从联通NSA现网ota log看，其UE-MRDC-Capability包含两个字段rf-ParameterMRDC和 featureSetCombinations。
FeatureSetCombination定义
在6.3.3节中定义了 FeatureSetCombination。
featureSetCombinations含义
A list of FeatureSetCombination:s for MR-DC. The FeatureSetDownlink:s and FeatureSetUplink:s referred to from these FeatureSetCombination:s are defined in the featureSets list in UE-NR-Capability.
38.331的5.6.1.4 的note 2 如下：
NOTE 2: In EN-DC, the gNB needs the capabilities for RAT types nr and eutra-nr and it uses the featureSets in the UE-NR-Capabilitie s together with the featureSetCombinations in the UE-MRDC-Capabilities to determine the NR UE capabilities for the supported MRDC band combinations. Similarly, the eNB needs the capabilities for RAT types eutra and eutra-nr and it uses the featureSetsEUTRA-r15 in the UE-EUTRA-Capabilities together with the featureSetCombinations in the UE-MRDC-Capabilities to determine the E-UTRA UE capabilities for the supported MRDC band combinations. Hence, the IDs used in the featureSets must match the IDs referred to in featureSetCombinations across all three containers. The requirement on consistency implies that there are no undefined feature sets and feature set combinations.
UE-MRDC-Capabilities 中的featureSetCombinations 最小元素（downlinkSetEUTRA, uplinkSetEUTRA, downlinkSetNR, uplinkSetNR）都是ID，指向UE-EUTRA-Capabilities 中的featureSetsEUTRA-r15 以及UE-NR-Capabilities中的featureSets IE。供网络了解终端支持的MRDC band combinations。
FeatureSetDownlinkId
以其中一个最小元素downlinkSetNR的类型FeatureSetDownlinkId为例。
The IE FeatureSetDownlinkId identifies a downlink feature set. The FeatureSetDownlinkId of a FeatureSetDownlink is the index position of the FeatureSetDownlink in the featureSetsDownlink list in the FeatureSets IE. The first element in that list is referred to by FeatureSetDownlinkId = 1. The FeatureSetDownlinkId=0 is not used by an actual FeatureSetDownlink but means that the UE does not support a carrier in this band of a band combination.
FeatureSetDownlinkId指向FeatureSets IE中的featureSetsDownlink列表 中的对应FeatureSetDownlink。FeatureSetDownlinkId = 1指featureSetsDownlink 中的第一个FeatureSetDownlink。为0时指这个band不支持band combination。
FeatureSets
那么接下来要看FeatureSets 。
The IE FeatureSets is used to provide pools of downlink and uplink features sets. A FeatureSetCombination refers to the IDs of the feature set(s) that the UE supports in that FeatureSetCombination. The BandCombination entries in the BandCombinationList then indicate the ID of the FeatureSetCombination that the UE supports for that band combination.
FeatureSets 提供上行和下行 features sets的集合。UE-MRDC-Capability 中的FeatureSetCombination 指向FeatureSets ，UE-MRDC-Capability中的rf-ParameterMRDC 的BandCombination 子项指向FeatureSetCombination 。
The entries in the lists in this IE are identified by their index position. For example, the FeatureSetUplinkPerCC-Id = 4 identifies the 4th element in the featureSetsUplinkPerCC list.
NOTE: When feature sets (per CC) IEs require extension in future versions of the specification, new versions of the FeatureSetDownlink, FeatureSetUplink, FeatureSets, FeatureSetDownlinkPerCC and/or FeatureSetUplinkPerCC will be created and instantiated in corresponding new lists in the FeatureSets IE. For example, if new capability bits are to be added to the FeatureSetDownlink, they will instead be defined in a new FeatureSetDownlink-rxy which will be instantiated in a new featureSetDownlinkList-rxy list. If a UE indicates in a FeatureSetCombination that it supports the FeatureSetDownlink with ID #5, it implies that it supports both the features in FeatureSetDownlink #5 and FeatureSetDownlink-rxy #5 (if present). The number of entries in the new list(s) shall be the same as in the original list(s).
如果一个FeatureSetCombination 中支持FeatureSetDownlinkID #5，那么是指终端支持featureSetDownlinkList #5和featureSetDownlinkList-rxy#5中的所有feature。
FeatureSets结构定义
