WO2017049599A1

WO2017049599A1 - Csi reporting for beamformed csi-rs based fd-mimo

Info

Publication number: WO2017049599A1
Application number: PCT/CN2015/090753
Authority: WO
Inventors: Yu Zhang; Chao Wei
Original assignee: Qualcomm Incorporated
Priority date: 2015-09-25
Filing date: 2015-09-25
Publication date: 2017-03-30

Abstract

Channel state information (CSI) reporting configurations for beamformed CSI-reference signal (CSI-RS) based full-dimensional multiple input, multiple output (FD-MIMO) is disclosed. In response to transmitted beamformed CSI-RS, CSI reporting by UEs includes transmission of a dedicated beam selection indicator identifying CSI-RS resources selected for CSI reporting. Further CSI reporting includes transmitting at least the PMI which indicates the selected antenna ports of the selected resources. The precoder may then be determined based on the beam selection indicator, the PMI, and the type of CSI-RS beamforming used. Communication configurations may then be updated based on the CSI feedback.

Description

CSI REPORTING FOR BEAMFORMED CSI-RS BASED FD-MIMO

BACKGROUND

Field

Aspects of the present disclosure relate generally to wireless communication systems, and more particularly, to channel state information (CSI) reporting for beamformed CSI-reference signal (CSI-RS) based full-dimensional multiple input, multiple output (FD-MIMO) .

Background

Wireless communication networks are widely deployed to provide various communication services such as voice, video, packet data, messaging, broadcast, and the like. These wireless networks may be multiple-access networks capable of supporting multiple users by sharing the available network resources. Such networks, which are usually multiple access networks, support communications for multiple users by sharing the available network resources. One example of such a network is the Universal Terrestrial Radio Access Network (UTRAN) . The UTRAN is the radio access network (RAN) defined as a part of the Universal Mobile Telecommunications System (UMTS) , a third generation (3G) mobile phone technology supported by the 3rd Generation Partnership Project (3GPP) . Examples of multiple-access network formats include Code Division Multiple Access (CDMA) networks, Time Division Multiple Access (TDMA) networks, Frequency Division Multiple Access (FDMA) networks, Orthogonal FDMA (OFDMA) networks, and Single-Carrier FDMA (SC-FDMA) networks.

A wireless communication network may include a number of base stations or node Bs that can support communication for a number of user equipments (UEs) . A UE may communicate with a base station via downlink and uplink. The downlink (or forward link) refers to the communication link from the base station to the UE, and the uplink (or reverse link) refers to the communication link from the UE to the base station.

A base station may transmit data and control information on the downlink to a UE and/or may receive data and control information on the uplink from the UE. On the downlink, a transmission from the base station may encounter interference due to transmissions from neighbor base stations or from other wireless radio frequency (RF) transmitters. On the uplink, a transmission from the UE may encounter interference from uplink transmissions of other UEs communicating with the neighbor base stations or from other wireless RF transmitters. This interference may degrade performance on both the downlink and uplink.

As the demand for mobile broadband access continues to increase, the possibilities of interference and congested networks grows with more UEs accessing the long-range wireless communication networks and more short-range wireless systems being deployed in communities. Research and development continue to advance the UMTS technologies not only to meet the growing demand for mobile broadband access, but to advance and enhance the user experience with mobile communications.

SUMMARY

In one aspect of the disclosure, a method of wireless communication includes transmitting one or more beamformed channel state information (CSI) -reference signal (RS) and a CSI-RS beamforming type indicator to one or more UEs within a coverage area, receiving a beam selection indicator from the one or more UEs, wherein the beam selection indicator identifies one of a plurality of CSI-RS resources selected by the one or more UEs on which to report CSI, receiving a precoding matrix indicator (PMI) from the one or more UEs, wherein the PMI is associated with the selected one of the plurality of CSI-RS resources, determining a precoder based, at least in part, on the beam selection indicator, the PMI, and the CSI-RS beamforming type indicator, and transmitting data to the one or more UEs according to one or more transmission parameters selected based, at least in part, on the precoder.

In an additional aspect of the disclosure, a method of wireless communication includes detecting a plurality of cell-specific CSI-RS resources, selecting one of the plurality of cell-specific CSI-RS resources for reporting CSI feedback, measuring the selected one of the plurality of cell-specific CSI-RS resources, and transmitting the CSI feedback to a serving base station, wherein the CSI feedback includes at least one of: a beam selection indicator identifying the selected one of the plurality of cell-specific CSI-RS resources, a rank indicator (RI) , a first PMI, one or more second PMI, and a channel quality indicator (CQI) .

In an additional aspect of the disclosure, a method of wireless communication includes detecting a plurality of UE-specific channel state information CSI-RS, selecting one of the plurality of UE-specific CSI-RS resources for reporting CSI feedback, measuring the selected one of the plurality of UE-specific CSI-RS resources, and transmitting the CSI feedback to a serving base station, wherein the CSI feedback includes at least, one of: a beam selection indicator identifying the selected one of the plurality of UE-specific CSI-RS resources, a RI, one or more second PMI, and a CQI.

In one aspect of the disclosure, an apparatus configured for wireless communication includes means for transmitting one or more beamformed CSI-RS and a CSI-RS beamforming type indicator to one or more UEs within a coverage area, means for receiving a beam selection indicator from the one or more UEs, wherein the beam selection indicator identifies one of a plurality of CSI-RS resources selected by the one or more UEs on which to report CSI, means for receiving a PMI from the one or more UEs, wherein the PMI is associated with the selected one of the plurality of CSI-RS resources, means for determining a precoder based, at least in part, on the beam selection indicator, the PMI, and the CSI-RS beamforming type indicator, and means for transmitting data to the one or more UEs according to one or more transmission parameters selected based, at least in part, on the precoder.

In an additional aspect of the disclosure, an apparatus configured for wireless communication includes means for detecting a plurality of cell-specific CSI-RS resources, means for selecting one of the plurality of cell-specific CSI-RS resources for reporting CSI feedback, means for measuring the selected one of the plurality of cell-specific CSI-RS resources, and means for transmitting the CSI feedback to a serving base station, wherein the CSI feedback includes at least one of: a beam selection indicator identifying the selected one of the plurality of cell-specific CSI-RS resources, a RI, a first PMI, one or more second PMI, and a CQI.

In an additional aspect of the disclosure, an apparatus configured for wireless communication includes means for detecting a plurality of UE-specific channel state information CSI-RS, means for selecting one of the plurality of UE-specific CSI-RS resources for reporting CSI feedback, means for measuring the selected one of the plurality of UE-specific CSI-RS resources, and means for transmitting the CSI feedback to a serving base station, wherein the CSI feedback includes at least, one of: a beam selection indicator identifying the selected one of the plurality of UE-specific CSI-RS resources, a RI, one or more second PMI, and a CQI.

In an additional aspect of the disclosure, a non-transitory computer-readable medium having program code recorded thereon. The program code further includes code to transmit one or more beamformed CSI-RS and a CSI-RS beamforming type indicator to one or more UEs within a coverage area, code to receive a beam selection indicator from the one or more UEs, wherein the beam selection indicator identifies one of a plurality of CSI-RS resources selected by the one or more UEs on which to report CSI, code to receive a PMI from the one or more UEs, wherein the PMI is associated with the selected one of the plurality of CSI-RS resources, code to determine a precoder based, at least in part, on the beam selection indicator, the PMI, and the CSI-RS beamforming type indicator, and code to transmit data to the one or more UEs according to one or more transmission parameters selected based, at least in part, on the precoder.

In an additional aspect of the disclosure, a non-transitory computer-readable medium having program code recorded thereon. The program code further includes code to detect a plurality of cell-specific CSI-RS resources, code to select one of the plurality of cell-specific CSI-RS resources for reporting CSI feedback, code to measure the selected one of the plurality of cell-specific CSI-RS resources, and code to transmit the CSI feedback to a serving base station, wherein the CSI feedback includes at least one of: a beam selection indicator identifying the selected one of the plurality of cell-specific CSI-RS resources, a RI, a first PMI, one or more second PMI, and a CQI.

In an additional aspect of the disclosure, a non-transitory computer-readable medium having program code recorded thereon. The program code further includes code to detect a plurality of UE-specific channel state information CSI-RS, code to select one of the plurality of UE-specific CSI-RS resources for reporting CSI feedback, code to measure the selected one of the plurality of UE-specific CSI-RS resources, and code to transmit the CSI feedback to a serving base station, wherein the CSI feedback includes at least, one of: a beam selection indicator identifying the selected one of the plurality of UE-specific CSI-RS resources, a RI, one or more second PMI, and a CQI.

In an additional aspect of the disclosure, an apparatus configured for wireless communication is disclosed. The apparatus includes at least one processor, and a memory coupled to the processor. The processor is configured to transmit one or more beamformed CSI-RS and a CSI-RS beamforming type indicator to one or more UEs within a coverage area, to receive a beam selection indicator from the one or more UEs, wherein the beam selection indicator identifies one of a plurality of CSI-RS resources selected by the one or more UEs on which to report CSI, to receive a PMI from the one or more UEs, wherein the PMI is associated with the selected one of the plurality of CSI-RS resources, to determine a precoder based, at least in part, on the beam selection indicator, the PMI, and the CSI-RS beamforming type indicator, and to transmit data to the one or more UEs according to one or more transmission parameters selected based, at least in part, on the precoder.

In an additional aspect of the disclosure, an apparatus configured for wireless communication is disclosed. The apparatus includes at least one processor, and a memory coupled to the processor. The processor is configured to detect a plurality of cell-specific CSI-RS resources, to select one of the plurality of cell-specific CSI-RS resources for reporting CSI feedback, to measure the selected one of the plurality of cell-specific CSI-RS resources, and to transmit the CSI feedback to a serving base station, wherein the CSI feedback includes at least one of: a beam selection indicator identifying the selected one of the plurality of cell-specific CSI-RS resources, a RI, a first PMI, one or more second PMI, and a CQI.

In an additional aspect of the disclosure, an apparatus configured for wireless communication is disclosed. The apparatus includes at least one processor, and a memory coupled to the processor. The processor is configured to detect a plurality of UE-specific channel state information CSI-RS, to select one of the plurality of UE-specific CSI-RS resources for reporting CSI feedback, to measure the selected one of the plurality of UE-specific CSI-RS resources, and to transmit the CSI feedback to a serving base station, wherein the CSI feedback includes at least, one of: a beam selection indicator identifying the selected one of the plurality of UE-specific CSI-RS resources, a RI, one or more second PMI, and a CQI.

The foregoing has outlined rather broadly the features and technical advantages of examples according to the disclosure in order that the detailed description that follows may be better understood. Additional features and advantages will be described hereinafter. The conception and specific examples disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present disclosure. Such equivalent constructions do not depart from the scope of the appended claims. Characteristics of the concepts disclosed herein, both their organization and method of operation, together with associated advantages will be better understood from the following description when considered in connection with the accompanying figures. Each of the figures is provided for the purpose of illustration and description, and not as a definition of the limits of the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

A further understanding of the nature and advantages of the present disclosure may be realized by reference to the following drawings. In the appended figures, similar components or features may have the same reference label. Further, various components of the same type may be distinguished by following the reference label by a dash and a second label that distinguishes among the similar components. If just the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the second reference label.

FIG. 1 is a block diagram illustrating details of a wireless communication system.

FIG. 2 is a block diagram conceptually illustrating a design of a base station/eNB and a UE configured according to one aspect of the present disclosure.

FIG. 3 is a block diagram illustrating a typical 2D active antenna array.

FIG. 4 is a block diagram illustrating example blocks executed to implement one aspect of the present disclosure.

FIG. 5 is a block diagram illustrating an eNB configured according to one aspect of the present disclosure.

FIG. 6 is a block diagram illustrating a UE configured according to one aspect of the present disclosure.

FIGs. 7A and 7B are block diagrams illustrating example resource allocations and reporting for FD-MIMO by a UE configured according to one aspect of the present disclosure.

FIG. 8 is a block diagram illustrating example blocks executed to implement one aspect of the present disclosure.

FIG. 9 is a block diagram illustrating a transmission stream from a UE configured according to one aspect of the present disclosure.

FIGs. 10A and 10B are block diagrams illustrating transmission streams from a UE configured according to aspects of the present disclosure.

FIG. 11 is a block diagram illustrating a transmission stream from a UE configured according to one aspect of the present disclosure.

FIG. 12 is a block diagram illustrating a transmission stream from a UE configured according to one aspect of the present disclosure.

FIG. 13 is a block diagram illustrating two UEs configured according to one aspect of the present disclosure.

DETAILED DESCRIPTION

The detailed description set forth below, in connection with the appended drawings, is intended as a description of various possible configurations and is not intended to limit the scope of the disclosure. Rather, the detailed description includes specific details for the purpose of providing a thorough understanding of the inventive subject matter. It will be apparent to those skilled in the art that these specific details are not required in every case and that, in some instances, well-known structures and components are shown in block diagram form for clarity of presentation.

This disclosure relates generally to providing or participating in authorized shared access between two or more wireless communications systems, also referred to as wireless communications networks. In various embodiments, the techniques and apparatus may be used for wireless communication networks such as code division multiple access (CDMA) networks, time division multiple access (TDMA) networks, frequency division multiple access (FDMA) networks, orthogonal FDMA (OFDMA) networks, single-carrier FDMA (SC-FDMA) networks, LTE networks, GSM networks, as well as other communications networks. As described herein, the terms “networks” and “systems” may be used interchangeably.

A CDMA network may implement a radio technology such as universal terrestrial radio access (UTRA) , cdma2000, and the like. UTRA includes wideband-CDMA (W-CDMA) and low chip rate (LCR) . CDMA2000 covers IS-2000, IS-95, and IS-856 standards.

A TDMA network may implement a radio technology such as Global System for Mobile Communications (GSM) . 3GPP defines standards for the GSM EDGE (enhanced data rates for GSM evolution) radio access network (RAN) , also denoted as GERAN. GERAN is the radio component of GSM/EDGE, together with the network that joins the base stations (for example, the Ater and Abis interfaces) and the base station controllers (A interfaces, etc. ) . The radio access network represents a component of a GSM network, through which phone calls and packet data are routed from and to the public switched telephone network (PSTN) and Internet to and from subscriber handsets, also known as user terminals or user equipments (UEs) . A mobile phone operator's network may comprise one or more GERANs, which may be coupled with UTRANs in the case of a UMTS/GSM network. An operator network may also include one or more LTE networks, and/or one or more other networks. The various different network types may use different radio access technologies (RATs) and radio access networks (RANs) .

An OFDMA network may implement a radio technology such as evolved UTRA (E-UTRA) , IEEE 802.11, IEEE 802.16, IEEE 802.20, flash-OFDM and the like. UTRA, E-UTRA, and GSM are part of universal mobile telecommunication system (UMTS) . In particular, long term evolution (LTE) is a release of UMTS that uses E-UTRA. UTRA, E-UTRA, GSM, UMTS and LTE are described in documents provided from an organization named “3rd Generation Partnership Project” (3GPP) , and cdma2000 is described in documents from an organization named “3rd Generation Partnership Project 2” (3GPP2) . These various radio technologies and standards are known or are being developed. For example, the 3rd Generation Partnership Project (3GPP) is a collaboration between groups of telecommunications associations that aims to define a globally applicable third generation (3G) mobile phone specification. 3GPP long term evolution (LTE) is a 3GPP project aimed at improving the universal mobile telecommunications system (UMTS) mobile phone standard. The 3GPP may define specifications for the next generation of mobile networks, mobile systems, and mobile devices. For clarity, certain aspects of the apparatus and techniques may be described below for LTE implementations or in an LTE-centric way, and LTE terminology may be used as illustrative examples in portions of the description below； however, the description is not intended to be limited to LTE applications. Indeed, the present disclosure is concerned with shared access to wireless spectrum between networks using different radio access technologies or radio air interfaces.

A new carrier type based on LTE/LTE-Aincluding in unlicensed spectrum has also been suggested that can be compatible with carrier-grade WiFi, making LTE/LTE-Awith unlicensed spectrum an alternative to WiFi. LTE/LTE-A, when operating in unlicensed spectrum, may leverage LTE concepts and may introduce some modifications to physical layer (PHY) and media access control (MAC) aspects of the network or network devices to provide efficient operation in the unlicensed spectrum and meet regulatory requirements. The unlicensed spectrum used may range from as low as several hundred Megahertz (MHz) to as high as tens of Gigahertz (GHz) , for example. In operation, such LTE/LTE-Anetworks may operate with any combination of licensed or unlicensed spectrum depending on loading and availability. Accordingly, it may be apparent to one of skill in the art that the systems, apparatus and methods described herein may be applied to other communications systems and applications.

System designs may support various time-frequency reference signals for the downlink and uplink to facilitate beamforming and other functions. A reference signal is a signal generated based on known data and may also be referred to as a pilot, preamble, training signal, sounding signal, and the like. A reference signal may be used by a receiver for various purposes such as channel estimation, coherent demodulation, channel quality measurement, signal strength measurement, and the like. MIMO systems using multiple antennas generally provide for coordination of sending of reference signals between antennas； however, LTE systems do not in general provide for coordination of sending of reference signals from multiple base stations or eNBs.

In some implementations, a system may utilize time division duplexing (TDD) . For TDD, the downlink and uplink share the same frequency spectrum or channel, and downlink and uplink transmissions are sent on the same frequency spectrum. The downlink channel response may thus be correlated with the uplink channel response. Reciprocity may allow a downlink channel to be estimated based on transmissions sent via the uplink. These uplink transmissions may be reference signals or uplink control channels (which may be used as reference symbols after demodulation) . The uplink transmissions may allow for estimation of a space-selective channel via multiple antennas.

In LTE implementations, orthogonal frequency division multiplexing (OFDM) is used for the downlink–that is, from a base station, access point or eNodeB (eNB) to a user terminal or UE. Use of OFDM meets the LTE requirement for spectrum flexibility and enables cost-efficient solutions for very wide carriers with high peak rates, and is a well-established technology. For example, OFDM is used in standards such as IEEE 802.11a/g, 802.16, High Performance Radio LAN-2 (HIPERLAN-2, wherein LAN stands for Local Area Network) standardized by the European Telecommunications Standards Institute (ETSI) , Digital Video Broadcasting (DVB) published by the Joint Technical Committee of ETSI, and other standards.

Time frequency physical resource blocks (also denoted here in as resource blocks or “RBs” for brevity) may be defined in OFDM systems as groups of transport carriers (e.g. sub-carriers) or intervals that are assigned to transport data. The RBs are defined over a time and frequency period. Resource blocks are comprised of time-frequency resource elements (also denoted here in as resource elements or “REs” for brevity) , which may be defined by indices of time and frequency in a slot. Additional details of LTE RBs and REs are described in the 3GPP specifications, such as, for example, 3GPP TS 36.211.

UMTS LTE supports scalable carrier bandwidths from 20 MHz down to 1.4 MHZ. In LTE, an RB is defined as 12 sub-carriers when the subcarrier bandwidth is 15 kHz, or 24 sub-carriers when the sub-carrier bandwidth is 7.5 kHz. In an exemplary implementation, in the time domain there is a defined radio frame that is 10 ms long and consists of 10 subframes of 1 millisecond (ms) each. Every subframe consists of 2 slots, where each slot is 0.5 ms. The subcarrier spacing in the frequency domain in this case is 15 kHz. Twelve of these subcarriers together (per slot) constitute an RB, so in this implementation one resource block is 180 kHz. Six Resource blocks fit in a carrier of 1.4 MHz and 100 resource blocks fit in a carrier of 20 MHz.

Various other aspects and features of the disclosure are further described below. It should be apparent that the teachings herein may be embodied in a wide variety of forms and that any specific structure, function, or both being disclosed herein is merely representative and not limiting. Based on the teachings herein one of an ordinary level of skill in the art should appreciate that an aspect disclosed herein may be implemented independently of any other aspects and that two or more of these aspects may be combined in various ways. For example, an apparatus may be implemented or a method may be practiced using any number of the aspects set forth herein. In addition, such an apparatus may be implemented or such a method may be practiced using other structure, functionality, or structure and functionality in addition to or other than one or more of the aspects set forth herein. For example, a method may be implemented as part of a system, device, apparatus, and/or as instructions stored on a computer readable medium for execution on a processor or computer. Furthermore, an aspect may comprise at least one element of a claim.

FIG. 1 shows a wireless network 100 for communication, which may be an LTE-Anetwork. The wireless network 100 includes a number of evolved node Bs (eNBs) 110 and other network entities. An eNB may be a station that communicates with the UEs and may also be referred to as a base station, a node B, an access point, and the like. Each eNB 110 may provide communication coverage for a particular geographic area. In 3GPP, the term “cell” can refer to this particular geographic coverage area of an eNB and/or an eNB subsystem serving the coverage area, depending on the context in which the term is used.

An eNB may provide communication coverage for a macro cell, a pico cell, a femto cell, and/or other types of cell. A macro cell generally covers a relatively large geographic area (e.g., several kilometers in radius) and may allow unrestricted access by UEs with service subscriptions with the network provider. A pico cell would generally cover a relatively smaller geographic area and may allow unrestricted access by UEs with service subscriptions with the network provider. A femto cell would also generally cover a relatively small geographic area (e.g., a home) and, in addition to unrestricted access, may also provide restricted access by UEs having an association with the femto cell (e.g., UEs in a closed subscriber group (CSG) , UEs for users in the home, and the like) . An eNB for a macro cell may be referred to as a macro eNB. An eNB for a pico cell may be referred to as a pico eNB. And, an eNB for a femto cell may be referred to as a femto eNB or a home eNB. In the example shown in FIG. 1, the eNBs 110a, 110b and 110c are macro eNBs for the macro cells 102a, 102b and 102c, respectively. The eNB 110x is a pico eNB for a pico cell 102x. And, the eNBs 110y and 110z are femto eNBs for the femto cells 102y and 102z, respectively. An eNB may support one or multiple (e.g., two, three, four, and the like) cells.

The wireless network 100 also includes relay stations. A relay station is a station that receives a transmission of data and/or other information from an upstream station (e.g., an eNB, a UE, or the like) and sends a transmission of the data and/or other information to a downstream station (e.g., another UE, another eNB, or the like) . A relay station may also be a UE that relays transmissions for other UEs. In the example shown in FIG. 1, a relay station 110r may communicate with the eNB 110a and a UE 120r, in which the relay station 110r acts as a relay between the two network elements (the eNB 110a and the UE 120r) in order to facilitate communication between them. A relay station may also be referred to as a relay eNB, a relay, and the like.

The wireless network 100 may support synchronous or asynchronous operation. For synchronous operation, the eNBs may have similar frame timing, and transmissions from different eNBs may be approximately aligned in time. For asynchronous operation, the eNBs may have different frame timing, and transmissions from different eNBs may not be aligned in time.

The UEs 120 are dispersed throughout the wireless network 100, and each UE may be stationary or mobile. A UE may also be referred to as a terminal, a mobile station, a subscriber unit, a station, or the like. A UE may be a cellular phone, a personal digital assistant (PDA) , a wireless modem, a wireless communication device, a handheld device, a tablet computer, a laptop computer, a cordless phone, a wireless local loop (WLL) station, or the like. A UE may be able to communicate with macro eNBs, pico eNBs, femto eNBs, relays, and the like. In FIG. 1, a solid line with double arrows indicates desired transmissions between a UE and a serving eNB, which is an eNB designated to serve the UE on the downlink and/or uplink. A dashed line with double arrows indicates interfering transmissions between a UE and an eNB.

LTE/-Autilizes orthogonal frequency division multiplexing (OFDM) on the downlink and single-carrier frequency division multiplexing (SC-FDM) on the uplink. OFDM and SC-FDM partition the system bandwidth into multiple (K) orthogonal subcarriers, which are also commonly referred to as tones, bins, or the like. Each subcarrier may be modulated with data. In general, modulation symbols are sent in the frequency domain with OFDM and in the time domain with SC-FDM. The spacing between adjacent subcarriers may be fixed, and the total number of subcarriers (K) may be dependent on the system bandwidth. For example, K may be equal to 72, 180, 300, 600, 900, and 1200 for a corresponding system bandwidth of 1.4, 3, 5, 10, 15, or 20 megahertz (MHz) , respectively. The system bandwidth may also be partitioned into sub-bands. For example, a sub-band may cover 1.08 MHz, and there may be 1, 2, 4, 8 or 16 sub-bands for a corresponding system bandwidth of 1.4, 3, 5, 10, 15, or 20MHz, respectively.

FIG. 2 shows a block diagram of a design of a base station/eNB 110 and a UE 120, which may be one of the base stations/eNBs and one of the UEs in FIG. 1. For a restricted association scenario, the eNB 110 may be the macro eNB 110c in FIG. 1, and the UE 120 may be the UE 120y. The eNB 110 may also be a base station of some other type. The eNB 110 may be equipped with antennas 234a through 234t, and the UE 120 may be equipped with antennas 252a through 252r.

At the eNB 110, a transmit processor 220 may receive data from a data source 212 and control information from a controller/processor 240. The control information may be for the PBCH, PCFICH, PHICH, PDCCH, etc. The data may be for the PDSCH, etc. The transmit processor 220 may process (e.g., encode and symbol map) the data and control information to obtain data symbols and control symbols, respectively. The transmit processor 220 may also generate reference symbols, e.g., for the PSS, SSS, and cell-specific reference signal. A transmit (TX) multiple-input multiple-output (MIMO) processor 230 may perform spatial processing (e.g., precoding) on the data symbols, the control symbols, and/or the reference symbols, if applicable, and may provide output symbol streams to the modulators (MODs) 232a through 232t. Each modulator 232 may process a respective output symbol stream (e.g., for OFDM, etc. ) to obtain an output sample stream. Each modulator 232 may further process (e.g., convert to analog, amplify, filter, and upconvert) the output sample stream to obtain a downlink signal. Downlink signals from modulators 232a through 232t may be transmitted via the antennas 234a through 234t, respectively.

At the UE 120, the antennas 252a through 252r may receive the downlink signals from the eNB 110 and may provide received signals to the demodulators (DEMODs) 254a through 254r, respectively. Each demodulator 254 may condition (e.g., filter, amplify, downconvert, and digitize) a respective received signal to obtain input samples. Each demodulator 254 may further process the input samples (e.g., for OFDM, etc. ) to obtain received symbols. A MIMO detector 256 may obtain received symbols from all the demodulators 254a through 254r, perform MIMO detection on the received symbols if applicable, and provide detected symbols. A receive processor 258 may process (e.g., demodulate, deinterleave, and decode) the detected symbols, provide decoded data for the UE 120 to a data sink 260, and provide decoded control information to a controller/processor 280.

On the uplink, at the UE 120, a transmit processor 264 may receive and process data (e.g., for the PUSCH) from a data source 262 and control information (e.g., for the PUCCH) from the controller/processor 280. The transmit processor 264 may also generate reference symbols for a reference signal. The symbols from the transmit processor 264 may be precoded by a TX MIMO processor 266 if applicable, further processed by the modulators 254a through 254r (e.g., for SC-FDM, etc. ) , and transmitted to the eNB 110. At the eNB 110, the uplink signals from the UE 120 may be received by the antennas 234, processed by the demodulators 232, detected by a MIMO detector 236 if applicable, and further processed by a receive processor 238 to obtain decoded data and control information sent by the UE 120. The processor 238 may provide the decoded data to a data sink 239 and the decoded control information to the controller/processor 240.

The controllers/

processors

240 and 280 may direct the operation at the eNB 110 and the UE 120, respectively. The controller/processor 240 and/or other processors and modules at the eNB 110 may perform or direct the execution of various processes for the techniques described herein. The controllers/processor 280 and/or other processors and modules at the UE 120 may also perform or direct the execution of the functional blocks illustrated in FIGS. 5-7, and/or other processes for the techniques described herein. The

memories

242 and 282 may store data and program codes for the eNB 110 and the UE 120, respectively. A scheduler 244 may schedule UEs for data transmission on the downlink and/or uplink.

Multiple-input multiple-output (MIMO) technology generally allows communication to take advantage of the spatial dimension through use of channel state information (CSI) feedback at the eNB. An eNB may broadcast cell-specific CSI reference signals (CSI-RS) for which the UE measures CSI based on configurations signaled by eNB via RRC. A UE may report CSI at CSI reporting instances also configured by the eNB. As a part of CSI reporting the UE generates and reports channel quality indicator (CQI) , precoding matrix indicator (PMI) , and rank indicator (RI) . The CSI can be reported either via PUCCH or via PUSCH. When reported via PUCCH, the payload size for CSI may be limited.

In order to increase system capacity, full-dimensional (FD) -MIMO technology has been considered, in which an eNB uses a two-dimensional (2D) active antenna array with a large number of antennas with antenna ports having both horizontal and vertical axes, and has a larger number of transceiver units. For conventional MIMO systems, beamforming has typically implemented using only azimuth dimension, although of a 3D multi-path propagation. However, for FD-MIMO each transceiver unit has its own independent amplitude and phase control. Such capability together with the 2D active antenna array allows the transmitted signal to be steered not only in the horizontal direction, as in conventional multi-antenna systems, but also simultaneously in both the horizontal and the vertical direction, which provides more flexibility in shaping beam directions from an eNB to a UE. Thus, FD-MIMO technologies may take advantage of both azimuth and elevation beamforming, which would greatly improve MIMO system capacity.

FIG. 3 is a block diagram illustrating a typical 2D active antenna array 30. Active antenna array 30 is a 64-transmitter, cross-polarized uniform planar antenna array comprising four columns, in which each column includes eight cross-polarized vertical antenna elements. Active antenna arrays are often described according to the number of antenna columns (N) , the polarization type (P) , and the number of vertical elements having the same polarization type in one column (M) . Thus, active antenna array 30 has four columns (N＝4) , with eight vertical (M＝8) cross-polarized antenna elements (P＝2) .

For a 2D array structure, in order to exploit the vertical dimension by elevation beamforming the CSI is needed at the base station. The CSI, in terms of PMI, RI, and CQI, can be fed back to the base station by a mobile station based on downlink channel estimation and predefined PMI codebook (s) . However, different from the conventional MIMO system, the eNB capable of FD-MIMO is typically equipped with a large scale antenna system and, thus, the acquisition of full array CSI from the UE is quite challenging due to the complexity of channel estimation and both excessive downlink CSI-RS overhead and uplink CSI feedback overhead.

A CSI process is associated with K CSI-RS resources/configurations, with N_k ports for the kth CSI-RS resource (K≥1) . A CSI process can be configured with either of the two CSI reporting classes: Class A, in which a UE reports CSI according to the codebook associated with the total number of CSI-RS ports configured in a CSI process； and Class B, in which a UE reports CSI according to the codebook associated with L CSI-RS ports. CSI reporting Class A provides non-precoded CSI-RS with a two-dimension codebook, while CSI reporting Class B provides beamformed CSI-RS with both cell-specific and UE-specific beamforming. In Class B, the L-port CSI is defined under one of four alternative assumptions as presented in Table 1 below.

Table 1–Class B CSI Reporting

In alternative one, the UE reports an indicator for beam selection and L-port CQI/PMI/RI for the selected beam. The total configured number of ports across all CSI-RS resources in the CSI process is larger than L. Alternative two provides for an L-port precoder selected from a codebook reflecting both beam selection (s) along with co-phasing across two polarizations jointly. In such alternative, the total configured number of ports in the CSI process is L. Alternative three provides for a codebook reflecting beam selection and L-port CSI for the selected beam. As with alternative one, the total configured number of ports across all CSI-RS resources in the CSI process for alternative three is larger than L. Alternative four provides for an L-port CQI/PMI/RI with a total configured number of ports in the CSI process of L. If CSI measurement restriction is supported, the alternative four will generally be configured.

For alternatives one, two, and three of CSI reporting class B, it is assumed that K CSI-RS resources/configurations, with N_k ports for the k_th CSI-RS resource, are associated with a CSI process. A UE may select one of the CSI-RS resources or a subset of antenna ports within a single CSI-RS resource for CSI reporting. The difference between each of these alternatives is how the UE feeds back beam selection, e.g., via an explicit beam selection indicator or implicitly using selections from a codebook or a PMI. For alternative four of CSI reporting class B, there may be one CSI-RS resource associated with a CSI process, which is dynamically shared among multiple UEs. Therefore, the UE reports CSI by applying measurement restriction. The reported CSI feedback may also be different for each alternative, for example, either by reusing or extending the existing 2-, 4-or 8-ports CSI.

An issue with alternative one is support of higher ranks. Because the reported CSI is based on the selected CSI-RS resource, the reported rank may then be limited by the number of CSI-RS ports in the CSI-RS resource. For example, for supporting

ranks

3 and 4 CSI reporting, at least one 4-port CSI-RS resource may be configured and associated to the CSI process. However, if the existing 4-port codebook, e.g., Rel-8 4Tx codebook or Rel-12 enhanced 4Tx codebook, is used for the selected CSI-RS resource, the precoder for

rank

1 and 2 will use each of the 4-ports for jointly precoding. Thus, to enable port selection for rank 1-2 CSI reporting, a new codebook design for 4-port CSI-RS may be considered. In such way, the same beam selection and cross polarization co-phasing can be applied to rank 1-2 CSI reporting for both 2-port and 4-port CSI-RS resource configuration. The maximum rank is limited by L, the number of ports in the selected subset. Given the CSI-RS overhead, more ports used in each CSI-RS resource result in fewer CSI-RS resources available. Additionally, alternative one may not quickly adapt, as the CSI-RS can be reconfigure semi-statically via RRC signaling.

Alternatives one and three may also have issues regarding support of UE-specific beamformed CSI-RS. Because the UE-specific beam is much narrower than cell-specific beams, a short-term beam selection may be preferable. Other alternatives, such as alternative two may have an issue supporting cell-specific beamformed CSI-RS. With alternative two short-term beam selection may not be preferable for cell-specific beamformed CSI-RS, because the cell-specific beam is much wider and a long-term reporting should be sufficient. Alternative two may also have issues supporting more than 2 ports in a CSI-RS resource. In order to support more than 2 ports in a CSI-RS resource, a larger codebook would be used to indicate beam selection by PMI reporting. For example, in consideration of N_k＝4 and K＝4, at least a 6-bit PMI would be used to indicate the selection of 2 ports and the co-phasing between them.

In consideration of the issues with each of the individual alternatives for Class B CSI feedback, aspects of the present disclosure are directed to providing support for both cell-specific and UE-specific beamformed CSI-RS. FIG. 4 is a block diagram illustrating example blocks executed to implement one aspect of the present disclosure. The features and acts illustrated in FIG. 4 will also be described with respect to an exemplary base station, eNB 500 in FIG. 5. FIG. 5 is a block diagram illustrating an eNB 500 configured according to one aspect of the present disclosure. eNB 500 include similar hardware, components, and features illustrated in FIG. 2 for eNB 110. For example, eNB 500 includes controller/processor 240 which operates and controls the componentry of eNB 500 and executes logic stored in memory 242 in order to provide the features and functionality of eNB 500. eNB 500 also includes antennas 234a-t and wireless radios, which includes components and hardware such as modulator/demodulators 232a-t, MIMO detector 236, receive processor 238, transmit processor 220, and TX MIMO processor 230 (FIG. 2) .

At block 400, a base station, such as eNB 500, transmits one or more beamformed CSI-RS and a CSI-RS beamforming type indicator to one or more UEs within a coverage area. eNB 500, under control of controller/processor 240, executes CSI-RS generator logic 506, stored in memory 242, which operates the componentry of eNB 500 to generate beamformed CSI-RS. Depending on whether a cell-specific or UE-specific CSI-RS is generated, eNB 500 will also transmit the CSI-RS beamforming type indicator in order to indicate to the receiving UEs the type of beamforming. The CSI-RS and beamforming type indicator are transmitted via wireless radios 501a-t and antennas 234a-t.

At block 401, the base station, such as eNB 500, receives a beam selection indicator via antennas 234a-t and wireless radios 501a-t from the one or more UEs, wherein the beam selection indicator identifies one of a plurality of CSI-RS resources selected by the UEs on which to report CSI. The UE reports a beam selection indicator that indicates which of the CSI-RS resources is selected. The reported beam selection indicator can be either long-term or short-term reporting.

At block 402, the base station, eNB 500, receives a PMI from the one or more UEs, wherein the PMI is associated with the selected one of the plurality of CSI-RS resources. The UE reports L-port CQI/PMI/RI, where L＝N_k. eNB 500 stores this CSI feedback 502 in memory 242.

At block 403, the base station, eNB 500, determines a precoder based, at least in part, on the beam selection indicator, the PMI, and the CSI-RS beamforming type indicator. The PMI and RI indicate a precoder W having the following relationship:

W＝W₁W₂ (1)

where W₁ is the long-term, wideband precoding matrix and W₂ is the wideband or subband precoding matrix, which would be updated more frequently. When the CSI-RS beamforming type indicator indicates that the beamformed CSI-RS is cell-specific, then both W₁ and W₂ are selected from W₁ codebook 505 and W₂ codebook 504, stored in memory 242. Alternatively, when the CSI-RS beamforming type indicator indicates that the beamformed CSI-RS is UE-specific, the long-term, wideband precoding matrix, W₁, is fixed and depends on N_k. eNB 500 will identify the fixed matrix in the index of fixed W ₁ 503, stored in memory 242. Thus, eNB 500 would identify the fixed matrix using N_k. W₂ may then be selected from W₂ codebook 504. With the fixed W₁ and the selected W₂, eNB 500 may then calculate the precoder W.

At block 404, the base station, eNB 500, may then transmit data to the one or more UEs according to one or more transmission parameters selected based, at least in part, on the precoder. The precoder and additional CSI feedback may then be used by eNB 500 to adjust transmission parameters for improving communications with the UEs being served.

FIG. 6 is a block diagram illustrating a UE 600 configured according to one aspect of the present disclosure. As described with respect to FIGs. 4 and 5, UE 600 includes various components, hardware, and software that, when executed and controlled by controller/processor 280, will generate the operational environment that provides the features and functionalities of UE 600. UE 600, under control of controller/processor 280, will monitor for CSI-RS using antennas 252a-r and wireless radios 601a-r. Wireless radios 601a-r include additional components and hardware, as illustrated in FIG. 2 for UE 120. For example, wireless radios 601a-r may include demodulator/modulators 254a-r, MIMO detector 256, receive processor 258, transmit processor 264, and TX MIMO processor 266.

UE 600 executes measurement logic 602, stored in memory 282, to measure the long term quality of each CSI-RS resources detected, in order to select the CSI-RS resource for reporting CSI-RS feedback. The execution environment of measurement logic 602 will also direct UE 600 to measure and determine the CQI/PMI/RI for the selected CSI-RS resources. The measured parameters may then be compiled into CSI feedback by execution of CSI report generator 603 from memory 282 by controller/processor 280. The CSI feedback report may then be transmitted by wireless radios 601a-r and antennas 252a-r. Depending on whether the CSI-RS beamforming type indicator indicates the CSI-RS is cell-specific or UE-specific, the precoder, W, for transmission and selecting PMI/RI, and the like may either be calculated from W₁ and W₂ each selected from W₁ codebook 606 and W₂ codebook 605, respectively, when the beamformed CSI-RS is cell-specific, or the UE may select W₂ from W₂ codebook 605 and identify a fixed W₁ in index of fixed W ₁ 604, when the beamformed CSI-RS is UE-specific.

FIGs. 7A and 7B are block diagrams illustrating

example resource allocations

70 and 71 and reporting for FD-MIMO by a UE configured according to one aspect of the present disclosure. The UE, such as UE 600 detects CSI-RS transmissions in CSI-

RS resources

0 and 1. In resource allocation 70 of FIG. 7A, CSI-RS resource 0 includes four antenna ports (N₀＝4) , P0-P3, while CSI-RS resource 1 includes two antenna ports (N₁＝2) . In resource allocation 70, the UE, such as UE 600 selects CSI-RS resource 0 for measuring and reporting CSI. UE 600 will indicate this selection by transmitting the beam selection indicator 701 (k ＝0). Resource allocation 70 also reflects an example rank reporting of Rank-1 or -2 with port selection of antenna ports P0 and P2, as identified by PMI 700. PMI 700 may also indicate the co-phasing between antennas ports P0 and P2.

Resource allocation 71 of FIG. 7B reflects a special case of Rank-3 or 4 with all ports selected. A UE, such as UE 600 would select CSI-RS resource 0 and transmit beam selection indicator 703 identifying such resource selection. PMI 702 reported by UE 600 would identify that all of the antenna ports of CSI-RS resource 0 are selected and provides co-phasing for between antenna ports.

FIG. 8 is a block diagram illustrating example blocks executed to implement one aspect of the present disclosure. The CSI feedback reporting procedure illustrated according to one aspect may operate with either cell-specific beamformed CSI-RS and UE-specific beamformed CSI-RS. At alternative block 800a, in a first option, a UE, such as UE 600, may detect a plurality of cell-specific CSI-RS resources. In a second option, at alternative 800b, UE 600 may detect a plurality of UE-specific CSI-RS resources. The UE determines whether the CSI-RS resources are cell-specific or UE-specific by receiving and reading the CSI-RS beamforming type indicator from the serving base station.

At block 801, the UE, such as UE 600, selects one of the plurality of CSI-RS resources, whether cell-specific beamformed from alternative block 800a, or UE-specific beamformed from alternative block 800b, for reporting CSI feedback. The UE 600 selects a particular cell-specific or UE-specific CSI-RS resource by performing measurements of the long-term quality of each resource. UE 600 may then select the resource with the best available long-term quality.

At block 802, UE 600 measures the selected one of the plurality of CSI-RS resources for obtaining the CSI, such as CQI/PMI/RI.

At block 803, the UE, such as UE 600, transmits the CSI feedback to a serving base station, wherein the CSI feedback includes at least, one of: a beam selection indicator identifying the selected one of the plurality of CSI-RS resources, a RI, a first PMI (reported for cell-specific CSI-RS) , one or more second PMI, or a CQI. The CSI feedback may be transmitted by UE 600 in multiple report messages in which the configuration of the messages may depend on whether the CSI-RS resources are cell-specific or UE-specific, and the configured transmission mode.

FIG. 9 is a block diagram illustrating transmission stream 90 from a UE configured according to one aspect of the present disclosure. The UE transmitting CSI report messaging in transmission stream 90 is transmitting CSI reporting based on cell-specific beamformed CSI-RS on PUCCH Mode 1-1. For cell-specific beamformed CSI-RS, the beam selection is generally wideband and long-term. Therefore, for CSI feedback on PUCCH, aspects of the present disclosure provide for transmitting beam selection indicator (BI) feedback. One option may be to have an independent beam selection indicator reporting with a long period. However, this approach may have a few disadvantages. Firstly, there is potential rank mismatch during two beam selection indicator reports. For example, the last reported RI may not be appropriate for the latest beam selection indicator. Secondly, the impact of an error in a beam selection indicator report would be substantial, because the CQI/PMI/RI are dependent on the reported RI.

Therefore, according to the various aspects of the present disclosure, as illustrated in transmission stream 90 from a UE configured according to one aspect of the present disclosure, the beam selection indicator is multiplexed in the first CSI reporting message with the RI. Considering the impact on PUCCH performance, the size of the beam selection indicator may be selected as 1 bit for beam selection indicator feedback on PUCCH. The multiplexed first message with the beam selection indicator and RI are transmitted at a period of M_RI·N_pd subframes. The period for the second report message including the wideband CQI and first and second PMI is N_pd subframes over a total of (M_RI–1) reports.

FIGs. 10A and 10B are block diagrams illustrating

transmission streams

1000 and 1001 from a UE configured according to one aspect of the present disclosure. The UE, such as UE 600 transmitting CSI feedback reports in

transmission streams

1000 and 1001 are providing CSI reporting based on cell-specific beamformed CSI-RS on PUCCH Mode 2-1. In reporting CSI feedback according to one aspect of the present disclosure on PUCCH Mode 2-1, the first report includes RI, BI. and a precoding type indicator (PTI) . The value of the PTI will determine the content of the second and third report messages for the CSI reporting. For example, as illustrated in transmission stream 1000, PTI has a value of 0. In such circumstances, with PTI＝0, the second report of the CSI reporting will include the first PMI, while the third report will include wideband CQI and the second PMI. For operations in which PTI＝1, such as in transmission stream 1001, the second report of the CSI reporting will include wideband CQI and second PMI, while the third report will include subband CQI and second PMI.

As illustrated in FIGs. 10A and 10B, the first report of CSI feedback of cell-specific beamformed CSI-RS on PUCCH Mode 2-1 are transmitted at a period of M_RI·H·N_pd subframes. The second report is transmitted at a period of H·N_pd subframes, and the third report is transmitted at a period of N_pd for (H–1) reports.

FIG. 11 is a block diagram illustrating transmission stream 1100 from a UE configured according to one aspect of the present disclosure. The UE, such as UE 600, that may transmit CSI feedback reports in transmission stream 1100 are providing CSI reporting based on UE-specific beamformed CSI-RS on PUCCH Mode 1-1. In reporting CSI feedback according to one aspect of the present disclosure on PUCCH Mode 1-1, the first report includes the RI, while the second report alternates between the beam selection indicator and wideband PMI and CQI. The beam selection indicator reporting and wideband CQI/PMI reporting have the same reporting periodicity of N_pd subframes. The alternating beam selection indicator reporting and wideband CQI/PMI reporting are multiplexed in time over a total of (M_RI–1) reports. The first report, including RI, is transmitted according to a period of M_RI·N_pd subframes.

FIG. 12 is a block diagram illustrating transmission stream 1200 from a UE configured according to one aspect of the present disclosure. The UE, such as UE 600, that may transmit the CSI feedback reports in transmission stream 1200 are providing CSI reporting based on UE-specific beamformed CSI-RS on PUCCH Mode 2-1. In reporting CSI feedback according to one aspect of the present disclosure on PUCCH Mode 2-1, the first report includes RI, while the second report includes two consecutive sub-reports. The first sub-report includes a beam selection indicator, while the second sub-report includes wideband CQI/PMI. A third report is also transmitted with the UE-specific beamformed CSI-RS on PUCCH Mode 2-1 including subband CQI. The first report of RI is transmitted at a period of M_RI·H·N_pd subframes. The second report, including the two sub-reports, is transmitted at a period of H·N_pd subframes with a timer interval between the two sub-reports is N_pd subframes. The third report is transmitted at a period of N_pd subframes for a total of (H –2) reports.

For UE-specific beamformed CSI-RS, for which the CSI feedback is measured and transmitted in FIGs. 11 and 12, the beam selection can be wideband but with short period because the UE-specific beam is generally narrow. Therefore, the beam selection indicator feedback could be different from cell-specific beamformed CSI-RS. Various aspects of the present disclosure are proposed to have the same reporting periodicity as PMI/CQI for the beam selection indicator reporting, and beam selection indicator feedback is time multiplexed with wideband CQI/PMI. FIGs. 11 and 12 illustrate examples of extensions of PUCCH modes 1-1 and 2-1 for supporting UE-specific beamformed CSI-RS. In such case, the maximum size of beam selection indicator may be more than 1 bit, e.g., 2 bits or 3 bits. It may also be possible to configure multiple PUCCH cyclic shift resources to correspond to different beam selections. The selection of PUCCH resources can be based on the reported beam selection indicator. In such case, the same PUCCH reporting types and modes for 2-port and 4-port CSI-RS can be reused for UE-specific beamformed CSI-RS.

It should be noted that the various periodicities for the CSI report messages illustrated in FIGs. 9-12 may be configured by higher-layer signaling.

Both cell-and UE-specific beamformed CSI-RS based CSI reporting can be supported with the various aspects of the present disclosure as described herein. The aspects of the present disclosure allow for the CSI-RS resources to be dynamically shared among multiple UEs. The effective ports for CSI reporting are selected by both the beam selection indicator and the PMI.

FIG. 13 is a block diagram illustrating two UEs configured according to one aspect of the present disclosure. CSI-

RS resources

0, 1, and 2 are allocated to UE #1 and UE #2 according to resource allocation 1300. For example, UE #1 is configured with CSI-

RS resources

0 and 1, while UE #2 is configured with CSI-

RS resources

1 and 2. UEs #1 and #2 share the CSI-RS resource 1. The CSI-RSs on

antenna ports

0 and 1 are beamformed specifically for UE #1, while the CSI-RSs on

antenna ports

2 and 3 are beamformed specifically for UE #2. This resource sharing is transparent to both UEs and both UEs use 4-port codebook for CSI reporting if CSI-RS resource 1 is selected. Port selection within CSI-RS resource 1 may be achieved by proper design of the 4-port codebook.

In furtherance of the details and description of the various aspects of the present disclosure, the following numbered statements 51-100 are provided in support and further description of the various aspects of the present disclosure:

51. A non-transitory computer-readable medium having program code recorded thereon, the program code comprising: program code for causing a computer to transmit one or more beamformed channel state information (CSI) -reference signal (RS) and a CSI-RS beamforming type indicator to one or more UEs within a coverage area； program code for causing the computer to receive a beam selection indicator from the one or more UEs, wherein the beam selection indicator identifies one of a plurality of CSI-RS resources selected by the one or more UEs on which to report CSI； program code for causing the computer to receive a precoding matrix indicator (PMI) from the one or more UEs, wherein the PMI is associated with the selected one of the plurality of CSI-RS resources； program code for causing the computer to determine a precoder based, at least in part, on the beam selection indicator, the PMI, and the CSI-RS beamforming type indicator； and program code for causing the computer to transmit data to the one or more UEs according to one or more transmission parameters selected based, at least in part, on the precoder.

52. The non-transitory computer-readable medium of numbered statement 51, wherein the CSI-RS beamforming type indicator indicates that the one or more beamformed CSI-RS is one of: cell-specific or UE-specific.

53. The non-transitory computer-readable medium of numbered statement 52, wherein the CSI-RS beamforming type indicator indicates the one or more beamformed CSI-RS are cell-specific, wherein, the program code for causing the computer to receive the PMI includes program code for causing the computer to receive a first PMI and one or more second PMI.

54. The non-transitory computer-readable medium of numbered statement 52, wherein the CSI-RS beamforming type indicator indicates the one or more beamformed CSI-RS are UE-specific, wherein the program code for causing the computer to receive the PMI includes program code for causing the computer to receive a second PMI.

55. The non-transitory computer-readable medium of numbered statement 54, wherein the program code for causing the computer to determine the precoder includes: program code for causing the computer to identify a fixed precoding matrix, wherein the fixed precoding matrix corresponds to a total number of antenna ports assigned to the selected one of the plurality of CSI-RS resources； and program code for causing the computer to calculate the precoder using the fixed precoding matrix, the beam selection indicator, and the PMI received from the one or more UEs.

56. The non-transitory computer-readable medium of numbered statement 51, further including: program code for causing the computer to receive at least a channel quality indicator (CQI) and a rank indicator (RI) from the one or more UEs, wherein the one or more transmission parameters are selected based further on the CQI and RI.

57. The non-transitory computer-readable medium of any combination of numbered statements 51-56.

58. A non-transitory computer-readable medium having program code recorded thereon, the program code comprising: program code for causing a computer to detect a plurality of cell-specific channel state information (CSI) -reference signal (RS) resources； program code for causing the computer to select one of the plurality of cell-specific CSI-RS resources for reporting CSI feedback； program code for causing the computer to measure the selected one of the plurality of cell-specific CSI-RS resources； and program code for causing the computer to transmit the CSI feedback to a serving base station, wherein the CSI feedback includes at least one of: a beam selection indicator identifying the selected one of the plurality of cell-specific CSI-RS resources, a rank indicator (RI) , a first precoding matrix indicator (PMI) , one or more second PMI, and a channel quality indicator (CQI) .

59. The non-transitory computer-readable medium of numbered statement 58, wherein the CSI feedback includes at least two CSI report messages when the CSI feedback is transmitted on a physical uplink control channel (PUCCH) .

60. The non-transitory computer-readable medium of numbered statement 59, wherein a first report of the at least two CSI report messages includes the RI multiplexed with the beam selection indicator, and wherein the first report is transmitted at a first periodicity, and wherein a second report of the at least two CSI report messages includes one or more of a wideband CQI, the first PMI, and a second PMI, and wherein the second report is transmitted at a second periodicity which is shorter than the first periodicity.

61. The non-transitory computer-readable medium of numbered statement 60, wherein the beam selection indicator reported in the first report is subsampled.

62. The non-transitory computer-readable medium of numbered statement 59, wherein the RI and the beam selection indicator of the first report are further multiplexed with a precoding type indicator, and wherein the second report is divided into a second report message transmitted at a second periodicity shorter than the first periodicity and a third report message transmitted at a third periodicity shorter than the second periodicity.

63. The non-transitory computer-readable medium of numbered statement 62, wherein contents of the second report message and the third report message are determined based on a value of the precoding type indicator.

64. The non-transitory computer-readable medium of numbered statement 63, wherein, when the precoding type indicator equals 0, the second report message includes the first PMI, and the third report message includes the wideband CQI and the second PMI, and wherein, when the precoding type indicator equals 1, the second report message includes the wideband CQI and the second PMI, and the third report message includes a subband CQI and the second PMI.

65. The non-transitory computer-readable medium of numbered statement 62, further including: program code for causing the computer to receive one or more configuration signals from the serving base station on which the first periodicity, the second periodicity, and the third periodicity are based.

66. The non-transitory computer-readable medium of any combination of numbered statements 58-65.

67. A non-transitory computer-readable medium having program code recorded thereon, the program code comprising: program code for causing a computer to detect a plurality of user equipment (UE) -specific channel state information (CSI) -reference signal (RS) resources； program code for causing the computer to select one of the plurality of UE-specific CSI-RS resources for reporting CSI feedback； program code for causing the computer to measure the selected one of the plurality of UE-specific CSI-RS resources； and program code for causing the computer to transmit the CSI feedback to a serving base station, wherein the CSI feedback includes at least, one of: a beam selection indicator identifying the selected one of the plurality of UE-specific CSI-RS resources, a rank indicator (RI) , one or more second precoding matrix indicator (PMI) , and a channel quality indicator (CQI) .

68. The non-transitory computer-readable medium of numbered statement 67, wherein the one or more second PMI identifies at least a set of antenna ports associated with the selected one of the plurality of CSI-RS resources.

69. The non-transitory computer-readable medium of numbered statement 67, wherein the CSI feedback includes at least two CSI report messages when the CSI feedback is transmitted on a physical uplink control channel (PUCCH) .

70. The non-transitory computer-readable medium of numbered statement 69, wherein a first report of the at least two CSI report messages includes the RI transmitted at a first periodicity, and wherein a second report of the at least two CSI report messages includes a first sub-report having a beam selection indicator identifying the selected one of the plurality of CSI-RS resources, and a second sub-report having a wideband CQI and a second PMI.

71. The non-transitory computer-readable medium of numbered statement 70, wherein the first sub-report and the second sub-report are time interleaved at a second periodicity, wherein the second periodicity is shorter than the first periodicity.

72. The non-transitory computer-readable medium of numbered statement 71, wherein the first sub-report and the second sub-report alternate for a predetermined number of subframes.

73. The non-transitory computer-readable medium of numbered statement 69, wherein a third report of the at least two CSI report messages includes a subband CQI transmitted at a third periodicity for a predetermined number of subframes, wherein the third periodicity is shorter than the second periodicity.

74. The non-transitory computer-readable medium of numbered statement 73, further including:

program code for causing the computer to receive one or more configuration signals from the serving base station on which the first periodicity, the second periodicity, and the third periodicity are based

75. The non-transitory computer-readable medium of any combination of numbered statements 67-74.

76. An apparatus configured for wireless communication, the apparatus comprising: at least one processor； and a memory coupled to the at least one processor, wherein the at least one processor is configured: to transmit one or more beamformed channel state information (CSI) -reference signal (RS) and a CSI-RS beamforming type indicator to one or more UEs within a coverage area； to receive a beam selection indicator from the one or more UEs, wherein the beam selection indicator identifies one of a plurality of CSI-RS resources selected by the one or more UEs on which to report CSI； to receive a precoding matrix indicator (PMI) from the one or more UEs, wherein the PMI is associated with the selected one of the plurality of CSI-RS resources； to determine a precoder based, at least in part, on the beam selection indicator, the PMI, and the CSI-RS beamforming type indicator； and to transmit data to the one or more UEs according to one or more transmission parameters selected based, at least in part, on the precoder.

77. The apparatus of numbered statement 76, wherein the CSI-RS beamforming type indicator indicates that the one or more beamformed CSI-RS is one of: cell-specific or UE-specific.

78. The apparatus of numbered statement 77, wherein the CSI-RS beamforming type indicator indicates the one or more beamformed CSI-RS are cell-specific, wherein, the configuration of the at least one processor to receive the PMI includes configuration to receive a first PMI and one or more second PMI.

79. The apparatus of numbered statement 77, wherein the CSI-RS beamforming type indicator indicates the one or more beamformed CSI-RS are UE-specific, wherein the configuration of the at least one processor to receive the PMI includes configuration to receive one or more second PMI.

80. The apparatus of numbered statement 79, wherein the configuration of the at least one processor to determine the precoder includes configuration of the at least one processor: to identify a fixed precoding matrix, wherein the fixed precoding matrix corresponds to a total number of antenna ports assigned to the selected one of the plurality of CSI-RS resources； and to calculate the precoder using the fixed precoding matrix, the beam selection indicator, and the PMI received from the one or more UEs.

81. The apparatus of numbered statement 76, wherein the at least one processor is further configured to receive at least a channel quality indicator (CQI) and a rank indicator (RI) from the one or more UEs, wherein the one or more transmission parameters are selected based further on the CQI and RI.

82. The apparatus of any combination of numbered statements 76-81.

83. An apparatus configured for wireless communication, the apparatus comprising: at least one processor； and a memory coupled to the at least one processor,

wherein the at least one processor is configured: to detect a plurality of cell-specific channel state information (CSI) -reference signal (RS) resources； to select one of the plurality of cell-specific CSI-RS resources for reporting CSI feedback； to measure the selected one of the plurality of cell-specific CSI-RS resources； and to transmit the CSI feedback to a serving base station, wherein the CSI feedback includes at least one of: a beam selection indicator identifying the selected one of the plurality of cell-specific CSI-RS resources, a rank indicator (RI) , a first precoding matrix indicator (PMI) , one or more second PMI, and a channel quality indicator (CQI) .

84. The apparatus of numbered statement 83, wherein the CSI feedback includes at least two CSI report messages when the CSI feedback is transmitted on a physical uplink control channel (PUCCH) .

85. The apparatus of numbered statement 84, wherein a first report of the at least two CSI report messages includes the RI multiplexed with the beam selection indicator, and wherein the first report is transmitted at a first periodicity, and wherein a second report of the at least two CSI report messages includes one or more of a wideband CQI, the first PMI, and a second PMI, and wherein the second report is transmitted at a second periodicity which is shorter than the first periodicity.

86. The apparatus of numbered statement 85, wherein the beam selection indicator reported in the first report is subsampled.

87. The apparatus of numbered statement 84, wherein the RI and the beam selection indicator of the first report are further multiplexed with a precoding type indicator, and wherein the second report is divided into a second report message transmitted at a second periodicity shorter than the first periodicity and a third report message transmitted at a third periodicity shorter than the second periodicity.

88. The apparatus of numbered statement 87, wherein contents of the second report message and the third report message are determined based on a value of the precoding type indicator.

89. The apparatus of numbered statement 88, wherein, when the precoding type indicator equals 0, the second report message includes the first PMI, and the third report message includes the wideband CQI and the second PMI, and wherein, when the precoding type indicator equals 1, the second report message includes the wideband CQI and the second PMI, and the third report message includes a subband CQI and the second PMI.

90. The apparatus of numbered statement 87, wherein the at least one processor is further configured to receive one or more configuration signals from the serving base station on which the first periodicity, the second periodicity, and the third periodicity are based.

91. The apparatus of any combination of numbered statements 83-90.

92. An apparatus configured for wireless communication, the apparatus comprising: at least one processor； and a memory coupled to the at least one processor, wherein the at least one processor is configured: to detect a plurality of user equipment (UE) -specific channel state information (CSI) -reference signal (RS) resources； to select one of the plurality of UE-specific CSI-RS resources for reporting CSI feedback； to measure the selected one of the plurality of UE-specific CSI-RS resources； and to transmit the CSI feedback to a serving base station, wherein the CSI feedback includes at least, one of: a beam selection indicator identifying the selected one of the plurality of UE-specific CSI-RS resources, a rank indicator (RI) , one or more second precoding matrix indicator (PMI) , and a channel quality indicator (CQI) .

93. The apparatus of numbered statement 92, wherein the one or more second PMI identifies at least a set of antenna ports associated with the selected one of the plurality of CSI-RS resources.

94. The apparatus of numbered statement 92, wherein the CSI feedback includes at least two CSI report messages when the CSI feedback is transmitted on a physical uplink control channel (PUCCH) .

95. The apparatus of numbered statement 94, wherein a first report of the at least two CSI report messages includes the RI transmitted at a first periodicity, and wherein a second report of the at least two CSI report messages includes a first sub-report having a beam selection indicator identifying the selected one of the plurality of CSI-RS resources, and a second sub-report having a wideband CQI and a second PMI.

96. The apparatus of numbered statement 95, wherein the first sub-report and the second sub-report are time interleaved at a second periodicity, wherein the second periodicity is shorter than the first periodicity.

97. The apparatus of numbered statement 96, wherein the first sub-report and the second sub-report alternate for a predetermined number of subframes.

98. The apparatus of numbered statement 94, wherein a third report of the at least two CSI report messages includes a subband CQI transmitted at a third periodicity for a predetermined number of subframes, wherein the third periodicity is shorter than the second periodicity.

99. The apparatus of numbered statement 98, wherein the at least one processor is further configured to receive one or more configuration signals from the serving base station on which the first periodicity, the second periodicity, and the third periodicity are based.

100. The apparatus of any combination of numbered statements 92-99.

Those of skill in the art would understand that information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

The functional blocks and modules in FIGs. 5-7 may comprise processors, electronics devices, hardware devices, electronics components, logical circuits, memories, software codes, firmware codes, etc., or any combination thereof.

Those of skill would further appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the disclosure herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present disclosure. Skilled artisans will also readily recognize that the order or combination of components, methods, or interactions that are described herein are merely examples and that the components, methods, or interactions of the various aspects of the present disclosure may be combined or performed in ways other than those illustrated and described herein.

The various illustrative logical blocks, modules, and circuits described in connection with the disclosure herein may be implemented or performed with a general-purpose processor, a digital signal processor (DSP) , an application specific integrated circuit (ASIC) , a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

The steps of a method or algorithm described in connection with the disclosure herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a user terminal. In the alternative, the processor and the storage medium may reside as discrete components in a user terminal.

In one or more exemplary designs, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Computer-readable media includes both computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. Computer-readable storage media may be any available media that can be accessed by a general purpose or special purpose computer. By way of example, and not limitation, such computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code means in the form of instructions or data structures and that can be accessed by a general-purpose or special-purpose computer, or a general-purpose or special-purpose processor. Also, a connection may be properly termed a computer-readable medium. For example, if the software is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, or digital subscriber line (DSL) , then the coaxial cable, fiber optic cable, twisted pair, or DSL, are included in the definition of medium. Disk and disc, as used herein, includes compact disc (CD) , laser disc, optical disc, digital versatile disc (DVD) , floppy disk and blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media.

As used herein, including in the claims, the term “and/or, ” when used in a list of two or more items, means that any one of the listed items can be employed by itself, or any combination of two or more of the listed items can be employed. For example, if a composition is described as containing components A, B, and/or C, the composition can contain A alone； B alone； C alone； A and B in combination； A and C in combination； B and C in combination； or A, B, and C in combination. Also, as used herein, including in the claims, “or” as used in a list of items prefaced by “at least one of” indicates a disjunctive list such that, for example, a list of “at least one of A, B, or C” means A or B or C or AB or AC or BC or ABC (i.e., A and B and C) or any of these in any combination thereof.

The previous description of the disclosure is provided to enable any person skilled in the art to make or use the disclosure. Various modifications to the disclosure will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other variations without departing from the spirit or scope of the disclosure. Thus, the disclosure is not intended to be limited to the examples and designs described herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

WHAT IS CLAIMED IS:

Claims

A method of wireless communication, comprising:

transmitting one or more beamformed channel state information (CSI) -reference signal (RS) and a CSI-RS beamforming type indicator to one or more UEs within a coverage area；

receiving a beam selection indicator from the one or more UEs, wherein the beam selection indicator identifies one of a plurality of CSI-RS resources selected by the one or more UEs on which to report CSI；

receiving a precoding matrix indicator (PMI) from the one or more UEs, wherein the PMI is associated with the selected one of the plurality of CSI-RS resources；

determining a precoder based, at least in part, on the beam selection indicator, the PMI, and the CSI-RS beamforming type indicator； and

transmitting data to the one or more UEs according to one or more transmission parameters selected based, at least in part, on the precoder.
The method of claim 1, wherein the CSI-RS beamforming type indicator indicates that the one or more beamformed CSI-RS is one of: cell-specific or UE-specific.
The method of claim 2, wherein the CSI-RS beamforming type indicator indicates the one or more beamformed CSI-RS are cell-specific,

wherein, the receiving the PMI includes receiving a first PMI and one or more second PMI.
The method of claim 2, wherein the CSI-RS beamforming type indicator indicates the one or more beamformed CSI-RS are UE-specific,

wherein the receiving the PMI includes receiving one or more second PMI.
The method of claim 4, wherein the determining the precoder includes:

identifying a fixed precoding matrix, wherein the fixed precoding matrix corresponds to a total number of antenna ports assigned to the selected one of the plurality of CSI-RS resources； and

calculating the precoder using the fixed precoding matrix, the beam selection indicator, and the PMI received from the one or more UEs.
The method of claim 1, further including:

receiving at least a channel quality indicator (CQI) and a rank indicator (RI) from the one or more UEs, wherein the one or more transmission parameters are selected based further on the CQI and RI.
The method of any combination of claims 1-6.
A method of wireless communication, comprising:

detecting a plurality of cell-specific channel state information (CSI) -reference signal (RS) resources；

selecting one of the plurality of cell-specific CSI-RS resources for reporting CSI feedback；

measuring the selected one of the plurality of cell-specific CSI-RS resources； and

transmitting the CSI feedback to a serving base station, wherein the CSI feedback includes at least one of: a beam selection indicator identifying the selected one of the plurality of cell-specific CSI-RS resources, a rank indicator (RI) , a first precoding matrix indicator (PMI) , one or more of a second PMI, and a channel quality indicator (CQI) .
The method of claim 8, wherein the CSI feedback includes at least two CSI report messages when the CSI feedback is transmitted on a physical uplink control channel (PUCCH) .
The method of claim 9, wherein a first report of the at least two CSI report messages includes the RI multiplexed with the beam selection indicator, and wherein the first report is transmitted at a first periodicity, and

wherein a second report of the at least two CSI report messages includes one or more of a wideband CQI, the first PMI, and a second PMI, and wherein the second report is transmitted at a second periodicity which is shorter than the first periodicity.
The method of claim 10, wherein the beam selection indicator reported in the first report is subsampled.
The method of claim 9,

wherein the RI and the beam selection indicator of the first report are further multiplexed with a precoding type indicator, and

wherein the second report is divided into a second report message transmitted at a second periodicity shorter than the first periodicity and a third report message transmitted at a third periodicity shorter than the second periodicity.
The method of claim 12, wherein contents of the second report message and the third report message are determined based on a value of the precoding type indicator.
The method of claim 13,

wherein, when the precoding type indicator equals 0, the second report message includes the first PMI, and the third report message includes the wideband CQI and the second PMI, and

wherein, when the precoding type indicator equals 1, the second report message includes the wideband CQI and the second PMI, and the third report message includes a subband CQI and the second PMI.
The method of claim 12, further including:

receiving one or more configuration signals from the serving base station on which the first periodicity, the second periodicity, and the third periodicity are based.
The method of any combination of claims 8-15.
A method of wireless communication, comprising:

detecting a plurality of user equipment (UE) -specific channel state information (CSI) -reference signal (RS) resources；

selecting one of the plurality of UE-specific CSI-RS resources for reporting CSI feedback；

measuring the selected one of the plurality of UE-specific CSI-RS resources； and

transmitting the CSI feedback to a serving base station, wherein the CSI feedback includes at least, one of: a beam selection indicator identifying the selected one of the plurality of UE-specific CSI-RS resources, a rank indicator (RI) , one or more second precoding matrix indicator (PMI) , and a channel quality indicator (CQI) .
The method of claim 17, wherein the one or more second PMI identifies at least a set of antenna ports associated with the selected one of the plurality of CSI-RS resources；
The method of claim 17, wherein the CSI feedback includes at least two CSI report messages when the CSI feedback is transmitted on a physical uplink control channel (PUCCH) .
The method of claim 19, wherein a first report of the at least two CSI report messages includes the RI transmitted at a first periodicity, and

wherein a second report of the at least two CSI report messages includes a first sub-report having a beam selection indicator identifying the selected one of the plurality of CSI-RS resources, and a second sub-report having a wideband CQI and a second PMI.
The method of claim 20, wherein the first sub-report and the second sub-report are time interleaved at a second periodicity, wherein the second periodicity is shorter than the first periodicity.
The method of claim 21, wherein the first sub-report and the second sub-report alternate for a predetermined number of subframes.
The method of claim 19, wherein a third report of the at least two CSI report messages includes a subband CQI transmitted at a third periodicity for a predetermined number of subframes, wherein the third periodicity is shorter than the second periodicity.
The method of claim 23, further including:

receiving one or more configuration signals from the serving base station on which the first periodicity, the second periodicity, and the third periodicity are based
The method of any combination of claims 17-24.
An apparatus configured for wireless communication, comprising:

means for transmitting one or more beamformed channel state information (CSI) -reference signal (RS) and a CSI-RS beamforming type indicator to one or more UEs within a coverage area；

means for receiving a beam selection indicator from the one or more UEs, wherein the beam selection indicator identifies one of a plurality of CSI-RS resources selected by the one or more UEs on which to report CSI；

means for receiving a precoding matrix indicator (PMI) from the one or more UEs, wherein the PMI is associated with the selected one of the plurality of CSI-RS resources；

means for determining a precoder based, at least in part, on the beam selection indicator, the PMI, and the CSI-RS beamforming type indicator； and

means for transmitting data to the one or more UEs according to one or more transmission parameters selected based, at least in part, on the precoder.
The apparatus of claim 26, wherein the CSI-RS beamforming type indicator indicates that the one or more beamformed CSI-RS is one of: cell-specific or UE-specific.
The apparatus of claim 27, wherein the CSI-RS beamforming type indicator indicates the one or more beamformed CSI-RS are cell-specific,

wherein, the means for receiving the PMI includes means for receiving a first PMI and one or more second PMI.
The apparatus of claim 27, wherein the CSI-RS beamforming type indicator indicates the one or more beamformed CSI-RS are UE-specific,

wherein the means for receiving the PMI includes means for receiving one or more second PMI.
The apparatus of claim 29, wherein the means for determining the precoder includes:

means for identifying a fixed precoding matrix, wherein the fixed precoding matrix corresponds to a total number of antenna ports assigned to the selected one of the plurality of CSI-RS resources； and

means for calculating the precoder using the fixed precoding matrix, the beam selection indicator, and the PMI received from the one or more UEs.
The apparatus of claim 26, further including:

means for receiving at least a channel quality indicator (CQI) and a rank indicator (RI) from the one or more UEs, wherein the one or more transmission parameters are selected based further on the CQI and RI.
The apparatus of any combination of claims 26-31.
An apparatus configured for wireless communication, comprising:

means for detecting a plurality of cell-specific channel state information (CSI) -reference signal (RS) resources；

means for selecting one of the plurality of cell-specific CSI-RS resources for reporting CSI feedback；

means for measuring the selected one of the plurality of cell-specific CSI-RS resources； and

means for transmitting the CSI feedback to a serving base station, wherein the CSI feedback includes at least one of: a beam selection indicator identifying the selected one of the plurality of cell-specific CSI-RS resources, a rank indicator (RI) , a first precoding matrix indicator (PMI) , one or more of a second PMI, and a channel quality indicator (CQI) .
The apparatus of claim 33, wherein the CSI feedback includes at least two CSI report messages when the CSI feedback is transmitted on a physical uplink control channel (PUCCH) .
The apparatus of claim 34, wherein a first report of the at least two CSI report messages includes the RI multiplexed with the beam selection indicator, and wherein the first report is transmitted at a first periodicity, and

wherein a second report of the at least two CSI report messages includes one or more of a wideband CQI, the first PMI, and a second PMI, and wherein the second report is transmitted at a second periodicity which is shorter than the first periodicity.
The apparatus of claim 35, wherein the beam selection indicator reported in the first report is subsampled.
The apparatus of claim 34,

wherein the RI and the beam selection indicator of the first report are further multiplexed with a precoding type indicator, and

wherein the second report is divided into a second report message transmitted at a second periodicity shorter than the first periodicity and a third report message transmitted at a third periodicity shorter than the second periodicity.
The apparatus of claim 37, wherein contents of the second report message and the third report message are determined based on a value of the precoding type indicator.
The apparatus of claim 38,

wherein, when the precoding type indicator equals 0, the second report message includes the first PMI, and the third report message includes the wideband CQI and the second PMI, and

wherein, when the precoding type indicator equals 1, the second report message includes the wideband CQI and the second PMI, and the third report message includes a subband CQI and the second PMI.
The apparatus of claim 37, further including:

means for receiving one or more configuration signals from the serving base station on which the first periodicity, the second periodicity, and the third periodicity are based.
The apparatus of any combination of claims 33-40.
An apparatus configured for wireless communication, comprising:

means for detecting a plurality of user equipment (UE) -specific channel state information (CSI) -reference signal (RS) resources；

means for selecting one of the plurality of UE-specific CSI-RS resources for reporting CSI feedback；

means for measuring the selected one of the plurality of UE-specific CSI-RS resources； and

means for transmitting the CSI feedback to a serving base station, wherein the CSI feedback includes at least, one of: a beam selection indicator identifying the selected one of the plurality of UE-specific CSI-RS resources, a rank indicator (RI) , one or more second precoding matrix indicator (PMI) , and a channel quality indicator (CQI) .
The apparatus of claim 42, wherein the one or more second PMI identifies at least a set of antenna ports associated with the selected one of the plurality of CSI-RS resources；
The apparatus of claim 42, wherein the CSI feedback includes at least two CSI report messages when the CSI feedback is transmitted on a physical uplink control channel (PUCCH) .
The apparatus of claim 44, wherein a first report of the at least two CSI report messages includes the RI transmitted at a first periodicity, and

wherein a second report of the at least two CSI report messages includes a first sub-report having a beam selection indicator identifying the selected one of the plurality of CSI-RS resources, and a second sub-report having a wideband CQI and a second PMI.
The apparatus of claim 45, wherein the first sub-report and the second sub-report are time interleaved at a second periodicity, wherein the second periodicity is shorter than the first periodicity.
The apparatus of claim 46, wherein the first sub-report and the second sub-report alternate for a predetermined number of subframes.
The apparatus of claim 44, wherein a third report of the at least two CSI report messages includes a subband CQI transmitted at a third periodicity for a predetermined number of subframes, wherein the third periodicity is shorter than the second periodicity.
The apparatus of claim 48, further including:

means for receiving one or more configuration signals from the serving base station on which the first periodicity, the second periodicity, and the third periodicity are based
The apparatus of any combination of claims 42-49.