System information block 2 (SIB2) in LTE

After initial cell synchronization process is completed, UE will read master information block which contains important information regarding downlink cell bandwidth, PHICH configuration and System frame number. Then UE can read System information block 1 and System information block 2 to obtain useful information related to cell access, SIB scheduling and radio resource configuration

System information block 2 carries radio resource configuration information which is common for all UEs.

SIB2 information can be divided in following sub categories
  • Random access channel (RACH) related parameters 
  • Idle mode paging configurations 
  • Uplink physical control channel (PUCCH) and shared channel (PUSCH) configurations 
  • Uplink power control and Sounding reference signal configurations 
  • Uplink carrier frequency / Bandwidth 
  • Cell barring information 

SIB2 Example

Example SIB2 info is shown below (Taken from UE logs). This SIB2 does not represent any real network

value BCCH-DL-SCH-Message ::= 
  message c1 : systemInformation : 
        criticalExtensions systemInformation-r8 : 
              sib2 : 
                        numberOfRA-Preambles n40,
                          sizeOfRA-PreamblesGroupA n32,
                          messageSizeGroupA b144,
                          messagePowerOffsetGroupB dB10
                        powerRampingStep dB2,
                        preambleInitialReceivedTargetPower dBm-104
                        preambleTransMax n10,
                        ra-ResponseWindowSize sf5,
                        mac-ContentionResolutionTimer sf32
                      maxHARQ-Msg3Tx 3
                      modificationPeriodCoeff n8
                      defaultPagingCycle rf64,
                      nB oneT
                      rootSequenceIndex 30,
                        prach-ConfigIndex 4,
                        highSpeedFlag FALSE,
                        zeroCorrelationZoneConfig 8,
                        prach-FreqOffset 3
                      referenceSignalPower 11,
                      p-b 1
                        n-SB 1,
                        hoppingMode interSubFrame,
                        pusch-HoppingOffset 6,
                        enable64QAM FALSE
                        groupHoppingEnabled FALSE,
                        groupAssignmentPUSCH 0,
                        sequenceHoppingEnabled FALSE,
                        cyclicShift 0
                      deltaPUCCH-Shift ds2,
                      nRB-CQI 1,
                      nCS-AN 0,
                      n1PUCCH-AN 36
                    soundingRS-UL-ConfigCommon release : NULL,
                      p0-NominalPUSCH -100,
                      alpha al1,
                      p0-NominalPUCCH -100,
                        deltaF-PUCCH-Format1 deltaF0,
                        deltaF-PUCCH-Format1b deltaF1,
                        deltaF-PUCCH-Format2 deltaF0,
                        deltaF-PUCCH-Format2a deltaF0,
                        deltaF-PUCCH-Format2b deltaF0
                      deltaPreambleMsg3 1
                    ul-CyclicPrefixLength len1
                    t300 ms200,
                    t301 ms200,
                    t310 ms500,
                    n310 n10,
                    t311 ms3000,
                    n311 n1
                    ul-CarrierFreq 20600,
                    ul-Bandwidth n50,
                    additionalSpectrumEmission 12
                  timeAlignmentTimerCommon sf10240

Definition of important Parameters

Rach Configurations

numberOfRA-Preambles: Total number of random access preambles available for contention based random access. Since there are maximum 64 preambles sequences available, others could be reserved by eNB for Non-Contention based random access. Range of this parameter is 4 to 64
sizeOfRA-PreamblesGroupA: Total number of random access preambles sequences available within Group A. Preambles are divided into Group A and Group B. Group A preambles are intended for sending small packets and Group B preambles are intended for sending large packets. Range of this parameter is 4 to 60
messageSizeGroupA: Message size threshold for selecting preamble Group A in term of bits (56, 144, 208 or 256 bits)
messagePowerOffsetGroupB: Power offset for selecting preamble Group B (0, 5, 8, 10, 12, 15 or 18 dB)
powerRampingStep: power ramping step size with possible values of 0, 2, 4 or 6 dB
preambleInitialReceivedTargetPower: Preamble initial received target power with values from -120 dBm to -90 dBm with step size of 2 dBm 
preambleTransMax: Maximum number of preambles transmissions. Possible values are 3, 4, 5, 6, 7, 8, 10 ,20, 50, 100, 200.
ra-ResponseWindowSize: Duration of RA response window. RA response window size is in unit of subframes (2, 3, 4, 5, 6, 7, 8, or 10 subframes)
mac-ContentionResolutionTimer: Mac contention resolution timer in unit of subframes (8, 16, 24, 32, 40, 58, 56 or 64 subframes)
maxHARQ-Msg3Tx: Maximum number of HARQ retransmissions for message 3 of RACH process (contention-based Random access) with possible values from 1 to 8 in step of 1

BCCH Configurations

modificationPeriodCoeff: The value (2,4,6,8) of this parameter is multiplied with default DRX cycle (e.g. 320ms, 640ms) to generate the BCCH modification period. It is the period in which the change in SI is repeated to UEs so that the change in SI is acquired by UE.
BCCH modification period = modificationPeriodCoeff x idle mode DRX cycle

PCCH Configurations

defaultPagingCycle: The default DRX cycle in idle mode in unit of radio frames (rf64 means 640ms )
nB: This parameter value is used in finding the actual paging frames and paging occasions in RRC idle mode with the following formula
    SFN modT = (T/N) x (UE_ID mod N)

T = Drx cycle 
N = Min (T, nB)  (nB is broadcasted in SIB2) 
UE_ID = IMSI mod 1024

PRACH Configurations

rootSequenceIndex: RA preambles are generated from  Zadoff Chu sequence which consists of series of root sequences. Each root sequence can be cyclic shifted to obtain preamble sequence. Range of rootSequenceIndex is 0 to 837. 
prach-ConfigIndex: This parameter defines exactly when UE should send RACH in frequency/time grids  (Details TS36.211 Table 5.7.1-2)
highSpeedFlag: For high speed UEs , as this can impact the correlation between cycles
zeroCorrelationZoneConfig: The zero correlation zone is used to guarantee orthogonality of generated sequences. The value depends on particular condition in the cell
prach-FreqOffset: With this information cell informs UE and other neighbor cells know about which PRB is available for RACH access

PDSCH Configurations

referenceSignalPower: This defines the energy per resource element for the reference signal using a range from -60 to 50 dBm. 
p-b: It is used to calculate the power difference between PDSCH and Reference Signal. Value is from 0 to 3

PUSCH Configurations

n-SB: Number of subbands (range 1 to 4)
hoppingMode: Hopping mode can be inter-subframe, intra or inter-subframe
pusch-HoppingOffset: Offset values range from 1 to 98
enable64QAM: if 64QAM capable UE should use it (True or False)

groupHoppingEnabled: True or False
groupAssignmentPUSCH: Gives sequence shift pattern for group hopping (0 to 29)
sequenceHoppingEnabled: True or False
cyclicShift: Frequency shift for demodulation (0 to 7)

PUCCH Config

deltaPUCCH-Shift: 1,2 or 3
nRB-CQI: Number of PRBs per slot for PUCCH2 (0 to 98)
nCS-AN: Cyclic shift used for PUCCH1 (0 to 7)
n1PUCCH-AN: PUCCH to be used for HARQ (0 TO 2047)

Sounding Reference Signaling Configurations:

The uplink Sounding Reference Signal (SRS) is configured in terms of bandwidth and subframes

Uplink Power Control

p0-NominalPUSCH: It impacts the calculation of PUSCH transmit power and applicable to non-persistent scheduling only (-126 to 24 dBm)
alpha: It also impacts the calculation of PUSCH transmit power and also scales the contribution of path loss. Possible values are 0, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 and 1
p0-NominalPUCCH: This parameter impacts the calculation of PUCCH transmit power (-127 to -96 dBm)
deltaFList-PUCCH: These parameters impacts the calculation of PUCCH  transmit power

deltaPreambleMsg3: It impacts the transmit power of PUSCH when responding to random access response grant (-1 to 6dB)

ul-CyclicPrefixLength:  To differentitate between normal (len1) OR extended (len2) cyclic prefix for uplink transmission

UE Timers and Constants

T300: Time during which UE waits for RRC connection request message response (100, 200, 300, 400, 600, 1000, 1500, 2000 ms)
T301: Started after RRC Connection Reestablishment request message. On expiration UE will go to RRC idle (100, 200, 300, 400, 600, 1000, 1500, 2000 ms)
T310: Started after receiving N310 out of sync indications (0, 50, 100, 200, 500, 1000, 2000 ms)
T311: Started after initiating connection re-establishment procedure. On expiration UE goes to RRC idle mode if it is unable to locate suitable cell (1, 3, 5, 10, 15, 20, 30 seconds)
N310: Consecutive out of sync indications (1, 2, 3, 4, 6, 8, 10, 20)
N311: Consecutive in-sync indications (1, 2, 3, 4, 6, 8, 10, 20)

Frequency Information

ul-CarrierFreq: Defined in terms of EARFCN
ul-Bandwidth: Defined in terms of resource blocks
additionalSpectrumEmission: This allows spectrum emission limits to be configured according to local requirements (1 to 32)

timeAlignmentTimerCommon: it tells UE how long it should consider itself to be time aligned in uplink in unit of subframes. (500, 750, 1280, 1920, 2560, 5120, 10240 or infinity subframes)