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5G/NR - CORESET Resource Allocation Unit in NR is similar to LTE case, but a few new units (e.g, REG bundle, CORESET) are introduced in NR. Basic definition of these units and relationship among these units are described in 38.211 - 7.3.2.2 Control-resource set (CORESET) What is CORESET ? CORESET is a set of physical resources(i.e, a specific area on NR Downlink Resource Grid) and a set of parameters that is used to carry PDCCH/DCI. It is equivalent to LTE PDCCH area (the first 1,2,3,4 OFDM symbols in a subframe). But in LTE PDCCH region, the PDCCH always spread across the whole channel bandwidth, but NR CORESET region is localized to a specific region in frequency domain. NR CORESET vs LTE Control Region As mentioned above, CORESET in NR is equivalent to the Control Region in LTE. The main difference between CORESET and LTE Control Region can be illustrated as follows. As you may notice, the control region in LTE spreaded across the whole channel band width(CBW) and NR CORESET is localized within each BWP. Frequency Domain Parameter : Since Control Region in LTE is always spreaded across the whole channel band width, there is no parameters defining the frequency domain region for LTE control region, but in NR we need a parameter defining the frequency domain width for CORESET since the frequency domain width can be set in any value in the multiples of 6 RBs. Time Domain Parameter : Both NR CORESET and LTE Control Region can vary in time domain length. So we need the parameter for time domain length both in LTE in NR. In LTE, the time domain length of control region is defined by the physical channel called PCFICH but in NR the time domain length of CORESET is defined by the RRC parameter (ControlResourceSet.duration). Parameters for CORESET Resource Element : This is same as LTE. It is the smallest unit of the resource grid made up of one subcarrier in frequency domain and one OFDM symbol in time domain. Resource Element Group (REG) : One REG is made up of one resource block (12 resource element in frequency domain) and one OFDM symbol in time domain. REG Bundles : One REG bundle is made up of multiple REGs. The bundle size is specified by the parameter 'L'. The L is determined by the RRC parameter reg-bundle-size. Control Channel Element(CCE) : A CCE is made up multiple REGs. The number REG bundles within a CCE varies. Aggregation Level : Aggregation Level indicates how many CCEs are allocated for a PDCCH. Aggregation Level and the number of allocated CCE is defined in following table. (LTE has similar mapping between Aggregation Level and the Number of CCEs as described here ) < 38.211-Table 7.3.2.1-1: Supported PDCCH aggregation levels. > Control Resource Set(CORESET): A CORESET is made up of multiples resource blocks (i.e, multiples of 12 REs) in frequency domain and '1 or 2 or 3' OFDM symbols in time domain. Defined in 38.211 - 7.3.2.2 Control-resource set (CORESET). CORESET is equivalent to the control region in LTE subframe. In LTE, the frequency domain of the control region is always same as the total system bandwidth, so no parameter is needed to define the frequency domain region for LTE control region. Time domain region can be {1,2,3} which is determined by PCFICH. However, in NR both frequency region and time domain region can be defined by RRC signaling message. | | | Number of RBs in frequency domain in a CORESET. Determined by RRC Parameter CORESET-freq-dom | | Number of symbols in time domain in a CORESET. Determined by RRC Parameter CORESET-time-dur. This can be 1 or 2 or 3, but 3 is possible only when DL-DMRS-typeA-pos = 3 | | Number of REGs in a CORESET | | REG Bundle Size, set by CORESET-REG-bundle-size |
The RRC parameters defining the CORESET are as follows (based on 38.331 v15.3.0) : ControlResourceSet ::= SEQUENCE { controlResourceSetId ControlResourceSetId, frequencyDomainResources BIT STRING (SIZE (45)), duration INTEGER (1..maxCoReSetDuration), //maxCoReSetDuration = 3 cce-REG-MappingType CHOICE { interleaved SEQUENCE { reg-BundleSize ENUMERATED {n2, n3, n6}, interleaverSize ENUMERATED {n2, n3, n6}, shiftIndex INTEGER(0..maxNrofPhysicalResourceBlocks-1) }, nonInterleaved NULL },, precoderGranularity ENUMERATED {sameAsREG-bundle, allContiguousRBs}, tci-StatesPDCCH SEQUENCE(SIZE (1..maxNrofTCI-StatesPDCCH)) OF TCI-StateId tci-PresentInDCI ENUMERATED {enabled} OPTIONAL pdcch-DMRS-ScramblingID BIT STRING (SIZE (16)) OPTIONAL } controlResourceSetId : this corresponds to L1 parameter 'CORESET-ID' · Value 0 identifies the common CORESET configured in MIB and in ServingCellConfigCommon · Values 1..maxNrofControlResourceSets-1 identify CORESETs configured by dedicated signalling · The controlResourceSetId is unique among the BWPs of a ServingCell. frequencyDomainResources: Frequency domain resources (this should be within BWP assigned to UE). This corresponds to L1 parameter L1 parameter 'CORESET-freq-dom'. · Each bit corresponds a group of 6 RBs, with grouping starting from PRB 0, which is fully contained in the bandwidth part within which the CORESET is configured. · The most significant bit corresponds to the group of lowest frequency which is fully contained in the bandwidth part within which the CORESET is configured, each next subsequent lower significance bit corresponds to the next lowest frequency group fully contained within the bandwidth part within which the CORESET is configured, if any. Bits corresponding to a group not fully contained within the bandwidth part within which the CORESET is configured are set to zero. duration : Contiguouse time duration of the CORESET in number of symbols cce-reg-MappingType : Mapping method of Control Channel Elements (CCE) to Resource Element Groups (REG). reg-BundleSize : The number of REGs within a REG Bundle. Corresponds to L1 parameter 'CORESET-REG-bundle-size' interleaveSize : Corresponds to L1 parameter 'CORESET-interleaver-size' shiftIndex : Corresponds to CORESET-shift-index precoderGranularity: Precoder granularity in frequency domain. It corresponds to L1 parameter 'CORESET-precoder-granuality. tci-StatesPDCCH : Reference to a configured TCI State providing QCL configuration/indication for PDCCH tci-PresentInDCI : Corresponds to L1 parameter 'CORESET-precoder-granuality' pdcch-DMRS-ScramblingID : PDCCH DMRS scrambling initalization Example > Here is an example showing to procedure to map from RE to CCE. For simplicity, I assume that interleaving is not applied. How many RBs do you need for CORESET ? The answer to this question is dependent on following factors as follows : · What is the maximum number of DCIs/PDCCHs do you want to allow to send in a slot ? ==> This is determined by the none zero value (i.e, the value other than n0) in SearchSpace.nrofCandidates as shown below. · How large search space you want to allocate for each DCI/PDCCH ? ==> this is determined by the aggregationLevel with the none zero numbers in SearchSpace parameter. · How many RBs you want to allocate for each REG/CCE ? ==> This is determined by reg-BundleSize (CCE Size) in ControlResourceSet parameter · How many number of OFDM symbols you want allocate for CORESET ? ==> This is determined by 'duration' in ControlResourceSet parameter SearchSpace ::= SEQUENCE { ... nrofCandidates SEQUENCE { aggregationLevel1 ENUMERATED {n0, n1, n2, n3, n4, n5, n6, n8}, aggregationLevel2 ENUMERATED {n0, n1, n2, n3, n4, n5, n6, n8}, aggregationLevel4 ENUMERATED {n0, n1, n2, n3, n4, n5, n6, n8}, aggregationLevel8 ENUMERATED {n0, n1, n2, n3, n4, n5, n6, n8}, aggregationLevel16 ENUMERATED {n0, n1, n2, n3, n4, n5, n6, n8} } OPTIONAL, -- Cond Setup ... } ControlResourceSet ::= SEQUENCE { ... duration INTEGER (1..maxCoReSetDuration), //maxCoReSetDuration = 3 cce-REG-MappingType CHOICE { interleaved SEQUENCE { reg-BundleSize ENUMERATED {n2, n3, n6}, ... }, ... },, ... } Example > Number of DCI/PDCCH = 1 Size of a SearchSpace Candidates (AggregationLevel) = 16 Number of SearchSpace Candidates = 1 Number of OFDM Symbols for CORESET = 1 Number of PRBs to allocate for each REG/CCE = 6 Then minimum number of PRB would be 16 CCE(=16 x 6=96 PRB) within one OFDM symbol and a possible RRC Setting would be as follows. SearchSpace ::= SEQUENCE { ... nrofCandidates SEQUENCE { aggregationLevel1 n0, aggregationLevel2 n0, aggregationLevel4 n0, aggregationLevel8 n0, aggregationLevel16 n1 } OPTIONAL, -- Cond Setup ... } ControlResourceSet ::= SEQUENCE { ... frequencyDomainResources 11111111111111110000.... duration 1, cce-REG-MappingType CHOICE { interleaved SEQUENCE { reg-BundleSize n6, ... }, ... },, ... } Reference [1] 3GPP TSG RAN WG1Meeting NR-AH#3 : R1-1716542 Configuration of CORESET and search space design [2] 3GPP TSG RAN WG1 Meeting NR#3 : R1-1716564 - Discussion on the CORESET configuration [3] 3GPP TSG RAN WG1 Meeting NR#3 : R1-1716477 Frequency-first REG bundling for multi-symbol CORESETs [4] 3GPP TSG RAN WG1 Meeting NR#3 : R1-1716475 Remaining issues related to CORESET configuration [5] 3GPP TSG RAN WG1 Meeting NR #3 : R1-1716044 Common CORESET design for RMSI scheduling [6] 3GPP TSG RAN WG1 Meeting NR#3 : R1-1715842 RMSI delivery and CORESET configuration
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发表于 2021-7-10 17:28:58
