SIB1 and Power Control in 5G NR

Jyothi
4 min readFeb 25, 2022

System Information Block1 is also called as RMSI(Remaining minimum system information) which is received on PDSCH (Physical Downlink shared channel).
It is received after receiving MIB on PBCH (Physical Broadcast channel).
SIB1 is decoded using MIB information.
SIB1 contains the information about whether UE is accessed to permit gNB and it also contains scheduling information and the other system information
which is common to all UEs.
SIB1 is transmitted on DLSCH with a periodicity of 160ms.
SIB1 includes information regarding the availability and scheduling (e.g. mapping of SIBs to SI message, periodicity, SI-window size) of other SIBs with an indication whether one or more SIBs are only provided on-demand and, in that case, the configuration needed by the UE to perform the SI request. SIB1 contains cell-specific SIB information.
It also contains radio resource configuration information that is common for all UEs and barring information is applied to the unified access control.
SIB1 contains the below information:
- cellSelectionInfo : Parameters to the cell selection related to serving cell
- cellAccessRelatedInfo: cell access related information for the cell
- connEstFailureControl: parameters for connection establishment failure control
- si-SchedulingInfo: Information needed for acquisition of SI messages
- servingCellConfigCommon: configuration of the serving cell
- ims-EmergencySupport: Indicate whether cell supports IMS emergency services
- ue-TimersAndConstants: Timer and constant values used by UE
- uac-BarringInfo: Barring Information
- useFullResumeID: resume identifier

Power Control
SIB1 contains servingCellConfigCommon information element that specifies the service cell configuration.

PRACH Power control parameters
servingCellConfigCommon IE contains the RACH-ConfigCommon IE. RACH-ConfigCommon parameter structure provides the UE with the information required to complete the random access procedure. For example, it specifies the PRACH Configuration Index, the Zero Correlation Zone configuration, the PRACH Root Sequence, the grouping of PRACH preambles, PRACH power control parameters and RSRP thresholds for initiating the random access procedure with a specific beam, etc.

Following Power control parameters related to PRACH are received from cell:
- preambleReceivedTargetPower field in RACH-ConfigGeneric IE: This parameter is used in open loop power control calculations. It specifies the target power level at network receiver side. Only multiples 2dBm may be chosen.
- powerRampingSlep field in RACH-ConfigGeneric IE: It defines the increase in transmit power between successive PRACH preamble transmissions.
- prach-ConfigurationIndex field in RACH-ConfigGeneric IE: It defines short/long preamble format. Its values range from 0 to 255. Table 6.3.3.2–2 and Table 6.3.3.2–4 in 3GPP TS38.211 lists the PRACH configuration index values and values corresponding to preamble format, SFN, subframe number, starting symbol, number of PRACH slots within a subframe, number of time domain PRACH occasions within a PRACH slot, PRACH duration parameters.
Delta preamble values are used in PRACH power control. Delta preamble values vary based on PRACH long/short preamble formats.
- ss-PBCH-BlockPower in ServingCellConfigCommonSIB IE: It specifies average EPRE (energy per resource element) of the resources elements that carry
secondary synchronization signals in dBm that the NW used for SSB transmission. The Base Station uses the ss-PBCH-BlockPower information element to provide the UE with an absolute value of transmit power of the SSS. ss-PBCH-BlockPower represents transmit power of single resource element. It can have any integer value within the range from -60 to 50 dBm.
UE will use this field to compute the path loss.

Path loss = ss-PBCH-BlockPower(reference signal power) -higher layer filtered RSRP value.

PUSCH power control parameters
-
pusch-configcommon in servingCellConfigCommon IE: This IE is used to configure cell specific PUSCH parameters. This parameter structure
provides UE with the information to allocate time domain resources, power control information, etc.

- msg3-DeltaPreamble in pusch-configcommon: msg3-DeltaPreamble specifies the power offset between msg3 and RACH preamble transmission. This specifies the transmit power difference between between the most recent PRACH preamble and MSG3.
MSG3 transmit power — Most recent PRACH preamble transmit power = 2 * msg3-DeltaPreamble
- p0-NominalWithGrant: This specifies the p0 value for PUSCH with grant. It is not applicable MSG3. This is cell specific value only even numbers are allowed.
It specifies the target received power for PUSCH open loop power control calculations (PO_nominal_pusch,f,c(j)) when using dynamic grants.

PUCCH power control parameters

PUCCH-ConfigCommon IE in servingCellConfigCommon IE is used to configure cell specific PUCCH parameters. It also provides power control information and group/sequence hopping information.

p0-nominal in PUCCH-ConfigCommon value ranges from -202 to 24 dB. Its a Power control parameter p0 for PUCCH transmission. The -202 dBm minimum value for p0-nominal is significantly lower than a normal received power level. This extremely low value has been specified to cater for Supplemental Uplink scenarios which involve the UE measuring the
downlink path loss in one band and transmitting the PUCCH in another band. For example, a UE could measure the downlink path loss
at 70 GHz while configured to transmit the PUCCH using a Supplemental Uplink at 700 MHz. In this case, the downlink path loss measured at 70 GHz is significantly greater than the uplink path loss at 700 MHz. The combination of air-interface propagation loss and building penetration loss could be more than 70 dB higher at 70 GHz when compared to 700 MHz. Configuring a very low value for the nominal power helps to ensure that the UE transmits at a power level which is appropriate for the lower operating band.

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