NR RRC changes on June 2021

Some interesting changes

R2-2106555 NR-DC Cell Group capability filtering

This CR R2-2106555 introduces cell grouping in UE capability enquiry for NR-DC. In Release 15, NR-DC is limited to FR1 MCG and FR2 SCG. But from Releae 16, this limitation is removed. It introduces ambiguity that which MCG and SCG configuration UE supports. To remove the ambiguity, the network can enquiry UE with CellGrouping:

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UE-CapabilityRequestFilterCommon ::=            SEQUENCE {
    -- Omitted
    [[
    requestedCellGrouping-r16      SEQUENCE (SIZE (1..maxCellGroupings-r16)) OF CellGrouping-r16    OPTIONAL    -- Cond NRDC
    ]]
}

CellGrouping-r16 ::     SEQUENCE {
    mcg-r16                 SEQUENCE (SIZE (1..maxBands)) OF FreqBandIndicatorNR,
    scg-r16                 SEQUENCE (SIZE (1..maxBands)) OF FreqBandIndicatorNR,
    mode-r16                ENUMERATED {sync, async}
}

For example, the network can enquiry UE with the following cell grouping filter:

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{ mcg: [1, 2, 3], scg: [256, 257], mode:  sync },
{ mcg: [1, 2, 3], scg: [256, 257], mode: async },
{ mcg: [1, 2, 3], scg: [ 66,  77], mode:  sync },

UE receiving the filter, it reports supported band combinations with supportedCellGrouping:

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CA-ParametersNRDC-v16xy ::=                     SEQUENCE {
    supportedCellGrouping-r16                         BIT STRING (SIZE (1..maxCellGroupings-r16))        OPTIONAL
}

If the first bit of a bit string is set to 1, a given band combination supports NR-DC with the first cell grouping configuration.

R2-2106712 Correction to ca-ParametersNR-ForDC

I believe the main point of this CR R2-2106712 is to clarify that ca-ParametersNR[-ForDC[-vABCD]] applies separately. I doubt that it is less likely to be misunderstood, but at the same time, I believe it is good to refine the statement.

ca-ParametersNR-forDC (with and without suffix)
If this field is present for a band combination, it reports the UE capabilities when NR-DC is configured with the band combination. If no a version of this field (i.e., with and or without suffix) is present absent for a band combination, the corresponding ca-ParametersNR field versions (with and without suffix) in BandCombination are is applicable to the UE configured with NR-DC for the band combination. If a version of this field (i.e., with or without suffix) is present for a band combination but does not contain any parameters, the UE does not support the corresponding field version when configured with NR-DC for the band combination.

R2-2106754 Clarification on the Timing Reference of PSCell SMTC Configuration

targetCellSMTC-SCG was originally introduced as name smtc in last September, but renamed for more clarity in the next RAN Plenary. It is useful when MCG and SCG have different timing reference. This CR R2-2106754 clarifies how UE applies SMTC in a MCG mobility case.

R2-2105462 Clarification on SCellFrequencies

It was a bug in the specification that ASN.1 structure and description of its interpretation. According to the below structure scellFrequencies can be absent:

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CG-Config-v1590-IEs ::= SEQUENCE {
    scellFrequenciesSN-NR       SEQUENCE (SIZE (1.. maxNrofServingCells-1)) OF ARFCN-ValueNR       OPTIONAL,
    scellFrequenciesSN-EUTRA    SEQUENCE (SIZE (1.. maxNrofServingCells-1)) OF ARFCN-ValueEUTRA    OPTIONAL,
    nonCriticalExtension        CG-Config-v1610-IEs                                                OPTIONAL
}

However, the below statement specifies that the receiving node shall maintain the previous configuration:

As an exception to this general rule, the absence of the below listed fields means that a receiving node maintains the values informed via the previous message.
(Omitted)

  • scellFrequenciesSN-EUTRA;
  • scellFrequenciesSN-NR.

Comparing the structure and the statement, an obvious inconsistency exists that a sending node may omit the IE if no SCell exists. So this CR R2-2105462 removes two IEs from the statement so that the receiving node shall overwrite the previous configuration with the new one.