Reducing CSI coefficients in CSI reporting

Abstract

Embodiments of the present invention relate to a first communication device and a second communication device for reducing CSI coefficients in CSI reporting. The first communication device (100) sends a CSI report (510) to the second communication device (300), the CSI report (510) indicating a subset of CSI coefficients of the complete set of CSI coefficients according to a CSI omission rule. The second communication device (300) receives the CSI report (510) and determines the complete set of CSI coefficients based on the subset of CSI coefficients in the CSI report (510). In addition, the embodiments of the invention also relate to a corresponding method and a computer program.

Description

TECHNICAL FIELD

[0001] Embodiments of the present application relate to a first communication device and a second communication device for reducing CSI coefficients in CSI reporting. Furthermore, embodiments of the present application also relate to corresponding methods and a computer program. BACKGROUND

[0002] Artificial intelligence (AI) and, more precisely, machine learning (ML) methods, have proven their worth in multiple domains, covering different problems, including classification, regression, pattern detection, dimensionality reduction, and interaction with dynamic environments. As a result, machine learning is expected to become a key technology in wireless communication networks for both radio access networks and core networks. Indeed, machine learning models are able to capture complex dependencies and patterns in data that cannot be exploited by traditional signal processing techniques commonly used in the air interface. Therefore, exploiting their potential in the air interface of wireless communication networks can bring significant performance gains in terms of the main network key performance indicators (KPIs) such as throughput, latency, reliability, and energy efficiency.

[0003] In this context, 3GPP agreed to launch a study item in Rel-18, namely “AI / ML for NR air interface”, to study the potential enhancements, performance gains, common framework, and standard impacts that machine learning methods can bring to the air interface. Several important use cases include beam management, channel state information (CSI) reporting, and positioning performance enhancements.

[0004] While these specific use cases are extremely challenging and important, it is worth highlighting that the potential of AI / ML can also be applied to other important use cases, such as, for example, link adaptation enhancements, hardware impairment and mobile terminal (MT) / gNB-side implementation enhancements, L1 / L2 mobility support enhancements, adaptation to different traffic types, and cross-link interference measurement and management, given that NR is a beamforming-based air interface. SUMMARY

[0005] It is an object of embodiments of the present application to provide a solution that reduces or solves the drawbacks and problems of the conventional solutions.

[0006] It is another object of embodiments of the present application to provide a solution that reduces the payload of CSI and data reporting in a communication system.

[0007] The above and other objects are achieved by subjects of the independent claims. Further embodiments of the application can be found in the dependent claims.

[0008] According to a first aspect of the present application, the above and other objects are achieved by a first communication device for a communication system, the first communication device configured to:

[0009] measure a set of reference signals transmitted in a set of transmit beams of a second communication device and received in a set of receive beams of the first communication device;

[0010] determine a set of channel state information (CSI) coefficients based on the measured set of reference signals;

[0011] reduce the set of CSI coefficients to a subset of CSI coefficients by omitting at least one CSI coefficient based on a CSI omission rule;

[0012] transmit a CSI report to the second communication device, the CSI report indicating the subset of CSI coefficients.

[0013] The first communication device according to the first aspect has the advantage that it can reduce the CSI reporting overhead with minimal loss of information. Thus, the resource usage can be reported more efficiently in the communication system. This advantage can be exploited when the reporting resources cannot accommodate the entire payload of the report, when higher priority signals need to be transmitted, or when the goal is to reduce the power consumption of the first communication device. Furthermore, a new CSI omission rule is defined, which is applicable to ML operations in the air interface, and which exploits the existing CSI framework in standardized communication systems such as 3GPP NR to guarantee the quality of the collected training data. Moreover, the new CSI omission rule allows the omitted CSI coefficients to be retrieved at the second communication device (i.e. receiver side) with limited complexity.

[0014] In an implementation form of the first communication device according to the first aspect, the CSI omission rule comprises omitting the CSI coefficients in spatial and / or time domain.

[0015] This implementation form has the advantage that it can support spatial and time domain beam and beam pair prediction at the same time. Furthermore, depending on the used beam codebook, one or more dimensions can be prioritized in the omission process in addition to the speed and deployment scenario of the respective communication device. For example, in case of fast moving communication devices, the omission of coefficients in time domain can be reduced in order to capture fast changing beams or beam pairs.

[0016] In an implementation form of the first communication device according to the first aspect, the CSI omission rule comprises omitting the CSI coefficients by any of: a spatial offset, a temporal offset, a spatial sampling rate, and a temporal sampling rate.

[0017] The advantage of this implementation form is that the payload of the CSI report can be significantly reduced while minimizing the loss of information. Since the first communication device can select the parameters to be omitted, i.e. the spatial sampling offset, the temporal sampling offset, the spatial sampling rate, and the temporal sampling rate, the first communication device can make the omission selection such that the reconstruction of the entire report at the second communication device can be performed accurately.

[0018] In an implementation form of the first communication device according to the first aspect, the CSI omission rule comprises omitting the CSI coefficients for one or more of: a transmit beam, a receive beam, and a beam pair comprising a transmit beam and a receive beam.

[0019] The advantage of this implementation form is that beam and beam pair prediction can be supported at the same time.

[0020] In an implementation form of the first communication device according to the first aspect, the CSI omission rule comprises omitting the CSI coefficients for a time sequence of CSI coefficients in the set of CSI coefficients.

[0021] The advantage of this implementation form is that beam and beam pair prediction in time domain can be supported. At this time, the reported CSI coefficients constitute a time sequence of measurement results for each beam or beam pair. Therefore, the omission according to the proposed method does not destroy the time structure of the CSI report, i.e. the order of measurement time labels and measurement results.

[0022] In an implementation form of the first communication device according to the first aspect, the set of CSI coefficients comprises one or more of: a reference resource indicator, a beam index, a reference resource pair indicator, a beam pair index, a reference signal received power, and a signal-to-interference noise ratio.

[0023] The advantage of this implementation form is that all beam or beam pair reporting quantities can be supported, regardless of whether interference measurement results are included.

[0024] In an implementation form of the first communication device according to the first aspect, the CSI omission rule comprises omitting the CSI coefficients by reducing the set of measured reference signals to a subset of measured reference signals.

[0025] The advantage of this implementation form is that an aperiodic omission pattern in spatial domain can be supported. At this time, the omission of measurement results for specific resources can be further adjusted according to the propagation environment.

[0026] In a further implementation form of the first communication device according to the first aspect as such or according to the first aspect as combined with any of the preceding implementation forms of the first aspect, the measured reference signal subset is at least one pre-configured reference signal group in channel measurement resources and / or interference measurement resources.

[0027] This implementation form has the advantage that the second communication device can configure the reference signal resource groups based on its proprietary beam implementation without disclosing any further information. Moreover, the second communication device can also optimize the reference signal resource grouping based on data previously collected for the same or different first communication devices.

[0028] In a further implementation form of the first communication device according to the first aspect as such or according to the first aspect as combined with any of the preceding implementation forms of the first aspect, the first communication device is configured to:

[0029] receive a first control signal from the second communication device, the first control signal indicating the CSI omission rule.

[0030] This implementation form has the advantage that different omission rules can be supported and the selection of the omission rule to be used can be based on auxiliary information available at the second communication device, such as the spatial structure of the propagation channel, other measurement results from the same or different first communication devices, the beam codebook used at the second communication device, and the average beam dwell time.

[0031] In a further implementation form of the first communication device according to the first aspect as such or according to the first aspect as combined with any of the preceding implementation forms of the first aspect, the first control signal is a radio resource control (RRC) signal.

[0032] This implementation form has the advantage that the omission rule to be used can be part of the CSI, radio resource measurement or data collection configuration in RRC.

[0033] In a further implementation form of the first communication device according to the first aspect as such or according to the first aspect as combined with any of the preceding implementation forms of the first aspect, the first communication device is configured to:

[0034] receive a second control signal from the second communication device, the second control signal indicating an activation or deactivation of the CSI omission rule.

[0035] This implementation form has the advantage that the second communication device can control the applicability of the omission rule. Indeed, the requirements on the collected measurement results can vary depending on whether these measurement results are used for training, inference or monitoring of one or more machine learning models for beam or beam pair prediction. Thus, in some critical situations (e.g., when a drop in model accuracy is detected), the second communication device can deactivate the CSI omission rule, thus prioritizing the acquisition of the full CSI measurement report.

[0036] In a further implementation form of the first communication device according to the first aspect as such or according to the first implementation form of the first aspect, the second control signal is a downlink control information or a downlink medium access control control element.

[0037] The advantage of this implementation form is that the activation or deactivation command can be transmitted with minimal latency. Thus, timely adaptation to model performance and propagation conditions can be achieved.

[0038] In a further implementation form of the first communication device according to the first aspect as such or according to the first implementation form of the first aspect, the CSI report further indicates information on the omission of the CSI coefficients in the spatial and / or time domain by any of the following: spatial offset, time offset, spatial sampling rate, and time sampling rate; and / or omission of the CSI coefficients by reducing the set of measured reference signals to a subset of measured reference signals based on a preconfigured reference signal group in at least one of a channel measurement resource and / or an interference measurement resource.

[0039] The advantage of this implementation form is that when decoding the CSI report received from the first communication device, there is no ambiguity at the second communication device and a suitable subsequent reconstruction can be performed.

[0040] According to a second aspect of the present application, the above mentioned and other objectives are achieved by a second communication device for a communication system, the second communication device being configured to:

[0041] transmit a set of reference signals to a set of receive beams of a first communication device in a set of transmit beams of the second communication device;

[0042] receive a CSI report from the first communication device, the CSI report indicating a subset of CSI coefficients out of a set of CSI coefficients based on a CSI omission rule, the set of CSI coefficients corresponding to one or more of the following: the set of transmit beams, the set of receive beams, and a set of beam pairs comprising the set of transmit beams and the set of receive beams;

[0043] determine the set of CSI coefficients based on the subset of CSI coefficients.

[0044] The second communication device according to the second aspect has the advantage that resource usage can be reported more efficiently in the communication system. This advantage can be exploited when the reporting resources cannot accommodate the entire payload of the report, when higher priority signals need to be transmitted, or when the goal is to reduce the power consumption of the first communication device. Furthermore, a new CSI omission rule is defined which is suitable for ML operations in the air interface, and which leverages the existing CSI framework in standardized communication systems such as 3GPP NR to guarantee the quality of the collected training data. Moreover, the new CSI omission rule allows the retrieval of the omitted CSI coefficients at the second communication device (i.e. receiver side) with limited complexity.

[0045] In a further implementation form of the second communication device according to the second aspect as such or any preceding implementation form, the second communication device is configured to:

[0046] determine the set of CSI coefficients based on an interpolation or extrapolation of the subset of CSI coefficients.

[0047] This implementation form has the advantage that the second communication device can reconstruct at least partially the omitted CSI coefficients. Based on the received subset of CSI coefficients, the entire report can be reconstructed with an acceptable accuracy by interpolation (e.g. polynomial interpolation, spline interpolation or linear interpolation) and extrapolation.

[0048] In a further implementation form of the second communication device according to the second aspect as such or any preceding implementation form, the second communication device is configured to:

[0049] determine the set of CSI coefficients based on an interpolation or extrapolation of the subset of CSI coefficients.

[0050] transmit a first control signal to the first communication device, the first control signal indicating the CSI omission rule.

[0051] This implementation form has the advantage that different omission rules can be supported and the selection of the omission rule to be used can be based on auxiliary information available at the second communication device, such as the spatial structure of the propagation channel, other measurement results from the same or different first communication devices, the beam codebook used at the second communication device and the average beam dwell time.

[0052] In a further implementation form of the second communication device according to the second aspect as such or any preceding implementation form, the second communication device is configured to:

[0053] the first control signal is an RRC signal.

[0054] This implementation form has the advantage that the omission rule to be used can be part of a CSI, radio resource measurement or data collection configuration in RRC.

[0055] In a further implementation form of the second communication device according to the second aspect as such or any preceding implementation form, the second communication device is configured to:

[0056] the CSI omission rule comprises omitting at least one CSI coefficient in the spatial and / or time domain.

[0057] This implementation form has the advantage that beam and beam pair prediction in the spatial and time domain can be supported at the same time. Furthermore, depending on the used beam codebook, one or more dimensions can be prioritized in the omission process in addition to the speed and deployment scenario of the respective communication device. For example, in case of a fast moving communication device, the omission of coefficients in the time domain can be reduced in order to capture fast changing beams or beam pairs.

[0058] In a further implementation form of the second communication device according to the second aspect as such or any preceding implementation form, the second communication device is configured to:

[0059] The CSI omission rule comprises omitting the CSI coefficients by any of: spatial offset, time offset, spatial sampling rate and time sampling rate.

[0060] The advantage of this implementation is that the payload of the CSI report can be significantly reduced while minimizing the loss of information. Since the first communication device can select the parameters to omit, i.e. spatial sampling offset, time sampling offset, spatial sampling rate and time sampling rate, the first communication device can make the omission selection so that the reconstruction of the entire report can be performed accurately at the second communication device.

[0061] In an implementation form of the second communication device according to the second aspect,

[0062] The CSI omission rule comprises omitting the CSI coefficients for one or more of: transmit beam, receive beam and beam pair comprising a transmit beam and a receive beam.

[0063] The advantage of this implementation is that beam and beam pair prediction can be supported simultaneously.

[0064] In an implementation form of the second communication device according to the second aspect,

[0065] The CSI omission rule comprises omitting the CSI coefficients for a time sequence of CSI coefficients in the set of CSI coefficients.

[0066] The advantage of this implementation is that time domain beam and beam pair prediction can be supported. At this time, the reported CSI coefficients constitute a time sequence of measurement results for each beam or beam pair. Therefore, the omission according to the proposed method does not destroy the time structure of the CSI report, i.e. the order of measurement time labels and measurement results.

[0067] In an implementation form of the second communication device according to the second aspect,

[0068] The set of CSI coefficients comprises one or more of: reference resource indicator, beam index, reference resource pair indicator, beam pair index, reference signal received power and signal to interference noise ratio.

[0069] The advantage of this implementation is that all beam or beam pair reporting quantities can be supported, regardless of whether or not interference measurement results are included.

[0070] In an implementation form of the second communication device according to the second aspect, the CSI omission rule comprises omitting at least one CSI coefficient by reducing the set of measured reference signals to a subset of measured reference signals.

[0071] The advantage of this implementation form is that non-periodic omission patterns in the spatial domain can be supported. At this point, the omission of measurement results for specific resources can be further adjusted depending on the propagation environment.

[0072] In an implementation form of the second communication device according to the second aspect,

[0073] The measured reference signal subset is at least one preconfigured reference signal group in channel measurement resources and / or interference measurement resources.

[0074] The advantage of this implementation form is that the second communication device can configure the reference signal resource groups based on its proprietary beam implementation without disclosing any further information. Furthermore, the second communication device can also optimize the reference signal resource grouping depending on data previously collected for the same or different first communication devices.

[0075] In an implementation form of the second communication device according to the second aspect, the second communication device is configured to:

[0076] transmit a second control signal to the first communication device, the second control signal indicating an activation or deactivation of the CSI omission rule.

[0077] The advantage of this implementation form is that the second communication device can control the applicability of the omission rule. In fact, the requirements on the collected measurement results can differ depending on whether these measurement results are used for training, inference or monitoring of one or more machine learning models for beam or beam pair prediction. Thus, in some critical situations (e.g. when a drop in model accuracy is detected), the second communication device can deactivate the CSI omission rule, thus prioritizing the acquisition of the entire CSI measurement report.

[0078] In an implementation form of the second communication device according to the second aspect,

[0079] The second control signal is a downlink control information or a downlink medium access control control element.

[0080] The advantage of this implementation form is that the activation or deactivation command can be transmitted with minimal latency. Thus, timely adaptation to model performance and propagation conditions can be achieved.

[0081] In an implementation form of the second communication device according to the second aspect,

[0082] The CSI report is further indicative of information on omission of at least one CSI coefficient in the spatial domain and / or the time domain by any of: spatial offset, time offset, spatial sampling rate, and time sampling rate; and / or omission of at least one CSI coefficient by reducing the set of measured reference signals to a subset of measured reference signals based on at least one preconfigured reference signal group in a channel measurement resource and / or an interference measurement resource.

[0083] This implementation form has the advantage that there is no ambiguity at the second communication device when decoding the CSI report received from the first communication device and a proper subsequent reconstruction can be performed.

[0084] According to a third aspect of the present application, the above mentioned and other objectives are achieved, by a method for a first communication device, comprising:

[0085] measuring a set of reference signals transmitted in a set of transmit beams of a second communication device and received in a set of receive beams of the first communication device;

[0086] determining a set of channel state information, CSI, coefficients based on the set of measured reference signals;

[0087] reducing the set of CSI coefficients to a subset of CSI coefficients by omitting at least one CSI coefficient based on a CSI omission rule; and

[0088] transmitting a CSI report to the second communication device, the CSI report being indicative of the subset of CSI coefficients.

[0089] The method according to the third aspect can be extended to implementation forms corresponding to the implementation forms of the first communication device according to the first aspect. Thus, implementation forms of the method comprise one or more of the features of the corresponding implementation forms of the first communication device.

[0090] The method according to the third aspect has the same advantages as the corresponding implementation forms of the first communication device according to the first aspect.

[0091] According to a fourth aspect of the present application, the above mentioned and other objectives are achieved, by a method for a second communication device, comprising:

[0092] transmitting a set of reference signals to a set of receive beams of a first communication device in a set of transmit beams of the second communication device;

[0093] receiving a CSI report from the first communication device, the CSI report indicating a subset of CSI coefficients in a set of CSI coefficients based on a CSI omission rule, the set of CSI coefficients corresponding to one or more of the set of transmit beams, the set of receive beams, and a set of beam pairs comprising the set of transmit beams and the set of receive beams; and

[0094] determining the set of CSI coefficients based on the subset of CSI coefficients.

[0095] The method according to the fourth aspect can be extended to implementation corresponding to the implementation of the second communication device according to the second aspect. Therefore, the implementation of the method includes one or more features of the corresponding implementation of the second communication device.

[0096] The advantages of the method according to the fourth aspect are the same as those of the corresponding implementation of the second communication device according to the second aspect.

[0097] Embodiments of the application also relate to a computer program comprising a program code which, when executed by at least one processor, causes the at least one processor to perform any of the methods according to embodiments of the application. Furthermore, embodiments of the application also relate to a computer program product comprising a computer readable medium and the computer program, the computer program being included in the computer readable medium and can include one or more of the following group: read-only memory (ROM), programmable ROM (PROM), erasable PROM (EPROM), flash memory, electrically erasable PROM (EEPROM), hard disk drive, etc.

[0098] Other applications and advantages of embodiments of the application will be apparent from the following detailed description. BRIEF DESCRIPTION OF DRAWINGS

[0099] The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this application, illustrate embodiments of the application and together with the description serve to explain the principles of the application.

[0100] Figure 1 a first communication device according to an embodiment of the application is shown;

[0101] Figure 2 a flow chart of a method for a first communication device according to an embodiment of the application is shown;

[0102] Figure 3 a second communication device according to an embodiment of the application is shown;

[0103] Figure 4 A flowchart of a method for a second communication device according to an embodiment of the application is shown;

[0104] Figure 5 A communication system according to an embodiment of the application is shown;

[0105] Figure 6 Omission of CSI coefficients in spatial domain is shown;

[0106] Figure 7 Omission of CSI coefficients in time domain is shown;

[0107] Figure 8 Signaling diagram of other embodiments of the application is shown. DETAILED DESCRIPTION

[0108] With the emergence of ML-based beam management, the payload of the reported beam measurements for training, inference and / or monitoring is expected to increase. For example, due to the use of narrower beams, the number of variables in spatial domain increases. In addition, time domain beam prediction requires reporting of measurement time series which are to be used as input for network side models or as output for user equipment (UE) side models.

[0109] Therefore, the increase of the payload of the beam management reporting implies that other aspects of the CSI reporting need to be considered. This includes resource allocation for CSI reporting, time domain behavior of the reporting and reporting timeline requirements. In addition, the CSI omission rules (e.g. which can apply in case the resources are not sufficient to transmit all CSI reports) need to be revised to support the new requirements for efficient CSI reporting. Therefore, there is a need to provide adaptive and efficient omission rules for beam management CSI reporting to accommodate the reduced beam reporting payload. Therefore, the present disclosure relates to a first communication device and a second communication device for enabling reduced and efficient CSI reporting which can be used for beam management in a wireless communication system.

[0110] Figure 1 A first communication device 100 according to an embodiment of the application is shown. In Figure 1 In the shown embodiment, the first communication device 100 comprises a processor 102, a transceiver 104 and a memory 106. The processor 102 is coupled to the transceiver 104 and the memory 106 by communication means 108 known in the art. The first communication device 100 can be used for wireless communication in a communication system. The wireless communication capabilities can be provided by an antenna or antenna array 110 coupled to the transceiver 104.

[0111] The processor 102 can be referred to as one or more general-purpose central processing units (CPUs), one or more digital signal processors (DSPs), one or more application-specific integrated circuits (ASICs), one or more field programmable gate arrays (FPGAs), one or more programmable logic devices, one or more discrete gates or one or more chips sets. The memory 106 can be a read-only memory, a random access memory (RAM), or a non-volatile RAM (NVRAM). The transceiver 104 can be a transceiver circuit, a power controller, or an interface providing the ability to communicate with other communication modules or communication devices, such as network nodes and network servers. The transceiver 104, the memory 106, and / or the processor 102 can be implemented in separate chipsets or in a common chipset.

[0112] In the present disclosure, it can be understood that the first communication device 100 is configured to perform certain operations, which means that the first communication device 100 comprises suitable means, for example, the processor 102 and the transceiver 104, for performing these operations.

[0113] According to an embodiment of the present application, the first communication device 100 is configured to: measure a set of reference signals transmitted in a set of transmission beams of the second communication device 300 and received in a set of reception beams of the first communication device 100; determine a set of channel state information (CSI) coefficients based on the measured set of reference signals; reduce the set of CSI coefficients to a subset of CSI coefficients by omitting at least one CSI coefficient based on a CSI omission rule; and transmit a CSI report 510 to the second communication device 300, the CSI report 510 indicating the subset of CSI coefficients.

[0114] Furthermore, in one embodiment of the present invention, a first communication device 100 for a communication system 500 includes a processor configured to: measure a set of reference signals transmitted in a transmit beamset of a second communication device 300 and received in a receive beamset of the first communication device 100; determine a set of CSI coefficients based on the measured set of reference signals; and reduce the set of CSI coefficients to a subset of CSI coefficients by omitting at least one CSI coefficient based on a CSI omission rule. The first communication device 100 includes a transceiver configured to: send a CSI report 510 to the second communication device 300, the CSI report 510 indicating the subset of CSI coefficients.

[0115] Furthermore, in another embodiment of the invention, a first communication 100 for a communication system 500 includes a processor and a memory having computer-readable instructions stored thereon, which, when executed by the processor, cause the processor to: measure a set of reference signals transmitted in the transmit beam set of the second communication device 300 and received in the receive beam set of the first communication device 100; determine a set of CSI coefficients based on the measured set of reference signals; reduce the set of CSI coefficients to a subset of CSI coefficients by omitting at least one CSI coefficient based on a CSI omission rule; and send a CSI report 510 to the second communication device 300, the CSI report 510 indicating the subset of CSI coefficients.

[0116] Figure 2 This illustrates that communication can be performed in a first communication device 100 (such as, Figure 1 The flowchart illustrates the corresponding method 200 performed in the first communication device 100 shown. Method 200 includes: measuring 202 a set of reference signals transmitted in the transmit beamset of the second communication device 300 and received in the receive beamset of the first communication device 100; determining 204 a set of CSI coefficients based on the measured set of reference signals; reducing the set of CSI coefficients 206 to a subset of CSI coefficients by omitting at least one CSI coefficient based on a CSI omission rule; and sending 208 a CSI report 510 to the second communication device 300, the CSI report 510 indicating the subset of CSI coefficients.

[0117] Figure 3 A second communication device 300 according to an embodiment of the present invention is shown. Figure 3 In the illustrated embodiment, the second communication device 300 includes a processor 302, a transceiver 304, and a memory 306. The processor 302 is coupled to the transceiver 304 and the memory 306 via a communication component 308 known in the art. The second communication device 300 also includes an antenna or antenna array 310 coupled to the transceiver 304, indicating that the second communication device 300 is used for wireless communication in a communication system.

[0118] The processor 302 can be referred to as one or more general-purpose CPUs, one or more DSPs, one or more ASICs, one or more FPGAs, one or more programmable logic devices, one or more discrete gates, one or more transistor logic devices, one or more discrete hardware components, or one or more chipsets. The memory 306 can be a read-only memory, a RAM, or an NVRAM. The transceiver 304 can be a transceiver circuit, a power controller, or an interface that provides the ability to communicate with other communication modules or communication devices. The transceiver 304, the memory 306, and / or the processor 302 can be implemented in separate chipsets or in a common chipset.

[0119] In the present disclosure, it can be understood that the second communication device 300 is configured to perform certain operations, which means that the second communication device 300 includes appropriate components, such as the processor 302 and the transceiver 304, for performing these operations.

[0120] According to an embodiment of the present application, the second communication device 300 is configured to: transmit a set of reference signals to a set of receive beams of the first communication device 100 in a set of transmit beams of the second communication device 300; receive a CSI report 510 from the first communication device 100, the CSI report 510 indicating a subset of CSI coefficients in a set of CSI coefficients based on a CSI omission rule, the set of CSI coefficients corresponding to one or more of: the set of transmit beams, the set of receive beams, and a set of beam pairs including the set of transmit beams and the set of receive beams; and determine the set of CSI coefficients based on the subset of CSI coefficients.

[0121] In addition, in one embodiment of the present application, the second communication device 300 for the communication system 500 includes a transceiver configured to: transmit a set of reference signals to a set of receive beams of the first communication device 100 in a set of transmit beams of the second communication device 300; and receive a CSI report 510 from the first communication device 100, the CSI report 510 indicating a subset of CSI coefficients in a set of CSI coefficients based on a CSI omission rule, the set of CSI coefficients corresponding to one or more of: the set of transmit beams, the set of receive beams, and a set of beam pairs including the set of transmit beams and the set of receive beams. The second communication device 300 includes a processor configured to determine the set of CSI coefficients based on the subset of CSI coefficients.

[0122] Furthermore, in yet another embodiment of the application, a second communication device 300 for a communication system 500 comprises a processor and a memory having computer readable instructions stored thereon that, when executed by the processor, cause the processor to: transmit a set of reference signals to a set of receive beams of a first communication device 100 in a set of transmit beams of the second communication device 300; receive a CSI report 510 from the first communication device 100, the CSI report 510 indicating a subset of CSI coefficients in a set of CSI coefficients based on a CSI omission rule, the set of CSI coefficients corresponding to one or more of: the set of transmit beams, the set of receive beams, and a set of beam pairs comprising the set of transmit beams and the set of receive beams; and determine the set of CSI coefficients based on the subset of CSI coefficients.

[0123] Figure 4 A flowchart of a corresponding method 400 is shown that can be performed in a second communication device 300 (such as, Figure 3 A flowchart of a corresponding method 400 is shown that can be performed in a second communication device 300 (such as,

[0124] Figure 5 A communication system 500 according to an embodiment of the application is shown. The communication system 500 in the disclosed embodiments comprises a first communication device 100 and a second communication device 300 for communicating and operating in the communication system 500 using suitable protocols and communication interfaces. For simplicity, the shown communication system 500 only comprises one first communication device 100 and one second communication device 300. However, the communication system 500 can comprise any number of first communication devices 100 and any number of second communication devices 300 without deviating from the scope of the application.

[0125] In Figure 5In the particular example shown, the first communication device 100 is configured as a client device, such as a UE, while the second communication device 300 is configured as a network access node, such as a base station. The network access node can be part of a radio access network (RAN) and connected to a network (NW), such as a 3GPP core network (CN), through suitable communication interfaces. However, the opposite case is also possible, i.e. the first communication device 100 is configured as a network access node, while the second communication device 300 is configured as a client device. However, in further examples of the application, not shown in the figure, both the first communication device 100 and the second communication device 300 can be configured as client devices in a sidelink communication scenario.

[0126] According to the present solution, the first communication 100 is configured to receive a reference signal (RS) in a receive beam of the first communication device 100. The reference signal can be transmitted in a downlink (DL) in a transmit beam of the second communication device 300 over a suitable air interface. Based on the measurement results of the received reference signal, the first communication device 100 derives a CSI report 510 and transmits the CSI report 510 to the second communication device 300. The CSI report 510 indicates a subset of CSI coefficients of a complete set of CSI coefficients according to a CSI omission rule. Thus, a solution is disclosed herein to reduce the number of CSI coefficients by omitting at least one CSI coefficient according to a CSI omission rule, since the subset of CSI coefficients comprises less CSI coefficients than the complete set of CSI coefficients. Thereby, the payload can be reduced to improve the performance of the communication system 500.

[0127] The CSI omission rule proposed herein comprises omitting one or more CSI coefficients in the spatial and / or time domain, as shown in the examples Figure 6 and Figure 7 In this regard, the CSI omission rule can comprise omitting a CSI coefficient by one or more of the following: spatial offset, time offset, spatial sampling rate, and time sampling rate. Depending on the considered beam or beam pair prediction solution, one or more of these parameters need to be considered. In time domain beam prediction, the second communication device 300 can use an ML model that predicts a beam or beam pair in the time domain. The input to such an ML model can be a time series of measurement results for each beam or beam pair. When omitting in this case, the first communication device 100 reduces the number of reported CSI coefficients by resampling (with or without offset) the measured time series. Thus, in embodiments of the application, the CSI omission rule comprises omitting one or more CSI coefficients for a time series of CSI coefficients in the set of CSI coefficients.

[0128] Typically, to move the sampling points in time, the sampling period is increased and an offset is applied. Eventually, the sampling period / rate and the offset are chosen by the first communication device 100 so that the subsequent interpolation at the second communication device 300 can be performed with sufficient accuracy.

[0129] Let the CSI coefficients / quantities acquired at the first communication device 100 be denoted as:

[0130] ,

[0131] wherein denotes the L1-RSRP or L1-SINR of the measured reference signal resource at time , denotes the number of DL reference signal resources, and denotes the number of measurements in time. According to examples of the present application, after CSI coefficient omission, when the sampling rate in time is and the offset is , the first communication device 100 reports the following measurement quantities and associated beam or beam pair indicator:

[0132] .

[0133] In case of spatial domain beam or beam pair prediction, the second communication device 300 can use an ML model that predicts beams or beam pairs in a large size beam or beam pair codebook based on measurements from a limited size codebook. At this time, the measurement resources are ordered and the sampling rate and offset are applied based on the ordered reference signal resources.

[0134] Let the CSI quantities acquired at the first communication device 100 be denoted as:

[0135] ,

[0136] wherein denotes the L1-RSRP or L1-SINR of the measured reference signal resource . According to examples of the present application, after CSI coefficient omission, when the sampling rate in spatial domain is and the offset is , the first communication device 100 reports the following measurement quantities and associated beam or beam pair indicator:

[0137] .

[0138] ​Further aspects of the solution relate to the type of beams to which the CSI omission rule applies. According to embodiments of the application, the CSI omission rule comprises omitting CSI coefficients for one or more of the following: a transmit beam of the second communication device 300, a receive beam of the first communication device 100, and a beam pair comprising the transmit beam of the second communication device 300 and the receive beam of the first communication device 100. Furthermore, the CSI coefficients of the CSI report 510 can comprise one or more of the following: a reference resource indicator, a beam index, a reference resource pair indicator, a beam pair index, a reference signal received power (RSRP), and a signal-to-noise and interference ratio (SINR).

[0139] Figure 6 Omission of CSI coefficients in spatial domain is shown, Figure 7 Omission of CSI coefficients in spatial and time domain is shown. Figure 6 and Figure 7 Reference signal resources are shown arranged in a grid, where the grid represents the elevation angle of the corresponding beam on the y-axis and the azimuth angle of the corresponding beam on the x-axis. The grey boxes represent RS resources for which the measurement results are omitted, and the slanted dashed boxes represent RS resources for which the measurement results are included in the CSI reporting.

[0140] Figure 6 Two omission options for a set of B beams are shown, which have the same sampling rate but different offsets. In omission option 1, resources with offset 1 are considered, and the sampling rate is ½. In omission option 2, resources with offset 0 are considered, and the sampling rate is ½. When reporting the reduced CSI report, the first communication device 100 can also indicate to the second communication device 300 the selected sampling rate and offset.

[0141] Figure 7 It is shown that the omission of CSI coefficients in time domain can also be combined with the omission in spatial domain, and vice versa. In time domain, resources with offset 0 are considered, and the sampling rate is ½. In spatial domain, resources with offset 1 are considered, and the sampling rate is ½.

[0142] In yet some embodiments of the application, the CSI omission rule comprises omitting the CSI coefficients by reducing the measured reference signal set to a measured reference signal subset. More specifically, the measured reference signal subset can be a pre-configured reference signal group for at least one of channel measurement resource and / or interference measurement resource. The measurement resource in the CSI reporting configuration where the first communication device 100 measures to calculate the CSI coefficients is configured as a channel measurement resource (CMR) or an interference measurement resource (IMR). The CMR is configured in the resourcesForChannelMeasurement information element, and the IMR is configured in the csi-IM-ResourcesForInterference information element (for zero-power interference measurement reference signal) and nzp-CSI-RS-ResourcesForInterference information element (for non-zero-power interference measurement reference signal), respectively. If a pre-configured reference signal grouping of resources is adopted, multiple resource groups / sets can be configured in the CMR and IMR. Each resource reference signal group / set can have a given priority in the omission process.

[0143] Figure 8 A signaling diagram illustrating the signaling aspect of the solution disclosed according to embodiments of the application is shown. It is to be noted that, Figure 8 Some of the steps described in the method can be optional steps.

[0144] In Figure 8 In step I of the method, the second communication device 300 sends a first control signal 520 to the first communication device 100. The first control signal 520 comprises a CSI reporting configuration, which comprises a CSI omission rule. Thus, the first control signal 520 indicates a CSI omission rule, which can relate to omission in the spatial domain, the time domain and / or for pre-configured measurement groups as described above. The first control signal 520 can be sent to the first communication device 100 as a radio resource control (RRC) signal.

[0145] However, it should be mentioned that in an example, the CSI reporting configuration can be fully pre-configured in the first communication device 100. In another example, a part of the CSI reporting configuration can be pre-configured in the first communication device 100, while another part or a complementary part of the CSI reporting configuration can be indicated in the first control signal 520.

[0146] In Figure 8In step II of the method, the first communication device 100 receives the first control signal 520 from the second communication device 300. Based on the CSI omission rule, the first client device 100 prepares and adapts its CSI reporting behavior, which means that the first client device 100 is configured according to the received CSI omission rule for CSI reporting. However, if the first communication device 100 is already pre-configured with a CSI omission rule, no configuration can be necessary.

[0147] In step III of the method, Figure 8 In step III of the method, the second communication device 300 can also send a second control signal 530 indicating the activation or deactivation of the CSI omission rule. Thus, an activation / deactivation mechanism of the CSI omission rule is provided. By sending the second control signal 530 in a downlink control information (DCI) or a downlink medium access control (MAC) control element (CE), the second communication device 300 can control the activation / deactivation in a short time.

[0148] In step IV of the method, Figure 8 In step IV of the method, the first communication device 100 is activated or deactivated to use or not to use the CSI omission rule configured in the first control signal and / or configured as a pre-configured CSI omission rule.

[0149] In step V of the method, Figure 8 In step V of the method, the first communication device 100 sends a CSI report 510 to the second communication device 300. Assuming that the CSI omission rule has been activated, the CSI report 510 indicates a subset of CSI coefficients of the entire or full set of CSI coefficients as described previously.

[0150] In step VI of the method, Figure 8 In step VI of the method, the second communication device 300 determines the set of CSI coefficients based on the subset of CSI coefficients received in the CSI report. Many different techniques can be employed to derive the set of CSI coefficients from the subset of CSI coefficients. Two non-limiting examples are by interpolating or extrapolating the subset of CSI coefficients.

[0151] In order to simplify and speed up the process of deriving the whole or complete set of CSI coefficients, the first communication device 100 can inform the second communication device 300 which CSI coefficients are omitted in the CSI report 510. Thus, in embodiments of the present application, the CSI report 510 can also indicate information about the omission of CSI coefficients in the spatial and / or time domain. That is, information about the specific omission rule applied by the first communication device 100 for reducing the number of CSI coefficients. Thus, the CSI report 510 can also indicate any of the following omission information: spatial offset, time offset, spatial sampling rate and time sampling rate; and / or omitting CSI coefficients by reducing the set of reference signals to a subset of measured reference signals based on at least one preconfigured reference signal group in the channel measurement resource and / or the interference measurement resource.

[0152] For example, when the preconfigured reference signal groups are already preconfigured in the CSI reporting configuration, each reference signal group can be assigned an index, e.g. [0, 1, 2, 3,... N]. Thus, when the first communication device 100 performs CSI coefficient omission based on reference signal groups, the first communication device 100 reduces the number of CSI coefficients and transmits CSI coefficients for multiple reference signal groups. In the CSI report 510, the first communication device 100 can indicate the indices of the reference signal groups for which CSI reporting has been performed or not performed. This information can be needed for two reasons: First, the second communication device 300 can need to know the reference signal groups that have been dropped in order for it to be able to correctly determine the size of the uplink control information (UCI) and correctly decode the UCI. Second, beam indication can be done within the reference signal groups, thus eventually reducing the overhead. When the CSI coefficient omission involves sampling rate and offset omission, the omission information can be needed in order for the second communication device 300 to be able to correctly determine the size of the UCI and correctly decode the UCI. Furthermore, in order to have the correct mapping in the time dimension when performing interpolation in a later step.

[0153] The first communication device 100 herein can also be denoted as a client device or a network access node. Correspondingly, the second communication device 300 herein can also be denoted as a network access node or a client device.

[0154] The network access node herein can also be denoted as a radio network access node, an access network access node, an access point (AP), or a base station (BS), e.g., a radio base station (RBS), which in some networks can be referred to as transmitter, "gNB", "gNodeB", "eNB", "eNodeB", "NodeB" or "B node", depending on the standard, technology and terminology used. Based on transmission power and thereby also cell size, wireless network access nodes can be of different classes or types such as macro eNodeB, home eNodeB or pico base station. The wireless network access node can also be a station that is any device that contains an IEEE 802.11 conformant media access control (MAC) and physical layer (PHY) interface to the wireless medium (WM). The wireless network access node can be used for communication in 3GPP related long term evolution (LTE), LTE-Advanced, fifth generation (5G) wireless systems such as new radio (NR) and evolution thereof, and IEEE related Wi-Fi, worldwide interoperability for microwave access (WiMAX) and evolution thereof.

[0155] The client device herein can be denoted as user equipment (UE), mobile station, internet of things (IoT) device, sensor device, wireless terminal and / or mobile terminal, enabled to communicate wirelessly in a wireless communication system, sometimes also referred to as a cellular radio system. The UE can further be referred to as a mobile telephone, cellular telephone, a tablet or laptop with wireless capability, etc. The UE in this context can be portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, etc., enabled to communicate voice and / or data, with another communication entity, such as another receiver or server, over a wireless access network. The UE can also be a station that is any device that contains an IEEE 802.11 conformant MAC and PHY interface to the WM. The UE can be used for communication in 3GPP related LTE, LTE-Advanced, 5G wireless systems such as NR and evolution thereof, and IEEE related Wi-Fi, WiMAX and evolution thereof.

[0156] Furthermore, any of the methods according to embodiments of the application can be implemented in a computer program, having code means, which when run by processing means causes the processing means to execute the steps of the method. The computer program is included in a computer readable medium of a computer program product. The computer readable medium can comprise essentially any memory, such as the previously mentioned ROM, PROM, EPROM, EEPROM or hard disk drive.

[0157] Furthermore, it should be appreciated that the first and second communication devices comprise the necessary communication capabilities in the form of functions, means, units, elements etc. for performing or realizing embodiments of the application. Examples of other such means, units, elements and functions are: processors, memories, buffers, control logic, encoders, decoders, rate matchers, rate dematchers, mapping units, multipliers, decision units, selection units, switches, interleavers, de interleavers, modulators, modems, inputs, outputs, antennas, amplifiers, receiving units, transmitting units, DSPs, TCM encoders, TCM decoders, power supply units, power feeders, communication interfaces, communication protocols, etc. which are suitably arranged together to perform the scheme.

[0158] Hence, the one or more processors of the first and second communication devices can comprise, e.g., one or more instances of a CPU, processing unit, processing circuit, processor, ASIC, microprocessor, or other processing logic that can interpret and execute instructions. Hence, the expression “processor” can mean any processing circuitry comprising a plurality of processing circuits, such as, e.g., any, some or all of the above mentioned ones. The processing circuitry can further comprise data processing stateful functions for data input, output and processing, including data buffering, as well as device control functions, such as call processing control, user interface control, etc.

[0159] Finally, it should be understood that the present application is not limited to the embodiments described above, but also relates to and incorporates all embodiments within the scope of the appended independent claims.

Claims

1. A first communication device (100) for a communication system (500), characterized in that The first communication device (100) is configured to: measure a set of reference signals transmitted in a set of transmission beams of a second communication device (300) and received in a set of reception beams of the first communication device (100); determine a set of channel state information, CSI, coefficients based on the measured set of reference signals; reduce the set of CSI coefficients to a subset of CSI coefficients by omitting at least one CSI coefficient based on a CSI omission rule; and transmit a CSI report (510) to the second communication device (300), the CSI report (510) indicating the subset of CSI coefficients.

2. The first communication device (100) according to claim 1, characterized by The CSI omission rule comprises omitting the CSI coefficients in a spatial domain and / or a time domain.

3. The first communication device (100) according to claim 2, characterized by The CSI omission rule comprises omitting the CSI coefficients by any of: a spatial offset, a time offset, a spatial sampling rate, and a time sampling rate.

4. The first communication device (100) according to claim 2 or 3, characterized by The CSI omission rule comprises omitting the CSI coefficients for one or more of: a transmission beam, a reception beam, and a beam pair comprising a transmission beam and a reception beam.

5. The first communication device (100) according to claim 2 or 3, characterized by The CSI omission rule comprises omitting the CSI coefficients for a time sequence of CSI coefficients in the set of CSI coefficients.

6. The first communication device (100) according to any one of the preceding claims, wherein The set of CSI coefficients comprises one or more of: a reference resource indicator, a beam index, a reference resource pair indicator, a beam pair index, a reference signal received power, and a signal-to-interference-and-noise ratio.

7. The first communication device (100) according to any one of the preceding claims, characterized by The CSI omission rule comprises omitting the CSI coefficients by reducing the measured set of reference signals to a subset of measured reference signals.

8. The first communication device (100) according to claim 7, characterized by The subset of measured reference signals is a set of at least one preconfigured reference signal in a channel measurement resource and / or an interference measurement resource.

9. The first communication device (100) according to any one of the preceding claims, characterized by The first communication device (100) is configured to: receive a first control signal (520) from the second communication device (300), the first control signal (520) indicating the CSI omission rule.

10. The first communication device (100) according to claim 9, characterized by The first control signal (520) is a radio resource control, RRC, signal.

11. The first communication device (100) according to any one of the preceding claims, characterized by The first communication device (100) is configured to: receive a second control signal (530) from the second communication device (300), the second control signal (530) indicating an activation or a deactivation of the CSI omission rule.

12. The first communication device (100) according to claim 11, characterized by The second control signal (530) is a downlink control information or a downlink medium access control control element.

13. The first communication device (100) according to any one of the preceding claims, characterized by The CSI report (510) further indicates information about omitting the CSI coefficients in a spatial domain and / or a time domain by any of: a spatial offset, a time offset, a spatial sampling rate, and a time sampling rate; and / or omitting the CSI coefficients by reducing the measured set of reference signals to a subset of measured reference signals based on a set of at least one preconfigured reference signal in a channel measurement resource and / or an interference measurement resource.

14. A second communication device (300) for a communication system (500), characterized by The second communication device (300) is configured to: transmit a set of reference signals in a set of transmission beams of the second communication device (300) to a set of reception beams of a first communication device (100); receiving (510), from the first communication device (100), a CSI report (510) indicating a subset of CSI coefficients in a set of CSI coefficients based on a CSI omission rule, the set of CSI coefficients corresponding to one or more of: the set of transmit beams, the set of receive beams, and a set of beam pairs comprising the set of transmit beams and the set of receive beams; and determining (512), based on the subset of CSI coefficients, the set of CSI coefficients.

15. The second communication device (300) according to claim 14, characterized by for determining: based on interpolation or extrapolation of the subset of CSI coefficients, determining the set of CSI coefficients.

16. The second communication device (300) according to claim 14 or 15, characterized by for determining: transmitting (520), to the first communication device (100), a first control signal (520) indicating the CSI omission rule.

17. The second communication device (300) according to claim 16, characterized by The first control signal (520) is an RRC signal.

18. The second communication device (300) according to any one of claims 14 to 17, characterized by The CSI omission rule comprises omitting at least one CSI coefficient in spatial and / or time domain.

19. The second communication device (300) according to claim 18, characterized by The CSI omission rule comprises omitting the CSI coefficient by any of: spatial offset, time offset, spatial sampling rate, and time sampling rate.

20. The second communication device (300) according to claim 18 or 19, characterized by The CSI omission rule comprises omitting the CSI coefficient for one or more of: transmit beam, receive beam, and beam pair comprising transmit beam and receive beam.

21. The second communication device (300) according to claim 19 or 20, characterized by The CSI omission rule comprises omitting the CSI coefficient for a time sequence of CSI coefficients in the set of CSI coefficients.

22. The second communication device (300) according to any one of claims 14 to 21, characterized by The set of CSI coefficients comprises one or more of: reference resource indicator, beam index, reference resource pair indicator, beam pair index, reference signal received power, and signal-to-interference-and-noise ratio.

23. The first communication device (100) according to any one of claims 14 to 22, characterized by The CSI omission rule comprises omitting at least one CSI coefficient by reducing a set of measured reference signals to a subset of measured reference signals.

24. The second communication device (300) according to claim 23, characterized by The subset of measured reference signals is at least one preconfigured reference signal group in channel measurement resource and / or interference measurement resource.

25. The second communication device (300) according to any one of claims 14 to 24, characterized by for determining: transmitting (530), to the first communication device (100), a second control signal (530) indicating activation or deactivation of the CSI omission rule.

26. The second communication device (300) according to claim 25, characterized by The second control signal (530) is a downlink control information or a downlink medium access control control element.

27. The second communication device (300) according to any one of claims 14 to 26, characterized by The CSI report (510) further indicates information on omitting at least one CSI coefficient in spatial and / or time domain by any of: spatial offset, time offset, spatial sampling rate, and time sampling rate; and / or based on at least one preconfigured reference signal group in channel measurement resource and / or interference measurement resource, by reducing a set of measured reference signals to a subset of measured reference signals.

28. A method (200) for a first communication device (100), characterized by, The method (200) comprises: measuring (202) a set of reference signals transmitted in a set of transmit beams of a second communication device (300) and received in a set of receive beams of the first communication device (100); determining (204) a set of channel state information, CSI, coefficients based on the set of measured reference signals; reducing (206), based on a CSI omission rule, the set of CSI coefficients to a subset of CSI coefficients by omitting at least one CSI coefficient; and transmitting (208) a CSI report (510) to the second communication device (300), the CSI report (510) indicating the subset of CSI coefficients.

29. A method (400) for a second communication device (200), characterized by, The method (400) comprises: transmitting (402) a set of reference signals to a set of receive beams of a first communication device (100) in a set of transmit beams of the second communication device (300); receiving (404) a CSI report (510) from the first communication device (100), the CSI report (510) indicating a subset of CSI coefficients in a set of CSI coefficients based on a CSI omission rule, the set of CSI coefficients corresponding to one or more of: the set of transmit beams, the set of receive beams, and a set of beam pairs comprising the set of transmit beams and the set of receive beams; and determining (406) the set of CSI coefficients based on the subset of CSI coefficients.

30. A computer program having a program code for performing a method according to one of the preceding claims 27 to 29 when the program code is executed on a computer. The program code causes the computer to perform the method according to claim 28 or 29 when the computer program is run on the computer.

Images