Atty. Docket No. CS37679
`
`METHOD OF PRECODER INFORMATION FEEDBACK IN
`MULTI-ANTENNA WIRELESS COMMUNICATION SYSTEMS
`
`FIELD OF THE DISCLOSURE
`
`[0001]
`
`The
`
`present
`
`disclosure
`
`relates
`
`generally
`
`to wireless
`
`communications and, more particularly, to a feedback framework in wireless
`
`communication systems.
`
`BACKGROUND
`
`[0002]
`
`In wireless communication systems, channel state information at a
`
`transmitter, for example, at a base station, is important for beam-forming
`
`transmissions (also referred to as precoding) that deliver more power to a
`
`targeted user while minimizing interference on other users. Precoding
`
`operations can be in the context of single-user multiple in.put multiple output
`
`(SU-MIMO) or multi-user MIMO (MU-MIMO), where two or more users are
`
`served by a single base station. An eNB needs accurate spatial channel
`
`information in order to perform a high rank transmission to a single UE or to
`
`perform precoding to two or more UEs simultaneously so that the mutual
`
`interference among multiple transmissions can be minimized at each UE.
`
`[0003]
`
`Precoding operations may also be in the context of SU /MU-
`
`MIMO users served by coordinated multi-point (CoMP) transmissions where
`
`antennas belonging to different eNBs, rather than to the sarn.e eNB, can
`
`coordinate their precoding to serve multiple users simultaneously. Further
`
`support for up to eight transmit antennas is enabled in the next generation
`
`cellular standards like 3GPP L TE Release-10. Due to such a relatively large
`
`number of antennas (4-Tx or 8-Tx) involved in such transmissions, it is
`
`desirable that the UE feedback be designed efficiently with good performance
`
`LG Elecs. Ex. 1006
`LG Elecs. v. Pantech Corp.
`IPR2023-01273 Page 1
`
`
`
`METHOD OF PRECODER INFORMATION FEEDBACK IN
`MULTI-ANTENNA WIRELESS COMMUNICATION SYSTEMS
`
`FIELD OF THE DISCLOSURE
`
`[0001]
`
`The
`
`present
`
`disclosure
`
`relates
`
`generally
`
`to wireless
`
`communications and, more particularly, to a feedback framework in wireless
`
`communication systems.
`
`BACKGROUND
`
`[0002]
`
`In wireless communication systems, channel state information at a
`
`transmitter, for example, at a base station, is important for beam-forming
`
`transmissions (also referred to as precoding) that deliver more power to a
`
`targeted user while minimizing interference on other users. Precoding
`
`operations can be in the context of single-user multiple in.put multiple output
`
`(SU-MIMO) or multi-user MIMO (MU-MIMO), where two or more users are
`
`served by a single base station. An eNB needs accurate spatial channel
`
`information in order to perform a high rank transmission to a single UE or to
`
`perform precoding to two or more UEs simultaneously so that the mutual
`
`interference among multiple transmissions can be minimized at each UE.
`
`[0003]
`
`Precoding operations may also be in the context of SU /MU-
`
`MIMO users served by coordinated multi-point (CoMP) transmissions where
`
`antennas belonging to different eNBs, rather than to the sarn.e eNB, can
`
`coordinate their precoding to serve multiple users simultaneously. Further
`
`support for up to eight transmit antennas is enabled in the next generation
`
`cellular standards like 3GPP L TE Release-10. Due to such a relatively large
`
`number of antennas (4-Tx or 8-Tx) involved in such transmissions, it is
`
`desirable that the UE feedback be designed efficiently with good performance
`
`LG Elecs. Ex. 1006
`LG Elecs. v. Pantech Corp.
`IPR2023-01273 Page 1
`
`
`
`Atty. Docket No. CS37679
`
`overhead trade-off, so that feedback does not scale linearly with the increasing
`
`number of antennas.
`
`[0004]
`
`The antenna configurations which support a large number of
`
`antennas in practice rn.ust allow large beamforming gains and also larger
`
`spatial multiplexing gains achieved
`
`from higher
`
`rank
`
`transmission.
`
`Beamforming allows efficient support for low geometry users and also for
`
`multi-user
`
`transmission
`
`thereby
`
`improving cell-edge and cell-average
`
`throughput with larger number of users in the system, while spatial
`
`multiplexing allows higher peak spectral efficiency. A
`
`typical antenna
`
`configuration to achieve this would be to have groups of antennas where each
`
`group is a set of correlated antennas and each group is uncorrelated with the
`
`other groups. A cross-polarized antenna configuration is one such setup. The
`
`correlated antenna elements provide the required beamforming gains and the
`
`uncorrelated antenna elements enable high rank transmissions.
`
`[0005]
`
`The above structure in the antennas has some unique spatial
`
`characteristics that can be exploited. For example, the correlation among
`
`correlated antennas changes slowly and is confined to a smaller vector space
`
`on an average. This can be used to feedback the correlated and uncorrelated
`
`channel characteristics, i.e., two components, at different rates and/ or with
`
`different levels of quantization/ overhead in time and frequency to reduce
`
`feedback overhead. One of the components representing the correlated
`
`channel characteristics can be fed back on a wideband basis and/ or slowly in
`
`tin1.e, while the other component is fed back on a subband basis and/ or more
`
`frequently in time.
`
`2
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`IPR2023-01273 Page 2
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`
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`Atty. Docket No. CS37679
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`[0006]
`
`However, one of the key challenges in designing such a two
`
`component feedback system is identifying the parameters used in the two
`
`components and the construction of the final precoder matrix as a function of
`
`the two components.
`
`[0007]
`
`The various aspects, features and advantages of the invention will
`
`become more fully apparent to those having ordinary skill in the art upon a
`
`careful consideration of the following Detailed Description thereof with the
`
`accompanying drawings described below. The drawings may have been
`
`simplified for clarity and are not necessarily drawn to scale.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`[0008]
`
`FIG. 1 illustrates a wireless communication system.
`
`[0009]
`
`FIG.2 illustrates an embodiment with a base station transmitting
`
`to a device.
`
`[00010]
`
`FIG.3 illustrates an example of a frame structure used in the 3GPP
`
`LTE Release-8 (Rel-8) specification and different reference symbols.
`
`[00011]
`
`FIG. 4 illustrates exemplary antenna configurations at a base unit.
`
`[00012]
`
`FIG. 5 illustrates a first subset of antennas and a second subset of
`
`antennas transmitting two spatial layers to a device.
`
`3
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`IPR2023-01273 Page 3
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`Atty. Docket No. CS37679
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`[00013]
`
`FIG. 6 illustrates a wideband and subbands, each of which is
`
`further composed of contiguous subcarriers.
`
`DETAILED DESCRIPTION
`
`[00014]
`
`In FIG. 1, a wireless con1.munication system 100 comprises one or
`
`more fixed base infrastructure units 110 and120 forming a network distributed
`
`over a geographical region for serving remote units in the time and/ or
`
`frequency domain. The base infrastructure unit may also be referred to as the
`
`transmitter, access point (AP), access terminal (AT), base, base station (BS),
`
`base unit (BU), Node-B (NB), enhanced Node-B (eNB), Home Node-B (HNB),
`
`Home eNB (HeNB) or by other terminology used in the art. The base units are
`
`generally part of a radio access network that includes one or more controllers
`
`communicably coupled to one or more corresponding base units. The access
`
`network is generally communicably coupled to one or more core networks,
`
`which may be coupled to other packet or data networks, like the Internet, and
`
`to public switched telephone networks (PSTN), among other networks. These
`
`and other elements of access and core networks are not illustrated but they are
`
`well known generally by those having ordinary skill in the art.
`
`[00015]
`
`The one or more base units each comprise one or more
`
`transmitters for downlink transmissions and one or more receivers for
`
`receiving uplink transmissions from the remote units as described further
`
`below. The one or more base units serve a number of remote units, for
`
`example, remote unit 102 and 104 in FIG. 1, within a corresponding serving
`
`area, for example, a cell or a cell sector of the base unit, via a wireless
`
`communication link. The remote units may be fixed units or wireless
`
`communication devices. The remote unit may also be referred to as a receiver,
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`IPR2023-01273 Page 4
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`Atty. Docket No. CS37679
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`subscriber station (SS), mobile, mobile station (MS), mobile terminal, user,
`
`terminals, user equipment (UE), user terminal (UT) or by other terminology
`
`used in the art. The remote units also comprise one or more transmitters and
`
`one or more receivers.
`
`In FIG. 1, the base unit 110 transmits downlink
`
`communication signals to serve remote unit 102 in the time and/ or frequency
`
`domain. The remote unit 102 communicates directly with base unit 110 via
`
`uplink communication sigr1als.
`
`[00016]
`
`The term II transmitter" is used herein to refer to a source of a
`
`transmission intended for receipt by a user or receiver. A transmitter may
`
`have rn.ultiple co-located antennas each of which emits, possibly different,
`
`waveforms based on the same information source.
`
`In FIG. 1, for exam.pie,
`
`antennas 112 and 114 are co-located. A transmitter is typically associated with
`
`a cell or a cell sector in the case of a base unit having or serving multiple
`
`sectors. Also, if a base unit has geographically separated antennas (i.e.,
`
`distributed antennas with remote radio heads), the scenario is also referred to
`
`as
`
`II a
`
`transmitter". Thus generally one or n1.ore base units transmit
`
`information from multiple antennas for reception by a remote unit.
`
`[00017]
`
`In the diagram 200 of FIG. 2, at 210, a base unit transmits from a
`
`plurality of antennas. Also in FIG.2, a remote unit receives transmissions from
`
`a plurality of antennas, which may or may not be co-located. In a typical
`
`embodiment, a base unit n1.ay be associated with a cell-ID, by which it
`
`identifies itself to a remote unit. As a conventional mode of operation, also
`
`sometimes referred to as a single-point transmission scheme, a remote unit 240
`
`receives transn1.issions from a plurality of antennas of a single base unit 210.
`
`Such a base unit is also referred to as a serving cell (or serving base unit) to the
`
`user device/ remote unit.
`
`5
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`IPR2023-01273 Page 5
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`Atty. Docket No. CS37679
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`[00018]
`
`In one implementation, the wireless communication system is
`
`compliant with the Third Generation Partnership Project (3GPP) Universal
`
`Mobile Telecommunications System (UMTS) Long Term Evolution protocol,
`
`also referred to as Evolved Universal Terrestrial Radio Access (EUTRA), or
`
`some future generation thereof, wherein the base unit transmits using an
`
`orthogonal frequency division multiplexing (OFDM) modulation scheme on
`
`the downlink and the user terminals transmit on the uplink using a single
`
`carrier frequency division multiple access (SC-FDMA) scheme.
`
`In another
`
`implementation, the wireless communication system is compliant with the
`
`IEEE 802.16 protocol or a future generation thereof. More generally, however,
`
`the wireless communication system may implement some other open or
`
`proprietary communication protocol where channel feedback is useful or
`
`desired. Thus the disclosure is not intended to be limited to or by the
`
`implementation of any particular wireless communication system architecture
`
`or protocol. The teachings herein are more generally applicable to any system
`
`or operation that utilizes multiple antennas in a transmission, whether the
`
`multiple antennas belong to a single base unit or to multiple base units or
`
`whether the multiple antennas are geographically co-located (e.g., belong to a
`
`single base unit) or distributed (belong to either remote radio heads or
`
`multiple cells).
`
`[00019]
`
`In a general embodiment, pilots or reference symbols are sent
`
`from each antenna in a transmitter. These pilots occupy the operational
`
`bandwidth to allow users to estimate the channel state information (CSI) of the
`
`entire bandwidth. Typically the pilots from different antennas are orthogonal
`
`so the pilots do not inter£ ere with each other. Such orthogonality can be
`
`ensured if the pilots are sent using different time and/ or frequency resources
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`IPR2023-01273 Page 6
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`Atty. Docket No. CS37679
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`or code resources. For example, in systems based on OFDM technology, the
`
`pilots can occupy different subcarriers in frequency or different OFDM
`
`symbols in time or share the same set of resources, but different code
`
`sequences.
`
`[00020]
`
`In FIG. 3 illustrates a fram.e structure used in the 3GPP LTE
`
`Release-8 (Rel-8) protocol to illustrate a possible reference symbol (RS) pattern
`
`in an OFDM system.. A subframe 310 in a radio fram.e 302 spans 14 OFDM
`
`symbols in time. Further a subframe 310 contains multiple resource blocks
`
`312, each spanning 12 consecutive subcarriers in frequency. In typical OFDM
`
`based systems like 3GPP LTE, a block of consecutive OFDM symbols are
`
`referred to as a subframe. Each sub-carrier location in each of the OFDM
`
`symbols is referred to as a resource element (RE), since a single data
`
`n1.odulation symbol can be mapped to such a resource element. A resource
`
`block (RB) is defined as a block of REs comprising a set of consecutive sub(cid:173)
`
`carrier locations in frequency and a set of symbols. In LTE Rel-8, a slot is
`
`defined to span 7 symbols and each subframe is made of two slots, and hence
`
`14 symbols. A minimun1. resource unit allocated to a user is the two RBs
`
`corresponding to two slots in a subframe for a total of 2x12x7 REs. A resource
`
`block may be more generally defined as a set of resource elements/OFDM
`
`subcarrier resources in time and frequency domain.
`
`[00021]
`
`Some of the REs in a RB are reserved for reference symbols ( also
`
`referred to as pilots) to help in the demodulation and other measurements at
`
`the UE. These reference symbols, as defined in Release 8 specification of L TE
`
`can be further divided into two types. The first type is cell-specific reference
`
`symbols, which are cell-specific and "common" to all users, and are
`
`transmitted in all the RBs. A common reference symbol (CRS) may or may not
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`Atty. Docket No. CS37679
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`correspond to actual physical antennas of the transmitter, but CRSs are
`
`associated with one or more antenna "ports", either physical or virtual. In
`
`FIG. 3, as an example only, RE 304, 305, 306, 307, 308 and 309 may be a CRS.
`
`The second type is user-specific or a dedicated reference symbol (DRS), which
`
`are user-specific and hence applicable only to that user, and allocated in the
`
`RB's allocated to that user's data. Furthermore, DRS typically correspond to
`
`"precoded" or beam-formed RSs, which can be directly used by a user for the
`
`demodulation of the data streams. The precoding operation is explained later.
`
`In FIG. 4, as an example only, RE 320, 325, 330, 335, 340, 345, 350 and 355 may
`
`be a DRS. In LTE Release-10, a new spare RS, namely CSI-RS are defined to
`
`enable channel measurements, while DRSs are primarily relied upon for
`
`demodulation. These can be used similar to CRSs in LTE Release- 8 to derive
`
`channel feedback information.
`
`[00022]
`
`The location of the reference symbols is known to the UE from
`
`higher layer configurations. For example, depending on the number of
`
`antenna ports as configured by a transmission unit, UE knows the location of
`
`all the reference symbols corresponding to all configured antenna ports. As
`
`another example, when a UE is instructed to use a DRS, the UE also knows the
`
`DRS locations, which may depend on the user identification.
`
`[00023]
`
`In typical FDD operation of a LTE Rel-8 system, CRSs are used for
`
`both channel related measurements at the UE and also for dem.odulation. If
`
`eNB employs a precoder at the transmitter, such information is made available
`
`to the UE, which allows it to construct the channel for demodulation based on
`
`the CRSs. In a FDD operation of a future LTE Rel-10 system, CSI-RS (and
`
`possibly CRSs that may still be available) may be used for channel related
`
`measurements, while DRSs are used for demodulation. Hence an eNB may
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`Atty. Docket No. CS37679
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`apply precoder which are not exactly the same as the UE feedback, and does
`
`not have to signal the precoder explicitly. This is further described in detail
`
`later.
`
`[00024]
`
`The fl precoding" operation is explained in the following. The
`
`base station transmits a signal via weighting each antenna signal with a
`
`complex value, an operation referred to as precoding, which may be
`
`mathematically represented by the matrix equation:
`
`[00025]
`
`Y=HVs +n
`
`[00026]
`
`in which, when transmitting one spatial layer of data, or rank-1,
`
`may be represented as:
`
`[00027]
`
`[00028]
`
`in which, when transmitting two spatial layers of data, or rank-2,
`
`may be represented as:
`
`[00029]
`
`[00030]
`
`where Yi ... yNR may be the received data at the UE receive antenna
`
`#1 to #NR, respectively.
`
`In the example with a rank-1 transmission, or a
`
`transmission with one data stream denoted as fl s", the Matrix V may be a
`
`9
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`IPR2023-01273 Page 9
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`Atty. Docket No. CS37679
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`precoding vector with weights v1,1 ••• vNr,1 for base station transmit antenna #1
`
`to #NT respectively.
`
`In an embodiment with a rank-2 transmission, or a
`
`transmission with two data streams s1 and s2 on the same subcarrier, V may
`
`be a precoding matrix. Precoding vector and precoding matrix can be referred
`
`to as precoding matrix given vector is a degenerated case of matrix.
`
`[00031]
`
`Matrix H may be the propagation channel matrix between
`
`transmit antennas and receive antennas with entry foj representing a channel
`
`between the jth transmit and ith receive antennas. Value n may represent
`
`noise and interference. The precoding weights V, either a vector or matrix,
`
`may be determined by the base station, typically based on the channel
`
`particular to the UE or can be DE-specific and may also take into account a
`
`preference indicated by feedback from the UE. Further the matrix HV can be
`
`referred to as the effective channel between a user's data streams and its
`
`receivers. The effective channel, instead of the propagation channel H, is all a
`
`UE needs for demodulation purposes. The precoding weights m.ay or may not
`
`be constrained to a predefined codebook that consists of a set of pre-defined
`
`vectors or matrices.
`
`In an embodiment with constrained precoding, the
`
`precoding matrix may be signaled by the base unit efficiently with a precoding
`
`matrix index (PMI) or with an index to a precoding matrix within a predefined
`
`codebook. The term "matrix" in this context may include the degenerated
`
`special case of vector, which applies to single stream transmission. In the most
`
`generic sense, the term "precoding" refers to any possible transmission scheme
`
`that may be deemed as mapping a set of data streams to an antenna set using a
`
`matrix V.
`
`[00032]
`
`The applied precoding could be based on corresponding feedback
`
`from the UE or channel measurements at a base station. In a simple single-
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`user single base unit scheme, one set of DRSs could be defined corresponding
`
`to the effective precoded channel (i.e., "HV" in the above equation). If two
`
`streams are transmitted to a user in a rank-2 transmission, then only 2 DRS
`
`ports (i.e., 2 subsets of DRS each corresponding to a precoded antenna port)
`
`are sufficient, even though the actual signal transmission may come from all
`
`the Nr antennas at the base unit where Nr can be greater than 2. In FIG. 3, as
`
`an example only, RE 320, 340, 330 and 350 may correspond to one DRS port
`
`while RE 325, 345, 335 and 355 m.ay correspond to another DRS port.
`
`[00033]
`
`In a future migration of a system, for example in 3GPP L TE
`
`Release 10 and beyond, user-specific RS (or DRS) are expected to be used
`
`widely with advanced Multiple-Input Multiple-Output (MIMO) modes like
`
`Coordinated Multipoint transmission (CoMP) and multi-user (MU) MIMO
`
`n1.odes described earlier. As described earlier, DRSs are sufficient to enable
`
`demodulation. This is also helpful since an eNB is not required to signal exact
`
`transmission parameters like precoders, co-ordinating points, etc. However,
`
`an estin1.ate of the actual (un-precoded or explicit) channel is required at the
`
`eNB to derive such transmission parameters.
`
`So as mentioned before,
`
`feedback measurements for this purpose are enabled in L TE Release-10 by
`
`defining lower density reference signals specifically for the purpose of
`
`feedback measurements (CSI-RS).
`
`Since they do not need to support
`
`demodulation, like CRS in LTE Release 8, a lower density is sufficient.
`
`Further, with CoMP, CSI-RS n1.ay be setup to enable measurements at the user
`
`device on a plurality of antennas from multiple base units. In FIG. 3, as an
`
`example only, RE 304,305,306,307,308 and 309 may also be CSI-RS.
`
`[00034]
`
`From either CRS or CSI-RS, the remote unit receiver can estimate
`
`the CSL For the OFDM example, the receiver estimates CSI at each subcarrier
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`between each receiver antenna and each transmitter antenna. The CSI may be
`
`denoted as a channel matrix on a sub-carrier k represented by
`
`[00035]
`
`t1i 1
`H- h21
`
`k -
`
`tli2
`
`tliNt
`
`hNrl
`
`hNrNt
`
`[00036]
`
`where hij is the channel matrix from j th transmit antenna to the
`
`i th receive antenna.
`
`[00037]
`
`A correlation between antenna port i and antenna port j may be
`
`computed as follows
`
`[00038]
`
`[00039]
`
`where hki is the channel measured corresponding to antenna port
`
`i on subcarrier k, S is a set of subcarriers, typically corresponding to the
`
`whole operational bandwidth ( denoted as Rws) or a sub-band / narrowband
`
`( denoted as RNs).
`
`[00040]
`
`More generally, an antenna correlation matrix that represents the
`
`spatial covariance among a plurality of transmit antennas can be computed as
`
`follows
`
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`Atty. Docket No. CS37679
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`[00041]
`
`R--l_LHHH -
`- Is I kES
`k -
`k
`
`[00042]
`
`The Eigen Decomposition of R may be expressed in a well-defined
`
`format as
`
`VDVH
`
`(1)
`
`where Vis a unitary matrix of Eigen vectors, where the first column is the
`
`most dominant vector, the second column the second dominant vector and so
`
`on. Dis a diagonal matrix with diagonal entries as Eigen values of R. The full
`
`knowledge
`
`of
`
`R
`
`at
`
`the
`
`transmitter will
`
`enable
`
`advanced
`
`beamforming/ precoding techniques that will improve spectral efficiency and
`
`system throughput. However, the overhead may be large and approximations
`
`suitable to the transmission mode are applied.
`
`[00043]
`
`For SU-MIMO precoding,
`
`the Eigen space
`
`information as
`
`represented by V above can be viewed as optimal precoding transmission
`
`weights in a capacity maximizing sense.
`
`[00044]
`
`Existing 4th Generation (4G) air interfaces (i.e., 3GPP LTE and
`
`IEEE 802.16e) already support beamforming operation via the precoding
`
`operation as described earlier. To support precoding operation from the base
`
`station, a user terminal will be reporting back to the base station a preferred
`
`Precoding Matrix Index (PMI) which is an index to a set of predetermined
`
`precoding matrices. The recommended precoding matrix is obtained at the
`
`user terminal based on a certain metric such as maximizing the post-precoding
`
`link quality or throughput and is selected from one of the quantized codebook
`
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`Atty. Docket No. CS37679
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`entries, wherein the codebook is known to the transmitter and the receiver.
`
`Specifically, the standard requires the UE to feedback the PMI that supports a
`
`MCS (modulation and coding schem.e) with the highest rate, while satisfying a
`
`probability if block error target. In future releases, different or more explicit
`
`definitions of PMI may be defined. However, in general, the preferred PMI
`
`approximately represents a vector quantization of the dominant Eigenspace of
`
`R. Further PMI is feedback with an associated rank and as such PMI is an
`
`quantized approximation of V(l:r), where ;r' is the rank.
`
`[00045]
`
`FIG. 4 illustrates some exemplary antenna configurations at a base
`
`unit. A closely spaced ULA, with a typical spacing of 0.5 to 1 wavelengths, is
`
`illustrated in 410. A large spaced ULA with typical spacing of 4 to 10
`
`wavelengths is illustrated in 420. A cross-polarized configuration with two
`
`sets of cross-poles each with two antennas at + / - 45 polarizations is illustrated
`
`in 440. Depending on the configuration, the correlation between different
`
`antenna elements may have a certain structure. Some exemplary cases are
`
`described herein.
`
`[00046]
`
`We now illustrate how the structure of the antenna configuration
`
`can be used to develop efficient precoder structures.
`
`[00047]
`
`One of the structures that can be exploited is a Kronecker based
`
`approximation of the channel covariance. For example, an 8x8 long term
`
`covariance matrix corresponding to 8 antennas, as in FIG. 4 at 460, for the
`
`transmitter can be approximated as a Kronecker product of a 4x4 correlation
`
`matrix corresponding to the ULA and a 2x2 correlation matrix, corresponding
`
`to the cross-polarized component i.e.,
`
`14
`
`IPR2023-01273 Page 14
`
`
`
`Atty. Docket No. CS37679
`
`[00048]
`
`[00049]
`
`Conceptually, the ULA Kronecker component R,__ILA captures the
`
`correlation submatrix between two non-overlapping subsets of antennas with
`
`similar ULA configuration, which in FIG. 4 at 460 are antenna sets (461-464)
`
`and (465-468). The polarization Kronecker component RPol captures the
`
`correlation
`
`submatrix between
`
`subsets with
`
`similar cross-polarized
`
`configuration, namely antenna subsets (461,465), (462,466), (463,467) and
`
`(464,468) in FIG. 4. More generally, the spacing/location and polarization of
`
`antenna elements introduce some redundant structure in the antenna
`
`correlation, which lead to good Kronecker approximations and can be used as
`
`effective compression schemes for feedback overhead reduction. The above
`
`representation in the covariance matrix also translates to sin1.ilar structure for
`
`the precoder.
`
`[00050]
`
`Even for ULA, the transmit antennas can also be divided into two
`
`non-overlapping subsets of antennas. An example is shown in FIG. 4 for
`
`subset 431 and 432.
`
`[00051]
`
`The final precoder for SU-MIMO rank-r may be computed as
`
`[00052]
`
`The principal Eigenvectors and Eigenvalues of the constructed
`
`matrix are related to that of the Kronecker components as
`
`(0.2)
`
`15
`
`IPR2023-01273 Page 15
`
`
`
`Atty. Docket No. CS37679
`
`D = permute(D XP ® DuLA)
`V = permute(v_¥P ® VuLA)
`
`(0.3)
`
`where the "permute" operation performs re-ordering of Eigen values.
`
`[00053]
`
`We can further illustrate how the reordering influences the
`
`structure of the precoder for a 4 Tx cross-pole as an example, where both the
`
`ULA and cross-pole sub-matrices are of size 2x2, i.e.,
`
`and
`
`A2
`
`fl
`[ vula,l' vula,2]
`
`Rur.A = [ Vu/a ,1' Vala,2 i[ ~ 0]
`RXP = [ vxp,1 'vxp,2] 0 0]
`
`[ K,
`
`K2
`
`H
`[vxp,1' vxp,2]
`
`(0.4)
`
`(0.5)
`
`Let us consider a rank-2 SU-MIMO transmission as a further example.
`
`Typically the cross-pole covariance matrix is highly rank-2 and ULA
`
`covariance can be approximated as rank 1. To express it quantitatively, if the
`
`two Eigen values ratios satisfyA_>s_, then the rank-2 SU-MIMO precoder,
`A2
`K2
`
`after corresponding re-ordering, can be approximated as
`
`On the other hand, in case of }'1 < _5_ (which is less likely but could occur on
`}½
`K2
`
`short-term basis, like a subband of contiguous subcarriers), then the rank-2
`
`precoder may be approximated as
`
`(0.6)
`
`16
`
`IPR2023-01273 Page 16
`
`
`
`Atty. Docket No. CS37679
`
`]
`] (8) [
`V xp 1 X V ula 1 V ula 2 =
`[
`'
`'
`'
`
`[Vula,lVxp,11
`V
`V
`ula,l xp,12
`
`(0.7)
`
`[00054]
`
`As can be seen, two structures are shown which allow expressing
`
`the overall precoder as a Kronecker product of two precoders. Further, the
`
`ULA component of
`
`the precoder may be
`
`feedback at a different
`
`time/frequency granularity than the cross-pole component of the precoder,
`
`and allows two component feedback schemes.
`
`[00055]
`
`Though
`
`the Kronecker representation
`
`leads
`
`to an elegant
`
`separation to two component precoders and is one way to achieve two(cid:173)
`
`component feedback, it also imposes some limitations, where either the ULA
`
`or the cross-pol component is assumed to be rank 1 for deriving an overall
`
`rank-2 precoder.
`
`In general, however a more general two-component
`
`precoder structure is useful for higher ranks, which will be further discussed
`
`below.
`
`[00056]
`
`For the purpose of discussion, we will assume the long-
`
`term/ correlated component corresponds to a wide frequency band such as the
`
`whole system bandwidth and the short-tern component corresponds to a
`
`subband/narrowband that is composed of a set of contiguous subcarriers and
`
`is a part of the wideband.
`
`[00057]
`
`The optimal precoding vector V ( optimal in an information
`
`theoretic capacity maximizing sense) can be obtained from the Eigen
`
`decomposition of the narrowband covariance matrix for band indexed ;b' as
`
`follows.
`
`17
`
`IPR2023-01273 Page 17
`
`
`
`Atty. Docket No. CS37679
`
`(0.8)
`
`For the rank-2 or 2-layer precoder, the ideal precoder is simply the first two
`
`columns of V,vB,b. Let us denote the rank-2 Eigen decomposition based
`
`precoder as follows (a partition based representation of V,vB,b)
`
`(0.9)
`
`where vii is a 4x1 (assuming 8-Tx eNB) vector. Clearly, each block corresponds
`
`to a vector of weights applied on a subset of antennas ( e.g., ULA subset)
`
`corresponding to one spatial layer of data stream.
`
`[00058]
`
`In a preferred embodiment, we approximate or otherwise
`
`represent V,vB,b as
`
`and then we can irn.pose the constraint II vll 11=11 v 12 11=11 v 21 11=11 v 22 II= 1 and rij are
`
`real values and 01 , 02 E [O, 21r] .
`
`(0.10)
`
`[00059]
`
`Clearly, the above precoder representation is based on a matrix
`
`with a block of sub-matrices, where each sub-matrix is represented with a
`
`vector multiplied with a
`
`scalar. More
`
`importantly, each sub-matrix
`
`corresponds to transmission from a subgroup of antennas, and as one special
`
`case, where they all have the same polarization.
`
`18
`
`IPR2023-01273 Page 18
`
`
`
`Atty. Docket No. CS37679
`
`[00060]
`
`FIG. 5 further describes the above precoding operation from two
`
`subsets of antennas. Two non-overlapping subsets of antennas 510, 520 are
`
`weighted by a first and a second sub-precoder matrix, respectively. Each sub(cid:173)
`
`precoder matrix corresponds
`
`to one or more spatial
`
`layers of data
`
`transmission, for example in FIG 5, the first sub-precoder is for spatial layer 1
`
`(530) and layer-2 (540). Similarly for the second-precoder, it corresponds to
`
`two spatial layers. Mathematically, as an example with eight antennas
`
`composed of two groups of 4 antennas, where the first subgroup is number 1-
`
`4, and second subgroup numbered 5-8, a rank r precoder may be expressed as
`
`follows
`
`Vil
`
`V12
`
`Vlr
`
`V21
`
`V31
`
`V51
`
`V52
`
`Vsr
`
`V61
`
`V71
`
`Vg1
`
`V8r
`
`(11)
`
`In the above the first sub-precoder is the top 4 rows(l-4) and the second sub(cid:173)
`
`precoder is the bottom 4 rows (5-8)
`
`[00061]
`
`A precoder matrix of one or more vectors associated with one or
`
`n1.ore spatial layers consists of a first sub-precoder n1.atrix, which con1.prises of
`
`a first set of weights on a first subsets of transmit antennas of the base station,
`
`and a second sub-precoder matrix which comprises of a second set of weights
`
`on a second subset of transmit antennas of the base station as illustrated above.
`
`The set of weights here can be for one or more spatial layers of transmission.
`
`19
`
`IPR2023-01273 Page 19
`
`
`
`Atty. Docket No. CS37679
`
`[00062]
`
`In the final precoder matrix, the first sub-precoder matrix is one or
`
`more column vectors, which are of length equal to the number of antennas in
`
`the first subgroup, multiplied by one or more scalars. Similarly for the second
`
`sub-precoder.
`
`[00063]
`
`For practical reasons, it is often preferred to have the precoder
`
`satisfy two constraints, namely i) Full power utilization on each transmit
`
`antenna, for maximum Power Amplifier (PA) use and ii) Equal power on each
`
`transmitted stream. These constraints can be imposed on the precoder
`
`structure above [00058]. To satisfy equal power constraint on each transmit
`
`stream, we can impose additional constraint of y11 + y 21 = y12 + y 22 • To satisfy full
`
`power utilization on each individual transmit antenna, we could impose as a
`
`sufficient condition, that y11 + y12 = y 21 + y 22 and that vu are constant modulus
`
`vectors. With these constraints, we have another preferred embodiment of the
`
`precoder structure as follows,
`
`[00064]
`
`[00065]
`
`The above discussion on the precoder structure is tied to feedback
`
`n1.ethod
`
`in
`
`this
`
`invention.
`
`In
`
`the
`
`feedback scheme
`
`for a wireless
`
`communication device to send a precoder matrix information to a base station,
`
`the wireless communication device sends a first representation of a first matrix
`
`chosen from a first codebook, wherein the first n1.atrix has at least two colulll.n
`
`vectors. The wireless communication device sends a second representation of
`
`a second matrix chosen fron1. a second codebook, wherein
`
`the first
`
`representation and the second representation together convey a precoder
`
`20
`
`IPR2023-01273 Page 20
`
`
`
`Atty. Docket No. CS37679
`
`matrix of one or more vectors associated with one or more spatial layers. The
`
`precoder matrix comprises a first sub-precoder matrix including a first set of
`
`weights on a first subsets of transmit antennas of the base station and a second
`
`sub-precoder matrix including a second set of weights on a second subset of
`
`transmit antennas of the base station. The first sub-precoder matrix is one or
`
`n1.ore column vectors of
`
`the first matrix corresponding
`
`to
`
`the first
`
`representation, multiplied by one or more entries of the second matrix
`
`corresponding to the second representation, and the second sub-precoder
`
`matrix is one ore more column vectors of the first matrix corresponding to the
`
`first representation, mu
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