Methods and apparatuses for joint CSI measurement in NCJT

Methods and apparatuses for joint channel state information (CSI) measurement are described herein. A method may include receiving channel state information reference signals (CSI-RSs) from first and second transmit/receive points (TRPs), determining CSI, and selecting one of the TRPs as a primary TRP and a remaining one of the first TRP or the second TRP as a secondary TRP. The method may include reporting information indicating a first CSI for the primary TRP and receiving second CSI-RSs from the TRPs. The method may include determining a second CSI and a precoding matrix indicator (PMI) for the primary TRP, and determining channel coding information for the primary TRP. The method may include determining a second CSI for the secondary TRP, determining, based on channel coding information and the second CSI for the secondary TRP and a PMI for the secondary TRP, and reporting information indicating the PMI for the second TRP.

BACKGROUND

In Third Generation Partnership Project (3GPP) specifications for Multiple Input-Multiple Output (MIMO) in New Radio (NR), enhancements for CSI reporting for DL multi-transmit/receive point (TRP) and/or multi-panel transmission may enable more dynamic channel/interference hypotheses for Non-Coherent Joint Transmission (NCJT), targeting both Frequency Range 1 (FR1) and/or Frequency Range 2 (FR2). NCJT, as may be understood in the multi-TRP context, may refer to transmissions performed by cooperating TRPs without prior phase-mismatch correction and tight synchronization. In NCJT, a receiving device may combine the received transmissions non-coherently (i.e., without knowing the phase shift between channels).

Consistent with Release 16 specifications for multiple transmit receive point (M-TRP) scenarios, spatial division multiplexed (SDM) NCJT schemes may provide for different layers of the same codeword corresponding to different TRPs or panels, which may imply different Transmission Configuration Information (TCI) states. Precise measurement and reporting of Channel State Information (CSI) (including channel quality indicator (CQI), rank indicator (RI), precoding matrix indicator (PMI), etc.) for NCJT with a single reporting setting may be subject to efficient configuration and interpretation of the CSI resources for channel and interference measurements.

SUMMARY

Methods and apparatuses for joint channel state information (CSI) measurement are described herein. A method may include receiving channel state information reference signals (CSI-RSs) from first and second transmit/receive points (TRPs), determining CSI, and selecting one of the TRPs as a primary TRP and a remaining one of the first TRP or the second TRP as a secondary TRP. The method may include reporting information indicating a first CSI for the primary TRP and receiving second CSI-RSs from the TRPs. The method may include determining a second CSI and a precoding matrix indicator (PMI) for the primary TRP, and determining channel coding information for the primary TRP. The method may include determining a second CSI for the secondary TRP, determining, based on channel coding information and the second CSI for the secondary TRP and a PMI for the secondary TRP, and reporting information indicating the PMI for the second TRP.

DETAILED DESCRIPTION

In an embodiment, the base station114aand the WTRUs102a,102b,102cmay implement a radio technology such as NR Radio Access, which may establish the air interface116using NR.

The RAN104may be in communication with the CN106, which may be any type of network configured to provide voice, data, applications, and/or voice over internet protocol (VoIP) services to one or more of the WTRUs102a,102b,102c,102d. The data may have varying quality of service (QoS) requirements, such as differing throughput requirements, latency requirements, error tolerance requirements, reliability requirements, data throughput requirements, mobility requirements, and the like. The CN106may provide call control, billing services, mobile location-based services, pre-paid calling, Internet connectivity, video distribution, etc., and/or perform high-level security functions, such as user authentication. Although not shown inFIG.1A, it will be appreciated that the RAN104and/or the CN106may be in direct or indirect communication with other RANs that employ the same RAT as the RAN104or a different RAT. For example, in addition to being connected to the RAN104, which may be utilizing a NR radio technology, the CN106may also be in communication with another RAN (not shown) employing a GSM, UMTS, CDMA 2000, WiMAX, E-UTRA, or WiFi radio technology.

The CN106shown inFIG.1Cmay include a mobility management entity (MME)162, a serving gateway (SGW)164, and a packet data network (PDN) gateway (PGW)166. While the foregoing elements are depicted as part of the CN106, it will be appreciated that any of these elements may be owned and/or operated by an entity other than the CN operator.

The CN106may facilitate communications with other networks. For example, the CN106may include, or may communicate with, an IP gateway (e.g., an IP multimedia subsystem (IMS) server) that serves as an interface between the CN106and the PSTN108. In addition, the CN106may provide the WTRUs102a,102b,102cwith access to the other networks112, which may include other wired and/or wireless networks that are owned and/or operated by other service providers. In one embodiment, the WTRUs102a,102b,102cmay be connected to a local DN185a,185bthrough the UPF184a,184bvia the N3 interface to the UPF184a,184band an N6 interface between the UPF184a,184band the DN185a,185b.

According to some schemes to which embodiments described herein may be directed, it may be possible to have CSI reference signal (RS) (e.g., non-zero power (NZP) CSI-RS) resources for channel measurements associated with different TRPs, panels, and/or TCI states at the resource level for CSI measurements in NCJT with a single reporting setting. As such, the channel measurement resources (CMRs) corresponding to different TRPs/panels/TCI states may be configured within the same CSI-RS resource set and may have the same number of CSI-RS ports.

Questions may remain whether to use CSI-RSs or CSI interference measurements (IMs) for the interference measurement. Methods for evaluating channel measurements for the different TRPs, panels, and or TCI states, and how to associate the CMR and IMR attributes may be considered.

There may exist a fundamental problem in establishing the CSI measurements for an SDM NCJT based on CMR and interference measurement resources (IMR) as described in Release 16 specifications. It may due to the fact that inter-layer interference from another TRP/panel presented by the other TCI state may not be the same as interference measured using techniques employing CSI-IM or NZP-CSI-RS. Such techniques may result in inaccurate estimation of the channel information.

In SDM NCJT multi-TRP/panel networks, signals may be constrained into the desired subspaces through cooperative precoding at the TRPs/panels. As such, the desired signal may be recovered at the receiver as different layers of the same codeword. Instead of treating the signals from other TRPs/panels as interference, signals may be considered in association with pre-coded signals from the primary TRP/panel. Thus, CSI may be calculated accurately and with no down-estimation.

One question addressed in the following embodiments may be how to measure and report CSI including PMI, RI, CQI, and other metrics to decrease the inter-layer interference for NCJT CSI with a single reporting setting.

Some solutions may provide for an association of precoders in joint CSI measurements for the NCJT with a single report configuration. In some methods, a WTRU may associate and employ the CSI-RS resource signals received from the TRPs/panels in joint CSI measurements for the NCJT with a single report configuration. The WTRU may measure, generate, and report the CSI and in particular the precoder/transmitter filters to be used at the TRPs/panels. As such, the signals transmitted from the TRPs/panels may be received at the WTRU as transmission layers of the same codeword. The terms precoder and transmit filter may be referred to interchangeably herein.

A WTRU may measure and report CSI in a single-TRP/panel mode or in a multi-TRP/panel connection mode, wherein the channel state information (CSI) reporting for each connection mode may include or be configured with one or more of following parameters, rules, or configurations. For example, the configuration for each connection mode may include a CSI report configuration, including one or more of the following: a CSI report quantity (such as a Channel Quality Indicator (CQI), Rank Indicator (RI), Precoding Matrix Indicator (PMI), CSI-RS Resource Indicator (CRI), Layer Indicator (LI), etc); a CSI report type (such as aperiodic, semi persistent, or periodic types); a CSI report codebook configuration (e.g., Type I, Type II, Type II port selection, etc); or a CSI reporting frequency.

The CSI resources to be measured in each connection mode may be configured in a CSI-RS resource set, and may include one or more of the following: a CSI-RS resource for channel measurement (e.g., an NZP CSI-RS resource for channel measurement); a CSI-RS resource for interference measurement (e.g., an NZP CSI-RS resource for interference measurement); or a CSI-IM resource for interference measurement.

The CSI resource to be measured in each connection mode may include NZP CSI-RS resources, which may be associated with one or more of the following parameters: an NZP CSI-RS resource ID; periodicity and offset; QCL Info and TCI-state; or a resource mapping (e.g., number of ports, density, CDM type, etc).

In some solutions, a WTRU may be configured with a single CSI report configuration with at least one CSI-RS resource set, and each CSI-RS resource set may include at least as many CSI-RS resources as the number of the TRPs/panels. In some examples, each CSI resource set may include channel and/or interference measurement resource for each TRP/panel/TCI-state.

In some embodiments, two or more TRPs/panels may coordinate in communicating with a WTRU. A scheme as provided in this disclosure may provide for a two-TRP/panel system hereafter. However, the methodologies, procedures and computations may be expanded to more TRPs/panels, if required.

In some examples, in a two-TRP/panel model, a WTRU may be configured with at least one CSI-RS resource set, where each CSI-RS resource set may be configured with at least two CSI-RS resources. In some examples, each CSI-resource set may include channel and/or interference measurement resources for each TRP/panel/TCI state.

A CSI-RS resource set may include at least a first CSI-RS resource corresponding to the first TCI-state, which may be linked to the first TRP/panel, and at least a second CSI-RS resource corresponding to the second TCI-state, which may be linked to the second TRP/panel. The first CSI-RS resource or resources may be associated with the second CSI-RS resource or resource set.

The CSI-RS resource set corresponding to each TRP/panel may include one or more CSI-RS resources (e.g., NZP CSI-RS resources) for channel measurements. The CSI-RS resource set corresponding to each TRP/panel may include one or more CSI-RS resources (e.g., NZP CSI-RS resources) for interference measurements, where the CSI-RS resource for interference measurements included in the second CSI-RS resource set may be the same as the CSI-RS resource for interference measurements included in the first CSI-RS resource set.

Alternatively, or additionally, a WTRU may receive configuration information indicating multiple CORESETs and/or search spaces. Each CORESET or search space may be configured with, or associated with, a TCI-state that may correspond to a TRP/panel.

A WTRU may be configured with at least one CSI-RS resource set. Each CSI-RS resource set may be configured with a single CSI-RS resource. As such, the same CSI-RS resource set may be used for both TRPs. A WTRU may assume that the CSI-RSs from the same resource set do not collide in time or frequency. In other words, the CSI-RS resources of the same resource set may be orthogonal. When a WTRU monitors a search space, the TCI-state corresponding to the received CSI-RS may be determined based on the TCI-state configured for that search space. As such, the corresponding TRP may be determined.

In some examples, in a multi-TRP/panel system with more than two TRPs/panels, a WTRU may be configured with at least one CSI-RS resource set. The CSI-RS resource set may include at least as many CSI-RS resources as the number of the TRPs/panels, where one or more of the CSI-RS resources may correspond to one of the TCI-states linked to one of the TRPs/panels. The CSI-RS resource or resources corresponding to each TRP/panel may include one or more NZP CSI-RS resources for the channel measurement. The CSI-RS resource or resources corresponding to each TRP/panel may include one or more NZP CSI-RS resources for the interference measurement. The NZP CSI-RS resources for the interference measurement corresponding to different TRPs/panels may be associated pairwise, or in a one-to-one relationship with each other. The NZP CSI-RS resources for the interference measurement corresponding to the CSI-RS resource setting linked to a TCI-state/TRP/panel may be the same as the NZP CSI-RS resources for interference measurements corresponding to the CSI-RS resources linked to another TCI-state/TRP/panel.

In some solutions, a WTRU may receive information triggering or activating the multi-TRP/panel CSI reporting configuration. The WTRU may measure and report the CSI in two successive reporting modes, namely, single-TRP/panel reporting mode and multi-TRP/panel reporting mode.

Some procedures as descried herein may define a two-step CSI measurement process for a MTRP NCJT transmission. In procedures as may be implemented in a WTRU, each step may include two events: reception of CSI-RSs, and reporting of CSI.

In a first step, a first TRP (i.e., TRP1) may be configured to transmit first CSI-RSs (e.g., an NZP CSI-RS) and second TRP (i.e., TRP2) may be configured to transmit second CSI-RSs (e.g., an NZP CSI-RS). A WTRU may receive the first NZP CSI-RSs and the second NZP CSI-RSs from a first and a second TRP according to their corresponding configured TCI information. A WTRU may receive each of the NZP CSI-RSs according to their time/frequency configuration. A WTRU may assume that received NZP CSI-RSs do not collide in time or frequency. In some solutions, a WTRU may assume to have multiple CSI-RS resource configurations where it may use each for a different step. In some solutions, a WTRU may assume to employ a single CSI-RS configuration for all steps. Alternatively, or additionally, a WTRU may receive a single CSI-RS configuration where its content includes information for more than one CSI-RS resource that is required for both steps.

In a second step, a WTRU may report CSI measurements following reception of the NZP CSI-RSs. In some solutions, a WTRU may assume to have multiple CSI measurement content configurations and reporting resources, and it may use each of the multiple measurement content configurations and/or reporting resources for a different step. In some solutions, a WTRU may employ a single CSI measurement content configuration and reporting resources for all steps. Alternatively, or additionally, a WTRU may receive a single configuration for CSI measurement content and reporting resources where its content includes more than one CSI measurement content and reporting resources required for both steps.

FIG.2illustrates an exemplary CSI measurement and reporting process as may be implemented in a system having multiple TRPs. The procedure shown may provide for an association between precoders in CSI measurement for MTRP NCJT with single CSI reporting, consistent with at least some of the methods described above.

The process shown inFIG.2may be outlined as follows. In a first step210of the process, the WTRU may receive CSI-RS transmitted by TRP1and TRP2on the first and second CSI-RS resources respectively. The WTRU may measure the received CSI-RSs. Based on the measurements of the received CSI-RSs, the WTRU may report CSI, which may include information indicating at least a preferred PMI associated with TRP1. At this step, CSI-RSs received from the second TRP may provide a reference for determining the interference present within the channel carrying CSI-RSs from the first TRP, and such information may be necessary for computation of the PMI for TRP1. In other words, the WTRU may use the CSI-RS received from the second TRP to measure channel characteristics to determine the PMI for TRP1.

In a second step220of the process, a WTRU may perform a similar measurement and reporting but for the second TRP. For example, the WTRU may receive CSI-RSs transmitted by TRP1and TRP2, respectively. The WTRU may perform measurements on the received CSI-RSs. Based on the measurements performed on CSI-RS resources for TRP1and TRP2, the WTRU may report CSI, including information indicating at least a preferred PMI for TRP2. Here, the CSI-RS received from TRP1in step220may provide a reference for determining the interference present within the channel carrying CSI-RSs from the second TRP, and such information may be necessary for computation of the PMI for TRP2. In this step, the WTRU, having reported CSI to TRP1(including, e.g., an indication of the preferred PMI) in the previous step210may assume that received CSI-RSs from TRP1are precoded based on the PMI determined for TRP1(e.g., PMI-1). Therefore, in computing the preferred PMI for TRP2, the WTRU may emulate, or account for inter-layer interference based on the measurement of the CSI-RSs from TRP1and associated PMI, determined in step210.

FIG.3AandFIG.3Bare a flow chart and a diagram respectively illustrating an exemplary procedure for multi-TRP CSI estimation and reporting. Some procedures consistent with the procedure shown may be summarized as follows.

FIG.3AandFIG.3Bdescribe a procedure as may be performed by a device, operating in a multi-TRP system, that receives CSI-RSs, and measures and reports CSI. The device operating in the multi-TRP system may be, as described in the following paragraphs, a WTRU, though it should be appreciated that a corresponding procedure may be performed by a base station, a network node, a nodeB, a TRP, an AP, a STA, or a UE.

FIG.3Adescribes generalized steps of the procedure, whileFIG.3Billustrates signaling of the involved system participants performing steps in accordance with the generalized procedure outlined inFIG.3A. As described substantially in paragraphs above, though not depicted inFIG.3AorFIG.3B, a WTRU that performs the described procedure may initially receive configuration information indicating resources for receiving CSI-RSs. The CSI-RS resources may carry CSI-RSs that may be used to calculate channel interference and inter-layer interference between TRPs of the system. The CSI-RSs subsequently received may be different CSI-RSs, and may be orthogonal to each other. The CSI-RSs may be NZP CSI-RSs.

As shown inFIG.3A, at310, a WTRU may receive one or more first CSI-RSs from a first TRP (i.e., TRP1) and a second TRP (i.e., TRP2) for channel measurement and transmit a report including respective first and second CSI quantities to a primary TRP. The first CSI-RSs may be used for measurement or estimation of the channel(s) on which TRP1and TRP2operate. With reference toFIG.3B, the one or more respective first CSI-RSs are shown by elements311and312. The WTRU may measure and determine the respective first CSI quantity for each of TRP1and TRP2based on the respectively received one or more first CSI-RSs. The WTRU may select the primary TRP as either TRP1or TRP2and may select the other TRP as a secondary TRP. The selection may be based on the first CSI quantities of TRP1and TRP2, and the CSI quantity may include one or more of a reference signal received power (RSRP), a signal to interference ratio (SINR), or a channel quality indicator (CQI). A selection based on the first CSI quantities may be further based on a threshold (i.e., a comparison of one or both of CSI quantities to an absolute threshold or a relative threshold). As shown at313inFIG.3B, the report may be transmitted, at least including the determined first CSI quantity for the primary TRP. A device that receives the report (e.g., the primary TRP, a base station or network node, and/or possibly the secondary TRP(s)), may be aware of the selection of the primary TRP. For example, a CSI resource indicator may be included in the report and may be an implicit indication of the selection.

As shown at320, the WTRU may receive one or more second CSI-RSs (321and322, as shown respectively inFIG.3B) from the primary TRP and from the secondary TRP. The CSI-RS321received from the primary TRP may be precoded based on the CSI reported for the primary TRP in step310, and may be used for measurement or estimation of inter-layer interference between TRP1and TRP2. The CSI-RS322received from the secondary TRP may be used for measurement or estimation of the channel(s) on which TRP2operates. The WTRU may determine a second CSI quantity and/or a PMI for the primary TRP based on the one or more second CSI-RSs received from the primary TRP. The WTRU may also determine channel coding parameters (e.g., a null space of a channel matrix) associated with the one or more second CSI-RSs received from the primary TRP. As shown at323, the WTRU may report the second CSI quantity and/or PMI for the primary TRP that was determined based on the received CSI-RS321.

As shown at330, the WTRU may determine a second CSI quantity for the secondary TRP based on the CSI-RS322. The WTRU may determine a PMI (i.e., a preferred PMI) for the secondary TRP based on the determined channel coding parameters (i.e., the determined null space, such that a preferred precoding matrix indicated by the PMI lies within the null space of a channel matrix associated with the primary TRP) and the determined second CSI quantity for the secondary TRP. The WTRU may report the determined PMI for the secondary TRP. The determined PMI may be such that inter-layer interference between the primary TRP and the secondary TRP is minimized.

Further details as to the single-TRP/panel reporting mode are described herein. In the single-TRP/panel reporting mode, a WTRU may measure and report CSI corresponding to the TRPs/panels independently and separately based on CSI-RSs for the channel measurement. The procedure may include one or more of the following procedures or conditions.

For example, a WTRU may receive CSI-RSs from first and second TRPs. The WTRU may use the received CSI-RSs for channel measurement for the TRPs/panels. The CSI-RSs for channel measurement may be different and orthogonal. A WTRU may measure the CSI for each TRP/panel separately. A WTRU may select one of the TRPs/panels as the primary TRP/panel and the other TRP/panel as the secondary TRP/panel. A WTRU may measure the CSI quantities corresponding to the primary TRP/panel, including the RI and PMI, and may report the CSI corresponding to the primary TRP/panel to a network node (e.g., a TRP, base station, nodeB, or another device).

As for the selection of the TRPs/panels to be primary or secondary, a WTRU may select the TRPs/panels based on different sets of parameters. In some examples, a WTRU may be configured by a base station, nodeB, or other network node (e.g., through RRC messaging, a MAC CE, or any logical equivalent message) with an indication of which TRP/panel should be selected as the primary TRP and which TRP(s) or panel(s) should be selected as a secondary TRP. In some examples, a WTRU may select the primary TRP/panel based on the higher L1-RSRP, L1-SINR, CQI, and/or according to a predetermined/configured threshold.

Further details as to the multi-TRP/panel reporting mode are described herein. In a procedure involving two or more steps, this mode may follow the single-TRP/panel reporting mode. Based on the CSI reported by the WTRU operating in the single-TRP/panel reporting mode, a network node (e.g., a TRP, base station, nodeB, or another device) may determine a precoder/transmitter filter to be used for the transmission layers corresponding to the primary TRP/panel. The network node may use this precoder/transmitter filter (or send configuration information indicating to use the determined precoder/transmitter filter) for the transmission of CSI-RSs from the primary TRP/panel in the multi-TRP/panel reporting mode.

In the multi-TRP/panel reporting mode, the procedure may include one or more of the following conditions or procedures. For example, a WTRU may receive precoded CSI-RSs (e.g., NZP CSI-RSs) from the primary TRP/panel, where the NZP CSI-RS is precoded based on the PMI reported previously and during the single-TRP/panel reporting mode. The received precoded CSI-RS may be used to measure interference between the primary TRP/panel and a secondary TRP/panel. Based on, for example, release 16 technical specifications, a WTRU may assume the CSI-RS configured for interference measurement corresponds to a transmission layer.

A WTRU may also receive CSI-RSs, to be used for channel measurement, from the secondary TRP/panel.

A WTRU may determine the precoder/transmitter filter to be used at the first and the second TRP/panel. The WTRU may measure the CSI and determine, specifically, the PMI for the primary TRP/panel based on the corresponding CSI-RS resource for the interference measurement. The WTRU may measure the CSI for secondary TRP/panel based on the corresponding CSI-RS to be used for the channel measurement. The WTRU may select the PMI for the secondary TRP/panel based on a null space of the precoded CSI-RS received from the primary TRP/panel. In the process of measuring the CSI for the secondary TRP/panel, the WTRU may consider the precoded signals received from the primary TRP/panel as another layer of the same codeword of a NCJT.

In other words, a WTRU may consider the signals received from the primary TRP/panel as the basis to calculate the CSI/PMI for the secondary TRP/panel, as if they were transmitted from the secondary TRP/panel. The WTRU may determine a PMI linked for the secondary TRP/panel so that it is consistent with a TCI-state of the secondary TRP/panel, oriented in line with beams' carrying signals from the secondary TRP/panel, and orthogonal with signals received from the primary TRP/panel. The formulation may be provided as follows, such that it is based on a null-space of the precoding matrix selected based on the precoded CSI-RS received from the first TRP/panel.

At the conclusion of procedures performed in the multi-TRP/panel reporting mode, a network node (e.g., a TRP (such as one the primary and/or secondary TRPs), a base station, a nodeB, or another device) may have access to both single-TRP/panel and multi-TRP/panel CSI from the WTRU. As such, switching at the network node between the single and multi-TRP/panel schemes may be accomplished dynamically and based on the provided CSI reports.

In some solutions, a multi-TRP/panel reporting mode may be used independent of a single-TRP/panel reporting mode. For example, a WTRU may determine a PMI for CSI-RSs for TRP1(i.e., PMI-1) in a multi-TRP/panel reporting mode, and then determine a PMI for the CSI-RSs for TRP2(i.e., PMI-2) with emulated interference that is based on the CSI-RSs for TRP1and its associated PMI. One or more of following conditions or procedures may apply.

For example, a WTRU may report both PMI-1and PMI-2in a single CSI report with associated CQI and RI. One or more PMI-1may be determined or selected by a WTRU. For example, the WTRU may select and/or determine the best-M (e.g., M>=1) PMI-1that may provide a highest observed CQI value for a given channel condition measured from CSI-RS received from TRP-1. When more than one PMI-1is selected, determined, or used, the WTRU may also select/determine PMI-2for each PMI-1value; As a result, M sets of PMI-1and PMI-2values may be selected or determined. The WTRU may report the M sets of PMI values (PMI-1, PMI-2) and their associated CQI and/or RI. When a single PMI-1is selected, determined, or used, the WTRU may select or determine a single PMI-2based on the determined PMI-1. The Mth value may be determined based on at least one of following: a number of TRPs/panels configured for a Multi-TRP/panel reporting mode; a number of CSI-RS resources for channel measurement in the associated CSI resource setting; a configuration information provided in a message from a network node (e.g., an RRC message, a MAC-CE, or another logically equivalent message); a reporting channel capacity (e.g., number of bits available for the reporting); a channel quality metric (e.g., SINR range, RSRP range, CQI, RI, etc.); or a WTRU capability.

In some solutions, one or more multi-TRP/panel reporting modes may be used, configured, or defined. For example, a first multi-TRP/panel reporting mode (e.g., a Type-1multi-TRP/panel reporting mode) may be based on the CSI reporting per TRP/panel without the successive PMI determination/selection for the emulated interference (e.g., inter-layer interference). A second multi-TRP/panel reporting (e.g., Type-2multi-TRP/panel reporting mode) may be based on the CSI reporting for multiple TRP/panels with the successive PMI determination/selection. The type of multi-TRP/panel reporting mode may be determined based on at least one of following: a WTRU capability; configuration information received from a network node (e.g., an RRC message, MAC-CE, or another logical equivalent); or an indication in a triggering DCI (e.g., for aperiodic/semi-persistent reporting).

Formulas as may be used in embodiments throughout are described. In order to calculate the optimal precoders linked to a secondary TRP/panel, the precoder may be associated with the null space of the primary TRP/panel.

A procedure for the determination of the secondary PMI in the multi-TRP/panel reporting mode may be carried out in accordance with one or more of the following rules or criteria. For example, the procedure may consider the TCI-state associated with the secondary TRP/panel, and may involve the computation of one or more corresponding channel coding parameters (e.g, HPand HSas channel matrices, along with other related variables) from the primary and secondary TRPs/panels, respectively. Theoretically, zero inter-layer interference may require that the precoding for the secondary TRP/panel lie in the null space of the HP. The rank of the HPmay be defined as RP=rank(HP). The singular value decomposition (SVD) may be defined by: HP=UPΣP[VP(1)VP(0)]Hwhere VP(1)holds the first RPright singular vectors and VP(0)holds the last (nT−RP) right singular vectors, and where nTis the number of CSI-RS ports (antennas) at TRPs/panels. VP(0)may form an orthogonal basis for the null space of HP, and its columns may be the candidates for the precoding matrix of the secondary TRP/panel. Finally, the WTRU may select the PMI (e.g., based on channel coding parameters including channel matrices and/or null spaces) to minimize the mismatch between the precoder and the secondary TRP/panel channel matrix and/or minimize the mismatch between the precoder and the null space of the primary TRP/panel channel matrix.

Some solutions may involve the joint selection of antenna ports associated with CSI-RSs based on UL/DL angle reciprocity. For example, in some methods, a WTRU may employ CSI-RS port selection in joint CSI measurements for the NCJT in a single TRP/panel reporting mode, in which the CSI-RSs may be associated. The WTRU may measure the CSI based on precoded CSI-RSs received from the multiple TRPs/panels. Consistent with, for example, release 16 technical specifications, a WTRU may assume the CSI-RSs may be used to measure interference between different transmission layers. The WTRU may jointly select and report the most favorable port-pair from the TRPs/panels.

A WTRU may measure and report the selection of antenna ports associated with the CSI port selection, wherein the CSI for each connection mode may include or be configured with one or more configurations, parameters, or resources. For example, the CSI may be provided consistent with a CSI Report Configuration that includes information indicating one or more of the following: a CSI report quantity, e.g., Channel Quality Indicator (CQI), Rank Indicator (RI), Precoding Matrix Indicator (PMI), Layer Indicator (LI), etc.; a CSI report type, e.g., aperiodic, semi persistent, or periodic report types; a CSI report codebook configuration (defined, for example, as TypeII-PortSelection or TypeII-PortSelection-r16); or a CSI report frequency.

The CSI may be reported for resources of a CSI-RS resource set, including one or more of the following CSI resources: an NZP CSI-RS resource for channel measurement; an NZP CSI-RS resource for interference measurement; or a CSI-IM resource for interference measurement.

The CSI may be reported for CSI-RS resources, including one or more of the following: an NZP CSI-RS resource ID; a periodicity and offset; QCL Info and TCI-state; or a resource mapping, such as a number of ports, density, CDM type, etc.

In some solutions, a network node (e.g., a TRP, a base station, a nodeB, or another device) may precode CSI-RSs for interference measurement based on UL measurements corresponding to the resources for transmission of the CSI-RS. For example, the WTRU may transmit sounding reference signals, which may be received by the network node. The network node may measure the SRS received from the WTRU and the angel reciprocity of the UL and DL may be exploited to determine how to precode CSI-RSs that are to be subsequently transmitted.

In a two-TRP/panel model, the WTRU may be configured with a single CSI report configuration, with at least one CSI-RS resource set, wherein each CSI-RS resource set includes at least two resources for transmission of CSI-RSs (e.g., for channel and interference measurements per each TRP/panel/TCI state). The CSI-RS resource set may include first CSI-RS resources corresponding to the first TCI-state linked to the first TRP/panel and second CSI-RS resources corresponding to the second TCI-state linked to the second TRP/panel. The CSI-RS resources corresponding to the first TCI-state and the second TCI-state may be associated with each other. The CSI-RS resources corresponding to each TRP/panel may include one or more NZP CSI-RS resources for the channel measurement. The CSI-RS resources corresponding to each TRP/panel may include one or more NZP CSI-RS resource for the interference measurement.

The CSI-RS resources for channel measurement and interference measurement corresponding to the TRPs/panels may be paired resource-wise with each other. In other words, the CSI-RS resource for the channel measurement for the first TRP/panel may be configured to be the same as the CSI-RS resource for the interference measurement of for second TRP/panel. Likewise, the CSI-RS resource for the channel measurement of the second TRP/panel may be configured to be the same as the CSI-RS resource for the interference measurement of the first TRP/panel.

FIG.4depicts an example procedure for CSI reporting that exploits the angle reciprocity from SRS measurements.

Although not depicted inFIG.4, it should be appreciated that a WTRU may receive information triggering or an activating a multi-TRP/panel non-PMI port selection report configuration. The procedure to measure and report the CSI as illustrated inFIG.4may include one or more of the following conditions, steps, or procedures. For example, a WTRU may receive precoded CSI-RSs (e.g., NZP CSI-RSs) from the TRPs/panels. The CSI-RS resource used to carry CSI-RSs for the channel measurement from the first TRP/panel may be configured as a CSI-RS resource for carrying CSI-RSs for the interference measurement from the second TRP/panel. Likewise, the CSI-RS resource carrying CSI-RSs for the channel measurement from the second TRP/panel may be configured as the CSI-RS resource carrying CSI-RSs for the interference measurement from the first TRP/panel. The association between the CSI-RS resource may be configured based on the TCI-states linked to the TRPs/panels.

The procedure to measure and report the CSI as provided inFIG.4may involve the WTRU measuring the CSI for all pairs of the ports corresponding to the precoded CSI-RSs received from the TRPs/panels.

The procedure to measure and report the CSI as provided inFIG.4may involve the WTRU reporting the most favorable pair of the ports corresponding to the precoded CSI-RSs received from the TRPs/panels.

As for the selection of the most favorable pair, a WTRU may select the pairs based on different sets of parameters. In some examples, the WTRU may select the favorable pair based on the a signal quality measurement (e.g., L1-RSRP, L1-SINR, CQI) and according to a predetermined/configured threshold.

The solution shown inFIG.4may be an exemplary two-step CSI measurement process for a M-TRP NCJT transmission. The two step process may be outlined as follows. In a first step410, a WTRU may transmit at least one sounding reference signal (SRS) using configured SRS resources. If a WTRU embarks on a single SRS transmission event, it may use only a single spatial filter that may be defined by the configured spatial relation information. However, if it transmits more than one SRS as shown in step410by signals411and412, it may use different spatial filters (i.e., different spatial relation information that may correspond to different TRPs.

In some solutions, a WTRU may use a specific subset of SRS resources or SRS resource sets for the SRS transmissions in the first step. A WTRU may use the specific subset to trigger CSI-RS transmissions from TRPs, shown in step420and described in further detail herein. In some solutions, if SRS-based CSI acquisition for M-TRP architectures is activated, a WTRU may always expect reception of CSI-RS from TRPs at a pre-determined time and frequency resources. For example, the WTRU may expect to receive CSI-RS in a slot offset from the transmission of the SRS (e.g., slot n+4, where n is the slot in which the WTRU transmits one or more SRSs)t. Alternatively, or additionally, a WTRU may determine whether requested CSI-RS transmission as depicted in step420is available implicitly or explicitly. For example, a WTRU may monitor a dedicated CORESET or search space. On the other hand, a WTRU may receive a DCI or MAC CE, or another logical equivalent, including information indicating the transmission of the requested CSI-RS implicitly or explicitly.

In the second step of the process420, based on the performed measurements on received NZP CSI-RSs from the first and second TRP (shown inFIG.4by elements421and422, a WTRU may report CSI information indicating at least its preferred PMIs for each TRP. At this step, CSI-RSs received from one TRP may be considered a basis for determining inter-layer interference needed for computation of PMI of the other TRP.

In some solutions, the second step420may include two or events: the WTRU receiving a CSI-RS, and the WTRU reporting CSI.

In some solutions, in the reception of CSI-RS, a WTRU may receive an indication of a first set and a second set of NZP CSI-RS resources from a first and a second TRP according to their corresponding configured TCI information. A WTRU may receive NZP CSI-RSs from each TRP according to their time/frequency configuration. A WTRU may assume that the received NZP CSI-RSs do not collide in time or frequency. In some solutions, a WTRU may receive multiple CSI-RS resource configurations, which may correspond to different TRPs, from one of the TRPs. For example, the WTRU may receive information indicating the CSI-RS resource configuration via DCI from the primary TRP. In some solutions, a WTRU may receive multiple CSI-RS resource configurations related to each TRP from their corresponding TRP, e.g., through multiple DCI.

In some solutions, for WTRU reporting of CSI, a WTRU may report CSI measurements following reception of NZP CSI-RS resources. In some solutions, a WTRU may have multiple CSI measurement content configurations and reporting resources, and it may use each set of CSI measurement content configurations and reporting resources for a different TRP. In some solutions, a WTRU may employ a single CSI measurement content configuration and reporting resources for all TRPs. Alternatively, or additionally, a WTRU may receive information providing a single configuration for CSI measurement content and reporting resources. The configuration may indicate more than one type of CSI measurement content to be reported and reporting resources required for both TRPs.

Solutions involving dynamic switching between single and multiple TRPs/panel CSI reporting modes are described herein. In some solutions, a WTRU may dynamically switch a CSI reporting type between multiple CSI reporting types (e.g., between single TRP/panel CSI reporting, or multi-TRP/panel CSI reporting).

In some examples, CSI reporting for a single TRP/panel mode may include one or more of the following: a measurement based on a single CSI-RS resource; a single Rank Indicator (RI); a single CSI-RS Resource Indicator (CRI); a single quality indicator (e.g., one or more of Channel Quality Indicator (CQI), L1-RSRP and L1-SINR); a single set of Precoding Matrix Indicators (PMI), e.g., wideband w1and wideband w2, wideband w1and subband w2s, or similar; or a single Layer Indicator (LI).

In some examples, CSI reporting for multi-TRP/panel may include one or more of the following: a measurement based on multiple CSI-RS resources; multiple RIs; multiple CRIs; multiple quality indicators (e.g., one or more of Channel Quality Indicator (CQI), L1-RSRP and L1-SINR); multiple sets of PMIs e.g., wideband w1and wideband w2, wideband w1and subband w2s, or similar; or multiple Ls.

In some solutions, a WTRU may determine a CSI reporting type based on one or more configurations or parameters.

A WTRU may determine a CSI reporting type based on configuration information received from a network node (e.g., a TRP, a base station, a nodeB, or another device). For example, the WTRU may receive configuration information (e.g., in a CSI reporting configuration) indicating a CSI type. The WTRU may receive information in a CSI-RS resource/resource set configuration indicating the CSI type. The WTRU may receive configuration information for multiple associated CSI-RS resources/resource sets that indicates the CSI type. If the WTRU receives a CSI-RS that does not have an associated CSI-RS resource, the WTRU may determine a first CSI reporting type (e.g., whether to perform CSI reporting for a single TRP/panel). If the WTRU receives a CSI-RS with one or more associated CSI-RS resources, the WTRU may determine a second CSI reporting type (e.g., to perform CSI reporting for multiple TRPs/panels).

In some examples, the WTRU may receive configuration information indicating a CSI type by receiving multiple associated CSI reporting configurations. For example, if the WTRU receives a CSI reporting configuration without an associated CSI reporting configuration, the WTRU may determine a first CSI reporting type (e.g., CSI reporting for a single TRP/panel). If the WTRU receives a CSI report config with one or more associated CSI reporting configuration, the WTRU may determine a second CSI reporting type (e.g., CSI reporting for multiple TRPs/panels).

A WTRU may determine a CSI reporting type based on a measurement and determined quality. For example, the WTRU may receive multiple CSI-RS configurations (e.g., indicating CSI-RS resources or resource sets). Based on the multiple CSI-RS configurations, the WTRU may measure a first CSI-RS. If the measured (and determined) quality of the first CSI-RS is higher than a threshold, the WTRU may determine a first CSI reporting type (e.g., CSI reporting for single TRP/panel). If the WTRU measured (and determined) a quality of the first CSI-RS configuration that is lower than (or equal to) the threshold, the WTRU may determine a second CSI reporting type, measure, and determine a joint quality based on the multiple CSI-RS configurations. The first CSI-RS configuration may indicate a CSI-RS resource/resource set for CSI reporting and additional CSI-RS resource/resource set configurations for CSI reporting type determinations.

In some examples, the WTRU may receive multiple CSI-RS configurations (e.g., resources or resource sets). Based on the multiple CSI-RS configurations, the WTRU may measure first CSI-RSs and second CSI-RSs. If the difference between a first quality of the first CSI-RSs and a second quality of the second CSI-RSs is higher than a threshold, the WTRU may determine a first CSI reporting type (e.g., CSI reporting for single TRP/panel). If the difference is lower than (or equal to) the threshold, the WTRU may determine a second CSI reporting type, measure and determine a joint quality based on the multiple CSI-RS configurations.

For example, the WTRU may receive multiple CSI-RS configurations (e.g., indicating resources or resource sets). Based on the multiple CSI-RS configurations, the WTRU may measure multiple CSI-RSs. If the measured (and determined) quality (e.g., averaged values) of the multiple CSI-RSs is higher than a threshold, the WTRU may determine a first CSI reporting type (e.g., CSI reporting for single TRP/panel). If the WTRU measured (and determined) a quality that is lower than (or equal to) the threshold, the WTRU may determine a second CSI reporting type, measure and determine a joint quality based on the multiple CSI-RSs.

A quality metric may include one or more of rank, CQI, SINR, RSRP, RSRQ, pathloss, location information, environment type (e.g., indoor or outdoor), amount of interference (e.g., interference quality indicator (IQI), P-MPR, or another metric.

If the WTRU supports multiple types of quality for the determination, the WTRU may receive a type of the multiple types from a network node (e.g., a TRP, base station, nodeB, or another device) for example via an RRC configuration per WTRU, CSI reporting configuration, CSI-RS configuration or another logical equivalent.

One or more thresholds may be used in the determination based on one or more of following: predefined values; indicated values (e.g., provided via RRC, MAC CE, DCI or any other logical equivalent); or WTRU-determined values (e.g., based on WTRU implementation or measurements). The term CSI reporting configuration may be interchangeably used with the term CSI-RS configuration but consistent with the described embodiments.

Rules for determination of overlapped PDCCHs in multi-TRP systems are described herein. PDDCH repetition by multi-TRP transmission is one technique that may be used to enhance PDCCH reliability.

FIG.5illustrates an example of a basic operation for PDCCH reliability enhancement carried out via repetition. For enhanced PDCCH reliability with repetition, encoding and/or rate matching may be based on one repetition, and the same coded bits may be repeated for another repetition. The number of linked PDCCH candidates may be, for example, two, and each repetition may have the same number of CCEs and coded bits and correspond to the same DCI payload. For PDCCH repetition, a number (e.g., two) of linked PDCCH candidates may be received in two different CORESETs configured in two different search spaces. As shown inFIG.5, two PDCCH candidates, i.e., PDCCH1(1) and PDCCH1(2), may be replicas of each other and may be transmitted from two different TRPs for enhanced reliability. Two search space sets510and520associated with corresponding CORESETs may be linked together, and the linkage between the two may be configured at a WTRU by messaging received from a network node (e.g., the linkage between the PDCCH candidates may be indicated by RRC message, or another logical equivalent). The two SS sets510and520may have the same aggregation level (AL) and the same candidate index and have the same number of candidates for each AL.

Further, the two linked SS sets510and520may be configured with the same SS set type (USS/CSS), the same DCI formats for monitoring, the same periodicity and offset (e.g., as indicated in messaging from a network node containing the monitoringSlotPeriodicityAndOffset element), and the same duration. It may be assumed that the two SS sets510and520may have the same number of monitoring occasions within a slot, where the n-th monitoring occasion of one SS set is linked to the n-th monitoring occasion of the other SS set.

In some embodiments, when two SS sets are linked for PDCCH repetition, they may not contain individual PDCCH candidates. For configuration of individual PDCCH candidates, a different SS set may be configured by the network (e.g., via downlink transmissions, RRC messages, MAC CEs or other logical equivalents), and it may be possible for one of the configured CORESETs in a SS for linked PDCCH to be shared by the search space of an individual PDCCH, i.e., a non-linked PDCCH.

FIG.6AandFIG.6Billustrate another example operation for PDCCH enhancement through two different cases in which PDCCH candidates are linked. As shown in both case (a) and case (b), respectfully illustrated byFIG.6AandFIG.6B, one of the linked PDCCH candidates, PDCCH1, uses the same set of CCEs as an individual (unlinked) PDCCH candidate, PDCCH2, and both are associated with the same DCI size, scrambling, and CORESET. From the decoding perspective, depending on a WTRU receiver's processing and blind decoding (BD) capability, different outcomes may be expected.

As shown inFIG.6AandFIG.6B, r1and r2may be extracted signals from corresponding CORESETs in a first search space, SS #1(shown by element610), and a second search space, SS #2(shown by element620), respectively. For a WTRU with three-BD capability, in general, the WTRU may attempt to perform blind decoding three times as follows. In a first instance, the WTRU may attempt decoding of r1; in a second instance, the WTRU may attempt decoding of r2; and in a third instance, the WTRU may attempt decoding of a soft-combination of signals r1and r2

Assuming the above order for decoding attempts and a given relative power, there may be no clear difference in decoding performance for the cases (a) or (b) shown inFIG.6AandFIG.6B. However, knowing which repetition of PDCCH1is overlapped with the individual PDCCH may provide better performance and opportunities for power saving.

For a WTRU with a two-BD capability, in general, the WTRU may attempt to perform blind decoding twice as follows. In a first instance, the WTRU may attempt decoding of r1; in a second instance, the WTRU may attempt decoding of r2. Assuming the above order for decoding attempts and a given relative power, there may be no difference in decoding performance between the cases (a), shown inFIG.6A, or (b), shown inFIG.6B.

For a WTRU with two-BD and soft-combining capabilities, in general, the WTRU may attempt to perform blind decoding twice as follows. In a first instance, the WTRU may attempt decoding of r1; in a second instance, the WTRU may attempt blind decoding of a soft-combination of signals r1and r2. Unlike the two previous cases, there may be a difference in decoding performance of the above order between cases (a) and (b) inFIG.6Aand inFIG.6B. For instance, adopting the above order of attempts for case (b) may result in worse performance than for case (a).

In some embodiments, a WTRU may prioritize decoding of the extracted candidates, i.e., r1, r2, and/or the soft-combined signals r1and r2based on some information, e.g., a relative signal level, or whether the PDCCHs are overlapped, etc. In some solutions, based on one or more rules as described herein in further detail, a WTRU may determine which of the extracted signals, i.e., r1or r2, carries the overlapped PDCCHs.

For example, a WTRU may determine whether a PDCCH candidate location contains only one of the linked PDCCH candidates based on the search space index. In some solutions, a WTRU may assume that an individual PDCCH may be received only in a search space with the highest (or lowest) ID.

A WTRU may determine whether a PDCCH candidate location contains only one of the linked PDCCH candidates based on a time reference. In some solutions, a WTRU may assume that an individual PDCCH transmission may be received only in a search space that starts earlier (or later) in time than another search space. Alternatively, or additionally, a WTRU may assume that an individual PDCCH transmission may be received only in a CORESET that starts earlier (or later) in time than another CORESET.

A WTRU may determine whether a PDCCH candidate location contains only one of the linked PDCCH candidates based on the CORESET index. In some solutions, a WTRU may assume that an individual PDCCH may be received only in a CORESET with a highest (or lowest) ID.

A WTRU may determine whether a PDCCH candidate location contains only one of the linked PDCCH candidates based on the configured TCI state or associated CORESET pool index (i.e., an associated CORESETpoolIndex element indicated in a message from a network node) of a search space. In some solutions, a WTRU may assume that an individual PDCCH may be received only in a CORESET or search space associated with CORESETpoolIndex=0 (or 1). Alternatively, or additionally, a WTRU may assume that an individual PDCCH transmission may be received only in a CORESET or search space associated with a TCI that is Quasi-Co-Located (QCL-ed) with a specific RS, e.g., a Synchronization Signal Block (SSB).

If a WTRU does not have the capability for simultaneous multi-beam reception, a WTRU may assume that the overlapped PDCCHs, i.e., PDCCH1(2) and the individual PDCCH2in case (a) ofFIG.6Aare both transmitted from a same TRP, e.g., sharing a same TCI. Therefore, a same QCL Type D may be used for reception of both PDCCH transmissions. Alternatively, or additionally, in the same example, if a WTRU does not have capability for simultaneous multi-beam reception, a WTRU may use at least one of the following for determination of the QCL Type D parameters. For example, the WTRU may use the QCL Type D parameter of the PDCCH, i.e., PDCCH1(2) or the individual PDCCH2, that corresponds to the stronger link, e.g., highest RSRP; the QCL Type D parameter of the linked PDCCH, i.e., PDCCH1(2); the QCL Type D parameter of the individual PDCCH; or the QCL Type D of the PDCCH candidate with higher search space priority.

In some solutions, a WTRU with simultaneous multi-beam reception capability may also consider at least one the above conditions.