Type i codebook supporting more than 32 channel state information reference signal ports

Abstract

A baseband processor is configured to receive a set of channel state information (CSI) reference signals (CSI-RS) from a network device, according to a reference signal configuration. The reference signal configuration is based at least in part on CSI-RS ports of the network device. The baseband processor is also configured to measure the set of CSI-RS; determine, based in part on the measurement of the set of CSI-RS and for a Type I codebook supporting more than 32 CSI-RS ports, CSI including a precoding matrix per layer in a set of layers; and transmit the precoding matrix per layer. The precoding matrix for a particular layer is based at least in part on a set of spatial bases for a spatial basis selection matrix, and a matrix containing a set of linear combination coefficients for the set of spatial bases and a set of frequency bases.

Description

TYPE I CODEBOOK SUPPORTING MORE THAN 32 CHANNEL STATE INFORMATION REFERENCE SIGNAL PORTSCROSS-REFERENCE TO RELATED APPLICATION

[0001] This Patent Cooperation Treaty patent application claims priority to U.S. Provisional Patent Application No. 63 / 574,848, filed April 4, 2024, and titled “Type I Codebook Supporting More Than 32 Channel State Information Reference Signal Ports,” the contents of which are incorporated herein by reference as if fully disclosed herein in its entirety.TECHNICAL FIELD

[0002] This application relates generally to wireless communication systems, including systems, apparatuses, and methods in which a user equipment (UE) may measure time and frequency resources associated with a set of channel state information (CSI) reference signals (CSI-RS) and transmit a CSI report to a network.BACKGROUND

[0003] Wireless mobile communication technology uses various standards and protocols to transmit data between a network device (e.g., a base station, a radio head, etc.) and a wireless communication device. Wireless communication system standards and protocols can include, for example, 3rd Generation Partnership Project (3GPP) long term evolution (LTE) (e.g., 4G), 3GPP new radio (NR) (e.g., 5G), and IEEE 802.11 standard for wireless local area networks (WLAN) (commonly known to industry groups as Wi-Fi®).

[0004] As contemplated by the 3GPP, different wireless communication systems standards and protocols can use various radio access networks (RANs) for communicating between a network device of the RAN (which may also sometimes be referred to generally as a RAN node, a network node, or simply a node) and a wireless communication device known as a UE. 3GPP RANs can include, for example, global system for mobile communications (GSM), enhanced data rates for GSM evolution (EDGE) RAN (GERAN), Universal Terrestrial Radio Access Network (UTRAN), Evolved Universal Terrestrial Radio Access Network (E-UTRAN), and / or Next-Generation Radio Access Network (NG-RAN).

[0005] Each RAN may use one or more radio access technologies (RATs) to perform communication between the network device and the UE. For example, the GERAN implements GSM and / or EDGE RAT, the UTRAN implements universal mobile telecommunication system(UMTS) RAT or other 3GPP RAT, the E-UTRAN implements LTE RAT (sometimes simply referred to as LTE), and NG-RAN implements NR RAT (sometimes referred to herein as 5G RAT, 5G NR RAT, or simply NR). In certain deployments, the E-UTRAN may also implement NR RAT. In certain deployments, NG-RAN may also implement LTE RAT.

[0006] A network device used by a RAN may correspond to that RAN. One example of an E-UTRAN network device is an Evolved Universal Terrestrial Radio Access Network (E-UTRAN) Node B (also commonly denoted as evolved Node B, enhanced Node B, eNodeB, or eNB). One example of an NG-RAN network device is a next generation Node B (also sometimes referred to as a g Node B or gNB).

[0007] A RAN provides its communication services with external entities through its connection to a core network (CN). For example, E-UTRAN may utilize an Evolved Packet Core (EPC), while NG-RAN may utilize a 5G Core Network (5GC).BRIEF DESCRIPTION OF THE DRAWINGS

[0008] To easily identify the discussion of any particular element or act, the most significant digit or digits in a reference number refer to the figure number in which that element is first introduced.

[0009] FIG. 1 shows an example wireless communications system, according to one or more aspects described herein..

[0010] FIG. 2 shows an example method of wireless communication by a UE, according to one or more aspects described herein.

[0011] FIG. 3 shows an example structure of a Type I codebook supporting more than 32 CSI- RS ports.

[0012] FIG. 4 illustrates an example architecture of a wireless communication system, according to one or more aspects described herein.

[0013] FIG. 5 illustrates an example system for performing signaling between a wireless device and a network device, according to one or more aspects described herein.DETAILED DESCRIPTION

[0014] Various embodiments are described with regard to a user equipment (UE). However, reference to a UE is merely provided for illustrative purposes. The example embodiments may be utilized with any electronic component that may establish a connection to a network and is configured with the hardware, software, and / or firmware to exchange information and data with a network. Therefore, the UE as described herein is used to represent any appropriate electronic device (e.g., a mobile phone, a computer (e.g., a laptop or tablet computer), a wearable device (e.g., an electronic watch, fitness device, or head-mounted device), or an Internet of Things (loT) device).

[0015] A CSI report is used by a UE operating within a 3GPP system to report the parameters of one or more downlink (DL) transmissions received via one or more ports. An antenna port on which a CSI report is based may be referred to as a channel state information (CSI) reference signal (CSI- RS) antenna port, which means that a network device (e.g., a network device of a RAN, such as a gNB) has configured one or more CSI-RS resources to be received by the UE and measured, and indicated the CSI-RS resources to the UE in a channel measurement resource (CMR) configuration. A CSI report may include parameters such as a CSI-RS resource indicator (CRI), a rank indicator (RI), a channel quality indicator (CQI), a precoding matrix indicator (PMI), a layer indication (LI), and so on. CSI reports can be particularly important for DL multiple-input and multiple-output (MIMO) operation.

[0016] At a high level, there are two types of CSI codebook: Type I and Type II. Type I codebook is for relatively lower resolution CSI feedback and currently supports up to 8 layers. Type II codebook is for relatively higher resolution CSI feedback and currently supports up to 4 layers. Each type of codebook assumes a two-dimensional linear antenna structure (i.e., an Ni x N2 array of antenna elements).

[0017] An NR CSI report currently supports up to 32 CSI-RS ports, wherein the number of CSI-RS ports (P CSI-RS) is defined as:PCSI-RS = 2 * Nr* N2where is the number of antenna elements of a network device (e.g., a gNB) along a first direction (e.g., a horizontal direction) and N is the number of antenna elements of the network device along a second direction, orthogonal to the first direction (e.g., a vertical direction). The factor 2 is a result of each antenna element having a horizontal polarization (H-Pol) and a vertical polarization (V-Pol).

[0018] The combinations of Ni and N2 that are currently supported by NR systems are set forth in Table 5.2.2.2.1 -2 of 3GPP Technical Specification (TS) 38.214 VI 8.0.0 (2023-09). 32 CSI-RS ports are currently supported for values of (Ni, N2) equal to (4, 4), (8, 2), and (16, 1). However, it is desirable and likely that more than 16 antenna elements, each associated with an H-Pol and a V- Pol, will ultimately be supported. It is also desirable and likely that more than 32 CSI-RS ports will ultimately be supported (e.g., up to 128 CSI-RS ports). Currently available Type I codebooks for CSI do not support more than 32 CSI-RS ports. A new Type I codebook, supporting more than the 32 CSI-RS ports (e.g., up to 128 CSI-RS ports) would be useful.

[0019] A Type I codebook for CSI was defined in 3 GPP Release 15 (Rel-15), in accord with the following design principles: a single spatial basis with structured PMI construction; different designs for Rank 1 / 2, Rank 3 / 4, Rank 5 / 6, Rank 7, and Rank 8; different designs within Rank 3 / 4, depending on whether the number of CSI-RS ports is <16 or >16; and a different spatial basis for Rank 3 / 4 in the case of >16 CSI-RS ports.

[0020] Described herein are Type I codebook alternatives that support more than 32 CSI-RS ports (e.g., up to 128 CSI-RS ports). The Type I codebook alternatives are more robust than currently available Type I codebooks, but in most cases require less overhead than Type II codebooks.

[0021] FIG. 1 shows an example wireless communications system 100, according to one or more aspects described herein.

[0022] Wireless communications system 100 includes a UE 102 and a network device 104. One or more UEs including the UE 102 may be served by (e.g., have an established radio resource control (RRC) connection with) the network device 104 via communication link 120. In one or more embodiments, communication link 120 may include a downlink connection and / or an uplink connection.

[0023] In one or more embodiments, the network device 104 may utilize beam steering, which may also be, include, or be referred to as electronic beam steering. Additionally, in one or more embodiments, UE 102 may utilize beam steering to receive signals, transmit signals, or both. As used herein, electronic beam steering refers, without limitation, to the ability of a device (e.g., network device 104) to perform beamforming, beam shaping, or other multiple antenna or multiple antenna-element techniques that control, direct, or otherwise shape electromagnetic energy radiated from the network device 104 in different directions and with different magnitudes or amplitudes. Electronic beam steering also refers to the network device 104 adjusting antennas or antenna elements to increase or decrease the ability to receive electromagnetic radiation from a particular direction. Such reception beamforming may be referred to as “receive beams,” asopposed to transmit beamforming using “transmit beams.” The network device 104 may use beam steering for the transmission of signals to UEs (e.g., UE 102) served by the network device 104. Such signals can include data signals, control signals, or both. By way of example, control signals may include reference signals, synchronization signals, configuration signals, control channels, or combinations of these. The resulting transmit beams or receive beams are represented by a beam sweep 106.

[0024] The network device 104 may utilize at least one antenna array 130 for communication with the UE 102. Tn the example illustrated for wireless communications system 100, the antenna array 130 of the network device may include an array of antenna element pairs arranged in four rows and four columns, with a total of 32 antenna elements. Each antenna element pair include a first antenna element 132 that is oriented orthogonally to a second antenna element 134. In this example, each of the first antenna element 132 is oriented at +45° to the antenna array 130 and each of the second antenna element is oriented at -45° to the antenna array 130 (e.g., the antenna elements are cross-polarized). In other examples, more or fewer antenna elements, arranged in antenna element pairs or otherwise, may be used by the network device 104. Various proposals have been presented in 3GPP meetings regarding how more than 32 antenna elements may be supported by a network device.

[0025] In one or more embodiments, the network device 104 may utilize beam steering to transmit reference signals (e.g., a set of CSI-RS) that the UE 102 may use (e.g., measure) to determine CSI. Techniques described herein, however, may apply to other reference signals that may be used to determine CSI. According to one or more techniques described herein, each CSI- RS port may correspond to an antenna port.

[0026] In some examples, an antenna port may correspond to a particular physical antenna element of the antenna array 130, but the correspondence need not be one-to-one, and ports may correspond to different configurations of physical antenna elements (e.g., logical antenna ports) according to other examples.

[0027] In the example wireless communications system 100, a set of CSI-RS 122 may be transmitted by the network device 104 during a set of time-frequency resources 140. In some examples, the set of time-frequency resources 140 include a slot and a physical resource block (PRB), although it should be understood that the set of CSI-RS 122 may be transmitted periodically, aperiodically, according to a semi-persistent configuration, or span more than one PRB, or span multiple slots in other examples. The set of time-frequency resources 140 may include, for example, first CSI-RS resources 142 and second CSI-RS resources 144.

[0028] According to one or more examples described herein, the UE 102 may receive configuration signaling 124 that indicates parameters of a set of CSI-RS ports.

[0029] FIG. 2 shows an example method 200 of wireless communication by a UE. In some cases, the UE may be the wireless device 102, 404, or 502, or one of the other UEs described herein. In some cases, the method 200 may be performed by a baseband processor of the UE, using a transceiver of the UE or other components of the UE. The baseband processor may include a memory, and the memory may store instructions that, when executed by the baseband processor, cause the baseband processor to perform the method 200. The transceiver may be operable to transmit and receive over an air interface, using a set of antenna elements of the UE.

[0030] At 202, the method 200 may include receiving a set of CSI-RS from a network device (via the transceiver), according to a reference signal configuration. The reference signal configuration may be based at least in part on a set of CSI-RS ports of the network device. The network device (e.g., a gNB) may sound the set of CSI-RS ports simultaneously (e.g., by transmitting multi-port orthogonal CSI-RS).

[0031] At 204, the method 200 may include measuring (e.g., estimating the channel quality of) the set of CSI-RS.

[0032] At 206, the method 200 may include determining, based at least in part on the measurement of the set of CSI-RS and for a Type I codebook supporting more than 32 CSI-RS ports, CSI including a precoding matrix (Wl) per layer in a set of layers, where I is a total number of layers. The determination of the precoding matrix for a particular layer in the set of layers may be based at least in part on the operations 208, 210, and / or 212.

[0033] At 208, the method 200 may include determining (e.g., selecting) a set of spatial bases for a spatial basis selection matrix (W ). The spatial basis selection matrix may include L spatial bases, where L is the total number of (i.e., one or more) spatial bases selected for a layer I in the spatial basis selection matrix.

[0034] At 210, the method 200 may optionally include determining (and in some cases selecting) a set of frequency bases for a frequency basis selection matrix ((Vk ) )• The frequency basis selection matrix may include M frequency bases, where M is the total number of (i.e., one or more) frequency bases selected (or predetermined by a standard, or configured by the network device) for a layer I in the spatial basis selection matrix.

[0035] At 212, the method 200 may include determining a matrix (VK )- The matrix may contain a set of linear combination coefficients (c) for the L spatial bases and M frequency bases.

[0036] At 214, the method 200 may include transmitting (reporting) the precoding matrix per layer (e.g., via the transceiver and to the network device).

[0037] The method 200 may be variously embodied, extended, or adapted, as described in the following paragraphs and elsewhere in this description.

[0038] An example structure of a Type I codebook 300 supporting more than 32 CSI-RS ports is shown in FIG. 3. The codebook 300 includes a precoding matrix (VF() per layer in a set of I layers. The precoding matrix Wlmay include a term (Wl(i)) per subband i in a set of N3 subbands, where N3 is the total number of subbands (i.e., i = 1, 2,..., Ns)- In some embodiments, the precoding matrix per layer may be determined for a wide band, in which case i may be equal to 1.

[0039] Each precoding matrix, Wl, may be a product of a spatial basis selection matrix, a matrix containing a set of linear combination coefficients, and a frequency basis selection matrix.

[0040] The spatial basis selection matrix (W^) may be determined per layer I, for L spatial bases. The spatial basis selection matrixmay include a term (v- ) per subband, where i = 0, . . ., L-l is the (z+l)''1spatial basis for layer I. In some embodiments, the spatial basis selection matrix may include up to 2L terms, to provide a term per polarization state (e.g., a term per horizontal polarization state and a term per vertical polarization state) of each antenna element of a network device that is involved in generating a reference signal configuration.

[0041] The frequency basis selection matrix (is optional, but in some embodiments may be determined per layer I, for M frequency bases. The frequency basis selection matrixmay include a termfor the j* selected frequency basis. Alternatively, and in some embodiments, the frequency basis selection matrix may be predetermined by a standard, or configured by a network. In these embodiments, frequency-related information may be integrated into the matrix W\ .

[0042] The matrix (VIZ2 ) may be determined per layer I. The matrix may contain a set of linear combination coefficients (c) for the L spatial bases and M frequency bases.

[0043] The variables I, N3, L, and M are all integers and may be equal to or greater than one (>1). In some examples, not all of the terms or matrices indicated in FIG. 3 need be determined by a UE.

[0044] Returning to the method 200 and / or Type I codebook structure supporting more than 32 CSI-RS ports, and in some embodiments, the Type I codebook may only support a single antenna panel of the network device. In such a case, the set of CSI-RS ports of the network device would need to be associated with only a single antenna panel of the network device. Alternatively, theType I codebook may support both a single antenna panel of the network device or multiple antenna panels of the network device. Tn this latter case, the set of CSI-RS ports of the network device may be associated with a single antenna panel of the network device or multiple antenna panels of the network device. In some embodiments, support of multiple antenna panels may require that the multiple antenna panels be quasi-co-located (QCL’d). In some embodiments, support of multiple antenna panels may require a precoding matrix per layer and per antenna panel. Whether the Type I codebook supporting more than 32 CSI-RS ports supports only a single antenna panel or single and multiple antenna panels may be specified in a standard (e.g., a 3GPP Technical Specification (TS)).

[0045] In some embodiments of the method 200 and / or Type I codebook structure supporting more than 32 CSI-RS ports, the Type I codebook may support both a wideband CSI report and a subband CSI report, as specified in a standard (e.g., a 3GPP TS). A subband CSI report is a report that includes CSI for i subbands, with i > 2. In these embodiments, a network (e.g., the network device that transmits the set of CSI-RS) may transmit, and the UE may receive, configuration signaling (e.g., radio resource control (RRC) signaling) indicating whether the UE is to transmit a wideband CSI report or a subband CSI report. In some of these embodiments, the method 200 may include transmitting an indication of whether the UE supports subband CSI reporting (e.g., in addition to wideband CSI reporting, with wideband-only CSI reporting being the default assumption). The indication may in some cases be transmitted in RRC signaling. Alternatively, the Type I codebook may only support a wideband CSI report as specified in a standard (e.g., a 3GPP TS).

[0046] There are various ways to select, determine, and / or report the set of spatial bases for the spatial basis selection matrix described with reference to the method 200 and / or Type I codebook structure supporting more than 32 CSI-RS ports. In some embodiments of the method 200, determining the set of spatial bases for the spatial basis selection matrix, for a particular layer, may include constructing the spatial basis selection matrix for the particular layer as an N1XN2 matrix (e.g., from a Kronecker operation of M-length Discrete Fourier Transform (DFT) vectors with N2- length DFT vectors), where Ni is a first number of antenna elements along a first dimension of a linear antenna array of the network device, and N2 is a second number of antenna elements along a second dimension of the linear antenna array. The second dimension (e.g., a vertical dimension) may be orthogonal to the first dimension (e.g., a horizontal dimension).

[0047] In some embodiments, determining the set of spatial bases for the spatial basis selection matrix, for a particular layer, may further or alternatively include determining the spatial basis selection matrix based at least in part on a first oversampling number (0 / ) along the first dimensionand a second oversampling number (O2) along the second dimension as optionally specified in a standard (e.g., a 3GPP TS). Tn some embodiments, a combination of the first oversampling number and the second oversampling number (Gy, O2) may be equal to one of (4, 4), (2, 2), or (1, 1), as hardcoded in a standard, or a network may configure the combination based on candidate values of 4, 2, and 1. Other options are possible. In some cases, the support of more than 32 CSI-RS ports, and up to 128 CSI-RS ports, may enable the use of lower oversampling rates (i.e., lower oversampling numbers) and / or no oversampling. In some embodiments, the method 200 may include transmitting an indication of oversampling numbers or combinations of oversampling numbers that the UE supports (e.g., supported candidate values selected from 4, 2, and 1). The indication may in some cases be transmitted in RRC signaling.

[0048] In some embodiments, determining the set of spatial bases for the spatial basis selection matrix, for a particular layer, may further or alternatively include determining the spatial basis selection matrix based at least in part on an oversampling factor selection among [0 Oj-1 ] and [0 O2-I]. In some embodiments, the oversampling factor selection may be for the particular layer (i.e., the oversampling factor may be selected independently for each layer). Alternatively, the oversampling factor selection may be common to each layer in the set of layers (i.e., a common oversampling factor may be selected for all layers).

[0049] In some embodiments, determining the set of spatial bases for the spatial basis selection matrix, for a particular layer, may further or alternatively include selecting the set of spatial bases for the particular layer, independently of any other layer in the set of layers. The set of spatial bases for a layer may or may not be the same of the set of spatial bases for a different layer. In some of these embodiments, only a single spatial basis may be selected per layer, to simplify the Type I codebook CSI reporting. In other embodiments, more than one (e.g., L > 1) spatial basis may be selected for one or more (or each) layer.

[0050] In some embodiments, determining the set of spatial bases for the spatial basis selection matrix, for a particular layer, may further or alternatively include selecting the set of spatial bases for the particular layer and a paired layer, independently of any other pair of layers in the set of layers. The set of spatial bases for one pair of layers may or may not be the same as the set of spatial bases for one or more other pairs of layers. In some of these embodiments, only a single spatial basis may be selected per pair of layers, to simplify the Type I codebook CSI reporting. In other embodiments, more than one (e.g., L > 1) spatial basis may be selected for one or more (or each) pair of layers.

[0051] In some embodiments, determining the set of spatial bases for the spatial basis selection matrix, for a particular layer, may further or alternatively include selecting the set of spatial basesfor the particular layer from a pool of spatial bases. The pool of spatial bases may be common to all layers in the set of layers (i.e., the set of spatial bases for each layer may be selected from a common pool of spatial bases).

[0052] In some embodiments, determining the set of spatial bases for the spatial basis selection matrix, for a particular layer, may further or alternatively include determining a common oversampling factor selection and a common set of spatial bases for both of two orthogonal polarization states (e.g., vertical polarization (V-Pol) and horizontal polarization (H-Pol)) of a set of antenna elements of the network device. Alternatively, determining the set of spatial bases for the spatial basis selection matrix, for a particular layer, may further or alternatively include determining independent oversampling factor selections and sets of spatial bases for each of the two orthogonal polarizations. Whether the selections are common or independent may be determined by a standard, configured by the network, or indicated by the UE.

[0053] In some embodiments, determining the set of spatial bases for the spatial basis selection matrix, for a particular layer, may further or alternatively include determining a common oversampling factor selection and a common set of spatial bases for all frequency bases in a set of frequency bases. Alternatively, determining the set of spatial bases for the spatial basis selection matrix, for a particular layer, may further or alternatively include determining independent oversampling factor selections and sets of spatial bases for each frequency basis in a set of frequency bases.

[0054] In some embodiments, determining the set of spatial bases for the spatial basis selection matrix, for a particular layer, may further or alternatively include determining a common oversampling factor selection and a common set of spatial bases for all subbands in a set of subbands. Alternatively, determining the set of spatial bases for the spatial basis selection matrix, for a particular layer, may further or alternatively include determining independent oversampling factor selections and sets of spatial bases for each subband in a set of subbands.

[0055] There are various ways to select, determine, and / or report the set of frequency bases for the frequency basis selection matrix described with reference to the method 200 and / or Type I codebook structure supporting more than 32 CSI-RS ports. In some embodiments of the method 200, determining the set of frequency bases for the frequency basis selection matrix, for a particular layer, may include constructing the frequency basis selection matrix for the particular layer from an N3 N3 identity matrix, where N3 is the total number of subbands. In the case of an identity matrix of size N3 N3, or IN3= diag{l,l, ... , 1], all of the frequency bases are selected. If an identity matrix is required by a standard or configured by a network, this may simplify CSI reporting, in that the UE may transmit the precoding matrix per layer, at 214, without transmitting a frequencybasis selection matrix (i.e., because the construction of the frequency basis selection matrix is already known).

[0056] Alternatively, determining the set of frequency bases for the frequency basis selection matrix, for a particular layer, may include constructing the frequency basis selection matrix for the particular layer from a DFT matrix of size N3 N3. In these embodiments, the method 200 may include selecting M frequency bases from among Nj orthogonal frequency bases. In terms of the frequency basis selection, the first frequency basis may be a DFT vector with 0 phase ramp ([ 1 , 1 ,. ..,! ]), but may not be reported at 214. The remaining A / -1 frequency bases may be selected among N3-I orthogonal frequency basis and reported at 214. In some embodiments, the remaining M-l frequency bases may be selected freely. In other embodiments, the remaining M-l orthogonal frequency bases may be selected from among a subset of N3-I orthogonal frequency bases. The subset of N3-I orthogonal frequency bases may be, for example, a window of consecutive orthogonal frequency bases. The remaining M-l orthogonal frequency bases may be selected independently for each layer, or independently per pair of layers, or may be common to all of the layers.

[0057] There are various ways to select, determine, and / or report the set of linear combination coefficients for the matrix of linear combination coefficients described with reference to the method 200 and / or Type I codebook structure supporting more than 32 CSI-RS ports. In embodiments of the method 200 in which the set of spatial bases for a particular layer may be determined independently of any other layer in the set of layers, and when a single spatial basis is selected for each layer, determining the set of linear combination coefficients for the matrix of linear combination coefficients, for the particular layer, may include determining a single linear combination coefficient (< / >„) for each subband n of the particular layer I. The corresponding precoder for subband n and the particular layer / may then be where vlis the selectedspatial basis for layer I and is common for H-Pol and V-Pol. In the example precoder, one of the polarizations (e.g., H-Pol) is assumed to have a linear combination coefficient of 1, and the other polarization (e.g., V-Pol) is subjected to the reported linear combination coefficient < >„. In embodiments of the method 200 in which the set of spatial bases for a particular layer may be determined independently of any other layer in the set of layers, and when multiple spatial bases (e.g., L>\ spatial bases) are selected for each layer, only a single spatial basis may be selected for each subband n, and determining the set of linear combination coefficients for the matrix of linear combination coefficients, for the particular layer, may include determining a single linear combination coefficient (< >„) for each subband n of the particular layer I. Each precoder per subband may be determined or reported as described for the single spatial basis per layer case.

[0058] In embodiments of the method 200 in which the set of spatial bases for the particular layer and a paired layer (i.e., a particular pair of layers) may be determined independently of any other pair of layers in the set of layers, and when a single spatial basis is selected for each pair of layers, determining the set of linear combination coefficients for the matrix of linear combination coefficients, for the particular pair of layers, may include determining a single linear combination coefficient (< >„) for each subband n of the particular of layers (e.g., I and / +1). The corresponding precoder for subband n and the particular layer / may then and the correspondingprecoder for subband n and the layer l+l may be the orthogonal precoder f where vlis \~(Pn 'v / the selected spatial basis for layer I and is common for H-Pol and V-Pol and the pair of layers. In the example precoders, one of the polarizations (e.g., H-Pol) is assumed to have a linear combination coefficient of 1, and the other polarization (e.g., V-Pol) is subjected to the reported linear combination coefficient < >„ for layer I and —for layer l+l. In some embodiments, only (f>n need be reported at 214, therefore simplifying CSI reporting (and the network device may compute —< >„. In embodiments of the method 200 in which the set of spatial bases for a particular pair of layers may be determined independently of any other pair of layers in the set of layers, and when multiple spatial bases (e.g., L>1 spatial bases) are selected for each pair of layers, only a single spatial basis may be selected for each subband n, and determining the set of linear combination coefficients for the matrix of linear combination coefficients, for the particular pair of layers, may include determining a single linear combination coefficient (< >„) for each subband n of the particular pair of layers. Each precoder per subband may be determined or reported as described for the single spatial basis per layer case.

[0059] In embodiments of the method 200 in which the set of spatial bases for a particular layer may be selected from a pool of spatial bases that is common to all layers in the set of layers, the method 200 may include selecting a single spatial basis for the particular layer from among the pool of spatial bases, and determining the set of linear combination coefficients for the matrix of linear combination coefficients, for the particular layer, by determining a linear combination coefficient (0^) for each subband n of the particular layer I. The corresponding precoder for subband n and the particular layer I may then be where vlis the selected spatial basisfor layer I and is common for H-Pol and V-Pol. In the example precoder, one of the polarizations (e.g., H-Pol) is assumed to have a linear combination coefficient of 1, and the other polarization (e.g., V-Pol) is subjected to the reported linear combination coefficient < >„. In embodiments of the method 200 in which the set of spatial bases for a particular layer and a paired layer (i.e., aparticular pair of layers) may be determined independently of any other pair of layers in the set of layers, the method 200 may include selecting a single spatial basis for the particular pair of layers from among the pool of spatial bases, and determining the set of linear combination coefficients for the matrix of linear combination coefficients, for the particular pair of layers, by determining a linear combination coefficient (< >„) for each subband n of the particular pair of layers.

[0060] In some embodiments, the linear combination coefficients (e.g., < >„) in a matrix containing a set of linear combination coefficients may be independently (i.e., separately) encoded for different layers and / or different subbands. In other embodiments, the linear combination coefficients may be encoded differentially, in which one or more linear combination coefficients are encoded differentially with respect to another linear combination coefficient. In these latter embodiments, differential encoding may be applied across different subbands in a single layer (and a separate differential encoding may be applied across different subbands and a different layer); or differential encoding may be applied across different layers and a single subband (and a separate differential encoding may be applied across different layers and a different subband); or differential encoding may be applied across all subbands and all layers.

[0061] In some embodiments, the linear combination coefficients (e.g., < >„) may be encode to only carrier phase information. In other embodiments, each linear combination coefficient may be reported as a set of bits (e.g., Q bits), uniformly quantized within 2n. In the latter embodiments, each quantized codepoint may be: q ■ 2n 2<? where q = 0,1,2, ... , 2° — 1. Example values for Q are 3 or 4 bits.

[0062] Embodiments contemplated herein include one or more non-transitory computer- readable media storing instructions to cause an electronic device, upon execution of the instructions by one or more processors of the electronic device, to perform one or more elements of the method 200. The non-transitory computer-readable media may be, for example, a memory of a UE (such as a memory 506 of a wireless device 502 that is a UE, as described herein).

[0063] Embodiments contemplated herein include an apparatus having logic, modules, or circuitry to perform one or more elements of the method 200. The apparatus may be, for example, an apparatus of a UE (such as a wireless device 502 that is a UE).

[0064] Embodiments contemplated herein include an apparatus having one or more processors and one or more computer-readable media, using or storing instructions that, when executed by the one or more processors, cause the one or more processors to perform one or more elements ofthe method 200. The apparatus may be, for example, an apparatus of a UE (such as a wireless device 502 that is a UE, as described herein).

[0065] Embodiments contemplated herein include a signal as described in or related to one or more elements of the method 200.

[0066] Embodiments contemplated herein include a computer program or computer program product having instructions, wherein execution of the program by a processor (e.g., a baseband processor) causes the processor to carry out one or more elements of the method 200. The processor may be a processor of a UE (such as a processor(s) 504 of a wireless device 502 that is a UE, as described herein), and the instructions may be, for example, located in the processor and / or on a memory of the UE (such as a memory 506 of a wireless device 502 that is a UE, as described herein).

[0067] FIG. 4 illustrates an example architecture of a wireless communication system, according to embodiments described herein. The following description is provided for an example wireless communication system 400 that operates in conjunction with the LTE system standards or specifications and / or 5G or NR system standards or specifications, as provided by 3GPP technical specifications.

[0068] As shown, the wireless communication system 400 includes UE 402 and UE 404 (although any number of UEs may be used). In this example, the UE 402 and the UE 404 are illustrated as smartphones (e.g., handheld touchscreen mobile computing devices connectable to one or more cellular networks) but may also comprise any mobile or non-mobile computing device configured for wireless communication.

[0069] The UE 402 and UE 404 may be configured to communicatively couple with a RAN 406. In embodiments, the RAN 406 may be NG-RAN, E-UTRAN, etc. The UE 402 and UE 404 utilize connections (or channels) (shown as connection 408 and connection 410, respectively) with the RAN 406, each of which comprises a physical communications interface. The RAN 406 can include one or more network devices, such as base station 412 and base station 414, that enable the connection 408 and connection 410.

[0070] In this example, the connection 408 and connection 410 are air interfaces to enable such communicative coupling and may be consistent with RAT(s) used by the RAN 406, such as, for example, an LTE and / or NR.

[0071] In some embodiments, the UE 402 and UE 404 may also directly exchange communication data via a sidelink interface 416. The UE 404 is shown to be configured to access an access point (shown as AP 418) via connection 420. By way of example, the connection 420can comprise a local wireless connection, such as a connection consistent with any IEEE 802.11 protocol, wherein the AP 418 may comprise a Wi-Fi® router. In this example, the AP 418 may be connected to another network (for example, the Internet) without going through a CN 424.

[0072] In embodiments, the UE 402 and UE 404 can be configured to communicate using orthogonal frequency-division multiplexing (OFDM) communication signals with each other or with the base station 412 and / or the base station 414 over a multicarrier communication channel in accordance with various communication techniques, such as, but not limited to, an orthogonal frequency-division multiple access (OFDMA) communication technique (e.g., for downlink communications) or a single carrier frequency division multiple access (SC-FDMA) communication technique (e.g., for uplink and ProSe or sidelink communications), although the scope of the embodiments is not limited in this respect. The OFDM signals can comprise a plurality of orthogonal subcarriers.

[0073] In some embodiments, all or parts of the base station 412 or base station 414 may be implemented as one or more software entities running on server computers as part of a virtual network. In addition, or in other embodiments, the base station 412 or base station 414 may be configured to communicate with one another via interface 422. In embodiments where the wireless communication system 400 is an LTE system (e.g., when the CN 424 is an EPC), the interface 422 may be an X2 interface. The X2 interface may be defined between two or more network devices of a RAN (e.g., two or more eNBs and the like) that connect to an EPC, and / or between two eNBs connecting to the EPC. In embodiments where the wireless communication system 400 is an NR system (e.g., when CN 424 is a 5GC), the interface 422 may be an Xn interface. The Xn interface is defined between two or more network devices of a RAN (e.g., two or more gNBs and the like) that connect to the 5GC, between a base station 412 (e.g., a gNB) connecting to the 5GC and an eNB, and / or between two eNBs connecting to the 5GC (e.g., CN 424).

[0074] The RAN 406 is shown to be communicatively coupled to the CN 424. The CN 424 may comprise one or more network elements 426, which are configured to offer various data and telecommunications services to customers / subscribers (e.g., users of UE 402 and UE 404) who are connected to the CN 424 via the RAN 406. The components of the CN 424 may be implemented in one physical device or separate physical devices including components to read and execute instructions from a machine-readable or computer-readable medium (e.g., a non-transitory machine-readable storage medium).

[0075] In embodiments, the CN 424 may be an EPC, and the RAN 406 may be connected with the CN 424 via an S I interface 428. In embodiments, the SI interface 428 may be split into two parts, an S 1 user plane (S 1-U) interface, which carries traffic data between the base station 412 orbase station 414 and a serving gateway (S-GW), and the Sl-MME interface, which is a signaling interface between the base station 412 or base station 414 and mobility management entities (MMEs).

[0076] In embodiments, the CN 424 may be a 5GC, and the RAN 406 may be connected with the CN 424 via an NG interface 428. In embodiments, the NG interface 428 may be split into two parts, an NG user plane (NG-U) interface, which carries traffic data between the base station 412 or base station 414 and a user plane function (UPF), and the S I control plane (NG-C) interface, which is a signaling interface between the base station 412 or base station 414 and access and mobility management functions (AMFs).

[0077] Generally, an application server 430 may be an element offering applications that use internet protocol (IP) bearer resources with the CN 424 (e.g., packet switched data services). The application server 430 can also be configured to support one or more communication services (e.g., VoIP sessions, group communication sessions, etc.) for the UE 402 and UE 404 via the CN 424. The application server 430 may communicate with the CN 424 through an IP communications interface 432.

[0078] FIG. 5 illustrates an example system 500 for performing signaling 538 between a wireless device 502 and a network device 520, according to embodiments described herein. The system 500 may be a portion of a wireless communication system as herein described. The wireless device 502 may be, for example, a UE of a wireless communication system. The network device 520 may be, for example, a base station (e.g., an eNB or a gNB) or a radio head of a wireless communication system.

[0079] The wireless device 502 may include one or more processor(s) 504. The processor(s) 504 may execute instructions such that various operations of the wireless device 502 are performed, as described herein. The processor(s) 504 may include one or more baseband processors implemented using, for example, a central processing unit (CPU), a digital signal processor (DSP), an application specific integrated circuit (ASIC), a controller, a field programmable gate array (FPGA) device, another hardware device, a firmware device, or any combination thereof configured to perform the operations described herein.

[0080] The wireless device 502 may include a memory 506. The memory 506 may be a non- transitory computer-readable storage medium that stores instructions 508 (which may include, for example, the instructions being executed by the processor(s) 504). The instructions 508 may also be referred to as program code or a computer program. The memory 506 may also store data used by, and results computed by, the processor(s) 504.

[0081] The wireless device 502 may include one or more transceiver! s) 510 (also collectively referred to as a transceiver 510) that may include radio frequency (RF) transmitter and / or receiver circuitry that use the antenna(s) 512 of the wireless device 502 to facilitate signaling (e.g., the signaling 538) to and / or from the wireless device 502 with other devices (e.g., the network device 520) according to corresponding RATs.

[0082] The wireless device 502 may include one or more antenna(s) 512 (e.g., one, two, four, eight, or more; also referred to herein as antenna elements). For embodiments with multiple antenna(s) 512, the wireless device 502 may leverage the spatial diversity of such multiple antenna(s) 512 to send and / or receive multiple different data streams on the same time and frequency resources. This behavior may be referred to as, for example, MIMO behavior (referring to the multiple antennas used at each of a transmitting device and a receiving device that enable this aspect). MIMO transmissions by the wireless device 502 may be accomplished according to precoding (or digital beamforming) that is applied at the wireless device 502 that multiplexes the data streams across the antenna(s) 512 according to known or assumed channel characteristics such that each data stream is received with an appropriate signal strength relative to other streams and at a desired location in the spatial domain (e.g., the location of a receiver associated with that data stream). Some embodiments may use single user MIMO (SU-MIMO) methods (where the data streams are all directed to a single receiver) and / or multi user MIMO (MU-MIMO) methods (where individual data streams may be directed to individual (different) receivers in different locations in the spatial domain).

[0083] In some embodiments having multiple antennas, the wireless device 502 may implement analog beamforming techniques, whereby phases of the signals sent by the antenna(s) 512 are relatively adjusted such that the (joint) transmission of the antenna(s) 512 can be directed (this is sometimes referred to as beam steering).

[0084] The wireless device 502 may include one or more interface(s) 514. The interface(s) 514 may be used to provide input to or output from the wireless device 502. For example, a wireless device 502 that is a UE may include interface(s) 514 such as microphones, speakers, a touchscreen, buttons, and the like in order to allow for input and / or output to the UE by a user of the UE. Other interfaces of such a UE may be made up of transmitters, receivers, and other circuitry (e.g., other than the transceiver(s) 510 / antenna(s) 512 already described) that allow for communication between the UE and other devices and may operate according to known protocols (e.g., Wi-Fi®, Bluetooth®, and the like).

[0085] The wireless device 502 may include CSI reporting module(s) 516. The CSI reporting module(s) 516 may be implemented via hardware, software, or combinations thereof. For example,the CSI reporting module(s) 516 may be implemented as a processor, circuit, and / or instructions 508 stored in the memory 506 and executed by the processor(s) 504. In some examples, the CSI reporting module(s) 516 may be integrated within the processor(s) 504 and / or the transceivers ) 510. For example, the CSI reporting module(s) 516 may be implemented by a combination of software components (e.g., executed by a DSP or a general processor) and hardware components (e.g., logic gates and circuitry) within the processor(s) 504 or the transceiver(s) 510.

[0086] The CSI reporting module(s) 516 may be used for various aspects of the present disclosure, for example, aspects of FIGs. 1 -3, from a wireless device or UE perspective. The CSI reporting module(s) 516 may be configured to, for example, receive a set of CSI- RS, measure one or more of the CSI-RS, determine CSI, and transmit a CSI report to a network (e.g., to the network device 520).

[0087] The network device 520 may include one or more processor(s) 522. The processor(s) 522 may execute instructions such that various operations of the network device 520 are performed, as described herein. The processor(s) 522 may include one or more baseband processors implemented using, for example, a CPU, a DSP, an ASIC, a controller, an FPGA device, another hardware device, a firmware device, or any combination thereof configured to perform the operations described herein.

[0088] The network device 520 may include a memory 524. The memory 524 may be a non- transitory computer-readable storage medium that stores instructions 526 (which may include, for example, the instructions being executed by the processor(s) 522). The instructions 526 may also be referred to as program code or a computer program. The memory 524 may also store data used by, and results computed by, the processor(s) 522.

[0089] The network device 520 may include one or more transceiver(s) 528 (also collectively referred to as a transceiver 528) that may include RF transmitter and / or receiver circuitry that use the antenna(s) 530 of the network device 520 to facilitate signaling (e.g., the signaling 538) to and / or from the network device 520 with other devices (e.g., the wireless device 502) according to corresponding RATs.

[0090] The network device 520 may include one or more antenna(s) 530 (e.g., one, two, four, or more; also referred to herein as antenna elements). In embodiments having multiple antenna(s) 530, the network device 520 may perform MIMO, digital beamforming, analog beamforming, beam steering, etc., as has been described.

[0091] The network device 520 may include one or more interface(s) 532. The interface(s) 532 may be used to provide input to or output from the network device 520. For example, a networkdevice 520 of a RAN (e.g., a base station, a radio head, etc.) may include interface(s) 532 made up of transmitters, receivers, and other circuitry (e.g., other than the transceiver(s) 528 / antenna(s) 530 already described) that enables the network device 520 to communicate with other equipment in a network, and / or that enables the network device 520 to communicate with external networks, computers, databases, and the like for purposes of operations, administration, and maintenance of the network device 520 or other equipment operably connected thereto.

[0092] The network device 520 may include one or more CSI management module(s) 534. The CSI management module(s) 534 may be implemented via hardware, software, or combinations thereof. For example, the CSI management module(s) 534 may be implemented as a processor, circuit, and / or instructions 526 stored in the memory 524 and executed by the processor(s) 522. In some examples, the CSI management module(s) 534 may be integrated within the processor(s) 522 and / or the transceiver(s) 528. For example, the CSI management module(s) 534 may be implemented by a combination of software components (e.g., executed by a DSP or a general processor) and hardware components (e.g., logic gates and circuitry) within the processor(s) 522 or the transceiver(s) 528.

[0093] The CSI management module(s) 534 may be used for various aspects of the present disclosure, for example, aspects of FIGs. 1-3, from a network device perspective. The CSI management module(s) 534 may be configured to, for example, configure a number of CSI-RS resources for use by a wireless device (e.g., the wireless device 502 and / or other wireless devices) to measure and report CSI, transmit a set of CSI-RS, and receive and interpret a CSI report.

[0094] For one or more embodiments, at least one of the components set forth in one or more of the preceding figures may be configured to perform one or more operations, techniques, processes, and / or methods as set forth herein. For example, a baseband processor (or processor) as described herein in connection with one or more of the preceding figures may be configured to operate in accordance with one or more of the examples set forth herein. For another example, circuitry associated with a UE, network device, network element, etc. as described above in connection with one or more of the preceding figures may be configured to operate in accordance with one or more of the examples set forth herein.

[0095] Any of the above-described embodiments may be combined with any other embodiment (or combination of embodiments), unless explicitly stated otherwise. The foregoing description of one or more implementations provides illustration and description, but is not intended to be exhaustive or to limit the scope of embodiments to the precise form described. Modifications and variations are possible in light of the above teachings or may be acquired from practice of various embodiments.

[0096] Embodiments and implementations of the systems and methods described herein may include various operations, which may be embodied in machine-executable instructions to be executed by a computer system. A computer system may include one or more general-purpose or special-purpose computers (or other electronic devices). The computer system may include hardware components that include specific logic for performing the operations or may include a combination of hardware, software, and / or firmware.

[0097] The systems described herein pertain to specific embodiments but are provided as examples. These embodiments can be combined into single systems, partially combined into other systems, split into multiple systems or divided or combined in other ways. In addition, it is contemplated that parameters, attributes, aspects, etc. of one embodiment can be used in another embodiment. The parameters, attributes, aspects, etc. are merely described in one or more embodiments for clarity, and it is recognized that the parameters, attributes, aspects, etc. can be combined with or substituted for parameters, attributes, aspects, etc. of another embodiment unless specifically disclaimed herein.

[0098] It is well understood that the use of personally identifiable information should follow privacy policies and practices that are generally recognized as meeting or exceeding industry or governmental requirements for maintaining the privacy of users. In particular, personally identifiable information data should be managed and handled so as to minimize risks of unintentional or unauthorized access or use, and the nature of authorized use should be clearly indicated to users.

[0099] Although the foregoing has been described in some detail for purposes of clarity, it will be apparent that changes and modifications may be made without departing from the principles thereof. It should be noted that there are many alternative ways of implementing both the processes and apparatuses described herein. Accordingly, the present embodiments are to be considered illustrative and not restrictive, and the description is not to be limited to the details given herein, but may be modified within the scope and equivalents of the appended claims.

Claims

CLAIMS1. A baseband processor comprising a memory and configured to: receive a set of channel state information (CSI) reference signals (CSI-RS) from a network device, according to a reference signal configuration, the reference signal configuration based at least in part on a set of CSI-RS ports of the network device; measure the set of CSI-RS; determine, based at least in part on the measurement of the set of CSI-RS and for a Type I codebook supporting more than 32 CSI-RS ports, CSI including a precoding matrix per layer in a set of layers, the precoding matrix for a particular layer in the set of layers is determined based at least in part on: a set of spatial bases for a spatial basis selection matrix; and a matrix containing a set of linear combination coefficients for the set of spatial bases and a set of frequency bases; and transmit the precoding matrix per layer.

2. The baseband processor of claim 1 , wherein the Type I codebook supports one of: the set of CSI-RS ports of the network device associated with only a single antenna panel of the network device; or the set of CSI-RS ports of the network device associated with a single antenna panel of the network device or multiple antenna panels of the network device.

3. The baseband processor of claim 1, wherein the Type I codebook supports one of: a wideband CSI report or a subband CSI report; or only a wideband CSI report.

4. The baseband processor of claim 3, wherein: the Type I codebook supports the wideband CSI report and the subband CSI report; and the baseband processor is configured to at least one of, receive RRC signaling indicating whether a user equipment (UE) is to transmit the wideband CSI report or the subband CSI report; or transmit an indication of whether the UE supports subband CSI reporting.

5. The baseband processor of claim 1 , wherein the set of spatial bases for the spatial basis selection matrix, for the particular layer, is determined based at least in part on:constructing the spatial basis selection matrix as an N1 N2 matrix, from a Kronecker operation of / / / -length Discrete Fourier Transform (DFT) vectors with / -length DFT vectors, where Ni is a first number of antenna elements along a first dimension of a linear antenna array of the network device, and N2 is a second number of antenna elements along a second dimension of the linear antenna array, the second dimension orthogonal to the first dimension.

6. The baseband processor of claim 5, wherein the set of spatial bases for the spatial basis selection matrix, for the particular layer, is determined based at least in part on: determining the spatial basis selection matrix based at least in part on a first oversampling number (Oi along the first dimension and a second oversampling number (C ) along the second dimension, wherein a combination of the first oversampling number and the second oversampling number (C , Ch) is equal to: one of (4, 4), (2, 2), or (1, 1), as hardcoded in a standard; or a network configured combination based on candidate values of 4, 2, and 1.

7. The baseband processor of claim 6, wherein the set of spatial bases for the spatial basis selection matrix, for the particular layer, is based at least in part on: determining the spatial basis selection matrix based at least in part on an oversampling factor selection among [0 Oi- 1 ] and [0 Ch- 1 , wherein the oversampling factor selection is common to each layer in the set of layers.

8. The baseband processor of claim 7, wherein the set of spatial bases for the spatial basis selection matrix, for the particular layer, is based at least in part on: selecting the set of spatial bases for the particular layer, independently of any other layer in the set of layers.

9. The baseband processor of claim 8, wherein the matrix containing the set of linear combination coefficients for the set of spatial bases and the set of frequency bases, for the particular layer, is based at least in part on: selecting a single spatial basis for the particular layer, and determining a linear combination coefficient for each subband in a set of subbands used by the particular layer; or selecting more than one spatial basis for the particular layer, consisting of a single spatial basis for each subband in the set of subbands, and determining a linear combination coefficient for each subband in the set of subbands.

10. The baseband processor of claim 7, wherein the set of spatial bases for the spatial basis selection matrix, for the particular layer, is determined based at least in part on: selecting the set of spatial bases for the particular layer and a paired layer, independently of any other pair of layers in the set of layers.

11. The baseband processor of claim 10, wherein the matrix containing the set of linear combination coefficients for the set of spatial bases and the set of frequency bases, for the particular layer and the paired layer, is determined based at least in part on: selecting a single spatial basis for the particular layer and the paired layer, and determining a linear combination coefficient for each subband in a set of subbands used by the particular layer and the paired layer; or selecting more than one spatial basis for the particular layer and the paired layer, consisting of a single spatial basis for each subband in the set of subbands, and determining a linear combination coefficient for each subband in the set of subbands.

12. The baseband processor of claim 7, wherein the set of spatial bases for the spatial basis selection matrix, for the particular layer, is determined based at least in part on: selecting the set of spatial bases for the particular layer from a pool of spatial bases that is common to all layers in the set of layers.

13. The baseband processor of claim 12, wherein: the set of spatial bases for the spatial basis selection matrix, for the particular layer, is determined based at least in part on: selecting a single spatial basis for the particular layer from among the pool of spatial bases that is common to all layers in the set of layers; and the matrix containing the set of linear combination coefficients for the set of spatial bases and the set of frequency bases, for the particular layer, is determined based at least in part on: a linear combination coefficient for each subband in a set of subbands used by the particular layer; or the set of spatial bases for the spatial basis selection matrix, for the particular layer, is determined based at least in part on: selecting a single spatial basis for the particular layer and a paired layer, from among the pool of spatial bases that is common to all layers in the set of layers; and the matrix containing the set of linear combination coefficients for the set of spatial bases and the set of frequency bases, for the particular layer, is determined based at least in part on:a linear combination coefficient for each subband in a set of subbands used by the particular layer and the paired layer.

14. The baseband processor of claim 5, wherein the set of spatial bases for the spatial basis selection matrix, for the particular layer, is determined based at least in part on: a common oversampling factor selection and a common set of spatial bases for both of two orthogonal polarizations of a set of antenna elements of the network device.

15. The baseband processor of claim 5, wherein: the precoding matrix for the particular layer in the set of layers is determined based at least in part on: a set of frequency basis for a frequency basis selection matrix; and the set of spatial bases for the spatial basis selection matrix for the particular layer is determined based at least in part on: a common oversampling factor selection and a common set of spatial bases for all frequency bases in the set of frequency bases.

16. The baseband processor of claim 5, wherein the set of spatial bases for the spatial basis selection matrix, for the particular layer, is determined based at least in part on: a common oversampling factor selection and a common set of spatial bases for all subbands in a set of subbands.

17. The baseband processor of claim 1, wherein the precoding matrix for the particular layer in the set of layers is determined based at least in part on: a set of frequency basis for a frequency basis selection matrix.

18. The baseband processor of claim 17, wherein the frequency basis selection matrix is constructed from: an NsxNs identity matrix, where N3 is a number of subbands; or a Discrete Fourier Transform (DFT) matrix of size NJ NJ.

19. The baseband processor of claim 1, wherein the matrix containing the set of linear combination coefficients for the set of spatial bases and the set of frequency bases, for the particular layer, comprises:different linear combination coefficients encoded independently for at least one of different layers or different subbands; or differentially encoded linear combination coefficients across different subbands in the particular layer; or differentially encoded linear combination coefficients across different layers, including the particular layer, in a single subband; or differentially encoded linear combination coefficients across different layers, including the particular layer, and different subbands.

20. The baseband processor of claim 1, wherein the matrix containing the set of linear combination coefficients for the set of spatial bases and the set of frequency bases, for the particular layer, comprises: only phase information encoded in the linear combination coefficients of the set of linear combination coefficients; or linear combination coefficients reported as a set of bits, uniformly quantized within 2TI.

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