Abstract:
Methods and apparatuses for CSI reporting mechanisms are provided. A user equipment (UE) apparatus includes a transceiver and a processor. The transceiver is configured to receive configuration information for a channel state information (CSI) reporting and receive configuration information for a plurality of precoding codebook parameters. The processor is operably connected to the transceiver, and configured to calculate, in response to receipt of the configuration information for the CSI reporting and the configuration information for the plurality of precoding codebook parameters, a first precoding matrix indicator (PMI) and a second PMI, wherein the first PMI includes one or two codebook indices. The transceiver is further configured to transmit the CSI reporting on an uplink channel, the CSI reporting including a channel quality indicator (CQI), a rank indicator (RI), and the calculated first and second PMIs.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS AND CLAIM OF PRIORITY 
       [0001]    This application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application No. 62/157,828 filed May 6, 2015; and U.S. Provisional Patent Application No. 62/203,172 filed Aug. 10, 2015. The above-identified provisional patent applications are hereby incorporated by reference in their entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The present disclosure relates generally to transmission mode and channel state information (CSI) reporting for multiple transmit antennas which includes two dimensional arrays. Such two dimensional arrays can be associated with a type of multiple-input multiple-output (MIMO) system often termed “full-dimension” MIMO (FD-MIMO) or massive MIMO or 3D-MIMO. 
       BACKGROUND 
       [0003]    Wireless communication has been one of the most successful innovations in modern history. The demand of wireless data traffic is rapidly increasing due to the growing popularity among consumers and businesses of smart phones and other mobile data devices, such as tablets, “note pad” computers, net books, eBook readers, and machine type of devices. To meet the high growth in mobile data traffic and support new applications and deployments, improvements in radio interface efficiency and coverage is of paramount importance. 
         [0004]    A mobile device or user equipment can measure the quality of the downlink channel and report this quality to a base station so that a determination can be made regarding whether or not various parameters should be adjusted during communication with the mobile device. Existing channel quality reporting processes in wireless communications systems do not sufficiently accommodate reporting of channel state information associated with large, two dimensional array transmit antennas or, in general, antenna array geometry which accommodates a large number of antenna elements. 
       SUMMARY 
       [0005]    Various embodiments of the present disclosure provide methods and apparatuses for codebook design and signaling. 
         [0006]    In one embodiment, a user equipment (UE) is provided. The UE includes a transceiver and a processor. The transceiver is configured to receive configuration information for a channel state information (CSI) reporting and receive configuration information for a plurality of precoding codebook parameters. The processor is operably connected to the transceiver, and configured to calculate, in response to receipt of the configuration information for the CSI reporting and the configuration information for the plurality of precoding codebook parameters, a first precoding matrix indicator (PMI) and a second PMI, wherein the first PMI includes one or two codebook indices. The transceiver is further configured to transmit the CSI reporting on an uplink channel, the CSI reporting including a channel quality indicator (CQI), a rank indicator (RI), and the calculated first and second PMIs. 
         [0007]    In another embodiment, a base station (BS) is provided. The BS includes a transceiver and a processor operably connected to the transceiver. The processor is configured to configure a user equipment (UE) with a channel state information (CSI) reporting; configure the UE with a plurality of precoding codebook parameters; cause the transceiver to transmit configuration information for the CSI reporting and precoding codebook parameters; and receive a CSI report from the UE including a channel quality indicator (CQI), a rank indicator (RI), and codebook indices from a first and a second precoding matrix indicators (PMIs). 
         [0008]    In another embodiment, a method for operating a UE is provided. The method includes receiving, by the UE, configuration information for a channel state information (CSI) reporting; receiving, by the UE, configuration information for a plurality of precoding codebook parameters; in response to receipt of the configuration information for the CSI reporting and the configuration information for the plurality of precoding codebook parameters, calculating, by the UE, a first precoding matrix indicator (PMI) and a second PMI, wherein the first PMI includes one or two codebook indices; and transmitting, by the UE, the CSI reporting on an uplink channel, the CSI reporting including a channel quality indicator (CQI), a rank indicator (RI), and the calculated first and second PMIs. 
         [0009]    Other technical features may be readily apparent to one skilled in the art from the following figures, descriptions, and claims. 
         [0010]    Before undertaking the DETAILED DESCRIPTION below, it can be advantageous to set forth definitions of certain words and phrases used throughout this patent document. The term “couple” and its derivatives refer to any direct or indirect communication between two or more elements, whether or not those elements are in physical contact with one another. The terms “transmit,” “receive,” and “communicate,” as well as derivatives thereof, encompass both direct and indirect communication. The terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation. The term “or” is inclusive, meaning and/or. The phrase “associated with,” as well as derivatives thereof, means to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, have a relationship to or with, or the like. The term “controller” means any device, system or part thereof that controls at least one operation. Such a controller can be implemented in hardware or a combination of hardware and software and/or firmware. The functionality associated with any particular controller can be centralized or distributed, whether locally or remotely. The phrase “at least one of,” when used with a list of items, means that different combinations of one or more of the listed items can be used, and only one item in the list can be needed. For example, “at least one of: A, B, and C” includes any of the following combinations: A, B, C, A and B, A and C, B and C, and A and B and C. 
         [0011]    Moreover, various functions described below can be implemented or supported by one or more computer programs, each of which is formed from computer readable program code and embodied in a computer readable medium. The terms “application” and “program” refer to one or more computer programs, software components, sets of instructions, procedures, functions, objects, classes, instances, related data, or a portion thereof adapted for implementation in a suitable computer readable program code. The phrase “computer readable program code” includes any type of computer code, including source code, object code, and executable code. The phrase “computer readable medium” includes any type of medium capable of being accessed by a computer, such as read only memory (ROM), random access memory (RAM), a hard disk drive, a compact disc (CD), a digital video disc (DVD), or any other type of memory. A “non-transitory” computer readable medium excludes wired, wireless, optical, or other communication links that transport transitory electrical or other signals. A non-transitory computer readable medium includes media where data can be permanently stored and media where data can be stored and later overwritten, such as a rewritable optical disc or an erasable memory device. 
         [0012]    Definitions for other certain words and phrases are provided throughout this patent document. Those of ordinary skill in the art should understand that in many if not most instances, such definitions apply to prior as well as future uses of such defined words and phrases. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    For a more complete understanding of the present disclosure and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which like reference numerals represent like parts: 
           [0014]      FIG. 1  illustrates an example wireless network according to various embodiments of the present disclosure; 
           [0015]      FIGS. 2A and 2B  illustrate example wireless transmit and receive paths according to various embodiments of the present disclosure; 
           [0016]      FIG. 3A  illustrates an example user equipment according to various embodiments of the present disclosure; 
           [0017]      FIG. 3B  illustrates an example enhanced NodeB (eNB) according to various embodiments of the present disclosure; 
           [0018]      FIG. 4  illustrates example two-dimensional (2D) antenna arrays constructed from 16 dual-polarized elements arranged in a 4×2 or 2×4 rectangular format which can be utilized in various embodiments of the present disclosure; 
           [0019]      FIG. 5  illustrates an example CSI calculation procedure which responds to a CSI-RS resource pattern or codebook parameter and calculates a two-dimensional PMI/RI for two-dimensional pattern; 
           [0020]      FIG. 6  illustrates an example CSI calculation procedure which responds to a CSI-RS resource pattern or codebook parameter and a PMI/RI configuration for a second dimension; 
           [0021]      FIG. 7  illustrates an example CSI calculation procedure which responds to a CSI-RS resource pattern or codebook parameter and assumes a wideband PMI with RI=1 for a second dimension; 
           [0022]      FIG. 8  illustrates an example method wherein a UE receives configuration information containing at least a CSI reporting configuration and codebook parameters and reports a first PMI composed of either one or two codebook indices conditioned on at least two codebook parameters. 
           [0023]      FIG. 9  illustrates an example method wherein an eNB configures a UE with CSI reporting and codebook parameters and in turn receives a CSI report including at least CQI, RI, a first PMI, and a second PMI wherein the number of codebook indices associated with the first PMI is conditioned on at least two codebook parameters. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]      FIGS. 1 through 10 , discussed below, and the various embodiments used to describe the principles of the present disclosure in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the disclosure. Those skilled in the art will understand that the principles of the present disclosure can be implemented in any suitably arranged wireless communication system. 
         [0025]    List of Acronyms 
         [0026]    2D: two-dimensional 
         [0027]    MIMO: multiple-input multiple-output 
         [0028]    SU-MIMO: single-user MIMO 
         [0029]    MU-MIMO: multi-user MIMO 
         [0030]    3GPP: 3rd generation partnership project 
         [0031]    LTE: long-term evolution 
         [0032]    UE: user equipment 
         [0033]    eNB: evolved Node B or “eNB” 
         [0034]    DL: downlink 
         [0035]    UL: uplink 
         [0036]    CRS: cell-specific reference signal(s) 
         [0037]    DMRS: demodulation reference signal(s) 
         [0038]    SRS: sounding reference signal(s) 
         [0039]    UE-RS: UE-specific reference signal(s) 
         [0040]    CSI-RS: channel state information reference signals 
         [0041]    SCID: scrambling identity 
         [0042]    MCS: modulation and coding scheme 
         [0043]    RE: resource element 
         [0044]    CQI: channel quality information 
         [0045]    PMI: precoding matrix indicator 
         [0046]    RI: rank indicator 
         [0047]    MU-CQI: multi-user CQI 
         [0048]    CSI: channel state information 
         [0049]    CSI-IM: CSI interference measurement 
         [0050]    CoMP: coordinated multi-point 
         [0051]    DCI: downlink control information 
         [0052]    UCI: uplink control information 
         [0053]    PDSCH: physical downlink shared channel 
         [0054]    PDCCH: physical downlink control channel 
         [0055]    PUSCH: physical uplink shared channel 
         [0056]    PUCCH: physical uplink control channel 
         [0057]    PRB: physical resource block 
         [0058]    RRC: radio resource control 
         [0059]    AoA: angle of arrival 
         [0060]    AoD: angle of departure 
         [0061]    The following documents and standards descriptions are hereby incorporated by reference into the present disclosure as if fully set forth herein: 3GPP Technical Specification (TS) 36.211 version 12.4.0, “E-UTRA, Physical channels and modulation” (“REF 1”); 3GPP TS 36.212 version 12.3.0, “E-UTRA, Multiplexing and Channel coding” (“REF 2”); 3GPP TS 36.213 version 12.4.0, “E-UTRA, Physical Layer Procedures” (“REF 3”); and 3GPP TS 36.331 version 12.4.0, “E-UTRA, Radio Resource Control (RRC) Protocol Specification” (“REF 4”). 
         [0062]      FIG. 1  illustrates an example wireless network  100  according to various embodiments of the present disclosure. The embodiment of the wireless network  100  shown in  FIG. 1  is for illustration only. Other embodiments of the wireless network  100  could be used without departing from the scope of the present disclosure. The wireless network  100  includes an eNB (eNB)  101 , an eNB  102 , and an eNB  103 . The eNB  101  communicates with the eNB  102  and the eNB  103 . The eNB  101  also communicates with at least one Internet Protocol (IP) network  130 , such as the Internet, a proprietary IP network, or other data network. Depending on the network type, other well-known terms can be used instead of “eNB” or “eNB,” such as “base station” or “access point.” For the sake of convenience, the terms “eNB” and “eNB” are used in this patent document to refer to network infrastructure components that provide wireless access to remote terminals. Also, depending on the network type, other well-known terms can be used instead of “user equipment” or “UE,” such as “mobile station,” “subscriber station,” “remote terminal,” “wireless terminal,” or “user device.” For the sake of convenience, the terms “user equipment” and “UE” are used in this patent document to refer to remote wireless equipment that wirelessly accesses an eNB, whether the UE is a mobile device (such as a mobile telephone or smartphone) or is normally considered a stationary device (such as a desktop computer or vending machine). 
         [0063]    The eNB  102  provides wireless broadband access to the network  130  for a first plurality of user equipments (UEs) within a coverage area  120  of the eNB  102 . The first plurality of UEs includes a UE  111 , which can be located in a small business (SB); a UE  112 , which can be located in an enterprise (E); a UE  113 , which may be located in a WiFi hotspot (HS); a UE  114 , which can be located in a first residence (R); a UE  115 , which may be located in a second residence (R); and a UE  116 , which can be a mobile device (M) like a cell phone, a wireless laptop, a wireless PDA, or the like. The eNB  103  provides wireless broadband access to the network  130  for a second plurality of UEs within a coverage area  125  of the eNB  103 . The second plurality of UEs includes the UE  115  and the UE  116 . In some embodiments, one or more of the eNBs  101 - 103  can communicate with each other and with the UEs  111 - 116  using 5G, LTE, LTE-A, WiMAX, or other advanced wireless communication techniques. 
         [0064]    Dotted lines show the approximate extents of the coverage areas  120  and  125 , which are shown as approximately circular for the purposes of illustration and explanation only. It should be clearly understood that the coverage areas associated with eNBs, such as the coverage areas  120  and  125 , can have other shapes, including irregular shapes, depending upon the configuration of the eNBs and variations in the radio environment associated with natural and man-made obstructions. 
         [0065]    As described in more detail below, one or more of BS  101 , BS  102  and BS  103  include 2D antenna arrays as described in embodiments of the present disclosure. In some embodiments, one or more of BS  101 , BS  102  and BS  103  support channel quality measurement and reporting for systems having 2D antenna arrays. In various embodiments, one or more of BSs  101 - 103  and UEs  111 - 116  perform signaling, configuration and/or calculation for CSI reporting. 
         [0066]    Although  FIG. 1  illustrates one example of a wireless network  100 , various changes can be made to  FIG. 1 . For example, the wireless network  100  could include any number of eNBs and any number of UEs in any suitable arrangement. Also, the eNB  101  could communicate directly with any number of UEs and provide those UEs with wireless broadband access to the network  130 . Similarly, each eNB  102 - 103  could communicate directly with the network  130  and provide UEs with direct wireless broadband access to the network  130 . Further, the eNB  101 ,  102 , and/or  103  could provide access to other or additional external networks, such as external telephone networks or other types of data networks. 
         [0067]      FIGS. 2A and 2B  illustrate example wireless transmit and receive paths according to the present disclosure. In the following description, a transmit path  200  can be described as being implemented in an eNB (such as eNB  102 ), while a receive path  250  can be described as being implemented in a UE (such as UE  116 ). However, it will be understood that the receive path  250  could be implemented in an eNB and that the transmit path  200  could be implemented in a UE. In some embodiments, the receive path  250  is configured to support channel quality measurement and reporting for systems having 2D antenna arrays as described in embodiments of the present disclosure. 
         [0068]    The transmit path  200  includes a channel coding and modulation block  205 , a serial-to-parallel (S-to-P) block  210 , a size N Inverse Fast Fourier Transform (IFFT) block  215 , a parallel-to-serial (P-to-S) block  220 , an add cyclic prefix block  225 , and an up-converter (UC)  230 . The receive path  250  includes a down-converter (DC)  255 , a remove cyclic prefix block  260 , a serial-to-parallel (S-to-P) block  265 , a size N Fast Fourier Transform (FFT) block  270 , a parallel-to-serial (P-to-S) block  275 , and a channel decoding and demodulation block  280 . 
         [0069]    In the transmit path  200 , the channel coding and modulation block  205  receives a set of information bits, applies coding (such as convolutional, Turbo, or low-density parity check (LDPC) coding), and modulates the input bits (such as with Quadrature Phase Shift Keying (QPSK) or Quadrature Amplitude Modulation (QAM)) to generate a sequence of frequency-domain modulation symbols. The serial-to-parallel block  210  converts (such as de-multiplexes) the serial modulated symbols to parallel data in order to generate N parallel symbol streams, where N is the IFFT/FFT size used in the eNB  102  and the UE  116 . The size N IFFT block  215  performs an IFFT operation on the N parallel symbol streams to generate time-domain output signals. The parallel-to-serial block  220  converts (such as multiplexes) the parallel time-domain output symbols from the size N IFFT block  215  in order to generate a serial time-domain signal. The ‘add cyclic prefix’ block  225  inserts a cyclic prefix to the time-domain signal. The up-converter  230  modulates (such as up-converts) the output of the ‘add cyclic prefix’ block  225  to an RF frequency for transmission via a wireless channel. The signal can also be filtered at baseband before conversion to the RF frequency. 
         [0070]    A transmitted RF signal from the eNB  102  arrives at the UE  116  after passing through the wireless channel, and reverse operations to those at the eNB  102  are performed at the UE  116 . The down-converter  255  down-converts the received signal to a baseband frequency, and the remove cyclic prefix block  260  removes the cyclic prefix to generate a serial time-domain baseband signal. The serial-to-parallel block  265  converts the time-domain baseband signal to parallel time domain signals. The size N FFT block  270  performs an FFT algorithm to generate N parallel frequency-domain signals. The parallel-to-serial block  275  converts the parallel frequency-domain signals to a sequence of modulated data symbols. The channel decoding and demodulation block  280  demodulates and decodes the modulated symbols to recover the original input data stream. 
         [0071]    As described in more detail below, the transmit path  200  or the receive path  250  can perform signaling for a designed codebook. Each of the eNBs  101 - 103  may implement a transmit path  200  that is analogous to transmitting in the downlink to UEs  111 - 116  and can implement a receive path  250  that is analogous to receiving in the uplink from UEs  111 - 116 . Similarly, each of UEs  111 - 116  may implement a transmit path  200  for transmitting in the uplink to eNBs  101 - 103  and can implement a receive path  250  for receiving in the downlink from eNBs  101 - 103 . 
         [0072]    Each of the components in  FIGS. 2A and 2B  can be implemented using only hardware or using a combination of hardware and software/firmware. As a particular example, at least some of the components in  FIGS. 2A and 2B  can be implemented in software, while other components can be implemented by configurable hardware or a mixture of software and configurable hardware. For instance, the FFT block  270  and the IFFT block  215  can be implemented as configurable software algorithms, where the value of size N can be modified according to the implementation. 
         [0073]    Furthermore, although described as using FFT and IFFT, this is by way of illustration only and should not be construed to limit the scope of the present disclosure. Other types of transforms, such as Discrete Fourier Transform (DFT) and Inverse Discrete Fourier Transform (IDFT) functions, could be used. It will be appreciated that the value of the variable N can be any integer number (such as 1, 2, 3, 4, or the like) for DFT and IDFT functions, while the value of the variable N can be any integer number that is a power of two (such as 1, 2, 4, 8, 16, or the like) for FFT and IFFT functions. 
         [0074]    Although  FIGS. 2A and 2B  illustrate examples of wireless transmit and receive paths, various changes can be made to  FIGS. 2A and 2B . For example, various components in  FIGS. 2A and 2B  could be combined, further subdivided, or omitted and additional components could be added according to particular needs. Also,  FIGS. 2A and 2B  are meant to illustrate examples of the types of transmit and receive paths that could be used in a wireless network. Other suitable architectures could be used to support wireless communications in a wireless network. 
         [0075]      FIG. 3A  illustrates an example UE  116  according to the present disclosure. The embodiment of the UE  116  illustrated in  FIG. 3A  is for illustration only, and the UEs  111 - 115  of  FIG. 1  could have the same or similar configuration. However, UEs come in a wide variety of configurations, and  FIG. 3A  does not limit the scope of the present disclosure to any particular implementation of a UE. 
         [0076]    The UE  116  includes an antenna  305 , a radio frequency (RF) transceiver  310 , transmit (TX) processing circuitry  315 , a microphone  320 , and receive (RX) processing circuitry  325 . The UE  116  also includes a speaker  330 , a processor  340 , an input/output (I/O) interface (IF)  345 , an input  350 , a display  355 , and a memory  360 . The memory  360  includes an operating system (OS) program  361  and one or more applications  362 . 
         [0077]    The RF transceiver  310  receives, from the antenna  305 , an incoming RF signal transmitted by an eNB of the network  100 . The RF transceiver  310  down-converts the incoming RF signal to generate an intermediate frequency (IF) or baseband signal. The IF or baseband signal is sent to the RX processing circuitry  325 , which generates a processed baseband signal by filtering, decoding, and/or digitizing the baseband or IF signal. The RX processing circuitry  325  transmits the processed baseband signal to the speaker  330  (such as for voice data) or to the processor  340  for further processing (such as for web browsing data). 
         [0078]    The TX processing circuitry  315  receives analog or digital voice data from the microphone  320  or other outgoing baseband data (such as web data, e-mail, or interactive video game data) from the processor  340 . The TX processing circuitry  315  encodes, multiplexes, and/or digitizes the outgoing baseband data to generate a processed baseband or IF signal. The RF transceiver  310  receives the outgoing processed baseband or IF signal from the TX processing circuitry  315  and up-converts the baseband or IF signal to an RF signal that is transmitted via the antenna  305 . 
         [0079]    The processor  340  can include one or more processors or other processing devices and execute the OS program  361  stored in the memory  360  in order to control the overall operation of the UE  116 . For example, processor  340  could control the reception of forward channel signals and the transmission of reverse channel signals by the RF transceiver  310 , the RX processing circuitry  325 , and the TX processing circuitry  315  in accordance with well-known principles. In some embodiments, the processor  340  includes at least one microprocessor or microcontroller. 
         [0080]    The processor  340  is also capable of executing other processes and programs resident in the memory  360 , such as operations for channel quality measurement and reporting for systems having 2D antenna arrays as described in embodiments of the present disclosure as described in embodiments of the present disclosure. The processor  340  can move data into or out of the memory  360  as required by an executing process. In some embodiments, the processor  340  is configured to execute the applications  362  based on the OS program  361  or in response to signals received from eNBs or an operator. The processor  340  is also coupled to the I/O interface  345 , which provides the UE  116  with the ability to connect to other devices such as laptop computers and handheld computers. The I/O interface  345  is the communication path between these accessories and the processor  340 . 
         [0081]    The processor  340  is also coupled to the input  350  (e.g., keypad, touchscreen, button etc.) and the display  355 . The operator of the UE  116  can use the input  350  to enter data into the UE  116 . The display  355  can be a liquid crystal display or other display capable of rendering text and/or at least limited graphics, such as from web sites. 
         [0082]    The memory  360  is coupled to the processor  340 . Part of the memory  360  could include a random access memory (RAM), and another part of the memory  360  could include a Flash memory or other read-only memory (ROM). 
         [0083]    As described in more detail below, the UE  116  can perform signaling and calculation for CSI reporting. Although  FIG. 3A  illustrates one example of UE  116 , various changes can be made to  FIG. 3A . For example, various components in  FIG. 3A  could be combined, further subdivided, or omitted and additional components could be added according to particular needs. As a particular example, the processor  340  could be divided into multiple processors, such as one or more central processing units (CPUs) and one or more graphics processing units (GPUs). Also, while  FIG. 3A  illustrates the UE  116  configured as a mobile telephone or smartphone, UEs could be configured to operate as other types of mobile or stationary devices. 
         [0084]      FIG. 3B  illustrates an example eNB  102  according to the present disclosure. The embodiment of the eNB  102  shown in  FIG. 3B  is for illustration only, and other eNBs of  FIG. 1  could have the same or similar configuration. However, eNBs come in a wide variety of configurations, and  FIG. 3B  does not limit the scope of the present disclosure to any particular implementation of an eNB. eNB  101  and eNB  103  can include the same or similar structure as eNB  102 . 
         [0085]    As shown in  FIG. 3B , the eNB  102  includes multiple antennas  370   a - 370   n , multiple RF transceivers  372   a - 372   n , transmit (TX) processing circuitry  374 , and receive (RX) processing circuitry  376 . In certain embodiments, one or more of the multiple antennas  370   a - 370   n  include 2D antenna arrays. The eNB  102  also includes a controller/processor  378 , a memory  380 , and a backhaul or network interface  382 . 
         [0086]    The RF transceivers  372   a - 372   n  receive, from the antennas  370   a - 370   n , incoming RF signals, such as signals transmitted by UEs or other eNBs. The RF transceivers  372   a - 372   n  down-convert the incoming RF signals to generate IF or baseband signals. The IF or baseband signals are sent to the RX processing circuitry  376 , which generates processed baseband signals by filtering, decoding, and/or digitizing the baseband or IF signals. The RX processing circuitry  376  transmits the processed baseband signals to the controller/processor  378  for further processing. 
         [0087]    The TX processing circuitry  374  receives analog or digital data (such as voice data, web data, e-mail, or interactive video game data) from the controller/processor  378 . The TX processing circuitry  374  encodes, multiplexes, and/or digitizes the outgoing baseband data to generate processed baseband or IF signals. The RF transceivers  372   a - 372   n  receive the outgoing processed baseband or IF signals from the TX processing circuitry  374  and up-converts the baseband or IF signals to RF signals that are transmitted via the antennas  370   a - 370   n.    
         [0088]    The controller/processor  378  can include one or more processors or other processing devices that control the overall operation of the eNB  102 . For example, the controller/processor  378  could control the reception of forward channel signals and the transmission of reverse channel signals by the RF transceivers  372   a - 372   n , the RX processing circuitry  376 , and the TX processing circuitry  374  in accordance with well-known principles. The controller/processor  378  could support additional functions as well, such as more advanced wireless communication functions. In some embodiments, the controller/processor  378  includes at least one microprocessor or microcontroller. 
         [0089]    The controller/processor  378  is also capable of executing programs and other processes resident in the memory  380 , such as an OS. The controller/processor  378  is also capable of supporting channel quality measurement and reporting for systems having 2D antenna arrays as described in embodiments of the present disclosure. In some embodiments, the controller/processor  378  supports communications between entities, such as web RTC. The controller/processor  378  can move data into or out of the memory  380  as required by an executing process. 
         [0090]    The controller/processor  378  is also coupled to the backhaul or network interface  382 . The backhaul or network interface  382  allows the eNB  102  to communicate with other devices or systems over a backhaul connection or over a network. The interface  382  could support communications over any suitable wired or wireless connection(s). For example, when the eNB  102  is implemented as part of a cellular communication system (such as one supporting 5G or new radio access technology or NR, LTE, or LTE-A), the interface  382  could allow the eNB  102  to communicate with other eNBs over a wired or wireless backhaul connection. When the eNB  102  is implemented as an access point, the interface  382  could allow the eNB  102  to communicate over a wired or wireless local area network or over a wired or wireless connection to a larger network (such as the Internet). The interface  382  includes any suitable structure supporting communications over a wired or wireless connection, such as an Ethernet or RF transceiver. 
         [0091]    The memory  380  is coupled to the controller/processor  378 . Part of the memory  380  could include a RAM, and another part of the memory  380  could include a Flash memory or other ROM. In certain embodiments, a plurality of instructions, such as a BIS algorithm is stored in memory. The plurality of instructions are configured to cause the controller/processor  378  to perform the BIS process and to decode a received signal after subtracting out at least one interfering signal determined by the BIS algorithm. 
         [0092]    As described in more detail below, the transmit and receive paths of the eNB  102  (implemented using the RF transceivers  372   a - 372   n , TX processing circuitry  374 , and/or RX processing circuitry  376 ) perform configuration and signaling for CSI reporting. 
         [0093]    Although  FIG. 3B  illustrates one example of an eNB  102 , various changes can be made to  FIG. 3B . For example, the eNB  102  could include any number of each component shown in  FIG. 3 . As a particular example, an access point could include a number of interfaces  382 , and the controller/processor  378  could support routing functions to route data between different network addresses. As another particular example, while shown as including a single instance of TX processing circuitry  374  and a single instance of RX processing circuitry  376 , the eNB  102  could include multiple instances of each (such as one per RF transceiver). 
         [0094]      FIG. 4  depicts an example of a 2D dual-polarized antenna port array with M a  rows and N a  columns where (M a , N a )=(2,4) and (4,2) which can be utilized in one or more embodiments of the present disclosure. These arrangement results in a total of 2M a N a =16 ports, each mapped to one CSI-RS port. The three indexings  400 ,  410 , and  420  are three examples in indexing the 16 antenna ports as a means of mapping antenna ports to precoding matrix elements. For row-first indexing  400 , antenna ports associated with the same polarization group are indexed in a row-first manner regardless of (M a , N a ). For longer-first indexing  410 , antenna ports associated with the same polarization group are indexed in a column-first manner when M a &gt;N a , but row-first manner when M a ≦N a . For shorter-first indexing  420 , antenna ports associated with the same polarization group are indexed in a row-first manner when M a &gt;N a , but column-first manner when M a ≦N a . Indexing  400  is therefore termed row-first indexing while indexing  410  longer-first indexing and indexing  420  shorter-first indexing. 
         [0095]    In these illustrative embodiments, both M a  and N a  can be configured by an eNB for a UE. In another example, rather than defining M a  and N a  as the number of rows and columns of the rectangular array of ports or port pattern, respectively, these two parameters can be defined as two-dimensional precoding codebook parameters. The values of M a  and N a  partly determine the manner in which a codebook (hence each precoding matrix element in the codebook) is mapped onto antenna ports of a one- or two-dimensional antenna array. This configuration can be performed with and without signaling the total number of antenna ports. When a UE is configured with a codebook, these parameters can be included either in a corresponding CSI process configuration or NZP (non-zero-power) CSI-RS resource configuration. 
         [0096]    In legacy LTE systems, precoding codebooks are utilized for CSI reporting. Two categories of CSI reporting modes are supported: PUSCH-based aperiodic CSI (A-CSI) and PUCCH-based periodic CSI (P-CSI). In each category, different modes are defined based on frequency selectivity of CQI and/or PMI, that is, whether wideband (one CSI parameter calculated for all the “set S subbands”) or subband (one CSI parameter calculated for each “set S subband”) reporting is performed. The supported CSI reporting modes are given in TABLE 1 and 2. 
         [0000]    
       
         
               
             
               
               
             
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 CQI and PMI Feedback Types for PUSCH (Aperiodic) 
               
               
                 CSI Reporting Modes 
               
             
          
           
               
                   
                 PMI Feedback Type 
               
             
          
           
               
                   
                   
                 Single 
                 Multiple 
               
               
                   
                 No PMI 
                 PMI 
                 PMI 
               
               
                   
                   
               
             
          
           
               
                 PUSCH CQI 
                 Wideband 
                   
                   
                 Mode 1-2 
               
               
                 Feedback 
                 (wideband CQI) 
               
               
                 Type 
                 UE Selected 
                 Mode 2-0 
                   
                 Mode 2-2 
               
               
                   
                 (subband CQI) 
               
               
                   
                 Higher Layer- 
                 Mode 3-0 
                 Mode 3-1 
                 Mode 3-2 
               
               
                   
                 configured 
               
               
                   
                 (subband CQI) 
               
               
                   
               
             
          
         
       
     
         [0000]    
       
         
               
             
               
               
               
             
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 CQI and PMI Feedback Types for PUCCH (Periodic) 
               
               
                 CSI Reporting Modes 
               
             
          
           
               
                   
                 PMI Feedback Type 
                   
               
             
          
           
               
                   
                 No PMI 
                 Single PMI 
               
               
                   
                   
               
             
          
           
               
                 PUCCH CQI 
                 Wideband 
                 Mode 1-0 
                 Mode 1-1 
               
               
                 Feedback Type 
                 (wideband CQI) 
               
               
                   
                 UE Selected 
                 Mode 2-0 
                 Mode 2-1 
               
               
                   
                 (subband CQI) 
               
               
                   
               
             
          
         
       
     
         [0097]    Designing a CSI reporting mechanism which attains high accuracy with a reasonably low feedback overhead is challenging as more antenna ports are utilized. Especially relevant is an ability to adapt to long-term channel statistics including DL AoD profile. Unlike short-term channel coefficients, under certain circumstances it is possible to measure long-term channel statistics at an eNB even for FDD. Provided that UL-DL duplex distance is not too large, UL-DL long-term reciprocity holds and allows an eNB to measure DL AoD profile from uplink signals. If, for some reason, such a measurement scheme is infeasible, a low-rate CSI reporting which contains an indication of DL AoD profile can be employed. Therefore, there is a need to design codebooks for CSI reporting and its associated CSI reporting procedures, which slowly adapts to long-term channel statistics while maintaining low feedback overhead. 
         [0098]    Furthermore, to support two-dimensional precoding, straightforward extensions such as configuring a CSI reporting mode for each of the two dimensions independently and applying the same CSI reporting mode along with its associated configurations for both dimensions are either inefficient (resulting in too many CSI reporting modes) or restrictive (neglecting potential differences between horizontal and vertical dimensions). Therefore, there is a need to extend the CSI reporting modes given in TABLE 1 and 2 in a manner which avoids the above two drawbacks. This entails refined definition of each of the CSI reporting modes as well as each of the CSI parameters. This also entails facilitating flexible support of PMI reporting granularity, that is, independent configurations for each of the two (for example, horizontal and vertical) dimensions. 
         [0099]    A precoding matrix or a precoder, which can be used by an eNB (such as  102 ) to perform short-term precoding for transmitting to a UE and assumed by a UE to derive a CSI report, can be described as a dual-stage precoding matrix: 
         [0000]        W=W   1   W   2   (Equation 1)
 
         [0000]    Referring to  FIG. 4 , the size of the precoding matrix W is N TX ×N L  where N TX =2M a N a  is the total number of antenna or CSI-RS ports and N L  is the number of transmission layers (also termed the rank). The first-stage precoder W 1  pertains to a long-term component and is associated with long-term channel statistics. In addition, W 1  is wideband (the same W 1  for all the set S subbands). The second-stage precoder W 2  pertains to a short-term component which performs selection, co-phasing, or any linear operation to W 1 . Therefore, the number of columns of W 1  can be perceived as the number of basis vectors N b  for W 2 . In addition, W 2  can be either wideband (the same W 2  for all the set S subbands) or subband (one W 2  for each set S subband). 
         [0100]    For 2D (two-dimensional) rectangular port array, each of the first and the second stage precoders can be described as a Kronecker product of a first and a second precoder. In the present disclosure, A{circle around (×)}B denotes the Kronecker product between two matrices A and B. This example embodiment is termed the full Kronecker Product (full KP) codebook. The subscripts m and n in W m,n (i m,n ) denote precoding stage (first or second) and dimension (first or second, such as vertical or horizontal), respectively. Each of the precoders W m,n  is a function of an index which serves as a PMI component. Thus, the precoding matrix W can be described in terms of 4 PMI components i 1,1 , i 1,2 , i 2,1 , i 2,2  as follows. 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       
                         
                           W 
                            
                           
                             ( 
                             
                               
                                 i 
                                 
                                   1 
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                               , 
                               
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                                   1 
                                 
                               
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                         = 
                           
                          
                         
                           
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                                   W 
                                   
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                   ( 
                   
                     Equation 
                      
                     
                         
                     
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                   ) 
                 
               
             
           
         
       
     
         [0000]    Given a precoding codebook (a set of precoding matrices W(i 1,1 , i 1,2 , i 2,1 , i 2,2 )), a UE measures a CSI-RS in a subframe designated to carry CSI-RS, calculates a CSI (including PMI, RI, and CQI where each of these three CSI parameters can include multiple components) based on the measurement, and reports the calculated CSI to a serving eNB  102 . This PMI represents an index of a recommended precoding matrix in the precoding codebook. Different precoding codebooks can be used for different values of RI. 
         [0101]    Another example embodiment assumes that a precoder in a designated codebook can be described in (3), termed the partial Kronecker Product (partial KP) codebook. The subscripts m and n in W m,n (i m,n ) denote precoding stage (first or second stage) and dimension (first or second dimension), respectively. Each of the precoding matrices W m,n  is a function of an index which serves as a PMI component. Thus, the precoding matrix W can be described as a function of 3 PMI components i 1,1 , i 1,2 , i 2  as follows. 
         [0000]        W ( i   1,1   ,i   1,2   ,i   2 )=( W   1,1 ( i   1,1 )           W   1,2 ( i   1,2 ))( W   2 ( i   2 ))  (Equation 3)
 
         [0000]    Similar to the previous codebook embodiment, a UE measures a CSI-RS in a subframe designated to carry CSI-RS, calculates a CSI (including PMI, RI, and CQI where each of these three CSI parameters can include multiple components) based on the measurement, and reports the calculated CSI to a serving eNB  102 . 
         [0102]    In either of the above two embodiments, the number of columns of W 1,1  and W 1,2  can be perceived as the number of basis vectors, or the number of spatial beams associated with a first and a second dimensions, N b,1  and N b,2  for the second-stage precoder(s). To adapt to changes in long-term channel statistics such as AoD profiles, these two parameters can be configurable for a UE. Changing the values of N b,1  and N b,2  amounts to reconfiguring the codebook for the UE. Configuring these parameters can also be done implicitly, such as by configuring a codebook selection parameter which corresponds to at least one of these two codebook parameters. 
         [0103]    In the present disclosure, depending on the configured CSI-RS port pattern or the value of precoding codebook or codebook subset parameters received by a UE, the UE determines the manner in which CSI calculation and reporting is performed. This includes, for example, whether a 1D (one-dimensional) or a 2D (two-dimensional) CSI calculation and reporting is to be performed. As previously mentioned, such CSI-RS port pattern or precoding codebook parameters can include M a  and/or N a . 
         [0104]    Although CSI-RS port pattern or codebook parameters are sufficient in determining the manner in which CSI calculation and reporting is performed, a new transmission mode (TM)—termed, for instance, TM x—which supports FD-MIMO and transmission with 2D antenna array can also be defined and used in conjunction with the CSI-RS port pattern or precoding parameters to determine the manner in which CSI calculation and reporting is performed. 
         [0105]    For instance, if a UE is not configured for TM x, 1D CSI calculation and reporting according to legacy LTE (such as Rel. 12) specification is performed. If a UE is configured for TM x, if it is inferred that M a =1 or N a =1 (either from a CSI-RS port pattern parameter or codebook or codebook subset parameters such as M a  or N a ), 1D CSI reporting is performed (which can include 1D codebooks for PMI reporting in addition to those already supported in legacy Rel. 12 LTE specification). Else, 2D CSI calculation and reporting is performed. When 1D CSI reporting is performed, the CSI reporting modes in TABLE 1 and 2 (hence the associated definition of CQI, PMI, and RI) are defined according to legacy Rel. 12 LTE specification (see e.g., REF3 section 7.2). On the other hand, when 2D CSI reporting is performed, several extensions of the CSI reporting modes in TABLE 1 and 2 are given below. 
         [0106]    If the Kronecker precoding structure defined in equation (2) is utilized (where W 2  can be described in terms of the Kronecker product of two precoders associated with two dimensions), then the following CSI reporting parameters are used. First, PMI/RI parameters i 2,V , i 1,V , v-RI for vertical dimension and i 2,H , i 1,H , h-RI for horizontal dimension. Alternatively, the four PMI values can be denoted as {i 1,1 , i 1,2 , i 2,1 , i 2,2 }. Here, i m,n  denotes PMI associated with the m-th stage precoding (m=1, 2) and n-th dimension (note that the first dimension is not necessarily vertical). Second, CQI parameter. A single CQI entity (including one or two CQI values depending on the number of codewords) which is calculated conditioned on vertical and horizontal (or the first-dimension and the second-dimension) PMI/RI parameters. 
         [0107]    If the Kronecker precoding structure defined in equation (3) is utilized (where W 2  is not described in terms of the Kronecker product of two precoders associated with two dimensions), then the following CSI reporting parameters are used. First, PMI/RI parameters i 1,V  for vertical dimension; i 1,H  for horizontal dimension; i 2  and RI associated with both dimensions. Alternatively, the three PMI values can be denoted as {i 1,1 , i 1,2 , i 2 } Here, i 1,n  denotes PMI associated with the first-stage precoding and n-th dimension (note that the first dimension is not necessarily vertical). Second, CQI parameter. A single CQI entity which is calculated conditioned upon vertical and horizontal (or the first-dimension and the second-dimension, respectively) PMI/RI parameters. 
         [0108]    In both cases, coupling between RI and PMI, at least for each dimension, takes place since a codebook is associated with a given transmission rank hypothesis. A UE calculates a single CQI entity for both dimensions, in contrast to two separate CQI entities, to avoid CSI mismatch at a serving eNB. Therefore, two separate CSI reporting mode configurations, each for one dimension, are unnecessary and in fact result in performance loss. 
         [0109]    Below are several exemplary embodiments, each corresponding to a distinct extension of the CSI reporting modes given in TABLE 1 and 2, where only one CSI reporting mode configuration is utilized for both horizontal and vertical (first and second) dimensions. In the following embodiments, only one CQI entity is calculated at a UE for both dimensions conditioned upon all the PMI/RI parameters. Each embodiment corresponds to a different PMI/RI construction for supporting 2D CSI-RS port pattern or 2D NZP CSI-RS resource or 2D codebook parameters. 
         [0110]    In a first CSI reporting embodiment, a joint 2D (two-dimensional) PMI/RI is calculated and reported for 2D CSI-RS port pattern or codebook configuration. In this embodiment, one RI value associated with both dimensions and two sets of PMI are defined. The first PMI set includes the first-stage or first PMI i 1  which represents {i 1,H , i 1,V } or {i 1,1 , i 1,2 } encoded jointly. The second PMI set includes the second-stage or second PMI i 2  which either represents {i 2,H , i 2,V } or {i 2,1 , i 2,2 } encoded jointly for precoding structure in equation (2), or simply a single index i 2  for precoding structure in equation (3). In this solution, a same reporting granularity (in time and frequency) is applied to all the PMI parameters for both dimensions. Therefore, the same description for the different CSI reporting modes in REF3 section 7.2 directly applies. 
         [0111]    The joint PMI parameters i 2  (if applicable) and i 1  can be defined with respect to one-dimensional PMIs. An example of such a definition for i 1  is given in TABLE 3 below. For illustrative purposes, the associated 1D codebook size is assumed to be 16. An analogous definition can be applied to i 2  if applicable (for instance, when precoder description in equation (2) is utilized). In the two exemplary tables of TABLE 3, a first dimension is associated with horizontal and a second dimension vertical (such as indexing  400  in  FIG. 4 ). Other associations are possible. For example, if indexing  410  in  FIG. 4  is assumed, the first dimension is associated with the shorter of the two dimensions. Else if indexing  420  in  FIG. 4  is assumed, the first dimension is associated with the longer of the two dimensions. Else, any of these two dimensions is not associated with any particular dimension. In any of these examples, the tables below can be applied with the corresponding dimension association. 
         [0000]    
       
         
               
             
               
               
               
             
               
             
               
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
               
                 Two exemplary definitions of joint 2D 
               
               
                   
               
             
             
               
                 (a) 
               
             
          
           
               
                 i 1  for 2D CSI-RS port 
                 i 1  for the first dimension 
                 i 1  for the second 
               
               
                 pattern or 2D codebook 
                 (i 1,1 ) 
                 dimension (i 1,2 ) 
               
               
                   
               
               
                 0 
                 0 
                 0 
               
               
                 1 
                   
                 1 
               
               
                 . . . 
                   
                 . . . 
               
               
                 15 
                   
                 15  
               
               
                 16 
                 1 
                 0 
               
               
                 17 
                   
                 1 
               
               
                 . . . 
                   
                 . . . 
               
               
                 31 
                   
                 15  
               
               
                 . . . 
                 . . . 
                 . . . 
               
               
                 240 
                 15  
                 0 
               
               
                 241 
                   
                 1 
               
               
                 . . . 
                   
                 . . . 
               
               
                 255 
                   
                 15  
               
               
                   
               
             
          
           
               
                 (b) 
               
             
          
           
               
                 i 1  for 2D CSI-RS port 
                 i 1  for the second 
                 i 1  for the first 
               
               
                 pattern or 2D codebook 
                 dimension (i 1,2 ) 
                 dimension (i 1,1 ) 
               
               
                   
               
               
                 0 
                 0 
                 0 
               
               
                 1 
                   
                 1 
               
               
                 . . . 
                   
                 . . . 
               
               
                 15 
                   
                 15  
               
               
                 16 
                 1 
                 0 
               
               
                 17 
                   
                 1 
               
               
                 . . . 
                   
                 . . . 
               
               
                 31 
                   
                 15  
               
               
                 . . . 
                 . . . 
                 . . . 
               
               
                 240 
                 15  
                 0 
               
               
                 241 
                   
                 1 
               
               
                 . . . 
                   
                 . . . 
               
               
                 255 
                   
                 15  
               
               
                   
               
             
          
         
       
     
         [0112]    In the example described in TABLE 3(a), the first PMI i 1  is constructed from concatenating the first PMI field i 1,1  and the second PMI field i 1,2 . Since the first PMI is signaled as a binary-valued codeword formed by a sequence of bits, the first PMI codeword i 1  is constructed from [i 1,1  i 1,2 ]. Written in terms of a bit sequence, this codeword can be described as b 1,0 , b 1,1 , . . . , b 1,L     1     −1 , b 2,0 , b 2,1 , . . . , b 2,L     2     −1  where b 1,0 , b 1,1 , . . . , B 1,L     1     −1  is the bit sequence associated with or binary representation of i 1,1  (wherein b 1,0  is the most significant bit and b 1,L     1     −1  the least significant bit of this bit sequence) and b 2,0 , b 2,1 , . . . , b 2,L     2     −1  is the bit sequence associated with or binary representation of i 1,2  (wherein b 2,0  is the most significant bit and b 2,L     2     −1  the least significant bit of this bit sequence). Likewise, in the example described in TABLE 3(b), the first PMI i 1  is constructed from concatenating the second PMI field i 1,2  and the first PMI field i 1,1 . Since the first PMI is signaled as a binary-valued codeword formed by a sequence of bits, the first PMI codeword i 1  is constructed from [i 1,2  i 1,1 ]. Written in terms of a bit sequence, this codeword can be described as b 2,0 , b 2,1 , . . . , b 2,L     2     −1 , b 1,0 , b 1,1 , . . . , b 1,L     1     −1  where b 1,0 , b 1,1 , . . . , b 1,L     1     −1  is the bit sequence associated with or binary representation of i 1,1  (wherein b 1,0  is the most significant bit and b 1,L     1     −1  the least significant bit of this bit sequence) and b 2,0 , b 2,1 , . . . , b 2,L     2     −1  is the bit sequence associated with or binary representation of i 1,2  (wherein b 2,0  is the most significant bit and b 2,L     2     −1  the least significant bit of this bit sequence). 
         [0113]    This joint definition and encoding method for reporting the first PMI i 1  can be utilized for or in conjunction with any CSI calculation/reporting method pertaining to 2D CSI-RS port pattern or 2D precoding codebook where the first PMI i 1  includes two codebook indices associated with two dimensions. Therefore, it is also applicable to other CSI calculation/reporting embodiments in the present disclosure. 
         [0114]    For PUSCH-based aperiodic CSI reporting, the frequency granularity of PMI reporting inherent in a given CSI reporting mode (either wideband PMI, UE-selected sub-band PMI, or eNB-configured sub-band PMI) applies to each of the 2D PMI parameter(s). Since A-CSI is reported by a UE upon a request from a serving eNB, time granularity is not an issue. For PUCCH-based periodic CSI reporting mode 1-1, only wideband PMI is reported. Therefore, frequency granularity is not an issue. Time granularity follows the relation between i 1  and i 2  for a given P-CSI reporting mode. For example, P-CSI mode 1-1 submode 1 allows i 1  and i 2  to be configured with different periodicities. For P-CSI mode 1-1 submode 2, the same periodicity applies to i 1  and i 2  since they are reported together. 
         [0115]      FIG. 5  illustrates an example CSI calculation procedure  500  which responds to a CSI-RS resource pattern or codebook parameter and calculates a two-dimensional PMI/RI for two-dimensional pattern. In this example, transmission mode configuration is used in conjunction with CSI-RS port pattern or codebook parameters M a  and N a . However, this example method can operate without transmission mode configuration. Upon receiving a transmission mode configuration  501  and a CSI-RS resource pattern configuration  505 , a UE determines whether the pattern is 1D or 2D ( 515 ) if the UE is configured for a certain corresponding transmission mode. The criterion in embodiment  515  utilizes a CSI-RS port pattern or codebook parameters or codebook subset parameters such as M a  or N a . If it is associated with 1D configuration, a 1D PMI/RI definition such as the one given in section 7.2 of REF3 is used ( 530 ). Else, a 2D joint PMI/RI definition is used ( 520 ). In case of 2D configuration, this 2D joint PMI/RI corresponds to the horizontal (H) and vertical (V) dimensions—or a first and a second dimension—of the CSI-RS port pattern or codebook configuration. Having determined the dimensionality of PMI/RI, the UE calculates CSI in  525  given a CSI reporting mode configuration from a serving eNB ( 510 ). 
         [0116]    While this CSI reporting mode extension is simple, it is restrictive since it imposes the same time and frequency granularity for PMI reporting in both dimensions. In some notable cases, horizontal and vertical array dimensions can experience different channel characteristics. The next embodiment partially addresses this issue. 
         [0117]    In a second CSI reporting embodiment, the time and/or frequency granularity of PMI reporting for one of the dimensions is configurable for a UE. Since a single CQI entity is computed for dimensions, the CSI reporting modes given in TABLE 1 and 2 can be extended for 2D CSI-RS port pattern or codebook configuration via configuring time and/or frequency granularity of PMI reporting associated with one of the two dimensions. The choice of the two dimensions (whether the first or the second dimension) whose time and/or frequency granularity of PMI reporting is configurable can be configured via higher-layer or RRC signaling. Alternatively, this choice can be fixed. For example, it can be fixed to the second dimension. 
         [0118]    This second embodiment allows some additional flexibility over the time and/or frequency granularity of PMI reporting associated with each of the CSI reporting modes. The granularity inherent in the configured CSI reporting mode is applied to the other dimension—in this example, the first dimension. Configurable frequency granularity (wideband PMI or sub-band PMI) is applicable only for PUSCH-based aperiodic CSI reporting (A-CSI) given in TABLE 1. Configurable time granularity (reporting periodicity) is applicable only for PUCCH-based periodic CSI reporting (P-CSI) given in TABLE 2. This configuration can be performed by a serving eNB and signaled to the UE via higher-layer (RRC) signaling. As an example, this configuration parameter can be termed PMI_TF_Granularity_2ndD_freq and PMI_TF_Granularity_2ndD_time. 
         [0119]      FIG. 6  illustrates an example CSI calculation procedure  600  which responds to a CSI-RS resource pattern or codebook parameters and a PMI/RI configuration for a second dimension. In this example, transmission mode configuration is used in conjunction with CSI-RS port pattern or codebook parameters M a  and N a . However, this example method can operate without transmission mode configuration. Upon receiving a transmission mode configuration  601  and a CSI-RS port pattern or codebook parameter configuration  605 , the UE determines whether the pattern is 1D or 2D ( 615 ) if the UE is configured for a certain corresponding transmission mode. The criterion in the determination in  615  utilizes a CSI-RS port pattern or codebook parameters or codebook subset parameters such as M a  or N a . If it is associated with 1D configuration, a 1D PMI/RI definition such as the one given in section 7.2 of REF3 is used ( 620 ). Else, a 2D joint PMI/RI definition is used ( 625 ). In case of 2D CSI-RS port pattern, the UE receives and decodes the PMI granularity for a second dimension in  625  from a configuration parameter  607  (for instance, PMI_TF_Granularity_2ndD_freq and PMI_TF_Granularity_2ndD_time from higher-layer signaling). Having determined the dimensionality of PMI/RI, the UE calculates CSI in  630  given a CSI reporting mode configuration  610  from a serving eNB. The PMI granularity for a first dimension is inferred from the CSI reporting mode configuration  610 . 
         [0120]    An exemplary assignment for the first and second dimension is horizontal (H) and vertical (V), respectively. If indexing  410  is used, the first dimension is associated with the shorter of the two dimensions. Else, if indexing  420  is used, the first dimension is associated with the longer of the two dimensions. Else, any of these two dimensions is not associated with any particular dimension. 
         [0121]    For dual-stage precoding structure in equation (2), the first-stage precoding matrix W 1  is a wideband precoder. Therefore, frequency granularity given in the RRC parameter PMI_TF_Granularity_2ndD_freq associated with a second dimension only applies to W 2  when a UE reports PUSCH-based aperiodic CSI. Then it is applicable when W 2  can be described as a Kronecker product between horizontal and vertical (or a first dimension and a second dimension) precoding matrices (such as the description in equation (2)). At least two alternatives can be used for PMI_TF_Granularity_2ndD_freq. A first alternative is a one-bit indicator for the second dimension which selects between wideband PMI (calculated assuming transmission on the set S subbands) and subband PMI (calculated assuming transmission on the given subband). A second alternative is a one-bit indicator for the second dimension which selects between the default PMI granularity given by the choice of A-CSI reporting mode and its alternative PMI granularity. For example, for A-CSI mode 3-2, if PMI_TF_Granularity_2ndD_freq is set to default (e.g. 0), the PMI associated with the second dimension is subband. Otherwise, if PMI_TF_Granularity_2ndD_freq is set to alternative (e.g. 1), the PMI associated with the second dimension is wideband. 
         [0122]    In terms of time granularity, PMI_TF_Granularity_2ndD_time configures the time granularity of PUCCH-based periodic CSI reporting. For dual-stage precoding structure in equation (2), this applies to W 1  associated with a second dimension W 1,2 . It also applies to for the second dimension of W 2  if W 2  can be described as a Kronecker product between horizontal and vertical precoding matrices (or a first dimension and a second dimension). For 2D CSI-RS port pattern, this applies, for example, when the horizontal and vertical components of W 2  can be separated as exemplified in the precoder structure in equation (2). 
         [0123]    Some exemplary specifications for this embodiment are given below. Here (M a , N a ) represent 2D CSI-RS port pattern or codebook parameters for a given NZP CSI-RS resource where M a  and N a  are associated with a first and a second dimension, respectively. Two RRC parameters PMI_TF_Granularity_2ndD_time and PMI_TF_Granularity_2ndD_freq configure the time and frequency granularity as described above. The second dimension is assumed to be vertical. These definitions are exemplary and illustrative. For example, the criterion in embodiment for determining between 1D and 2D utilizes a CSI-RS port pattern or codebook parameters or codebook subset parameters such as M a  or N a . In addition, if indexing  410  is used, the first dimension is associated with the shorter of the two dimensions. Else, if indexing  420  is used, the first dimension is associated with the longer of the two dimensions. In that case, {i 1,V , i 1,H , i 2,V , i 2,H } can be replaced by {i 1,1 , i 1,2 , i 2,1 , i 2,2 } or {i 1,2 , i 1,1 , i 2,2 , i 2,1 }. Furthermore, if precoding description in equation (3) is used instead of (2), {i 2,V , i 2,H } is substituted with a single index i 2 . Furthermore, {i 1,V , i 1,H , i 2 } is replaced by {i 1,1  i 1,2 , i 2 } or {i 1,2 , i 1,1 , i 2 }. Moreover, ‘horizontal codebook’ can be renamed ‘a first codebook’ and ‘vertical codebook can be renamed ‘a second codebook.’ These definitions describe only the components applicable to the use of 2D CSI-RS port pattern or codebook. 
         [0124]    For example, for PUSCH-based aperiodic CSI reporting (see e.g., TABLE 1), mode 1-2 can be described as follows:
       For each subband a preferred first-dimension (for instance, horizontal) precoding matrix is selected from the first-dimension codebook subset assuming transmission only in the subband
           If M a &gt;1 and N a &gt;1 and PMI_TF_Granularity_2ndD_freq=WIDEBAND, a single preferred second-dimension (for instance, vertical) precoding matrix is selected from the second-dimension codebook subset assuming transmission on set S subbands.   If M a &gt;1 and N a &gt;1 and PMI_TF_Granularity_2ndD_freq=SUBBAND, a preferred second-dimension precoding matrix is selected from the second-dimension codebook subset assuming transmission only in the subband.   
           A UE reports one wideband CQI value per codeword which is calculated assuming the use of the corresponding selected first-dimension and second-dimension precoding matrices.   A UE reports the following precoding matrix indicators:
           If M a =1 or N a =1, a first precoding matrix indicator for all set S subbands and a second precoding matrix indicator for each set S subband.   If M a &gt;1 and N a &gt;1 and PMI_TF_Granularity_2ndD_freq=WIDEBAND, a first first-dimension and second-dimension precoding matrix indicator i 1,H  and i 1,V  for the set S subbands, a second first-dimension precoding matrix indicator i 2,H  for each set S subband, and a second second-dimension precoding matrix indicator i 2,V  for the set S subbands   If M a &gt;1 and N a &gt;1 and PMI_TF_Granularity_2ndD_freq=SUBBAND, a first first-dimension and second-dimension precoding matrix indicator i 1,H  and i 1,V  for the set S subbands, a second first-dimension precoding matrix indicator i 2,H  for each set S subband, and a second second-dimension precoding matrix indicator i 2,V  for each set S subband
               If precoding structure in equation (3) is used instead of (2), i 2,H  and i 2,V  for each set S subband are replaced by i 2  for each set S subband   
               
           Subband size is given by Table 7.2.1-3 in REF3.   For transmission modes 4, 8, 9, 10, and x the reported PMI and CQI values are calculated conditioned on the reported RI. For other transmission modes they are reported conditioned on rank 1.
 
Mode 3-1 can be described as follows:
   A single first-dimension (for instance, horizontal) precoding matrix is selected from the first-dimension codebook subset assuming transmission on set S subbands
           If M a &gt;1 and N a &gt;1 and PMI_TF_Granularity_2ndD_freq=WIDEBAND, a single preferred second-dimension (for instance, vertical) precoding matrix is selected from the second-dimension codebook subset assuming transmission on set S subbands.   If M a &gt;1 and N a &gt;1 and PMI_TF_Granularity_2ndD_freq=SUBBAND, a preferred second-dimension precoding matrix is selected from the second-dimension codebook subset assuming transmission only in the subband.   
           A UE reports one subband CQI value per codeword for each set S subband which are calculated assuming the use of the corresponding selected first-dimension and second-dimension precoding matrices and assuming transmission in the corresponding subband.   A UE reports a wideband CQI value per codeword which is calculated assuming the use of the corresponding selected first-dimension and second-dimension precoding matrices   A UE reports the following precoding matrix indicators:
           If M a =1 or N a =1, a first and second precoding matrix indicator corresponding to the selected single precoding matrix.   If M a &gt;1 and N a &gt;1 and PMI_TF_Granularity_2ndD_freq=WIDEBAND, a first first-dimension and second-dimension precoding matrix indicator i 1,H  and i 1,V  for the set S subbands, a second first-dimension and second-dimension precoding matrix indicator i 2,H  and i 2,V  for the set S subbands
               If precoding structure in equation (3) is used instead of (2), i 2,H  and i 2,V  for the set S subbands are replaced by i 2  for the set S subbands   
               If M a &gt;1 and N a &gt;1 and PMI_TF_Granularity_2ndD_freq=SUBBAND, a first first-dimension and second-dimension precoding matrix indicator i 1,H  and i 1,V  for the set S subbands, a second first-dimension precoding matrix indicator i 2,H  for the set S subbands, and a second second-dimension precoding matrix indicator i 2,V  for each set S subband   
           For transmission modes 4, 8, 9, 10, and x the reported PMI and CQI values are calculated conditioned on the reported RI. For other transmission modes they are reported conditioned on rank 1.
 
Mode 3-2 can be described as follows:
   For each subband a preferred first-dimension (for instance, horizontal) precoding matrix is selected from the first-dimension codebook subset assuming transmission only in the subband
           If M a &gt;1 and N a &gt;1 and PMI_TF_Granularity_2ndD_freq=WIDEBAND, a single preferred second-dimension (for instance, vertical) precoding matrix is selected from the second-dimension codebook subset assuming transmission on set S subbands.   If M a &gt;1 and N a &gt;1 and PMI_TF_Granularity_2ndD_freq=SUBBAND, a preferred second-dimension precoding matrix is selected from the second-dimension codebook subset assuming transmission only in the subband.   
           A UE reports a wideband CQI value per codeword which is calculated assuming the use of the corresponding selected first-dimension and second-dimension precoding matrices.   A UE reports the following precoding matrix indicators:
           If M a =1 or N a =1, a first precoding matrix indicator for all set S subbands and a second precoding matrix indicator for each set S subband.   If M a &gt;1 and N a &gt;1 and PMI_TF_Granularity_2ndD_freq=WIDEBAND, a first first-dimension and second-dimension precoding matrix indicator i 1,H  and i 1,V  for the set S subbands, a second first-dimension precoding matrix indicator i 2,H  for each set S subband, and a second second-dimension precoding matrix indicator i 2,V  for the set S subbands   If M a &gt;1 and N a &gt;1 and PMI_TF_Granularity_2ndD_freq=SUBBAND, a first first-dimension and second-dimension precoding matrix indicator i 1,H  and i 1,V  for the set S subbands, a second first-dimension precoding matrix indicator i 2,H  for each set S subband, and a second second-dimension precoding matrix indicator i 2,V  for each set S subband
               If precoding structure in equation (3) is used instead of (2), i 2,H  and i 2,V  for each set S subband are replaced by i 2  for each set S subband   
               
           A UE reports one subband CQI value per codeword for each set S subband which are calculated assuming the use of the corresponding selected first-dimension and second-dimension precoding matrices and assuming transmission in the corresponding subband.   For transmission modes 4, 8, 9, 10, and x the reported PMI and CQI values are calculated conditioned on the reported RI. For other transmission modes they are reported conditioned on rank 1.
 
Description for mode 2-2 is analogous to the above description for modes 2-1, 3-1, and 3-2 and one of ordinary skill in the art would be able to derive the full description for mode 2-2 based on the above description for modes 2-1, 3-1, and 3-2.
       
 
         [0158]    An alternative embodiment for PUSCH-based aperiodic CSI mode 3-1 can be made by constraining the vertical PMI (or a second dimension PMI) to be wideband. This is applicable when, for instance, vertical channel variability is less than that of horizontal. In this case, PMI_TF_Granularity_2ndD_freq is not used. Therefore, mode 3-1 can be described as follows:
       A single first-dimension (for instance, horizontal) precoding matrix is selected from the first-dimension codebook subset assuming transmission on set S subbands
           If M a &gt;1 and N a &gt;1, a single preferred second-dimension (for instance, vertical) precoding matrix is selected from the second-dimension codebook subset assuming transmission on set S subbands.   
           A UE reports one subband CQI value per codeword for each set S subband which are calculated assuming the use of the corresponding selected first-dimension and second-dimension precoding matrices and assuming transmission in the corresponding subband.   A UE reports a wideband CQI value per codeword which is calculated assuming the use of the corresponding selected first-dimension and second-dimension precoding matrices   A UE reports the following precoding matrix indicators:
           If M a =1 or N a =1, a first and second precoding matrix indicator corresponding to the selected single precoding matrix.   If M a &gt;1 and N a &gt;1, a first first-dimension and second-dimension precoding matrix indicator i 1,H  and i 1,V  for the set S subbands, a second first-dimension and second-dimension precoding matrix indicator i 2,H  and i 2,V  for the set S subbands
               If precoding structure in equation (3) is used instead of (2), i 2,H  and i 2,V  for the set S subbands are replaced by i 2  for the set S subbands   
               
           For transmission modes 4, 8, 9, 10, and x the reported PMI and CQI values are calculated conditioned on the reported RI. For other transmission modes they are reported conditioned on rank 1.       
 
         [0168]    In a third CSI reporting embodiment, dual-stage precoding is applied only on one of the two dimensions. While such one dimension can be either horizontal or vertical, in some deployment scenarios, the horizontal dimension tends to exhibit more time variation. Therefore, single-stage precoding is applied on the vertical (in this example, second) dimension. 
         [0169]    In this case, a feature to configure a UE not to report at least one particular PMI parameter can be introduced. For example, a single-stage precoding can be performed on vertical dimension by turning off the second stage precoder W 2,V  and setting v-RI (rank indicator associated with the vertical dimension) to 1. Thus, one-stage wideband vertical precoding is used. This precoder structure (assumed for CSI reporting) can be described as follows (assuming indexing  410  in  FIG. 4 ). Here, horizontal is assumed to be the first dimension and vertical the second dimension. 
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         [0000]    In this embodiment, the RRC configuration mechanism of PMI_TF_Granularity_2ndD_freq is not applicable. 
         [0170]    In terms of time granularity, PMI_TF_Granularity_2ndD_time is still applicable and configures the time granularity of PUCCH-based periodic CSI reporting. For dual-stage precoding matrix in (2), this applies to W 1  associated with a second dimension. 
         [0171]      FIG. 7  illustrates an example CSI calculation procedure  700  which responds to a CSI-RS resource pattern or codebook parameter and assumes a wideband PMI with RI=1 for a second dimension. In this example, transmission mode configuration is used in conjunction with CSI-RS port pattern or codebook parameters M a  and N a . However, this example method can operate without transmission mode configuration. Upon receiving a transmission mode configuration  701  and a CSI-RS port pattern configuration or codebook parameters  705 , the UE determines whether the pattern is associated with 1D or 2D ( 715 ) if the UE is configured for a certain corresponding transmission mode. The criterion in the determination in  715  utilizes a CSI-RS port pattern parameter or codebook parameters or codebook subset parameters such as M a  or N a . If it is associated with 1D pattern, a 1D PMI/RI definition such as the one given in section 7.2 of REF3 is used ( 720 ). Else, a 2D joint PMI/RI definition is used where a single-stage wideband precoding is applied for a second dimension as described above ( 725 ). Since the first-stage PMIs granularity is always wideband and the second-stage PMI for the second dimension is non-existent, the PMI granularity for the second dimension in  725  is always wideband. That is, when single-stage wideband precoding is the only option for the second dimension (in this example, vertical) precoding, PMI_TF_Granularity_2ndD_freq is not needed. Only PMI_TF_Granularity_2ndD_time applies to P-CSI reporting ( 707 ). Having determined the dimensionality of PMI/RI, the UE calculates CSI in  730  given a CSI reporting mode configuration  710  from a serving eNB. The PMI granularity for a first dimension is inferred from the CSI reporting mode configuration  710 . An exemplary assignment for the first and second dimension is horizontal (H) and vertical (V), respectively. 
         [0172]    Some exemplary specifications for this embodiment are given below. Here (M a , N a ) represent 2D CSI-RS port pattern or codebook parameters for a given NZP CSI-RS resource where M a  and N a  are associated with a first and a second dimension, respectively. One RRC parameters PMI_TF_Granularity_2ndD_time configures the time granularity as described above. The second dimension is assumed to be vertical. These definitions are exemplary and illustrative. For example, the criterion in embodiment for determining between 1D and 2D utilizes a CSI-RS port pattern or codebook parameters or codebook subset parameters such as M a  or N a . In addition, if indexing  410  is used, the first dimension is associated with the shorter of the two dimensions. Else, if indexing  420  is used, the first dimension is associated with the longer of the two dimensions. In that case, {i 1,V , i 1,H , i 2,H } can be replaced by {i 1,1 , i 1,2 , i 2,1 } or {i 1,2 , i 1,1 , i 2,2 }. Furthermore, if precoding description in equation (3) is used instead of (2), {i 2,H , i 2,V } is substituted with a single index i 2 . Furthermore, {i 1,V , i 1,H , i 2 } is replaced by {i 1,1 , i 1,2 , i 2 } or {i 1,2 , i 1,1 , i 2 }. Moreover, ‘horizontal codebook’ can be renamed ‘a first codebook’ and ‘vertical codebook can be renamed ‘a second codebook.’ These definitions describe only the components applicable to the use of 2D CSI-RS port pattern or codebook. 
         [0173]    For example, for PUSCH-based aperiodic CSI reporting (see e.g., TABLE 1), mode 1-2 can be described as follows:
       For each subband a preferred first-dimension (for instance, horizontal) precoding matrix is selected from the first-dimension codebook subset assuming transmission only in the subband
           If M a &gt;1 and N a &gt;1, a preferred second-dimension precoding matrix is selected from the second-dimension codebook subset assuming transmission only in the subband.   
           A UE reports one wideband CQI value per codeword which is calculated assuming the use of the corresponding selected first-dimension and second-dimension precoding matrices.   A UE reports the following precoding matrix indicators:
           If M a =1 or N a =1, a first precoding matrix indicator for all set S subbands and a second precoding matrix indicator for each set S subband.   If M a &gt;1 and N a &gt;1, a first first-dimension and second-dimension precoding matrix indicator i 1,H  and i 1,V  for the set S subbands, a second first-dimension precoding matrix indicator i 2,H  (or i 2 ) for each set S subband   
           Subband size is given by Table 7.2.1-3 of REF3.   For transmission modes 4, 8, 9, 10, and x the reported PMI and CQI values are calculated conditioned on the reported RI. For other transmission modes they are reported conditioned on rank 1.
 
Mode 3-1 can be described as follows:
   A single first-dimension (for instance, horizontal) precoding matrix is selected from the first-dimension codebook subset assuming transmission on set S subbands
           If M a &gt;1 and N a &gt;1, a single preferred second-dimension (for instance, vertical) precoding matrix is selected from the rank-one second-dimension codebook subset assuming transmission on set S subbands.   
           A UE reports one subband CQI value per codeword for each set S subband which are calculated assuming the use of the corresponding selected first-dimension and second-dimension precoding matrices and assuming transmission in the corresponding subband.   A UE reports a wideband CQI value per codeword which is calculated assuming the use of the corresponding selected first-dimension and second-dimension precoding matrices   A UE reports the following precoding matrix indicators:
           If M a =1 or N a =1, a first and second precoding matrix indicator corresponding to the selected single precoding matrix.   If M a &gt;1 and N a &gt;1, a first first-dimension and second-dimension precoding matrix indicator i 1,H  and i 1,V  for the set S subbands, a second first-dimension i 2,H  (or i 2 ) for the set S subbands   
           For transmission modes 4, 8, 9, 10, and x the reported PMI and CQI values are calculated conditioned on the reported RI. For other transmission modes they are reported conditioned on rank 1.
 
Mode 3-2 can be described as follows:
   For each subband a preferred first-dimension (for instance, horizontal) precoding matrix is selected from the first-dimension codebook subset assuming transmission only in the subband
           If M a &gt;1 and N a &gt;1, a preferred second-dimension precoding matrix is selected from the second-dimension codebook subset assuming transmission only in the subband.   
           A UE reports a wideband CQI value per codeword which is calculated assuming the use of the corresponding selected first-dimension and second-dimension precoding matrices.   A UE reports the following precoding matrix indicators:
           If M a =1 or N a =1, a first precoding matrix indicator for all set S subbands and a second precoding matrix indicator for each set S subband.   If M a &gt;1 and N a &gt;1, a first first-dimension and second-dimension precoding matrix indicator i 1,H  and i 1,V  for the set S subbands, a second first-dimension precoding matrix indicator i 2,H  (or i 2 ) for each set S subband   
           A UE reports one subband CQI value per codeword for each set S subband which are calculated assuming the use of the corresponding selected first-dimension and second-dimension precoding matrices and assuming transmission in the corresponding subband.   For transmission modes 4, 8, 9, 10, and x the reported PMI and CQI values are calculated conditioned on the reported RI. For other transmission modes they are reported conditioned on rank 1.
 
Description for mode 2-2 is analogous to the above description for modes 2-1, 3-1, and 3-2 and one of ordinary skill in the art would be able to derive the full description for mode 2-2 based on the above description for modes 2-1, 3-1, and 3-2.
       
 
         [0198]    In a fourth CSI reporting embodiment, the CSI reporting modes in TABLE 1 and 2 are extended for supporting beamformed (BF) CSI-RS or ‘CLASS B’ or ‘beamformed’ eMIMO-Type with one NZP CSI-RS resource. Therefore, when a UE receives BF CSI-RS from a serving eNB or is configured with ‘CLASS B’ (‘beamformed’) eMIMO-Type, the UE can be configured to report PMI parameters associated with W 2  without W 1 . In this case, CSI reporting is done similarly to single-stage precoding. For example, as the UE receives and decodes an RRC parameter which configures the UE for either beamformed CSI-RS reception (or ‘CLASS B’ (‘beamformed’) eMIMO-Type) or turning OFF any PMI reporting associated with W 1 , the UE performs CSI reporting associated with single-stage precoding. In this case, RI/PMI definition, but only that which is associated with W 2 , from either embodiment 1, 2, or 3 is applicable. 
         [0199]    Exemplary descriptions which correspond to this embodiment are given below. The second dimension is assumed to be vertical. These definitions are exemplary and illustrative. It is assumed that the number of beamformed CSI-RS ports is already acquired by the UE. This number of ports determines the horizontal and/or vertical codebooks associated with W 2  (hence i 2,H  and i 2,V ). Moreover, ‘horizontal codebook’ can be renamed ‘a first codebook’ and ‘vertical codebook can be renamed ‘a second codebook.’ For PUSCH-based aperiodic CSI reporting (see e.g., TABLE 1), mode 1-2 can be described as follows:
       For each subband a preferred first-dimension (for instance, horizontal) precoding matrix is selected from the first-dimension codebook subset assuming transmission only in the subband
           If M a &gt;1 and N a &gt;1 and PMI_TF_Granularity_2ndD_freq=WIDEBAND, a single preferred second-dimension (for instance, vertical) precoding matrix is selected from the second-dimension codebook subset assuming transmission on set S subbands.   If M a &gt;1 and N a &gt;1 and PMI_TF_Granularity_2ndD_freq=SUBBAND, a preferred second-dimension precoding matrix is selected from the second-dimension codebook subset assuming transmission only in the subband.   
           A UE reports one wideband CQI value per codeword which is calculated assuming the use of the corresponding selected first-dimension and second-dimension precoding matrices.   A UE reports the following precoding matrix indicators:
           If M a =1 or N a =1, a second precoding matrix indicator for each set S subband.   If M a &gt;1 and N a &gt;1 and PMI_TF_Granularity_2ndD_freq=WIDEBAND, a second first-dimension precoding matrix indicator i 2,H  for each set S subband, and a second second-dimension precoding matrix indicator i 2,V  for the set S subbands   If M a &gt;1 and N a &gt;1 and PMI_TF_Granularity_2ndD_freq=SUBBAND, a second first-dimension precoding matrix indicator i 2,H  for each set S subband, and a second second-dimension precoding matrix indicator i 2,V  for each set S subband   
           Subband size is given by Table 7.2.1-3 of REF3.   For transmission modes 4, 8, 9, 10, and x the reported PMI and CQI values are calculated conditioned on the reported RI. For other transmission modes they are reported conditioned on rank 1.
 
Mode 3-1 can be described as follows:
   A single first-dimension (for instance, horizontal) precoding matrix is selected from the first-dimension codebook subset assuming transmission on set S subbands
           If M a &gt;1 and N a &gt;1 and PMI_TF_Granularity_2ndD_freq=WIDEBAND, a single preferred second-dimension (for instance, vertical) precoding matrix is selected from the second-dimension codebook subset assuming transmission on set S subbands.   If M a &gt;1 and N a &gt;1 and PMI_TF_Granularity_2ndD_freq=SUBBAND, a preferred second-dimension precoding matrix is selected from the second-dimension codebook subset assuming transmission only in the subband.   
           A UE reports one subband CQI value per codeword for each set S subband which are calculated assuming the use of the corresponding selected first-dimension and second-dimension precoding matrices and assuming transmission in the corresponding subband.   A UE reports a wideband CQI value per codeword which is calculated assuming the use of the corresponding selected first-dimension and second-dimension precoding matrices   A UE reports the following precoding matrix indicators:
           If M a =1 or N a =1, a second precoding matrix indicator corresponding to the selected single precoding matrix.   If M a &gt;1 and N a &gt;1 and PMI_TF_Granularity_2ndD_freq=WIDEBAND, a second first-dimension and second-dimension precoding matrix indicator i 2,H  and i 2,V  for the set S subbands   If M a &gt;1 and N a &gt;1 and PMI_TF_Granularity_2ndD_freq=SUBBAND, a second first-dimension precoding matrix indicator i 2,H  for the set S subbands, and a second second-dimension precoding matrix indicator i 2,V  for each set S subband   
           For transmission modes 4, 8, 9, 10, and x the reported PMI and CQI values are calculated conditioned on the reported RI. For other transmission modes they are reported conditioned on rank 1.
 
Mode 3-2 can be described as follows:
   For each subband a preferred first-dimension (for instance, horizontal) precoding matrix is selected from the first-dimension codebook subset assuming transmission only in the subband
           If M a &gt;1 and N a &gt;1 and PMI_TF_Granularity_2ndD_freq=WIDEBAND, a single preferred second-dimension (for instance, vertical) precoding matrix is selected from the second-dimension codebook subset assuming transmission on set S subbands.   If M a &gt;1 and N a &gt;1 and PMI_TF_Granularity_2ndD_freq=SUBBAND, a preferred second-dimension precoding matrix is selected from the second-dimension codebook subset assuming transmission only in the subband.   
           A UE reports a wideband CQI value per codeword which is calculated assuming the use of the corresponding selected first-dimension and second-dimension precoding matrices.   A UE reports the following precoding matrix indicators:
           If M a =1 or N a =1, a first precoding matrix indicator for all set S subbands and a second precoding matrix indicator for each set S subband.   If M a &gt;1 and N a &gt;1 and PMI_TF_Granularity_2ndD_freq=WIDEBAND, a second first-dimension precoding matrix indicator i 2,H  for each set S subband, and a second second-dimension precoding matrix indicator i 2,V  for the set S subbands   If M a &gt;1 and N a &gt;1 and PMI_TF_Granularity_2ndD_freq=SUBBAND, a second first-dimension precoding matrix indicator i 2,H  for each set S subband, and a second second-dimension precoding matrix indicator i 2,V  for each set S subband   
           A UE reports one subband CQI value per codeword for each set S subband which are calculated assuming the use of the corresponding selected first-dimension and second-dimension precoding matrices and assuming transmission in the corresponding subband.   For transmission modes 4, 8, 9, 10, and x the reported PMI and CQI values are calculated conditioned on the reported RI. For other transmission modes they are reported conditioned on rank 1.
 
Description for mode 2-2 is analogous to the above description for modes 2-1, 3-1, and 3-2 and one of ordinary skill in the art would be able to derive the full description for mode 2-2 based on the above description for modes 2-1, 3-1, and 3-2.
       
 
         [0230]    An alternative embodiment for PUSCH-based aperiodic CSI mode 3-1 can be made by constraining the vertical PMI (or, the PMI associated with one of the two dimensions) to be wideband. This is applicable when vertical channel variability is less than that of horizontal. In this case, PMI_TF_Granularity_2ndD_freq is not used. In this case, mode 3-1 can be described as follows:
       A single first-dimension (for instance, horizontal) precoding matrix is selected from the first-dimension codebook subset assuming transmission on set S subbands
           If M a &gt;1 and N a &gt;1, a single preferred second-dimension (for instance, vertical) precoding matrix is selected from the second-dimension codebook subset assuming transmission on set S subbands.   
           A UE reports one subband CQI value per codeword for each set S subband which are calculated assuming the use of the corresponding selected first-dimension and second-dimension precoding matrices and assuming transmission in the corresponding subband.   A UE reports a wideband CQI value per codeword which is calculated assuming the use of the corresponding selected first-dimension and second-dimension precoding matrices   A UE reports the following precoding matrix indicators:
           If M a =1 or N a =1, a second precoding matrix indicator corresponding to the selected single precoding matrix.   If M a &gt;1 and N a &gt;1, a second first-dimension and second-dimension precoding matrix indicator i 2,H  and i 2,V  for the set S subbands   
           For transmission modes 4, 8, 9, 10, and x the reported PMI and CQI values are calculated conditioned on the reported RI. For other transmission modes they are reported conditioned on rank 1.       
 
         [0239]    Furthermore, if precoder structure in equation (3) is used instead of (2), {i 2,V , i 2,H } can be replaced by {i 2 }. In this case, there is no need for a criterion to differentiate between 1D and 2D. Moreover, only a single precoding codebook is used. For PUSCH-based aperiodic CSI reporting (see e.g., TABLE 1), mode 1-2 can be described as follows:
       For each subband a preferred precoding matrix is selected from the codebook subset assuming transmission only in the subband
           If PMI_TF_Granularity_2ndD_freq=WIDEBAND, a single preferred precoding matrix is selected from the codebook subset assuming transmission on set S subbands.   If PMI_TF_Granularity_2ndD_freq=SUBBAND, a preferred precoding matrix is selected from the codebook subset assuming transmission only in the subband.   
           A UE reports one wideband CQI value per codeword which is calculated assuming the use of the corresponding selected precoding matrix.   A UE reports the following precoding matrix indicators:
           If PMI_TF_Granularity_2ndD_freq=WIDEBAND, a second precoding matrix indicator i 2  for each set S subband   If PMI_TF_Granularity_2ndD_freq=SUBBAND, a second precoding matrix indicator i 2  for each set S subband   
           Subband size is given by Table 7.2.1-3 of REF3.   For transmission modes 4, 8, 9, 10, and x the reported PMI and CQI values are calculated conditioned on the reported RI. For other transmission modes they are reported conditioned on rank 1.
 
Mode 3-1 can be described as follows:
   A single precoding matrix is selected from the codebook subset assuming transmission on set S subbands
           If PMI_TF_Granularity_2ndD_freq=WIDEBAND, a single preferred precoding matrix is selected from the codebook subset assuming transmission on set S subbands.   If PMI_TF_Granularity_2ndD_freq=SUBBAND, a preferred precoding matrix is selected from the codebook subset assuming transmission only in the subband.   
           A UE reports one subband CQI value per codeword for each set S subband which are calculated assuming the use of the corresponding selected precoding matrix and assuming transmission in the corresponding subband.   A UE reports a wideband CQI value per codeword which is calculated assuming the use of the corresponding selected precoding matrix   A UE reports the following precoding matrix indicators:
           If PMI_TF_Granularity_2ndD_freq=WIDEBAND, a second precoding matrix indicator i 2  for each set S subband   If PMI_TF_Granularity_2ndD_freq=SUBBAND, a second precoding matrix indicator i 2  for each set S subband   
           For transmission modes 4, 8, 9, 10, and x the reported PMI and CQI values are calculated conditioned on the reported RI. For other transmission modes they are reported conditioned on rank 1.
 
Mode 3-2 can be described as follows:
   For each subband a preferred precoding matrix is selected from the codebook subset assuming transmission only in the subband
           If PMI_TF_Granularity_2ndD_freq=WIDEBAND, a single preferred precoding matrix is selected from the codebook subset assuming transmission on set S subbands.   If PMI_TF_Granularity_2ndD_freq=SUBBAND, a preferred precoding matrix is selected from the codebook subset assuming transmission only in the subband.   
           A UE reports a wideband CQI value per codeword which is calculated assuming the use of the corresponding selected precoding matrix.   A UE report the following precoding matrix indicators:
           If PMI_TF_Granularity_2ndD_freq=WIDEBAND, a second precoding matrix indicator i 2  for each set S subband   If PMI_TF_Granularity_2ndD_freq=SUBBAND, a second precoding matrix indicator i 2  for each set S subband   
           A UE report one subband CQI value per codeword for each set S subband which are calculated assuming the use of the corresponding selected precoding matrix and assuming transmission in the corresponding subband.   For transmission modes 4, 8, 9, 10, and x the reported PMI and CQI values are calculated conditioned on the reported RI. For other transmission modes they are reported conditioned on rank 1.
 
Description for mode 2-2 is analogous to the above description for modes 2-1, 3-1, and 3-2 and one of ordinary skill in the art would be able to derive the full description for mode 2-2 based on the above description for modes 2-1, 3-1, and 3-2.
       
 
         [0267]    In a fifth embodiment, departing from TABLE 1 and 2, CSI calculation and reporting for a given UE is fully configured and characterized with time and/or frequency granularity parameters. Time granularity configuration can include reporting periodicity/interval. Frequency granularity configuration can include a two-value indicator used to configure a UE with either WIDEBAND or SUBBAND reporting. Alternatively, frequency granularity configuration can include subband size (for example, in terms of the number of RBs) wherein one possible value indicates wideband reporting (one report for all the RBs). 
         [0268]    In one alternative of this embodiment, the time/frequency granularity of CQI and PMI can be configured separately via higher-layer (RRC) signaling. For example, four RRC parameters CQI_T_Granularity, CQI_F_Granularity, PMI_T_Granularity, and PMI_F_Granularity can be used to configure CSI calculation/reporting for a UE. As mentioned before, time granularity does not apply to A-CSI. Therefore, only CQI_F_Granularity and PMI_F_Granularity apply. If P-CSI is associated with wideband-only reporting, frequency granularity does not apply to P-CSI. Therefore, only CQI_T_Granularity and PMI_T_Granularity apply. 
         [0269]    In another alternative of this embodiment, the time/frequency granularity of CQI and PMI is configured jointly via higher-layer (RRC) signaling. For example, two RRC parameters CQIPMI_T_Granularity and CQIPMI_F_Granularity can be used to configure CSI calculation/reporting for a UE. As mentioned before, time granularity does not apply to A-CSI. Therefore, only CQIPMI_F_Granularity applies. If P-CSI is associated with wideband-only reporting, frequency granularity does not apply to P-CSI. Therefore, only CQIPMI_T_Granularity applies. 
         [0270]    In addition to the above, different PMI reporting granularities can be introduced for two different dimensions when 2D CSI-RS port pattern or 2D precoding codebook structure is used. For the first alternative, the RRC parameter PMI_T_Granularity can be substituted with PMI_T_Granularity_1stD and PMI_T_Granularity_2ndD whereas the RRC parameter PMI_F_Granularity can be substituted with PMI_F_Granularity_1stD and PMI_F_Granularity_2ndD. For dual-stage precoder/codebook, different PMI reporting frequency granularities for different dimensions applies for the structure in equation (2), but not for the structure in equation (3). 
         [0271]      FIG. 8  illustrates an example method  800  wherein a UE receives configuration information containing at least a CSI reporting configuration and codebook parameters ( 801 ). The CSI reporting configuration can include a choice of CSI reporting mode. Two of the codebook parameters are M a  and N a  which can correspond to the number of rows and columns in a two-dimensional dual-polarized port array with a total of 2M, N a  ports. In response to at least the codebook parameters M a  and N a  ( 802 ), the UE calculates a first PMI i 1 . If at least one of M a  and N a  equals to 1, i 1  includes one codebook index associated with a first-stage precoding ( 805 ). If each of M a  and N a  equals to a value greater than 1, i 1  includes two codebook indices associated with a first-dimension i 1,1  and a second-dimension i 1,2  of the first-stage precoding, respectively ( 810 ). In either case, the UE calculates a second PMI i 2  ( 806  and  811 ) and transmits a CSI report including at least CQI, RI, and {i 1 , i 2 } ( 807  and  812 ). 
         [0272]      FIG. 9  illustrates an example method  900  wherein an eNB configures a UE (labeled as UE-k for illustrative purposes) with CSI reporting and codebook parameters ( 901 ). The CSI reporting configuration can include a choice of CSI reporting mode. Two of the codebook parameters are M a  and N a  which can correspond to the number of rows and columns in a two-dimensional dual-polarized port array with a total of 2M, N a  ports. The eNB transmits this configuration information to UE-k via a DL channel ( 902 ). The eNB also receives a CSI report from UE-k ( 903 ), in response to the transmitted configuration information, which includes at least a CQI, a RI, a first PMI, and a second PMI. Upon receiving the CSI report, the eNB decodes the CQI, the RI, and a second-stage codebook index from the second PMI ( 904 ). If at least one of M a  and N a  equals to 1 at  905 , i 1  includes one codebook index associated with a first-stage precoding ( 906 ). If each of M a  and N a  equals to a value greater than 1, i 1  includes two codebook indices associated with a first-dimension i 1,1  and a second-dimension i 1,2  of the first-stage precoding, respectively ( 907 ). 
         [0273]    The above configuration information is signaled to the UE via higher-layer or RRC signaling. At least one of the codebook parameters can also be signaled to the UE via higher-layer or RRC signaling. In another example, signaling via a DL control channel can be used at least for one of the codebook parameters. 
         [0274]    Although  FIGS. 8 and 9  illustrate examples of processes for receiving configuration information and configuring a UE, respectively, various changes could be made to  FIGS. 8 and 9 . For example, while shown as a series of steps, various steps in each figure could overlap, occur in parallel, occur in a different order, occur multiple times, or not be performed in one or more embodiments. 
         [0275]    Although the present disclosure has been described with an example embodiment, various changes and modifications can be suggested by or to one skilled in the art. It is intended that the present disclosure encompass such changes and modifications as fall within the scope of the appended claims.