CN112119617B

CN112119617B - Eigenvalue based channel hardening and explicit feedback

Info

Publication number: CN112119617B
Application number: CN201880093411.6A
Authority: CN
Inventors: 毛小矛; F·沃克; R·阿梅德; W·J·希勒里; E·维索特斯基
Original assignee: Nokia Shanghai Bell Co Ltd; Nokia Solutions and Networks Oy
Current assignee: Nokia Shanghai Bell Co Ltd; Nokia Solutions and Networks Oy
Priority date: 2018-05-17
Filing date: 2018-05-17
Publication date: 2023-04-25
Anticipated expiration: 2038-05-17
Also published as: CN112119617A; EP3794785A4; WO2019218317A1; EP3794785A1

Abstract

An apparatus includes at least one processor and at least one memory including computer program code. The at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to: one or more eigenvectors associated with one or more uplink reference signals are calculated. The at least one memory and the computer program code are also configured to, with the at least one processor, cause the apparatus to: one or more channel hardening matrices based on one or more eigenvectors are applied to one or more downlink channel state information reference signals. The at least one memory and the computer program code are also configured to, with the at least one processor, cause the apparatus to: explicit channel state information is received from the user equipment.

Description

Eigenvalue based channel hardening and explicit feedback

Technical Field

Some embodiments may relate to a communication system. For example, some embodiments may relate to channel state information feedback.

Background

Channel State Information (CSI) may include implicit feedback, explicit feedback, and/or a linear combined codebook, which is a mixture of implicit feedback and explicit feedback. Explicit feedback returns channel information directly. A Discrete Fourier Transform (DFT) vector may be selected and applied to the hardened channel, which may reduce the dimension of the channel from m·n to b·n, where M is the number of transmit antennas, N is the number of receive antennas, and B is the number of precoders employed. Since the DFT precoder is considered as a narrow beam applied to the channel, the resulting aggregate channel matrix becomes thinner due to the channel hardening effect. However, providing explicit feedback typically requires a significant amount of network resources for reporting functions to maintain accuracy of CSI reporting.

Disclosure of Invention

According to one embodiment, a method may include: one or more eigenvectors associated with one or more uplink reference signals are calculated by a network entity. The method may further comprise: one or more channel hardening matrices based on the one or more eigenvectors are applied by the network entity to one or more user equipment downlink channel state information reference signals. The method may further comprise: explicit channel state information is received by the network entity from the user equipment.

According to one embodiment, an apparatus may include at least one processor and at least one memory including computer program code. The at least one memory and the computer program code may be configured to, with the at least one processor, cause the apparatus at least to: one or more eigenvectors associated with one or more uplink reference signals are calculated. The at least one memory and the computer program code may be configured to, with the at least one processor, cause the apparatus at least to: one or more channel hardening matrices based on the one or more eigenvectors are applied to one or more user equipment downlink channel state information reference signals. The at least one memory and the computer program code may be configured to, with the at least one processor, cause the apparatus to: explicit channel state information is received from the user equipment.

According to one embodiment, an apparatus may include: means for calculating one or more eigenvectors associated with one or more uplink reference signals. The apparatus may further include: means for applying one or more channel hardening matrices based on the one or more eigenvectors to one or more user equipment downlink channel state information reference signals. The apparatus may further include: means for receiving explicit channel state information from a user equipment.

According to one embodiment, in some embodiments, a non-transitory computer-readable medium may be encoded with instructions that, when executed in hardware, may perform a process. The process may include a method that may calculate one or more eigenvectors associated with one or more uplink reference signals. The process may include a method that may apply one or more channel hardening matrices based on one or more eigenvectors to one or more user equipment downlink channel state information reference signals. The process may include a method that may receive explicit channel state information from a user equipment.

According to one embodiment, a computer program product may have instructions encoded for performing a process according to some embodiments. The process may include a method that may calculate one or more eigenvectors associated with one or more uplink reference signals. The process may include a method that may further apply one or more channel hardening matrices based on one or more eigenvectors to one or more user equipment downlink channel state information reference signals. The process may include a method that may also receive explicit channel state information from a user equipment.

According to one embodiment, an apparatus may include circuitry configured to calculate one or more eigenvectors associated with one or more uplink reference signals. The apparatus may also include circuitry configured to apply one or more channel hardening matrices based on the one or more eigenvectors to one or more user equipment downlink channel state information reference signals. The apparatus may also include circuitry configured to receive explicit channel state information from a user equipment.

According to one embodiment, a method may include: one or more downlink channels are aggregated by a user equipment by collecting one or more channel impulse responses. The method may further comprise: one or more channel state information reference signals (CSI-RS) are estimated by the user equipment based on the aggregated one or more downlink channels. The method may further comprise: explicit channel state information feedback is sent by the user equipment to the network entity based on the estimated one or more CSI-RSs.

According to one embodiment, an apparatus may include at least one processor and at least one memory including computer program code. The at least one memory and the computer program code may be configured to, with the at least one processor, cause the apparatus at least to: one or more downlink channels are aggregated by collecting one or more channel impulse responses. The at least one memory and the computer program code may be configured to, with the at least one processor, further cause the apparatus at least to: one or more channel state information reference signals (CSI-RS) are estimated based on the aggregated one or more downlink channels. The at least one memory and the computer program code may be configured to, with the at least one processor, further cause the apparatus at least to: explicit channel state information feedback is sent to the network entity based on the estimated one or more CSI-RSs.

According to one embodiment, an apparatus may include means for aggregating one or more downlink channels by collecting one or more channel impulse responses. The apparatus may also include means for estimating one or more channel state information reference signals (CSI-RS) based on the aggregated one or more downlink channels. The apparatus may also include means for transmitting explicit channel state information feedback to the network entity based on the estimated one or more CSI-RSs.

According to one embodiment, in some embodiments, a non-transitory computer-readable medium may be encoded with instructions that, when executed in hardware, may perform a process. The process may include a method of aggregating one or more downlink channels by collecting one or more channel impulse responses. The process may include a method that may further estimate one or more channel state information reference signals (CSI-RS) based on the aggregated one or more downlink channels. The process may include a method that may also send explicit channel state information feedback to the network entity based on the estimated one or more CSI-RSs.

According to one embodiment, an apparatus may include circuitry configured to aggregate one or more downlink channels by collecting one or more channel impulse responses. The apparatus may include circuitry further configured to estimate one or more channel state information reference signals (CSI-RS) based on the aggregated one or more downlink channels. The apparatus may include circuitry further configured to send explicit channel state information feedback to a network entity based on the estimated one or more CSI-RSs.

According to one embodiment, an apparatus may include at least one processor and at least one memory including computer program code. The at least one memory and the computer program code may be configured to, with the at least one processor, cause the apparatus at least to: one or more downlink channels are aggregated by collecting one or more channel impulse responses. The at least one memory and the computer program code may be configured to, with the at least one processor, cause the apparatus at least to: one or more channel state information reference signals (CSI-RS) are estimated based on the aggregated one or more downlink channels. The at least one memory and the computer program code may be configured to, with the at least one processor, cause the apparatus at least to: one or more CSI-RSs based on the estimation are sent to the network entity, and explicit channel state information feedback is sent to the network entity.

Drawings

For a proper understanding of the present disclosure, reference should be made to the accompanying drawings, in which:

fig. 1 illustrates an example of a signaling diagram in accordance with certain embodiments.

Fig. 2 illustrates an example of a method performed by a network entity in accordance with certain embodiments.

Fig. 3 illustrates an example of a method performed by a user device in accordance with certain embodiments.

FIG. 4 illustrates an example of a system according to some embodiments.

Detailed Description

The particular features, structures, or characteristics of some embodiments described throughout the specification may be combined in any suitable manner in one or more embodiments. For example, the use of the phrases "certain embodiments," "some embodiments," "other embodiments," or other similar language throughout this specification refers to the fact that: the particular features, structures, or characteristics described in connection with this embodiment may be included in at least one embodiment of the invention. Thus, appearances of the phrases "in certain embodiments," "in some embodiments," "in other embodiments," or other similar language throughout this specification do not necessarily refer to the same group of embodiments, and the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

Some embodiments may help improve explicit feedback of the user equipment. Example embodiments described herein may have various benefits and/or advantages. For example, some embodiments may reduce the amount of network resources required for explicit reporting by the user equipment while maintaining CSI reporting accuracy. The eigenvectors may be used to harden the channel, resulting in a sparse channel that utilizes less network resource overhead. Furthermore, uplink (UL) and/or Downlink (DL) channel reciprocity and channel hardening at a network entity, such as a gNB, may make the channel hardening transparent to a User Equipment (UE), thereby eliminating the UE from having to report a feature vector or DFT precoder index. A reduction in network resource usage may be further achieved while maintaining high accuracy of explicit feedback using eigen decomposition techniques. Accordingly, certain embodiments are directed to improvements in computer-related technology, particularly by conserving network resources and reducing power consumption by UEs and/or network entities located within a network.

Fig. 1 shows an example of a signaling diagram illustrating communication between a user equipment 130 and a network entity 140. User device 130 may be similar to user device 410 and network entity 140 may be similar to network entity 420, both shown in fig. 4. In step 101, UE 130 may send one or more UE reference signals to network entity 140. In step 103, the network entity 140 may estimate one or more uplink reference signals based on the UE reference signals received from the UE 130.

In step 105, the network entity 140 may calculate one or more UE channel feature vectors based on the estimated one or more uplink reference signals. In some embodiments, one or more downlink channel matrices at physical resource block/subband i estimated from uplink sounding reference signals may be estimated from h _i And (3) representing. R can then be used _i (n)＝h _i ^H ·h _i To determine a spatial channel covariance matrix with the current subframe n, where H is the conjugate transpose of the matrix (such as the spatial channel covariance matrix). In addition, R can be used _i (n)＝U _i ·Λ _i ·U _i ^H To determine R _i (n) feature decomposition, wherein U _i Is a square matrix, U _i The j th column q _i，j Is R _i Feature vector of (n), Λ _i Is a diagonal matrix, Λ _i Is a corresponding eigenvalue, in particular lambda _i，j Where i represents a PRB index or subband index and j indicates an element index of a j-th row and a j-th column in the diagonal matrix. In some embodiments, one or more taps of the channel impulse response may be preserved after each selected feature vector is applied by channel hardening. By applying one or more channel hardening matrices to one or more CSI-RS ports, one or more aggregated channels at the UE may be sparse, resulting in a reduction in the number of CIR taps observed in the time domain. In some embodiments, the number of taps may be limited to one, causing the UE to report explicit feedback with reduced overhead.

In step 107, the network entity 140 may select one or more of the one or more UE channel feature vectors. For example, the number of feature vectors selected may be represented as B _i . In some embodiments, one or more feature vectors may be selected to harden one by setting a threshold t for the feature valueOr multiple channels. The characteristic values may be in random order, ascending order, or descending order, such as lambda _i，1 ≥λ _i，2 ≥λ _i，3 ≥λ _i，… . When the eigenvalues are ordered in decreasing order, the jth eigenvector may be used to form a channel hardening matrix if the jth eigenvalue is greater than the threshold t. In one embodiment, feature vectors 1, 2, &..once again, j can be used _max To form a channel hardening matrix, where j _max ＝max{j：λ _i，j > t }. In some embodiments, the threshold t may depend on the network entity, the UE channel, and/or the network entity scheduling capability.

When eigenvectors in the hardening matrix are considered the basis of the beam, one or more values (such as B _i ) May need to be greater than the total number of transmit layers (such as r) in order to form orthogonality between layers, e.g., B _i ＝max(j _max R). For an explicit polarization (X-pol) antenna array, where B can be determined by providing orthogonality between layers using cross-polarization isolation _i Wherein B is _i ＝max(j _max R/2). In embodiments using an X-pol antenna array, the transmitted polarization layer may experience reduced polarization interference. In addition, in the case where multiple co-located x-pol antenna arrays experience channel variations, one or more channel hardening matrices may be applied in half the dimension associated with each polarization.

In some embodiments, the UE may be equipped with more Receive (RX) antennas than Transmit (TX) antennas. In this example, UE TX antenna switching may be provided to enhance UL/DL reciprocity and/or to acquire complete DL channel functionality by estimating one or more UL Sounding Reference Signals (SRS).

In various embodiments, UL/DL reciprocity may be preferably adjusted. For example, in a Frequency Division Duplex (FDD) system for paired spectrum, only long-term spatial information may be extracted from the UL and/or may be mapped to DL transmissions. Estimating a UE downlink channel matrix h for Physical Resource Blocks (PRBs)/subbands i from one or more UL SRS _i In an embodiment of (2), the spatial channel at the current subframe n may be determined by averaging all PRBs/subbandsCovariance matrix, e.g. R (n) = Σ _i h _i ^H ·h _i Where H is the conjugate transpose. Therefore, R (n) =u·Λ·u can be used ^H To determine a eigen decomposition of the spatial channel covariance matrix, such as R (n), where U is the square matrix and the j-th column of U is the eigenvector q of R (n) _j And Λ is a diagonal matrix, and the diagonal elements of Λ are corresponding eigenvalues.

In step 109, the network entity 140 may form one or more channel hardening matrices based on the one or more selected feature vectors. For example, one or more channel hardening matrices may be represented by Q _i Representing, and may be, a sub-band short-term channel hardening matrix and/or a wideband long-term channel hardening matrix. In such an embodiment, the data may be obtained by Φ _i ＝h _i ·Q _i To determine the resulting channel. In one embodiment, Q _i ＝[q _i，l ，q _i，2 ，…，q _i，Bi ]。

In addition, channel state information reporting in the time and/or frequency domain may be applied to Φ _i In order to provide explicit CSI feedback. For example, after eigen decomposition of the spatial channel covariance matrix, a plurality of eigenvectors (such as B _i ) And is used to form a matrix (such as Q) such that Q _i =q, thereby hardening the channels for all PRBs/subbands. A similar process may be performed in a Time Division Duplex (TDD) system.

In various embodiments, the formation of one or more channel hardening matrices may be based in part on one or more of the following: antenna array type, duplex mode (TDD or FDD), one or more thresholds, or other factors.

In step 111, the network entity 140 may apply one or more channel hardening matrices to one or more user equipment downlink channel state information reference signals. One or more channel hardening matrices may be applied as precoders to one or more user equipment downlink channel state information reference signals in several ways. For example, the network entity 140 may apply each precoder in one or more channel-hardening matrices to one or more antenna ports in a channel state information reference signal (CSI-RS) resource. In another example, the network entity may apply each precoder in one or more channel-hardening matrices to a single CSI-RS resource in the set of CSI-RS resources. In this example, each CSI-RS resource in the set of CSI-RS resources may have multiple antenna ports, allowing the UE to perform further channel hardening. In addition, the configuration of the precoder in the one or more channel-hardening matrices may be updated periodically, e.g., by transmitting semi-permanent and/or aperiodic CSI-RSs to the UE. In step 113, the network entity 140 may transmit one or more CSI-RS signals to the user equipment 130 through a downlink channel.

In step 115, the user equipment 130 may estimate one or more CSI-RSs. In addition, the user equipment may aggregate one or more downlink channels by collecting one or more channel impulse responses prior to estimating the one or more CSI-RSs. In some embodiments, the user equipment may aggregate one or more CSI-RSs in several ways. For example, the user equipment may aggregate one or more CSI-RS by collecting one or more channel impulse responses from each CSI-RS port in CSI-RS resources associated with each user equipment RX antenna. In another example, the user equipment may aggregate one or more CSI-RS by collecting channel impulse responses from each CSI-RS port associated with each CSI-RS in the CSI-RS resource set associated with each user equipment RX antenna. In some embodiments, the user equipment may support reporting one or more channel impulse responses of the aggregated channel in the time/frequency domain without having to transmit a DFT beam index.

In step 117, the user equipment 130 may send explicit channel state information feedback to the network entity. In some embodiments, the user equipment 130 may report one or more channel hardening precoder indices to the network entity 140 without a DFT beam index for the channel impulse response of the aggregated channel in the time/frequency domain. In addition, the user equipment 130 may report reciprocity-based explicit feedback in a PUCCH-based periodic CSI report.

Fig. 2 illustrates an example method performed by a network entity. The network entity may be similar to network entity 420 shown in fig. 4. In step 201, a network entity may receive one or more reference signals from a user equipment. As an example, the user device may be similar to user device 410 shown in fig. 4. In step 203, the network entity may estimate one or more uplink reference signals. In step 205, the network entity may obtain user equipment downlink channel information associated with a downlink channel of the user equipment.

In step 207, the network entity may calculate one or more eigenvectors associated with one or more uplink reference signals. In some embodiments, one or more downlink channel matrices at physical resource block/subband i estimated from uplink sounding reference signals may be estimated from h _i And (3) representing. R can then be used _i (n)＝h _i ^H ·h _i To determine a spatial channel covariance matrix with the current subframe n, where H is a conjugate transpose. In addition, R can be used _i (n)＝U _i ·Λ _i ·U _i ^H To determine R _i (n) feature decomposition, wherein U _i Is a square matrix, U _i The j th column q _i，j Is R _i Feature vector of (n), Λ _i Is a diagonal matrix, Λ _i Is a corresponding eigenvalue, in particular lambda _i，j Where i represents a PRB index or subband index and j represents an element index of a j-th row and a j-th column in the diagonal matrix. In some embodiments, one or more taps of the channel impulse response may be preserved after each selected feature vector is applied by channel hardening. By applying one or more channel hardening matrices to one or more CSI-RS ports, one or more aggregated channels at the UE may be sparse, resulting in a reduction in the number of CIR taps observed in the time domain. In some embodiments, the number of taps may be limited to one, where the UE may report explicit feedback with reduced overhead.

In step 209, the network entity may select one or more feature vectors. For example, the number of feature vectors selected may be represented as B _i . In some embodiments, one or more eigenvectors may be selected to harden one or more channels by setting a threshold t for eigenvalues. The characteristic values may be in random order, ascending order, or descending order, such as lambda _i，j ≥λ _i，2 ≥λ _i，3 ≥λ _i，… . When the eigenvalues are ordered in decreasing order, the jth eigenvalue may be used to form a channel hardening matrix if the jth eigenvalue is greater than the threshold t. In one embodiment, feature vectors 1, 2, &..once again, j can be used _max To form a channel hardening matrix, where j _max ＝max{j：λ _i，j > t }. In some embodiments, the threshold t may depend on the network entity, the UE channel, and/or the network entity scheduling capability.

Although eigenvectors in the hardening matrix may be considered the beam basis, one or more values (such as B _i ) May need to be greater than the total number of transmit layers (such as r) in order to form orthogonality between layers, e.g., B _i ＝max(j _max R). For an explicit polarization (X-pol) antenna array, where B can be determined by providing orthogonality between layers using cross-polarization isolation _i Wherein B is _i ＝max(j _max R/2). In embodiments using an X-pol antenna array, layers transmitted with one or more polarizations may experience reduced polarization interference. In addition, in the case where multiple co-located x-pol antenna arrays experience channel variations, one or more channel hardening matrices may be applied in half the dimension associated with each polarization.

In various embodiments, UL/DL reciprocity may be preferably adjusted. For example, in a Frequency Division Duplex (FDD) system for paired spectrum, long-term spatial information may be extracted from the UL and/or may be mapped to DL transmissions. Estimating UE downlink information for PRB/subband i from UL SRSTrack matrix h _i In an embodiment of (2), the spatial channel covariance matrix at the current subframe n may be determined by averaging all PRBs/subbands, e.g., R (n) = Σ _i h _i ^H ·h _i Where H is the conjugate transpose. Therefore, R (n) =u·Λ·u can be used ^H To determine a eigen decomposition of the spatial channel covariance matrix, where U is the square matrix and its j-th column is the eigenvector q of R (n) _j And Λ is a diagonal matrix, and the diagonal elements of Λ are corresponding eigenvalues.

In step 211, the network entity may form one or more channel hardening matrices based on the one or more selected feature vectors. For example, one or more channel hardening matrices may be represented by Q _i Representing, and may be, a sub-band short-term channel hardening matrix and/or a wideband long-term channel hardening matrix. In such an embodiment, the data may be obtained by Φ _i ＝h _i ·Q _i To determine the resulting channel phi _i . In one embodiment, Q _i ＝[q _i，l ，q _i，2 ，...，q _i，Bi ]。

In response, channel state information reporting in the time and/or frequency domain may be applied to Φ _i In order to provide explicit CSI feedback. For example, after eigen decomposition of the spatial channel covariance matrix, a plurality of eigenvectors (such as B _i ) And is used to form a matrix (such as Q). In an example embodiment, wherein Q _i Equal to Q, Q may harden the channel for all PRBs/subbands. A similar procedure may be performed in a TDD system.

The formation of one or more channel hardening matrices may be based on one or more of: antenna array type, duplexing method (TDD or FDD), one or more thresholds, or other factors.

In step 213, the network entity may apply one or more channel hardening matrices to one or more user equipment downlink channel state information reference signals. One or more channel hardening matrices may be applied as precoders to one or more user equipment downlink channel state information reference signals in several ways. For example, the network entity may apply each precoder in one or more channel-hardening matrices to one or more antenna ports in the CSI-RS resources. In another example, the network entity may apply each precoder in one or more channel-hardening matrices to a single CSI-RS resource in the set of CSI-RS resources. In this example, each CSI-RS resource in the set of CSI-RS resources may have multiple antenna ports, allowing the UE to perform further channel hardening. In addition, the configuration of the precoder in the one or more channel-hardening matrices may be updated periodically, e.g., by transmitting semi-permanent and/or aperiodic CSI-RSs to the UE.

In step 215, the network entity may send one or more downlink channel state information reference signals to the user equipment. In step 217, the network entity may receive explicit channel state information feedback from the user equipment.

Fig. 3 illustrates an example method performed by a user device similar to user device 410 illustrated in fig. 4. In step 301, a user equipment may send one or more UE reference signals to a network entity similar to network entity 420 in fig. 4. In step 303, the user equipment may aggregate one or more downlink channels by collecting one or more channel impulse responses from the network entity.

In step 305, the user equipment may estimate one or more channel state information reference signals (CSI-RS) based on the aggregated one or more downlink channels. In some embodiments, the user equipment may aggregate one or more CSI-RSs in several ways. For example, the user equipment may aggregate one or more CSI-RS by collecting one or more channel impulse responses from each CSI-RS port in CSI-RS resources associated with each user equipment RX antenna. In another example, the user equipment may aggregate one or more CSI-RS by collecting channel impulse responses from each CSI-RS port associated with each CSI-RS in a set of CSI-RS resources associated with each user equipment RX antenna. In some embodiments, the user equipment may support reporting one or more channel impulse responses of the aggregated channel in the time/frequency domain without having to transmit a DFT beam index.

In step 307, the user equipment may send explicit channel state information feedback to the network entity based on the estimated one or more CSI-RSs. In some embodiments, the user equipment may report the channel impulse response of the aggregated channel in the time/frequency domain without the DFT beam index. In some embodiments, the UE may send reciprocity-based explicit feedback in a PUCCH-based periodic CSI report.

FIG. 4 illustrates an example of a system according to some embodiments. In one embodiment, a system may include a plurality of devices, such as, for example, user device 410 and network entity 420.

UE 410 may include one or more of the following: mobile devices such as mobile phones, smart phones, personal Digital Assistants (PDAs), tablet computers, or portable media players; a digital camera; a portable video camera; a video game machine; a navigation unit, such as a Global Positioning System (GPS) device; desktop or portable computers; a single location device such as a sensor or smart meter; or any combination thereof. Network entity 420 may be one or more of the following: a base station, such as an evolved node B (eNB) or 5G or new radio node B (gNB); a service gateway; a server; and/or any other access node; or a combination thereof. Further, user device 410 and/or network entity 420 may be one or more of a citizen broadband radio service device (CBSD).

One or more of these devices may include at least one processor, indicated as 411 and 421, respectively. At least one memory may be provided in one or more of the devices indicated at 412 and 422. The memory may be fixed or removable. The memory may include computer program instructions or computer code embodied therein. The

processors

411 and 421 and the

memories

412 and 422 or a subset thereof may be configured to provide components corresponding to the respective blocks of fig. 1-3. Although not shown, the device may also include positioning hardware, such as GPS or microelectromechanical system (MEMS) hardware, which may be used to determine the location of the device. Other sensors are also permissible and may be included to determine position, altitude, orientation, etc., such as barometers, compasses, etc.

As shown in fig. 4,

transceivers

413 and 423 may be provided, and one or more of the devices may further include at least one antenna, shown as 414 and 424, respectively. The device may have many antennas, such as an antenna array configured for multiple-input multiple-output (MIMO) communication, or multiple antennas for multiple radio access technologies. For example, other configurations of these devices may be provided.

The

transceivers

413 and 423 may be transmitters, receivers, or both transmitters and receivers, or may be units or devices configured to transmit and receive both.

The

processors

411 and 421 may be embodied by any computing or data processing device, such as a Central Processing Unit (CPU), application Specific Integrated Circuit (ASIC), or similar device. A processor may be implemented as a single controller, or as multiple controllers or processors.

Memories

412 and 422 may independently be any suitable storage device such as a non-transitory computer readable medium. A Hard Disk Drive (HDD), random Access Memory (RAM), flash memory, or other suitable memory may be used. The memory may be combined as a processor on a single integrated circuit or may be separate from one or more processors. Furthermore, the computer program instructions stored in the memory and which may be processed by the processor may be any suitable form of computer program code, for example a compiled or interpreted computer program written in any suitable programming language. The memory may be removable or non-removable.

The memory and computer program instructions may be configured with a processor for a particular device to cause a hardware apparatus, such as a user device, to perform any of the processes described below (see, e.g., fig. 1-3). Thus, in certain embodiments, a non-transitory computer-readable medium may be encoded with computer instructions that, when executed in hardware, perform a process such as one of the processes described herein. Alternatively, some embodiments may be implemented entirely in hardware.

In some embodiments, an apparatus may include circuitry configured to perform any of the processes or functions shown in fig. 1-3. For example, the circuitry may be a hardware-only circuit implementation, such as analog and/or digital circuitry. In another example, the circuitry may be a combination of hardware circuitry and software, such as a combination of analog and/or digital hardware circuit(s) and software or firmware, and/or any portion of a hardware processor(s) in combination with software (including digital signal processor (s)), software, and at least one memory, that work together to cause the apparatus to perform various processes or functions. In yet another example, the circuitry may be hardware circuit(s) and/or processor(s), such as microprocessor(s) or a portion of microprocessor(s), including software, such as firmware for operation. When the hardware operation does not require software, software in the circuitry may not be present.

Those of ordinary skill in the art will readily appreciate that certain embodiments discussed above may be practiced with steps in a different order and/or with hardware elements of a different configuration than those disclosed. Thus, it will be apparent to those skilled in the art that certain modifications, variations, and alternative constructions will be apparent, while remaining within the spirit and scope of the invention. Accordingly, reference should be made to the appended claims for determining the metes and bounds of the invention.

Partial vocabulary

3GPP third Generation partnership project

5G fifth generation wireless system

ASIC specific integrated circuit

CBRS citizen broadband radio service

CIR channel impulse response

CPU central processing unit

CSI channel state information

CSI-RS channel state information reference signal

DFT discrete Fourier transform

DL downlink

eNBs evolved node B

FDD frequency division duplexing

FTT fast Fourier transform

gNB next generation node B

GPS global positioning system

HDD hard disk drive

Inverse fast fourier transform of IFFT

LTE long term evolution

MEMS micro-electromechanical system

MIMO multiple input multiple output

MU multi-user

NR RAN next generation radio access network

NR new radio

PDA personal digital assistant

PRB physical resource block

PUCCH physical uplink control channel

QCL quasi-co-location

RAM random access memory

RX reception

SRS sounding reference signal

TDD time division duplexing

TX transmission

UE user equipment

UL uplink

Claims

1. An apparatus for communication, comprising:

at least one processor; and

at least one memory including computer program code,

wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to:

receiving one or more uplink reference signals from a user equipment;

calculating one or more eigenvectors of a spatial channel covariance matrix associated with the one or more uplink reference signals;

forming one or more channel hardening matrices, the one or more channel hardening matrices comprising one or more selected feature vectors of the one or more feature vectors;

applying the one or more channel hardening matrices as precoders to one or more channel state information reference signals, CSI-RS;

transmitting the one or more channel state information reference signals (CSI-RSs) to the user equipment; and

explicit channel state information feedback is received from the user equipment.

2. The apparatus of claim 1, wherein the one or more channel hardening matrices are at least one of a subband short-term channel hardening matrix and/or a wideband long-term channel hardening matrix.

3. The apparatus of claim 1 or 2, wherein the formation of the one or more channel hardening matrices is based on one or more of a system configuration and a scheduling decision.

4. The apparatus of claim 1 or 2, wherein the at least one memory and the computer program code are further configured to, with the at least one processor, cause the apparatus to:

the spatial channel covariance matrix is determined in a current subframe based on one or more channel vectors at physical resource blocks/subbands estimated from the one or more uplink reference signals.

5. The device according to claim 1 or 2, wherein,

the explicit channel state information feedback includes one or more channel hardening precoder indexes.

6. An apparatus for communication, comprising:

at least one processor; and

at least one memory including computer program code,

transmitting one or more uplink reference signals to a network entity;

receiving one or more channel state information reference signals, CSI-RS, from the network entity, the one or more channel state information reference signals, CSI-RS, being applied as one or more channel hardening matrices of a precoder;

estimating channel state information based on the received one or more channel state information reference signals CSI-RS; and

and sending explicit channel state information feedback to the network entity based on the estimated channel state information.

7. The apparatus of claim 6, wherein one or more downlink channels are aggregated by collecting one or more channel impulse responses from one or more CSI-RS ports in one or more CSI-RS resources associated with one or more receive antennas.

8. The apparatus of claim 6, wherein one or more downlink channels are aggregated by collecting one or more channel impulse responses from one or more CSI-RS ports associated with one or more CSI-RS in one or more CSI-RS resources associated with one or more receive antennas.

9. A method for communication, comprising:

receiving, by a network entity, one or more uplink reference signals from a user equipment;

calculating, by the network entity, one or more eigenvectors of a spatial channel covariance matrix associated with the one or more uplink reference signals;

forming, by the network entity, one or more channel hardening matrices, the one or more channel hardening matrices comprising one or more selected feature vectors of the one or more feature vectors;

applying, by the network entity, the one or more channel hardening matrices as precoders to one or more channel state information reference signals, CSI-RS;

transmitting, by the network entity, one or more channel state information reference signals, CSI-RS, to the user equipment; and

explicit channel state information feedback is received by the network entity from the user equipment.

10. The method of claim 9, wherein the one or more channel hardening matrices are at least one of a subband short-term channel hardening matrix and/or a wideband long-term channel hardening matrix.

11. The method of claim 9 or 10, wherein the formation of the one or more channel hardening matrices is based on one or more of a system configuration and a scheduling decision.

12. The method of claim 9 or 10, further comprising:

the spatial channel covariance matrix is determined by the network entity in a current subframe based on one or more channel vectors at physical resource blocks/subbands estimated from the one or more uplink reference signals.

13. The method according to claim 9 or 10, wherein,

14. A method for communication, comprising:

transmitting, by the user equipment, one or more uplink reference signals to the network entity;

receiving, by the user equipment, one or more channel state information reference signals, CSI-RS, from the network entity, the one or more channel state information reference signals, CSI-RS, applied as one or more channel hardening matrices of a precoder;

estimating, by the user equipment, channel state information based on the received one or more channel state information reference signals CSI-RS; and

explicit channel state information feedback is sent by the user equipment to the network entity based on the estimated channel state information.

15. The method of claim 14, wherein one or more downlink channels are aggregated by collecting one or more channel impulse responses from one or more CSI-RS ports in one or more CSI-RS resources associated with one or more receive antennas.

16. The method of claim 14, wherein one or more downlink channels are aggregated by collecting one or more channel impulse responses from one or more CSI-RS ports associated with one or more CSI-RS in one or more CSI-RS resources associated with one or more receive antennas.

17. A non-transitory computer readable medium encoding instructions that, when executed in hardware, perform the method of any of claims 9 to 16.

18. An apparatus comprising means for performing the method of any one of claims 9 to 16.

19. An apparatus comprising circuitry configured to cause the apparatus to perform the method of any one of claims 9 to 16.