Reporting of measurements on downlink reference signals

Abstract

There is provided techniques for reporting measurements on a plurality of downlink reference signals to a network node. A method is performed by a UE. The method comprises obtaining configuration. The method comprises performing measurements on the plurality of downlink reference signals according to the configuration and with respect to at least one CSI reporting quantity. The method comprises selecting only a subset of the plurality of downlink reference signals for which the measurements are to be reported. The subset of the plurality of downlink reference signals is selected based on an evaluation criterion for the measurements with respect to the CSI reporting quantity. The method comprises sending a report of the measurements to the network node. A measurement portion of the report comprises the measurements for only the selected subset of the plurality of downlink reference signals.

Description

[0001]REPORTING OF MEASUREMENTS ON DOWNLINK REFERENCE SIGNALS TECHNICAL FIELD Embodiments presented herein relate to a method, a user equipment, a computer program, and a computer program product for reporting measurements on a plurality of downlink reference signals to a network node. Embodiments presented herein further relate to a method, a network node, a computer program, and a computer program product for receiving reporting of measurements on a plurality of downlink reference signals from the user equipment. BACKGROUND In communications networks, there may be a challenge to obtain good performance and capacity for a given communications protocol, its parameters and the physical environment in which the communications network is deployed. For example, in Release 18 of the New Radio (NR) suite of telecommunication standards, coherent joint downlink transmission (CJT) from multiple transmission and reception points (TRPs) is supported by extending the enhanced type II codebook (as specified in Release 16) and the further enhanced type II port selection codebook (as specified in Release 17) across multiple TRPs. In general terms, in CJT, all layers are transmitted from the multiple TRPs used for CJT. Reference is here made to the communication network 100 of Fig.1 where twolayers (denoted “Layers 1 & 2”) are transmitted in a signal ^^ = [^^1 ^^2]^^ from two TRPs 130-1, 130-2 towardsone and the same user equipment (UE) 110. In further detail, the data symbols of the two layers are transmittedfrom the two TRPs 130-1, 130-2 by different precoding matrices ^^ = [^^1 ^^2]^^being applied at TRP 130-1 and TRP 130-2, respectively. The two precoders are designed such that for each layer, the signals received from the two TRPs 130-1, 130-2 are phase aligned at the UE 110 and thus, can be coherently combined, yielding areceived signal ^^ = 2 √^^1 ^^1^^1^^ + 2 √^^1 ^^1^^1^^ + ^^ at the UE 110, where ^^1 and ^^2 are the receivedpowers, ^^1and ^^2represent the propagation channels, and ^^ is a noise vector. Some of the challenges in supporting CJT will be summarized next. Firstly, propagation delays between different TRPs and a UE can be quite different. These large delay differences, or offsets, could result in a large frequency selective composite channel, i.e., where the channel amplitude and phase vary rapidly across frequency. In existing procedures for providing channel state information (CSI) feedback from the UE, the UE reports a precoding matrix per subband. The subband size can vary between 2 resource blocks (RBs) to 32 RBs. Table 1 shows phase variation within a subband for different subband sizes with one microsecond (µs) delay difference between two TRPs. Subband size [RB] Subband size [MHz] Delay [µs] Phase change [deg] 2 0.36 1 130 4 0.72 1 259 8 1.44 1 518 16 2.88 1 1037 32 5.76 1 2074 Table 1: Example showing phase variation over a subband for a 1 µs delay offset. It can be seen that even with a subband size of 2 RBs, the phase variation exceeds 130 degrees. In this respect, for constructive combining of two signals, their phase difference should be less than 90 degrees. Therefore, with current subband sizes and per subband CSI feedback, signals from multiple TRPs cannot be coherently combined with even a comparatively small delay difference. Secondly, even though a same nominal transmit frequency may be used at multiple TRPs, due to local oscillator stability, there will be some actual transmit frequency difference, or offsets, between the multiple TRPs. In this respect, the maximum transmit frequency error for a base station are specified in the technical specification 3GPP TS 38.104 “NR; Base Station (BS) radio transmission and reception” version 18.5.0. For the most stringent requirement (+ / -0.05 ppm), there will be some residual frequency errors. These frequency errors means that the phase of a signal will change over time. In Fig.2 is schematically illustrated a communication network 200 as in Fig.1 with two TRPs 230-1, 230-2 transmitting the same signal ^^(^^) to a UE 210. The signal ^^(^^) is multiplied by two co-phasing / pre-compensation coefficients ^^1and ^^2at the two TRPs 230-1, 230-2 before being transmitted to the UE 210. The effective propagation channels from the two TRPs 230-1, 230-2 to the UE 210, including transmitter and receiver circuitries and antenna patterns associated with the two TRPs 230-1, 230-2, are denoted by ℎ1and ℎ2, respectively. Further, ^^1and ^^2are the transmit frequencies and ^^1and ^^2are the random initial phases at the two TRPs 230-1, 230-2. Further, ^^ is the propagation delay (including possible timing offsets) difference between the two TRPs 230-1, 230-2. The composite signal as received at the UE 210 can be expressed as: For narrow-band signal and when the delay ^^ is small, the signal envelope doesn’t change much, i.e., ^^(^^ −^^) ≈ ^^(^^). Thus, Equation (1) can be revised as:^^(^^) ≈ ℎ ^^(2^^^^ ^^+^^ )1^^1^^(^^)^^ 1 1 + ℎ2^^2^^(^^)^^^^(2^^^^2(^^−^^)+^^2)(2) or To coherently combine the signals from the two TRPs 230-1, 230-2, the following co-phasing / pre-compensation coefficients can be used: where ∠(^^)denotes the angle of a complex variable ^^. The resulted composite signal, when the above co- phasing, or pre-compensation coefficients, in Equations (4a)-(4b) are applied, is then: Alternatively, the co-phasing / pre-compensation coefficients can be expressed as follows: ^^1 = 1 (6^^) The resulted composite signal, when the above co-phasing / pre-compensation coefficients in Equations (6a)-(6b) are applied, can then be expressed as: The above applies also in case of multiple antenna ports are deployed in each of the TRPs 230-1, 230-2. In that case, additional precoding or beamforming is applied to ^^(^^), where ^^(^^)is data associated with a multiple-input multiple-output (MIMO) layer of a physical downlink shared channel (PDSCH) or a demodulation reference signal (DMRS). For a given MIMO layer, the signal received from TRP 230-1 would be ^^1^^1^^1^^(^^)^^^^(2^^^^1^^+^^1), where is a ^^1-by-^^ channel matrix, ^^1is an ^^1-by-1 precoding vector associated with the corresponding MIMO layer, where ^^1is the number of antenna ports deployed at TRP 230-1, and ^^ is the number of receive antennas at the UE 210. Similarly, for the given MIMO layer, the signal received from TRP 230-2 would be ^^2^^2^^2^^(^^)^^^^(2^^^^2(^^−^^)+^^2), where ^^2is a ^^2-by-^^ channel matrix, where ^^2is an ^^2-by- 1 precoding vector associated with the corresponding MIMO layer, and where ^^2is the number of antenna ports deployed at TRP 230-2. CJT from multiple TRPs is possible for the case of multiple PDSCH layers. For R PDSCH layers, each TRP will use a corresponding ^^1-by-^^ precoding matrix where each column in the precoding matrix corresponds to one of the ^^ MIMO layers. In the case of ^^ PDSCH layers, the transmitted signal ^^(^^) will consists of ^^ different symbols (i.e., one symbol corresponding to each of the ^^ PDSCH layers). For CJT, it is envisioned that precoding matrices, or vectors, and the co-phasing / pre-compensation coefficients {^^1,^^2} can be reported by the UE to the network. In order to derive the co-phasing / pre-compensation coefficients ^^1and ^^2, one or more of the following need to be reported from the UE to the network: transmit frequency associated with a TRP, transmit frequency difference between two TRPs, delay associated with a TRP, delay difference between two TRPs. In summary, as disclosed above, with downlink CJT, the same data, or layers, are transmitted from multiple cooperative TRPs and the signals from multiple TRPs are coherently combined at the UE. This is made possible due to proper joint antenna precoding at the TRPs. This can be achieved by CSI feedback where the UE measures the channels associated with the TRPs and reports back a joint precoder across the multiple TRPs such that the precoded signals from these TRPs are phase-aligned when they reach the UE. Alternatively, this can also be achieved by reciprocity-based downlink transmission, where knowledge of the channel is obtained in the network via measurements on uplink reference signals, such as sounding reference signals (SRSs) sent by the UE and received by the TRPs. As further disclosed above, there are a number of challenges in CJT. For instance, the cooperated TRPs may not be perfectly synchronized in time, such timing misalignment, together with the propagation delay differences between the different TRPs, may result in a large frequency selective composite channel, i.e., the channel amplitude and / or phase vary rapidly across frequency. In addition, although the same nominal transmit frequency may be considered for the cooperative TRPs, due to local oscillator stability, there may be some actual transmit frequency drifts for different TRPs. In such cases, the UE needs to measure the delay, the frequency and / or the phase differences between the TRPs and report them back to the network, so that the network can compensate for them. Additionally, depending on the considered deployment, such delay / frequency / phase difference reports may result in high reporting overhead. Hence, there is still a need for improved reporting of channel state information, especially with respect to the reporting overhead. SUMMARY An object of embodiments herein is to provide reporting of channel state information with reduced reporting overhead compared to the above. According to a first aspect there is presented a method for reporting measurements on a plurality of downlink reference signals to a network node. The method is performed by a UE. The method comprises obtaining configuration of the plurality of downlink reference signals and configuration of reporting the measurements on the plurality of downlink reference signals to the network node. The configuration of reporting the measurements comprises at least one CSI reporting quantity. The method comprises performing measurements on the plurality of downlink reference signals according to the configuration of the plurality of downlink reference signals and with respect to the at least one CSI reporting quantity. The method comprises selecting only a subset of the plurality of downlink reference signals for which the measurements are to be reported. The subset of the plurality of downlink reference signals is selected based on an evaluation criterion for the measurements with respect to the CSI reporting quantity. The method comprises sending a report of the measurements according to the configuration of reporting the measurements to the network node. A measurement portion of the report comprises the measurements for only the selected subset of the plurality of downlink reference signals. According to a second aspect there is presented a UE for reporting measurements on a plurality of downlink reference signals to a network node. The UE comprises processing circuitry. The processing circuitry is configured to cause the UE to obtain configuration of the plurality of downlink reference signals and configuration of reporting the measurements on the plurality of downlink reference signals to the network node. The configuration of reporting the measurements comprises at least one CSI reporting quantity. The processing circuitry is configured to cause the UE to perform measurements on the plurality of downlink reference signals according to the configuration of the plurality of downlink reference signals and with respect to the at least one CSI reporting quantity. The processing circuitry is configured to cause the UE to select only a subset of the plurality of downlink reference signals for which the measurements are to be reported. The subset of the plurality of downlink reference signals is selected based on an evaluation criterion for the measurements with respect to the CSI reporting quantity. The processing circuitry is configured to cause the UE to send a report of the measurements according to the configuration of reporting the measurements to the network node. A measurement portion of the report comprises the measurements for only the selected subset of the plurality of downlink reference signals. According to a third aspect there is presented a computer program for reporting measurements on a plurality of downlink reference signals to a network node. The computer program comprises computer code which, when run on processing circuitry of a UE, causes the UE to perform actions. One action comprises the UE to obtain configuration of the plurality of downlink reference signals and configuration of reporting the measurements on the plurality of downlink reference signals to the network node. The configuration of reporting the measurements comprises at least one CSI reporting quantity. One action comprises the UE to perform measurements on the plurality of downlink reference signals according to the configuration of the plurality of downlink reference signals and with respect to the at least one CSI reporting quantity. One action comprises the UE to select only a subset of the plurality of downlink reference signals for which the measurements are to be reported. The subset of the plurality of downlink reference signals is selected based on an evaluation criterion for the measurements with respect to the CSI reporting quantity. One action comprises the UE to send a report of the measurements according to the configuration of reporting the measurements to the network node. A measurement portion of the report comprises the measurements for only the selected subset of the plurality of downlink reference signals. According to a fourth aspect there is presented a method for receiving reporting of measurements on a plurality of downlink reference signals from a UE wherein the method is performed by a network node. The method comprises providing configuration of the plurality of downlink reference signals and configuration of reporting the measurements on the plurality of downlink reference signals to the UE. The configuration of reporting the measurements comprises at least one CSI reporting quantity. The method comprises initiating transmission of the plurality of downlink reference signals. The method comprises receiving a report of the measurements with respect to at least one CSI reporting quantity from the UE. A measurement portion of the report comprises only a subset of the measurements. According to a fifth aspect there is presented a network node for receiving reporting of measurements on a plurality of downlink reference signals from a UE the network node comprises processing circuitry. The processing circuitry is configured to cause the network node to provide configuration of the plurality of downlink reference signals and configuration of reporting the measurements on the plurality of downlink reference signals to the UE. The configuration of reporting the measurements comprises at least one CSI reporting quantity. The processing circuitry is configured to cause the network node to initiate transmission of the plurality of downlink reference signals. The processing circuitry is configured to cause the network node to receive a report of the measurements with respect to at least one CSI reporting quantity from the UE. A measurement portion of the report comprises only a subset of the measurements. According to a sixth aspect there is presented a computer program for receiving reporting of measurements on a plurality of downlink reference signals from a UE. The computer program comprises computer code which, when run on processing circuitry of a network node, causes the network node to perform actions. One action comprises the network node to provide configuration of the plurality of downlink reference signals and configuration of reporting the measurements on the plurality of downlink reference signals to the UE. The configuration of reporting the measurements comprises at least one CSI reporting quantity. One action comprises the network node to initiate transmission of the plurality of downlink reference signals. One action comprises the network node to receive a report of the measurements with respect to at least one CSI reporting quantity from the UE. A measurement portion of the report comprises only a subset of the measurements. According to a seventh aspect there is presented a computer program product comprising a computer program according to at least one of the third aspect and the sixth aspect and a computer readable storage medium on which the computer program is stored. The computer readable storage medium could be a non-transitory computer readable storage medium. All the above listed aspects are based on that the UE needs to report measurements for only the selected subset of the plurality of downlink reference signals. Advantageously, this enables the reporting overhead of the reporting of the channel state information to be reduced compared to the above. Further advantageously, based on that the UE is using an evaluation criterion for selecting for which downlink reference signals the measurements are to be reported, this enables the quality of delay, frequency and / or phase difference, or offset, compensation to be improved. This is, because of the evaluation criterion, the UE will not report back measurements which may result in inaccurate CSI reporting quantities. Advantageously, reducing the number of measurements received by the network node also reduces the computational complexity with respect to processing the measurements at the network node. For example, this could reduce the computational complexity needed for the aforementioned compensation performed by the network node based on the measurements. Other objectives, features and advantages of the enclosed embodiments will be apparent from the following detailed disclosure, from the attached dependent claims as well as from the drawings. Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a / an / the element, apparatus, component, means, module, step, etc." are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, module, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated. BRIEF DESCRIPTION OF THE DRAWINGS The inventive concept is now described, by way of example, with reference to the accompanying drawings, in which: Figs.1, 2, and 3 are schematic diagrams illustrating a communication network according to embodiments; Figs.4, 5, and 6 are flowcharts of methods according to embodiments; Fig.7 is a schematic diagram showing structural units of a UE according to an embodiment; Fig.8 is a schematic diagram showing structural units of a network node according to an embodiment; Fig.9 shows one example of a computer program product comprising computer readable means according to an embodiment. DETAILED DESCRIPTION The inventive concept will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments of the inventive concept are shown. This inventive concept may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive concept to those skilled in the art. Like numbers refer to like elements throughout the description. Any step or feature illustrated by dashed lines should be regarded as optional. As disclosed above, there still a need for improved reporting of channel state information, especially with respect to the reporting overhead. In this respect, the inventors of the present disclosure have realized that, in some scenarios, the UE may not need to report all the measurements. However, how to reduce the reporting overhead of measurement quantities with respect to delay, frequency and / or phase offsets is an open problem. Hereinafter will therefore be disclosed techniques for reducing the overhead of inter-TRP measurement reports, enabling efficient CJT. As will be disclosed in more detail below, based on the measurements, quality-of-service (QoS) requirements, etc. the UE determines, via some evaluation criterion for the measurements with respect to the CSI reporting quantity, which subset of TRPs is useful for CJT and / or which subset of measurements should be reported back to the network. Accordingly, the UE selects only a subset of TRPs and / or measurements for reporting to the network. Reference is here made to the communication network 300 of Fig.3. The communication network 300 comprises TRPs 330-1:330-6 and a network node 320. The TRPs 330-1:330-6 are operatively connected to, and controlled by, the network node 320. The network node could be a gNB or any evolution thereof. The TRPs 330-1:330-6 are configured to communicate with a UE 310 and thus provide network access for the UE 310. It is noted that although some terms associated with a certain telecommunications standard is used, the embodiments as disclosed hereinafter are not limited to any particular telecommunications standard, or release with respect to 3GPP. Although six TRPs are illustrated in Fig.3 it is generally assumed that there are at least two TRPs in the communication network 300. It is here noted that the TRPs 330-1:330-6 generally are configured to communicate with a plurality of such UEs 310. The UE 310 could be any of: a portable wireless device, mobile station, mobile phone, handset, wireless local loop phone, smartphone, laptop computer, tablet computer, wireless modem, wireless sensor device, network equipped vehicle, or the like.In further detail, in Fig.3 is illustrated an example where there are ^^ = 6 (non-zero power) downlink referencesignal (DL-RS) resource sets configured. Each DL-RS resource set could comprise one or more CSI-RS, tracking reference signal (TRS), downlink synchronization signal, or the like. Further, the plurality of DL-RSs might be aperiodically, semi-persistently or periodically transmitted. Each DL-RS resource set is used by a respective TRP.In this example, the ^^^^ℎ (^^ = 1, 2, 3, 4, 5, 6) DL-RS is transmitted from the ^^^^ℎ TRP. The propagation delayassociated with each TRP is also shown in the figure where the propagation delay corresponding to the ^^^^ℎTRP is denoted as The received power at the UE 310 associated with each DL-RS transmitted from the respective TRP is also shown. The received power at the UE 310 corresponding to the ^^^^ℎDL-RS transmitted from the ^^^^ℎTRP is denoted as ^^^^. Reference is now made to Fig.4 illustrating a method for reporting measurements on a plurality of DL-RSs to a network node 320, 800 as performed by the UE 310, 700 according to an embodiment. S102: The UE 310 obtains configuration of the plurality of DL-RSs and configuration of reporting the measurements on the plurality of DL-RSs to the network node 320. The configuration of reporting the measurements comprising at least one CSI reporting quantity. S104: The UE 310 performs measurements on the plurality of DL-RSs according to the configuration of the plurality of DL-RSs and with respect to the at least one CSI reporting quantity. S106: The UE 310 selects only a subset of the plurality of DL-RSs for which the measurements are to be reported. The subset of the plurality of DL-RSs is selected based on an evaluation criterion for the measurements with respect to the CSI reporting quantity. S108: The UE 310 sends a report of the measurements according to the configuration of reporting the measurements to the network node 320. A measurement portion of the report comprises the measurements for only the selected subset of the plurality of DL-RSs. Embodiments relating to further details of reporting measurements on a plurality of DL-RSs to a network node 320 as performed by the UE 310 will now be disclosed with continued reference to Fig.4. Further aspects of the UE 310 obtaining the configuration of the plurality of DL-RSs in step S102 will be disclosed next. The plurality of DL-RSs might belong to resource sets of at least two TRPs 330-1:330-6. Therefore, in some embodiments, according to the configuration of the plurality of DL-RSs, the plurality of DL-RSs belong to DL-RS resource sets of at least two of the TRPs 330-1:330-6, and the measurements are reported for less than all theTRPs 330-1:330-6. In further detail, the of DL-RSs may be a plurality of NZP CSI-RS resource sets (e.g., ^^ > 1different NZP CSI-RS resource sets). Each of the plurality of NZP CSI-RS resource sets contain at least one NZP CSI-RS resource. In some aspects, each of the ^^ different NZP CSI-RS resource sets is configured with a higher layer parameter indicating that the NZP CSI-RS resources in each of the ^^ NZP CSI-RS resource sets belong to a TRS. Each of the ^^ NZP CSI-RS resource sets corresponds to a respective TRP and the ^^ NZP CSI-RS resource sets might represent ^^ TRSs. In an alternative aspect, the ^^ NZP CSI-RS resource sets are be configured as ^^ TRS resource sets. In some aspects, the CSI reporting quantity and evaluation criterion are specified in the configuration. That is, in some embodiments, the configuration of reporting the measurements on the plurality of DL-RSs indicates the at least one CSI reporting quantity and the evaluation criterion. In some embodiments, the configuration of the plurality of DL-RSs and the configuration of reporting the measurements on the plurality of DL-RSs are received from the network node 320. In some aspects, the DL-RS resource sets are configured as part of a plurality of CSI-ResourceConfig information elements (IEs) as defined in the technical specification 3GPP TS 38.331, “NR; Radio Resource Control (RRC); Protocol specification”, version 17.6.0. For example, a parameter that points to the ID of a CSI-ResourceConfig IE that contains at least one of the different DL-RS resource sets can be configured in a CSI reporting configuration. Hence, in some embodiments, the configuration of the plurality of DL-RSs is provided in at least one CSI- ResourceConfig information element. In other aspects, the DL-RS resource sets are configured as part of CSI-AssociatedReportConfigInfo in the CSI- AperiodicTriggerStateList IE as defined in the aforementioned technical specification 3GPP TS 38.331. Hence, in some embodiments, the configuration of the plurality of DL-RSs is provided as part of CSI- AssociatedReportConfigInfo in at least one CSI-AperiodicTriggerStateList information element. Further aspects of the UE 310 obtaining the configuration of reporting the measurements on the plurality of DL- RSs to the network node 320 in step S102 will be disclosed next. The configured DL-RSs are used as channel measurement resources for the CSI reporting configuration. In some aspects, the UE 310 receives either an explicit or an implicit indication of whether the UE 310 shall select a subset of TRPs and / or DL-RSs for reporting among all configured DL-RSs. Therefore, in some embodiments, the configuration of reporting the measurements comprises an indication for the UE 310 to report the measurements for a subset of the plurality of DL-RSs. In some aspects, the UE 310 is configured with the maximum number of delay differences, frequency differences and / or phase differences, or offsets, to be reported by the UE 310, may be configured to the UE 310 by the network node 320 in the CSI reporting configuration. Therefore, in some embodiments, the configuration of reporting the measurements comprises an indication of how many measurements on the plurality of DL-RSs the UE 310 is to report to the network node 320. Further aspects of the UE 310 performing the measurements on the plurality of DL-RSs in step S104 will be disclosed next. In step S104 the UE 310 performs measurements on all DL-RSs that are configured as measurement resources in the CSI reporting configuration configured for the one or more CSI reporting quantity of interest. In this respect, there could be different CSI reporting quantities, for example delays, frequencies, phases, or corresponding differences, or offsets. In particular, in some non-limiting examples, the CSI reporting quantity pertains to at least one of: delay, frequency, phase, delay offset, frequency offset, phase offset of the plurality of DL-RSs. In some aspects, the UE measures and determines the received signal power on each of the plurality of DL-RSs that are configured as channel measurement resources in the CSI reporting configuration configured for reporting the one or more CSI reporting quantity of interest. Referring to the example in Fig.3, the UE 310 can determine^^^^ corresponding to each TRS ^^ (^^ = 1, 2, 3, 4, 5, 6) in this step. In some aspects, the ^^^^ corresponding to TRS^^ is determined by averaging the received power across all the plurality of DL-RSs corresponding to TRS ^^. Finally, along with the received power measurement, the UE measures the one or more CSI reporting quantity of interest according to the received configuration. In some aspects, the measurements are computed with respect to a reference DL-RS. That is, in some embodiments, the measurements are reported with respect to measurements on one of the plurality of DL-RSs as reference. In this way, delay difference(s), frequency difference(s), and / or phase difference(s), or offset(s) may be computed with respect to a reference DL-RS. In some aspects, if the reference DL-RS has not been indicated by the network node 320, for a given threshold, the UE 310 selects the appropriate reference DL-RS such that the report overhead is minimized (e.g., the DL-RS with highest received power, lowest delay, or lowest frequency error, etc.). In other aspects, the subset of DL-RSs for which the measurements are to be reported and the reference DL-RS are determined jointly. Further aspects of the UE 310 selecting only the subset of the plurality of DL-RSs in step S106 will be disclosed next. As disclosed in step S106, the subset of the plurality of DL-RSs is selected based on an evaluation criterion for the measurements with respect to the CSI reporting quantity. Further aspects of the evaluation criterion will now be disclosed. In some aspects, the evaluation criterion is based on the UE 310 selecting, for reporting, a subset of DL-RSs that is useful for CJT. That is, in some embodiments, the evaluation criterion pertains to measurements for coherent joint downlink transmission. In some non-limiting examples, the evaluation criterion pertains to selection of measurements based on at least one of: quality-of-service requirements for the UE 310, capabilities of the UE 310, a reference signal received power (RSRP) threshold, a signal to interference plus noise ratio (SINR) threshold. For example, the decision whether a measurement should be reported or not can be based on one or a combination of: the values of the measured delay difference(s), frequency difference(s) and / or phase difference(s), or offset(s), the report configuration received in step 102, the measured received power of the plurality of DL-RSs, the UE’s capability in delay difference(s), frequency difference(s) and / or phase difference(s) compensation, quality-of-service requirements, the number of configured DL-RSs, number of TRPs, the UE mobility, position, speed, moving trajectory, operation frequency, selected reference DL-RS, etc. There can be different ways in which the listed quantities can be used by the UE 310. In some examples, only the plurality of DL-RSs with received power (e.g., represented by RSRP or SINR) higher than the threshold are selected for reporting. That is, in some embodiments, according to the evaluation criterion, only the plurality of DL-RSs for which the measurements have a received power higher than a received power threshold are to be reported. Here, for instance, if the received signal power from a given DL-RS is low, it may not be useful for CJT and also its estimated delay / frequency / phase may be inaccurate. Thus, the UE 310 might not include the measurement for that given DL-RS in the selected subset of reported DL-RSs. In some examples, only the plurality of DL-RSs with delay, frequency and / or phase offsets higher than a first threshold and / or lower than a second threshold are selected to be reported. That is, in some embodiments, according to the evaluation criterion, only the plurality of DL-RSs for which the measurements have a delay, frequency, phase, delay offset, frequency offset, and / or phase offset which is higher than a first threshold and / or lower than a second threshold are to be reported. In some aspects, the delay difference(s), the frequency difference(s) and / or phase difference(s), or offset(s) of different DL-RSs are compared with different first and / or second thresholds, where only the plurality of DL-RSs with delay, frequency and / or phase difference(s), or offset(s), higher than the first threshold and / or lower than the second threshold are selected to be reported back to the network node 320. In some aspects, the different thresholds to decide whether the measurement of a given DL-RS should be reported or not are pre-defined, and, for example, provided in a 3GPP specification. In other aspects, the network node 320 informs the UE 310 about the different thresholds. In yet further aspects, the thresholds are determined by the UE itself and where the UE 130 may inform the network node 320 about the selected thresholds in the report in step S108. That is, in some embodiments, any threshold used by the UE 310 for selecting the subset of the plurality of DL-RSs for which the measurements are to be reported is preconfigured in the UE 310, received from the network node 320, or computed by the UE 310 itself. In some aspects, the UE 310 selects the subset of DL-RS for measurements which are expected to be accurate. That is, in some embodiments, the evaluation criterion pertains to selection of measurements estimated by the UE 310 to have an accuracy above an accuracy threshold. In this respect, the UE 310 might compare the measurements to some configuration received from the network node 320, e.g., in terms of threshold value, where a measurement is regarded as inaccurate if the received power falls below the configured threshold value, etc. Further aspects of the UE 310 sending the report of the measurements in step S108 will be disclosed next. In some aspects, the UE 310 informs the network node 320 about which reported values are associated with which DL-RSs. Therefore, in some embodiments, the report further comprises an indication of the subset of the plurality of DL-RSs for the measurements. In some aspects, the UE 310 informs the network node 320 about the considered thresholds for selecting the subset of measurements. Therefore in some embodiments, the report further comprises an indication of any threshold used by the UE 310 for selecting the subset of the plurality of DL-RSs for which the measurements are to be reported. Reference is now made to Fig.5 illustrating a method for receiving reporting of measurements on a plurality of DL-RSs from a UE 310, 700 as performed by the network node 320, 800 according to an embodiment. S202: The network node 320 provides configuration of the plurality of DL-RSs and configuration of reporting the measurements on the plurality of DL-RSs to the UE 310. The configuration of reporting the measurements comprising at least one CSI reporting quantity. S204: The network node 320 initiates transmission of the plurality of DL-RSs. S206: The network node 320 receives a report of the measurements with respect to at least one CSI reporting quantity from the UE 310. A measurement portion of the report comprises only a subset of the measurements. Hence, the network node 320 receives reporting of measurements on less than all the configured DL-RSs Embodiments relating to further details of receiving reporting of measurements on a plurality of DL-RSs from a UE 310, 700 as performed by the network node 320, 800 will now be disclosed with continued reference to Fig.5. Further aspects of the network node 320 providing the configuration of the plurality of DL-RSs in step S202 will be disclosed next. As disclosed above, each DL-RS set might belong to a respective TRP 330-1:330-6. In particular, in some embodiments, the plurality of DL-RSs belong to different DL-RS sets, where each of the DL-RS sets is associated with a respective TRP 330-1:330-6, and the transmission of the plurality of DL-RSs is initiated by the network node 320 providing the DL-RS sets to the TRPs 330-1:330-6 together with transmission instructions. As further disclosed above, in some embodiments, according to the configuration of the plurality of DL-RSs, the plurality of DL-RSs belong to DL-RS resource sets of at least two TRPs 330-1:330-6, and the report comprises measurements for less than all the TRPs 330-1:330-6. As disclosed above, DL-RS resource sets may be configured as part of a plurality of CSI-ResourceConfig information elements. That is, in some embodiments, the configuration of the plurality of DL-RSs is provided in at least one CSI-ResourceConfig information element. As further disclosed above, alternatively, the DL-RS resource sets might be configured as part of CSI-AssociatedReportConfigInfo in the CSI-AperiodicTriggerStateList IE. That is, in some embodiments, the configuration of the plurality of DL-RSs is provided as part of CSI- AssociatedReportConfigInfo in at least one CSI-AperiodicTriggerStateList information element. Further aspects of the network node 320 providing the configuration of reporting the measurements on the plurality of DL-RSs in step S202 will be disclosed next. As disclosed above, the CSI reporting quantity and evaluation criterion might be specified in the configuration. That is, in some embodiments, the configuration of reporting the measurements on the plurality of DL-RSs indicates the at least one CSI reporting quantity and the evaluation criterion. As disclosed above, in some non-limiting examples, the CSI reporting quantity pertains to at least one of: delay, frequency, phase, delay offset, frequency offset, phase offset of the plurality of DL-RSs. As disclosed above, the UE 310 might receive either an explicit or an implicit indication of whether or not the UE 310 shall select a subset of TRPs and / or DL-RSs for reporting among all configured DL-RSs. That is, in some embodiments, the configuration of reporting the measurements comprises an indication for the UE 310 to report the measurements for a subset of the plurality of DL-RSs. As disclosed above, the UE 310 might be configured with the maximum number of delay differences, frequency differences and / or phase differences, or offsets, to be reported by the UE 310. that is, in some embodiments, the configuration of reporting the measurements comprises an indication of how many measurements on the plurality of DL-RSs the UE 310 is to report to the network node 320. Further aspects of the network node 320 receiving reporting of measurements in step S206 will be disclosed next. As disclosed above, the UE 310 might inform the network node 320 which of the reported values that are associated with which DL-RSs. Therefore, in some embodiments, the report further comprises an indication of a subset of the plurality of DL-RSs for the measurements. As disclosed above, the UE 310 might inform the network node 320 about the considered thresholds for selecting the subset of measurements. Therefore, in some embodiments, the report further comprises an indication of any threshold used by the UE 310 for selecting the subset of the plurality of DL-RSs for which the measurements are reported. As disclosed above, the measurements might be computed with respect to a reference DL-RS. Therefore, in some embodiments, the measurements are reported with respect to measurements on one of the plurality of DL- RSs as reference. One particular embodiment for reporting of measurements on a plurality of DL-RSs based on at least some of the above disclosed embodiments will now be disclosed in detail with reference to the flowchart of Fig.6. S301: The UE receives, from the network node, configurations of a plurality of DL-RSs to be used for measuring one or more CSI reporting quantities of interest. S302: The UE receives, from the network node, configuration for a CSI reporting configuration for the CSI reporting quantity of interest, optionally also including which evaluation criterion to use. S303: The UE performs measurements on all DL-RSs that are configured as measurement resources in the CSI reporting configuration configured for reporting the CSI reporting quantity of interest. S304: The UE, based on the evaluation criterion, selects only a subset of DL-RSs and their CSI reporting quantity of interest to be reported back to the network. Four examples of evaluation criteria used by the UE to select the subset of DL-RSs to be reported based on different setups of the TRPs 310-1:310-6 in the communication network 300 will be disclosed next. Here, forsimplicity of notation, TRP 310-^^ is referred to as TRP^^, where ^^ = 1, 2, … , 6.Example 1: Consider a setup in where TRP1, TRP2, TRP3, TRP4 and TRP5 are quite time-synchronized butTRP6 has large delay offset compared to the other TRPs. That is, − ^^4 ≤^^thr, ^^1 − ^^thr but ^^1 − ^^6 ≥ ^^thr where ^^thr is a pre-defined threshold. In such a case, instead ofreporting all delay differences − ^^6, the UE only reports the delaydifference − ^^6 and then the network node knows that − ^^5 are small and donot need compensation. The same principle can be applied for the case with other CSI quantities, such as reporting with respect to frequency offset and / or phase offset. For instance, representing the frequencies ofdifferent TRPs by ^^^^ , ^^ = 1, … ,6, the UE may only select − ^^6 and ^^1 − ^^3 to be reported back, if they areunderstood to require compensation.Example 2: Consider a setup where ^^1 − ^^2 > CP, ^^1 − ^^3 > CP, ^^1 − ^^4 > CP, but −^^6 < ^^^^, where ^^^^ is the length of the cyclic prefix. In such a case, instead of reporting all delay differences,the UE only selects the delay difference − ^^5, ^^1 − ^^6 to be reported.Example 3: Consider a setup where ^^1 > ^^thr, ^^2 > ^^thr, but ^^3, ^^4, ^^5, ^^6 ≤ ^^thr where ^^thr is a receivedpower threshold. In such a case, instead of reporting all delay differences, the UE only reports the delaydifference ^^ − ^^2 if one of the TRP1 or TRP2 is the reference TRP. Otherwise, for instance, ^^ and ^^2 or theirrelative value compared to another reference TRP can be selected to be reported. Example 4: Consider a setup where TRP1-TRP3 have a delay spread smaller than the length of the cyclic prefix, but TRP4-TRP6 have delay spread larger than the length of the cyclic prefix. In this case, the UE only selects to report the propagation delay for TRP1-TRP3. S305: The UE reports only the CSI reporting quantity of interest for the measurements of the subset of DL-RSs selected in Step 304. In case the UE 310 informs the network node 320 about which reported values are associated with which DL- RSs, considering Example 1 or Example 2 above, the UE 310 might inform the network node 320 that thereported value τ1 − τ6 is associated with TRP6.In accordance with the above, the plurality of DL-RSs with negligible delay, frequency and / or phase difference(s), or offset(s), compared to a predefined threshold value can be excluded from the report. In further accordance with the above, the plurality of DL-RSs with large delay differences (e.g., larger than the length of the cyclic prefix), large delay spread, large frequency drift and / or low received power can be excluded from the report. That is, the length of the report will thus be variable and change depending on the number of reported measurements. Alternative ways of how the UE 310 might report the measurements for only the selected subset of the plurality of DL-RSs will be disclosed next. In some aspect, the associated measurements of the plurality of DL-RSs with negligible delay, frequency and / or phase difference, compared to the reference DL-RS, are indicated by a pre-defined value (e.g., zero, or a value close to zero). Here, if the UE 310 understands that the delay / frequency / phase difference between two DL-RSs is less than a threshold (it is non-zero but not much that needs pre-compensation at the network side), the UE 310 excludes the delay / frequency / phase difference, or offset(s), between those two DL-RSs from the report to the network node 320. The UE 310 still performs measurement on all configured DL-RSs. In another aspect, the plurality of DL-RSs with large delay differences (e.g., larger than the length of the cyclic prefix), large frequency drift and / or low received power are indicated by a default, or, pre-defined, indication (e.g., “not a number”, “invalid”, or “out of range”, etc.). In some aspects, this default, or pre-defined, indication is specified in a 3GPP specification. In summary, the herein disclosed embodiments not only reduce the reporting overhead but also decreases the computational complexity at the network node 320 because only the plurality of DL-RSs that are really useful for CJT and their associated delay, frequency and / or phase differences that can be properly pre-compensated are reported by the UE 310. Fig.7 schematically illustrates, in terms of a number of structural units, the components of a UE 700 according to an embodiment. Processing circuitry 710 is provided using any combination of one or more of a suitable central processing unit (CPU), multiprocessor, microcontroller, digital signal processor (DSP), etc., capable of executing software instructions stored in a computer program product 910a (as in Fig.9), e.g. in the form of a storage medium 730. The processing circuitry 710 may further be provided as at least one application specific integrated circuit (ASIC), or field programmable gate array (FPGA). Particularly, the processing circuitry 710 is configured to cause the UE 700 to perform a set of operations, or steps, as disclosed above. For example, the storage medium 730 may store the set of operations, and the processing circuitry 710 may be configured to retrieve the set of operations from the storage medium 730 to cause the UE 700 to perform the set of operations. The set of operations may be provided as a set of executable instructions. Thus the processing circuitry 710 is thereby arranged to execute methods as herein disclosed. The storage medium 730 may also comprise persistent storage, which, for example, can be any single one or combination of magnetic memory, optical memory, solid state memory or even remotely mounted memory. The UE 700 may further comprise a communications (comm.) interface 720 for communications with other entities, functions, nodes, and devices, such as TRPs and network nodes. As such the communications interface 720 may comprise one or more transmitters and receivers, comprising analogue and digital components. The processing circuitry 710 controls the general operation of the UE 700 e.g. by sending data and control signals to the communications interface 720 and the storage medium 730, by receiving data and reports from the communications interface 720, and by retrieving data and instructions from the storage medium 730. Other components, as well as the related functionality, of the UE 700 are omitted in order not to obscure the concepts presented herein. Fig.8 schematically illustrates, in terms of a number of structural units, the components of a network node 800 according to an embodiment. Processing circuitry 810 is provided using any combination of one or more of a suitable central processing unit (CPU), multiprocessor, microcontroller, digital signal processor (DSP), etc., capable of executing software instructions stored in a computer program product 910b (as in Fig.9), e.g. in the form of a storage medium 830. The processing circuitry 810 may further be provided as at least one application specific integrated circuit (ASIC), or field programmable gate array (FPGA). Particularly, the processing circuitry 810 is configured to cause the network node 800 to perform a set of operations, or steps, as disclosed above. For example, the storage medium 830 may store the set of operations, and the processing circuitry 810 may be configured to retrieve the set of operations from the storage medium 830 to cause the network node 800 to perform the set of operations. The set of operations may be provided as a set of executable instructions. Thus the processing circuitry 810 is thereby arranged to execute methods as herein disclosed. The storage medium 830 may also comprise persistent storage, which, for example, can be any single one or combination of magnetic memory, optical memory, solid state memory or even remotely mounted memory. The network node 800 may further comprise a communications interface 820 for communications with other entities, functions, nodes, and devices, such as UEs and network nodes. As such the communications interface 820 may comprise one or more transmitters and receivers, comprising analogue and digital components. The processing circuitry 810 controls the general operation of the network node 800 e.g. by sending data and control signals to the communications interface 820 and the storage medium 830, by receiving data and reports from the communications interface 820, and by retrieving data and instructions from the storage medium 830. Other components, as well as the related functionality, of the network node 800 are omitted in order not to obscure the concepts presented herein. The network node 320, 800 may be provided as a standalone device or as a part of at least one further device. For example, the network node 320, 800 may be provided in a node of a (radio) access network or in a node of a core network. Alternatively, functionality of the network node 320, 800 may be distributed between at least two devices, or nodes. These at least two nodes, or devices, may either be part of the same network part (such as the (radio) access network or the core network) or may be spread between at least two such network parts. In general terms, instructions that are required to be performed in real time may be performed in a device, or node, operatively closer to the cell than instructions that are not required to be performed in real time. Thus, a first portion of the instructions performed by the network node 320, 800 may be executed in a first device, and a second portion of the instructions performed by the network node 320, 800 may be executed in a second device; the herein disclosed embodiments are not limited to any particular number of devices on which the instructions performed by the network node 320, 800 may be executed. Hence, the methods according to the herein disclosed embodiments are suitable to be performed by a network node 320, 800 residing in a cloud computational environment. Therefore, although a single processing circuitry 810 is illustrated in Fig.8 the processing circuitry 810 may be distributed among a plurality of devices, or nodes. The same applies to the computer program 920b of Fig.9. Fig.9 shows one example of a computer program product 910a, 910b comprising computer readable means 930. On this computer readable means 930, a computer program 920a can be stored, which computer program 920a can cause the processing circuitry 710 and thereto operatively coupled entities and devices, such as the communications interface 720 and the storage medium 730, to execute methods according to embodiments described herein. The computer program 920a and / or computer program product 910a may thus provide means for performing any steps of the UE 310, 700 as herein disclosed. On this computer readable means 930, a computer program 920b can be stored, which computer program 920b can cause the processing circuitry 810 and thereto operatively coupled entities and devices, such as the communications interface 820 and the storage medium 830, to execute methods according to embodiments described herein. The computer program 920b and / or computer program product 910b may thus provide means for performing any steps of the network node 320, 800 as herein disclosed. In the example of Fig.9, the computer program product 910a, 910b is illustrated as an optical disc, such as a CD (compact disc) or a DVD (digital versatile disc) or a Blu-Ray disc. The computer program product 910a, 910b could also be embodied as a memory, such as a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM), or an electrically erasable programmable read-only memory (EEPROM) and more particularly as a non-volatile storage medium of a device in an external memory such as a USB (Universal Serial Bus) memory or a Flash memory, such as a compact Flash memory. Thus, while the computer program 920a, 920b is here schematically shown as a track on the depicted optical disk, the computer program 920a, 920b can be stored in any way which is suitable for the computer program product 910a, 910b. The inventive concept has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the inventive concept, as defined by the appended patent claims.

Claims

CLAIMS 1. A method for reporting measurements on a plurality of downlink reference signals to a network node (320, 800), wherein the method is performed by a user equipment, UE (310, 700), and wherein the method comprises: obtaining (S102) configuration of the plurality of downlink reference signals and configuration of reporting the measurements on the plurality of downlink reference signals to the network node (320, 800), wherein the configuration of reporting the measurements comprising at least one channel state information, CSI, reporting quantity; performing (S104) measurements on the plurality of downlink reference signals according to the configuration of the plurality of downlink reference signals and with respect to the at least one CSI reporting quantity; selecting (S106) only a subset of the plurality of downlink reference signals for which the measurements are to be reported, wherein the subset of the plurality of downlink reference signals is selected based on an evaluation criterion for the measurements with respect to the CSI reporting quantity; and sending (S108) a report of the measurements according to the configuration of reporting the measurements to the network node (320, 800), wherein a measurement portion of the report comprises the measurements for only the selected subset of the plurality of downlink reference signals.

2. The method according to claim 1, wherein, according to the configuration of the plurality of downlink reference signals, the plurality of downlink reference signals belong to downlink reference signal resource sets of at least two transmission and reception points, TRPs (330-1:330-6), and wherein the measurements are reported for less than all the TRPs associated to the plurality of downlink reference signals (330-1:330-6).

3. The method according to claim 1 or 2, wherein the configuration of reporting the measurements on the plurality of downlink reference signals further indicates the evaluation criterion.

4. The method according to any of claims 1 to 3, wherein the configuration of the plurality of downlink reference signals and the configuration of reporting the measurements on the plurality of downlink reference signals are received from the network node (320, 800).

5. The method according to claim 4, wherein the configuration of the plurality of downlink reference signals is provided in at least one CSI-ResourceConfig information element.

6. The method according to claim 4, wherein the configuration of the plurality of downlink reference signals is provided as part of CSI-AssociatedReportConfigInfo in at least one CSI-AperiodicTriggerStateList information element.

7. The method according to any preceding claim, wherein the configuration of reporting the measurements comprises an indication for the UE (310, 700) to report the measurements for a subset of the plurality of downlink reference signals.

8. The method according to any preceding claim, wherein the configuration of reporting the measurements comprises an indication of how many measurements on the plurality of downlink reference signals the UE (310, 700) is to report to the network node (320, 800).

9. The method according to any preceding claim, wherein the CSI reporting quantity pertains to at least one of: delay, frequency, phase, delay offset, frequency offset, phase offset of the plurality of downlink reference signals.

10. The method according to any preceding claim, wherein the measurements are reported with respect to measurements on one of the plurality of downlink reference signals as reference.

11. The method according to any preceding claim, wherein the evaluation criterion pertains to measurements for coherent joint downlink transmission.

12. The method according to any preceding claim, wherein the evaluation criterion pertains to selection of measurements estimated by the UE (310, 700) to have an accuracy above an accuracy threshold.

13. The method according to any preceding claim, wherein the evaluation criterion pertains to selection of measurements based on at least one of: quality of service requirements for the UE (310, 700), capabilities of the UE (310, 700), a reference signal received power threshold, a reference signal to interference plus noise ratio threshold.

14. The method according to any preceding claim, wherein, according to the evaluation criterion, only the plurality of downlink reference signals for which the measurements have a received power higher than a received power threshold are to be reported.

15. The method according to any preceding claim, wherein, according to the evaluation criterion, only the plurality of downlink reference signals for which the measurements have a delay, frequency, phase, delay offset, frequency offset, and / or phase offset which is higher than a first threshold and / or lower than a second threshold are to be reported.

16. The method according to any preceding claim, wherein any threshold used by the UE (310, 700) for selecting the subset of the plurality of downlink reference signals for which the measurements are to be reported is preconfigured in the UE (310, 700), received from the network node (320, 800), or computed by the UE (310, 700) itself.

17. The method according to any preceding claim, wherein the report further comprises an indication of the subset of the plurality of downlink reference signals for the measurements.

18. The method according to any preceding claim, wherein the report further comprises an indication of any threshold used by the UE (310, 700) for selecting the subset of the plurality of downlink reference signals for which the measurements are to be reported.

19. A method for receiving reporting of measurements on a plurality of downlink reference signals from a user equipment, UE (310, 700), wherein the method is performed by a network node (320, 800), and wherein the method comprises: providing (S202) configuration of the plurality of downlink reference signals and configuration of reporting the measurements on the plurality of downlink reference signals to the UE (310, 700), wherein the configuration of reporting the measurements comprising at least one channel state information, CSI, reporting quantity; initiating (S204) transmission of the plurality of downlink reference signals; and receiving (S206) a report of the measurements with respect to the at least one CSI reporting quantity from the UE (310, 700), wherein a measurement portion of the report comprises only a subset of the measurements.

20. The method according to claim 19, wherein the plurality of downlink reference signals belong to different downlink reference signal resource sets, where each of the plurality of downlink reference signal resource sets is associated with a respective transmission and reception point, TRP (330-1:330-6), and wherein the transmission of the plurality of downlink reference signals is initiated by the network node (320, 800) providing the plurality of downlink reference signal resource sets to the TRPs (330-1:330-6) together with transmission instructions.

21. The method according to claim 19 or 20, wherein the configuration of reporting the measurements on the plurality of downlink reference signals indicates the at least one CSI reporting quantity and the evaluation criterion.

22. The method according to any of claims 19 to 21, wherein, according to the configuration of the plurality of downlink reference signals, the plurality of downlink reference signals belong to downlink reference signal resource sets of at least two transmission and reception points, TRPs (330-1:330-6), and wherein the report comprises measurements for less than all the TRPs (330-1:330-6).

23. The method according to any of claims 19 to 22, wherein the configuration of the plurality of downlink reference signals is provided in at least one CSI-ResourceConfig information element.

24. The method according to any of claims 19 to 22, wherein the configuration of the plurality of downlink reference signals is provided as part of CSI-AssociatedReportConfigInfo in at least one CSI- AperiodicTriggerStateList information element.

25. The method according to any of claims 19 to 24, wherein the configuration of reporting the measurements comprises an indication for the UE (310, 700) to report the measurements for a subset of the plurality of downlink reference signals.

26. The method according to any of claims 19 to 25, wherein the configuration of reporting the measurements comprises an indication of how many measurements on the plurality of downlink reference signals the UE (310, 700) is to report to the network node (320, 800).

27. The method according to any of claims 19 to 26, wherein the CSI reporting quantity pertains to at least one of: delay, frequency, phase, delay offset, frequency offset, phase offset of the plurality of downlink reference signals.

28. The method according to any of claims 19 to 27, wherein the measurements are reported with respect to measurements on one of the plurality of downlink reference signals as reference.

29. The method according to any of claims 19 to 28, wherein the report further comprises an indication of a subset of the plurality of downlink reference signals for the measurements.

30. The method according to claim 29, wherein the report further comprises an indication of any threshold used by the UE (310, 700) for selecting the subset of the plurality of downlink reference signals for which the measurements are reported.

31. A user equipment, UE (310, 700), for reporting measurements on a plurality of downlink reference signals to a network node (320, 800), the UE (310, 700) comprising processing circuitry (710), the processing circuitry being configured to cause the UE (310, 700) to: obtain configuration of the plurality of downlink reference signals and configuration of reporting the measurements on the plurality of downlink reference signals to the network node (320, 800), wherein the configuration of reporting the measurements comprising at least one channel state information, CSI, reporting quantity; perform measurements on the plurality of downlink reference signals according to the configuration of the plurality of downlink reference signals and with respect to the at least one CSI reporting quantity;select only a subset of the plurality of downlink reference signals for which the measurements are to be reported, wherein the subset of the plurality of downlink reference signals is selected based on an evaluation criterion for the measurements with respect to the CSI reporting quantity; and send a report of the measurements according to the configuration of reporting the measurements to the network node (320, 800), wherein a measurement portion of the report comprises the measurements for only the selected subset of the plurality of downlink reference signals.

32. The UE (310, 700) according to claim 31, further being configured to perform the method according to any of claims 2 to 18.

33. A network node (320, 800) for receiving reporting of measurements on a plurality of downlink reference signals from a user equipment, UE (310, 700), the network node (320, 800) comprising processing circuitry (810), the processing circuitry being configured to cause the network node (320, 800) to: provide configuration of the plurality of downlink reference signals and configuration of reporting the measurements on the plurality of downlink reference signals to the UE (310, 700), wherein the configuration of reporting the measurements comprising at least one channel state information, CSI, reporting quantity; initiate transmission of the plurality of downlink reference signals; and receive a report of the measurements with respect to the at least one CSI reporting quantity from the UE (310, 700), wherein a measurement portion of the report comprises only a subset of the measurements.

34. The network node (320, 800) according to claim 33, further being configured to perform the method according to any of claims 19 to 30.

35. A computer program (920a) for reporting measurements on a plurality of downlink reference signals to a network node (320, 800), the computer program comprising computer code which, when run on processing circuitry (710) of a user equipment, UE (310, 700), causes the UE (310, 700) to: obtain (S102) configuration of the plurality of downlink reference signals and configuration of reporting the measurements on the plurality of downlink reference signals to the network node (320, 800), wherein the configuration of reporting the measurements comprising at least one channel state information, CSI, reporting quantity; perform (S104) measurements on the plurality of downlink reference signals according to the configuration of the plurality of downlink reference signals and with respect to the at least one CSI reporting quantity;select (S106) only a subset of the plurality of downlink reference signals for which the measurements are to be reported, wherein the subset of the plurality of downlink reference signals is selected based on an evaluation criterion for the measurements with respect to the CSI reporting quantity; and send (S108) a report of the measurements according to the configuration of reporting the measurements to the network node (320, 800), wherein a measurement portion of the report comprises the measurements for only the selected subset of the plurality of downlink reference signals.

36. A computer program (920b) for receiving reporting of measurements on a plurality of downlink reference signals from a user equipment, UE (310, 700), the computer program comprising computer code which, when run on processing circuitry (810) of a network node (320, 800), causes the network node (320, 800) to: provide (S202) configuration of the plurality of downlink reference signals and configuration of reporting the measurements on the plurality of downlink reference signals to the UE (310, 700), wherein the configuration of reporting the measurements comprising at least one channel state information, CSI, reporting quantity; initiate (S204) transmission of the plurality of downlink reference signals; and receive (S206) a report of the measurements with respect to the at least one CSI reporting quantity from the UE (310, 700), wherein a measurement portion of the report comprises only a subset of the measurements.

37. A computer program product (910a, 910b) comprising a computer program (920a, 920b) according to at least one of claims 35 and 36, and a computer readable storage medium (930) on which the computer program is stored.

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