5G
NR system information in general is discussed in detail in the post 5G NR:System Information. This
post discusses SIB4 in detail.
SIB4 contains
information relevant only for inter-frequency cell re-selections i.e.
information about other NR frequencies and inter-frequency neighbouring cells
relevant for cell re-selection. It includes cell re-selection parameters common
for a frequency as well as cell specific re-selection parameters.
General
Information
SIB4
is mapped to BCCH logical channel and is 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.
SIB4
is carried in SystemInformation (SI) messages,
which are transmitted on the DL-SCH. SIB1 contains scheduling
information for SI-message carrying SIB4. For more information about
scheduling of SI-messages, refer to 5G NR:System Information.
SIB4
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 SIB4
Most of the SIB4 contents are
discussed in detail in this section.
interFreqCarrierFreqList
As
shown below, interFreqCarrierFreqList
provides a list of up to 8 entries of InterFreqCarrierFreqInfo,
each containing neighbouring carrier frequency and frequency specific cell
re-selection information.
| SIB4 | |
| interFreqCarrierFreqList | List of 1 to 8 InterFreqCarrierFreqInfo |
The
contents of the IE InterFreqCarrierFreqInfo are given in the below table.
| InterFreqCarrierFreqInfo | ||
| dl-CarrierFreq | INTEGER (0 … 3279165) | |
| frequencyBandList | MultiFrequencyBandListNR-SIB | |
| frequencyBandListSUL | MultiFrequencyBandListNR-SIB | |
| nrofSS-BlocksToAverage | INTEGER (2 … maxNrofSS-BlocksToAverage) INTEGER (2 … 16) | |
| absThreshSS-BlocksConsolidation | ThresholdNR | |
| smtc | SSB-MTC | |
| ssbSubcarrierSpacing (kHz) | ENUMERATED {15, 30, 60, 120, 240, spare3, spare2, spare1} | |
| ssb-ToMeasure | SSB-ToMeasure | |
| deriveSSB-IndexFromCell | BOOLEAN | |
| ss-RSSI-Measurement | SS-RSSI-Measurement | |
| q-RxLevMin | Q-RxLevMin | INTEGER (-70 … -22) |
| q-RxLevMinSUL | Q-RxLevMin | INTEGER (-70 … -22) |
| q-QualMin | Q-QualMin | INTEGER (-43 … -12) |
| p-Max | P-Max | INTEGER (-30 … 33) |
| t-ReselectionNR | T-Reselection | INTEGER (0 … 7) |
| t-ReselectionNR-SF | SpeedStateScaleFactors | |
| threshX-HighP | ReselectionThreshold | INTEGER (0 … 31) |
| threshX-LowP | ReselectionThreshold | INTEGER (0 … 31) |
| threshX-HighQ | ReselectionThresholdQ | INTEGER (0 … 31) |
| threshX-LowQ | ReselectionThresholdQ | INTEGER (0 … 31) |
| cellReselectionPriority | CellReselectionPriority | INTEGER (0 … 7) |
| cellReselectionSubPriority | CellReselectionSubPriority | ENUMERATED {0.2, 0.4, 0.6, 0.8} |
| q-OffsetFreq | Q-OffsetRange | |
| interFreqNeighCellList | List of 1 to 16 InterFreqNeighCellInfo | |
| interFreqBlackCellList | InterFreqBlackCellList | |
dl-CarrierFreq indicates
center frequency (ARFCN) of the SS block of the inter-frequency neighbour cell(s),
where the frequency corresponds to a GSCN value.
frequencyBandList indicates
a list of (up to 8) frequency bands for which the NR cell re-selection
parameters apply. Each entry in the list corresponds to IE NR-MultiBandInfo
and 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) |
The
fields nrofSS-BlocksToAverage and absThreshSS-BlocksConsolidation applicable for
inter-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.
smtc defines Measurement
Timing Configuration for inter-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 in this frequency. The contents
of this IE are given below.
| smtc: 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.
ssbSubcarrierSpacing configures
SCS of the SSB. Only the values {15 kHz or 30 kHz} for FR1 and {120 kHz or 240 kHz}
for FR2 are applicable.
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 the timing
of any detected cell on the given frequency to derive the SSB index of all
neighbour cells on that frequency. If this field is set to true, the UE
assumes SFN and frame boundary alignment across cells on the neighbour
frequency.
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.
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 the concerned frequency, 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.
p-Max is
the maximum permitted transmit power (in dBm) applicable for the neighbouring
NR cells on the given carrier frequency.
t-ReselectionNR is
the parameter TreselectionNR in 38.304 and specifies
cell reselection timer value per NR 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 summarises the SpeedStateScaleFactors
contents.
| t-ReselectionNR-SF: SpeedStateScaleFactors | |
| sf-Medium | ENUMERATED {oDot25, oDot5, oDot75, 1Dot0} |
| sf-High | ENUMERATED {oDot25, oDot5, oDot75, 1Dot0} |
threshX-HighP is the parameter
ThreshX, HighP and threshX-HighQ
is the parameter ThreshX, HighQ in 38.304
section 5.2.4.5. These parameters are used in cell reselection procedure to a
cell on a higher priority NR frequency or inter-RAT frequency than
serving frequency.
-
ThreshX,
HighP specifies Srxlev
(RSRP) threshold (in dB) used by the UE when reselecting towards a higher
priority RAT/frequency than the current serving frequency. Each frequency of NR
and E-UTRAN might have a specific threshold.
-
ThreshX,
HighQ specifies Squal
(RSRQ) threshold (in dB) used by the UE when reselecting towards a higher
priority RAT/frequency than the current serving frequency. Each frequency of NR
and E-UTRAN might have a specific threshold.
-
For
ThreshX, HighP, actual value = field value *2 (dB) and if the field is absent, a
default value of infinity shall be applied. For, ThreshX, HighQ, actual value = field value
and if the field is absent, a default value of 0 dB shall be applied.
The
higher priority inter-frequency and inter-RAT cell reselection procedure
is as follows;
-
If
threshServingLowQ is broadcast in SIB2 and a cell of a higher
priority NR or EUTRAN RAT/frequency fulfils Squal > ThreshX, HighQ during a
time interval TreselectionRAT, the UE can perform reselection
to that cell.
-
Otherwise
(threshServingLowQ is not broadcast in SIB2), if a cell of a
higher priority RAT/frequency fulfils Srxlev > ThreshX, HighP during a
time interval TreselectionRAT, the UE can perform reselection
to that cell.
threshX-LowP is the parameter
ThreshX, LowP and threshX-LowQ
is the parameter ThreshX, LowQ in 38.304
section 5.2.4.5. These parameters are used in cell reselection procedure to a
cell on a lower priority NR frequency or inter-RAT frequency than
serving frequency.
-
ThreshX,
LowP specifies Srxlev
(RSRP) threshold (in dB) used by the UE when reselecting towards a lower
priority RAT/frequency than the current serving frequency. Each frequency of NR
and E-UTRAN might have a specific threshold.
-
ThreshX,
LowQ specifies Squal
(RSRQ) threshold (in dB) used by the UE when reselecting towards a lower
priority RAT/frequency than the current serving frequency. Each frequency of NR
and E-UTRAN might have a specific threshold.
-
For
ThreshX, LowP, actual value = field value *2 (dB) and if the field is absent, a
default value of infinity shall be applied. For, ThreshX, LowQ, actual value = field value
and if the field is absent, a default value of 0 dB shall be applied.
The
lower priority inter-frequency and inter-RAT cell reselection procedure is
as follows;
-
If
threshServingLowQ is broadcast in SIB2 and the serving
cell quality is below ThreshServing, LowQ and a cell
of a lower priority NR or EUTRAN RAT/frequency fulfils Squal > ThreshX, LowQ
during a time interval TreselectionRAT, the UE can perform reselection
to that cell.
-
Otherwise
(threshServingLowQ is not broadcast in SIB2), if the serving cell
RSRP is below ThreshServing, LowP and a cell of a lower
priority RAT/frequency fulfils Srxlev > ThreshX, LowP during a time interval TreselectionRAT,
the UE can perform reselection to that cell.
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)
q-OffsetFreq is the parameter
Qoffsetfrequency in 38.304 which specifies frequency specific
offset for equal priority NR frequencies.
This
offset contributes to Qoffset used in the evaluation of cell-ranking
(R-) criteria for the concerned neighboring cell. The higher the value of this
field, the lower the rank of the concerned cell.
Rn = Qmeas,n - Qoffset - Qoffsettemp
| Q-OffsetRange | |
| Q-OffsetRange (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} |
interFreqNeighCellList configures
a list of (up to 16) neighbouring cells’ cell re-selection information using IE
InterFreqNeighCellInfo. These neighbouring cells belong to the frequency
specified by dl-CarrierFreq. The
contents of InterFreqNeighCellInfo are
given below;
| InterFreqNeighCellInfo | |
| physCellId | INTEGER (0 … 1007) |
| q-OffsetCell | Q-OffsetRange |
| q-RxLevMinOffsetCell | INTEGER (1 … 8) |
| q-RxLevMinOffsetCellSUL | INTEGER (1 … 8) |
| q-QualMinOffsetCell | INTEGER (1 … 8) |
| Q-OffsetRange | |
| Q-OffsetRange (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} |
-
physCellId identifies
the physical cell identity (PCI) of the concerned neighbouring cell.
-
q-OffsetCell is
the parameter Qoffsets,n in 38.304 which configures
offset between serving and the neighbour cell (determined by physCellId).
This offset (Qoffset) is used in the evaluation of cell-ranking (R-)
criteria for the concerned neighboring cell. The higher the value of this
field, the lower the rank of the concerned cell.
Rn
= Qmeas,n - Qoffset
- Qoffsettemp
- q-RxLevMinOffsetCell specifies the cell specific Rx level offset in dB to Qrxlevmin.
Qrxlevmin is used to indicate the required ‘minimum received RSRP
level’ (in dBm) in the (NR) cell for cell selection and re-selection. The cell
specific offset q-RxLevMinOffsetCell is added to the corresponding Qrxlevmin
to achieve the required minimum RX level in the concerned cell. Actual value Qrxlevminoffsetcell
= field value * 2
[dB]. q-RxLevMinOffsetCellSUL serves the same purpose as q-RxLevMinOffsetCell
but if the UE supports SUL for neighbouring cell.
-
q-QualMinOffsetCell specifies the cell specific quality level
offset in dB to Qqualmin. Qqualmin is used to indicate the
required ‘minimum received RSRQ level’ (in dB) in the (NR) cell for cell
selection and re-selection. The cell specific offset q-QualMinOffsetCell is
added to the corresponding Qqualmin to achieve the required minimum quality
level in the concerned cell.
interFreqBlackCellList
provides a list of blacklisted inter-frequency
neighbouring cells. The following table summarizes interFreqBlackCellList
fields.
| InterFreqBlackCellList | |
| InterFreqBlackCellList | List of 1 to 16 PCI-Range |
| PCI-Range | |
| start | PhysCellId INTEGER (0 … 1007) |
| range | ENUMERATED {n4, n8, n12, n16, n24, n32, n48, n64, n84, n96, n128, n168, n252, n504, n1008, spare1} |
It
is possible to configure up to 16 PCI ranges to be blacklisted. Each PCI range
is characterized by a start value and the range
of PCIs as shown in the above table. Basically, the PCI range is encoded by
using a start value and by indicating the number of consecutive physical
cell identities (including start) in the range. For example, start = 5
and range = n4 would mean to blacklist PCIs 5, 6, 7, and 8.
Reference: 3GPP TS 38.331, and 38.304
