Patent Description:
The present disclosure relates to a cellular communications system and, in particular, to a cellular communications system that supports Multi-Transmission/Reception Point (TRP) transmission.

In Third Generation Partnership Project (3GPP) New Radio (NR), Phase Tracking Reference Signal (PTRS or PT-RS) can be configured for downlink and uplink transmissions in order for the receiver to correct phase noise related errors. The PTRS configuration is User Equipment (UE)-specific, and the PTRS is associated with one of the Demodulation Reference Signal (DMRS or DM-RS) ports used for the transmission. This means that DMRS and its associated PTRS are transmitted using the same precoder and the modulated symbol used for the PTRS is taken from the DMRS, whatever DMRS sequence is configured. This means that there is no specific configuration of the PTRS sequence, as it borrows from the DMRS.

The UE assumes that the Physical Downlink Shared Channel (PDSCH) DMRS is mapped to physical resources according to type <NUM> or type <NUM> as given by the higher-layer parameter DL-DMRS-config-type. The UE assumes the sequence r(m) is mapped to physical Resource Elements (REs) according to: <MAT> <MAT> <MAT> <MAT> where wf(k'), wt(l'), and Δ are given by Tables <NUM>. <NUM>-<NUM> and <NUM>. <NUM>-<NUM> in 3GPP Technical Specification (TS) <NUM> V15. <NUM> (reproduced below as Tables <NUM> and <NUM>) and the following condition is fulfilled:.

The reference point for k is the start of the carrier bandwidth part i in which the PDSCH is transmitted with k = <NUM> corresponding to the lowest-numbered subcarrier in the bandwidth part. The offset n<NUM> is given by: <MAT> where <MAT> is the start of the carrier bandwidth part within which the Physical Uplink Shared Channel (PUSCH) is transmitted.

The reference point for l and the position l<NUM> of the first DMRS symbol depends on the mapping type:.

The position(s) of additional DMRS symbols is given by l and the last Orthogonal Frequency Division Multiplexing (OFDM) symbol used for PDSCH in the slot according to Tables <NUM>. <NUM>-<NUM> and <NUM>. <NUM>-<NUM> in 3GPP TS <NUM> V15. <NUM> (reproduced below as Tables <NUM> and <NUM>).

The time-domain index l' and the supported antenna ports p are given by Table <NUM>. <NUM>-<NUM> (reproduced below as Table <NUM>) where:.

In <FIG>, the mapping of the different DMRS ports for DMRS type <NUM> and <NUM> for single front-loaded cases is shown. An important aspect is that PTRS is not scheduled when using Time Domain Orthogonal Cover Code(s) (TD-OCC(s)) for the DMRS. Therefore, PTRS will never be present when using DMRS ports <NUM>-<NUM> for DMRS type <NUM> and ports <NUM>-<NUM> for DMRS type <NUM>.

In addition, when the rank is <NUM>-<NUM>, the PDSCH contains two codewords, while for rank <NUM>-<NUM> only a single codeword is transmitted. When PTRS is present, the maximum rank is <NUM>. The following DMRS ports are used for the case of two codeword transmissions:.

When a PDSCH is transmitted with two codewords, there is a rule that decides how the layers of each codeword, CW0 and CWI1, are mapped to the total number of Multiple Input Multiple Output (MIMO) layers. This rule is as follows:.

In NR Release <NUM> PDSCH transmission, one PTRS port is supported and associated with the PDSCH transmission. For PUSCH, two PTRS ports can be associated with the PUSCH transmission.

Regarding the mapping of PTRS in the frequency domain, each PTRS port is scheduled with at most one subcarrier per Physical Resource Block (PRB). Also, the subcarrier used for a PTRS port must be one of the subcarriers also used for the DMRS port associated with the PTRS port. In <FIG>, an example of allowed PTRS mapping is shown. In <FIG>, an example of a not allowed PTRS mapping is shown. Hence, if a comb-based structure is used for DMRS with a repetition factor (RPF) of two (as in DMRS configuration type <NUM>), then DMRS is mapped to every second subcarrier. Consequently, the PTRS can only be mapped to <NUM> out of <NUM> subcarriers in this example.

Since there are six alternative subcarriers in Type <NUM>, there is a procedure defined to determine which subcarrier the DMRS is mapped to. An offset dependent on <MAT> is specified, see Table <NUM>. <NUM>-<NUM> in 3GPP TS <NUM> V15. <NUM> (reproduced as Table <NUM> below), where for example, if DMRS port <NUM> is indicated when scheduling PDSCH and the higher layer parameter resourceElementOffset is configured to <NUM>, then the table gives <MAT> and hence the PTRS is mapped to subcarrier <NUM>, as in <FIG>. Table <NUM> (Reproduction of Table <NUM>. <NUM>-<NUM>: The parameter <MAT>, from 3GPP TS <NUM> v15.

In addition, the NR specification states that if a PDSCH contains two codewords, i.e. two separately encoded transport blocks, then:
If a UE is scheduled with two codewords, the PT-RS antenna port is associated with the lowest indexed DM-RS antenna port among the DM-RS antenna ports assigned for the codeword with the higher MCS. If the MCS indices of the two codewords are the same, the PT-RS antenna port is associated with the lowest indexed DM-RS antenna port.

The reason for this is that it is beneficial to map the PTRS to MIMO layers which have the strongest signal to noise ratio, since it improves phase tracking performance. Due to Channel State Information (CSI) feedback, the NR base station (gNB) can adjust the Modulation and Coding Scheme (MCS) per codeword. If a higher MCS is selected, it means that the layers used by that codeword have higher signal to noise ratios at the receiver, and thus the PTRS is associated with one of the DMRS ports of that "stronger" codeword.

In regard to PTRS power allocation, according to 3GPP NR specification TS <NUM> V15. <NUM>, when a UE is scheduled with a PTRS port associated with a PDSCH, if the UE is configured with a higher layer parameter epre-Ratio, the ratio of PTRS Energy Per Resource Element (EPRE) to PDSCH EPRE per layer per RE for PTRS port, ρPTRS, is given by Table <NUM>-<NUM> in TS <NUM> V15. <NUM> (reproduced below as Table <NUM>) according to the epre-Ratio, where the unit of ρPTRS is in decibels (dB). The PTRS scaling factor βPTRS specified in subclause <NUM>. <NUM> of 3GPP TS <NUM> V15. <NUM> is given by: <MAT> Otherwise, if the UE is not configured with epre-Ratio, the UE assumes epre-Ratio is set to state '<NUM>' in Table <NUM>-<NUM> if not configured.

Several signals can be transmitted from the same base station antenna from different antenna ports. These signals can have the same large-scale properties, for instance in terms of Doppler shift/spread, average delay spread, or average delay. These antenna ports are then said to be QCL.

The network can then signal to the UE that two antenna ports are QCL. If the UE knows that two antenna ports are QCL with respect to a certain parameter (e.g., Doppler spread), the UE can estimate that parameter based on one of the antenna ports and use that estimate when receiving the other antenna port. Typically, the first antenna port is represented by a measurement reference signal such as CSI Reference Signal (CSI-RS) (known as the source Reference Signal (RS)) and the second antenna port is a DMRS (known as the target RS).

For instance, if antenna ports A and B are QCL with respect to average delay, the UE can estimate the average delay from the signal received from antenna port A (source RS) and assume that the signal received from antenna port B (target RS) has the same average delay. This is useful for demodulation since the UE can know beforehand the properties of the channel when trying to measure the channel utilizing the DMRS.

Information about what assumptions can be made regarding QCL is signaled to the UE from the network. In NR, four types of QCL relations between a transmitted source RS and transmitted target RS were defined:.

QCL Type D was introduced to facilitate beam management with analog beamforming and is known as spatial QCL. There is currently no strict definition of spatial QCL, but the understanding is that, if two transmitted antenna ports are spatially QCL, the UE can use the same receive (Rx) beam to receive them. Note that for beam management, the discussion mostly revolves around QCL Type D, but it is also necessary to convey a Type A QCL relation for the RSs to the UE so that it can estimate all the relevant large-scale parameters.

Typically, this is achieved by configuring the UE with a CSI-RS for Tracking RS (TRS) for time/frequency offset estimation. To be able to use any QCL reference, the UE would have to receive it with a sufficiently good Signal to Interference plus Noise Ratio (SINR). In many cases, this means that the TRS has to be transmitted in a suitable beam to a certain UE.

To introduce dynamics in beam and Transmission/Reception Point (TRP) selection, the UE can be configured through Radio Resource Control (RRC) signaling with N TCI states, where N is up to <NUM> in frequency range <NUM> (FR2) and up to <NUM> in frequency range <NUM> (FR1), depending on UE capability. Each TCI state contains QCL information, i.e. one or two source downlink RSs, each source RS associated with a QCL type. For example, a TCI state contains a pair of RSs, each associated with a QCL type, e.g. two different CSI-RSs {CSI-RS1, CSI-RS2} is configured in the TCI state as {qcl-Type1,qcl-Type2} = {Type A, Type D}. This means the UE can derive Doppler shift, Doppler spread, average delay, delay spread from CSI-RS1, and spatial Rx parameter (i.e., the Rx beam to use) from CSI-RS2. In case Type D (spatial information) is not applicable, such as low or mid-band operation, then a TCI state contains only a single source RS.

Each of the N states in the list of TCI states can be interpreted as a list of N possible beams transmitted from the network or a list of N possible TRPs used by the network to communicate with the UE. A first list of available TCI states is configured for PDSCH, and a second list for PDCCH contains pointers, known as TCI state Identifiers (IDs), to a subset of the TCI states configured for PDSCH. The network then activates one TCI state for PDCCH (i.e., provides a TCI for PDCCH) and activates up to M TCI states for PDSCH. The number M of active TCI states the UE can support is a UE capability but the maximum in NR Release <NUM> is eight (<NUM>).

Each configured TCI state contains parameters for the QCL associations between source RSs (CSI-RS or Synchronization Signal (SS)/Physical Broadcast Channel (PBCH)) and target RSs (e.g., PDSCH/PDCCH DMRS ports). TCI states are also used to convey QCL information for the reception of CSI-RS.

Assume a UE is configured with four active TCI states from a list of sixty-four (<NUM>) configured TCI states. Hence, sixty TCI states are inactive, and the UE need not be prepared to have large-scale parameters estimated for those inactive TCI states. But the UE continuously tracks and updates the large-scale parameters for the four active TCI states by measurements and analysis of the source RSs indicated by each TCI state.

In NR Release <NUM>, when scheduling a PDSCH to a UE, the DCI contains a pointer to one active TCI. The UE then knows which large-scale parameter estimate to use when performing PDSCH DMRS channel estimation and thus PDSCH demodulation.

In NR Release <NUM>, there are discussions ongoing on the support of PDSCH with multiple TRPs (i.e., with multi-TRPs). One mechanism that is being considered in NR Release <NUM> is a single Physical Downlink Control Channel (PDCCH) scheduling one or multiple PDSCHs from different TRPs. The single PDCCH is received from one of the TRPs. <FIG> shows an example where a DCI received by the UE in a PDCCH from TRP1 schedules two PDSCHs. The first PDSCH (PDSCH1) is received from TRP1, and the second PDSCH (PDSCH2) is received from TRP2. Alternatively, the single PDCCH schedules a single PDSCH where PDSCH layers are grouped into two groups and where layer group <NUM> is received from TRP1 and layer group <NUM> is received from TRP2. In such cases, each PDSCH or layer group is transmitted from a different TRP and has a different TCI state associated with it. In the example of <FIG>, PDSCH1 is associated with TCI State p, and PDSCH <NUM> is associated with TCI state q.

In the RAN1 AdHoc meeting in January <NUM>, the following was agreed:.

TCI indication framework shall be enhanced in Rel-<NUM> at least for eMBB:.

According to the above agreement, each code point in the DCI Transmission Configuration Indication field can be mapped to either <NUM> or <NUM> TCI states. This can be interpreted as follows: A DCI in PDCCH schedules <NUM> or <NUM> PDSCHs (or <NUM> or <NUM> layer groups if a single PDSCH) where each PDSCH or layer group is associated with a different TCI state; the code point of the Transmission Configuration Indication field in DCI indicates the <NUM>-<NUM> TCI states associated with the <NUM> or <NUM> PDSCHs or layer groups scheduled. In this case, the two DMRSs of the two PDSCHs or the two layer groups respectively are not mapped to the same DMRS Code Division Multiplexing (CDM) group. When two TCI states are indicated by a TCI code point, for DMRS type <NUM> and type <NUM>, if indicated DMRS ports are from two CDM groups, the first TCI state corresponds to the CDM group of the first antenna port indicated by the antenna port indication table.

In a Release <NUM> work item in 3GPP, it has been agreed:.

Support two PTRS ports for single-PDCCH based multi-TRP/Panel transmission at least for eMBB and URLLC scheme 1a if two TCI states are indicated by one TCI code point, whereas the first/second PTRS port is associated with the lowest indexed DMRS port within the DMRS ports corresponding to the first/second indicated TCI state, respectively.

In case of rank <NUM> or <NUM> scheduling (two codewords), this agreement means you select the lowest DMRS port index from each TCI state.

There currently exist certain challenge(s). The recent agreement on two PTRS ports and the association to TCI states does not allow for mapping the PTRS ports to the strongest MIMO layers. This degrades the performance of the phase tracking functionality of PTRS and increases the block error rate which reduces the throughput. How to allocate transmit power for each of the two PTRS ports is another issue which is a problem to be resolved.

Document "<NPL>, discloses MIMO enhancement objectives for NR to enhance multi-TRP/panel transmission with ideal and non-ideal backhaul.

Document "<NPL>, discloses, inter alia, single PDCCH based multi-TRP/Panel transmission. TCI indication framework shall be enhanced at least for eMBB, i.e., each TCI code point in a DCI can correspond to <NUM> or <NUM> TCI states: when <NUM> TCI states are activated within a TCI code point, each TCI state corresponds to one CDM group, at least for DMRS type <NUM>, and for TCI state configuration in order to enable one or two TCI states per a TCI code point, support MAC-CE enhancement to map one or two TCI states for a TCI code point where further detailed design is determined in RAN2.

Document "<NPL>, discloses a change proposal for 3GPP TS <NUM> V15. <NUM> residing in deleting the concept of DMRS ports groups.

Systems and methods for Phase Tracking Reference Signal (PTRS) to Demodulation Reference Signal (DMRS) association when two or more Transmission Configuration Indication (TCI) states are indicated for a Physical Downlink Shared Channel (PDSCH) transmission in a cellular communications system are disclosed.

According to the present disclosure, methods, wireless communication devices and network nodes according to the independent claims are provided. Developments are set forth in the dependent claims.

According to the present disclosure, there are provided methods, a wireless communication device, computer-readable storage media and a network node according to the independent claims. Developments are set forth in the dependent claims.

Radio Access Node: As used herein, a "radio access node" or "radio network node" or "radio access network node" is any node in a Radio Access Network
(RAN) of a cellular communications network that operates to wirelessly transmit and/or receive signals.

Core Network Node: As used herein, a "core network node" is any type of node in a core network or any node that implements a core network function. Some examples of a core network node include, e.g., a Mobility Management Entity (MME), a Packet Data Network Gateway (P-GW), a Service Capability Exposure Function (SCEF), a Home Subscriber Server (HSS), or the like. Some other examples of a core network node include a node implementing an Access and Mobility Function (AMF), a User Plane Function (UPF), a Session Management Function (SMF), an Authentication Server Function (AUSF), a Network Slice Selection Function (NSSF), a Network Exposure Function (NEF), a Network Function (NF) Repository Function (NRF), a Policy Control Function (PCF), a Unified Data Management (UDM), or the like.

As discussed above, there currently exist certain challenge(s) with respect to Phase Tracking Reference Signal (PTRS) port to Multiple Input Multiple Output (MIMO) layer mapping and allocation of transmit power to PTRS ports. In particular, the recent agreement on two PTRS ports and the association to Transmission Configuration Indication (TCI) states does not allow for mapping the PTRS ports to the strongest MIMO layers. This degrades the performance of the phase tracking functionality of PTRS and increases the block error rate which reduces the throughput. Further, how to allocate transmit power for each of the two PTRS ports is a problem that needs to be resolved.

Certain aspects of the present disclosure and their embodiments may provide solutions to the aforementioned or other challenges. According to the present disclosure, the UE is scheduled with two codewords and with two PTRS ports enabled, i.e. rank <NUM>-<NUM> transmission, and the PTRS port to Demodulation Reference Signal (DMRS) port association for each TCI state is determined from the subset of DMRS ports that belong to the codeword that has the highest Modulation and Coding Scheme (MCS).

In some embodiments, each TCI state is associated to a set of DMRS ports. The PTRS port to DMRS port association depends on the MCS of the codeword that use DMRS ports associated with the TCI state.

In some embodiments, power allocation for a PTRS port associated to a TCI state is determined by the number PDSCH layers associated with the same TCI state indicated by a DCI.

Certain embodiments may provide one or more of the following technical advantage(s): lower Block Error Rate (BLER), better resilience to phase noise, higher UE throughput, lower probability of retransmission and thus lower physical layer latency, and correct PTRS power allocation can be done when two PTRS ports are configured.

<FIG> illustrates one example of a cellular communications system <NUM> in which embodiments of the present disclosure may be implemented. In the embodiments described herein, the cellular communications system <NUM> is a <NUM> System (5GS) including a NR RAN or LTE RAN (i.e., Evolved Universal Terrestrial Radio Access (E-UTRA) RAN) or an Evolved Packet System (EPS) including an LTE RAN. In this example, the RAN includes Transmission/Reception Points (TRPs) <NUM>-<NUM> and <NUM>-<NUM>. The TRPs <NUM>-<NUM> and <NUM>-<NUM> may also be referred to herein as "transmit points. " The TRPs <NUM>-<NUM> and <NUM>-<NUM> may be, e.g., base stations, which in LTE are referred to as eNBs (when connected to a Evolved Packet Core (EPC)) and in <NUM> NR are referred to as gNBs or next generation eNBs (ng-eNBs) (i.e., LTE RAN nodes connected to a <NUM> Core (5GC)), or other types of radio access nodes (e.g., low power nodes (e.g., small base stations such as, e.g., pico or femto base stations), Remote Radio Heads (RRHs), or the like).

In the embodiments described herein, the TRPs <NUM>-<NUM> and <NUM>-<NUM> perform a single-control channel (i.e., a single Physical Downlink Control Channel (PDCCH) in this example) multi-TRP (or multi-panel) transmission to a Wireless Communication Device (WCD) <NUM> (e.g., a UE). More specifically, a network node <NUM> causes the TRPs <NUM>-<NUM> and <NUM>-<NUM> to perform the single-control channel (i.e., a single PDCCH in this example) multi-TRP (or multi-panel) transmission to the WCD <NUM> (e.g., a UE). Note that, in many of the example embodiments described below, the WCD <NUM> is a UE and, as such, is sometimes referred to as UE <NUM>. The network node <NUM> includes a scheduler and other intelligence to control, instruct, or otherwise cause the TRPs <NUM>-<NUM> and <NUM>-<NUM> to perform the single-control channel (i.e., a single PDCCH in this example) multi-TRP (or multi-panel) transmission to the WCD <NUM> (e.g., a UE). Note that the network node <NUM> may be separate from the TRPs <NUM>-<NUM> and <NUM>-<NUM>, may be implemented within one of the TRPs <NUM>-<NUM> and <NUM>-<NUM> (e.g., implemented in a base station that serves as the TRP <NUM>-<NUM> and, e.g., where the TRP <NUM>-<NUM> is another base station or some other type of RAN node such as, e.g., a RRH). In some embodiments, the multi-TRP transmission is the transmission of a first Physical Downlink Shared Channel (PDSCH) (PDSCH1) from the TRP <NUM>-<NUM> (also denoted herein as TRP1) and a second PDSCH (PDSCH2) from the TRP <NUM>-<NUM> (also denoted herein as TRP2). In some other embodiments, a single PDSCH is transmitted where the PDSCH layers are grouped into a first layer group (layer group <NUM>) transmitted from the TRP <NUM>-<NUM> and a second layer group (layer group <NUM>) transmitted from the TRP <NUM>-<NUM>.

In the embodiments described herein, two PTRS ports are supported for single-PDCCH based multi-TRP (or multi-panel) transmission if two TCI states are indicated by one TCI code point in the PDCCH. Embodiments described herein relate to PTRS port to DMRS port association for two PTRS ports for single PDCCH based multi-TRP (or multi-panel) transmission if two TCI states are indicated by one TCI code point in the PDCCH (i.e., when two codewords (CWs) are scheduled). Embodiments related to allocation of transmit power for each of the PTRS ports is are also disclosed. While these embodiments may be described separately, they may be used separately or in any desired combination. Note that while the embodiments described herein relate to two PTRS ports and two TCI states, the present disclosure is not limited thereto. For example, there may be X PTRS ports and X TCI states, where X ≥ <NUM>.

Further, the description of the following embodiments focuses on NR; however, the embodiments may be applied to other types of radio access technologies.

If a UE <NUM> is scheduled with two codewords, i.e. rank <NUM> or rank <NUM> transmission, and PTRS is enabled and:.

If the MCS indices of the two codewords are the same, then the first/second PTRS port is associated with the lowest indexed DMRS port within the DMRS ports corresponding to the first/second indicated TCI state respectively.

In the following examples, port x is denoted as port x-<NUM> for simplicity, e.g. port <NUM> is described as port <NUM>.

Also, note that TCI state <NUM> and <NUM> for DMRS type <NUM> is equivalent to selecting DMRS ports in Code Division Multiplexing (CDM) group λ=<NUM> and <NUM> respectively. Hence, these can be interchanged in the text above and below. For DMRS type <NUM>, TCI state <NUM> is equivalent to CDM group <NUM>. It is an open problem whether TCI state <NUM> is equivalent to CDM group <NUM> or CDM group <NUM>+<NUM>. In the following, it is assumed that TCI state <NUM> is equivalent to CDM group <NUM>+<NUM>.

Example <NUM>: For Type <NUM> DMRS, ports <NUM>,<NUM>,<NUM>,<NUM> belong to first a CDM group (λ=<NUM>) and ports <NUM>,<NUM>,<NUM>,<NUM> belong to a second CDM group (λ=<NUM>). Assume rank <NUM> scheduling where ports <NUM>-<NUM> are used assuming type <NUM> DMRS, then according to the Codeword to Layer (CW2L) mapping, CW0 uses ports <NUM>,<NUM> and CW1 uses ports <NUM>,<NUM>,<NUM>. This leads to the following possible outcomes due to the present disclosure:.

Moreover, if DMRS type <NUM> is used, and the PDSCH uses ports from all three CDM groups as in the case of two codeword transmission of rank <NUM> or <NUM>, then the first TCI state is associated with DMRS ports for the first CDM group (e.g., CDM group <NUM> in <FIG>) and the second TCI state is associated with DMRS ports of the second and third CDM groups (e.g., CDM groups <NUM> and <NUM> in <FIG>).

Example <NUM>: For type <NUM> DMRS, ports <NUM>,<NUM>,<NUM>,<NUM> (λ=<NUM>) belong to a first CDM group and ports <NUM>,<NUM>,<NUM>,<NUM> belong to a second CDM group (λ=<NUM>) and port <NUM>,<NUM>,<NUM>,<NUM> belongs to a third CDM group (λ=<NUM>). Assume rank <NUM> scheduling where ports <NUM>-<NUM> are used assuming type <NUM> DMRS, then according to CW2L mapping, CWO uses ports <NUM>,<NUM> and CW1 uses ports <NUM>,<NUM>,<NUM>. This implies that a codeword is mapped to one.

TCI state only and this leads to no change in behavior of the PTRS to DMRS association depending on MCS, i.e.:.

Assume instead rank <NUM> scheduling where ports <NUM>-<NUM> are used assuming type <NUM> DMRS, then according to CW2L mapping, CWO uses port <NUM>,<NUM>,<NUM> and CW1 uses port <NUM>,<NUM>,<NUM>. This implies that CW0 is associated to two TCI states (i.e., may be transmitted across two transmission points), see <FIG>, and hence:.

In another embodiment, when two TCI states are indicated in a Downlink Control Information (DCI) while DMRS ports within a single CDM group are indicated in the same DCI, a single PTRS port is used, if configured. The PTRS port is associated with the lowest indexed DMRS port in the indicated DMRS ports. The DMRS port is associated with the first TCI state in PDSCH resources allocated for the first TCI state and with the second TCI state in PDSCH resources allocated for the second TCI state.

<FIG> illustrates the operation of the network node <NUM>, the TRPs <NUM>-<NUM> and <NUM>-<NUM>, and the WCD <NUM> to perform a single-PDCCH multi-TRP transmission in which the PTRS port to DMRS port associations are determined as described above, in accordance with some embodiments of the present disclosure. Optional steps are represented by dashed lines/boxes. As illustrated, the network node <NUM> causes transmission of a PDCCH including DCI scheduling a multi-TRP transmission to the WCD <NUM> from the TRP <NUM>-<NUM> (step <NUM>). In some embodiments, the PDCCH, or DCI, includes an indication of two TCI states via a single TCI code point, as described above. In this example, two PTRS ports are configured. The network node <NUM> determines the PTRS port to DMRS port associations for the multi-TRP transmission in the manner described above (step <NUM>). The network node <NUM> causes the TRPs <NUM>-<NUM> and <NUM>-<NUM> to transmit the multi-TRP transmission to the WCD <NUM> (steps 1004A and 1004B).

At the WCD <NUM>, the WCD <NUM> receives and decodes the PDCCH in step <NUM>. Using the information comprised in the DCI carried by the PDCCH, the WCD <NUM> determines the PTRS port to DMRS port associations for the multi-TRP transmission, as described above (step <NUM>). Optionally, the WCD <NUM> performs one or more actions using the determined PTRS port to DMRS port associations for the multi-TRP transmission (step <NUM>). For example, the WCD <NUM> may perform measurements on the PTRS in accordance with the determined PTRS port to DMRS port associations and, e.g., perform one or more operations using the performed measurements, as will be understood by those of ordinary skill in the art.

<FIG> is a flow chart that illustrates the operation of a node (e.g., the network node <NUM> or the WCD <NUM>) to determine the PTRS port to DMRS port associations for a multi-TRP transmission (e.g., a single-PDCCH multi-TRP PDSCH transmission) in accordance with at least some aspects of the embodiments described above. Note that this process may be performed in, e.g., step <NUM> and/or step <NUM> of <FIG>.

In this example, two (or more) PTRS ports are configured and two (or more) TCI states are indicated by, e.g., a single TCI code point in the PDCCH. As illustrated, the node initializes a TCI state counter (i) to <NUM> (step <NUM>). The node determines whether TCI state i is associated to two (or more) MCSs (i.e., if TCI state i is associated with DMRS ports containing two (or more) codewords) (step <NUM>). If so, the node determines that the PTRS port of TCI state i is associated to the lowest indexed DMRS port assigned for the codeword with the higher MCS that is within the DMRS ports corresponding to TCI state i (step <NUM>). Otherwise (if TCI state i is associated to only one MCS), the node determines that the PTRS port of TCI state i is associated to the lowest indexed DMRS port associated to TCI state i (step <NUM>).

The node then determines whether TCI state i is the last TCI state (step <NUM>). If not, the TCI state counter, i, is incremented (step <NUM>), and the process returns to step <NUM> and is repeated for the next TCI state. Once the PTRS port to DMRS port association is determined for all TCI states, the process ends.

When a PDSCH and the associated PTRS is transmitted from a single TRP, the PTRS transmit power may be boosted when the PDSCH contains more than one spatial layer. In other words, the ratio of PTRS Energy Per Resource Element (EPRE) to PDSCH EPRE per layer per Resource Element (RE) for PTRS port can be greater than <NUM> decibels (dB). This is because for PTRS, only a single layer is transmitted while PDSCH can have multiple layers. For the same power amplifier output power, more power per layer can be allocated to PTRS compared to PDSCH when the PDSCH has more than one layer.

When a PDSCH with multiple layers is scheduled with two TCI states, a subset of the layers is transmitted from each of the two TRPs (i.e., a first subset of the layers is associated with a first TCI state that corresponds to a first TRP and a second subset of the layers is associated with a second TCI state that corresponds to the second TRP). If two PTRS ports are configured, each PTRS port is transmitted from one of the two TRPs (i.e., a first PTRS port is associated with the first TCI state that corresponds to the first TRP and a second PTRS port is associated with the second TCI state that corresponds to the second TRP). In this case, the amount of PTRS power allocation for a PTRS port would depend on the number of PDSCH layers scheduled over the same TRP (i.e., would depend on the number of PDSCH layers associated with the same TCI state). Thus, as an example, the amount of PTRS power allocation for a PTRS port in steps 1004A and 1004B of <FIG> depends on the number of PDSCH layers scheduled over the same TRP (i.e., depends on the number of PDSCH layers associated with the same TCI state), in some embodiments.

For example, consider a scenario in which a PDSCH with <NUM> layers is scheduled with two layers over TRP1 and one layer over TRP2. DMRS ports #<NUM> and #<NUM> are associated with the TRP1 and DMRS port #<NUM> is associated with TRP2. If two PTRS ports are configured, PTRS port #<NUM> would be associated with DMRS port #<NUM> and PTRS port #<NUM> with DMRS port #<NUM>. Then the power boosting ratio for PTRS port #<NUM> can be up to <NUM> dB, while for PTRS port #<NUM>, no power boosting can be done. Therefore, in general the amount of power boosting for the two PTRS ports can be different. Table <NUM> is an example of PTRS power allocation when two PTRS are configured and a UE is scheduled with two TCI states.

Some example embodiments of the present disclosure are described below as proposals for issues in 3GPP RAN WG1 #<NUM> related to multi-TRP operation in NR.

<FIG> is a schematic block diagram of a network node <NUM> according to some embodiments of the present disclosure. Optional features are represented by dashed boxes. The network node <NUM> may be, for example, the network node <NUM> a network node that implements all or part of the functionality of the network node (e.g., a base station implementing the functionality of the network node <NUM> and, e.g., the TRP <NUM>-<NUM>) described herein. As illustrated, the network node <NUM> includes a control system <NUM> that includes one or more processors <NUM> (e.g., Central Processing Units (CPUs), Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs), and/or the like), memory <NUM>, and a network interface <NUM>. The one or more processors <NUM> are also referred to herein as processing circuitry. In addition, if the network node <NUM> is a radio access node, the network node <NUM> may include one or more radio units <NUM> that each includes one or more transmitters <NUM> and one or more receivers <NUM> coupled to one or more antennas <NUM>. The radio units <NUM> may be referred to or be part of radio interface circuitry. In some embodiments, the radio unit(s) <NUM> is external to the control system <NUM> and connected to the control system <NUM> via, e.g., a wired connection (e.g., an optical cable). However, in some other embodiments, the radio unit(s) <NUM> and potentially the antenna(s) <NUM> are integrated together with the control system <NUM>. The one or more processors <NUM> operate to provide one or more functions of the network node <NUM> or a network node that implements at least part of the functionality of the network node, as described herein. In some embodiments, the function(s) are implemented in software that is stored, e.g., in the memory <NUM> and executed by the one or more processors <NUM>.

<FIG> is a schematic block diagram that illustrates a virtualized embodiment of the network node <NUM> according to some embodiments of the present disclosure. As used herein, a "virtualized" network node is an implementation of the network node <NUM> in which at least a portion of the functionality of the network node <NUM> is implemented as a virtual component(s) (e.g., via a virtual machine(s) executing on a physical processing node(s) in a network(s)). As illustrated, in this example, the radio access node <NUM> includes one or more processing nodes <NUM> coupled to or included as part of a network(s) <NUM>. Each processing node <NUM> includes one or more processors <NUM> (e.g., CPUs, ASICs, FPGAs, and/or the like), memory <NUM>, and a network interface <NUM>. If the network node <NUM> is a radio access node, the network node <NUM> may include the control system <NUM> and/or the one or more radio units <NUM>, as described above. The control system <NUM> may be connected to the radio unit(s) <NUM> via, for example, an optical cable or the like. If present, the control system <NUM> or the radio unit(s) are connected to the processing node(s) <NUM> via the network <NUM>.

In this example, functions <NUM> of the network node <NUM> described herein (e.g., one or more functions of the network node <NUM> described herein) are implemented at the one or more processing nodes <NUM> or distributed across the one or more processing nodes <NUM> and the control system <NUM> and/or the radio unit(s) <NUM> in any desired manner. In some particular embodiments, some or all of the functions <NUM> of the network node <NUM> described herein are implemented as virtual components executed by one or more virtual machines implemented in a virtual environment(s) hosted by the processing node(s) <NUM>. As will be appreciated by one of ordinary skill in the art, additional signaling or communication between the processing node(s) <NUM> and the control system <NUM> is used in order to carry out at least some of the desired functions <NUM>. Notably, in some embodiments, the control system <NUM> may not be included, in which case the radio unit(s) <NUM> communicate directly with the processing node(s) <NUM> via an appropriate network interface(s).

In some embodiments, a computer program including instructions which, when executed by at least one processor, causes the at least one processor to carry out the functionality of the network node <NUM> or a node (e.g., a processing node <NUM>) implementing one or more of the functions <NUM> of the network node <NUM> in a virtual environment according to any of the embodiments described herein is provided.

<FIG> is a schematic block diagram of the network node <NUM> according to some other embodiments of the present disclosure. The module(s) <NUM> provide the functionality of the network node <NUM> described herein (e.g., one or more functions of the network node <NUM> described herein).

<FIG> is a schematic block diagram of a wireless communication device <NUM> (e.g., the WCD <NUM> or UE described herein) according to some embodiments of the present disclosure. As illustrated, the wireless communication device <NUM> includes one or more processors <NUM> (e.g., CPUs, ASICs, FPGAs, and/or the like), memory <NUM>, and one or more transceivers <NUM> each including one or more transmitters <NUM> and one or more receivers <NUM> coupled to one or more antennas <NUM>. The transceiver(s) <NUM> includes radio-front end circuitry connected to the antenna(s) <NUM> that is configured to condition signals communicated between the antenna(s) <NUM> and the processor(s) <NUM>, as will be appreciated by on of ordinary skill in the art. The processors <NUM> are also referred to herein as processing circuitry. The transceivers <NUM> are also referred to herein as radio circuitry. In some embodiments, the functionality of the wireless communication device <NUM> described above (e.g., one or more functions of a UE or the WCD <NUM> described herein) may be fully or partially implemented in software that is, e.g., stored in the memory <NUM> and executed by the processor(s) <NUM>. Note that the wireless communication device <NUM> may include additional components not illustrated in <FIG> such as, e.g., one or more user interface components (e.g., an input/output interface including a display, buttons, a touch screen, a microphone, a speaker(s), and/or the like and/or any other components for allowing input of information into the wireless communication device <NUM> and/or allowing output of information from the wireless communication device <NUM>), a power supply (e.g., a battery and associated power circuitry), etc..

In some embodiments, a computer program including instructions which, when executed by at least one processor, causes the at least one processor to carry out the functionality of the wireless communication device <NUM> according to any of the embodiments described herein (e.g., one or more functions of a UE or the WCD <NUM> described herein) is provided.

The module(s) <NUM> provide the functionality of the wireless communication device <NUM> described herein (e.g., one or more functions of a UE or the WCD <NUM> described herein).

With reference to <FIG>, in accordance with an embodiment, a communication system includes a telecommunication network <NUM>, such as a 3GPP-type cellular network, which comprises an access network <NUM>, such as a RAN, and a core network <NUM>. The access network <NUM> comprises a plurality of base stations 1706A, 1706B, 1706C, such as Node Bs, eNBs, gNBs, or other types of wireless Access Points (APs), each defining a corresponding coverage area 1708A, 1708B, 1708C. Each base station 1706A, 1706B, 1706C is connectable to the core network <NUM> over a wired or wireless connection <NUM>. A first UE <NUM> located in coverage area 1708C is configured to wirelessly connect to, or be paged by, the corresponding base station 1706C. A second UE <NUM> in coverage area 1708A is wirelessly connectable to the corresponding base station 1706A.

It is noted that the host computer <NUM>, the base station <NUM>, and the UE <NUM> illustrated in <FIG> may be similar or identical to the host computer <NUM>, one of the base stations 1706A, 1706B, 1706C, and one of the UEs <NUM>, <NUM> of <FIG>, respectively.

The wireless connection <NUM> between the UE <NUM> and the base station <NUM> is in accordance with the teachings of the embodiments described throughout this disclosure. One or more of the various embodiments improve the performance of OTT services provided to the UE <NUM> using the OTT connection <NUM>, in which the wireless connection <NUM> forms the last segment. More precisely, the teachings of these embodiments may improve the data rate and thereby provide benefits such as, e.g., reduced user waiting time, relaxed restriction on file size, better responsiveness, or the like.

Claim 1:
A method performed by a Wireless Communication Device, WCD, (<NUM>, <NUM>), the method comprising:
• receiving (<NUM>) a Physical Downlink Control Channel, PDCCH, comprising Downlink Control Information, DCI, that indicates:
∘ two Transmission Configuration Indication, TCI, states for a Physical Downlink Shared Channel, PDSCH, transmission to the WCD (<NUM>); and
∘ Demodulation Reference Signal, DMRS, ports within a single Code Division Multiplexing, CDM, group; and
• receiving (1004A, 1004B) a single Phase Tracking Reference Signal, PTRS, port for the PDSCH transmission, wherein the single PTRS port is associated with a lowest indexed DMRS port in the DMRS ports indicated in the DCI,
• wherein a lowest indexed DMRS port in the DMRS ports indicated in the DCI is: (a) associated with a first TCI state from among the two TCI states for the PDSCH transmission in PDSCH resources allocated for the first TCI state and (b) associated with a second TCI state from among the two TCI states for the PDSCH transmission in PDSCH resources allocated for the second TCI state,
• wherein the single PTRS port is one of two PTRS ports configured for the WCD (<NUM>) and wherein the WCD (<NUM>) is scheduled with two codewords, and
• wherein a PTRS port to DMRS port association for each TCI state is determined from a subset of DMRS ports that belong to the codeword that has the highest Modulation and Coding Scheme, MCS.