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What is CORESET?

  • ControlResourceSet

What is Coreset?

A control resource set (CORESET) is defined as a set of REGs under given numerology (i.e., subcarrier spacing) , Particularly, in the frequency domain, a CORESET is a set of contiguous or distributed physical resource blocks (PRBs) configured using a 6-PRB granularity, within which the UE attempts to blindly decode the DCI. There is no restriction on the maximum number of segments for a given CORESET
A DCI with Aggregation Level(AL)
L is mapped to physical resources in a given BWP, where necessary parameters such as frequency and time-domain resources, and scrambling sequence identity for the DMRS for the PDCCH are configured to a UE by means
of control resource set (CORESET)
.

In the time domain, a CORESET spans 1, 2, or 3 contiguous OFDM symbol, and the exact duration is configured to the UE by a higher layer such as SI or UE-specific RRC depending on whether it is common CORESET or UE-specific CORESET. Compared to LTE PDCCH, the configurability of CORESETs enable efficient resource sharing between DL control and shared channels, thereby allowing for efficient Layer 1 signaling overhead management.

  • A UE may be configured with up to three CORESETs (using UE-specific or common higher-layer signaling)on each of up to four BWP on a serving cell.
  • Limiting the maximum number of CORESETs is beneficial for enabling more practical RRC signaling and help enable better UE dimensioning.
  • Note that, the scheduling flexibility may not be impacted by limiting the maximum number of CORESETs since different monitoring occasions can be configured flexibly even with the association to the same CORESET.
  • Here, it is important to note that the concept of PDCCH monitoring periodicity is defined per search space set and is not configured at the CORESET-level.
  • Every configured search space with a certain monitoring periodicity (in terms of slots and starting symbols within the monitored slots) is associated with a CORESET.

The  ControlResourceSet is used to configure a time/frequency control resource set (CORESET) in which to search for downlink control information

  • A CORESET consists of 3 symbols in the time domain and N_RB^CORESET RBs, multiple of 6 RB in the frequency domain, it means in general CORESET are configured in units of six PRBs on a six PRB frequency grid( starting from a reference point referred to as a point A & and one, two, or three consecutive OFDM symbols in the time domain .
  • Coreset might not exist in all the BWP as it is cell level configuration and UE specific
  • Used CORESET can be allocated for PDSCH or user data.

Control Resource Set(CORESET): A CORESET is made up of multiples resource blocks (i.e, multiples of 12 REs) in the frequency domain and ‘1 or 2 or 3’ OFDM symbols in time domain.

 

 

Example of CORESET configurations on BWP :


ControlResourceSet ::=              SEQUENCE {

    controlResourceSetId                ControlResourceSetId,
frequencyDomainResources            BIT STRING (SIZE (45)),
   duration                            INTEGER (1..maxCoReSetDuration),
   cce-REG-MappingType                 CHOICE {
       interleaved                         SEQUENCE {
           reg-BundleSize                      ENUMERATED {n2, n3, n6},
           interleaverSize                     ENUMERATED {n2, n3, n6},
           shiftIndex                          INTEGER(0..maxNrofPhysicalResourceBlocks-1)       OPTIONAL -- Need S
       },
       nonInterleaved                      NULL
   },
   precoderGranularity                 ENUMERATED {sameAsREG-bundle, allContiguousRBs},
   tci-StatesPDCCH-ToAddList           SEQUENCE(SIZE (1..maxNrofTCI-StatesPDCCH)) OF TCI-StateId OPTIONAL, -- Cond NotSIB1-initialBWP
   tci-StatesPDCCH-ToReleaseList       SEQUENCE(SIZE (1..maxNrofTCI-StatesPDCCH)) OF TCI-StateId OPTIONAL, -- Cond NotSIB1-initialBWP
   tci-PresentInDCI                        ENUMERATED {enabled}                                  OPTIONAL, -- Need S
    pdcch-DMRS-ScramblingID                 INTEGER (0..65535)                                    OPTIONAL, -- Need S
...,
    [[
rb-Offset-r16                       INTEGER (0..5)                                            OPTIONAL, -- Need S
tci-PresentForDCI-Format1-2-r16     INTEGER (1..3)                                            OPTIONAL, -- Need S
coresetPoolIndex-r16                INTEGER (0..1)                                            OPTIONAL, -- Need S
controlResourceSetId-v1610          ControlResourceSetId-v1610                                OPTIONAL  -- Need S

    ]]

}

 

Control Resource set

ControlResourcesetID

0 to 11

frequencyDomainResources

45 bits 

 

 

 

cce-regMappingType

Choice

Interleaved

 

nonInterleaved

 

reg-BundleSize

2,3,6

 

interleaveSize

2,3,6

shiftIndex

0 to 274

precoder Granularity

SameAsREG-bundle,allContiguousRBs

 tci-StatesPDCCH

Seqeunce

 tci-PresentInDCI

enable

pdcch-DMRS-ScramblingID

0 to 65535

 

ControlResourceSet field descriptions

cce-REG-MappingType

Mapping of Control Channel Elements (CCE) to Resource Element Groups (REG) (see TS 38.211 [16], clauses 7.3.2.2 and 7.4.1.3.2).

controlResourceSetId

Identifies the instance of the ControlResourceSet IE. Value 0 identifies the common CORESET configured in MIB and in ServingCellConfigCommon (controlResourceSetZero) and is hence not used here in the ControlResourceSet IE. Other values identify CORESETs configured by dedicated signalling or in SIB1. The controlResourceSetId is unique among the BWPs of a serving cell.

If the field controlResourceSetId-v1610 is present, the UE shall ignore the controlResourceSetId field (without suffix).

coresetPoolIndex

The index of the CORESET pool for this CORESET as specified in TS 38.213 [13] (clauses 9 and 10) and TS 38.214 [19] (clauses 5.1 and 6.1). If the field is absent, the UE applies the value 0.

duration

Contiguous time duration of the CORESET in number of symbols (see TS 38.211 [16], clause 7.3.2.2).

frequencyDomainResources

Frequency domain resources for the CORESET. Each bit corresponds a group of 6 RBs, with grouping starting from the first RB group (see TS 38.213 [13], clause 10.1) in the BWP. The first (left-most / most significant) bit corresponds to the first RB group in the BWP, and so on. A bit that is set to 1 indicates that this RB group belongs to the frequency domain resource of this CORESET. Bits corresponding to a group of RBs not fully contained in the bandwidth part within which the CORESET is configured are set to zero (see TS 38.211 [16], clause 7.3.2.2).

interleaverSize

Interleaver-size (see TS 38.211 [16], clause 7.3.2.2).

pdcch-DMRS-ScramblingID

PDCCH DMRS scrambling initialization (see TS 38.211 [16], clause 7.4.1.3.1). When the field is absent the UE applies the value of the physCellId configured for this serving cell.

precoderGranularity

Precoder granularity in frequency domain (see TS 38.211 [16], clauses 7.3.2.2 and 7.4.1.3.2).

rb-Offset

Indicates the RB level offset in units of RB from the first RB of the first 6RB group to the first RB of BWP (see 38.213 [13], clause 10.1). When the field is absent, the UE applies the value 0.

reg-BundleSize

Resource Element Groups (REGs) can be bundled to create REG bundles. This parameter defines the size of such bundles (see TS 38.211 [16], clause 7.3.2.2).

shiftIndex

When the field is absent the UE applies the value of the physCellIdconfigured for this serving cell (see TS 38.211 [16], clause 7.3.2.2).

tci-PresentInDCI

This field indicates if TCI field is present or absent in DCI format 1_1. When the field is absent the UE considers the TCI to be absent/disabled. In case of cross carrier scheduling, the network sets this field to enabled for the ControlResourceSet used for cross carrier scheduling in the scheduling cell (see TS 38.214 [19], clause 5.1.5).

tci-PresentForDCI-Format1-2

Configures the number of bits for “Transmission configuration indicator” in DCI format 1_2. When the field is absent the UE applies the value of 0 bit for the “Transmission configuration indicator” in DCI format 1_2 (see TS 38.212, clause 7.3.1 and TS 38.214, clause 5.1.5).

tci-StatesPDCCH-ToAddList

A subset of the TCI states defined in pdsch-Config included in the BWP-DownlinkDedicated corresponding to the serving cell and to the DL BWP to which the ControlResourceSet belong to. They are used for providing QCL relationships between the DL RS(s) in one RS Set (TCI-State) and the PDCCH DMRS ports (see TS 38.213 [13], clause 6.). The network configures at most maxNrofTCI-StatesPDCCH entries.

 

Conditional Presence

Explanation

NotSIB1-initialBWP

The field is absent in SIB1 and in the PDCCH-ConfigCommon of the initial BWP in ServingCellConfigCommon, if SIB1 is broadcasted. Otherwise, it is optionally present, Need N.

 

ControlResourceSetId

The ControlResourceSetId IE concerns a short identity, used to identify a control resource set within a serving cell. The ControlResourceSetId = 0 identifies the ControlResourceSet#0 configured via PBCH (MIB) and in controlResourceSetZero (ServingCellConfigCommon). The ID space is used across the BWPs of a Serving Cell. The number of CORESETs per BWP is limited to 3 (including common and UE-specific CORESETs) in Release 15.

-- ASN1START

-- TAG-CONTROLRESOURCESETID-START
ControlResourceSetId ::=                INTEGER (0..maxNrofControlResourceSets-1)
ControlResourceSetId-r16 ::=            INTEGER (0..maxNrofControlResourceSets-1-r16)
ControlResourceSetId-v1610 ::=          INTEGER (maxNrofControlResourceSets..maxNrofControlResourceSets-1-r16)


ControlResourceSetZero

The IE ControlResourceSetZero is used to configure CORESET#0 of the initial BWP (see TS 38.213 [13], clause 13).

ControlResourceSetZero ::=                  INTEGER (0..15)




 

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