Patent Description:
Implicit CSI feedback is a CSI feedback method based on a predefined codebook (see, R1-<NUM>, 3GPP TSG RAN WG1 Meeting #<NUM>). The UE may estimate the channel and calculate a best rank/precoder selected within the predefined codebook, then provide feedback indicating the rank/precoder index to the eNB/gNB.

In some instances, UE assisted dynamic eigenvector reporting may be implemented. In these instances, the number of the total reported eigenvectors may be determined based on UE measurement. Although UE assisted dynamic eigenvector reporting adapts to the number of reported eigenvectors, the total report overhead will increase linearly with the number of reported eigenvectors.

<CIT> discloses a channel state information feedback solution utilizing precoding matrices from a main codebook and auxiliary codebook.

<CIT> beam forming method comprising an initialisation phase and a working phase. <CIT> discloses a method of feeding back of the dominant eigenvectors and eigenvalues so that the BS combines them to obtain the precoder.

This section is intended to include examples and is not intended to be limiting.

According to an aspect of the present invention, there is provided a method of claim <NUM>. According to an aspect of the present invention, there is provided an apparatus of claim <NUM>.

The foregoing and other aspects of embodiments of this invention are made more evident in the following Detailed Description, when read in conjunction with the attached Drawing Figures, wherein:.

In the example embodiments as described herein a novel method and apparatus is proposed to implement an explicit CSI reporting method in which a device (such as a UE) may report one vector, which may be a dominant eigenvector, or a single vector that may be a combination of multiple eigenvectors, according to the angular spread at an eNB/gNB and a UE speed. The overhead may be fixed for particular port configurations based on the one vector (dominant eigenvector or single vector) that is reported.

Turning to <FIG>, this figure shows a block diagram of one possible and non-limiting exemplary system in which the exemplary embodiments may be practiced. In <FIG>, a user equipment (UE) <NUM> is in wireless communication with a wireless network <NUM>. A UE is a wireless, typically mobile device that can access a wireless network. The UE <NUM> includes one or more processors <NUM>, one or more memories <NUM>, and one or more transceivers <NUM> interconnected through one or more buses <NUM>. The one or more buses <NUM> may be address, data, or control buses, and may include any interconnection mechanism, such as a series of lines on a motherboard or integrated circuit, fiber optics or other optical communication equipment, and the like. The UE <NUM> includes a control module <NUM>, comprising one of or both parts <NUM>-<NUM> and/or <NUM>-<NUM>, which may be implemented in a number of ways. The control module <NUM> may be implemented in hardware as control module <NUM>-<NUM>, such as being implemented as part of the one or more processors <NUM>. The control module <NUM>-<NUM> may be implemented also as an integrated circuit or through other hardware such as a programmable gate array. In another example, the control module <NUM> may be implemented as control module <NUM>-<NUM>, which is implemented as computer program code <NUM> and is executed by the one or more processors <NUM>. For instance, the one or more memories <NUM> and the computer program code <NUM> may be configured to, with the one or more processors <NUM>, cause the user equipment <NUM> to perform one or more of the operations as described herein. The UE <NUM> communicates with eNB <NUM> via a wireless link <NUM>.

The eNB (evolved NodeB) <NUM> is a base station (e.g., for LTE, long term evolution) that provides access by wireless devices such as the UE <NUM> to the wireless network <NUM>. The eNB <NUM> includes one or more processors <NUM>, one or more memories <NUM>, one or more network interfaces (N/W I/F(s)) <NUM>, and one or more transceivers <NUM> interconnected through one or more buses <NUM>. The eNB <NUM> includes a control module <NUM>, comprising one of or both parts <NUM>-<NUM> and/or <NUM>-<NUM>, which may be implemented in a number of ways. The control module <NUM> may be implemented in hardware as control module <NUM>-<NUM>, such as being implemented as part of the one or more processors <NUM>. The control module <NUM>-<NUM> may be implemented also as an integrated circuit or through other hardware such as a programmable gate array. In another example, the control module <NUM> may be implemented as control module <NUM>-<NUM>, which is implemented as computer program code <NUM> and is executed by the one or more processors <NUM>. For instance, the one or more memories <NUM> and the computer program code <NUM> are configured to, with the one or more processors <NUM>, cause the eNB <NUM> to perform one or more of the operations as described herein. Two or more eNBs <NUM> communicate using, e.g., link <NUM>. The link <NUM> may be wired or wireless or both and may implement, e.g., an X2 interface.

The one or more buses <NUM> may be address, data, or control buses, and may include any interconnection mechanism, such as a series of lines on a motherboard or integrated circuit, fiber optics or other optical communication equipment, wireless channels, and the like. For example, the one or more transceivers <NUM> may be implemented as a remote radio head (RRH) <NUM>, with the other elements of the eNB <NUM> being physically in a different location from the RRH, and the one or more buses <NUM> could be implemented in part as fiber optic cable to connect the other elements of the eNB <NUM> to the RRH <NUM>.

The wireless network <NUM> may include a network control element (NCE) <NUM> that may include MME (Mobility Management Entity)/SGW (Serving Gateway) functionality, and which provides connectivity with a further network, such as a telephone network and/or a data communications network (e.g., the Internet). The eNB <NUM> is coupled via a link <NUM> to the NCE <NUM>. The link <NUM> may be implemented as, e.g., an S1 interface. The NCE <NUM> includes one or more processors <NUM>, one or more memories <NUM>, and one or more network interfaces (N/W I/F(s)) <NUM>, interconnected through one or more buses <NUM>. The one or more memories <NUM> and the computer program code <NUM> are configured to, with the one or more processors <NUM>, cause the NCE <NUM> to perform one or more operations.

The computer readable memories <NUM>, <NUM>, and <NUM> may be of any type suitable to the local technical environment and may be implemented using any suitable data storage technology, such as semiconductor based memory devices, flash memory, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory. The computer readable memories <NUM>, <NUM>, and <NUM> may be means for performing storage functions. The processors <NUM>, <NUM>, and <NUM> may be of any type suitable to the local technical environment, and may include one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on a multi-core processor architecture, as non-limiting examples. The processors <NUM>, <NUM>, and <NUM> may be means for performing functions, such as controlling the UE <NUM>, eNB <NUM>, and other functions as described herein.

Having thus introduced one suitable but non-limiting technical context for the practice of the exemplary embodiments of this invention, the exemplary embodiments will now be described with greater specificity.

According to an example embodiment of an explicit CSI reporting method, one dominant eigenvector or one vector which is a combination of multiple eigenvectors may be reported according to the angular spread at the eNB <NUM> (or gNB) and UE <NUM> speed. As only one vector will be reported, the overhead is fixed for a certain port configuration. However, reporting one dominant eigenvector or one vector which is a combination of multiple eigenvectors may achieve diversity gain comparable to multiple eigenvectors being reported in a high eNB <NUM> (or gNB) angular spread or high UE <NUM> speed scenario, and high beamforming gain in instances in which one dominant eigenvector is reported in a low <NUM> (or gNB) angular spread and low UE <NUM> speed scenario.

With regard to CSI feedback from UEs <NUM>, systems or devices may require extensive simulations to determine the optimal number of eigenvectors that is to be reported so that the best tradeoff between overhead and performance may be attained. For example, 3GPP LTE MIMO may support up to <NUM> ports for transmission, and up to rank <NUM> for transmission. Further, the actual number of reported eigenvectors may be UE-specific and highly dependent on the channel characteristic between eNB <NUM> (or gNB) and UE <NUM>. In instances in which the angular spread at the eNB <NUM> (or gNB) is high and all channel paths contribute similarly to the received signal, reporting multiple eigenvectors may enable the system to achieve diversity gain and, in instances of MU transmission, the reporting of multiple eigenvectors may provide greater flexibility for beam allocation (when compared to reporting of a single eigenvector). In contrast, in instances in which the angular spread at the eNB <NUM> (or gNB) is low, transmitting with full power by the dominant eigenvector (as the dominant beam) produces the best beamforming gain. In addition to angular spread, UE <NUM> speed is another factor impacting the number of reported eigenvectors. When determining the tradeoff between overhead for reporting eigenvectors and performance, for a high speed UE <NUM>, more reported eigenvectors may provide more diversity and therefore more robust performance, while a single dominant eigenvector may be preferable for low speed UEs <NUM> as high beamforming gain is achieved with low overhead.

UE <NUM> speed may be determined based on the Doppler offset (which may be estimated) and which may then be used in calculating the speed of UE <NUM>. Angular spread may be linked to rank estimation (such as performed by the UE <NUM>). The number of eigenvectors may be combined based on the reported rank from the UE <NUM>. For example, in instances in which the UE <NUM> reports rank <NUM>, two eigenvectors may be combined, if the UE <NUM> reports rank x (where x is a positive integer greater than one), the system (for example, the UE <NUM> or eNB <NUM>) may combine x eigenvectors.

Angular spread is a measuring for channel characteristics, eigenvectors can be seen multiple paths, the associated eigenvalues may be seen as the scaling of signal power on each of the multiple path. If the total power is spread across several paths, for example. In instances in which there are several eigenvectors with non-zero eigenvalues, the angular spread may be defined (or determined) to comprise high angular spread. In instances in which there are only a few non-zero eigenvalues, or, in extreme instances in which there is only one non-zero eigenvalue, the angular spread may be defined (or determined) to comprise small angular spread (for example, in a line of sight case).

Explicit CSI feedback may be applied to LTE enhanced Full Dimension (eFD) MIMO and NR MIMO. Explicit CSI feedback may be transmitted by a UE <NUM> reporting in terms of quantized amplitudes and phases of the channel covariance matrix or the corresponding eigenvectors (for example, using PUCCH, PUSCH, etc.). Specifically, the eNB <NUM> (or gNB) may determine the reporting bit width of the coefficients and phases, and then the UE <NUM> may quantize the estimated channel covariance matrix or eigenvector elements according to the bit width and feed the results back to the eNB <NUM> (or gNB). For sparse channels, eigenvector reporting may be efficient, as only one or two eigenvectors with non-zero eigenvalues may be required to be fed back, and these eigenvectors represent the main channel paths between the eNB <NUM> (or gNB) and the UE <NUM>.

In MIMO/beamforming (BF) implementation, either UE-to-eNB feedback or reciprocity-based uplink channel estimation may be used to provide CSI to enable MIMO/BF operation at the eNB <NUM>. In addition to rank (RI) and channel quality (CQI) indication feedback from the UEs <NUM>, the selection of the precoding matrix (note that a vector is a one dimensional matrix) as a precoder from a predefined codebook based on precoding matrix indicator (PMI) feedback from the UE <NUM>, or the selection of the transmit beamforming weight as a beam based on UE <NUM> uplink channel estimates, may be utilized for optimizing MIMO/BF system performance. For the UE-to-eNB feedback method, implicit CSI feedback may use a predefined codebook and report of PMIs. Explicit CSI feedback may use UE <NUM> feedback directly to provide precoders (precoding vectors) by quantizing the phase and amplitude of each element of the precoders.

In explicit CSI feedback, the UE <NUM> provides feedback precoders (precoding vectors) to the eNB <NUM>. The UE <NUM> may calculate the precoder using an eigen based method, calculate the channel covariance matrix and apply eigen decomposition and use the resulting eigenvectors as the precoders.

According to example embodiments, based on the eigen-decomposition of the channel covariance matrix, the UE <NUM> may report one dominant eigenvector or one vector which is a combination of multiple eigenvectors, in order to achieve the best trade-off between overhead and performance. Specifically, the channel covariance matrix R may be defined based on UE <NUM> channel estimation and eigen-decomposition may be applied to R. The eigen-decomposition of R may produce eigenvectors U = (U<NUM>, U<NUM>,. , UN) and corresponding eigenvalues Λ = (λ<NUM>, λ<NUM>,. , λN) (assuming the eigen values are listed in a decreasing order), where and λ<NUM> denotes the dominant eigenvector and eigenvalue. H denotes a Hermitian operator. <MAT> <MAT> <MAT>.

Referring to <FIG> an example method for implementing an explicit CSI reporting method in which a device (such as a UE <NUM>) may report one vector, which may be a dominant eigenvector, or a single vector that is a combination of multiple eigenvectors, according to the angular spread at an eNB <NUM> (or gNB) and a UE <NUM> speed is shown.

An example embodiment of the explicit CSI reporting method <NUM> includes three parts, as shown in <FIG>. At block <NUM>, the first part of the explicit CSI reporting method may include determining a number of eigenvectors to be used in providing a single vector to include in an explicit CSI report. According to an embodiment, this may include determining a number of eigenvectors to combine. This may be done by measuring the angular spread of the transmission from the eNB <NUM> (or gNB) to the UE <NUM>, the UE <NUM> speed, or a combination of measuring both the eNB <NUM> angular spread and the UE <NUM> speed. Alternatively, the method may include selecting a dominant eigenvector (in other words, selecting one single vector).

At block <NUM>, in instances in which multiple eigenvectors are determined, the second part of the explicit CSI reporting method may include determining a manner of combining the eigenvectors, which (for non-zero eigenvectors) compose an orthogonal subspace. The non-zero eigenvectors may be used as an orthogonal basis to build (or determine) one vector carrying the necessary channel spatial information.

At block <NUM>, the third part of the explicit CSI reporting method may include performing the measurements and signalling to enable the explicit CSI reporting (for example, from the UE <NUM> to the eNB <NUM> or other component of network <NUM>).

Example embodiments may be targeted to explicit CSI reporting in high angular spread and high UE <NUM> speed scenarios, for which high rank transmission is not required and in which a transmission with a rank indicator of rank <NUM> is sufficient for reporting requirements. High rank transmission brings more inter-layer interference than low rank transmission, are more suitable for stable channel because the high speed scenario cannot achieve high rank transmission. After acquiring the feedback dominant eigenvector or the vector as a combination of several eigenvectors, the eNB <NUM> may construct orthogonality between polarizations based on the feedback vector if a cross-polarized antenna array is used, and may thereby perform rank <NUM> transmission using the explicit CSI reporting method <NUM>. An example of constructing rank <NUM> precoder may use the rank <NUM> codebook (second column) in 3GPP <NUM> table <NUM>. <NUM>-<NUM> (table <NUM> in <FIG>), for example as shown in <FIG>. As shown in <FIG>, table <NUM> includes a codebook index <NUM> and columns <NUM> and <NUM> corresponding to a number of layers.

Referring to <FIG> an example method for determining the number of eigenvectors to combine, for example with respect to implementing block <NUM> of method <NUM>, is shown.

When determining the number of combined eigenvectors the angular spread may be reflected by (or determined based on) the eigen-decomposition results as shown at block <NUM>. The eigenvectors represent the channel paths with different steering while the eigenvalues represent the power gains for the channel paths. If the eigen-decomposition results include several non-zero eigenvalues that are quite similar and the eigenvectors associated with them span a wide steering direction, the angular spread may be determined to be high. Specifically, angular spread may be calculated as <MAT>.

The definition of the symbols are as follows: Threshold ρ defines the power gain difference and threshold ξ defines the steering direction difference, and if λ<NUM> - λi < ρ and s(U<NUM>) - s(Ui) < ξ, eigenvector Ui should be fed back. If only satisfies the aforementioned conditions, then only the dominant eigenvector is reported. If i ≥ <NUM>, eigenvectors U<NUM>,. Ui may be combined into one vector and this vector may be reported. Here, s(*) represents the function abstracting the steering direction for the precoder or eigenvector.

An exemplary embodiment of an implementation to calculate the steering direction of an eigenvector is shown as below, for the dominant eigenvector U<NUM>, <MAT> <MAT>.

In which N represents the number of antenna ports and angle (*) returns the phase information from a complex number. Similarly, the steering direction of other eigenvectors may be determined. Another embodiment to calculate the number of combined eigenvectors may be based on the rank estimation. The Number of rank indicates the best number of transmission layers. The estimation may be performed based on the trade-off between spatial multiplexing and inter-layer interference. In instances in which rank j is reported, the first j eigenvectors may be combined and provided as feedback to eNB <NUM> (or gNB).

UE <NUM> speed is another factor that may be determined (as shown at block <NUM>) and considered (or used as a basis for calculation) when determining the combined eigenvector. Explicit CSI feedback may be effective in instances in which UE <NUM> speed is low. For a high UE <NUM> speed scenario, implicit CSI feedback (for example, codebook based) may outperform explicit feedback, which depicts the channel in more detail and thus requires a relatively static environment to provide superior feedback in comparison to implicit feedback. Explicit CSI feedback provides higher resolution of channel and may bring better performance than implicit CSI feedback. However, in instances in which the speed exceeds a particular threshold, the advantage of explicit CSI feedback may be overridden and may even bring less favorable performance than implicit CSI feedback. Therefore, an example embodiment may use the UE <NUM> speed measurement as a switch enabling the combined vector feedback when UE <NUM> speed is high and explicit feedback is configured. Specifically, we define a UE <NUM> speed threshold τ. In other instances the speed threshold may include a velocity threshold (for example, the threshold may be determined based on the direction of the UE <NUM>). If UE <NUM> speed v ≥ τ, then combined vector feedback will be enabled. The speed of a UE <NUM> may be calculated based on Doppler, an exemplary implementation may be <MAT>.

Where, Δf is the Doppler offset, f<NUM> is the carrier frequency and c is the speed of light.

At block <NUM>, the number of eigenvectors to be combined may be determined based on the angular spread and/or UE <NUM> speed.

Referring to <FIG> an example method for combining eigenvectors, for example with respect to implementing block <NUM> of method <NUM>, is shown.

When combing eigenvectors, as described above with respect to block <NUM> of method <NUM>, if multiple eigenvectors result from the first part at block <NUM> of method <NUM>, as shown at block <NUM>, the multiple eigenvectors may be combined into one feedback vector using MRC, as shown at block <NUM>. Multiple eigenvectors span an orthogonal subspace and may be used as an orthogonal basis in determining one feedback vector. Combining the selected eigenvectors by adding them together allows the system or reporting device (for example, UE <NUM>, etc.) to achieve diversity gain. The eigenvalues represent the power gains of the channel paths. The reporting device may use MRC to combine the selected eigenvectors with eigenvalues as the combining coefficients as follows: <MAT>.

The resulting feedback vector U may be normalized to U* and then an explicit CSI feedback procedure can be triggered to report U* to the eNB <NUM> (or gNB).

Referring to <FIG> an example method for performing the measurements and signalling to enable the explicit CSI reporting (or handling the measurements and the signalling for explicit CSI reporting), for example with respect to implementing block <NUM> of method <NUM>, is shown.

The number of combined eigenvectors may be determined based on measurements of the angular spread and UE <NUM> speed as described above with respect to <FIG> and method <NUM>. CSI feedback may be triggered by the eNB <NUM> (or gNB), and the UE <NUM> may in response perform the measurement and report the resulting one vector back to the eNB <NUM> (or gNB).

Alternatively, as shown at block <NUM>, the UE <NUM> may report the measurements, particularly the speed, back to the eNB <NUM> (or gNB) and let the eNB <NUM> (or gNB) determine the method of reporting, such as whether the combined method is to be applied in that particular instance (as shown at block <NUM>).

At block <NUM>, the method may include the UE <NUM> receiving a signal (or message) with instructions for applying the combined method (based on the determination by the eNB <NUM> (or gNB)).

At block <NUM>, the method may include the UE <NUM> following the instruction of the eNB <NUM> (or gNB) and completing the CSI reporting procedure. Having UEs <NUM> feedback their speed measurements and letting eNB <NUM> (or gNB) determine whether the combined reporting method is to be applied (for example, the feature is to be enabled) provides additional utility than allowing the UE <NUM> to make the decision, because in instances in which the eNB <NUM> (or gNB) makes the determination, the eNB <NUM> (or gNB) may collect information from all UEs <NUM> in a cell and better schedule and coordinate CSI reporting among the UEs <NUM>.

According to an embodiment, an explicit CSI feedback method reports either one dominant eigenvector or one vector combining all selected eigenvectors. To determine the number of combined eigenvectors, UE <NUM> speed and the eNB <NUM> (or gNB) angular spread may be used as a metric. MRC may be used as the combining method to combine all relevant eigenvectors into one feedback vector. The explicit CSI feedback method may provide more diversity gain in a high UE <NUM> speed scenario and comparatively less cost overhead when angular spread is high.

Certain abbreviations that may be found in the description and/or in the Figures are herewith defined as follows:.

Without in any way limiting the scope, interpretation, or application of the claims appearing below, a technical effect of one or more of the example embodiments disclosed herein is a diversity gain comparable (or approximate) to multiple eigenvectors being reported in a high eNB/gNB angular spread or high UE speed scenario. Another technical effect of one or more of the example embodiments disclosed herein is high beamforming gain comparable (or approximate) to a dominant eigenvector being reported in a low eNB/gNB angular spread and low UE speed scenario.

An apparatus comprising, means for determining a number of eigenvectors to be used in providing a single vector to include in an explicit channel state information (CSI) report, to be transmitted from a user terminal to at least one device in a network, means for combining the eigenvectors to form the single vector in response to a determination that the number of eigenvectors to be used in providing the single vector is greater than one, and means for configuring to signal to transmit the explicit CSI report including the single vector from the user terminal to the at least one device in the network.

An example method may comprise evaluating a number of constituent precoders to be used in providing a single precoder to include in an explicit channel state information (CSI) report, to be transmitted from a user terminal to at least one device in a network, combining the constituent precoders to form the single precoder in response to a determination that the number of constituent precoders to be used in providing the single precoder is greater than one, and configuring to signal to transmit the explicit CSI report including the single precoder from the user terminal to the at least one device in the network.

The constituent precoders may comprise eigenvectors and the single precoder may comprise at least one of a dominant eigenvector and a single vector combined of several eigenvectors
The determining of the number of eigenvectors to be used in providing the single vector may further comprise determining an angular spread associated with the at least one device in the network.

The determining the angular spread may further comprise determining an angular spread associated with the at least one device in the network based on eigen-decomposition of a channel covariance matrix.

The determining the angular spread may further comprise determining whether λ<NUM> - λi < ρ and s(U<NUM>) - s(Ui) < ξ , where threshold ρ denotes a power gain difference and threshold ξ denotes a steering direction difference; and selecting eigenvector Ui to be included in the number of vectors in response to a determination that λ<NUM> - λi < ρ and s(U<NUM>) - s(Ui) < ξ, wheres(*) represents a function abstracting a steering direction of the user terminal.

An example method may further comprise determining whether i = <NUM>; and reporting only a dominant eigenvector in response to a determination that i = <NUM>.

An example method may further comprise determining whether i ≥ <NUM>; and combining eigenvectors U<NUM>,. Ui into one vector and reporting the one vector in response to a determination thati ≥ <NUM>.

The determining the number of eigenvectors to be used in providing the single vector may further comprise accessing a user terminal speed threshold, where the user terminal speed threshold is denoted as τ, determining a user terminal speed, v, of the user terminal; and switch enabling the combined vector feedback if the user terminal speed v ≥ τ and enabling combined vector feedback.

The determining the user terminal speed of the user terminal may further comprise determining the user terminal speed based on a Doppler offset, where <MAT>, where, Δf is the Doppler offset, f<NUM> is a carrier frequency and c is a speed of light.

The combining the eigenvectors to form the single vector may further comprise applying MRC to combine the eigenvectors with eigenvalues as the combining coefficients.

The determining the number of eigenvectors to be used in providing the single vector to include in the explicit CSI report based on eigen-decomposition of the channel covariance matrix may further comprise applying eigen-decomposition to R, where U denotes an eigenvector, A denotes an eigenvalue, U<NUM> denotes a dominant eigenvector and denotes a dominant eigenvalue, and <MAT> <MAT> and <MAT>.

The configuring to signal to transmit the explicit CSI report may further comprise reporting a user terminal speed from the user terminal to the at least one device in the network, where the at least one device in the network is configured to determine whether to combine the eigenvectors based on the user terminal speed, configuring to receive instructions from the at least one device in the network to combine the eigenvectors, combining the eigenvectors, and configuring to send the explicit CSI report to the at least one device in the network including the combined eigenvectors.

An example apparatus may comprise at least one processor; and at least one non-transitory 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 to: determine a number of eigenvectors to be used in providing a single vector to include in an explicit channel state information (CSI) report, to be transmitted from a user terminal to at least one device in a network, combine the eigenvectors to form the single vector in response to a determination that the number of eigenvectors to be used in providing the single vector is greater than one; and perform measurements and signalling to transmit the explicit CSI report including the single vector from the user terminal to the at least one device in the network.

When determining the number of eigenvectors to be used in providing the single vector, the at least one memory and the computer program code may be configured to determine an angular spread associated with the at least one device in the network based on eigen-decomposition of a channel covariance matrix.

When determining the angular spread, the at least one memory and the computer program code may be configured to, with the at least one processor, cause the apparatus to attempt to determine whether λ<NUM> - λi < ρ and s(UO) - s(Ui) < ξ, where threshold ρ denotes a power gain difference and threshold ξ denotes a steering direction difference; and select eigenvector Ui to be included in the number of vectors in response to a determination that λ<NUM> - λi < ρ and s(U<NUM>) - s(Ui) < ξ, where s(*) represents a function abstracting a steering direction of the user terminal.

The at least one memory and the computer program code may be further configured to determine whether i = <NUM>; and report only a dominant eigenvector in response to a determination that i = <NUM>.

The at least one memory and the computer program code may be further configured to determine whether i ≥ <NUM>; and combine eigenvectors U<NUM>,. Ui into one vector and reporting the one vector in response to a determination that i ≥ <NUM>.

When determining the number of eigenvectors to be used in providing the single vector, the at least one memory and the computer program code may be configured to, with the at least one processor, cause the apparatus to access a user terminal speed threshold, where the user terminal speed threshold is denoted as τ; determine a user terminal speed, v, of the user terminal; and switch enable the combined vector feedback if the user terminal speed v ≥ τ and enabling combined vector feedback.

When determining the user terminal speed of the user terminal, the at least one memory and the computer program code may be configured to, with the at least one processor, cause the apparatus to determine the user terminal speed based on a Doppler offset, where <MAT>, where, Δ f is the Doppler offset, f<NUM> is a carrier frequency and c is a speed of light.

When combining the eigenvectors to form the single vector, the at least one memory and the computer program code may be configured to, with the at least one processor, cause the apparatus to apply MRC to combine the eigenvectors with eigenvalues as the combining coefficients.

When determining the number of eigenvectors to be used in providing the single vector to include in the explicit CSI report based on eigen-decomposition of the channel covariance matrix, the at least one memory and the computer program code may be configured to, with the at least one processor, cause the apparatus to apply eigen-decomposition to R, where U denotes an eigenvector, A denotes an eigenvalue, U<NUM> denotes a dominant eigenvector and λ<NUM> denotes a dominant eigenvalue, and R = UΛU^H, Λ = (λ<NUM>, λ<NUM>,. , λN) and U = (U<NUM>, U<NUM>,.

A non-transitory computer program product may comprise a computer-readable medium bearing computer program code embodied therein for use with a computer, the computer program code comprising code for determining a number of eigenvectors to be used in providing a single vector to include in an explicit channel state information (CSI) report, to be transmitted from a user terminal to at least one device in a network; combining the eigenvectors to form the single vector in response to a determination that the number of eigenvectors to be used in providing the single vector is greater than one; and configuring to signal to transmit the explicit CSI report including the single vector from the user terminal to the at least one device in the network.

Embodiments herein may be implemented in software (executed by one or more processors), hardware (e.g., an application specific integrated circuit), or a combination of software and hardware. In an example embodiment, the software (e.g., application logic, an instruction set) is maintained on any one of various conventional computer-readable media. In the context of this document, a "computer-readable medium" may be any media or means that can contain, store, communicate, propagate or transport the instructions for use by or in connection with an instruction execution system, apparatus, or device, such as a computer, with one example of a computer described and depicted, e.g., in <FIG>. A computer-readable medium may comprise a computer-readable storage medium (e.g., memories <NUM>, <NUM>, <NUM> or other device) that may be any media or means that can contain, store, and/or transport the instructions for use by or in connection with an instruction execution system, apparatus, or device, such as a computer. A computer-readable storage medium does not comprise propagating signals.

Although various aspects are set out above, other aspects comprise other combinations of features from the described embodiments, and not solely the combinations described above.

It is also noted herein that while the above describes example embodiments, these descriptions should not be viewed in a limiting sense. Rather, there are several variations and modifications which may be made without departing from the scope of the present invention.

It is also noted herein that while the above describes example embodiments, these descriptions should not be viewed in a limiting sense. Rather, there are several variations and modifications which may be made without departing from the scope of the present invention as defined in the appended claims.

In general, the various embodiments may be implemented in hardware or special purpose circuits, software, logic or any combination thereof.

Embodiments may be practiced in various components such as integrated circuit modules.

The foregoing description has provided by way of exemplary and non-limiting examples a full and informative description of the best method and apparatus presently contemplated by the inventors for carrying out the invention. However, various modifications and adaptations may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings and the appended claims. However, all such and similar modifications of the teachings of this invention will still fall within the scope of this invention.

It should be noted that the terms "connected," "coupled," or any variant thereof, mean any connection or coupling, either direct or indirect, between two or more elements, and may encompass the presence of one or more intermediate elements between two elements that are "connected" or "coupled" together. The coupling or connection between the elements can be physical, logical, or a combination thereof. As employed herein two elements may be considered to be "connected" or "coupled" together by the use of one or more wires, cables and/or printed electrical connections, as well as by the use of electromagnetic energy, such as electromagnetic energy having wavelengths in the radio frequency region, the microwave region and the optical (both visible and invisible) region, as several non-limiting and non-exhaustive examples.

Claim 1:
A method for transmitting an explicit channel state information, CSI, report, from a user terminal to at least one device in a network, the report comprising at least one of: a dominant eigenvector, or a combination of multiple eigenvectors as a single vector, the method comprising:
evaluating (<NUM>) a number of constituent precoders to be used in providing a single precoder,;the constituent precoders comprising eigenvectors;
combining (<NUM>) the constituent precoders to form the single precoder in response to a determination that the number of constituent precoders to be used in providing the single precoder is greater than one, wherein combining the eigenvectors into the single vector further comprises applying maximum ratio combining, MRC, to combine the eigenvectors with the square root of eigenvalues as combining coefficients; and
configuring (<NUM>) a signal to transmit the explicit CSI report including the single precoder from the user terminal to the at least one device in the network
wherein a user terminal speed threshold is defined and denoted as τ; a user terminal speed, v, is determined; and enabling explicit channel state information, CSI, report as combined vector feedback if the user terminal speed v ≥ τ.