Patent Description:
Aspects of the present disclosure provide apparatus, methods, processing systems, and computer readable mediums for reporting feedback, for example, channel state information (CSI) with spatial and time domain compression. As will be described in greater detail below, the feedback may indicate taps corresponding to a number of non-zero values. The information regarding these taps may represent CSI (e.g., for a single receive antenna and transmit beam (RX/TB) pair across one or more subbands). Each tap may be associated with an amplitude and phase of the reference signal at a given time of (delay associated with) the tap. The UE may report the tap information (e.g., tap location/index, amplitude, and phase for each tap associated with each RX/TB pair) to the BS as the CSI. For example, the BS may use the tap information to reconstruct the CSI and may also consider the tap information as decoder feedback (e.g., allowing the BS to strategically adjust encoding). The schemes described herein relate to reducing the overhead associated with the CSI feedback reporting. For example, in certain embodiments, a multi-stage compression technique is described for compressing tap information, thereby reducing the overhead associated with reporting the tap information.

For example, the wireless communication network <NUM> may be a New Radio (NR) or <NUM> network. In another example, the wireless communication network <NUM> may be an LTE network, in which a UE <NUM> provides CSI feedback (e.g., tap information). As described in greater detail below, the tap information may represent CSI (e.g., for a single receive antenna and transmit beam (RX/TB) pair across one or more subbands) and may also be considered as decoder feedback.

As illustrated in <FIG>, the wireless network <NUM> may include a number of base stations (BSs) <NUM> and other network entities. A BS may be a station that communicates with user equipments (UEs). Each BS <NUM> may provide communication coverage for a particular geographic area. In 3GPP, the term "cell" can refer to a coverage area of a Node B (NB) and/or a Node B subsystem serving this coverage area, depending on the context in which the term is used. In NR systems, the term "cell" and next generation NodeB (gNB), new radio base station (NR BS), <NUM> NB, access point (AP), or transmission reception point (TRP) may be interchangeable. In some examples, the base stations may be interconnected to one another and/or to one or more other base stations or network nodes (not shown) in wireless communication network <NUM> through various types of backhaul interfaces, such as a direct physical connection, a wireless connection, a virtual network, or the like using any suitable transport network.

In some examples, access to the air interface may be scheduled, wherein a. A scheduling entity (e.g., a base station) allocates resources for communication among some or all devices and equipment within its service area or cell.

<FIG> illustrates example components of BS <NUM> and UE <NUM> (as depicted in <FIG>), which may be used to implement aspects of the present disclosure. For example, antennas <NUM>, processors <NUM>, <NUM>, <NUM>, and/or controller/processor <NUM> of the UE <NUM> and/or antennas <NUM>, processors <NUM>, <NUM>, <NUM>, and/or controller/processor <NUM> of the BS <NUM> may be used to perform the various techniques and methods described herein (e.g., operations described in <FIG>).

A mini-slot is a subslot structure (e.g., <NUM>, <NUM>, or <NUM> symbols).

As channel conditions between a user equipment (UE) and a base station (BS) change, it is important for the UE to report (e.g., periodically or aperiodically) feedback. For example, a US may report, as feedback to the BS, certain indications (e.g., channel quality indicator (CQI), precoding matrix index (PMI), and rank indicator (RI)) about the latest channel conditions to the BS.

The BS then utilizes the received CSI report to improve communications with the UE. In certain aspects, such as under the NR-<NUM> standards, CSI reporting with two types of spatial information feedback is supported. Type I CSI feedback generally refers to a CSI feedback scheme that is also used by wireless communications devices comporting to the LTE standards. Type I CSI feedback comprises codebook-based PMI feedback with normal spatial resolution. Type II CSI feedback generally refers to an enhanced feedback scheme, enabling explicit feedback and/or codebook-based feedback with higher spatial resolution.

<FIG> shows a comparison between the Type <NUM> and Type <NUM> precoder feedback. As shown, a Type I CSI feedback corresponds to a lower resolution and smaller payload while Type II CSI corresponds to a higher resolution and larger payload. That is because Type II CSI feedback includes information such as amplitude, phase, etc. of transmit antennas associated with different widebands and subbands for different beams.

For Type II CSI feedback, at least one of Categories <NUM>, <NUM>, and/or <NUM> may be used. Category <NUM> relates to reporting a precoder feedback based on a linear combination of dual-stage codebooks. In certain aspects, a linear combination of the dual-stage codebooks supports up to four beam combinations with a certain precoder structure. For example, the PMI codebook may assume the following precoder structure:.

For rank <NUM>: <MAT> where W is normalized to <NUM>. W<NUM> and W<NUM> indicate precoding weights for rank <NUM> (or transmission layer <NUM>). For rank <NUM>: <MAT> where columns of W are normalized to <MAT>. Based on such a precoder structure, the UE may feed the following information back to the BS: <MAT> (weighted combination of L beams). In this formula, r stands for polarization and l stands for transmission layer. In addition, up to L wideband orthogonal beams are selected. As shown, the UE reports the wideband amplitude as well as the subband differential amplitude. Also, a number of bits (e.g., <NUM> or <NUM> bits) are used to report the subband phase with amplitude dependent quantization.

Because Type II CSI reporting provides a higher resolution (more granular channel information over a number of subbands, transmission layers, and/or beams etc.), the overhead associated with Type II CSI reporting is large even if the reporting is performed for only two transmission layers (e.g., up to rank <NUM>). For example, the total PMI bits may be more than, for example, <NUM> bits in the worst case scenario for 3GPP's Rel. <NUM> type-II CSI. Also, a trivial extension to a higher rank may result in even larger payload bits. In addition, payload (or overhead) increases linearly as the number of beams and/or ranks increases.

<FIG> shows the linear relationship between payload and the number of subbands, beams, and ranks, over which reporting is performed. As shown, the UE may feedback a spatial compression matrix (BNt,Nb) with a payload size corresponding to <MAT>, which increases as L (the number of Discrete Fourier Transform beam basis) increases. Similarly, as shown, each of the wideband amplitude, subband amplitude, and subband phase corresponds to payload that increases as L and/or R increase. <FIG> illustrates the increase in payload bits for each subband with different numbers of beams (L) and ranks (r).

Accordingly, certain embodiments described herein relate to performing a compression of the PMI that is reported to the BS in order to reduce the overhead associated with the CSI feedback reporting.

<FIG> illustrates example operations <NUM> performed by a first wireless communications device, according to aspects of the present disclosure. In certain aspects, the first wireless communications device may be a UE (e.g., UE <NUM>).

Operations <NUM> begin, at <NUM>, by receiving one or more signals from a second wireless communications device. At <NUM>, operations <NUM> continue by determining a precoder matrix index (PMI) based on the signals. At <NUM>, operations <NUM> continue by performing a channel-tap compression of the PMI. At <NUM>, operations <NUM> continue by transmitting the channel-tap compressed PMI to the second wireless communications device.

<FIG> illustrates example operations <NUM> performed by a second wireless communications device, according to aspects of the present disclosure. In certain aspects, the second wireless communications device may be a BS (e.g., BS <NUM>).

Operations <NUM> begin, at <NUM>, by transmitting one or more signals to a first wireless communications device. At <NUM>, operations <NUM> continue by receiving a channel-tap compressed PMI from the first wireless communications device. At <NUM>, operations <NUM> continue by decompressing the channel-tap compressed PMI to derive a PMI. At <NUM>, operations <NUM> continue by adjusting a configuration of one or more antennas of the BS based on the PMI.

In certain aspects, prior to transmitting PMI to the BS, the UE compresses the PMI. The compression, in certain aspects, involves a spatial compression as well as a time domain compression.

<FIG> illustrates an example flow diagram of PMI compression at the UE side as well as PMI decompression at the BS side. PMI is shown in <FIG> as VNsb,Nt, which includes precoder weights for Nt transmit antennas over Nsb subbands. As shown, in certain aspects, the PMI is spatially compressed using a spatial compression matrix (e.g., DTF matrix) with a certain basis (e.g., DFT basis). In certain aspects, the basis may be known to both the UE and the BS. As such, the UE is not required to report the basis of the compression matrix to the BS, thereby, reducing the overhead associated with the CSI reporting. In certain aspects, the spatial compression matrix may be denoted as BNt,Nb.

In certain aspects, after spatially compressing the PMI, the UE may derive a time-domain representation of the spatially compressed PMI. In certain aspects, this is performed by using a DFT matrix. For example, the UE may perform a Fast Fourier Transform (FFT) operation to derive the time domain representation of the spatially compressed PMI. In certain aspects, the UE utilizes a DFT matrix FNsb,Nsb having a size of "Nsb x Nsb" for deriving the time domain representation.

In certain aspects, prior to deriving the time domain representation of the spatially compressed PMI, the UE may search the basis of BNt,Nb, and perform a pre-rotation of the spatially compressed PMI based on a dominant eigen vector of the PMI. The dominant eigen vector may be denoted as vNsb. In certain aspects, the UE may extract the phase of vNsb, denoted as pNsb. In certain aspects, pNsb can be extracted using a phase extraction function angle(), where: <MAT>.

In certain aspects, once pNsb is extracted, a phase rotation of the PMI ( <MAT>) may be performed using pNsb. A phase-rotated PMI equals: <MAT>
where diag() represents a function for making a Nsb length vector into Nsb × Nsb size matrix having a diagonal component that is the same as the vector. As described above, in order to derive the time domain representation of the phase-rotated and spatially compressed PMI, the UE may then perform a FFT operation.

In certain aspects, the UE may subsequently perform a time domain compression of the time-domain representation of the spatially compressed PMI. In certain aspects, the time domain compression involves performing a channel-tap selection of the time-domain representation of the spatially compressed PMI (referred to as a channel-tap compression). Channel-tap selection, in certain aspects, involves selecting active (e.g., dominant) taps from a number of taps in the time-domain representation of the spatially compressed PMI. In certain aspects, for each active tap (Tr,b,pa), the amplitude and the phase of the active tap is quantized. For example, the amplitude and the phase may be quantized with <NUM> bits, or <NUM> bits for either amplitude or phase. In certain aspects, the level of quantization may be configurable.

The channel-tap information resulting from the channel-tap selection is shown in <FIG> as <MAT>. In certain aspects, <MAT> comprises a maximum payload of R · <NUM>L · Na · 2Q + Nts bits. In the function above, R corresponds to number of ranks. L corresponds to the number of beams. Na corresponds to the maximum number of active-channel taps selected and quantized per beam. Na, in certain aspects, is configurable by the BS. In certain aspects, Na is reported to the BS by the UE reported. In certain aspects, Na is associated with the number of subbands (Nsb).

Further, in the function above, Na · <NUM>Q corresponds to the amplitude/phase quantization (e.g., with the same quantization level). The value of Na · <NUM>Q is normalized, as the maximum value in the CSI feedback for active-channel taps has 0dB amplitude. Nts corresponds to the number of bits for reporting the selected channel-taps. In certain aspects, Nts is compressed. In certain aspects, the UE may compress Nts in different stages (e.g., multi-stage compression). In certain aspects, the channel-tap selection compression may be performed in two stages. In the first stage, the UE may explore the correlation between tap profiles of various beams, based on which the UE may select a number of active taps (e.g., a superset of taps) based on the correlation. Na,max indicates the number of first stage selected taps that are selected from a number of subbands Nsb.

In certain aspects, Na,max is configurable by the BS. In certain aspects, the Na,max is reported by the UE to the BS. In certain aspects, the Na,max is associated with Nsb. In certain aspects, Na,max may correspond to all beams and layers (e.g., corresponding overhead is <MAT>), or a single beam with different layers (e.g., corresponding overhead is <MAT>), or a single layer with different beams (e.g., corresponding overhead is <MAT>).

After performing the first stage of the channel-tap selection, resulting in Na,max, the UE performs the second stage. The second stage involves selecting a number of taps Na from the maximum number of taps Na,max for each beam and/or layer. Note that Na ≤ Na,max.

After the multi-stage compression described above, the total number of bits for reporting the channel-tap selection is: <MAT>.

In certain aspects, the UE transmits the channel-tap compressed PMI along with the spatial compression matrix (e.g., BNt,Nb with an orthogonal DFT beam basis), used to spatially compress the PMI, to the BS. Once the BS receives the spatial compression matrix and the channel-tap compression PMI, the BS performs spatial and time domain decompression in order to recreate the original PMI. For example, the BS utilizes a matrix (e.g., DFT matrix FHNsb,Nsb having a size of "Nsb x Nsb") to transform the channel-tap compressed PMI ( <MAT>) and derive a frequency domain representation of the PMI ( <MAT>). In certain aspects, the BS is preconfigured with such a matrix. The BS then uses the spatial compression matrix BNt,Nb received from the UE to perform a spatial decompression of the frequency domain representation of the PMI in order to derive the original PMI ( <MAT>). For example, the BS may apply <MAT> for the spatial decompression. In certain aspects, the BS may be pre-configured with the spatial decompression matrix <MAT>. In such aspects, the UE does not transmit the BNt,Nb to the BS.

<FIG> illustrates an example of the two-stage channel-tap selection described above. As shown, in the first stage, the UE may examine the correlation between the tap profiles of Beams A-D. The UE may then select tap indexes of the most active or dominant taps among Beams A-D. In the example of <FIG>, the UE may determine that tap indexes <NUM>, <NUM>, <NUM> and <NUM> correspond to the most active taps in the tap profiles of Beams A-D. Na,max corresponds to the number of tap indexes (i.e., Na,max = <NUM>) out of the <NUM> possible tap indexes (Nsb = <NUM>). In the second stage, the most active taps from tap indexes <NUM>, <NUM>, <NUM>, and <NUM> are selected for each beam. For example, for Beam A, the most active taps are taps <NUM> and <NUM> (i.e., Na = <NUM>). For Beam B, the most active tap is tap <NUM> (i.e., Na = <NUM>). For Beam C, the most active taps are taps <NUM> and <NUM> (i.e., Na = <NUM>). Finally, for Beam D, the most active tap is tap <NUM> (i.e., Na = <NUM>).

Accordingly, in the example of <FIG>, compressing the channel-tap information reduces the payload associated with indicating the active taps associated with Beams A-D. For example, without compressing the channel-tap information, to indicate taps <NUM> and <NUM> for Beam A, tap <NUM> for Beam B, taps <NUM> and <NUM> for Beam B, and tap <NUM> for Beam D, the UE may need to use <NUM> bits (<NUM>*<NUM>). But by using the multi-stage compression technique above, the UE may use <NUM> bits to indicate tap indexes <NUM>, <NUM>, <NUM>, and <NUM> and only <NUM> bits to indicate the active taps out of tap indexes <NUM>, <NUM>, <NUM>, and <NUM> for each beam.

In certain aspects, the indication of the taps (e.g., information reported by the UE to the BS about the taps) may comprise or use an index of hypothesis corresponding to taps selected in the first stage and the second stage for each beam. In such aspects, at most <MAT> may be used for the indication, where Na,max = <NUM> and Nsb = <NUM>. In certain aspects, the indication of the taps may comprise or use a combination of hypothesis corresponding to taps selected in the first stage and the second stage for each beam. In such aspects, at most <MAT>, may be used for the indication. In certain aspects, the indication of the taps may comprise or use a combination of hypothesis corresponding to taps selected in the first stage (first subset of a plurality of taps).

In certain aspects, the indication of the taps may comprise or use a bitmap like indication corresponding to taps selected in the first stage and the second stage for each beam. In such aspects, the bitmap uses a sequence of '<NUM>' and '<NUM>' for the indication. Also, at most K<NUM> = Nsb = <NUM> bits may be used for the bit-map, where at most Na,max '<NUM>'s exist in <NUM>-bit sequence. In certain aspects, the indication of the taps may comprise or use a bitmap corresponding to taps selected in the second stage (second subsets of the first subset).

In certain aspects, a mixture of a bitmap and the combination of hypothesis may be used to indicate the taps selected in first stage and the second stage. For example, the indication of the taps may comprise or use a bitmap corresponding to taps selected in the second stage. The indication may further comprise a combination of hypothesis corresponding to taps selected in the first stage (first subset of a plurality of taps).

In certain aspects, the UE may omit some overhead if not enough payload is available. Under 3GPP's Rel. <NUM> Type-II PMI feedback scheme, the priority order for reporting PMI is as follows: PMI-<NUM>(wideband), PMI-<NUM>-even subbands, PMI-<NUM>-odd subbands. In other words, if there is not enough payload, bits associated with PMI-<NUM>-odd subbands may first be omitted, then bits associated with PMI-<NUM>-even subbands may be omitted, and so on. However, since PMI that is spatially and time domain compressed is not based on subbands, the priority orders of 3GPP's Rel. <NUM> Type-II PMI feedback are not applicable.

Accordingly, certain embodiments herein relate to a PMI feedback priority scheme that is based on taps/tap groups or beams/beam groups.

<FIG> illustrates the separation of taps and beams into different priority groups. In certain aspects, the UE may separate taps into different tap priority groups with different reporting priorities. For example, as shown in <FIG>, taps t<NUM> and t<NUM> are assigned to tap priority group <NUM> while taps t<NUM> and t<NUM> are assigned to tap priority group <NUM>, with tap priority group <NUM> having a higher reporting priority than tap priority group <NUM>. In another example, the UE may select half (i.e., Na/<NUM>) of the originally selected taps Na, which may correspond to at least <MAT>, and assign them to tap priority group <NUM> while assigning the rest to tap priority group <NUM>. In certain aspects, the different tap priority groups may be indicated by signaling.

In certain aspects, the UE may separate beams into different beam priority groups with different reporting priorities. For example, as shown in <FIG>, beams b<NUM> and b<NUM> are assigned to beam priority group <NUM> while beams b<NUM> and b<NUM> are assigned to beam priority group <NUM>, with priority group <NUM> having a higher reporting priority than priority group <NUM>. In another example, the UE may select half (i.e., Nb/<NUM>) of the originally selected beams Nb for reporting, which may correspond to at least <MAT> bits, and assign them to beam priority group <NUM> while assigning the rest to beam priority group <NUM>. In certain aspects, the different beam priority groups may be indicated by signaling. Note that a beam in the aspects described herein refers to a UE-calculated beam that is defined in or a part of the PMI.

<FIG> illustrates a wireless communications device <NUM> (the first wireless communications device corresponding to <FIG>) that may include various components (e.g., corresponding to means-plus-function components) configured to perform operations for the techniques disclosed herein, such as one or more of the operations illustrated in <FIG>. The transceiver <NUM> is configured to transmit and receive signals for the communications device <NUM> via an antenna <NUM>. The processing system <NUM> may be configured to perform processing functions for the communications device <NUM>, such as processing signals, etc..

The processing system <NUM> includes a processor <NUM> coupled to a computer-readable medium/memory <NUM> via a bus <NUM>. In certain aspects, the computer-readable medium/memory <NUM> is configured to store instructions that when executed by processor <NUM>, cause the processor <NUM> to perform one or more of the operations illustrated in <FIG>, or other operations for performing the various techniques discussed herein.

In certain aspects, the processing system <NUM> further includes a receiving component <NUM> for performing one or more of the operations illustrated at <NUM> in <FIG>. Additionally, the processing system <NUM> includes a determining component <NUM> for performing one or more of the operations illustrated at <NUM> in <FIG>. Additionally, the processing system <NUM> includes a performing component <NUM> for performing one or more of the operations illustrated at <NUM> in <FIG>. Additionally, the processing system <NUM> includes a transmitting component <NUM> for performing one or more of the operations illustrated at <NUM> in <FIG>.

The receiving component <NUM>, the determining component <NUM>, the performing component <NUM>, and the transmitting component <NUM> may be coupled to the processor <NUM> via bus <NUM>. In certain aspects, receiving component <NUM>, the determining component <NUM>, the performing component <NUM>, and the transmitting component <NUM> may be hardware circuits. In certain aspects, the receiving component <NUM>, the determining component <NUM>, the performing component <NUM>, and the transmitting component <NUM> may be software components that are executed and run on processor <NUM>.

<FIG> illustrates a wireless communications device <NUM> (the second wireless communications device corresponding to <FIG>) that may include various components (e.g., corresponding to means-plus-function components) configured to perform operations for the techniques disclosed herein, such as one or more of the operations illustrated in <FIG>. The transceiver <NUM> is configured to transmit and receive signals for the communications device <NUM> via an antenna <NUM>. The processing system <NUM> may be configured to perform processing functions for the communications device <NUM>, such as processing signals, etc..

In certain aspects, the processing system <NUM> further includes a transmitting component <NUM> for performing one or more of the operations illustrated at <NUM> in <FIG>. Additionally, the processing system <NUM> includes a receiving component <NUM> for performing one or more of the operations illustrated at <NUM> in <FIG>. Additionally, the processing system <NUM> includes a decompressing component <NUM> for performing one or more of the operations illustrated at <NUM> in <FIG>. Additionally, the processing system <NUM> includes an adjusting component <NUM> for performing one or more of the operations illustrated at <NUM> in <FIG>.

The transmitting component <NUM>, the receiving component <NUM>, the determining component <NUM>, and the adjusting component <NUM> may be coupled to the processor <NUM> via bus <NUM>. In certain aspects, the transmitting component <NUM>, the receiving component <NUM>, the determining component <NUM>, and the adjusting component <NUM> may be hardware circuits. In certain aspects, the transmitting component <NUM>, the receiving component <NUM>, the determining component <NUM>, and the adjusting component <NUM> may be software components that are executed and run on processor <NUM>.

For example, such a computer program product may comprise a computer-readable medium having instructions stored (and/or encoded) thereon, the instructions being executable by one or more processors to perform the operations (e.g., operations described in <FIG>) described herein.

Claim 1:
A method of wireless communications by a first wireless communications device, comprising:
receiving (<NUM>) one or more signals from a second wireless communications device;
determining (<NUM>) a precoder matrix index, PMI, based on the signals;
performing (<NUM>) a channel-tap compression of the PMI in two stages by determining a first subset of a plurality of taps corresponding to a plurality of beams based on a time domain representation of the PMI, based on a correlation between tap profiles of the plurality of beams, and for each of the plurality of beams, determining a second subset of the first subset, the second subset of taps being the most active taps of the first subset of taps for that beam; and
transmitting (<NUM>) the channel-tap compressed PMI to the second wireless communications device, wherein the channel-tap compressed PMI comprises information indicative of the first subset and each of the second subsets.