5G/NR - CSI RS Home : www.sharetechnote.com |
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As in LTE CSI, NR CSI (Channel Status Information) is a mechanism that a UE measure various radio channel quality and report the result to Network(gNB). There are pretty complicated factors involved in CSI operation, but this page would focus on CSI signal generation and Resource Mapping. Other CSI operation procedure will be explained in other page.
For most of LTE case, we don't need any special signal for CSI since we used Cell Specific Reference Signal. However, from LTE TM9 we stared using a special reference signal for CSI. So if you have some understandings on LTE CSI Reference signal in TM9 or higher, it would be relatively easier for you to understand this page even if NR CSI RS(Reference Signal) is constructed more complicated way comparing to LTE CSI RS.
Sequence Generation and Resource Mapping
As you may notice in the following equation, NR CSI is based on Pseudo Random Sequence. Then this sequence is multipied by sepcially designed weighting sequence in both time domain and frequency domain and than scaled by power scaling factor. And then this sequence is mapped to a set of specific resource elements in Resource Grid. All of these process can be summarized as follows and so many factors are involved in this procedure. If you are not the physical layer developer who need to implement this part, you don't need to go through this to the full details, but it will be beneficial to pay attention to various parameters (especially RRC parameters) involved in this process.
Tables for Resource Element Mapping
< 38.211-Table 7.4.1.5.3-1: CSI-RS locations within a slot. >
The reference location of CSI-RS in time domain is determined by RRC layer as below.
The reference location of CSI-RS in frequency domain (k1,k2,k3) is determined by RRC layer as below f(i) is the bit number of the i th bit in the bitmap(CSI-RS-ResourceMapping.frequencyDomainAllocation) set to one, repeated across every 1/density.
Ports, Density, cdm-Type are specified by following RRC parameters
Tables for CDM Sequence Generation
CDM table is used for CSI-RS signal generation as shown below.
Each element values of CDM tables are specified in 38.211 as shown below.
< 38.211 - Table 7.4.1.5.3-2: The sequences wf(k) f and wt(l) for cdm-Type equal to 'no CDM'. >
< 38.211 - Table 7.4.1.5.3-3: The sequences wf(k) f and wt(l) for cdm-Type equal to 'FD-CDM2'. >
< 38.211 - Table 7.4.1.5.3-4: The sequences wf(k) f and wt(l) for cdm-Type equal to 'CDM4'. >
< 38.211 - Table 7.4.1.5.3-5: The sequences wf(k) f and wt(l) for cdm-Type equal to 'CDM8'. >
RRC Parameter : NZP-CSI-RS-Resource
Almost all of the contents in this page is about the IE(Information Element) resourceMapping. The IE resourceMapping is a part of the NZP-CSI-RS-Resource as shown below.
NZP-CSI-RS-Resource ::= SEQUENCE { nzp-CSI-RS-ResourceId NZP-CSI-RS-ResourceId, resourceMapping CSI-RS-ResourceMapping, powerControlOffset INTEGER (-8..15), powerControlOffsetSS ENUMERATED{db-3, db0, db3, db6} OPTIONAL, -- Need R scramblingID ScramblingId, periodicityAndOffset CSI-ResourcePeriodicityAndOffset OPTIONAL,- qcl-InfoPeriodicCSI-RS TCI-StateId OPTIONAL, -- Cond Periodic ... }
resourceMapping : Refer to the section CSI-RS-ResourceMapping for the details.
powerControlOffset : Power offset of PDSCH RE to NZP CSI-RS RE. Value in dB
powerControlOffsetSS : Power offset of NZP CSI-RS RE to SSS RE. Value in dB
qcl-InfoPeriodicCSI-RS : For a target periodic CSI-RS, contains a reference to one TCI-State in TCI-States for providing the QCL source and QCL type. For periodic CSI-RS, the source can be SSB or another periodic-CSI-RS. Refers to the TCI-State which has this value for tci-StateId and is defined in tci-StatesToAddModList in the PDSCH-Config included in the BWPDownlink corresponding to the serving cell and to the DL BWP to which the resource belongs to. In short, this indicates the tci-StateId to which this CSI-RS is QCLed.
How UE figure out which CSI-RS the network is using ? (CSI-RS-ResourceMapping)
When Network allocate the CSI-RS, it selects a specific row from 38.211-Table 7.4.1.5.3-1 and fill in a set of resource elements with the specific signal. This part would be straightforward.. the challenging part is how UE can figure out which CSI-RS the gNB(Network) is using. The answer is that Network informs UE of all the details of CSI-RS via RRC message. Let's look into what kind of RRC parameters get involved in this process.
How to determine CSI-RS port and cdm (in Row number of 38.211 Table 7.4.1.5.3-1) ? : This is specified by nrofPorts and cdm-Type in CSI-RS-ResourceMapping as shown below.
CSI-RS-ResourceMapping ::= SEQUENCE { frequencyDomainAllocation CHOICE { row1 BIT STRING (SIZE (4)), row2 BIT STRING (SIZE (12)), row4 BIT STRING (SIZE (3)), other BIT STRING (SIZE (6)) }, nrofPorts ENUMERATED {p1,p2,p4,p8,p12,p16,p24,p32}, firstOFDMSymbolInTimeDomain INTEGER (0..13), firstOFDMSymbolInTimeDomain2 INTEGER (2..12) OPTIONAL, -- Need R cdm-Type ENUMERATED {noCDM, fd-CDM2, cdm4-FD2-TD2, cdm8-FD2-TD4}, density CHOICE { dot5 ENUMERATED {evenPRBs, oddPRBs}, one NULL, three NULL, spare NULL }, freqBand CSI-FrequencyOccupation, ... }
How to determine REs(Resource Elements) for the selected CSI-RS ? : This is configured by (k_bar, l_bar) column and frequencyDomainAllocation and firstOFDMSymbolInTimeDomain of CSI-RS-ResourceMapping as shown below.
CSI-RS-ResourceMapping ::= SEQUENCE { frequencyDomainAllocation CHOICE { row1 BIT STRING (SIZE (4)), row2 BIT STRING (SIZE (12)), row4 BIT STRING (SIZE (3)), other BIT STRING (SIZE (6)) }, nrofPorts ENUMERATED {p1,p2,p4,p8,p12,p16,p24,p32}, firstOFDMSymbolInTimeDomain INTEGER (0..13), firstOFDMSymbolInTimeDomain2 INTEGER (2..12) OPTIONAL, -- Need R cdm-Type ENUMERATED {noCDM, fd-CDM2, cdm4-FD2-TD2, cdm8-FD2-TD4}, density CHOICE { dot5 ENUMERATED {evenPRBs, oddPRBs}, one NULL, three NULL, spare NULL }, freqBand CSI-FrequencyOccupation, ... }
CSI-FrequencyOccupation ::= SEQUENCE { startingRB INTEGER (0..maxNrofPhysicalResourceBlocks-1), nrofRBs INTEGER (24..maxNrofPhysicalResourceBlocksPlus1), ... }
startingRB : PRB where this CSI resource starts in relation to common resource block #0 (CRB#0) on the common resource block grid. Only multiples of 4 are allowed (0, 4, ...)
nrofRBs : Number of PRBs across which this CSI resource spans. Only multiples of 4 are allowed. The smallest configurable number is the minimum of 24 and the width of the associated BWP. If the configured value is larger than the width of the corresponding BWP, the UE shall assume that the actual CSI-RS bandwidth is equal to the width of the BWP.
Combining thse two, we come come up with an example as shown below.
How to figure out what kind of (Logical) Antenna Configuration Network is using ? : This is another complicated story and is explained in a separate page here.
CSI RS Resource Mapping Examples
This section is to show various examples of configuring following RRC Parameters.
CSI-RS-ResourceMapping ::= SEQUENCE { frequencyDomainAllocation CHOICE { row1 BIT STRING (SIZE (4)), row2 BIT STRING (SIZE (12)), row4 BIT STRING (SIZE (3)), other BIT STRING (SIZE (6)) }, nrofPorts ENUMERATED {p1,p2,p4,p8,p12,p16,p24,p32}, firstOFDMSymbolInTimeDomain INTEGER (0..13), firstOFDMSymbolInTimeDomain2 INTEGER (2..12) OPTIONAL, -- Need R cdm-Type ENUMERATED {noCDM, fd-CDM2, cdm4-FD2-TD2, cdm8-FD2-TD4}, density CHOICE { dot5 ENUMERATED {evenPRBs, oddPRBs}, one NULL, three NULL, spare NULL }, freqBand CSI-FrequencyOccupation, ... }
Followings are some of the examples showing the location (Resource Elements) within a PRB(physical resource block). Since these examples are showing the location only within one RB, n N^RB_sc term is removed in the equation determining k value.
Given the following RRC parameters, density = three nrofPorts = p1 cdm-Type = noCDM frequencyDomainAllocation.row1 = 0001 firstOFDMSymbolinTimeDomain = 4
According to 38.211-Table 7.4.1.5.3-1,
k prime = {0} ==> k prime[0] = 0 l prime = {0} ==> l prime[0] = 0 According to the given, RRC parameters k0 = 0 (based on frequencyDomainAllocation.row1 = 0001) l0 = 4(based on firstOFDMSymbolinTimeDomain = 4) Based on all these information and , we get 38.211-Table 7.4.1.5.3-1, (k,l) = (k0+kprim[0],l0+lprim[0]) ,(k0+4+kprim[0],l0+lprim[0]) ,(k0+8+kprim[0],l0+lprim[0]) = (0+0,4+0) ,(0+4+0,4+0) ,(0+8+0,4+0) = (0,4) ,(4,4) ,(8,4)
Given the following RRC parameters, density = three nrofPorts = p1 cdm-Type = noCDM frequencyDomainAllocation.row1 = 0100 firstOFDMSymbolinTimeDomain = 4
According to 38.211-Table 7.4.1.5.3-1,
k prime = {0} ==> k prime[0] = 0 l prime = {0} ==> l prime[0] = 0 According to the given, RRC parameters k0 = 2 (based on frequencyDomainAllocation.row1 = 0100) l0 = 4(based on firstOFDMSymbolinTimeDomain = 4) Based on all these information and , we get 38.211-Table 7.4.1.5.3-1, (k,l) = (k0+kprim[0],l0+lprim[0]) ,(k0+4+kprim[0],l0+lprim[0]) ,(k0+8+kprim[0],l0+lprim[0]) = (2+0,4+0) ,(2+4+0,4+0) ,(2+8+0,4+0) = (2,4) ,(6,4) ,(10,4)
Given the following RRC parameters, (this example is based on TRS case in 38.508-1 Table 4.6.3-45: CSI-RS-ResourceMapping) density = three nrofPorts = p1 cdm-Type = noCDM frequencyDomainAllocation.row1 = 1000 // From density,nrofPorts we can guess that this is for row1. firstOFDMSymbolinTimeDomain = 4
According to 38.211-Table 7.4.1.5.3-1,
k prime = {0} ==> k prime[0] = 0 l prime = {0} ==> l prime[0] = 0 According to the given, RRC parameters k0 = 3 (based on frequencyDomainAllocation.row1 = 1000) l0 = 4(based on firstOFDMSymbolinTimeDomain = 4) Based on all these information and , we get 38.211-Table 7.4.1.5.3-1, (k,l) = (k0+kprim[0],l0+lprim[0]) ,(k0+4+kprim[0],l0+lprim[0]) ,(k0+8+kprim[0],l0+lprim[0]) = (3+0,4+0) ,(3+4+0,4+0) ,(3+8+0,4+0) = (3,4) ,(7,4) ,(11,4)
Given the following RRC parameters, density = one nrofPorts = p1 cdm-Type = noCDM frequencyDomainAllocation.row2 = 010000000000 firstOFDMSymbolinTimeDomain = 13
According to 38.211-Table 7.4.1.5.3-1, k prime = {0} ==> k prime[0] = 0 l prime = {0} ==> l prime[0] = 0 According to the given, RRC parameters k0 = 10 (based on frequencyDomainAllocation.row2 = 010000000000) l0 = 13(based on firstOFDMSymbolinTimeDomain = 13) Based on all these information and , we get 38.211-Table 7.4.1.5.3-1, (k,l) = (k0+kprim[0],l0+lprim[0]) = (10+0,13+0) = (10,13)
Given the following RRC parameters, density = one nrofPorts = p2 cdm-Type = FD-CDM2 frequencyDomainAllocation.other = 001000 firstOFDMSymbolinTimeDomain = 13 Assume that row = 3 (you need additional information to determine the row number other than 1,2,4. In this example, it is given)
According to 38.211-Table 7.4.1.5.3-1,
k prime = {0,1} ==> k prime[0] = 0, k prime[1] = 1 l prime = {0} ==> l prime[0] = 0 According to the given, RRC parameters k0 = 2 x 3(bit position) = 6 (based on frequencyDomainAllocation.other = 001000) l0 = 13(based on firstOFDMSymbolinTimeDomain = 13) Based on all these information and , we get 38.211-Table 7.4.1.5.3-1, (k,l) = (k0+kprim[0],l0+lprim[0]),(k0+kprim[1],l0+lprim[0]) = (6+0,13+0),(6+1,13+0) = (6,13),(7,13)
Given the following RRC parameters, (this example is based on FR1 case in 38.508-1 Table 4.6.3-45: CSI-RS-ResourceMapping) density = one nrofPorts = p8 cdm-Type = fd-CDM2 frequencyDomainAllocation.other = 011110 //From density,nrofPorts,cdm-Tye it is assumed that this is for row6. firstOFDMSymbolinTimeDomain = 3
According to 38.211-Table 7.4.1.5.3-1, k prime = {0,1} ==> k prime[0] = 0, k prime[1] = 1 l prime = {0} ==> l prime[0] = 0 According to the given, RRC parameters k0 = 2 (based on frequencyDomainAllocation.other = 011110) k1 = 4 (based on frequencyDomainAllocation.other = 011110) k2 = 6 (based on frequencyDomainAllocation.other = 011110) k3 = 8 (based on frequencyDomainAllocation.other = 011110) l0 = 3(based on firstOFDMSymbolinTimeDomain = 3) Based on all these information and , we get 38.211-Table 7.4.1.5.3-1, (k,l) = (k0+kprim[0],l0+lprim[0]) ,(k1+kprim[0],l0+lprim[0]) ,(k2+kprim[0],l0+lprim[0]), (k3+kprim[0],l0+lprim[0]) (k0+kprim[1],l0+lprim[0]) ,(k1+kprim[1],l0+lprim[0]) ,(k2+kprim[1],l0+lprim[0]), (k3+kprim[1],l0+lprim[0]) = (2+0,3+0) ,(4+0,3+0) ,(6+0,3+0),(8+0,3+0),(2+1,3+0) ,(4+1,3+0) ,(6+1,3+0),(8+1,3+0) = (2,3) ,(4,3) ,(6,3) ,(8,3), (3,3) ,(5,3) ,(7,3) ,(9,3)
NOTE : The above resource mapping is showing the CSI-RS for all antenna ports (8 ports in this case) superimposed in one resource grid. In real transmission, these resources are devided among the 8 CSI-RS antenna ports. How they are splitted among each CSI-RS antenna port is specified in 38.211 section 7.4.1.5.3. Applying the logic in the spec to this example, the antenna port distribution become as follows. Since this example is using FD-CDM2, it is assumed that 's' is determined by the index value of the following table and 'L' becomes 2. N is given in this example (38.211-Table 7.4.1.5.3-1) is 8.
< 38.211 - Table 7.4.1.5.3-3: The sequences wf(k) f and wt(l) for cdm-Type equal to 'FD-CDM2'. >
Based on this information, j and s can be calculated as follows. s = 0,1 (index of Table 7.4.1.5.3-3) j = 0,1,...,N/L-1 = 0,1,...,(8/2-1) = 0,1,2,3 Now we can calculate the antenna port as follows. p = 3000 + s + j L , where s = {0,1}, j = {0,1,2,3} = 3000 + {0,1} + {0,1,2,3} 2 = {3000, 3002, 3004, 3006, 3001, 3003, 3005, 3007} NOTE : I posted Matlab simulation for this case showing the resource mapping for each antenna port on this note.
Given the following RRC parameters, (this example is based on FR1 case in 38.508-1 Table 4.6.3-45: CSI-RS-ResourceMapping) density = one nrofPorts = p8 cdm-Type = fd-CDM2 frequencyDomainAllocation.other = 000110 //From density,nrofPorts,cdm-Tye it is assumed that this is for row7. firstOFDMSymbolinTimeDomain = 3
According to 38.211-Table 7.4.1.5.3-1, k prime = {0,1} ==> k prime[0] = 0, k prime[1] = 1 l prime = {0} ==> l prime[0] = 0 According to the given, RRC parameters k0 = 2 (based on frequencyDomainAllocation.other = 000110) k1 = 4 (based on frequencyDomainAllocation.other = 000110) l0 = 3(based on firstOFDMSymbolinTimeDomain = 3) Based on all these information and , we get 38.211-Table 7.4.1.5.3-1, (k,l) = (k0+kprim[0],l0+lprim[0]) ,(k1+kprim[0],l0+lprim[0]) , (k0+kprim[0],l0+lprim[0]+1), (k1+kprim[0],l0+lprim[0]+1) (k0+kprim[1],l0+lprim[0]) ,(k1+kprim[1],l0+lprim[0]) , (k0+kprim[1],l0+lprim[0]+1), (k1+kprim[1],l0+lprim[0]+1) = (2+0,3+0) ,(4+0,3+0) ,(2+0,3+0+1) ,(4+0,3+0+1),(2+1,3+0) ,(4+1,3+0) ,(2+1,3+0+1) ,(4+1,3+0+1) = (2,3) ,(4,3) ,(2,4),(4,4),(3,3),(5,3),(3,4),(5,4)
NOTE : The above resource mapping is showing the CSI-RS for all antenna ports (8 ports in this case) superimposed in one resource grid. In real transmission, these resources are devided among the 8 CSI-RS antenna ports. How they are splitted among each CSI-RS antenna port is specified in 38.211 section 7.4.1.5.3. Applying the logic in the spec to this example, the antenna port distribution become as follows. Since this example is using FD-CDM2, it is assumed that 's' is determined by the index value of the following table and 'L' becomes 2. N is given in this example (38.211-Table 7.4.1.5.3-1) is 8.
< 38.211 - Table 7.4.1.5.3-3: The sequences wf(k) f and wt(l) for cdm-Type equal to 'FD-CDM2'. >
Based on this information, j and s can be calculated as follows. s = 0,1 (index of Table 7.4.1.5.3-3) j = 0,1,...,N/L-1 = 0,1,...,(8/2-1) = 0,1,2,3 Now we can calculate the antenna port as follows. p = 3000 + s + j L , where s = {0,1}, j = {0,1,2,3} = 3000 + {0,1} + {0,1,2,3} 2 = {3000, 3002, 3004, 3006, 3001, 3003, 3005, 3007} NOTE : I posted Matlab simulation for this case showing the resource mapping for each antenna port on this note.
Given the following RRC parameters, (this example is based on FR1 case in 38.508-1 Table 4.6.3-45: CSI-RS-ResourceMapping) density = one nrofPorts = p8 cdm-Type = CDM4(FD2,TD2) frequencyDomainAllocation.other = 000110 //From density,nrofPorts,cdm-Tye it is assumed that this is for row8. firstOFDMSymbolinTimeDomain = 3
According to 38.211-Table 7.4.1.5.3-1, k prime = {0,1} ==> k prime[0] = 0, k prime[1] = 1 l prime = {0,1} ==> l prime[0] = 0, l prime[1] = 1 According to the given, RRC parameters k0 = 2 (based on frequencyDomainAllocation.other = 000110) k1 = 4 (based on frequencyDomainAllocation.other = 000110) l0 = 3(based on firstOFDMSymbolinTimeDomain = 3) Based on all these information and , we get 38.211-Table 7.4.1.5.3-1, (k,l) = (k0+kprim[0],l0+lprim[0]) ,(k1+kprim[0],l0+lprim[0]), (k0+kprim[1],l0+lprim[0]) ,(k1+kprim[1],l0+lprim[0]), (k0+kprim[0],l0+lprim[1]) ,(k1+kprim[0],l0+lprim[1]), (k0+kprim[1],l0+lprim[1]) ,(k1+kprim[1],l0+lprim[1]), = (2+0,3+0) ,(4+0,3+0) ,(2+1,3+0) ,(4+1,3+0),(2+0,3+1) ,(4+0,3+1) ,(2+1,3+1) ,(4+1,3+1) = (2,3) ,(4,3) ,(3,3),(5,3),(2,4),(4,4),(3,4),(5,4)
NOTE : wft0 = wf(0) wt(0), wft1 = wf(1) wt(1)
NOTE : The above resource mapping is showing the CSI-RS for all antenna ports (8 ports in this case) superimposed in one resource grid. In real transmission, these resources are devided among the 8 CSI-RS antenna ports. How they are splitted among each CSI-RS antenna port is specified in 38.211 section 7.4.1.5.3. Applying the logic in the spec to this example, the antenna port distribution become as follows. Since this example is using FD-CDM2, it is assumed that 's' is determined by the index value of the following table and 'L' becomes 4. N is given in this example (38.211-Table 7.4.1.5.3-1) is 8.
< 38.211 - Table 7.4.1.5.3-4: The sequences wf(k) f and wt(l) for cdm-Type equal to 'CDM4'. >
Based on this information, j and s can be calculated as follows. s = 0,1,2,3 (index of Table 7.4.1.5.3-4) j = 0,1,...,N/L-1 = 0,1,...,(8/4-1) = 0,1 Now we can calculate the antenna port as follows. p = 3000 + s + j L , where s = {0,1}, j = {0,1,2,3} = 3000 + {0,1,2,3} + {0,1} 4 = {3000, 3004, 3004, 3006, 3001, 3003, 3005, 3007} NOTE : I posted Matlab simulation for this case showing the resource mapping for each antenna port on this note.
CSI Transmission Timing in slot is determined by RRC parameter CSI-ResourcePeriodicityAndOffset based on following equation.
Resource for Interference Measurement (CSI-IM)
CSI IM resource is a set of specific resource elements reserved for Interference Measurement. This resources are configurable by RRC message. The frequency and time domain location is defined in 38.214 - 5.2.2.4 as illustrated below.
CSI-IM-Resource ::= SEQUENCE { csi-IM-ResourceId CSI-IM-ResourceId, csi-IM-ResourceElementPattern CHOICE { pattern0 SEQUENCE { subcarrierLocation-p0 ENUMERATED { s0, s2, s4, s6, s8, s10 }, symbolLocation-p0 INTEGER (0..12) }, pattern1 SEQUENCE { subcarrierLocation-p1 ENUMERATED { s0, s4, s8 }, symbolLocation-p1 INTEGER (0..13) } } OPTIONAL, -- Need M freqBand CSI-FrequencyOccupation OPTIONAL, periodicityAndOffset CSI-ResourcePeriodicityAndOffset OPTIONAL, PeriodicOrSemiPersistent ... }
pattern 0 / pattern1 : illustrated above.
CSI-FrequencyOccupation ::= SEQUENCE { startingRB INTEGER (0..maxNrofPhysicalResourceBlocks-1), nrofRBs INTEGER (24..maxNrofPhysicalResourceBlocksPlus1), ... }
startingRB : PRB where this CSI resource starts in relation to common resource block #0 (CRB#0) on the common resource block grid. Only multiples of 4 are allowed (0, 4, ...)
nrofRBs : Number of PRBs across which this CSI resource spans. Only multiples of 4 are allowed. The smallest configurable number is the minimum of 24 and the width of the associated BWP. If the configured value is larger than the width of the corresponding BWP, the UE shall assume that the actual CSI-RS bandwidth is equal to the width of the BWP.
Tracking Reference Signal (TRS)
NZP-CSI-RS-ResourceSet ::= SEQUENCE { nzp-CSI-ResourceSetId NZP-CSI-RS-ResourceSetId, nzp-CSI-RS-Resources SEQUENCE (SIZE (1..maxNrofNZP-CSI-RS-ResourcesPerSet)) OF NZP-CSI-RS-ResourceId, repetition ENUMERATED { on, off } OPTIONAL, aperiodicTriggeringOffset INTEGER(0..4) OPTIONAL, trs-Info ENUMERATED {true} OPTIONAL, ... }
38.331 defines trs-Info as follows.
trs-Info : Indicates that the antenna port for all NZP-CSI-RS resources in the CSI-RS resource set is same. If the field is absent or released the UE applies the value false
38.214-5.2.2.3.1 provides additional information as follows :
trs-Info in NZP-CSI-RS-ResourceSet is associated with a CSI-RS resource set and for which the UE can assume that the antenna port with the same port index of the configured NZP CSI-RS resources in the NZP-CSI-RSResourceSet is the same as described in Subclause 5.1.6.1.1 and can be configured when reporting setting is not configured or when the higher layer parameter reportQuantity associated with all the reporting settings linked with the CSI-RS resource set is set to 'none'.
38.214-5.1.6.1.1 specifies the condition about how multiple csi-rs is grouped into a trs as stated below.
For a NZP-CSI-RS-ResourceSet configured with the higher layer parameter trs-Info, the UE shall assume the antenna port with the same port index of the configured NZP CSI-RS resources in the NZP-CSI-RS-ResourceSet is the same. For frequency range 1(FR1), the UE may be configured with one or more NZP CSI-RS set(s), where a NZP-CSI-RS-ResourceSet consists of four periodic NZP CSI-RS resources in two consecutive slots with two periodic NZP CSI-RS resources in each slot. For frequency range 2(FR2) the UE may be configured with one or more NZP CSI-RS set(s), where a NZP-CSI-RSResourceSet consists of two periodic CSI-RS resources in one slot or with a NZP-CSI-RS-ResourceSet of four periodic NZP CSI-RS resources in two consecutive slots with two periodic NZP CSI-RS resources in each slot.
NOTE : trs-info setting affects the applicable QCL type which is described in this note.
The hierarchy to configure CSI-RS is pretty complicated. Overall hierachy (procedure) to configure CSI-RS can be described as follows. i) Configure CRS-RS resource element within single RB via CSI-RS-ResourceMapping ii) Configure the RB locations(Start RB and N_RB) in frequency domain via CSI-RS-ResourceMapping.freqBand iii) Configure the periodicity and offset of CSI-RS in time domain via ZP-CSI-RS-Resource and/or NZP-CSI-RS-Resource iv) Apply the whole setting(i, ii, iii) via PDSCH-Config or/and CSI-MeasConfig
PDSCH-Config ::= SEQUENCE { dataScramblingIdentityPDSCH INTEGER (0..1007) OPTIONAL, dmrs-DownlinkForPDSCH-MappingTypeA SetupRelease { DMRS-DownlinkConfig } OPTIONAL, dmrs-DownlinkForPDSCH-MappingTypeB SetupRelease { DMRS-DownlinkConfig } OPTIONAL, tci-StatesToAddModList SEQUENCE (SIZE(1..maxNrofTCI-States)) OF TCI-State OPTIONAL, -- Need N tci-StatesToReleaseList SEQUENCE (SIZE(1..maxNrofTCI-States)) OF TCI-StateId OPTIONAL, -- Need N vrb-ToPRB-Interleaver ENUMERATED {n2, n4}, resourceAllocation ENUMERATED { resourceAllocationType0, resourceAllocationType1, dynamicSwitch}, pdsch-AllocationList SEQUENCE (SIZE(1..maxNrofDL-Allocations)) OF PDSCH-TimeDomainResourceAllocation , pdsch-AggregationFactor ENUMERATED { n2, n4, n8 } OPTIONAL, rateMatchPatternToAddModList SEQUENCE (SIZE (1..maxNrofRateMatchPatterns)) OF RateMatchPattern OPTIONAL, -- Need N rateMatchPatternToReleaseList SEQUENCE (SIZE (1..maxNrofRateMatchPatterns)) OF RateMatchPatternId OPTIONAL, -- Need N rateMatchPatternGroup1 SEQUENCE (SIZE (1..maxNrofRateMatchPatterns)) OF RateMatchPatternId OPTIONAL, -- Need R rateMatchPatternGroup2 SEQUENCE (SIZE (1..maxNrofRateMatchPatterns)) OF RateMatchPatternId OPTIONAL, -- Need R rbg-Size ENUMERATED {config1, config2}, mcs-Table ENUMERATED {qam64, qam256}, maxNrofCodeWordsScheduledByDCI ENUMERATED {n1, n2} OPTIONAL, -- Need R prb-BundlingType CHOICE { static SEQUENCE { bundleSize ENUMERATED { n4, wideband } OPTIONAL }, dynamic SEQUENCE { bundleSizeSet1 ENUMERATED { n4, wideband, n2-wideband, n4-wideband } OPTIONAL, -- Need S bundleSizeSet2 ENUMERATED { n4, wideband } OPTIONAL -- Need S } }, zp-CSI-RS-ResourceToAddModList SEQUENCE (SIZE (1..maxNrofZP-CSI-RS-Resources)) OF ZP-CSI-RS-Resource OPTIONAL, -- Need N zp-CSI-RS-ResourceToReleaseList SEQUENCE (SIZE (1..maxNrofZP-CSI-RS-Resources)) OF ZP-CSI-RS-ResourceId OPTIONAL, -- Need M aperiodic-ZP-CSI-RS-ResourceSetsToAddModList SEQUENCE (SIZE (1..maxNrofZP-CSI-RS-Sets)) OF ZP-CSI-RS-ResourceSet OPTIONAL, -- Need N aperiodic-ZP-CSI-RS-ResourceSetsToReleaseList SEQUENCE (SIZE (1..maxNrofZP-CSI-RS-Sets)) OF ZP-CSI-RS-ResourceSetId OPTIONAL, -- Need N sp-ZP-CSI-RS-ResourceSetsToAddModList SEQUENCE (SIZE (1..maxNrofZP-CSI-RS-Sets)) OF ZP-CSI-RS-ResourceSet OPTIONAL, -- Need N sp-ZP-CSI-RS-ResourceSetsToReleaseList SEQUENCE (SIZE (1..maxNrofZP-CSI-RS-Sets)) OF ZP-CSI-RS-ResourceSetId OPTIONAL, -- Need N
... }
CSI-MeasConfig ::= SEQUENCE { nzp-CSI-RS-ResourceToAddModList SEQUENCE (SIZE (1..maxNrofNZP-CSI-RS-Resources)) OF NZP-CSI-RS-Resource OPTIONAL, nzp-CSI-RS-ResourceToReleaseList SEQUENCE (SIZE (1..maxNrofNZP-CSI-RS-Resources)) OF NZP-CSI-RS-ResourceId OPTIONAL, nzp-CSI-RS-ResourceSetToAddModList SEQUENCE (SIZE (1..maxNrofNZP-CSI-RS-ResourceSets)) OF NZP-CSI-RS-ResourceSet OPTIONAL, nzp-CSI-RS-ResourceSetToReleaseList SEQUENCE (SIZE (1..maxNrofNZP-CSI-RS-ResourceSets)) OF NZP-CSI-RS-ResourceSetId OPTIONAL, csi-IM-ResourceToAddModList SEQUENCE (SIZE (1..maxNrofCSI-IM-Resources)) OF CSI-IM-Resource OPTIONAL, csi-IM-ResourceToReleaseList SEQUENCE (SIZE (1..maxNrofCSI-IM-Resources)) OF CSI-IM-ResourceId OPTIONAL, csi-IM-ResourceSetToAddModList SEQUENCE (SIZE (1..maxNrofCSI-IM-ResourceSets)) OF CSI-IM-ResourceSet OPTIONAL, csi-IM-ResourceSetToReleaseList SEQUENCE (SIZE (1..maxNrofCSI-IM-ResourceSets)) OF CSI-IM-ResourceSetId OPTIONAL, csi-SSB-ResourceSetToAddModList SEQUENCE (SIZE (1..maxNrofCSI-SSB-ResourceSets)) OF CSI-SSB-ResourceSet OPTIONAL, csi-SSB-ResourceSetToAddReleaseList SEQUENCE (SIZE (1..maxNrofCSI-SSB-ResourceSets)) OF CSI-SSB-ResourceSetId OPTIONAL, csi-ResourceConfigToAddModList SEQUENCE (SIZE (1..maxNrofCSI-ResourceConfigurations)) OF CSI-ResourceConfig OPTIONAL, csi-ResourceConfigToReleaseList SEQUENCE (SIZE (1..maxNrofCSI-ResourceConfigurations)) OF CSI-ResourceConfigId OPTIONAL, csi-ReportConfigToAddModList SEQUENCE (SIZE (1..maxNrofCSI-ReportConfigurations)) OF CSI-ReportConfig OPTIONAL, csi-ReportConfigToReleaseList SEQUENCE (SIZE (1..maxNrofCSI-ReportConfigurations)) OF CSI-ReportConfigId OPTIONAL, reportTriggerSize INTEGER (0..6) OPTIONAL, aperiodicTriggerStateList SetupRelease { CSI-AperiodicTriggerStateList }, semiPersistentOnPUSCH-TriggerStateList SetupRelease { CSI-SemiPersistentOnPUSCH-TriggerStateList } OPTIONAL, ... }
ZP-CSI-RS-Resource ::= SEQUENCE { zp-CSI-RS-ResourceId ZP-CSI-RS-ResourceId, resourceMapping CSI-RS-ResourceMapping, periodicityAndOffset CSI-ResourcePeriodicityAndOffset OPTIONAL, ... }
ZP-CSI-RS-ResourceSet ::= SEQUENCE { zp-CSI-RS-ResourceSetId ZP-CSI-RS-ResourceSetId, zp-CSI-RS-ResourceIdList SEQUENCE (SIZE(1..maxNrofZP-CSI-RS-ResourcesPerSet)) OF ZP-CSI-RS-ResourceId, ... }
NZP-CSI-RS-Resource ::= SEQUENCE { nzp-CSI-RS-ResourceId NZP-CSI-RS-ResourceId, resourceMapping CSI-RS-ResourceMapping, powerControlOffset INTEGER (-8..15), powerControlOffsetSS ENUMERATED{db-3, db0, db3, db6} OPTIONAL, -- Need R scramblingID ScramblingId, periodicityAndOffset CSI-ResourcePeriodicityAndOffset OPTIONAL,- qcl-InfoPeriodicCSI-RS TCI-StateId OPTIONAL, -- Cond Periodic ... }
NZP-CSI-RS-ResourceSet ::= SEQUENCE { nzp-CSI-ResourceSetId NZP-CSI-RS-ResourceSetId, nzp-CSI-RS-Resources SEQUENCE (SIZE (1..maxNrofNZP-CSI-RS-ResourcesPerSet)) OF NZP-CSI-RS-ResourceId, repetition ENUMERATED { on, off } OPTIONAL, aperiodicTriggeringOffset INTEGER(0..4) OPTIONAL, trs-Info ENUMERATED {true} OPTIONAL, ... }
CSI-RS-ResourceMapping ::= SEQUENCE { frequencyDomainAllocation CHOICE { row1 BIT STRING (SIZE (4)), row2 BIT STRING (SIZE (12)), row4 BIT STRING (SIZE (3)), other BIT STRING (SIZE (6)) }, nrofPorts ENUMERATED {p1,p2,p4,p8,p12,p16,p24,p32}, firstOFDMSymbolInTimeDomain INTEGER (0..13), firstOFDMSymbolInTimeDomain2 INTEGER (2..12) OPTIONAL, -- Need R cdm-Type ENUMERATED {noCDM, fd-CDM2, cdm4-FD2-TD2, cdm8-FD2-TD4}, density CHOICE { dot5 ENUMERATED {evenPRBs, oddPRBs}, one NULL, three NULL, spare NULL }, freqBand CSI-FrequencyOccupation, ... }
CSI-ResourcePeriodicityAndOffset ::= CHOICE { slots4 INTEGER (0..3), slots5 INTEGER (0..4), slots8 INTEGER (0..7), slots10 INTEGER (0..9), slots16 INTEGER (0..15), slots20 INTEGER (0..19), slots32 INTEGER (0..31), slots40 INTEGER (0..39), slots64 INTEGER (0..63), slots80 INTEGER (0..79), slots160 INTEGER (0..159), slots320 INTEGER (0..319), slots640 INTEGER (0..639) }
CSI-FrequencyOccupation ::= SEQUENCE { startingRB INTEGER (0..maxNrofPhysicalResourceBlocks-1), nrofRBs INTEGER (24..maxNrofPhysicalResourceBlocksPlus1), ... }
CSI-IM-Resource ::= SEQUENCE { csi-IM-ResourceId CSI-IM-ResourceId, csi-IM-ResourceElementPattern CHOICE { pattern0 SEQUENCE { subcarrierLocation-p0 ENUMERATED { s0, s2, s4, s6, s8, s10 }, symbolLocation-p0 INTEGER (0..12) }, pattern1 SEQUENCE { subcarrierLocation-p1 ENUMERATED { s0, s4, s8 }, symbolLocation-p1 INTEGER (0..13) } } OPTIONAL, -- Need M freqBand CSI-FrequencyOccupation OPTIONAL, periodicityAndOffset CSI-ResourcePeriodicityAndOffset OPTIONAL, PeriodicOrSemiPersistent ... }
CSI-IM-ResourceSet ::= SEQUENCE { csi-IM-ResourceSetId CSI-IM-ResourceSetId, csi-IM-Resources SEQUENCE (SIZE(1..maxNrofCSI-IM-ResourcesPerSet)) OF CSI-IM-ResourceId, ... }
CSI-SSB-ResourceSet ::= SEQUENCE { csi-SSB-ResourceSetId CSI-SSB-ResourceSetId, csi-SSB-ResourceList SEQUENCE (SIZE(1..maxNrofCSI-SSB-ResourcePerSet)) OF SSB-Index, ... }
CSI-ResourceConfig ::= SEQUENCE { csi-ResourceConfigId CSI-ResourceConfigId, csi-RS-ResourceSetList CHOICE { nzp-CSI-RS-SSB SEQUENCE { nzp-CSI-RS-ResourceSetList SEQUENCE (SIZE (1..maxNrofNZP-CSI-RS-ResourceSetsPerConfig)) OF NZP-CSI-RS-ResourceSetId OPTIONAL, csi-SSB-ResourceSetList SEQUENCE (SIZE (1..maxNrofCSI-SSB-ResourceSetsPerConfig)) OF CSI-SSB-ResourceSetId OPTIONAL }, csi-IM-ResourceSetList SEQUENCE (SIZE (1..maxNrofCSI-IM-ResourceSetsPerConfig)) OF CSI-IM-ResourceSetId }, bwp-Id BWP-Id, resourceType ENUMERATED { aperiodic, semiPersistent, periodic }, ... }
CSI-ReportConfig ::= SEQUENCE { reportConfigId CSI-ReportConfigId, carrier ServCellIndex OPTIONAL, resourcesForChannelMeasurement CSI-ResourceConfigId, csi-IM-ResourcesForInterference CSI-ResourceConfigId OPTIONAL, nzp-CSI-RS-ResourcesForInterference CSI-ResourceConfigId OPTIONAL, reportConfigType CHOICE { periodic SEQUENCE { reportSlotConfig CSI-ReportPeriodicityAndOffset, pucch-CSI-ResourceList SEQUENCE (SIZE (1..maxNrofBWPs)) OF PUCCH-CSI-Resource }, semiPersistentOnPUCCH SEQUENCE { reportSlotConfig CSI-ReportPeriodicityAndOffset, pucch-CSI-ResourceList SEQUENCE (SIZE (1..maxNrofBWPs)) OF PUCCH-CSI-Resource }, semiPersistentOnPUSCH SEQUENCE { reportSlotConfig ENUMERATED {sl5, sl10, sl20, sl40, sl80, sl160, sl320}, reportSlotOffsetList SEQUENCE (SIZE (1.. maxNrofUL-Allocations)) OF INTEGER(0..32), p0alpha P0-PUSCH-AlphaSetId }, aperiodic SEQUENCE { reportSlotOffsetList SEQUENCE (SIZE (1..maxNrofUL-Allocations)) OF INTEGER(0..32) } }, reportQuantity CHOICE { none NULL, cri-RI-PMI-CQI NULL, cri-RI-i1 NULL, cri-RI-i1-CQI SEQUENCE { pdsch-BundleSizeForCSI ENUMERATED {n2, n4} OPTIONAL }, cri-RI-CQI NULL, cri-RSRP NULL, ssb-Index-RSRP NULL, cri-RI-LI-PMI-CQI NULL }, reportFreqConfiguration SEQUENCE { cqi-FormatIndicator ENUMERATED { widebandCQI, subbandCQI } OPTIONAL, pmi-FormatIndicator ENUMERATED { widebandPMI, subbandPMI } OPTIONAL, csi-ReportingBand CHOICE { subbands3 BIT STRING(SIZE(3)), subbands4 BIT STRING(SIZE(4)), subbands5 BIT STRING(SIZE(5)), subbands6 BIT STRING(SIZE(6)), subbands7 BIT STRING(SIZE(7)), subbands8 BIT STRING(SIZE(8)), subbands9 BIT STRING(SIZE(9)), subbands10 BIT STRING(SIZE(10)), subbands11 BIT STRING(SIZE(11)), subbands12 BIT STRING(SIZE(12)), subbands13 BIT STRING(SIZE(13)), subbands14 BIT STRING(SIZE(14)), subbands15 BIT STRING(SIZE(15)), subbands16 BIT STRING(SIZE(16)), subbands17 BIT STRING(SIZE(17)), subbands18 BIT STRING(SIZE(18)), ..., subbands19-v1530 BIT STRING(SIZE(19)) } OPTIONAL } OPTIONAL, timeRestrictionForChannelMeasurements ENUMERATED {configured, notConfigured}, timeRestrictionForInterferenceMeasurements ENUMERATED {configured, notConfigured}, codebookConfig CodebookConfig OPTIONAL, nrofCQIsPerReport ENUMERATED {n1, n2} OPTIONAL, groupBasedBeamReporting CHOICE { enabled NULL, disabled SEQUENCE { nrofReportedRS ENUMERATED {n1, n2, n3, n4} OPTIONAL } }, cqi-Table ENUMERATED {table1, table2, table3, spare1} OPTIONAL, subbandSize ENUMERATED {value1, value2}, non-PMI-PortIndication SEQUENCE (SIZE (1..maxNrofNZP-CSI-RS-ResourcesPerConfig)) OF PortIndexFor8Ranks OPTIONAL, ..., [[ semiPersistentOnPUSCH-v1530 SEQUENCE { reportSlotConfig-v1530 ENUMERATED {sl4, sl8, sl16} } OPTIONAL ]] }
CSI-ReportPeriodicityAndOffset ::= CHOICE { slots4 INTEGER(0..3), slots5 INTEGER(0..4), slots8 INTEGER(0..7), slots10 INTEGER(0..9), slots16 INTEGER(0..15), slots20 INTEGER(0..19), slots40 INTEGER(0..39), slots80 INTEGER(0..79), slots160 INTEGER(0..159), slots320 INTEGER(0..319) }
PUCCH-CSI-Resource ::= SEQUENCE { uplinkBandwidthPartId BWP-Id, pucch-Resource PUCCH-ResourceId }
PortIndexFor8Ranks ::= CHOICE { portIndex8 SEQUENCE{ rank1-8 PortIndex8 OPTIONAL, -- Need R rank2-8 SEQUENCE(SIZE(2)) OF PortIndex8 OPTIONAL, -- Need R rank3-8 SEQUENCE(SIZE(3)) OF PortIndex8 OPTIONAL, -- Need R rank4-8 SEQUENCE(SIZE(4)) OF PortIndex8 OPTIONAL, -- Need R rank5-8 SEQUENCE(SIZE(5)) OF PortIndex8 OPTIONAL, -- Need R rank6-8 SEQUENCE(SIZE(6)) OF PortIndex8 OPTIONAL, -- Need R rank7-8 SEQUENCE(SIZE(7)) OF PortIndex8 OPTIONAL, -- Need R rank8-8 SEQUENCE(SIZE(8)) OF PortIndex8 OPTIONAL -- Need R }, portIndex4 SEQUENCE{ rank1-4 PortIndex4 OPTIONAL, -- Need R rank2-4 SEQUENCE(SIZE(2)) OF PortIndex4 OPTIONAL, -- Need R rank3-4 SEQUENCE(SIZE(3)) OF PortIndex4 OPTIONAL, -- Need R rank4-4 SEQUENCE(SIZE(4)) OF PortIndex4 OPTIONAL -- Need R }, portIndex2 SEQUENCE{ rank1-2 PortIndex2 OPTIONAL, -- Need R rank2-2 SEQUENCE(SIZE(2)) OF PortIndex2 OPTIONAL -- Need R }, portIndex1 NULL }
CodebookConfig ::= SEQUENCE { codebookType CHOICE { type1 SEQUENCE { subType CHOICE { typeI-SinglePanel SEQUENCE { nrOfAntennaPorts CHOICE { two SEQUENCE { twoTX-CodebookSubsetRestriction BIT STRING (SIZE (6)) }, moreThanTwo SEQUENCE { n1-n2 CHOICE { two-one-TypeI-SinglePanel-Restriction BIT STRING (SIZE (8)), two-two-TypeI-SinglePanel-Restriction BIT STRING (SIZE (64)), four-one-TypeI-SinglePanel-Restriction BIT STRING (SIZE (16)), three-two-TypeI-SinglePanel-Restriction BIT STRING (SIZE (96)), six-one-TypeI-SinglePanel-Restriction BIT STRING (SIZE (24)), four-two-TypeI-SinglePanel-Restriction BIT STRING (SIZE (128)), eight-one-TypeI-SinglePanel-Restriction BIT STRING (SIZE (32)), four-three-TypeI-SinglePanel-Restriction BIT STRING (SIZE (192)), six-two-TypeI-SinglePanel-Restriction BIT STRING (SIZE (192)), twelve-one-TypeI-SinglePanel-Restriction BIT STRING (SIZE (48)), four-four-TypeI-SinglePanel-Restriction BIT STRING (SIZE (256)), eight-two-TypeI-SinglePanel-Restriction BIT STRING (SIZE (256)), sixteen-one-TypeI-SinglePanel-Restriction BIT STRING (SIZE (64)) }, typeI-SinglePanel-codebookSubsetRestriction-i2 BIT STRING (SIZE (16)) } }, typeI-SinglePanel-ri-Restriction BIT STRING (SIZE (8)) }, typeI-MultiPanel SEQUENCE { ng-n1-n2 CHOICE { two-two-one-TypeI-MultiPanel-Restriction BIT STRING (SIZE (8)), two-four-one-TypeI-MultiPanel-Restriction BIT STRING (SIZE (16)), four-two-one-TypeI-MultiPanel-Restriction BIT STRING (SIZE (8)), two-two-two-TypeI-MultiPanel-Restriction BIT STRING (SIZE (64)), two-eight-one-TypeI-MultiPanel-Restriction BIT STRING (SIZE (32)), four-four-one-TypeI-MultiPanel-Restriction BIT STRING (SIZE (16)), two-four-two-TypeI-MultiPanel-Restriction BIT STRING (SIZE (128)), four-two-two-TypeI-MultiPanel-Restriction BIT STRING (SIZE (64)) }, ri-Restriction BIT STRING (SIZE (4)) } }, codebookMode INTEGER (1..2) }, type2 SEQUENCE { subType CHOICE { typeII SEQUENCE { n1-n2-codebookSubsetRestriction CHOICE { two-one BIT STRING (SIZE (16)), two-two BIT STRING (SIZE (43)), four-one BIT STRING (SIZE (32)), three-two BIT STRING (SIZE (59)), six-one BIT STRING (SIZE (48)), four-two BIT STRING (SIZE (75)), eight-one BIT STRING (SIZE (64)), four-three BIT STRING (SIZE (107)), six-two BIT STRING (SIZE (107)), twelve-one BIT STRING (SIZE (96)), four-four BIT STRING (SIZE (139)), eight-two BIT STRING (SIZE (139)), sixteen-one BIT STRING (SIZE (128)) }, typeII-RI-Restriction BIT STRING (SIZE (2)) }, typeII-PortSelection SEQUENCE { portSelectionSamplingSize ENUMERATED {n1, n2, n3, n4} OPTIONAL, typeII-PortSelectionRI-Restriction BIT STRING (SIZE (2)) } }, phaseAlphabetSize ENUMERATED {n4, n8}, subbandAmplitude BOOLEAN, numberOfBeams ENUMERATED {two, three, four} } } }
Following is a simple example of CSI-RS allocation from 38.508-1. You would have more details configurations from the same specification that I summarized in this note.
< Based on 38.508-1 Table 4.6.3-45: CSI-RS-ResourceMapping >
< Based on 38.508-1 Table 4.6.3-33: CSI-FrequencyOccupation >
How to Avoid Collision with Other Signals ?
According to what is explained above, it would be possible to allocate the CSI-RS at any symbol and in any slot, but in real situation where various other physical channels and signals running we cannot enjoy such a full degree of freedom for allocating CSI-RS. In this aspect, I think I can list some tips that may helps.
Example 1 >
As an example, let's assume a case as follows.
SIB 1 :
ssb-PositionsInBurst { inOneGroup 'FF'H }, ssb-PeriodicityServingCell ms20, tdd-UL-DL-ConfigurationCommon { referenceSubcarrierSpacing kHz30, pattern1 { dl-UL-TransmissionPeriodicity ms5, nrofDownlinkSlots 7, nrofDownlinkSymbols 6, nrofUplinkSlots 2, nrofUplinkSymbols 4 } },
First thing I want to suggest you to do is to draw a diagram and mark the configuration of ssb bitmap and tdd-UL-DL config and some additional symbols where CSI-RS is not allowed to be assigned as below.
Now you have a bunck of white spaces where you can allocate CSI-RS. Not so many white spaces, right ? Actually if you want to put the CSI-RS to another 5ms period where SSB is not transmitted, it would be much easier to configure, but in this example I intentionaly picked up tough situation. There can be so many different ways of configuring the CSI-RS, but you can determine any valid configuration as you want and mark it as shown below (this is just one example) and then populate the configuration into RRC message. It would be very error prone if you try configuring RRC without this kind of drawing beforehand.
NOTE : I have tested this configuration with Amarisoft Callbox (gNB+Core) and two different UE (Amarisoft UE simulator and a commericial UE). Case 1 : I configured CSI for TRS at the different symbol number in slot 4 and 5. With this configuration, only Amarisoft UE simulator passed and commercial UE didn't pass (Radio Link broken right after RRC Setup). Case 2 : I configured CSI for TRS at the same symbol number in slot 4 and 5 then both DUT (Amarisoft UEsimulator and Commerical UE) passed. I think both configuration is compliant to 3GPP and I personally think it is due to UE implementation of the commercial UE that failed at case 1).
Reference
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