Config
defaultPagingCycle	Default paging cycle, used to derive ‘T’. Value rf32 corresponds to 32 radio frames
nB	is used as one of parameters to derive the Paging Frame and Paging Occasion
prach_Config	used to specify the PRACH configuration in the system information and in the mobility control information
rootSequenceIndex
prach_ConfigIndex	mentions the: Preamble format: 0-4 (For frame structure 1 preamble format is 0-3 and for frame structure 2 it is 0-4) SFN: whether it will be EVEN no. frmae OR any frame subframe number: carrier the subframe no. within the SFN (Look for the table in TS36.211 - Table 5.7.1-2)
highSpeedFlag	TRUE corresponds to Restricted set and FALSE to Unrestricted set
zeroCorrelationZoneConfig	used for Preamble generation
pdsch_Config	used to specify the common and the UE specific PDSCH configuration
pusch_Config	used to specify the common PUSCH configuration and the reference signal configuration for PUSCH and PUCCH
pucch_Config	used to specify the common and the UE specific PUCCH configuration
soundingRS_UL_Config	used to specify the uplink Sounding RS configuration
uplinkPowerControl	used to specify parameters for uplink power control in the system information and in the dedicated signalling
ue_TimersAndConstants	Timer values
freqInfo	UL carrier frequency and bandwidth
timeAlignmentTimerCommon	used to control how long the UE is considered uplink time aligned. Value in subframes