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SRS

 

SRS stands for Sounding Reference Signal. High level concept of NR SRS is same as in LTE SRS and some of lower level parameter are very similar to LTE SRS lower layer parameter. I would suggest you to go through LTE SRS first if you are new to this concept and then read this page since I would not explain on those basic concepts that are explained in LTE SRS.

 

 

 

 

Parameters defining SRS resources within a slot.

 

SRS resource mean the location of SRS in time and frequency domain in the resource grid. Following is the illustration for SRS Resource allocation based on 38.211-6.4.1.4.

NOTE : For more detailed example of SRS resource element allocation, refer to this page with Matlab 5G Toolbox.

 

 

 

Here goes the detailed algorithm and parameters of SRS RE mapping based on 38.211-6.4.1.4.3

 

    NOTE : from the equation for k(pi), you would notice that the multiple SRS port (i.e, 1001 ~ 1003} is interleaving in frequency domain within the same OFDM symbol.

 

 

Followings are some of the examples showing the key parameters of SRS resource allocation.

 

 

 

Since SRS resources are positioned in a certain interval in frequency domain as shown above, we can interleave (multiplex) multiple SRS along the frequency domain accupying the same OFDM symbols as shown below.

 

In case of comb2 configuration, you can multiplex two SRS signal as shown below.

 

 

 

In case of comb4 configuration, you can multiplex maximum 4 SRS signals as shown below.

 

 

 

 

SRS Bandwidth Configuration

 

Some of important factors defining the location and bandwith of SRS are defined by 38.211-Table 6.4.1.4.3-1. A couple of RRC parameters determines which row of the table is used for a specific SRS Resource set as indicated below.

 

 

 

< 38.211-Table 6.4.1.4.3-1: SRS bandwidth configuration. >

 

 

 

Antenna Switching

 

Following RRC parameter is to configure UE to do SRS antenna switching

        SRS-ResourceSet.usage = antennaSwitching

 

UE performs antenna switching in various way depending on RRC parameter setting in SRS-ResourceSet as described in 38.214 6.2.1.2.  Which of the following case should be applied ? It depends on UE capability on supportedSRS-TxPortSwitch which can be 1T2R or 1T4R or 2T4R or T=R

 

< Case 1 > 1T2R

  • Number of SRS ResourceSet = up to two
  • Each ResourceSet has two SRS Resources transmitting at different symbols
  • Each SRS Resource in a ResourceSet  consists of single SRS port  and the SRS port of the second resource in the set is associated with a different UE antenna port than the SRS port of the first resource in the same set
  • SRS-ResourceSet.resourceType : configured (aperiodic / semi-persistent / periodic)

 

< Case 2 > 2T4R

  • Number of SRS ResourceSet = up to two

  • Each ResourceSet has two SRS Resources transmitting at different symbols

  • Each SRS Resource in a ResourceSet  consists of two SRS ports  and the SRS port pair of the second resource in the set is associated with a different UE antenna port pair than the SRS port of the first resource in the same

  • SRS-ResourceSet.resourceType : configured (aperiodic / semi-persistent / periodic)

 

< Case 3 > 1T4R

  • Number of SRS ResourceSet = zero or one

  • Each ResourceSet has four SRS Resources transmitting at different symbols

  • Each SRS Resource in a ResourceSet  consists of single SRS ports  and the SRS port of each resource is associated with a different UE antenna port

  • SRS-ResourceSet.resourceType : configured (periodic / semi-persistent)

 

< Case 4 > : 1T4R

  • Number of SRS ResourceSet = zero or two
  • Each ResourceSet has four SRS Resources transmitting at different symbols of two different slot
  • SRS port of each SRS resource in given two sets is associated with a different UE antenna port
  • The two sets are each configured with two SRS resources, or one set is configured with one SRS resource and the other set is configured with three SRS resources.
  • SRS-ResourceSet.resourceType : configured (aperiodic)

 

< Case 5 > 1T=1R, or 2T=2R, or 4T=4R

  • Number of SRS ResourceSet = upto two

  • number of SRS ports for each resource is equal to 1, 2, or 4.

 

Does this description make clear sense to you ? I think I have read this part in 38.214 almost 10 times, but still not clear to me. It is extremly difficult to read those short section of the specification without falling asleep :). Then I gave up reading 38.214 and start trying to find TDocs with some picture and tables. With following tables and pictures from TDocs, finally the description on 38.214 start making sense.

 

Followings are the figure from R1-1800116

 

< Illustration of 1T4R antenna switching for aperiodic SRS >

 

 

Examples >

 

Examples in this section are the tables from R1-1800090 or other personal contributers.

 

 

Example 01 > 1T2R

 

< Association between SRS ports and UE antenna ports for 1T2R >

SRS Ports

UE Antenna Ports

SRS port 0 of the first SRS resource

UE antenna port 0

SRS port 0 of the second SRS resource

UE antenna port 1

 

 

 

Example 02 > 2T4R

 

< Association between SRS ports and UE antenna ports for 2T4R >

SRS Ports

UE Antenna Ports

SRS port 0 of the first SRS resource

UE antenna port 0

SRS port 1 of the first SRS resource

UE antenna port 1

SRS port 0 of the second SRS resource

UE antenna port 2

SRS port 1 of the second SRS resource

UE antenna port 3

 

 

 

Example 03 > 1T4R

 

< Association between SRS ports and UE antenna ports for 1T4R >

SRS Ports

UE Antenna Ports

SRS port 0 of the first SRS resource

UE antenna port 0

SRS port 0 of the second SRS resource

UE antenna port 1

SRS port 0 of the third SRS resource

UE antenna port 2

SRS port 0 of the fourth SRS resource

UE antenna port 3

 

 

 

 

Example 04 > 1T4R

 

This example is shared by Sean. He is an ardent reader of sharetechnote and an experts on many subjects related to real deployment. He has been giving me a lot of insight on many topics and this example is one of them.

 

Following diagram shows SRS resource allocation at slot level. This would give you an idea on how SRS can be allocated with TDD UL-DL configuration. Of course, this is not the only possible way, you can come up with various other configuration depending on UE capability, Network capability/requirement.

In this example, you would notice that SRS is allocated in Flexible slot and the overall repetition cycle is 40 ms.

 

 

Following diagram shows the Antenna selection status for each slot where SRS is transmitted.

 

 

 

 

 

RRC Parameters

 

BWP-UplinkDedicated ::= SEQUENCE {

   pucch-Config                   SetupRelease { PUCCH-Config } OPTIONAL, -- Need M

   pusch-Config                   SetupRelease { PUSCH-Config } OPTIONAL, -- Need M

   configuredGrantConfig          SetupRelease { ConfiguredGrantConfig } OPTIONAL, -- Need M

   srs-Config                     SetupRelease { SRS-Config } OPTIONAL, -- Need M

   beamFailureRecoveryConfig      SetupRelease { BeamFailureRecoveryConfig } OPTIONAL,

                           

   ...

}

 

 

SRS-Config ::= SEQUENCE {

   srs-ResourceSetToReleaseList           SEQUENCE (SIZE(1..maxNrofSRS-ResourceSets))

                                                OF SRS-ResourceSetId OPTIONAL, -- Need N

   srs-ResourceSetToAddModList            SEQUENCE (SIZE(1..maxNrofSRS-ResourceSets))

                                                OF SRS-ResourceSet OPTIONAL, -- Need N

   srs-ResourceToReleaseList              SEQUENCE (SIZE(1..maxNrofSRS-Resources))

                                                OF SRS-ResourceId OPTIONAL, -- Need N

   srs-ResourceToAddModList               SEQUENCE (SIZE(1..maxNrofSRS-Resources))

                                                OF SRS-Resource OPTIONAL, -- Need N

   tpc-Accumulation                       ENUMERATED {disabled} OPTIONAL, -- Need S

   ...

}

 

 

SRS-ResourceSet ::= SEQUENCE {

   srs-ResourceSetId               SRS-ResourceSetId,

   srs-ResourceIdList              SEQUENCE (SIZE(1..maxNrofSRS-ResourcesPerSet))

                                        OF SRS-ResourceId OPTIONAL, -- Cond Setup

   resourceType CHOICE {

      aperiodic                  SEQUENCE {

         aperiodicSRS-ResourceTrigger       INTEGER (1..maxNrofSRS-TriggerStates-1),

         csi-RS                             NZP-CSI-RS-ResourceId OPTIONAL, -- Cond NonCodebook

         slotOffset INTEGER (1..32) OPTIONAL, -- Need S

         ...,

         [[

            aperiodicSRS-ResourceTriggerList-v1530  SEQUENCE (SIZE(1..maxNrofSRS-TriggerStates-2))

                                                       OF INTEGER (1..maxNrofSRS-TriggerStates-1)

         ]]

      },

      semi-persistent            SEQUENCE {

         associatedCSI-RS                           NZP-CSI-RS-ResourceId OPTIONAL,

         ...

      },

      periodic                   SEQUENCE {

         associatedCSI-RS                           NZP-CSI-RS-ResourceId OPTIONAL,

      ...

      }

   },

   usage                 ENUMERATED {beamManagement, codebook, nonCodebook, antennaSwitching},

   alpha                 Alpha OPTIONAL, -- Need S

   p0                    INTEGER (-202..24) OPTIONAL, -- Cond Setup

   pathlossReferenceRS   CHOICE {

      ssb-Index                  SSB-Index,

      csi-RS-Index               NZP-CSI-RS-ResourceId

   } OPTIONAL, -- Need M

   srs-PowerControlAdjustmentStates         ENUMERATED { sameAsFci2, separateClosedLoop}

   ...

}

 

 

SRS-Resource ::= SEQUENCE {

   srs-ResourceId                   SRS-ResourceId,

   nrofSRS-Ports                    ENUMERATED {port1, ports2, ports4},

   ptrs-PortIndex                   ENUMERATED {n0, n1 } OPTIONAL, -- Need R

   transmissionComb CHOICE {

      n2      SEQUENCE {

         combOffset-n2 INTEGER (0..1),

         cyclicShift-n2 INTEGER (0..7)

      },

      n4      SEQUENCE {

         combOffset-n4 INTEGER (0..3),

         cyclicShift-n4 INTEGER (0..11)

      }

   },

   resourceMapping      SEQUENCE {

      startPosition                 INTEGER (0..5),

      nrofSymbols                   ENUMERATED {n1, n2, n4},

      repetitionFactor              ENUMERATED {n1, n2, n4}

   },

   freqDomainPosition               INTEGER (0..67),

   freqDomainShift                  INTEGER (0..268),

   freqHopping          SEQUENCE {

      c-SRS INTEGER (0..63),

      b-SRS INTEGER (0..3),

      b-hop INTEGER (0..3)

   },

   groupOrSequenceHopping            ENUMERATED { neither, groupHopping, sequenceHopping },

      resourceType CHOICE {

         aperiodic SEQUENCE {

         ...

      },

      semi-persistent SEQUENCE {

         periodicityAndOffset-sp         SRS-PeriodicityAndOffset,

         ...

      },

      periodic SEQUENCE {

         periodicityAndOffset-p          SRS-PeriodicityAndOffset,

         ...

      }

   },

   sequenceId                            INTEGER (0..1023),

   spatialRelationInfo                   SRS-SpatialRelationInfo OPTIONAL, -- Need R

   ...

}

 

 

SRS-SpatialRelationInfo ::= SEQUENCE {

   servingCellId                ServCellIndex OPTIONAL, -- Need S

   referenceSignal CHOICE {

      ssb-Index                 SSB-Index,

      csi-RS-Index              NZP-CSI-RS-ResourceId,

      srs SEQUENCE {

         resourceId             SRS-ResourceId,

         uplinkBWP              BWP-Id

      }

   }

}

 

SRS-ResourceId ::= INTEGER (0..maxNrofSRS-Resources-1)

 

SRS-PeriodicityAndOffset ::= CHOICE {

   sl1                     NULL,

   sl2                     INTEGER(0..1),

   sl4                     INTEGER(0..3),

   sl5                     INTEGER(0..4),

   sl8                     INTEGER(0..7),

   sl10                    INTEGER(0..9),

   sl16                    INTEGER(0..15),

   sl20                    INTEGER(0..19),

   sl32                    INTEGER(0..31),

   sl40                    INTEGER(0..39),

   sl64                    INTEGER(0..63),

   sl80                    INTEGER(0..79),

   sl160                   INTEGER(0..159),

   sl320                   INTEGER(0..319),

   sl640                   INTEGER(0..639),

   sl1280                  INTEGER(0..1279),

   sl2560                  INTEGER(0..2559)

}

 

 

Followings are for UE Capability Information

 

FeatureSetUplink ::= SEQUENCE {

   featureSetListPerUplinkCC                    SEQUENCE (SIZE (1.. maxNrofServingCells)) OF

                                                      FeatureSetUplinkPerCC-Id,

   scalingFactor                                ENUMERATED {f0p4, f0p75, f0p8} OPTIONAL,

   crossCarrierScheduling-OtherSCS              ENUMERATED {supported} OPTIONAL,

   intraBandFreqSeparationUL                    FreqSeparationClass OPTIONAL,

   searchSpaceSharingCA-UL                      ENUMERATED {supported} OPTIONAL,

   srs-TxSwitch                                 SRS-TxSwitch OPTIONAL,

   supportedSRS-Resources                       SRS-Resources OPTIONAL,

   twoPUCCH-Group                               ENUMERATED {supported} OPTIONAL,

   dynamicSwitchSUL                             ENUMERATED {supported} OPTIONAL,

   simultaneousTxSUL-NonSUL-v1530               ENUMERATED {supported} OPTIONAL,

   pusch-DifferentTB-PerSlot SEQUENCE {

      scs-15kHz                          ENUMERATED {upto2, upto4, upto7} OPTIONAL,

      scs-30kHz                          ENUMERATED {upto2, upto4, upto7} OPTIONAL,

      scs-60kHz                          ENUMERATED {upto2, upto4, upto7} OPTIONAL,

      scs-120kHz                         ENUMERATED {upto2, upto4, upto7} OPTIONAL

   } OPTIONAL,

   csi-ReportFramework CSI-ReportFramework OPTIONAL

}

 

SRS-TxSwitch ::= SEQUENCE {

   supportedSRS-TxPortSwitch             ENUMERATED {t1r2, t1r4, t2r4, t1r4-t2r4, tr-equal},

   txSwitchImpactToRx                    ENUMERATED {true} OPTIONAL

}

 

 

 

Reference

 

[1] 3GPP TSG RAN WG1 Ad Hoc-1801 Meeting : R1-1801085 - Summary of SRS

[2] 3GPP TSG RAN WG1 Ad Hoc Meeting    : R1-1800090 - Summary of remaining details of SRS design

[3] 3GPP TSG RAN WG1 Meeting AH 1801  : R1-1800370 - Clarification on intra-slot hopping for aperiodic SRS

[4] 3GPP TSG RAN WG1 Meeting AH 1801  : R1-1800439 - Issues on SRS

[5] 3GPP TSG RAN WG1 Meeting AH 1801  : R1-1800116 - Remaining details on SRS