5G
NR system information in general is discussed in detail in the post 5G NR:System Information. This
post discusses SIB2 in detail.
SIB2 contains
cell re-selection information common for intra-frequency, inter-frequency
and/or inter-RAT cell re-selections (i.e. applicable for more than one type of
cell re-selection but not necessarily all).
SIB2
also contains intra-frequency cell re-selection information other than
neighbouring cell related information.
General
Information
System
Information (SI) in NR consists of a MIB and a number of SIBs, which are
divided into Minimum SI and Other SI.
Minimum
SI carries basic information required for initial access
and for acquiring any other SI. Minimum SI consists of MIB and SIB1.
For a UE to be allowed to camp on a cell, it
must have acquired the contents of the Minimum SI from that cell.
As
MIB and SIB1 are called as ‘minimum SI’, SIB1 alone
is known as ‘Remaining Minimum System Information’ (RMSI).
Other
SI consists of all SIBs not broadcast in the Minimum
SI. The UE does not need to receive these SIBs before accessing the cell. Other
SI is also known as On-Demand SI because gNB transmits/broadcasts
these SIBs when explicitly requested by UE(s). SIB2 is part of Other SI.
SIB2
is mapped to BCCH logical channel and either broadcast
periodically on DL-SCH or broadcast on-demand on DL-SCH (i.e. upon request from
UEs in RRC_IDLE or RRC_INACTIVE) or sent in a dedicated manner on DL-SCH to UEs
in RRC_CONNECTED.
SIB2
is carried in SystemInformation (SI) messages,
which are transmitted on the DL-SCH. SIB1 contains scheduling
information for SI-message carrying SIB2. For more information about scheduling
of SI-message, refer to 5G NR: System Information.
SIB2
can be configured to be cell specific or area specific, using an indication in SIB1.
The cell specific SIB is applicable only within a cell that provides the
SIB while the area specific SIB is applicable within an area
referred to as SI Area, which consists of one or several cells and is
identified by systemInformationAreaID.
Contests of SIB2
Overview
of SIB2 contents presented below. Most of the SIB2 contents are
discussed in detail in subsequent sections.
| SIB2 | |
| cellReselectionInfoCommon | Common information for intra-frequency, inter-frequency and/or inter-RAT cell re-selections |
| cellReselectionServingFreqInfo | Common information for inter-frequency and inter-RAT cell re-selections |
| intraFreqCellReselectionInfo | Common information for intra-frequency cell re-selections |
1. cellReselectionInfoCommon
cellReselectionInfoCommon
provides cell re-selection information common for
intra-frequency, inter-frequency and/or inter-RAT cell re-selections.
The
following table summarizes cellReselectionInfoCommon fields.
| cellReselectionInfoCommon | |
| nrofSS-BlocksToAverage | INTEGER (2 … maxNrofSS-BlocksToAverage) INTEGER (2 … 16) |
| absThreshSS-BlocksConsolidation | ThresholdNR |
| rangeToBestCell | RangeToBestCell |
| q-Hyst (in dB) | ENUMERATED {0, 1, 2, 3, 4, 5, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24} |
| speedStateReselectionPars | |
| mobilityStateParameters | MobilityStateParameters |
| q-HystSF | |
| sf-Medium | ENUMERATED {dB-6, dB-4, dB-2, dB0} |
| sf-High | ENUMERATED {dB-6, dB-4, dB-2, dB0} |
The
fields nrofSS-BlocksToAverage and absThreshSS-BlocksConsolidation only applicable
for intra-frequency cell reselection. For cell reselection in multi-beam
operations, the measurement quantity of a cell is derived amongst the beams
corresponding to the same cell based on SSBs. The procedure is described below;
-
If
at least one of these two fields is not configured in SIB2, the UE
derives each cell measurement quantity based on SSB as the strongest beam measurement
quantity value.
-
If
both fields are configured, the UE derives each cell measurement quantity based
on SSB as the linear average of a set of beam measurement quantity values. The
beams are selected such that, each beam measurement is above a threshold given
by absThreshSS-BlocksConsolidation. The maximum number of beams to be
averaged shall not exceed nrofSS-BlocksToAverage.
The
field rangeToBestCell is used in intra-frequency
and equal priority inter-frequency cell reselection procedures. The UE first ranks
the cells according to R-criteria (section 5.2.4.6 from 38.304) and then uses
the parameter rangeToBestCell in deciding the candidate cell.
| RangeToBestCell | |
| RangeToBestCell (in dB) | ENUMERATED {-24, -22, -20, -18, -16, -14, -12, -10, -8, -6, -5, -4, -3, -2, -1, 0, 1, 2, 3, 4, 5, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24} |
-
If
rangeToBestCell is not configured, the UE shall perform cell reselection
to the highest ranked cell.
-
If
rangeToBestCell is configured, then the UE shall perform cell
reselection to the cell with the highest number of beams above the threshold
(i.e. absThreshSS-BlocksConsolidation) among the cells whose R value is
within rangeToBestCell of the R value of the highest ranked cell. If
there are multiple such cells, the UE shall perform cell reselection to the
highest ranked cell among them.
-
The
network should only configure non-negative (in dB) values for this parameter.
The
field q-Hyst specifies hysteresis
value for ranking criteria. It is the parameter Qhyst used in
the serving cell R-criteria for intra-frequency and equal priority
inter-frequency cell reselections.
speedStateReselectionPars
contains parameters to determine UE’s mobility state.
| MobilityStateParameters | |
| t-Evaluation | ENUMERATED {rs30, s60, s120, s180, s240, spare3, spare2, spare1} |
| t-HystNormal | ENUMERATED {rs30, s60, s120, s180, s240, spare3, spare2, spare1} |
| n-CellChangeMedium | INTEGER (1 … 16) |
| n-CellChangeHigh | INTEGER (1 … 16) |
2. cellReselectionServingFreqInfo
cellReselectionServingFreqInfo
provides information common for non-intra-frequency
cell re-selection i.e. cell re-selection to inter-frequency and inter-RAT
cells.
The
following table summarizes cellReselectionServingFreqInfo fields.
| cellReselectionServingFreqInfo | ||
| s-NonIntraSearchP | ReselectionThreshold | INTEGER (0 … 31) |
| s-NonIntraSearchQ | ReselectionThresholdQ | INTEGER (0 … 31) |
| threshServingLowP | ReselectionThreshold | INTEGER (0 … 31) |
| threshServingLowQ | ReselectionThresholdQ | INTEGER (0 … 31) |
| cellReselectionPriority | CellReselectionPriority | INTEGER (0 … 7) |
| cellReselectionSubPriority | CellReselectionSubPriority | ENUMERATED {0.2, 0.4, 0.6, 0.8} |
s-NonIntraSearchP is the
parameter SnonIntraSearchP and s-NonIntraSearchQ
is the parameter SnonIntraSearchQ in 38.304 section 5.2.4.7.
These parameters specifies Srxlev (RSRP) threshold and Squal
(RSRQ) threshold (in dB) respectively for inter-frequency and inter-RAT measurements.
For
s-NonIntraSearchP, actual
value = field value *2 (dB) and if the field is absent, a default value
of infinity shall be applied. For, s-NonIntraSearchQ, actual value = field value
and if the field is absent, a default value of 0 dB shall be applied.
The
UE uses these parameters and applies the following rules for NR inter-frequencies
and inter-RAT frequencies which are indicated in system information and for
which UE has priority provided.
-
For
an NR inter-frequency or inter-RAT frequency with a reselection priority higher
than the reselection priority of the serving NR frequency, the UE shall perform
measurements of higher priority NR inter-frequency or inter-RAT frequencies irrespective
of thresholds provided by s-NonIntraSearchP and s-NonIntraSearchQ.
-
For
a NR inter-frequency with an equal or lower reselection priority than the
reselection priority of the serving NR frequency and for inter-RAT frequency
with lower reselection priority than the reselection priority of the serving NR
frequency;
·
If
the serving cell fulfils Srxlev
> SnonIntraSearchP and Squal > SnonIntraSearchQ,
the UE doesn’t have to perform measurements of NR inter-frequencies or
inter-RAT frequency cells of equal or lower priority;
·
Otherwise,
the UE should measure NR inter-frequencies or inter-RAT frequency cells of
equal or lower priority.
The
parameters threshServingLowP and
threshServingLowQ specifies RSRP
and RSRQ thresholds respectively and are used by the UE on the serving cell
when reselecting towards a lower priority RAT/frequency (than serving).
For
threshServingLowP, actual
value = field value *2 (dB) and for, threshServingLowQ, actual value = field value.
-
In
case, threshServingLowQ is configured in SIB2, the UE shall
perform cell reselection to lower priority RAT/frequency (than serving) if the
serving cell quality is below a threshold given by threshServingLowQ and
the quality of the target cell is above certain threshold.
-
Otherwise
(threshServingLowQ is NOT configured in SIB2), the UE
shall perform cell reselection to lower priority RAT/frequency (than serving) based
on threshServingLowP. The UE shall proceed with the reselection only if
the serving cell RSRP is below a threshold given by threshServingLowP and
the RSRP of the target cell is above certain threshold.
CellReselectionPriority provides
the absolute priority of the concerned carrier frequency and is used in the
cell reselection procedure. Value 0 means lowest priority and value 7 means
highest priority. It is a mandatory field.
The
IE CellReselectionSubPriority indicates
a fractional value to be added to the value of cellReselectionPriority to
obtain the absolute priority of the concerned carrier frequency for E-UTRA and
NR. Value oDot2 corresponds to 0.2, value oDot4 corresponds to
0.4 and so on. This is an optional field.
Absolute priority = cellReselectionPriority
+ CellReselectionSubPriority (if configured)
3. intraFreqCellReselectionInfo
intraFreqCellReselectionInfo
provides cell re-selection information common for
intra-frequency cells.
The
following table summarizes intraFreqCellReselectionInfo fields.
| intraFreqCellReselectionInfo | ||
| q-RxLevMin | Q-RxLevMin | INTEGER (-70 … -22) |
| q-RxLevMinSUL | Q-RxLevMin | INTEGER (-70 … -22) |
| q-QualMin | Q-QualMin | INTEGER (-43 … -12) |
| s-IntraSearchP | ReselectionThreshold | INTEGER (0 … 31) |
| s-IntraSearchQ | ReselectionThresholdQ | INTEGER (0 … 31) |
| t-ReselectionNR | T-Reselection | INTEGER (0 … 7) |
| frequencyBandList | MultiFrequencyBandListNR-SIB | |
| frequencyBandListSUL | MultiFrequencyBandListNR-SIB | |
| p-Max | P-Max | INTEGER (-30 … 33) |
| smtc | SSB-MTC | |
| ss-RSSI-Measurement | SS-RSSI-Measurement | |
| ssb-ToMeasure | SSB-ToMeasure | |
| deriveSSB-IndexFromCell | BOOLEAN | |
| t-ReselectionNR-SF | SpeedStateScaleFactors | |
Q-RxLevMin is used
to indicate the required ‘minimum received RSRP level’ (in dBm) in the
(NR) cell for re-selection. Actual
value Qrxlevmin = field value * 2 [dBm]. Refer
to 38.304 cell re-selection criterion.
Q-RxLevMinSUL: If the
UE supports SUL frequency for this cell, Qrxlevmin (explained
above) is obtained from this field. Actual value Qrxlevmin = field value * 2 [dBm].
Q-QualMin is used
to indicate the required ‘minimum received RSRQ level’ (in dB) in the
(NR) cell for cell re-selection. If this field is absent, the UE applies the
(default) value of negative infinity for Qqualmin which means
that quality (RSRQ) check will always pass irrespective of the received signal
quality. Refer to 38.304 cell re-selection criterion.
s-IntraSearchP is the
parameter SIntraSearchP and s-IntraSearchQ
is the parameter SIntraSearchQ in 38.304 section 5.2.4.2.
These parameters specifies Srxlev (RSRP) threshold and Squal
(RSRQ) threshold (in dB) respectively for intra-frequency measurements.
-
For
s-IntraSearchP, actual
value = field value *2 (dB) and if the field is absent, a default value
of infinity shall be applied. For, s-IntraSearchQ, actual value = field value
and if the field is absent, a default value of 0 dB shall be applied.
-
If
the serving cell fulfils Srxlev
> SIntraSearchP and Squal > SIntraSearchQ,
the UE need not perform intra-frequency measurements. Otherwise, the UE shall
perform intra-frequency measurements.
t-ReselectionNR specifies
the cell reselection timer value for the concerned NR frequency.
frequencyBandList indicates
a list of frequency bands for which the NR cell reselection parameters apply. The
contents of this IE are given below;
| MultiFrequencyBandListNR-SIB | |
| MultiFrequencyBandListNR-SIB | List of 1 to 8 NR-MultiBandInfo |
| NR-MultiBandInfo | |
| freqBandIndicatorNR | INTEGER (1 … 1024) |
| nr-NS-PmaxList | NR-NS-PmaxList |
| NR-NS-PmaxList | |
| NR-NS-PmaxList | List of 1 to 8 NR-NS-PmaxValue |
| NR-NS-PmaxValue | |
| additionalPmax | P-Max |
| additionalSpectrumEmission | INTEGER (0 … 7) |
p-Max is
the maximum permitted transmit power (in dBm) applicable for the
intra-frequency neighbouring NR cells.
smtc defines Measurement
Timing Configuration for intra-frequency measurements i.e., timing occasions at
which the UE measures SSBs. If this field is absent, the UE assumes that SSB
periodicity is 5 ms for the intra-frequency cells. SSB-MTC
contents are given below.
| SSB-MTC | |
| periodicityAndOffset | |
| sf5 | INTEGER (0 … 4) |
| sf10 | INTEGER (0 … 9) |
| sf20 | INTEGER (0 … 19) |
| sf40 | INTEGER (0 … 39) |
| sf80 | INTEGER (0 … 79) |
| sf160 | INTEGER (0 … 159) |
| duration | ENUMERATED {sf1, sf2, sf3, sf4, sf5} |
-
duration
configures the duration
(in subframes) of the measurement window in which to receive SS/PBCH blocks.
-
periodicityAndOffset
configures periodicity
and offset of the measurement window in which to receive SS/PBCH blocks.
ss-RSSI-Measurement is
used to configure RSSI measurements based on synchronization reference signals.
ss-RSSI-Measurement contents are given below
| SS-RSSI-Measurement | |
| measurementSlots | BIT STRING ( SIZE (1 … 80) ) |
| endSymbol | INTEGER (0 … 3) |
-
measurementSlots
indicates the
slots in which the UE can perform RSSI measurements. The length of the BIT
STRING is equal to the number of slots in the configured SMTC window
(determined by the duration and SCS). The first (left-most / most significant)
bit in the bitmap corresponds to the first slot in the SMTC window, the second
bit in the bitmap corresponds to the second slot in the SMTC window, and so on.
The UE measures in slots for which the corresponding bit in the bitmap is set
to 1.
-
endSymbol: Within a slot that is configured for
RSSI measurements (see measurementSlots above), the UE measures the RSSI
from symbol 0 to symbol given by endSymbol.
ssb-ToMeasure
configures a set of SS blocks to be measured within the SMTC measurement
duration. When the field is absent the UE measures on all SS-blocks. SSB-ToMeasure
IE is given below.
| SSB-ToMeasure | |
| shortBitmap | BIT STRING ( SIZE (4) ) |
| mediumBitmap | BIT STRING ( SIZE (8) ) |
| longBitmap | BIT STRING ( SIZE (64) ) |
As
discussed in the post 5G NR: Synchronization Signal/PBCH block (SSB), the maximum number of SSBs within an SS burst set depends
upon the carrier frequency/band as described below.
-
fc
≤ 3 GHz: Maximum number
of SSBs within SS burst set equals to four, so 4 bits are good enough. For this purpose, a shortBitmap of
length 4 is defined.
-
3
GHz < fc ≤ 6 GHz: Maximum number of SSBs within SS burst set equals to eight,
so 8 bits are good enough. For
this purpose, a mediumBitmap of length 8 is defined.
-
fc
> 6 GHz: Maximum number
of SSBs within SS burst set is 64. For this purpose, a longBitmap of length
64 is defined.
deriveSSB-IndexFromCell
indicates whether the UE can utilize serving cell
timing to derive the index of SSB transmitted by neighbour cell. If this field
is set to true, the UE assumes SFN and frame boundary alignment across
cells on the serving frequency.
t-ReselectionNR-SF is
the parameter "Speed dependent ScalingFactor for TreselectionNR"
in 38.304. Based on the current mobility state (high or medium), the UE multiplies
TreselectionNR with sf-High or sf-Medium.
The value of TreselectionNR after applying the respective
scaling factor will always be less than or equal to TreselectionNR
before scaling. This in general implies that, the reselections are allowed
to occur faster (based on scaling factor) during medium or high mobility
states. The following table summarizes the SpeedStateScaleFactors
contents.
| SpeedStateScaleFactors | |
| sf-Medium | ENUMERATED {oDot25, oDot5, oDot75, 1Dot0} |
| sf-High | ENUMERATED {oDot25, oDot5, oDot75, 1Dot0} |
Reference: 3GPP TS 38.331, and 38.304
