WO2017166288A1

WO2017166288A1 - Csi-rs design for larger number of antenna ports for efd-mimo

Info

Publication number: WO2017166288A1
Application number: PCT/CN2016/078313
Authority: WO
Inventors: Chao Wei; Liangming WU; Bo Chen
Original assignee: Qualcomm Inc
Current assignee: Qualcomm Inc
Priority date: 2016-04-01
Filing date: 2016-04-01
Publication date: 2017-10-05
Anticipated expiration: 2018-10-01

Abstract

Design of channel state information (CSI) reference signal (CSI-RS) for larger number of antenna ports in enhanced full dimension multiple input, multiple output (eFD-MIMO) systems is discussed. Compatible base stations may identify a first CSI-RS resource configured for a first number of antenna ports and aggregate two or more CSI-RS resource configurations into the first CSI-RS resource. The a total number of antenna ports of the aggregated CSI-RS resource configurations equals the number of antenna ports of the CSI-RS resource and at least one of the two or more CSI-RS resource configurations has a different number of antenna ports than the other resource configurations. The base station may map the first number of antenna ports of the first CSI-RS resource to a first set of resource elements according to the CSI-RS resource configurations. The base station will then transmit the CSI-RS using the first CSI-RS resource.

Description

CSI-RS DESIGN FOR LARGER NUMBER OF ANTENNA PORTS FOR EFD-MIMO

BACKGROUND Field

Aspects of the present disclosure relate generally to wireless communication systems, and more particularly, to channel state information (CSI) reference signal (CSI-RS) design for larger number of antenna ports for enhanced full dimension multiple input, multiple output (eFD-MIMO) systems.

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 identifying a first channel state information (CSI) reference signal (CSI-RS) resource configured for a first number of antenna ports, aggregating two or more CSI-RS resource configurations into the first CSI-RS resource, wherein a total number of antenna ports of the aggregated two or more CSI-RS resource configurations equals the first number of antenna ports and at least one of the two or more CSI-RS resource configurations has a different number of antenna ports than the other of the two or more CSI-RS resource configurations, mapping the first number of antenna ports of the first CSI-RS resource to a first set of resource elements according to the two or more CSI-RS resource configurations, and transmitting a CSI-RS using the first CSI-RS resource.

In an additional aspect of the disclosure, an apparatus configured for wireless communication, including means for identifying a first CSI-RS resource configured for a first number of antenna ports, means for aggregating two or more CSI-RS resource configurations into the first CSI-RS resource, wherein a total number of antenna ports of the aggregated two or more CSI-RS resource configurations equals the first number of antenna ports and at least one of the two or more CSI-RS resource configurations has a different number of antenna ports than the other of the two or more CSI-RS resource configurations, means for mapping the first number of antenna ports of the first CSI-RS resource to a first set of resource elements according to the two or more CSI-RS resource configurations, and means for transmitting a CSI-RS using the first CSI-RS resource.

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 identify a first CSI-RS resource configured for a first number of antenna ports, code to aggregate two or more CSI-RS resource configurations into the first CSI-RS resource, wherein a total number of antenna ports of the aggregated two or more CSI-RS resource configurations equals the first number of antenna ports and at least one of the two or more CSI-RS resource configurations has a different number of antenna ports than the other of the two or more CSI-RS resource configurations, code to map the first number of antenna ports of the first CSI-RS resource to a first set of resource elements according to the two or more CSI-RS resource configurations, and code to transmit a CSI-RS using the first CSI-RS resource.

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 identify a first CSI-RS resource configured for a first number of antenna ports, to aggregate two or more CSI-RS resource configurations into the first CSI-RS resource, wherein a total number of antenna ports of the aggregated two or more CSI-RS resource configurations equals the first number of antenna ports and at least one of the two or more CSI-RS resource configurations has a different number of antenna ports than the other of the two or more CSI-RS resource configurations, to map the first number of antenna ports of the first CSI-RS resource to a first set of resource elements according to the two or more CSI-RS resource configurations, and to transmit a CSI-RS using the first CSI-RS resource.

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. 4A is a block diagram illustrating an example base station transmitting non-precoded CSI-RS.

FIG. 4B is a block diagram illustrating an example base station transmitting beamformed CSI-RS using CSI-RS resources.

FIG. 5 is a block diagram illustrating different port configurations and for a 12-port CSI-RS resource.

FIGs. 6A and 6B are block diagrams illustrating example aggregation of multiple 4-port CSI-RS resources into a 12-port CSI-RS resource.

FIGs. 7A and 7B are block diagrams illustrating the difference between antenna to RE mapping between a 20-port CSI-RS resource and a 16-port CSI-RS resource.

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

FIGs. 9A and 9B are block diagrams illustrating the antenna to RE mapping of an aggregated 20-port CSI-RS resource by a base station configured according to one aspect of the present disclosure.

FIG. 10 is a block diagram illustrating example blocks executed to implement one aspect of the present disclosure.

FIGs. 11A and 11B are block diagrams illustrating the antenna to RE mapping of aggregated 20-port CSI-RS resource by a base station configured according to one aspect of the present disclosure.

FIG. 12 is a block diagram illustrating an eNB 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 aspects, 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 (Ainterfaces, 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-A including in unlicensed spectrum has also been suggested that can be compatible with carrier-grade WiFi, making LTE/LTE-A with 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-A networks 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-A network. The wireless network 100 includes a number of evolved node Bs (eNBs) 105 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 105 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 or a small cell, such as a pico cell or 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 small cell, such as 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 small cell, such as 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 small cell may be referred to as a small cell eNB, a pico eNB, a femto eNB or a home eNB. In the example shown in FIG. 1, the

eNBs

105a, 105b and 105c are macro eNBs for the

macro cells

110a, 110b and 110c, respectively. The eNBs 105x, 105y, and 105z are small cell eNBs, which may include pico or femto eNBs that provide service to

small cells

110x, 110y, and 110z, respectively. An eNB may support one or multiple (e.g., two, three, four, and the like) cells.

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 115 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 lightning bolt (e.g., communication links 125) indicates wireless transmissions between a UE and a serving eNB, which is an eNB designated to serve the UE on the downlink and/or uplink, or desired transmission between eNBs. Wired backhaul communication 134 indicate wired backhaul communications that may occur between eNBs.

LTE/-A utilizes 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 (X) 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 (X) may be dependent on the system bandwidth. For example, X 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 105 and a UE 115, which may be one of the base stations/eNBs and one of the UEs in FIG. 1. For a restricted association scenario, the eNB 105 may be the small cell eNB 105z in FIG. 1, and the UE 115 may be the UE 115z, which in order to access small cell eNB 105z, would be included in a list of accessible UEs for small cell eNB 105z. The eNB 105 may also be a base station of some other type. The eNB 105 may be equipped with antennas 234a through 234t, and the UE 115 may be equipped with antennas 252a through 252r.

At the eNB 105, 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 115, the antennas 252a through 252r may receive the downlink signals from the eNB 105 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 115 to a data sink 260, and provide decoded control information to a controller/processor 280.

On the uplink, at the UE 115, 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 105. At the eNB 105, the uplink signals from the UE 115 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 115. 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 105 and the UE 115, respectively. The controller/processor 240 and/or other processors and modules at the eNB 105 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 115 may also perform or direct the execution of the functional blocks illustrated in FIGs. 8 and 10, and/or other processes for the techniques described herein. The

memories

242 and 282 may store data and program codes for the eNB 105 and the UE 115, 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, such as CSI-RS resource configuration and transmission mode. The CSI-RS are periodically transmitted at periodicities of 5, 10, 20, 40, 80 ms, or the like. 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 and may be reported either periodically or aperiodically, with potentially different granularity. 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. Providing dynamic beam steering in the vertical direction has been shown to result in significant gain in interference avoidance. Thus, FD-MIMO technologies may take advantage of both azimuth and elevation beamforming, which would greatly improve MIMO system capacity and signal quality.

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.

For CSI reporting in systems having FD-MIMO, a CSI process may be configured with either of two CSI reporting classes, class A non-precoded or class B beamformed. FIG. 4A is a block diagram illustrating an example base station 400 transmitting non-precoded CSI-RS 401. In class A non-precoded reporting, one non-zero power (NZP) CSI-RS resource per CSI process may be used for channel measurement in which the number of CSI-RS ports may be 8, 12, or 16. Interference measurement in class A reporting may include one CSI-interference measurement (IM) resource per CSI process.

Base station 400 serves

UEs

403 and 404 and

UEs

405 and 406 in structure 40. 2D CSI-RS ports transmit non-precoded CSI-RS 401 and PDSCH 402 to UEs 403-406. In reporting CSI feedback, UEs 403-406 measure the non-precoded CSI-RS and reports CQI, precoding matrix indicator (PMI) (2D codebook) , and rank indicator to base station 400.

FIG. 4B is a block diagram illustrating an example base station 407 transmitting beamformed CSI-RS using CSI-RS resources 408-410. CSI-RS resources 408-410 may be directed to serve different UE groups, such as UE group 415, including UEs 411 and 412, and UE group 416, including

UEs

413 and 414 in structure 41. Because different CSI-RS resources are used for different UE groups, when providing CSI feedback, UEs 411-414 report CQI, PMI (1D codebook) , rank indicator, as well as the CSI-RS resource indicator (CRI) , if K > 1, which identifies to base station 407 which of the CSI-RS resources the UE has measured and provided channel state information (CSI) feedback for.

In class B beamformed CSI reporting, each CSI process may be associated with K NZP CSI-RS resources/configurations, with N_k ports for the k^th CSI-RS resource (K could be ≥ 1) , in which N_k may be 1, 2, 4, or 8, and may be different for each CSI-RS resource. Each CSI-RS resource may also have different CSI-RS port virtualization, e.g., virtualized from different sets of antenna elements or from the same set of antenna elements but with different beamforming weights. Multiple CSI-IM per CSI process is also possible, with one-to-one linkage to each NZP CSI-RS resource.

For CSI-RS design, two things to be considered: port indexing and resource configuration with associated mapping. Port indexing includes mapping of CSI-RS port to the physical antenna. In Rel. -13, port indexing may be implicitly determined by the codebook. In other words, for the configured codebook parameters (N₁, N₂) , CSI-RS port numbering is firstly along the 2^nd dimension and then the 1^st dimension and polarization. Therefore, for the same antenna array, a different configuration of (N₁, N₂) may result in a different port numbering.

FIG. 5 is a block diagram illustrating

different port configurations

50 and 51 for a 12-port CSI-RS resource. Each of the antenna arrays illustrated in

port configurations

50 and 51 is a 12-port antenna array. However, depending on which number is designated for N₁ and N₂ will result in a different configuration of antenna ports. For example, with port configuration 50, N₁＝3 and N₂＝2. Therefore, port configuration 50 begins with port 15 with port 16 being designated as the first port in the row of ports above. In contrast, because port configuration 51 uses N₁＝2 and N₂＝3, after port 15, port 16 is in the next column of antenna ports. For Rel-14 or beyond, it is expected that the rules for CSI-RS port indexing will be reused.

The second design consideration is the resource configuration and associated mapping of CSI-RS ports to the physical resource elements (REs) . In Rel-13, a 12-port or 16-port CSI-RS resource is composed as an aggregation of K Rel-12 CSI-RS resources of the same antenna ports. For example, for CSI-RS port assignment to RE, depending on the configurable code division multiplex (CDM) length (e.g., 2 or 4) , the mapping approach could be different. For a CDM length of two, cross polarized antenna ports may be assigned to each of the aggregated CSI-RS resources of 4-ports or 8-ports to allow resource sharing with legacy UEs. For a CDM length of four, consecutive 4-ports or 8-ports that may not be on same polarization may be assigned to each of the aggregated CSI-RS resources of 4-ports or 8-ports. Table 1 below indicates the resource configuration for 12-and 16-port antennas.

Table 1

FIGs. 6A and 6B are block diagrams illustrating example aggregation of multiple 4-port CSI-RS resources into a 12-port CSI-RS resource 60. CSI-RS resource 60 is a 12-port (3, 2, 2) antenna array. When configured with a code division multiplex (CDM) length of 2, as illustrated in FIG. 6A, CSI-RS resource 60 is implemented through aggregation of three 4-port CSI-RS resources 600, in which the antenna ports of the 4-port CSI-RS resources 600 are selected based on cross-polarized antenna port sets. When configured with a CDM length of 4, as illustrated in FIG. 6B, CSI-RS resource 60 is also implemented through aggregation of three 4-port CSI-RS resources 601, in which the antenna ports of the 4-port CSI-RS resources 601 are sequential by antenna port index of the ports of CSI-RS resource 60 regardless of polarization.

It should be noted that CDM length 4 is typically applied to Rel-13 12/16-port CSI-RS resources, but usually not for Rel-12 4/8-port CSI-RS resources.

For Rel-14 {20, 24, 28, 32} CSI-RS design, one design target is to reduce CSI-RS overhead. For a cell with different types of UEs supporting different numbers of CSI-RS ports, it may be beneficial that CSI-RS resources with different numbers of ports could share REs as much as possible. It should be noted that the resource sharing referred to here means that one or multiple physical antennas mapped to different CSI-RS resources are assigned to the same REs according to each associated CSI-RS resource configuration. In such resource sharing, for a cell configure with 8, 12, 16, 32 port CSI-RS for different types of UEs, the total CSI-RS overhead is not necessarily the sum of CSI-RS ports of all the configured CSI-RS resources. However, due to different port mapping approaches associated with CSI-RS resource configuration, the RE sharing among multiple CSI-RS resources with different number of ports may not always be applicable. For example, resource sharing may not work out between 12-port and 8-port CSI-RS resources or between 16-port and 4-port CSI-RS resources. Under current design principles, the aggregation of K CSI-RS resources of the same antenna ports may not be supported for RE sharing between a Rel-14 CSI-RS resources, such as 20-port CSI-RS (e.g. 5x4-ports) and a Rel-13 16-port CSI-RS (e.g. 2x8-ports) .

FIGs. 7A and 7B are block diagrams illustrating the difference between antenna to RE mapping between a 20-port CSI-RS resource 70 and a 16-port CSI-RS resource 71. 20-port CSI-RS resource 70 will be aggregated by five 4-port CSI-RS resources 700. For a (2, 5, 2) antenna array, the subarray of antenna indices 0-7 and 10-17 may be configured as 16-port CSI-RS resource 71, while the full array may be configured as 20-port CSI-RS resource 70. Following Rel-13 resource aggregation and port numbering for 20-port CSI-RS resource 70, RE mapping 702 of antennas {2, 3, 6, 7, 10, 11, 14, 15} for 16-port CSI-RS resource 71, e.g. a 2x8-port configuration, is different from RE mapping 701 of the same antennas for 20-port CSI-RS resource 70, e.g. a 5x4-port configuration. When attempting RE sharing between 20-port CSI-RS resource 70 and 16-port CSI-RS resource 71, e.g., using a 20-port CSI-RS RE mapping for a 16-port CSI-RS, then antennas {0, 1, 10, 11, 4, 5, 14, 15} will be assumed by the UE as being the same polarization for 16-port PMI feedback, which may degrade performance.

Various aspects of the present disclosure may provide for aggregation based on a hybrid port CSI-RS resource configuration. For Rel-14 CSI-RS with {20, 24, 28, 32} ports, a CSI-RS resource for CSI reporting may be composed as an aggregation of K 4-ports and/or 8-ports CSI-RS configurations, where the difference from the Rel-13 approach is that the number of ports per CSI-RS configuration could be different. The CSI-RS port to RE mapping may be based on the following equation:

where

is a number of CSI-RS antenna ports in the k^th CSI-RS resource configuration, k is a CSI-RS resource configuration index in an aggregation list ranging from 0 to K-1, K is a total number of the two or more CSI-RS resource configurations, and p and p’ are CSI-RS antenna port indices in a Rel-14 CSI-RS resource and the k^th CSI-RS resource configuration, respectively.

FIG. 8 is a block diagram illustrating example blocks executed to implement one aspect of the present disclosure. The example blocks will also be described with respect to eNB 90 as illustrated in FIG. 12. FIG. 12 is a block diagram illustrating eNB 90 configured according to one aspect of the present disclosure. eNB 90 includes the structure, hardware, and components as illustrated for UE 105 of FIG. 2. For example, eNB 90 includes controller/processor 240, which operates to execute logic or computer instructions stored in memory 242, as well as controlling the components of eNB 90 that provide the features and functionality of eNB 90. eNB 90, under control of controller/processor 240, transmits and receives signals via wireless radios 1201a-t and antennas 234a-t. Wireless radios 1201a-t includes various components and hardware, as illustrated in FIG. 2 for eNB 105, including modulator/demodulators 232a-t, MIMO detector 236, receive processor 238, transmit processor 220, and TX MIMO processor 230.

At block 800, an eNB, such as eNB 90, identifies a first CSI-RS resource configured for a first number of antenna ports. Multiple CSI-RS resources may be configured and stored by eNB 90 in memory 242 in order to accommodate CSI-RS feedback operations with UEs having different configurations of antenna ports.

At block 801, the eNB aggregates two or more CSI-RS resource configurations into the first CSI-RS resource, wherein at least one of the two or more CSI-RS resource configurations has a different number of antenna ports than the others. For example, eNB 90, under control of controller/processor 240, executes CSI-RS resource aggregator logic 1203, stored in memory 242. The execution environment of the CSI-RS resource aggregator logic 1203 provides for eNB 90 to aggregate the multiple lower port CSI-RS resource configurations into the first CSI-RS resource. In prior aggregation operations, such higher-port CSI-RS resource were aggregated with a number of resource configurations each having the same number of antenna ports. Under various aspects of the present disclosure, the execution environment of CSI-RS resource aggregator logic 1203 allows for eNB 90 to aggregate using CSI-RS resource configurations that have different numbers of antenna ports. The total number of antenna ports of the aggregated resource configurations will add up to the total number of antenna ports configured for the CSI-RS resource.

At block 802, the eNB maps the first number of antenna ports of the first CSI-RS resource to a first set of REs according to the two or more CSI-RS resource configurations. For example, eNB 90, under control of controller/processor 240, executes RE mapping logic 1204 to map the antenna ports of the first CSI-RS resource aggregated by the multiple CSI-RS resource configurations to REs for CSI-RS transmission. Thus, the mapping of antenna ports to REs is guided by the antenna ports selected for each of CSI-RS resource configurations used in the aggregation. In order to accommodate CSI-RS for UEs configured for different numbers of antenna ports, additional CSI-RS resources may be configured by eNB 90, as stored in CSI-RS resources 1202, having different numbers of antenna ports. The additional CSI-RS resources configured by eNB 90 with a lower number of ports than the first CSI-RS resource may be configured in such a manner to share REs with the REs mapped to for the first number of antenna ports of the first CSI-RS resource.

It should be noted that in additional aspects of the present disclosure, the block 802 mapping may be implemented by applying a 8x8 Hadamard matrix to the two or more CSI-RS resource configurations. Such mapping may be used when the first CSI-RS resource is configured with a CDM length of 8. For example, the execution environment of RE mapping logic 1204 provides the corresponding Hadamard matrix for mapping the antenna ports of the multiple CSI-RS resource configurations to the specific REs.

At block 803, the eNB transmits CSI-RS using the first CSI-RS resource. For example, eNB 90 transmits the CSI-RS via wireless radios 1201a-t and antennas 234a-t. The CSI-RS transmitted are transmitted over the set of REs mapped based on the aggregated CSI-RS resource configurations.

FIGs. 9A and 9B are block diagrams illustrating the antenna to RE mapping of an aggregated 20-port CSI-RS resource 91 by a base station 90 configured according to one aspect of the present disclosure. For 20-port CSI-RS resource configuration 91, ports {15-18, 25-28} , corresponding to antennas 0-3 and 10-13, are mapped to a first 8-port CSI-RS resource 900 (k＝0 ) . Ports {19-22, 29-32} , corresponding to antennas 4-7 and 14-17, are mapped to a second 8-port CSI-RS resource 901 (k＝1) . And, ports {23, 24, 33, 34} , corresponding to antennas 8-9 and 18-19, are mapped to a 4-port CSI-RS resource 902 (k＝2) . It can be seen in

RE mappings

903 and 904 that antennas 0-7 and 10-17, which are also configured to a 16-port CSI-RS resource 92 using the same 2x8-port CSI-RS configuration are mapped to the same REs as 20-port CSI-RS resource 91.

FIG. 10 is a block diagram illustrating example blocks executed to implement one aspect of the present disclosure. If CDM length 4 is configured for {20, 24, 28, 32} ports, for supporting RE sharing with Rel-13 12/16-ports CSI-RS, an iterative RE mapping approach may be applied when a CSI-RS resource for {20, 24, 28, 32} is composed as an aggregation of K {4, 8, 12, 16} ports CSI-RS configurations. As with the aspect described with respect to FIG. 8, the CSI-RS configuration process begins similarly. At block 800, the eNB identifies a first CSI-RS resource configured for a first number of antenna ports. At block 801, the eNB aggregates two or more CSI-RS resource configurations into the first CSI-RS resource, wherein at least one of the CSI-RS resource configurations has a different number of antenna ports than the others. For example, the port index p of a {20, 24, 28, 32} CSI-RS resource may mapped to K CSI-RS resource configurations using the mapping approach in equation (1) .

With the CDM length 4, one of the aggregated CSI-RS resource configurations may include a 12-port or 16-port configuration. In such an instance, at block 1000, the eNB further aggregates two or more CSI-RS resource sub-configurations into a 12-port or 16-port CSI-RS resource configuration, wherein each antenna port assigned to the CSI-RS resource sub-configuration is sequential by antenna port index, regardless of polarization. For example, the execution environment of CSI-RS resource aggregator 1203 determines when one of the CSI-RS resource configurations used to aggregate the CSI-RS resource has port configuration of at least 12-ports (e.g., 12-port, 16-port configurations) . The further iteration of the associated higher-port CSI-RS resource configuration may be mapped by CSI-RS resource aggregator logic 1203 to K’ (e.g., K’ ＝2 for 16-port configuration or K’ ＝3 for 12-port configuration) 4-port or 8-port CSI-RS resource sub-configurations using sequential port numbering defined for CDM length 4, e.g.,

where the index of the 4/8-port CSI-RS resource configuration i∈ {0, ..., K'-1} ,

and

The relation between the CSI-RS port number p and the quantity

may be determined by the initial mapping according to equation (1) .

At block 1001, the eNB maps the first number of antenna ports of the first CSI-RS resource to a first set of REs according to the aggregated CSI-RS resource configurations. For example, eNB 90, under control of controller/processor 240 within the execution environment of RE mapping logic 1204, will map the antenna ports of the aggregated CSI-RS resource to the REs. Using this iterative aggregation and port mapping to RE, the RE may be shared by CSI-RS resources configured with different numbers of antenna ports. At block 1002, the eNB transmits CSI-RS using the first CSI-RS resource made up from the aggregated resource configurations and sub-configurations. For example, eNB 90 may then transmit CSI-RS using wireless radios 1201a-t and antennas 234a-t according to the RE mapping guided by the antenna ports selected through the aggregated resource configurations and sub-configurations.

FIGs. 11A and 11B are block diagrams illustrating the antenna to RE mapping of an aggregated 20-port CSI-RS resource 1100 with a CDM length of 4 by base station 90 configured according to one aspect of the present disclosure. 20-port CSI-RS resource 1100 is aggregated by a 1x12 port CSI-RS resource 1102 and 1x8-port CSI-RS resource 1103. For 20-port CSI-RS resource configuration 1100, ports {15-20, 25-30} , corresponding to antennas 0-5 and 10-15, are mapped to 12-port CSI-RS resource 1101 (k＝0) , which is further composed of 3x4-port CSI-RS resource sub-configurations 1103 (k’ ＝0.. 2) . The antenna ports for 4-port CSI-RS resource sub-configurations 1103 are selected by eNB 90 sequentially based on the antenna port indices of the antenna ports of 12-port CSI-RS resource configuration 1101. Ports {21-24, 31-34} , corresponding to antennas 6-9 and 16-19, are mapped to an 8-port CSI-RS resource 1102 (k＝1) . Using this iterative aggregation, which first aggregates 20-port CSI-RS resource from 12-port CSI-RS resource configuration 1101 and 8-port CSI-RS resource configuration, and then further aggregates 12-port CSI-RS resource configuration 1101 from 4-port CSI-RS resource sub-configurations with sequentially selected antenna ports, the REs to which the 20-port CSI-RS resource 1100 is mapped may be shared with the REs mapped from the 12-port CSI-RS resource 1106 that makes up part of the physical antenna resources of 20-port CSI-RS resource 1100.

As noted above, additional aspects of the present disclosure may provide for support of higher CDM length antennas, such as CDM length of 8 for 24 and 32 port antenna arrays. To improve the coverage of 24 and 32 ports, the CDM length 8 can be configured if multiple 8-ports CSI-RS resource configurations are aggregated for 24 and 32-ports CSI-RS. For CDM-length 8, each of ports {15, 16, 17, 18, 19, 20, 21, 22} are mapped to the same 8 REs within an 8-port CSI-RS resource configuration using an 8x8 Hadamard matrix shown in Table 2 below.

Table 2

The port mapping to RE for CDM length-8 may be same as defined in equation (1) .

One example implementation of an information element (IE) for RRC configuration of a {20, 24, 28, 32} port CSI-RS resource configuration is provided below in Table 3.

Table 3

It should be noted that the IE described in Table 3 is merely one example of an IE that may be provided for configuring resource aggregation according to one aspect of the present disclosure.

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 described herein 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 through computer-executable instructions 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:

identifying a first channel state information (CSI) reference signal (CSI-RS) resource configured for a first number of antenna ports；

aggregating two or more CSI-RS resource configurations into the first CSI-RS resource, wherein a total number of antenna ports of the aggregated two or more CSI-RS resource configurations equals the first number of antenna ports and at least one of the two or more CSI-RS resource configurations has a different number of antenna ports than the other of the two or more CSI-RS resource configurations；

mapping the first number of antenna ports of the first CSI-RS resource to a first set of resource elements according to the two or more CSI-RS resource configurations； and

transmitting a CSI-RS using the first CSI-RS resource.
The method of claim 1, further including:

identifying a second CSI-RS resource configured for a second number of antenna ports lower than the first number of antenna ports；

mapping the second number of antenna ports of the second CSI-RS resource to a second set of resource elements, wherein corresponding mapped antenna ports in the first and second number of antenna ports share resource elements included in both of the first and second set of resource elements； and

transmitting a second CSI-RS using the second CSI-RS resource.
The method of claim 1, wherein the mapping the first number of antenna ports occurs according to:

where
is a number of CSI-RS antenna ports in the k^th CSI-RS resource configuration, k is a CSI-RS resource configuration index in an aggregation list ranging from 0 to K-1, K is a total number of the two or more CSI-RS resource configurations, and p and p’ are CSI-RS antenna port indices in the first CSI-RS resource and the k^th CSI-RS resource configuration.
The method of claim 3, wherein each of the two or more CSI-RS resource configurations is configured with one of: 4, 8, 12, or 16 antenna ports.
The method of claim 4, wherein the first CSI-RS resource is configured with a code division multiplex (CDM) length of at least 4 the method further comprising:

further aggregating two or more CSI-RS resource sub-configurations into the at least one of the two or more CSI-RS resource configurations configured with at least 12 antenna ports, wherein each antenna port assigned to the two or more CSI-RS resource sub-configurations is sequential by antenna port index of the at least 12 antenna ports regardless of polarization.
The method of claim 1, wherein the first CSI-RS resource is configured with a code division multiplex (CDM) length of at least 8 and the first number of antenna ports is at least 24,

wherein the mapping includes:

mapping each antenna port of the two or more CSI-RS resource configurations to configured with at least 8 antenna ports using a 8x8 Hadamard matrix.
The method of any combination of claims 1-6.
An apparatus configured for wireless communication, comprising:

means for identifying a first channel state information (CSI) reference signal (CSI-RS) resource configured for a first number of antenna ports；

means for aggregating two or more CSI-RS resource configurations into the first CSI-RS resource, wherein a total number of antenna ports of the aggregated two or more CSI-RS resource configurations equals the first number of antenna ports and at least one of the two or more CSI-RS resource configurations has a different number of antenna ports than the other of the two or more CSI-RS resource configurations；

means for mapping the first number of antenna ports of the first CSI-RS resource to a first set of resource elements according to the two or more CSI-RS resource configurations； and

means for transmitting a CSI-RS using the first CSI-RS resource.
The apparatus of claim 8, further including:

means for identifying a second CSI-RS resource configured for a second number of antenna ports lower than the first number of antenna ports；

means for mapping the second number of antenna ports of the second CSI-RS resource to a second set of resource elements, wherein corresponding mapped antenna ports in the first and second number of antenna ports share resource elements included in both of the first and second set of resource elements； and

means for transmitting a second CSI-RS using the second CSI-RS resource.
The apparatus of claim 8, wherein the means for mapping the first number of antenna ports occurs according to:

where
is a number of CSI-RS antenna ports in the k^th CSI-RS resource configuration, k is a CSI-RS resource configuration index in an aggregation list ranging from 0 to K-1, K is a total number of the two or more CSI-RS resource configurations, and p and p’ are CSI-RS antenna port indices in the first CSI-RS resource and the k^th CSI-RS resource configuration.
The apparatus of claim 10, wherein each of the two or more CSI-RS resource configurations is configured with one of: 4, 8, 12, or 16 antenna ports.
The apparatus of claim 11, wherein the first CSI-RS resource is configured with a code division multiplex (CDM) length of at least 4 the apparatus further comprising:

means for further aggregating two or more CSI-RS resource sub-configurations into the at least one of the two or more CSI-RS resource configurations configured with at least 12 antenna ports, wherein each antenna port assigned to the two or more CSI-RS resource sub-configurations is sequential by antenna port index of the at least 12 antenna ports regardless of polarization.
The apparatus of claim 8, wherein the first CSI-RS resource is configured with a code division multiplex (CDM) length of at least 8 and the first number of antenna ports is at least 24,

wherein the means for mapping includes:

means for mapping each antenna port of the two or more CSI-RS resource configurations to configured with at least 8 antenna ports using a 8x8 Hadamard matrix.
The apparatus of any combination of claims 8-13.
A non-transitory computer-readable medium having program code recorded thereon, the program code comprising:

program code for causing a computer to identify a first channel state information (CSI) reference signal (CSI-RS) resource configured for a first number of antenna ports；

program code for causing the computer to aggregate two or more CSI-RS resource configurations into the first CSI-RS resource, wherein a total number of antenna ports of the aggregated two or more CSI-RS resource configurations equals the first number of antenna ports and at least one of the two or more CSI-RS resource configurations has a different number of antenna ports than the other of the two or more CSI-RS resource configurations；

program code for causing the computer to map the first number of antenna ports of the first CSI-RS resource to a first set of resource elements according to the two or more CSI-RS resource configurations； and

program code for causing the computer to transmit a CSI-RS using the first CSI-RS resource.
The non-transitory computer-readable medium of claim 15, further including:

program code for causing the computer to identify a second CSI-RS resource configured for a second number of antenna ports lower than the first number of antenna ports；

program code for causing the computer to map the second number of antenna ports of the second CSI-RS resource to a second set of resource elements, wherein corresponding mapped antenna ports in the first and second number of antenna ports share resource elements included in both of the first and second set of resource elements； and

program code for causing the computer to transmit a second CSI-RS using the second CSI-RS resource.
The non-transitory computer-readable medium of claim 15, wherein the program code for causing the computer to map the first number of antenna ports occurs according to:

where
is a number of CSI-RS antenna ports in the k^th CSI-RS resource configuration, k is a CSI-RS resource configuration index in an aggregation list ranging from 0 to K-1, K is a total number of the two or more CSI-RS resource configurations, and p and p’ are CSI-RS antenna port indices in the first CSI-RS resource and the k^th CSI-RS resource configuration.
The non-transitory computer-readable medium of claim 17, wherein each of the two or more CSI-RS resource configurations is configured with one of: 4, 8, 12, or 16 antenna ports.
The non-transitory computer-readable medium of claim 18, wherein the first CSI-RS resource is configured with a code division multiplex (CDM) length of at least 4 the non-transitory computer-readable medium further comprising:

program code for causing the computer to further aggregate two or more CSI-RS resource sub-configurations into the at least one of the two or more CSI-RS resource configurations configured with at least 12 antenna ports, wherein each antenna port assigned to the two or more CSI-RS resource sub-configurations is sequential by antenna port index of the at least 12 antenna ports regardless of polarization.
The non-transitory computer-readable medium of claim 15, wherein the first CSI-RS resource is configured with a code division multiplex (CDM) length of at least 8 and the first number of antenna ports is at least 24,

wherein the program code for causing the computer to map includes:

program code for causing the computer to map each antenna port of the two or more CSI-RS resource configurations to configured with at least 8 antenna ports using a 8x8 Hadamard matrix.
The non-transitory computer-readable medium of any combination of claims 15-20.
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 identify a first channel state information (CSI) reference signal (CSI-RS) resource configured for a first number of antenna ports；

to aggregate two or more CSI-RS resource configurations into the first CSI-RS resource, wherein a total number of antenna ports of the aggregated two or more CSI-RS resource configurations equals the first number of antenna ports and at least one of the two or more CSI-RS resource configurations has a different number of antenna ports than the other of the two or more CSI-RS resource configurations；

to map the first number of antenna ports of the first CSI-RS resource to a first set of resource elements according to the two or more CSI-RS resource configurations； and

to transmit a CSI-RS using the first CSI-RS resource.
The apparatus of claim 22, further including configuration of the at least one processor:

to identify a second CSI-RS resource configured for a second number of antenna ports lower than the first number of antenna ports；

to map the second number of antenna ports of the second CSI-RS resource to a second set of resource elements, wherein corresponding mapped antenna ports in the first and second number of antenna ports share resource elements included in both of the first and second set of resource elements； and

to transmit a second CSI-RS using the second CSI-RS resource.
The apparatus of claim 22, wherein the configuration of the at least one processor to map the first number of antenna ports occurs according to:

where
is a number of CSI-RS antenna ports in the k^th CSI-RS resource configuration, k is a CSI-RS resource configuration index in an aggregation list ranging from 0 to K-1, K is a total number of the two or more CSI-RS resource configurations, and p and p’ are CSI-RS antenna port indices in the first CSI-RS resource and the k^th CSI-RS resource configuration.
The apparatus of claim 24, wherein each of the two or more CSI-RS resource configurations is configured with one of: 4, 8, 12, or 16 antenna ports.
The apparatus of claim 25, wherein the first CSI-RS resource is configured with a code division multiplex (CDM) length of at least 4 the apparatus further comprising configuration of the at least one processor:

to further aggregate two or more CSI-RS resource sub-configurations into the at least one of the two or more CSI-RS resource configurations configured with at least 12 antenna ports, wherein each antenna port assigned to the two or more CSI-RS resource sub-configurations is sequential by antenna port index of the at least 12 antenna ports regardless of polarization.
The apparatus of claim 22, wherein the first CSI-RS resource is configured with a code division multiplex (CDM) length of at least 8 and the first number of antenna ports is at least 24,

wherein the configuration of the at least one processor to map includes configuration to map each antenna port of the two or more CSI-RS resource configurations to configured with at least 8 antenna ports using a 8x8 Hadamard matrix.
The apparatus of any combination of claims 22-27.