WO2021151258A1

WO2021151258A1 - Port multiplexing for csi-rs with the same sd-basis precoder grouping

Info

Publication number: WO2021151258A1
Application number: PCT/CN2020/074147
Authority: WO
Inventors: Kangqi LIU; Liangming WU; Chenxi HAO; Min Huang; Yu Zhang; Qiaoyu Li; Chao Wei; Hao Xu
Original assignee: Qualcomm Incorporated
Priority date: 2020-02-01
Filing date: 2020-02-01
Publication date: 2021-08-05

Abstract

Wireless communications systems and methods related to wireless communications in a system are provided. A method of communicating CSI-RS data from a base station (BS) to a user device (UE) includes estimating a parameter θ relating a first frequency basis fm with a second frequency basis fm+1; estimating channel functions for a group of ports with a first spatial basis and a first frequency basis; multiplexing the channel functions for the group of ports using the channel functions for the first spatial basis and the parameter θ into a single virtual port; and communicating the multiplexed functions.

Description

PORT MULTIPLEXING FOR CSI-RS WITH THE SAME SD-BASIS PRECODER GROUPING

Inventors: Kangqi LIU, Liangming WU, Chenxi HAO, Min HUANG, Yu ZHANG, Qiaoyu LI, Chao WEI, and Hao XU

TECHNICAL FIELD

This application relates to wireless communication systems, and more particularly to port multiplexing for CSI-RS with the same SD-Basis Precoder Grouping.

INTRODUCTION

Wireless communications systems are widely deployed to provide various types of communication content such as voice, video, packet data, messaging, broadcast, and so on. These systems may be capable of supporting communication with multiple users by sharing the available system resources (e.g., time, frequency, and power) . A wireless multiple-access communications system may include a number of base stations (BSs) , each simultaneously supporting communications for multiple communication devices, which may be otherwise known as user equipment (UE) .

To meet the growing demands for expanded mobile broadband connectivity, wireless communication technologies are advancing from the long-term evolution (LTE) technology to a next generation new radio (NR) technology, which may be referred to as 5 ^th Generation (5G) . For example, NR is designed to provide a lower latency, a higher bandwidth or a higher throughput, and a higher reliability than LTE. NR is designed to operate over a wide array of spectrum bands, for example, from low-frequency bands below about 1 gigahertz (GHz) and mid-frequency bands from about 1 GHz to about 6 GHz, to high-frequency bands such as millimeter wave (mmWave) bands. NR is also designed to operate across different spectrum types, from licensed spectrum to unlicensed and shared spectrum. Spectrum sharing enables operators to opportunistically aggregate spectrums to dynamically support high-bandwidth services. Spectrum sharing can extend the benefit of NR technologies to operating entities that may not have access to a licensed spectrum.

The mobility of a UE may allow the UE to easily move away from a serving BS. As the UE’s distance from the serving BS increases, it may be desirable to use more of the power at the UE’s disposal to transmit clear signals to the BS. If the UE transmits a signal that is not received by the BS (e.g., due to interference) , a call or data may drop and not reach the BS. If a UE is located near an edge of a coverage area served by the BS, it may be desirable for the UE to transmit at an increased or full power level to establish/maintain a connection and exchange data with the BS.

Channel Status Information (CSI) provides a mechanism for the UE to measure the radio channel quality and reporting that back to the network (gNB) . CSI-RS (reference signal) is one method for the UE to measure the CSI information and feedback to the gNB so that transmitted data can be precoded according to the channel characteristics to better transmit data between a BS and the UE. Currently, the averages number of CSI-RS resources per resource block (RB) can be high.

Consequently, it would be useful to reduce the number of resources used in transmitting the CSI-RS.

BRIEF SUMMARY OF SOME EXAMPLES

The following summarizes some aspects of the present disclosure to provide a basic understanding of the discussed technology. This summary is not an extensive overview of all contemplated features of the disclosure and is intended neither to identify key or critical elements of all aspects of the disclosure nor to delineate the scope of any or all aspects of the disclosure. Its sole purpose is to present some concepts of one or more aspects of the disclosure in summary form as a prelude to the more detailed description that is presented later.

A method of communicating CSI-RS data from a base station (BS) to a user device (UE) includes estimating a parameter θ relating a first frequency basis f _m with a second frequency basis f _m+1; estimating channel functions for a group of ports with a first spatial basis and a first frequency basis; multiplexing the channel functions for the group of ports using the channel functions for the first spatial basis and the parameter θ into a single virtual port; and communicating the multiplexed functions.

An apparatus operating as a base station, the apparatus includes a plurality of antennas; a transmit chain providing X ports coupled to the plurality of antennas; a CSI module configured to transmit CSI-RS data to a user equipment (UE) using the X ports, the CSI module estimating a parameter θ relating a first frequency basis f _m with a second frequency basis f _m+1; estimating channel functions for a group of ports with a first spatial basis and a first frequency basis; multiplexing the channel functions for the group of ports using the channel functions for the first spatial basis and the parameter θ into a single virtual port; and communicating the multiplexed functions.

Other aspects, features, and embodiments of the present invention will become apparent to those of ordinary skill in the art, upon reviewing the following description of specific, exemplary embodiments of the present invention in conjunction with the accompanying figures. While features of the present invention may be discussed relative to certain embodiments and figures below, all embodiments of the present invention can include one or more of the advantageous features discussed herein. In other words, while one or more embodiments may be discussed as having certain advantageous features, one or more of such features may also be used in accordance with the various embodiments of the invention discussed herein. In similar fashion, while exemplary embodiments may be discussed below as device, system, or method embodiments it should be understood that such exemplary embodiments can be implemented in various devices, systems, and methods.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a wireless communication network according to some aspects of the present disclosure.

FIG. 2 illustrates an example of a base station (BS) according to some aspects of the present disclosure.

FIG. 3 is a block diagram of a user equipment (UE) according to some aspects of the present disclosure.

FIG. 4 is a block diagram of a BS according to some aspects of the present disclosure.

FIGs. 5A and 5B illustrate communications of CSI-RS between a UE and a BS.

FIG. 6 illustrates distribution of reporting resources for transmitting CSI-RS data with four-port fd-CDM2.

FIGs. 7 A and 7B illustrate multiplexing of CSI-RS according to some embodiments.

FIG. 8 further illustrates the multiplexing of CSI-RS data according to some embodiments.

FIGs. 9A and 9B illustrates mapping of resources according to some embodiments.

FIG. 10 illustrates determining a parameter θ used in the multiplexing method according to some embodiments.

FIG. 11 illustrates a method of communicating CSI-RS data according to some embodiments of the invention.

DETAILED DESCRIPTION

The detailed description set forth below, in connection with the appended drawings, is intended as a description of various configurations and is not intended to represent the only configurations in which the concepts described herein may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of the various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. In some instances, well-known structures and components are shown in block diagram form to avoid obscuring such concepts.

This disclosure relates generally to 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, Global System for Mobile Communications (GSM) networks, 5 ^th Generation (5G) or new radio (NR) networks, as well as other communications networks. As described herein, the terms “networks” and “systems” may be used interchangeably.

An OFDMA network may implement a radio technology such as evolved UTRA (E-UTRA) , Institute of Electrical and Electronics Engineers (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 which was aimed at improving the UMTS mobile phone standard. The 3GPP may define specifications for the next generation of mobile networks, mobile systems, and mobile devices. The present disclosure is concerned with the evolution of wireless technologies from LTE, 4G, 5G, NR, and beyond with shared access to wireless spectrum between networks using a collection of new and different radio access technologies or radio air interfaces.

In particular, 5G networks contemplate diverse deployments, diverse spectrum, and diverse services and devices that may be implemented using an OFDM-based unified, air interface. To achieve these goals, further enhancements to LTE and LTE-Aare considered in addition to development of the new radio technology for 5G NR networks. The 5G NR will be capable of scaling to provide coverage (1) to a massive Internet of things (IoTs) with an Ultra-high density (e.g., ～1M nodes/km ²) , ultra-low complexity (e.g., ～10s of bits/sec) , ultra-low energy (e.g., ～10+ years of battery life) , and deep coverage with the capability to reach challenging locations; (2) including mission-critical control with strong security to safeguard sensitive personal, financial, or classified information, ultra-high reliability (e.g., ～99.9999%reliability) , ultra-low latency (e.g., ～ 1 ms) , and users with wide ranges of mobility or lack thereof; and (3) with enhanced mobile broadband including extreme high capacity (e.g., ～ 10 Tbps/km ²) , extreme data rates (e.g., multi-Gbps rate, 100+ Mbps user experienced rates) , and deep awareness with advanced discovery and optimizations.

The 5G NR may be implemented to use optimized OFDM-based waveforms with scalable numerology and transmission time interval (TTI) ; having a common, flexible framework to efficiently multiplex services and features with a dynamic, low-latency time division duplex (TDD) /frequency division duplex (FDD) design; and with advanced wireless technologies, such as massive multiple input, multiple output (MIMO) , robust millimeter wave (mmWave) transmissions, advanced channel coding, and device-centric mobility. Scalability of the numerology in 5G NR, with scaling of subcarrier spacing (SCS) , may efficiently address operating diverse services across diverse spectrum and diverse deployments. For example, in various outdoor and macro coverage deployments of less than 3GHz FDD/TDD implementations, SCS may occur with 15 kHz, for example over 5, 10, 20 MHz, and the like bandwidth (BW) . For other various outdoor and small cell coverage deployments of TDD greater than 3 GHz, SCS may occur with 30 kHz over 80/100 MHz BW. For other various indoor wideband implementations, using a TDD over the unlicensed portion of the 5 GHz band, the SCS may occur with 60 kHz over a 160 MHz BW. Finally, for various deployments transmitting with mmWave components at a TDD of 28 GHz, the SCS may occur with 120 kHz over a 500 MHz BW.

The scalable numerology of the 5G NR facilitates scalable TTI for diverse latency and quality of service (QoS) requirements. For example, shorter TTI may be used for low latency and high reliability, while longer TTI may be used for higher spectral efficiency. The efficient multiplexing of long and short TTIs to allow transmissions to start on symbol boundaries. 5G NR also contemplates a self-contained integrated subframe design with UL/downlink scheduling information, data, and acknowledgement in the same subframe. The self-contained integrated subframe supports communications in unlicensed or contention-based shared spectrum, adaptive UL/downlink that may be flexibly configured on a per-cell basis to dynamically switch between UL and downlink to meet the current traffic needs.

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 or examples 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 include at least one element of a claim.

A UE and a BS may each include one or more radio frequency (RF) chains, each RF chain can include a precoder and amplification. The precoder relates data to be transmitted with output symbols in accordance with the characteristics of the channels on which the data is transmitted. In general, precoding can take the form of Y=W·x , where x represents the symbols to be transmitted, W is a precoding matrix, and Y is the symbols for transmission according to the available resources. In many systems, as discussed below, the precoder can reacts according to the characteristics of a channel. In many systems, the channel can be analyzed to determining the channel characteristics.

In some systems, a channel status information (CSI) can be used to report radio channel quality information to the base station (BS) . In particular, the BS can provide precoded spatial domain basis b _i and receive from the UE frequency domain basis f _m ^H and linear combination coefficients c _i, m that relate the spatial domain basis b _i with the frequency domain basis f _m ^H from the UE. In some cases, the BS can provide precoded spatial domain basis b _i and frequency domain basis f _m ^H and receive the linear combination coefficients c _i, m from the UE. In CSI-RS (channel status information –reference signal) , there is a relationship between the spatial domain basis and the frequency domain basis that can be exploited to reduce the number of resources used in the CSI-RS transmission. The CSI-RS data describing the channel can be transmitted from the BS to the UE using the available resources.

The present disclosure describes mechanisms for transmitting CSI-RS utilizing the relationship between the spatial domain basis and the frequency domain basis to reduce the number of resources used in the transmission. In some embodiments, the number of resources can be reduced by half. In particular, using the relationship, the channel estimation between elements of the frequency domain basis can be related using a parameter θ so that estimations with the same spatial domain basis can be related by the parameter θ. As a consequence, the estimation channel characteristics can be transmitted using fewer resources.

FIG. 1 illustrates a wireless communication network 100 according to some aspects of the present disclosure. The network 100 may be a 5G network. The network 100 includes a number of base stations (BSs) 105 (individually labeled as 105a, 105b, 105c, 105d, 105e, and 105f) and other network entities. A BS 105 may be a station that communicates with UEs 115 and may also be referred to as an evolved node B (eNB) , a next generation eNB (gNB) , an access point, and the like. Each BS 105 may provide communication coverage for a particular geographic area. In 3GPP, the term “cell” can refer to this particular geographic coverage area of a BS 105 and/or a BS subsystem serving the coverage area, depending on the context in which the term is used.

A BS 105 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) . A BS for a macro cell may be referred to as a macro BS. A BS for a small cell may be referred to as a small cell BS, a pico BS, a femto BS or a home BS. In the example shown in FIG. 1, the

BSs

105d and 105e may be regular macro BSs, while the BSs 105a-105c may be macro BSs enabled with one of three dimension (3D) , full dimension (FD) , or massive MIMO. The BSs 105a-105c may take advantage of their higher dimension MIMO capabilities to exploit 3D beamforming in both elevation and azimuth beamforming to increase coverage and capacity. The BS 105f may be a small cell BS which may be a home node or portable access point. A BS 105 may support one or multiple (e.g., two, three, four, and the like) cells.

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

The UEs 115 are dispersed throughout the wireless network 100, and each UE 115 may be stationary or mobile. A UE 115 may also be referred to as a terminal, a mobile station, a subscriber unit, a station, or the like. A UE 115 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. In one aspect, a UE 115 may be a device that includes a Universal Integrated Circuit Card (UICC) . In another aspect, a UE may be a device that does not include a UICC. In some aspects, the UEs 115 that do not include UICCs may also be referred to as IoT devices or internet of everything (IoE) devices. The UEs 115a-115d are examples of mobile smart phone-type devices accessing network 100. A UE 115 may also be a machine specifically configured for connected communication, including machine type communication (MTC) , enhanced MTC (eMTC) , narrowband IoT (NB-IoT) and the like. The UEs 115e-115h are examples of various machines configured for communication that access the network 100. The UEs 115i-115k are examples of vehicles equipped with wireless communication devices configured for communication that access the network 100. A UE 115 may be able to communicate with any type of the BSs, whether macro BS, small cell, or the like. In FIG. 1, a lightning bolt (e.g., communication links) indicates wireless transmissions between a UE 115 and a serving BS 105, which is a BS designated to serve the UE 115 on the downlink (DL) and/or uplink (UL) , desired transmission between BSs 105, backhaul transmissions between BSs, or sidelink transmissions between UEs 115.

In operation, the BSs 105a-105c may serve the

UEs

115a and 115b using 3D beamforming and coordinated spatial techniques, such as coordinated multipoint (CoMP) or multi-connectivity. The macro BS 105d may perform backhaul communications with the BSs 105a-105c, as well as small cell, the BS 105f. The macro BS 105d may also transmits multicast services which are subscribed to and received by the

UEs

115c and 115d. Such multicast services may include mobile television or stream video, or may include other services for providing community information, such as weather emergencies or alerts, such as Amber alerts or gray alerts.

The BSs 105 may also communicate with a core network. The core network may provide user authentication, access authorization, tracking, Internet Protocol (IP) connectivity, and other access, routing, or mobility functions. At least some of the BSs 105 (e.g., which may be an example of a gNB or an access node controller (ANC) ) may interface with the core network through backhaul links (e.g., NG-C, NG-U, etc. ) and may perform radio configuration and scheduling for communication with the UEs 115. In various examples, the BSs 105 may communicate, either directly or indirectly (e.g., through core network) , with each other over backhaul links (e.g., X1, X2, etc. ) , which may be wired or wireless communication links.

The network 100 may also support mission critical communications with ultra-reliable and redundant links for mission critical devices, such as the UE 115e, which may be a drone. Redundant communication links with the UE 115e may include links from the

macro BSs

105d and 105e, as well as links from the small cell BS 105f. Other machine type devices, such as the UE 115f (e.g., a thermometer) , the UE 115g (e.g., smart meter) , and UE 115h (e.g., wearable device) may communicate through the network 100 either directly with BSs, such as the small cell BS 105f, and the macro BS 105e, or in multi-step-size configurations by communicating with another user device which relays its information to the network, such as the UE 115f communicating temperature measurement information to the smart meter, the UE 115g, which is then reported to the network through the small cell BS 105f. The network 100 may also provide additional network efficiency through dynamic, low-latency TDD/FDD communications, such as vehicle-to-vehicle (V2V) communications among the UEs 115i-115k, vehicle-to-everything (V2X) communications between a

UE

115i, 115j, or 115k and other UEs 115, and/or vehicle-to-infrastructure (V2I) communications between a

UE

115i, 115j, or 115k and a BS 105.

In some implementations, the network 100 utilizes OFDM-based waveforms for communications. An OFDM-based system may partition the system BW into multiple (K) orthogonal subcarriers, which are also commonly referred to as subcarriers, tones, bins, or the like. Each subcarrier may be modulated with data. In some instances, the SCS between adjacent subcarriers may be fixed, and the total number of subcarriers (K) may be dependent on the system BW. The system BW may also be partitioned into subbands. In other instances, the SCS and/or the duration of TTIs may be scalable.

In some aspects, the BSs 105 can assign or schedule transmission resources (e.g., in the form of time-frequency resource blocks (RB) ) for downlink (DL) and uplink (UL) transmissions in the network 100. DL refers to the transmission direction from a BS 105 to a UE 115, whereas UL refers to the transmission direction from a UE 115 to a BS 105. The communication can be in the form of radio frames. A radio frame may be divided into a plurality of subframes or slots, for example, about 10. Each slot may be further divided into mini-slots. In a FDD mode, simultaneous UL and DL transmissions may occur in different frequency bands. For example, each subframe includes an UL subframe in an UL frequency band and a DL subframe in a DL frequency band. A subframe may also be referred to as a slot. In a TDD mode, UL and DL transmissions occur at different time periods using the same frequency band. For example, a subset of the subframes (e.g., DL subframes) in a radio frame may be used for DL transmissions and another subset of the subframes (e.g., UL subframes) in the radio frame may be used for UL transmissions.

The DL subframes and the UL subframes can be further divided into several regions. For example, each DL or UL subframe may have pre-defined regions for transmissions of reference signals, control information, and data. Reference signals are predetermined signals that facilitate the communications between the BSs 105 and the UEs 115. For example, a reference signal can have a particular pilot pattern or structure, where pilot tones may span across an operational BW or frequency band, each positioned at a pre-defined time and a pre-defined frequency. For example, a BS 105 may transmit cell specific reference signals (CRSs) and/or channel state information –reference signals (CSI-RSs) to enable a UE 115 to estimate a DL channel. Similarly, a UE 115 may transmit sounding reference signals (SRSs) to enable a BS 105 to estimate an UL channel. Control information may include resource assignments and protocol controls. Data may include protocol data and/or operational data. In some aspects, the BSs 105 and the UEs 115 may communicate using self-contained subframes. A self-contained subframe may include a portion for DL communication and a portion for UL communication. A self-contained subframe can be DL-centric or UL-centric. A DL-centric subframe may include a longer duration for DL communication than for UL communication. An UL-centric subframe may include a longer duration for UL communication than for DL communication.

In some aspects, the network 100 may be an NR network deployed over a licensed spectrum. The BSs 105 can transmit synchronization signals (e.g., including a primary synchronization signal (PSS) and a secondary synchronization signal (SSS) ) in the network 100 to facilitate synchronization. The BSs 105 can broadcast system information associated with the network 100 (e.g., including a master information block (MIB) , remaining system information (RMSI) , and other system information (OSI) ) to facilitate initial network access. In some instances, the BSs 105 may broadcast the PSS, the SSS, and/or the MIB in the form of synchronization signal block (SSBs) over a physical broadcast channel (PBCH) and may broadcast the RMSI and/or the OSI over a physical downlink shared channel (PDSCH) .

In some aspects, a UE 115 attempting to access the network 100 may perform an initial cell search by detecting a PSS from a BS 105. The PSS may enable synchronization of period timing and may indicate a physical layer identity value. The UE 115 may then receive a SSS. The SSS may enable radio frame synchronization, and may provide a cell identity value, which may be combined with the physical layer identity value to identify the cell. The PSS and the SSS may be located in a central portion of a carrier or any suitable frequencies within the carrier.

After receiving the PSS and SSS, the UE 115 may receive a MIB, which may be transmitted in the physical broadcast channel (PBCH) . The MIB may include system information for initial network access and scheduling information for RMSI and/or OSI. After decoding the MIB, the UE 115 may receive RMSI, OSI, and/or one or more system information blocks (SIBs) . The RMSI and/or OSI may include radio resource control (RRC) information related to random access channel (RACH) procedures, paging, control resource set (CORESET) for physical downlink control channel (PDCCH) monitoring, physical UL control channel (PUCCH) , physical UL shared channel (PUSCH) , power control, and SRS. In some aspects, SIB1 may contain cell access parameters and scheduling information for other SIBs.

After obtaining the MIB, the RMSI and/or the OSI, the UE 115 can perform a random access procedure to establish a connection with the BS 105. After establishing a connection, the UE 115 and the BS 105 can enter a normal operation stage, where operational data may be exchanged. For example, the BS 105 may schedule the UE 115 for UL and/or DL communications. The BS 105 may transmit UL and/or DL scheduling grants to the UE 115 via a PDCCH. The scheduling grants may be transmitted in the form of DL control information (DCI) . The BS 105 may transmit a DL communication signal (e.g., carrying data) to the UE 115 via a PDSCH according to a DL scheduling grant. The UE 115 may transmit an UL communication signal to the BS 105 via a PUSCH and/or PUCCH according to an UL scheduling grant. In some aspects, the BS 105 may communicate with a UE 115 using HARQ techniques to improve communication reliability, for example, to provide a URLLC service.

In some aspects, the network 100 may operate over a system BW or a component carrier (CC) BW. The network 100 may partition the system BW into multiple BWPs (e.g., portions) . A BS 105 may dynamically assign a UE 115 to operate over a certain BWP (e.g., a certain portion of the system BW) . The assigned BWP may be referred to as the active BWP. The UE 115 may monitor the active BWP for signaling information from the BS 105. The BS 105 may schedule the UE 115 for UL or DL communications in the active BWP. In some aspects, a BS 105 may assign a pair of BWPs within the CC to a UE 115 for UL and DL communications. For example, the BWP pair may include one BWP for UL communications and one BWP for DL communications.

In some aspects, the network 100 may operate over a shared channel, which may include shared frequency bands or unlicensed frequency bands. For example, the network 100 may be an NR-unlicensed (NR-U) network operating over an unlicensed frequency band. In such an aspect, the BSs 105 and the UEs 115 may be operated by multiple network operating entities.

FIG. 2 illustrates an example of a BS 215 according to some aspects of the present disclosure. The BS 215 may be similar to the BSs 105 in FIG. 1 in the network 100. The BS 215 includes

antenna elements

202, 204, 206, and 208. An antenna element may also be referred to as an antenna, an antenna port, or a port. Although the BS 215 is illustrated as having four antenna elements, it should be understood that in other examples, the BS 215 may include fewer antenna elements (e.g., 1, 2, or 3) or more antenna elements (e.g., 5, 6, 7, 8, etc. ) . A communication channel between a pair of nodes (e.g., a BS and a UE) includes not only the physical channel, but also radio frequency (RF) transceiver chains, for example, including antennas, low-noise amplifiers (LNAs) , mixers, RF filters, and analog-to-digital (A/D) converters, and in-phase quadrature-phase (I/Q) imbalances, which may be different between different nodes and/or different antennas.

In the example illustrated in FIG. 2, the

antenna elements

202, 204, 206, and 208 are located on different edges of the BS 215, thus creating diversity and providing for directional communication. The BS 215 may use at least one of the

antenna elements

202, 204, 206, and/or 208 to transmit communication signals (e.g., CSI-RS data) to enable a UE (e.g., UE 115) to estimate an UL or DL channel. The BS 215 includes a baseband 240 and a transmit path 210 for DL transmissions using one or more antenna elements. The baseband 240 may perform data encoding, cyclic-prefix (CP) -OFDM and/or discrete Fourier transform-spread-fast Fourier transform (DFT-s-FFT) modulation to generate a baseband signal. The transmit path 210 includes four transmit

chains

212, 214, 216, and 218. Although the BS 215 is illustrated as having four transmit chains, it should be understood that in other examples, the BS 215 may include fewer transmit chains (e.g., 1, 2, or 3) or more transmit chains (e.g., 5, 6, 7, 8, etc. ) . In FIG. 2, each transmit

chain

212, 214, 216, and 218 may include a digital-to-analog converter (DAC) , a mixer, and a power amplifier that converts a baseband signal to a radio frequency (RF) signal for transmission.

BS 215 also includes a receive chain illustrate as receive path 240. As illustrated in FIG. 2, receive

chains

242, 244, 246, and 248 are coupled to receive signals from

ports

232, 234, 236, and 238, respectively. Receive

chains

242, 244, 246, and 248 may map directly to one of

ports

232, 234, 236, and 238 or may be logical or virtual ports. UE 215 may configure receive chains differently for different ports to produce signals with different powers and/or different directions. Each of receive

chains

242, 244, 246, and 248 may include amplifiers, filters, and an analog to digital converter (ADC) to provide digital signals to decoder 260. Decoder 260 provides base-band digital signal to baseband 240 of BS 215.

The BS 215 may receive a Sounding Reference Signal (SRS) from a UE on a combination of receive chains. The

ports

232, 234, 236, and/or 238 may or may not have a one-to-one mapping to the

antenna elements

202, 204, 206, and/or 208. When there is a one-to-one mapping, each

antenna element

202, 204, 206, and/or 208 may map to one of the

ports

232, 234, 236, and/or 238. When the

ports

232, 234, 236, and/or 238 are logical ports or virtual ports, the BS 215 may configure the transmit chains differently for different ports to produce signals with different powers and/or different direction. The BS can report CSI-RS through the transmit chains to the UE as a virtual port by applying precoder 230. Although precoder 230 is illustrated in relation to the transmit chains, the precoder 230 may be applied in the baseband 240. In response to an SRS, BS 215 may perform channel estimation and transmit precoded spatial or frequency domain basis, for example.

FIG. 3 is a block diagram of a UE 300 according to some aspects of the present disclosure. The UE 300 may be a UE 115 discussed above in FIG. 1. As shown, the UE 300 may include a processor 302, a memory 304, a CSI module 308, a precoding module 309, a transceiver 310 including a modem subsystem 312 and a radio frequency (RF) unit 314, and one or more antennas 316. These elements may be in direct or indirect communication with each other, for example via one or more buses.

The processor 302 may include a central processing unit (CPU) , a digital signal processor (DSP) , an application specific integrated circuit (ASIC) , a controller, a field programmable gate array (FPGA) device, another hardware device, a firmware device, or any combination thereof configured to perform the operations described herein. The processor 302 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 memory 304 may include a cache memory (e.g., a cache memory of the processor 302) , random access memory (RAM) , magnetoresistive RAM (MRAM) , read-only memory (ROM) , programmable read-only memory (PROM) , erasable programmable read only memory (EPROM) , electrically erasable programmable read only memory (EEPROM) , flash memory, solid state memory device, hard disk drives, other forms of volatile and non-volatile memory, or a combination of different types of memory. In an aspect, the memory 304 includes a non-transitory computer-readable medium. The memory 304 may store, or have recorded thereon, instructions 306. The instructions 306 may include instructions that, when executed by the processor 302, cause the processor 302 to perform the operations described herein with reference to the UEs 115 in connection with aspects of the present disclosure. Instructions 306 may also be referred to as program code. The program code may be for causing a wireless communication device to perform these operations, for example by causing one or more processors (such as processor 302) to control or command the wireless communication device to do so. The terms “instructions” and “code” should be interpreted broadly to include any type of computer-readable statement (s) . For example, the terms “instructions” and “code” may refer to one or more programs, routines, sub-routines, functions, procedures, etc. “Instructions” and “code” may include a single computer-readable statement or many computer-readable statements.

The CSI module 308 and/or the precoding module 309 may be implemented via hardware, software, or combinations thereof. The CSI module 308 and/or the precoding configuration module 309 may be implemented as a processor, circuit, and/or instructions 306 stored in the memory 304 and executed by the processor 302. In some instances, the CSI module 308 and/or the precoding module 309 can be integrated within the modem subsystem 312. The CSI module 308 and/or the precoding module 309 can be implemented by a combination of software components (e.g., executed by a DSP or a general processor) and hardware components (e.g., logic gates and circuitry) within the modem subsystem 312. The CSI module 308 and/or the precoding module 309 may be used for various aspects of the present disclosure.

In some aspects, the CSI module 308 may be configured to facilitate a CSI-RS process in the UE 300. In some examples, UE 300 may receive precoded spatial basis and may receive precoded frequency basis parameters and provides data regarding the channel quality to a corresponding base station. Embodiments of channel estimation are discussed further below.

The precoding module 309 may be configured to code data for transmission over the channel in accordance with the channel estimation. Channel estimation and precoding according to some embodiments is further discussed below.

As shown, the transceiver 310 may include the modem subsystem 312 and the RF unit 314. The transceiver 310 can be configured to communicate bi-directionally with other devices, such as the BSs 105 or BS 600. The modem subsystem 312 may be configured to modulate and/or encode the data from the memory 304, the capability indication module 308, and/or the precoding configuration module 309 according to a modulation and coding scheme (MCS) , e.g., a low-density parity check (LDPC) coding scheme, a turbo coding scheme, a convolutional coding scheme, a digital beamforming scheme, etc. The RF unit 314 may be configured to process (e.g., perform analog to digital conversion or digital to analog conversion, etc. ) modulated/encoded data from the modem subsystem 312 (on outbound transmissions) or of transmissions originating from another source such as a UE 115 or a BS 105. The RF unit 314 may be further configured to perform analog beamforming in conjunction with the digital beamforming. Although shown as integrated together in transceiver 310, the modem subsystem 312 and the RF unit 314 may be separate devices that are coupled together at the UE 115 to enable the UE 115 to communicate with other devices. The RF unit 314 may correspond to the RF transmit chains included within a transmit chain and receive chain, as discussed in the present disclosure with regard to FIG. 2.

The RF unit 314 may provide the modulated and/or processed data, e.g. data packets (or, more generally, data messages that may contain one or more data packets and other information) , to the antennas 316 for transmission to one or more other devices. The antennas 316 may further receive data messages transmitted from other devices. The antennas 316 may provide the received data messages for processing and/or demodulation at the transceiver 310. The transceiver 310 may provide the demodulated and decoded data (e.g., indication of the maximum transmit power capability or the transmit precoding configuration) to the capability indication module 308 and/or the precoding configuration module 309 for processing. The antennas 316 may include multiple antennas of similar or different designs in order to sustain multiple transmission links. The RF unit 314 may configure the antennas 316.

The antenna (s) 316 may correspond to the antenna element (s) or port (s) discussed in the present disclosure. The UE may determine, based on the transmit precoding configuration, a set of antennas to use for transmitting a communication signal. The UE may also determine, based on the transmit precoding configuration, a set of antennas to not use for transmitting the communication signal. The UE may transmit the communication signal at the maximum transmit power.

In some aspects, the transceiver 310 is configured to transmit an indication of channel estimation and transmit data that has been precoded according to the channel estimation in precoding module 309. In some aspects, the UE 300 can include multiple transceivers 310 implementing different radio access technologies (RATs) (e.g., NR and LTE) . In an aspect, the UE 300 can include a single transceiver 310 implementing multiple RATs (e.g., NR and LTE) . In an aspect, the transceiver 310 can include various components, where different combinations of components can implement different RATs.

FIG. 4 is a block diagram of a BS 400 according to some aspects of the present disclosure. The BS 400 may be a BS 105 as discussed above in FIG. 1 or BS 215 as discussed in FIG. 2. As shown, the BS 400 may include a processor 402, a memory 404, a CSI module 408, a precoding module 409, a transceiver 410 including a modem subsystem 412 and a RF unit 414, and one or more antennas 416. These elements may be in direct or indirect communication with each other, for example via one or more buses.

The processor 402 may have various features as a specific-type processor. For example, these may include a CPU, a DSP, an ASIC, a controller, a FPGA device, another hardware device, a firmware device, or any combination thereof configured to perform the operations described herein. The processor 402 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 memory 404 may include a cache memory (e.g., a cache memory of the processor 402) , RAM, MRAM, ROM, PROM, EPROM, EEPROM, flash memory, a solid state memory device, one or more hard disk drives, memristor-based arrays, other forms of volatile and non-volatile memory, or a combination of different types of memory. In some aspects, the memory 404 may include a non-transitory computer-readable medium. The memory 404 may store instructions 406. The instructions 406 may include instructions that, when executed by the processor 402, cause the processor 402 to perform operations described herein. Instructions 406 may also be referred to as code, which may be interpreted broadly to include any type of computer-readable statement (s) as discussed above with respect to FIG. 4.

The CSI module 408 and/or the precoding module 409 may be implemented via hardware, software, or combinations thereof. The CSI module 408 and/or the precoding module 409 may be implemented as a processor, circuit, and/or instructions 406 stored in the memory 404 and executed by the processor 402. In some instances, the CSI module 408 and/or the precoding module 409 can be integrated within the modem subsystem 412. The CSI module 408 and/or the precoding module 409 can be implemented by a combination of software components (e.g., executed by a DSP or a general processor) and hardware components (e.g., logic gates and circuitry) within the modem subsystem 412. The CSI module 408 and/or the precoding module 409 may be used for various aspects of the present disclosure.

In some aspects, the CSI module 408 may be configured to exchange CSI-RS data with a UE in order to analyze the performance of the communications channels between BS 400 and a corresponding UE. The precoding module 409 may be configured to encode data for transmission according to the channel estimations resulting from the channel analysis performed using the CSI-RS operation. Operation of CSI module 408 and precoding module 409 are further discussed below.

As shown, the transceiver 410 may include the modem subsystem 412 and the RF unit 414. The transceiver 410 can be configured to communicate bi-directionally with other devices, such as the UEs 115 and/or 500 and/or another core network element. The modem subsystem 412 may be configured to modulate and/or encode data according to a MCS, e.g., a LDPC coding scheme, a turbo coding scheme, a convolutional coding scheme, a digital beamforming scheme, etc. The RF unit 414 may be configured to process (e.g., perform analog to digital conversion or digital to analog conversion, etc. ) modulated/encoded data (e.g., grants, resource allocations) from the modem subsystem 412 (on outbound transmissions) or of transmissions originating from another source such as a UE 115 and/or UE 300. The RF unit 414 may be further configured to perform analog beamforming in conjunction with the digital beamforming. Although shown as integrated together in transceiver 410, the modem subsystem 412 and/or the RF unit 414 may be separate devices that are coupled together at the BS 105 to enable the BS 105 to communicate with other devices. The RF unit 414 may correspond to the RF transmit chains and receive chains included within a transmit chain or receive chain, as discussed in the present disclosure.

The RF unit 414 may provide the modulated and/or processed data, e.g. data packets (or, more generally, data messages that may contain one or more data packets and other information) , to the antennas 416 for transmission to one or more other devices. This may include, for example, transmission of information to complete attachment to a network and communication with a camped UE 115 or 300 according to some aspects of the present disclosure. The antennas 416 may further receive data messages transmitted from other devices and provide the received data messages for processing and/or demodulation at the transceiver 410. The transceiver 410 may provide the demodulated and decoded data (e.g., UCI, DMRS) to the CSI module 408 or the precoding module 409 for processing. The antennas 416 may include multiple antennas of similar or different designs in order to sustain multiple transmission links.

In an example, the transceiver 410 is configured to exchange data according to a CSI-RS process with a UE and to precode data for transmission according to channel estimation provided through the CSI-RS process. In some aspects, the BS 400 can include multiple transceivers 410 implementing different RATs (e.g., NR and LTE) . In an aspect, the BS 400 can include a single transceiver 410 implementing multiple RATs (e.g., NR and LTE) . In an aspect, the transceiver 410 can include various components, where different combinations of components can implement different RATs.

Channel status information (CSI) provides a mechanism that a UE uses to report various radio channel quality information back to the gNB, which is then used to determine precoding of data across the analyzed channels. In general, CSI refers to known channel properties of a communications link between a BS and a UE. Such channel properties include, for example, the combined effects of scattering, fading, and power decay with distance.

In the current standard, the average number of CSI-RS resources per resource block is ρ* (number_of-CSI-RS_ports) , where ρ is the CSI-RS Resource Mapping Density. In Type II CSI, the beamformers of different CSI-RS ports are related due to the common spatial domain (SD) basis and frequency domain (FD) basis. In accordance with embodiments of the present invention, these relationships can be used to implement port multiplexing for CSI-RS having the same SD-Basis precoder grouping. Such multiplexing can reduce the average number of CSI-RS resources per RB by half.

In particular, in regular Type II CSI, the elements of the spatial domain basis b _i and the frequency domain basis f _m ^H is related by the following relationship:

where c _i, m represent the linear combination coefficients. FIGs. 5A and 5B illustrate port selection Type II CSI analyzing the above relationship. In FIG. 5A, gNB (e.g. a BS 504) provides precoded CSI-RS via the spatial domain basis b _i and the UE 502 reports the frequency domain basis f _m ^H and the linear combination coefficients c _i, m. In FIG. 3B, gNB (e.g. BS 504) provides precoded CSI-RS via the spatial domain basis b _i and the frequency domain basis f _m ^H and the UE 502 reports the linear combination coefficients c _i, m.

FIG. 5A illustrates a signaling diagram illustrating a method 500 of CSI reporting between UE 502 and BS 504. As illustrated in FIG. 5A, method 500 includes a communication 508 of a sounding reference signal (SRS) transmitted from UE 502 and BS 504. BS 504 responds with precoded CSI-RS via the spatial basis b _i based on spatial reciprocity. UE 502 then responds with communication 512 by reporting the linear combination coefficients c _i, m and the frequency domain f _m ^H.

FIG. 5B illustrates another signaling diagram illustrate a method 520. In this example, in response to communication 508 where an SRS is transmitted. In this example, BS 304 provides communication 314 with the precoded CSI-RS via the spatial domain basis b _i and frequency domain basis f _m ^H. In communication 516, UE 502 reports the linear coefficients c _i, m. The example of FIG. 5B may be appropriate for mismatched upload (UL) /download (DL) bands, for example in frequency division duplex (FDD) signaling. Benefits include low overhead with low UE complexitiy and higher performance due to finer resolution of the frequency domain basis.

FIG. 6 illustrates an example resource allocation scheme 600 used in transmitting the channel estimation in CSI-RS for estimating and transmitting the channel estimation 600 as illustrated in FIG. 5B. FIG. 6 illustrates an example appropriate for fd-CDM2 (frequency divided CDM2) across N FD units 606 (FD unit 0 through FD unit N-1) on four ports 604 (ports 0-3) . As illustrated in FIG. 6, the channel estimation 602 on port 0 provides b _i and f _m ^H distributed across the FD units 406 and the ports 404. The channel

for each port is estimated separately, where H _n describes the channel n between the UE and the BS and occupies a resource element (designated as port and FD unit number) . Consequently, using resource block 0 (RB 0) as an example, for each RB, the output Y ₀ and Y ₁ can be precoded as provided below:

In the above equation, (k ₀, l ₀) represent resource elements where k ₀ represents a subcarrier in the frequency domain and l ₀ represents a symbol in the time domain, the sequences resulting in the matrices

and

are appropriate sequences for fd-CDM2, x ₀ and x ₁ represent elements of the transmission bits, and N ₀ and N ₁ represent noise factors.

In the channel estimation illustrated in Figure 6, each of the channels

is estimated separately. In other words, in the above relations,

and

are separately estimated and transmitted between the BS and the UE.

However, using the properties of certain FD basis, for example discreet Fourier transform (DFT) basis, the relationship of the same SD basis precoder can be shown as illustrated in FIG. 7A. As shown in FIG. 7A, port 0 and port 1 illustrated in ports 604 of FIG. 6 are combined into a virual port 0. Port 2 and port 3 can further be multiplexed into a virtual port 1, however in FIGs. 7A and 7B, the multiplexing of port 0 and port 1 (which are bundled as a spatial bundling group) is demonstrated for simplicity.

As is illustrated in FIG. 7A, using each of the elements that includes the same spatial basis b ₀ (i.e. ports 604 that includes ports 0 and 1) . The frequency basis f ₀ ^H and f ₁ ^H are related by a parameter θ. Consequently, instead of estimating H _nb ₀f ₀ ^H and H _nb ₀f ₁ ^H separately, the combination of H _nb ₀f ₀ ^H and θ can be estimated instead. The relationship in each FD unit 606 is provided in FIG. 7A in blocks 702 such that

Figure 7B then illustrates the multiplexing of blocks 702 into a single virtual port 706. Using the common spatial basis b ₀ spatial grouping, the CSI-RS is multiplexed by summing the channel estimation from port 0 and the newly estimated channel estimation that was originally on port 1. In particular, each two-port pair with the same spatial domain, resulting in the same SD precoder, can be treated as a bundling group and combined into a single virtual port 702 having channel estimation H _nb ₀f ₀ ^H with the relationship parameter θ. The advantage of this multiplexing is to reduce the CSI-RS resources, N _RE per RB/N _CSI-RS port from 1 to 0.5. In other words, in fd-CDM2 each pair of ports can be multiplexed into a single virtual port.

FIG. 8 illustrates this resource reduction. Using the fd-CDM2 example illustrated above, FIG. 8 illustrates a resource scheme 800, which is resource scheme 600 as was illustrated in FIG. 6 above. Concentrating on FD unit 0 and understanding that the same combination is accomplished in each FD unit,

resource elements

806 and 808 can be bundled in the bundling group 0 802 while

resource elements

810 and 812 are bundled into bundling group 1 804. As is illustrated, bunding group 0 802 shares a common spatial basis b ₀ while bundling group 1 804 shares a common spatial basis b ₁. As discussed above with respect to Figure 7B,

resource elements

806 and 808 are multiplexed into the single resource element 814 while

resource elements

810 and 812 are multiplexed into the single resource element 816. As such, the number of resource elements utilized is reduced by half.

FIGs. 9A and 9B further illustrate the multiplexing of the CSI-RS data. Figure 9A illustrates the resource map illustrating

resource elements

806, 808, 810 and 812 as shown in Figure 8. As illustrated,

resource elements

806, 808, 810, and 812 can be grouped in a block 902 according to FD unit 0. Each FD unit can include a 4x4 block of resource elements, of which block 906 for FD unit 1 and block 908 for FD unit N-1 are shown. Figure 9B illustrates the

blocks

902, 906, and 908 with multiplexing as discussed herein. As shown, in Figure 9B, in block 902 resource element 814 (multiplexing elements 806 and 808) and resource element 816 (multiplexing elements 810 and 812) are used, freeing blocks 918 for other purposes. Additionally, blocks 920 of block 906 are freed and blocks 922 of block 908 are freed.

Consequently, for each RB using CSI-RS can be calculated as follows in the example of RB 0 (k ₀, l ₀) as an example.

and

With multiplexing,

and

are estimated jointly. In particular, the channel function estimates

and

are estimated together by determining estimates

and θ and, instead of being transmitted in separate resources, are multiplexed into

based on the spatial basis grouping into a single resource.

As illustrated in the above calculation, the channel estimation can be provided to estimate the quantity

Consequently, the quantities

and θ are estimated. In some embodiments, Y (n) can be transformed to the time domain

which is illustrated in FIG. 10. Consequently, θ can be estimated first, for example using a cyclic shift. Once θ is estimated, then

can be estimated through a linear scheme.

In some embodiments, the parameter θ for particular frequency domain basis set can be chosen from a candidate set {θ ₁, θ ₂, ..., θ _n} . In some embodiments, the candidate set can be defined in advance so that it is held in memory of both the BS and the UE. In some embodiments, the candidate set can be sent to the UE in DCI or RRC configurations.

In some embodiments, threshold values of θ can be defined. For example, a threshold θ _th1 can be defined such that the candidate set satisfies the following relationship: min {θ ₁, θ ₂, ..., θ _n} ≥θ _th1.

Further, a threshold θ _th2 can be defined such that the candidate set satisfies the following relationship:

Such relationships may provide better performance in embodiments.

The above examples involve fd-CDM2 with four ports and results in fd-CDM2 using two virtual ports, freeing two ports to be used for other purposes. Embodiments of the present invention can be used for different CDM-types as well. For example, two-port fd-CDM2 can be accomplished with 1 multiplexed virtual port using noCDM. A 12-port fd-CDM2 in general can be converted to 6 virtual ports using fd-CDM2. However, current applications do not include a 6 port option, so the 12 port fd-CDM2 can be converted to a combination of multiplexed virtual ports and non-multiplexed ports, for example 4 multiplexed virtual ports (8 ports multiplexed) and 4 ports not multiplexed. In general, under current standards, X-port fd-CDM2 can result in X/2 virtual port fd-CDM2, where X=4, 8, 16, 24, or 32.

CDM4-FD2-TD2 can also be converted. Again, 12 port cdm4-FD2-TD2 can be converted to 8-virtual0port fd-CDM2 (four virtual ports) with 4 ports without port multiplexing. Again X-port CDM4-FD2-TD2, under present standards, can be converted to X/2-virtual-port fd-CDM2, where X=8, 16, 24, and 32. Similarly, X-port CDM8-FD2-TD4 can be converted to X/2 virtual port CDM4-FD2-TD2, where X=24, 32. In general, an X-port CDM CSI-RS communication can be provided with Y/2 virtual ports and Z ports such that Z+Y=X.

The multiplexing schemes provided here can reduce the CSI-RS resource requirements by half. Freeing up resources can increase the DL data rate as more resources can be allocated to the PDSCH for downlink data transmission.

Figure 11 illustrates a method of communicating CSI-RS data from a BS to a UE according to some embodiments of the present invention. According to method 1100 illustrated in Figure 11, in step 1102 the parameter θ that relates a first frequency basis f _m and frequency basis f _m+1 is estimated. This is accomplished within a bundling group having the same spatial basis b _i. In some embodiments, the parameter θ can be estimated using a cyclic basis as illustrated in Figure 10. In some embodiments, the parameter θ is chosen from a candidate set {θ ₁, θ ₂, ..., θ _n} that is either fixed or downloaded to the UE separately.

In step 1104, the channel functions within the spatial basis b _i,

is estimated. This estimation can be accomplished using a linear scheme. As a consequence, estimation is accomplished for

for even m (m=0, 2, 4, ... ) and the parameter θ is used to calculate the remaining functions.

In step 1106, the channel functions are multiplexed to form a virtual port having N FD units where the multiplexed channel function is given by

and the virtual port includes channel functions with a common spatial basis b _i.

In step 1108, the BS transmits the virtual port with the multiplexed channel functions to the UE in order to transmit the CSI-RS data.

The functions described herein may be implemented in hardware, software executed by a processor, firmware, or any combination thereof. If implemented in software executed by a processor, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Other examples and implementations are within the scope of the disclosure and appended claims. For example, due to the nature of software, functions described above can be implemented using software executed by a processor, hardware, firmware, hardwiring, or combinations of any of these. Features implementing functions may also be physically located at various positions, including being distributed such that portions of functions are implemented at different physical locations. Also, as used herein, including in the claims, “or” as used in a list of items (for example, a list of items prefaced by a phrase such as “at least one of” or “one or more of” ) indicates an inclusive 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) .

As those of some skill in this art will by now appreciate and depending on the particular application at hand, many modifications, substitutions and variations can be made in and to the materials, apparatus, configurations and methods of use of the devices of the present disclosure without departing from the spirit and scope thereof. In light of this, the scope of the present disclosure should not be limited to that of the particular embodiments illustrated and described herein, as they are merely by way of some examples thereof, but rather, should be fully commensurate with that of the claims appended hereafter and their functional equivalents.

Claims

A method of communicating CSI-RS data from a base station (BS) to a user device (UE) , comprising:

estimating a parameter θ relating a first frequency basis f _m with a second frequency basis f _m+1;

estimating channel functions for a group of ports with a first spatial basis and a first frequency basis;

multiplexing the channel functions for the group of ports using the channel functions for the first spatial basis and the parameter θ into a single virtual port; and

communicating the multiplexed functions.
The method of claim 1, wherein a 4-port fd-CDM2 CSI-RS communication is provided with 2 virtual ports.
The method of claim 1, wherein an X-port fd-CDM2 CSI-RS communication is provided with X/2 virtual ports.
The method of claim 1, wherein the wherein an X-port CDM CSI-RS communication is provided with Y/2 virtual ports and Z ports such that Z+Y=X.
The method of claim 1, wherein the channel functions are provided according to the spatial basis and the frequency basis to provide
and
multiplexed to
The method of claim 5, further including precoding based on the multiplexed channel functions.
The method of claim 1, wherein estimating the parameter θ includes using a cyclic shift of a time domain transform of the function
The method of claim 1, wherein the parameter θ can be selected from a candidate set {θ ₁, θ ₂, . . ., θ _n} .
The method of claim 8, wherein the candidate set is defined.
The method of claim 8, wherein the candidate set is transmitted prior to the CSI-RS communication.
The method of claim 8, wherein a minimum of the candidate set is greater than or equal to a first threshold.
The method of claim 8, wherein the minimum difference between different members of the set is greater than or equal to a second threshold.
An apparatus operating as a base station, the apparatus comprising:

a plurality of antennas;

a transmit chain providing X ports coupled to the plurality of antennas;

a CSI module configured to transmit CSI-RS data to a user equipment (UE) using the X ports, the CSI module

estimating a parameter θ relating a first frequency basis f _m with a second frequency basis f _m+1;

estimating channel functions for a group of ports with a first spatial basis and a first frequency basis;

multiplexing the channel functions for the group of ports using the channel functions for the first spatial basis and the parameter θ into a single virtual port; and

communicating the multiplexed functions.
The apparatus of claim 14, wherein an X-port CDM CSI-RS communication is provided with Y/2 virtual ports and Z ports such that Z+Y=X.
The apparatus of claim 14, wherein the channel functions are provided according to the spatial basis and the frequency basis to provide
and
multiplexed to
The apparatus of claim 14, wherein the CSI module estimates the parameter θ can be estimated using a cyclic shift of a time domain transform of the function
The apparatus of claim 14, wherein the parameter θ can be selected from a candidate set {θ ₁, θ ₂, . . ., θ _n} .
The apparatus of claim 18, wherein the candidate set is defined.
The apparatus of claim 18, wherein a minimum of the candidate set is greater than or equal to a first threshold.
The apparatus of claim 18, wherein the minimum difference between different members of the set is greater than or equal to a second threshold.
An apparatus for transmitting CSI-RS data, comprising:means for estimating a parameter θ relating a first frequency basis f _m with a second frequency basis f _m+1;

means for estimating channel functions for a group of ports with a first spatial basis and a first frequency basis;

means for multiplexing the channel functions for the group of ports using the channel functions for the first spatial basis and the parameter θ into a single virtual port; and

means for communicating the multiplexed functions.