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This article is a connected mode measurement study note. In fact, I was not very clear about NR measurement at the beginning, so I sorted out the relevant content. Therefore, this article is mainly used by me to clarify some concepts, which is more important in my personal opinion. Aggregation, not so deep, but it feels just right, the relevant specs mainly involve 38.300/38.331/38.321/38.133 and so on. There are four main types of NR connected measurement: intra-freq NR measurement, inter-freq NR measurement, inter RAT eutran measurement and Inter RAT utran measurement, which are also mainly related to the mobility of NR.
In the HO process, R15 MobilityFromNRCommand only supports handover from NR to LTE, but R16 supports rat utra-fdd, so compared with the R15 version, there are more utran measurements. The following will follow the measurement configuration structure, Measurement Model, definition of Intra-frequency and inter-frequency neighbor (cell) measurements, measurement gap and SMTC in order to see the relevant content.
Configuration structure of measurement (38.300/38.331)
Measurement-related parameters are mainly measurement objects, reporting configurations, and measurement identity. For each measurement type, one or more measObjects can be defined, and the definition of the measobject includes information such as the carrier freq that the UE wants to monitor. For each measObject, one or more reporting configurations can be defined, which will include reporting criteria; such as eventTriggered or periodic, etc. Finally, the association between measobject and reporting configurations is completed by meas Id; by using multiple meas Ids, multiple reporting configurations can be associated with one measobject; one reporting configuration can also be associated with multiple measobjects.
The meas id will be included in the report MR; each RAT will consider measurerment quantities separately; NG-RAN will use the corresponding measurement command to request UE start, modify or stop measurement; the measurement may involve HO, and the specific HO can be in the same RAT Execution within /CN may also involve a change of RAT or a change of CN.
Measurement reports have the following characteristics:
(1) MR includes the measurement identity of the relevant measurement configured to trigger the report;
(2) MR contains cell and beam measurement quantities configured on the network side;
(3) The number of reported non-serving cells can be limited through network configuration;
(4) When configuring measobject, some white cells or black cells may be configured. At this time, the cells belonging to the blacklist configured by the network are not used for event evaluation and reporting. On the contrary, when the whitelist is configured on the network, only the cells belonging to the whitelist are used. Event evaluation and reporting (such as the black (white) CellsToAddModList configuration in the above figure);
(5) The beam measurement that needs to be included in the measurement report is configured by the network. The configuration requirement may include only the beam identifier or the measurement result and the beam identifier, or beam reporting is not required.
When configuring measurement information on the network side, it will configure measObjectId to specify the object (NR/EUTRA/UTRA-FDD), reportConfigId to specify the measurement event, and finally bind measObjectId and reportConfigId through measId. After receiving the measurement configuration, the UE will perform measurement according to the situation. After meeting the reporting requirements, report through measurementReport, which will include measId and the measurement results of specific cells; in practical problems, it is inevitable to check the MR type, such as Event type, and the MTK log tool will directly display the event type when the UE reports MR. It is more convenient not to check the RRCReconfig message to confirm step by step; when Qualcomm’s log tool determines the specific content of the measurement report reported by the UE, it needs to check the RRCReconfig step by step according to the provisions of the agreement. After confirming the reportConfigId, it is confirmed to report the MR type. For example, when the MR in the above figure contains measId 1, it means that Event A3 is reported. The structure of MR in 38.331 is as follows.
In practice, you may often pay attention to the measurement of eventTriggered. The event is relatively easy to understand. The UE reports different Events, and the network side sends different configurations to the UE according to the Events reported by the UE. For example, Event B is usually used for inter rat HO, Event A3/4 may cause the UE to switch to a neighboring cell, etc. The following is a list of various events. For details, please refer to chapter 5.5.4 of 38.331, which is relatively easy to understand.
Event A1 (Serving becomes better than threshold)
Event A2 (Serving becomes worse than threshold)
Event A3 (Neighbour becomes offset better than SpCell)
Event A4 (Neighbour becomes better than threshold)
Event A5 (SpCell becomes worse than threshold1 and neighbour becomes better than threshold2)
Event A6 (Neighbour becomes offset better than SCell)
Event B1 (Inter RAT neighbour becomes better than threshold)
Event B2 (PCell becomes worse than threshold1 and inter RAT neighbour becomes better than threshold2)
Event I1 (Interference becomes higher than threshold)
Event C1 (The NR sidelink channel busy ratio is above a threshold)
Event C2 (The NR sidelink channel busy ratio is below a threshold)
s-MeasureConfig
When configuring measurement, s-MeasureConfig is more critical, which corresponds to the threshold of whether UE should measure non-serving cells, which can be configured as ssb-RSRP or csi-RSRP; the reportConfig applicable to reportType association is periodic, eventTriggered or In the case of condTriggerConfig; if s-MeasureConfig is not configured, the measurement of non-serving cells will be started directly; if s-MeasureConfig is configured, the UE will compare the resident NR SpCell RSRP with the configured threshold, and only the ssb below the configuration -RSRP or csi-RSRP, the UE needs to measure the non-serving cells, as shown in the figure below.
The MR-related configuration is basically as above, mainly the RRC layer configuration parameters, how to perform the specific measurement, a picture in 38.300 can well illustrate this process, as follows.
Measurement Model(38.300/38.331)
In RRC connected mode, the UE will measure multiple beams (at least one) of a cell, and the measurement results (power values) will be averaged to obtain the quality of the cell. At this time, the network side will configure a subset of detected beams for the UE for measurement . The measurement needs to be filtered, and this process is mainly carried out at two different levels: first obtain the beam quality at the physical layer, and then obtain the final cell quality from the measurement of multiple beams at the RRC layer. For the serving cell and the non-serving cell, the cell quality is derived from the beam measurement in the same way. If there is a corresponding configuration on the network side (for example, via maxNrofRS-IndexesToReport X), the UE also includes the measurement results of the X best beams in the measurement report.
Some requirements to be met by the measurement are described in 38.133, this is skipped, the above is the flow chart related to the measurement in 38.300, starting from the left:
K beams correspond to the parameters configured by gNB for RRC mobility, and are measured by the UE on the SSB or CSI-RS resources detected by L1. Point A corresponds to the measurement result of the specific beam sample at the physical layer; The input measurement is carried out with Layer 1 filtering. This part is a private algorithm of the manufacturer, which is not specified in the spec. The L1 filtering process is mainly a process of averaging the beams measurement; A1 corresponds to the measurement result reported to L3 after L1 filtering.
Let’s look at the branch Beam Consolidation/Selection first. Here, the UE will combine the beam-specific measurements to derive the cell quality. This part is specified in the 38.331 measurement part. It mainly depends on the configuration of the RRC layer parameters. At the same time, the cell quality corresponding to point B The report period of A1 is equal to a measurement period of A1; after that, the measurement of point B needs to go through Layer 3 filtering, and the behavior of L3 filtering is also standardized. The configuration of L3 filtering is provided by RRC signaling, which corresponds to chapter 5.5.3.2 of 38.331. The filtering report period is equal to a measurement period at B, and point C corresponds to the measured value after L3 filtering processing. This L3 filtering process will not bring delay to the available samples between B and C. At this time, the report rate at point C is the same as that at point B, and finally the UE can use the measured value for the Measuremrnt report criteria process.
After the Evaluation of reporting criteria (configured parameters such as MR event, corresponding to 38.331 5.5.4), the UE needs to check whether it needs to send MR at point D, and the evaluation can be based on multiple measurement processes at reference point C. For example, at this time, Event A3 Neighbor becomes offset better than SpCell is performed. At this time, C may correspond to the measurement result of the Spcell, C1 may correspond to the measurement result of the neighbor cell, and then the UE evaluates the new measurement result. Once assessed at point D, the actual MR needs to be sent.
If the meas result related to SSB is to be included in MR, it needs to go down the branch, and it also needs to go through L3 Beam filtering to perform filtering on the measurement value provided by point A1 (ie specific beam meas valye). L3 beam filtering is stipulated in the agreement. Specifically, in 38.331 5.5.3.3.a, the report period at E is equal to a measurement period at A1. Similarly, the report rate at E is the same as the report rate at A1, and L3 beam filtering does not Any delay will be introduced in the sample between E and F; then Beam Selection for beam reporting is performed, and X measurements are selected from the measurements provided by point E. X is determined by the configured measurement-related RRC parameters, and the measurement report about the beam measurement information is sent last.
The figure below shows a periodic MR related configuration under a real network. maxNrofRS-IndexesToReport =8 in reportConfig corresponds to the maximum number of RS indexes that can be included in MR. The ssb-ToMeasure corresponding to Freq 504990 in measObject shows that SSB 0 to 7 needs to be measured. measId 5 binds measobjectId 1 and reportConfigId 5, and finally MR reports measId 5, where 504990/957 in MR contains the measurement results of 8 SSB indexes.
Intra-frequency 和inter-frequency neighbour (cell) measurements(38.300/38.331)
Intra-freq and inter-freq measurements can be divided into the following categories:
1 SSB based intra-freq measurement: the center freq of the serving cell SSB is the same as the center freq of the adjacent cell SSB and the SCS of the two SSBs are also the same.
2 SSB based inter-freq measurement: The center freq of the serving cell SSB is different from the center freq of the adjacent cell SSB or the SCS of the two is different. During configuration, one measurement object corresponds to one SSB, and the UE regards different SSBs as different cells.
3 CSI-RS based intra-freq measurement:
(1) The SCS of the adjacent cell CSI-RS resource is the same as the CSI-RS SCS of the serving cell;
(2) When SCS=60KHZ, the CP type of the CSI-RS resources of the neighboring cell is the same as the CP type of the CSI-RS resources of the serving cell;
(3) The center freq of the CSI-RS resources of the neighboring cell is the same as the center freq of the CSI-RS resources of the serving cell.
Satisfying the above conditions at the same time is the CSI-RS based intra-freq measurement.
4 The CSI-RS based inter-freq measurement corresponds to the measurement that is not the CSI-RS based intra-freq measurement.
Whether the gap is needed for measurement depends on the capabilities of the UE.
1 For SSB based inter-freq measurement, R16 supports the UE to report the measurement gap requirement info. If the UE reports the measurement gap requirement info, then the network side may configure the gap; usually the UE is in the case of a single radio frequency, so the measurement gap needs to be configured. Inter freq or inter rat measurement.
2 For SSB based intra-freq measurement, if the UE reports the measurement gap requirement info, then the network side may configure the gap; but in the following cases, the measurement gap must be configured: In addition to the initial BWP, the BWP configured for the UE does not include The initial DL BWP is associated with the frequency domain resource of the SSB.
The reporting of the above measurement gap info involves IE nr-NeedForGap-Reporting-r16. If the UE supports it, the network side can request the UE to report the meas gap info through RRCReconfiguration or RRC resume, and then the UE is in RRCReconfigurationComplete or RRC resume Complete. The relevant configuration structure is as follows picture.
The types of measurement are defined above, that is, the distinction is made according to whether the SSB/CSI-RS center freq is the same and whether the SCS is the same. Specifically, whether the measurement gap is needed for the measurement of the adjacent cell needs to be determined according to the actual situation, mainly depending on whether the bwp of the UE's current serving cell active includes the frequency domain range of the SSB of the adjacent cell to be measured, that is, whether rf return is required. If the current active BWP includes the bandwidth to be measured in neighboring cells, rf return and measurement gap are not required; otherwise, measurement gap is required.
Combined with the above description, taking the SSB scene as an example, the blue square represents the currently activated BWP of the serving cell, and the yellow and green blocks correspond to the SSB of the serving cell and neighbor cell respectively.
In the above figure, A corresponds to the Measuremenr occasion bandwidth to be measured including neighboring cells in the currently activated BWP, and it is a neighboring cell with the same frequency, and no measurement gap is required; B corresponds to the Measuremenr occasion bandwidth to be measured not including neighboring cells in the currently activated BWP, and is the same frequency adjacent cell. Frequency adjacent cell, measurement gap is required; D corresponds to the Measuremenr occasion bandwidth to be measured that includes neighboring cells in the currently activated BWP, and is a different frequency adjacent cell, no measurement gap is required; C corresponds to the Measuremenr to be measured that does not include neighboring cells in the currently activated BWP Occasion bandwidth, and it is a different-frequency adjacent cell, requires a measurement gap.
Regarding the question of whether the measurement gap is required for the same frequency measurement, the following is the description in a certain book, and it will be very clear after reading it together.
When the center frequency point and subcarrier spacing of the target cell SSB are the same as those of the current serving cell and are within the working bandwidth of the UE, the network does not need to configure the measurement gap.
When the central frequency point of the SSB of the target search cell is not within the working bandwidth of the UE, the network needs to configure a measurement gap for identification and measurement of co-frequency adjacent cells.
In measurement scenarios where gaps are not required, the UE shall be able to perform such measurements without measuring gaps. In scenarios where gaps are required, it is assumed that the UE cannot perform such measurements without measuring gaps. The network side may require the UE to measure NR and E-UTRA carriers when RRC idle or inactive through the dedicated measurement configuration configured in SI or RRCRelease. If the UE is configured to perform measurements on NR and/or E-UTRA carriers in RRC_IDLE or RRC_INACTIVE, it may provide an indication of the availability of the corresponding measurement results to the gNB in the RRCSetupComplete message. Afterwards, the network side may find the UE to complete the security activation and report the corresponding measurement information.
The RRCRelease message configures the structure of the dedicated measurement:
An indication of the availability of the corresponding measurement results is provided to the gNB in the RRCSetupComplete message:
If the gNB requires the UE to perform NR E-UTRA measurement in RRC_inactive, the gNB will request the UE to provide relevant measurement results in RRCResume, and then the UE will include the corresponding results in RRCResumeComplete. In addition, the UE can also provide the indication of the availability of the measurement result in RRCResumeComplete, and then the gNB will then request the UE to provide the corresponding measurement result.
RRCResume requires the UE to provide relevant measurement results:
RRCResumeComplete contains the corresponding result or an indication of the availability of the measurement result:
measurement gap(38.321/38.331/38.133)
The meas gap is mentioned above, here is a centralized arrangement of the relevant content of the meas gap. Considering manufacturing cost and form factor, a UE often has only one RF module, which is responsible for performing all measurements as well as transmitting and receiving data.
The UE can easily measure intra-freq neighbor cell signals while sending and receiving serving cell data. When measuring inter freq and inter-rat cells, the UE must suspend communication with the serving cell (including Tx and Rx), and needs to adjust the RF module to the freq to be measured (freq parameters come from the configured Measobject), and in a period Connection between resume and serving cell after time. The time when the UE suspends communication with the serving cell to measure the inter freq neighbor or inter-rat neighbor is called the Measurement Gap. The following is the behavior of the UE during the meas gap in 38.321.
During the measurement gap, the UE cannot perform HARQ/SR/CSI transmission; nor can it perform SRS report; except for Msg3 or MSGA, it cannot transmit UL-SCH.
If ra-ResponseWindow/ra-ContentionResolutionTimer/msgB-ResponseWindow is running, it still needs to monitor PDCCH as required in order to process RAR/msgB reception and Contention Resolution process; in other cases, UE does not need to monitor PDCCH, but also stops DL -SCH reception.
Through the parameter configuration in 38.331, you can see that the 5G NR MGL is not fixed, but configurable. Why is measuring Gap configurable? Considering that the fixed meas gap may cause the Tput of the serving cell to decrease. Thus NR can support setting SMTC window and window duration to match SSB transmission and corresponding MGL. If the SMTC window duration is set to 2ms, and the MGL is set to 6ms, the remaining 4ms here will not be used for data transmission and reception in the serving cell, which will result in a decrease in DL/UL Tput. To reduce this unnecessary Tput drop, NR introduces a configurable MGL whose value can be 6ms, 5.5ms, 4ms, 3.5ms, 3ms or 1.5ms. The above figure is the parameter configuration structure and parameter definition of MeasGapConfig related to meas gap in 38.331. The relevant IE in the above figure is explained as follows:
gapFR1: The measurement gap configuration for FR1 applications. In the (NG)EN-DC scenario, it needs to be configured through LTE RRC signaling. In NE-DC, gapFR1 can only be configured through NR RRC; in NR-DC, gapFR1 can only be configured in measConfig in MCG. gapFR and gapUE cannot be configured at the same time. For the configuration of FR1 measuremrnt gap, refer to 38.133 Table 9.1.2-2 and Table 9.1.2-3. These two pictures are too large to be cut.
gapFR2: The measurement gap configuration for FR2 applications. In (NG)EN-DC or NE-DC scenarios, gapFR2 can only be configured through NR RRC (not LTE RRC); in NR-DC, gapFR2 can only be configured in measConfig in MCG. gapFR and gapUE cannot be configured at the same time. For the configuration of FR2 measuremrnt gap, refer to 38.133 Table 9.1.2-2 and Table 9.1.2-3.
gapUE: common measurement gap configuration for FR1 and FR2, so it cannot be configured with gapFR1 or gapFR2 at the same time. (NG)EN-DC, gapUE needs to be configured through LTE RRC signaling (cannot be configured through NR RRC); in NE-DC, gapUE can only be configured through NR RRC (LTE RRC cannot be configured per UE gap); in NR- DC, gapUE can only be configured in measConfig in MCG. Configuration reference 38.133 Table 9.1.2-2 and Table 9.1.2-3.
gapOffset: gapOffset is the gap offset offset of the MGRP gap pattern indicated in mgrp. The value range is [0,mgrp-1].
mgl: corresponds to the length of the measurement gap, the unit is ms; ms1dot5 corresponds to 1.5ms, ms3 corresponds to 3ms, if mgl-r16 is configured, mgl is ignored.
mgrp: corresponding to measurement gap repetition period.
mgta: The unit of the corresponding measurement gap TA value is ms; ms0 represents 0 ms, ms0dot25 represents 0.25 ms, and ms0dot5 represents 0.5 ms; in the FR2 scenario, it can only be configured as 0 ms and 0.25 ms.
refFR2ServCellAsyncCA: represents FR2 serving cell ID, whose SFN and subframe are used for FR2 gap calculation of FR2 carriers asynchronous CA gap pattern.
refServCellIndicator: indicates the serving cell whose SFN and subframe are used for gap calculation of the gap pattern. The value pCell corresponds to the PCell, pSCell corresponds to the PSCell, and mcg-FR2 corresponds to the serving cell on the FR2 frequency point in the MCG.
The following is the description in 38.331 5.5.2.9 that the UE confirms the specific gap according to the parameters.
After the UE receives the new gapFR1 setup configuration, it must first release the current setup configuration, and then start the new gap configuration; after receiving the gapFR1 release configuration, it releases the corresponding configuration.
The UE sets the FR1 measurement gap configuration indicated by measGapConfig according to the received gapOffset. The SFN and subframe where the first subframe opened by each gap should meet the following conditions:
SFN mod T=FLOOR(gapOffset/10);subframe=gapOffset mod 10，T=MGRP/10。
If mgta is configured, enable the gap after the gap subframe mgta ms determined by the above formula in advance.
In the above figure, gapOffset =10, mgl=4ms, mgrp=20ms, then the gap start frame should satisfy SFN mod 2=FLOOR(1)=1 subframe=10 mod 10=0, that is, from SFN that satisfies SFN mod 2=1 1, 3, 5, 7....) subframe 0 starts the gap, the duration corresponds to mgl 4ms, and the repetition period is mgrp 20ms, which corresponds to SFN 1, 3, 5, 7..... as shown below
Regarding the specific usage of mgta, the following pictures in 38.133 can basically explain clearly.
Sync scenes指all serving cells in synchronous EN-DC, NR standalone operation (with single carrier, NR CA and synchronous NR-DC configuration) and synchronous NE-DC, and for serving cells in MCG in NR standalone operation (with asynchronous NR-DC configuration)。
Async scenes指all serving cells in asynchronous EN-DC and asynchronous NE-DC, and for serving cells in SCG in NR standalone operation (with asynchronous NR-DC configuration)。
The following are the regulations of gapFR2 and gapUE, which are the same as those of gapFR1, so I won’t read them one by one.
For the configuration of gapFR2 sync CA/gapUE/gapFR1, the UE in the NE-DC/NR-DC scenario should determine the gap according to the SFN and subframe of the serving cell indicated by refServCellIndicator in gapFR2/gapUE/gapFR1; otherwise, use the serving cell SFN and subframe calculate the gap; for gapFR2 async CA, the UE in the NE-DC/NR-DC scenario shall determine the gap according to the SFN and subframe of the serving cell indicated by refServCellIndicator and refFR2ServCellAsyncCA in gapFR2, otherwise use the one specified by fefFR2ServCellAsyncCA serving cell to determine the gap.
SMTC(38,331)
SSB Measurement Timing Configuration (smtc) is mainly used for measurement. NR measurement needs to align the SSB of serving cell and neighbor cell. stmc is used for this, and smtc will be configured for both the same frequency and different frequency. smtc defines the duration and period that can be used to limit UE measurements on specific resources. During the smtc period, the UE will perform radio link monitoring/radio resource management measurements at the configured SSB. There are several different smtc IEs in NR, which are used in different scenarios. Let’s look at the differences in detail below.
smtc1
smtc1 is usually configured in measobject, both intra-freq and inter-freq will have smtc1, UE should set the measurement timing configuration of the first SSB according to the periodicityAndOffset parameter in the received smtc1 configuration (provide the Periodicity and Offset values for the following conditions) ( SMTC).
The first subframe and SFN of each SMTC occasion of NR Pcell meet the following conditions: SFN mod T=(FLOOR(Offset/10)), T=CEIL(Periodicity/10); if Periodicity is greater than sf5, then subframe=Offset mod 10 , otherwise subframe=Offset or (Offset+5).
Here we see that periodicity is 20 subframe; offset is 0, subframe= 0 mod 10 =0; SFN mod 2=0; duration is 2 subframe.
smtc2
smtc2: The second measurement timing configuration of the corresponding synchronization signal in MeasObjectNR, and the pci-List is the related PCI to be measured. The periodicity is indicated by periodicity in smtc2, and the timing offset is equal to the offset indicated in periodicityAndOffset modulo periodicity. The periodicity in smtc2 can only be set to a value strictly smaller than the period indicated by periodicityAndOffset in smtc1 (for example, if the periodicityAndOffset in smtc1 is sf10, then the periodicity can only be set to sf5, if the periodicityAndOffset in smtc1 indicates sf5, smtc2 cannot be configured) , it can be seen that stmc2 should be configured in combination with stmc1, and has a shorter cycle than smtc1, and is used for co-frequency measurement (as shown in the Cond intraFreqConnected behind smtc2 in the above figure, smtc2 may only be available in co-frequency measurement scenarios). For cells indicated in the same MeasObjectNR->smtc2 ->pci-List, the UE shall set an additional SSB measurement timing configuration (SMTC) according to the periodicity parameter in the received smtc2 configuration, and use Offset (from smtc1 periodicityAndOffset) and smtc1 configuration The duration parameter in . The first subframe of each SMTC occasion must also meet the conditions of SFN and subframe of NR SpCell above.
smtc2-LP
smtc2-LP: smtc2-LP is used for long-period configuration of co-frequency neighbor cell measurement timing; timing offset and duration use the offset and duration of stmc in intraFreqCellReselectionInfo.
The periodicity in smtc2-LP can only be set to a value strictly greater than the periodicity in smtc in intraFreqCellReselectionInfo (for example, if smtc indicates sf20, Long Periodicity can only be set to sf40, sf80 or sf160, if smtc indicates sf160, then smtc2-LP cannot be configured). The pci-List, if present, includes PCIs of co-frequency neighbors with long periodicity. If smtc2-LP does not exist, the UE assumes that there is no intra-frequency neighbor cell with long periodicity. This parameter can be configured in SIB2 and SIB4. The above is the description of the configuration in SIB2. When configuring in SIB4, just replace the above description with InterFreqCarrierFreqInfo.
For cells of the same frequency (same frequency cell reselection) or different frequency (different frequency cell reselection) indicated by pci-List in smtc2-LP, UE should set additional SSB measurement timing configuration (SMTC), according to smtc2-LP configuration The periodic parameter received in , and use the offset (obtained from periodicityAndOffset) and duration parameter in the smtc configuration of the freq. The first subframe of each SMTC opportunity satisfies the above-mentioned conditions of SFN and subframe of NR SpCell or serving cell (for cell reselection).
smtc3list
smtc3list: It is suitable for IAB-MT scenarios. I am not familiar with this, so I don’t want to say much. You can check 38.331 for specific usage.
For ssbFrequency, SSB-based RRM measurement and CSI-RS-based RRM measurement (except SFTD measurement), the UE does not consider the SSB in the subframe outside the SMTC opportunity.