WO2022027577A1

WO2022027577A1 - Port specific channel state information (csi) reference signal frequency domain density (fdd) for fdd reciprocity csi reporting

Info

Publication number: WO2022027577A1
Application number: PCT/CN2020/107780
Authority: WO
Inventors: Liangming WU; Chenxi HAO; Lei Xiao; Rui Hu; Yu Zhang
Original assignee: Qualcomm Incorporated
Priority date: 2020-08-07
Filing date: 2020-08-07
Publication date: 2022-02-10

Abstract

Methods, systems, and devices for wireless communications are described. In one example, a method for wireless communication at a user equipment (UE) includes receiving a configuration signal from a base station that indicates a frequency domain density (FDD) for one or more channel state information reference signal (CSI-RS) ports and performing CSI-RS measurements for the one or more CSI-RS ports based at least in part on the indicated FDD. The method may include generating a CSI report using the CSI-RS ports based on the CSI-RS measurements and transmitting the CSI report. Another example includes a base station performing channel measurements on a wireless channel between the base station and a UE, determining an FDD for one or more CSI-RS ports at the UE based at least in part on the channel measurements, and sending a configuration signal that indicates an FDD for the one or more CSI-RS ports.

Description

PORT SPECIFIC CHANNEL STATE INFORMATION (CSI) REFERENCE SIGNAL FREQUENCY DOMAIN DENSITY (FDD) FOR FDD RECIPROCITY CSI REPORTING

FIELD OF TECHNOLOGY

The following relates to wireless communications, including port specific channel state information (CSI) reference signal (CSI-RS) frequency domain density (FDD) for FDD reciprocity CSI reporting.

BACKGROUND

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) . Examples of such multiple-access systems include fourth generation (4G) systems such as Long Term Evolution (LTE) systems, LTE-Advanced (LTE-A) systems, or LTE-A Pro systems, and fifth generation (5G) systems which may be referred to as New Radio (NR) systems. These systems may employ technologies such as code division multiple access (CDMA) , time division multiple access (TDMA) , frequency division multiple access (FDMA) , orthogonal frequency division multiple access (OFDMA) , or discrete Fourier transform spread orthogonal frequency division multiplexing (DFT-S-OFDM) . A wireless multiple-access communications system may include one or more base stations or one or more network access nodes, each simultaneously supporting communication for multiple communication devices, which may be otherwise known as user equipment (UE) .

SUMMARY

The described techniques relate to improved methods, systems, devices, and apparatuses that support port specific CSI-RS FDD for FDD reciprocity CSI reporting. Generally, the described techniques provide for reducing overhead at the UE and the base station for CSI and PMI processing. A base station may reduce CSI-RS overhead by assigning different frequency domain densities for different CSI-RS ports at the UE. The techniques described herein also provide channel-pruning for the precoder processing. The FD precoding granularity of the CSI-RS may be port-specific, which saves CSI-RS overhead. The base station can use this to determine the frequency domain density for different CSI-RS ports and signal the configuration to the UE. The UE can measure CSI using the frequency domain density based on the reporting.

A method of wireless communication at a UE is described. The method may include receiving a configuration signal from a base station that indicates a frequency domain density for one or more channel state information reference signal ports, performing CSI-RS measurements for the one or more CSI-RS ports based on the indicated frequency domain density, generating a channel state information report using the one or more CSI-RS ports based on the CSI-RS measurements, and transmitting the CSI report to the base station.

An apparatus for wireless communication at a UE is described. The apparatus may include a processor, memory coupled with the processor, and instructions stored in the memory. The instructions may be executable by the processor to cause the apparatus to receive a configuration signal from a base station that indicates a frequency domain density for one or more channel state information reference signal ports, perform CSI-RS measurements for the one or more CSI-RS ports based on the indicated frequency domain density, generate a channel state information report using the one or more CSI-RS ports based on the CSI-RS measurements, and transmit the CSI report to the base station.

Another apparatus for wireless communication at a UE is described. The apparatus may include means for receiving a configuration signal from a base station that indicates a frequency domain density for one or more channel state information reference signal ports, performing CSI-RS measurements for the one or more CSI-RS ports based on the indicated frequency domain density, generating a channel state information report using the one or more CSI-RS ports based on the CSI-RS measurements, and transmitting the CSI report to the base station.

A non-transitory computer-readable medium storing code for wireless communication at a UE is described. The code may include instructions executable by a processor to receive a configuration signal from a base station that indicates a frequency domain density for one or more channel state information reference signal ports, perform CSI-RS measurements for the one or more CSI-RS ports based on the indicated frequency domain density, generate a channel state information report using the one or more CSI-RS ports based on the CSI-RS measurements, and transmit the CSI report to the base station.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, receiving the configuration signal from the base station may include operations, features, means, or instructions for receiving a first frequency domain density for a first CSI-RS port of the one or more CSI-RS ports, and receiving a second frequency domain density for a second CSI-RS port of the one or more CSI-RS ports, where the second frequency domain density may be different than the first frequency domain density.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, performing CSI-RS measurements for the one or more CSI-RS ports further may include operations, features, means, or instructions for measuring a channel quality indicator (CQI) for one or more resource blocks that overlap at the first CSI-RS port and the second CSI-RS port.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for limiting CQI measurement to overlapping resource blocks associated with CSI-RS ports having different frequency domain densities.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, the frequency domain density for each of the one or more CSI-RS ports may be based on a subband size associated with communications between the base station and the UE.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, generating the CSI report using the one or more CSI-RS ports may include operations, features, means, or instructions for generating a precoding matrix indicator based on the CSI-RS measurements for the one or more CSI-RS ports, where the CSI report includes the precoding matrix indicator.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, the precoding matrix indicator includes a wideband precoding matrix indicator.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, a total number of CSI-RS ports associated with the precoding matrix indicator may be based on a combination of CSI-RS resource blocks according to the indicated frequency domain density for the one or more CSI-RS ports.

A method of wireless communication at a base station is described. The method may include performing channel measurements on a wireless channel between the base station and a UE, determining a frequency domain density for one or more channel state information reference signal ports at the UE based on the channel measurements, and sending a configuration signal to the UE that indicates a frequency domain density for the one or more CSI-RS ports at the UE.

An apparatus for wireless communication at a base station is described. The apparatus may include a processor, memory coupled with the processor, and instructions stored in the memory. The instructions may be executable by the processor to cause the apparatus to perform channel measurements on a wireless channel between the base station and a UE, determine a frequency domain density for one or more channel state information reference signal ports at the UE based on the channel measurements, and send a configuration signal to the UE that indicates a frequency domain density for the one or more CSI-RS ports at the UE.

Another apparatus for wireless communication at a base station is described. The apparatus may include means for performing channel measurements on a wireless channel between the base station and a UE, determining a frequency domain density for one or more channel state information reference signal ports at the UE based on the channel measurements, and sending a configuration signal to the UE that indicates a frequency domain density for the one or more CSI-RS ports at the UE.

A non-transitory computer-readable medium storing code for wireless communication at a base station is described. The code may include instructions executable by a processor to perform channel measurements on a wireless channel between the base station and a UE, determine a frequency domain density for one or more channel state information reference signal ports at the UE based on the channel measurements, and send a configuration signal to the UE that indicates a frequency domain density for the one or more CSI-RS ports at the UE.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for determining precoders for one or more CSI-RSs based on the channel measurements for each subband of a sounding reference signal.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, determining the frequency domain density for the one or more CSI-RS ports further may include operations, features, means, or instructions for estimating the frequency domain density for the one or more CSI-RS ports based on the channel measurements.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, determining the frequency domain density for the one or more CSI-RS ports further may include operations, features, means, or instructions for determining a first frequency domain density for a first CSI-RS port of the one or more CSI-RS ports, and determining a second frequency domain density for a second CSI-RS port of the one or more CSI-RS ports, where the second frequency domain density may be different than the first frequency domain density and where the configuration signal indicates the first frequency domain density and the second frequency domain density.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, determining the frequency domain density for the one or more CSI-RS ports further may include operations, features, means, or instructions for comparing a first frequency domain fluctuation at a first CSI-RS port with a second frequency domain fluctuation at a second CSI-RS port, setting a first frequency domain density for the first CSI-RS port to be larger than a second frequency domain density for the second CSI-RS port when the first frequency domain fluctuation may be higher than the second frequency domain fluctuation, and setting the first frequency domain density for the first CSI-RS port to be smaller than the second frequency domain density for the second CSI-RS port when the first frequency domain fluctuation may be lower than the second frequency domain fluctuation.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for receiving a CSI report from the UE, where the CSI report may be based on the configuration signal.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, the CSI report may be limited to overlapping resource blocks associated with CSI-RS ports having different frequency domain densities.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, a total number of CSI-RS ports associated with the precoding matrix indicator may be based on a combination of CSI-RS resource blocks according to the frequency domain density for the one or more CSI-RS ports.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, the CSI report includes a precoding matrix indicator based on CSI-RS measurements for the one or more CSI-RS ports.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of a system for wireless communications that supports port specific CSI-RS FDD for FDD reciprocity CSI reporting in accordance with aspects of the present disclosure.

FIG. 2 illustrates an example of a swim diagram of a wireless communications system that supports port specific CSI-RS FDD for FDD reciprocity CSI reporting in accordance with aspects of the present disclosure.

FIG. 3 illustrates an example of a block diagram that supports port specific CSI-RS FDD for FDD reciprocity CSI reporting in accordance with aspects of the present disclosure.

FIG. 4 illustrates an example of a block diagram that supports port specific CSI-RS FDD for FDD reciprocity CSI reporting in accordance with aspects of the present disclosure.

FIG. 5 illustrates an example of a block diagram that supports port specific CSI-RS FDD for FDD reciprocity CSI reporting in accordance with aspects of the present disclosure.

FIG. 6 illustrates an example of block diagram that shows CSI reporting configuration for two CSI-RS ports with different frequency domain densities in accordance with aspects of the present disclosure.

FIGs. 7 and 8 show block diagrams of devices that support port specific CSI-RS FDD for FDD reciprocity CSI reporting in accordance with aspects of the present disclosure.

FIG. 9 shows a block diagram of a communications manager that supports port specific CSI-RS FDD for FDD reciprocity CSI reporting in accordance with aspects of the present disclosure.

FIG. 10 shows a diagram of a system including a device that supports port specific CSI-RS FDD for FDD reciprocity CSI reporting in accordance with aspects of the present disclosure.

FIGs. 11 and 12 show block diagrams of devices that support port specific CSI-RS FDD for FDD reciprocity CSI reporting in accordance with aspects of the present disclosure.

FIG. 13 shows a block diagram of a communications manager that supports port specific CSI-RS FDD for FDD reciprocity CSI reporting in accordance with aspects of the present disclosure.

FIG. 14 shows a diagram of a system including a device that supports port specific CSI-RS FDD for FDD reciprocity CSI reporting in accordance with aspects of the present disclosure.

FIGs. 15 through 18 show flowcharts illustrating methods that support port specific CSI-RS FDD for FDD reciprocity CSI reporting in accordance with aspects of the present disclosure.

DETAILED DESCRIPTION

Some wireless communications systems, such as New Radio (NR) /5G systems, may use multiple antennas at the transmitter and receiver sides in order to provide diversity against fading, improve beamforming, enable spatial multiplexing, and suppress interference, for example. A precoder matrix may be a transmission matrix that is applied to the signals to be transmitted, which results in multi-antenna precoding. The precoding may be applied to reference signals, such as channel state information reference signals (CSI-RS) for downlink channel sounding or sounding reference signals (SRSs) for uplink channel sounding. Channel sounding is a technique used to evaluate a radio environment in wireless communications.

A UE may provide a channel state information (CSI) report to a base station with information related to the channel conditions and precoding. The CSI report may include a Precoder Matrix Indicator (PMI) that indicates a suitable precoder matrix based on a selected transmission rank and a Channel-Quality Indicator (CQI) that indicates a suitable channel-coding rate and modulation scheme based at least in part on the selected precoder matrix.

The PMI reported by the UE indicates a suitable precoder matrix for the base station to use for downlink transmission to the device. A specific PMI value corresponds to one specific precoder matrix. A set of possible PMI values correspond to a set of different precoder matrices which are defined in a precoder codebook. The UE selects the PMI based on a number of antenna ports of the CSI-RS and the selected rank. There may be at least one codebook for each valid combination of antenna ports and rank.

However, the base station may or may not use the precoder indicated by the PMI for downlink transmissions. For example, the base station may decide to use a different precoder in an MU-MIMO scenario. In MU-MIMO, the transmitter may use multi-antenna precoding to enable simultaneous downlink transmissions to multiple UEs or other devices using the same time and frequency resources. In MU-MIMO, a precoding matrix may be selected in order to focus energy to the target device while also limiting interference with other simultaneously scheduled devices. Because of using MU-MIMO, the CSI may be a Type II CSI that is mostly for MU-MIMO scenarios. Type II CSI may also use Type II codebooks, which may allow for the PMI to provide channel information with higher spatial granularity than Type I codebooks, which are mainly for scenarios without MU-MIMO. This higher spatial granularity enables the transmitter to select a downlink precoder that focuses the transmitted energy at the target device and attempts to limit interference with other devices simultaneously scheduled on the same time and frequency resources. However, the higher spatial granularity for the PMI feedback in the Type II CSI comes with a large processing and signaling overhead. In other words, a base station may generate spatial domain (SD) and frequency domain (FD) precoded CSI-RS using a Type II precoder on a subband for joint SD and FD port emulation. However, a large overhead is needed for port specific SD and FD precoding.

Techniques described herein reduce the processing and signaling overhead for PMI feedback in Type II CSI. A base station may reduce CSI-RS overhead by assigning different frequency domain densities for different CSI-RS ports at the UE. In some examples, the CSI-RS can be configured to all or a fraction of a bandwidth part (BWP) . Where the CSI-RS is configured to all of the BWP, the CSI-RS is configured for transmission in every resource block, referred to as a CSI-RS density of one. Where the CSI-RS is configured to part of the bandwidth part, the CSI-RS may be configured for transmission for less than all resource blocks. For example, the CSI-RS may be configured for transmission every other resource block, for a CSI-RS density of 0.5.

The techniques described herein also provide channel-pruning for the precoder processing, which essentially acts as a low pass filter applied to subband channels for the wireless channel. For example, longer filtering taps may be used to achieve better DC tone power, and CSI-RS ports that have strong DC tone can support lower frequency domain density. The base station can determine the frequency domain density for different CSI-RS ports and signal the configuration to the UE. The UE can measure CSI using the frequency domain density based on the reporting. The FD precoding granularity of the CSI-RS may be port-specific, which saves CSI-RS overhead.

In some examples, a base station may perform techniques described herein related to setting frequency domain densities for CSI-RS ports. The base station may perform channel measurements on a wireless channel between the base station and a UE and determine an FDD for one or more CSI-RS ports at the UE based at least in part on the channel measurements. The base station may send a configuration signal to the UE that indicates an FDD for the one or more CSI-RS ports at the UE.

In other examples, a UE receives a configuration signal from a base station that indicates a frequency domain density for one or more CSI-RS ports, measures CSI at the CSI-RS ports accordingly, and sends a CSI report to the base station. Two different CSI-RS ports at the UE may be used with two different frequency domain densities. CQI may be computed for one or more resource blocks that overlap at the two or more CSI-RS ports having different frequency domain densities. In some examples, the FDD may be based at least in part on a subband size.

The described techniques may reduce overhead at the UE and the base station for PMI processing, reduce bit error rates, improve efficiencies, improve coding rates, decrease system latency, and improve user experience. The described techniques may improve CSI-RS overhead.

Aspects of the disclosure are initially described in the context of wireless communications systems. Aspects of the disclosure are further illustrated by and described with reference to a swim diagram and several block diagrams. Aspects of the disclosure are further illustrated by and described with reference to apparatus diagrams, system diagrams, and flowcharts that relate to port specific CSI-RS FDD for FDD reciprocity CSI reporting.

FIG. 1 illustrates an example of a wireless communications system 100 that supports port specific CSI-RS FDD for FDD reciprocity CSI reporting in accordance with aspects of the present disclosure. The wireless communications system 100 may include one or more base stations 105, one or more UEs 115, and a core network 130. In some examples, the wireless communications system 100 may be a Long Term Evolution (LTE) network, an LTE-Advanced (LTE-A) network, an LTE-A Pro network, or a New Radio (NR) network. In some examples, the wireless communications system 100 may support enhanced broadband communications, ultra-reliable (e.g., mission critical) communications, low latency communications, communications with low-cost and low-complexity devices, or any combination thereof.

The base stations 105 may be dispersed throughout a geographic area to form the wireless communications system 100 and may be devices in different forms or having different capabilities. The base stations 105 and the UEs 115 may wirelessly communicate via one or more communication links 125. Each base station 105 may provide a coverage area 110 over which the UEs 115 and the base station 105 may establish one or more communication links 125. The coverage area 110 may be an example of a geographic area over which a base station 105 and a UE 115 may support the communication of signals according to one or more radio access technologies.

The UEs 115 may be dispersed throughout a coverage area 110 of the wireless communications system 100, and each UE 115 may be stationary, or mobile, or both at different times. The UEs 115 may be devices in different forms or having different capabilities. Some example UEs 115 are illustrated in FIG. 1. The UEs 115 described herein may be able to communicate with various types of devices, such as other UEs 115, the base stations 105, or network equipment (e.g., core network nodes, relay devices, integrated access and backhaul (IAB) nodes, or other network equipment) , as shown in FIG. 1.

The base stations 105 may communicate with the core network 130, or with one another, or both. For example, the base stations 105 may interface with the core network 130 through one or more backhaul links 120 (e.g., via an S1, N2, N3, or other interface) . The base stations 105 may communicate with one another over the backhaul links 120 (e.g., via an X2, Xn, or other interface) either directly (e.g., directly between base stations 105) , or indirectly (e.g., via core network 130) , or both. In some examples, the backhaul links 120 may be or include one or more wireless links.

One or more of the base stations 105 described herein may include or may be referred to by a person having ordinary skill in the art as a base transceiver station, a radio base station, an access point, a radio transceiver, a NodeB, an eNodeB (eNB) , a next-generation NodeB or a giga-NodeB (either of which may be referred to as a gNB) , a Home NodeB, a Home eNodeB, or other suitable terminology.

A UE 115 may include or may be referred to as a mobile device, a wireless device, a remote device, a handheld device, or a subscriber device, or some other suitable terminology, where the “device” may also be referred to as a unit, a station, a terminal, or a client, among other examples. A UE 115 may also include or may be referred to as a personal electronic device such as a cellular phone, a personal digital assistant (PDA) , a tablet computer, a laptop computer, or a personal computer. In some examples, a UE 115 may include or be referred to as a wireless local loop (WLL) station, an Internet of Things (IoT) device, an Internet of Everything (IoE) device, or a machine type communications (MTC) device, among other examples, which may be implemented in various objects such as appliances, or vehicles, meters, among other examples.

The UEs 115 described herein may be able to communicate with various types of devices, such as other UEs 115 that may sometimes act as relays as well as the base stations 105 and the network equipment including macro eNBs or gNBs, small cell eNBs or gNBs, or relay base stations, among other examples, as shown in FIG. 1.

The UEs 115 and the base stations 105 may wirelessly communicate with one another via one or more communication links 125 over one or more carriers. The term “carrier” may refer to a set of radio frequency spectrum resources having a defined physical layer structure for supporting the communication links 125. For example, a carrier used for a communication link 125 may include a portion of a radio frequency spectrum band (e.g., a bandwidth part (BWP) ) that is operated according to one or more physical layer channels for a given radio access technology (e.g., LTE, LTE-A, LTE-A Pro, NR) . Each physical layer channel may carry acquisition signaling (e.g., synchronization signals, system information) , control signaling that coordinates operation for the carrier, user data, or other signaling. The wireless communications system 100 may support communication with a UE 115 using carrier aggregation or multi-carrier operation. A UE 115 may be configured with multiple downlink component carriers and one or more uplink component carriers according to a carrier aggregation configuration. Carrier aggregation may be used with both frequency division duplexing and time division duplexing (TDD) component carriers.

In some examples (e.g., in a carrier aggregation configuration) , a carrier may also have acquisition signaling or control signaling that coordinates operations for other carriers. A carrier may be associated with a frequency channel (e.g., an evolved universal mobile telecommunication system terrestrial radio access (E-UTRA) absolute radio frequency channel number (EARFCN) ) and may be positioned according to a channel raster for discovery by the UEs 115. A carrier may be operated in a standalone mode where initial acquisition and connection may be conducted by the UEs 115 via the carrier, or the carrier may be operated in a non-standalone mode where a connection is anchored using a different carrier (e.g., of the same or a different radio access technology) .

The communication links 125 shown in the wireless communications system 100 may include uplink transmissions from a UE 115 to a base station 105, or downlink transmissions from a base station 105 to a UE 115. Carriers may carry downlink or uplink communications (e.g., in an FDD mode) or may be configured to carry downlink and uplink communications (e.g., in a TDD mode) .

A carrier may be associated with a particular bandwidth of the radio frequency spectrum, and in some examples the carrier bandwidth may be referred to as a “system bandwidth” of the carrier or the wireless communications system 100. For example, the carrier bandwidth may be one of a number of determined bandwidths for carriers of a particular radio access technology (e.g., 1.4, 3, 5, 10, 15, 20, 40, or 80 megahertz (MHz) ) . Devices of the wireless communications system 100 (e.g., the base stations 105, the UEs 115, or both) may have hardware configurations that support communications over a particular carrier bandwidth or may be configurable to support communications over one of a set of carrier bandwidths. In some examples, the wireless communications system 100 may include base stations 105 or UEs 115 that support simultaneous communications via carriers associated with multiple carrier bandwidths. In some examples, each served UE 115 may be configured for operating over portions (e.g., a sub-band, a BWP) or all of a carrier bandwidth.

Signal waveforms transmitted over a carrier may be made up of multiple subcarriers (e.g., using multi-carrier modulation (MCM) techniques such as orthogonal frequency division multiplexing (OFDM) or discrete Fourier transform spread OFDM (DFT-S-OFDM) ) . In a system employing MCM techniques, a resource element may consist of one symbol period (e.g., a duration of one modulation symbol) and one subcarrier, where the symbol period and subcarrier spacing are inversely related. The number of bits carried by each resource element may depend on the modulation scheme (e.g., the order of the modulation scheme, the coding rate of the modulation scheme, or both) . Thus, the more resource elements that a UE 115 receives and the higher the order of the modulation scheme, the higher the data rate may be for the UE 115. A wireless communications resource may refer to a combination of a radio frequency spectrum resource, a time resource, and a spatial resource (e.g., spatial layers or beams) , and the use of multiple spatial layers may further increase the data rate or data integrity for communications with a UE 115.

One or more numerologies for a carrier may be supported, where a numerology may include a subcarrier spacing (Δf) and a cyclic prefix. A carrier may be divided into one or more BWPs having the same or different numerologies. In some examples, a UE 115 may be configured with multiple BWPs. In some examples, a single BWP for a carrier may be active at a given time and communications for the UE 115 may be restricted to one or more active BWPs.

The time intervals for the base stations 105 or the UEs 115 may be expressed in multiples of a basic time unit which may, for example, refer to a sampling period of T _s= 1/ (Δf _max·N _f) seconds, where Δf _max may represent the maximum supported subcarrier spacing, and N _f may represent the maximum supported discrete Fourier transform (DFT) size. Time intervals of a communications resource may be organized according to radio frames each having a specified duration (e.g., 10 milliseconds (ms) ) . Each radio frame may be identified by a system frame number (SFN) (e.g., ranging from 0 to 1023) .

Each frame may include multiple consecutively numbered subframes or slots, and each subframe or slot may have the same duration. In some examples, a frame may be divided (e.g., in the time domain) into subframes, and each subframe may be further divided into a number of slots. Alternatively, each frame may include a variable number of slots, and the number of slots may depend on subcarrier spacing. Each slot may include a number of symbol periods (e.g., depending on the length of the cyclic prefix prepended to each symbol period) . In some wireless communications systems 100, a slot may further be divided into multiple mini-slots containing one or more symbols. Excluding the cyclic prefix, each symbol period may contain one or more (e.g., N _f) sampling periods. The duration of a symbol period may depend on the subcarrier spacing or frequency band of operation.

A subframe, a slot, a mini-slot, or a symbol may be the smallest scheduling unit (e.g., in the time domain) of the wireless communications system 100 and may be referred to as a transmission time interval (TTI) . In some examples, the TTI duration (e.g., the number of symbol periods in a TTI) may be variable. Additionally or alternatively, the smallest scheduling unit of the wireless communications system 100 may be dynamically selected (e.g., in bursts of shortened TTIs (sTTIs) ) .

Physical channels may be multiplexed on a carrier according to various techniques. A physical control channel and a physical data channel may be multiplexed on a downlink carrier, for example, using one or more of time division multiplexing (TDM) techniques, frequency division multiplexing (FDM) techniques, or hybrid TDM-FDM techniques. A control region (e.g., a control resource set (CORESET) ) for a physical control channel may be defined by a number of symbol periods and may extend across the system bandwidth or a subset of the system bandwidth of the carrier. One or more control regions (e.g., CORESETs) may be configured for a set of the UEs 115. For example, one or more of the UEs 115 may monitor or search control regions for control information according to one or more search space sets, and each search space set may include one or multiple control channel candidates in one or more aggregation levels arranged in a cascaded manner. An aggregation level for a control channel candidate may refer to a number of control channel resources (e.g., control channel elements (CCEs) ) associated with encoded information for a control information format having a given payload size. Search space sets may include common search space sets configured for sending control information to multiple UEs 115 and UE-specific search space sets for sending control information to a specific UE 115.

In some examples, a base station 105 may be movable and therefore provide communication coverage for a moving geographic coverage area 110. In some examples, different geographic coverage areas 110 associated with different technologies may overlap, but the different geographic coverage areas 110 may be supported by the same base station 105. In other examples, the overlapping geographic coverage areas 110 associated with different technologies may be supported by different base stations 105. The wireless communications system 100 may include, for example, a heterogeneous network in which different types of the base stations 105 provide coverage for various geographic coverage areas 110 using the same or different radio access technologies.

The wireless communications system 100 may support synchronous or asynchronous operation. For synchronous operation, the base stations 105 may have similar frame timings, and transmissions from different base stations 105 may be approximately aligned in time. For asynchronous operation, the base stations 105 may have different frame timings, and transmissions from different base stations 105 may, in some examples, not be aligned in time. The techniques described herein may be used for either synchronous or asynchronous operations.

Some UEs 115, such as MTC or IoT devices, may be low cost or low complexity devices and may provide for automated communication between machines (e.g., via Machine-to-Machine (M2M) communication) . M2M communication or MTC may refer to data communication technologies that allow devices to communicate with one another or a base station 105 without human intervention. In some examples, M2M communication or MTC may include communications from devices that integrate sensors or meters to measure or capture information and relay such information to a central server or application program that makes use of the information or presents the information to humans interacting with the application program. Some UEs 115 may be designed to collect information or enable automated behavior of machines or other devices. Examples of applications for MTC devices include smart metering, inventory monitoring, water level monitoring, equipment monitoring, healthcare monitoring, wildlife monitoring, weather and geological event monitoring, fleet management and tracking, remote security sensing, physical access control, and transaction-based business charging.

The wireless communications system 100 may be configured to support ultra-reliable communications or low-latency communications, or various combinations thereof. For example, the wireless communications system 100 may be configured to support ultra-reliable low-latency communications (URLLC) or mission critical communications. The UEs 115 may be designed to support ultra-reliable, low-latency, or critical functions (e.g., mission critical functions) . Ultra-reliable communications may include private communication or group communication and may be supported by one or more mission critical services such as mission critical push-to-talk (MCPTT) , mission critical video (MCVideo) , or mission critical data (MCData) . Support for mission critical functions may include prioritization of services, and mission critical services may be used for public safety or general commercial applications. The terms ultra-reliable, low-latency, mission critical, and ultra-reliable low-latency may be used interchangeably herein.

In some examples, a UE 115 may also be able to communicate directly with other UEs 115 over a device-to-device (D2D) communication link 135 (e.g., using a peer-to-peer (P2P) or D2D protocol) . One or more UEs 115 utilizing D2D communications may be within the geographic coverage area 110 of a base station 105. Other UEs 115 in such a group may be outside the geographic coverage area 110 of a base station 105 or be otherwise unable to receive transmissions from a base station 105. In some examples, groups of the UEs 115 communicating via D2D communications may utilize a one-to-many (1: M) system in which each UE 115 transmits to every other UE 115 in the group. In some examples, a base station 105 facilitates the scheduling of resources for D2D communications. In other cases, D2D communications are carried out between the UEs 115 without the involvement of a base station 105.

The core network 130 may provide user authentication, access authorization, tracking, Internet Protocol (IP) connectivity, and other access, routing, or mobility functions. The core network 130 may be an evolved packet core (EPC) or 5G core (5GC) , which may include at least one control plane entity that manages access and mobility (e.g., a mobility management entity (MME) , an access and mobility management function (AMF) ) and at least one user plane entity that routes packets or interconnects to external networks (e.g., a serving gateway (S-GW) , a Packet Data Network (PDN) gateway (P-GW) , or a user plane function (UPF) ) . The control plane entity may manage non-access stratum (NAS) functions such as mobility, authentication, and bearer management for the UEs 115 served by the base stations 105 associated with the core network 130. User IP packets may be transferred through the user plane entity, which may provide IP address allocation as well as other functions. The user plane entity may be connected to the network operators IP services 150. The network operators IP services 150 may include access to the Internet, Intranet (s) , an IP Multimedia Subsystem (IMS) , or a Packet-Switched Streaming Service.

Some of the network devices, such as a base station 105, may include subcomponents such as an access network entity 140, which may be an example of an access node controller (ANC) . Each access network entity 140 may communicate with the UEs 115 through one or more other access network transmission entities 145, which may be referred to as radio heads, smart radio heads, or transmission/reception points (TRPs) . Each access network transmission entity 145 may include one or more antenna panels. In some configurations, various functions of each access network entity 140 or base station 105 may be distributed across various network devices (e.g., radio heads and ANCs) or consolidated into a single network device (e.g., a base station 105) .

The wireless communications system 100 may operate using one or more frequency bands, typically in the range of 300 megahertz (MHz) to 300 gigahertz (GHz) . Generally, the region from 300 MHz to 3 GHz is known as the ultra-high frequency (UHF) region or decimeter band because the wavelengths range from approximately one decimeter to one meter in length. The UHF waves may be blocked or redirected by buildings and environmental features, but the waves may penetrate structures sufficiently for a macro cell to provide service to the UEs 115 located indoors. The transmission of UHF waves may be associated with smaller antennas and shorter ranges (e.g., less than 100 kilometers) compared to transmission using the smaller frequencies and longer waves of the high frequency (HF) or very high frequency (VHF) portion of the spectrum below 300 MHz.

The wireless communications system 100 may utilize both licensed and unlicensed radio frequency spectrum bands. For example, the wireless communications system 100 may employ License Assisted Access (LAA) , LTE-Unlicensed (LTE-U) radio access technology, or NR technology in an unlicensed band such as the 5 GHz industrial, scientific, and medical (ISM) band. When operating in unlicensed radio frequency spectrum bands, devices such as the base stations 105 and the UEs 115 may employ carrier sensing for collision detection and avoidance. In some examples, operations in unlicensed bands may be based on a carrier aggregation configuration in conjunction with component carriers operating in a licensed band (e.g., LAA) . Operations in unlicensed spectrum may include downlink transmissions, uplink transmissions, P2P transmissions, or D2D transmissions, among other examples.

A base station 105 or a UE 115 may be equipped with multiple antennas, which may be used to employ techniques such as transmit diversity, receive diversity, multiple-input multiple-output (MIMO) communications, or beamforming. The antennas of a base station 105 or a UE 115 may be located within one or more antenna arrays or antenna panels, which may support MIMO operations or transmit or receive beamforming. For example, one or more base station antennas or antenna arrays may be co-located at an antenna assembly, such as an antenna tower. In some examples, antennas or antenna arrays associated with a base station 105 may be located in diverse geographic locations. A base station 105 may have an antenna array with a number of rows and columns of antenna ports that the base station 105 may use to support beamforming of communications with a UE 115. Likewise, a UE 115 may have one or more antenna arrays that may support various MIMO or beamforming operations. Additionally or alternatively, an antenna panel may support radio frequency beamforming for a signal transmitted via an antenna port.

The base stations 105 or the UEs 115 may use MIMO communications to exploit multipath signal propagation and increase the spectral efficiency by transmitting or receiving multiple signals via different spatial layers. Such techniques may be referred to as spatial multiplexing. The multiple signals may, for example, be transmitted by the transmitting device via different antennas or different combinations of antennas. Likewise, the multiple signals may be received by the receiving device via different antennas or different combinations of antennas. Each of the multiple signals may be referred to as a separate spatial stream and may carry bits associated with the same data stream (e.g., the same codeword) or different data streams (e.g., different codewords) . Different spatial layers may be associated with different antenna ports used for channel measurement and reporting. MIMO techniques include single-user MIMO (SU-MIMO) , where multiple spatial layers are transmitted to the same receiving device, and multiple-user MIMO (MU-MIMO) , where multiple spatial layers are transmitted to multiple devices.

Beamforming, which may also be referred to as spatial filtering, directional transmission, or directional reception, is a signal processing technique that may be used at a transmitting device or a receiving device (e.g., a base station 105, a UE 115) to shape or steer an antenna beam (e.g., a transmit beam, a receive beam) along a spatial path between the transmitting device and the receiving device. Beamforming may be achieved by combining the signals communicated via antenna elements of an antenna array such that some signals propagating at particular orientations with respect to an antenna array experience constructive interference while others experience destructive interference. The adjustment of signals communicated via the antenna elements may include a transmitting device or a receiving device applying amplitude offsets, phase offsets, or both to signals carried via the antenna elements associated with the device. The adjustments associated with each of the antenna elements may be defined by a beamforming weight set associated with a particular orientation (e.g., with respect to the antenna array of the transmitting device or receiving device, or with respect to some other orientation) .

A base station 105 or a UE 115 may use beam sweeping techniques as part of beam forming operations. For example, a base station 105 may use multiple antennas or antenna arrays (e.g., antenna panels) to conduct beamforming operations for directional communications with a UE 115. Some signals (e.g., synchronization signals, reference signals, beam selection signals, or other control signals) may be transmitted by a base station 105 multiple times in different directions. For example, the base station 105 may transmit a signal according to different beamforming weight sets associated with different directions of transmission. Transmissions in different beam directions may be used to identify (e.g., by a transmitting device, such as a base station 105, or by a receiving device, such as a UE 115) a beam direction for later transmission or reception by the base station 105.

Some signals, such as data signals associated with a particular receiving device, may be transmitted by a base station 105 in a single beam direction (e.g., a direction associated with the receiving device, such as a UE 115) . In some examples, the beam direction associated with transmissions along a single beam direction may be determined based on a signal that was transmitted in one or more beam directions. For example, a UE 115 may receive one or more of the signals transmitted by the base station 105 in different directions and may report to the base station 105 an indication of the signal that the UE 115 received with a highest signal quality or an otherwise acceptable signal quality.

In some examples, transmissions by a device (e.g., by a base station 105 or a UE 115) may be performed using multiple beam directions, and the device may use a combination of digital precoding or radio frequency beamforming to generate a combined beam for transmission (e.g., from a base station 105 to a UE 115) . The UE 115 may report feedback that indicates precoding weights for one or more beam directions, and the feedback may correspond to a configured number of beams across a system bandwidth or one or more sub-bands. The base station 105 may transmit a reference signal (e.g., a cell-specific reference signal (CRS) , a CSI-RS, which may be precoded or not precoded. The UE 115 may provide feedback for beam selection, which may be a PMI or codebook-based feedback (e.g., a multi-panel type codebook, a linear combination type codebook, a port selection type codebook) . Although these techniques are described with reference to signals transmitted in one or more directions by a base station 105, a UE 115 may employ similar techniques for transmitting signals multiple times in different directions (e.g., for identifying a beam direction for subsequent transmission or reception by the UE 115) or for transmitting a signal in a single direction (e.g., for transmitting data to a receiving device) .

In FIG. 1, a base station 105 may include a base station communications manager 165. The base station communications manager 165 may perform techniques described herein related to setting frequency domain densities for CSI-RS ports. The base station communications manager 165 may perform channel measurements on a wireless channel between the base station 105 and a UE 115. The channel measurements may be based on a SRS, for example. The base station communications manager 165 may determine an FDD for one or more CSI-RS ports at the UE based at least in part on the channel measurements. The base station communications manager 165 may also send a configuration signal to the UE that indicates an FDD for the one or more CSI-RS ports at the UE 115.

A UE 115 may include a UE communications manager 160. The UE communications manager 160 may perform techniques described herein related to setting frequency domain densities for CSI-RS ports. The UE communications manager 160 may receive a configuration signal from a base station 105 that indicates a FDD for one or more CSI-RS ports. The UE communications manager 160 may perform CSI-RS measurements for the one or more CSI-RS ports based at least in part on the indicated FDDs. For example, if an FDD for a first CSI-RS port is indicated to be 1 and an FDD for a second CSI-RS port is indicated to be 0.5, the UE communications manager 160 will perform CSI-RS measurements for the first and second CSI-RS ports accordingly.

In some examples, the UE communications manager 160 may generate a channel state information (CSI) report using the one or more CSI-RS ports based at least in part on the CSI-RS measurements. The UE communications manager 160 may transmit the CSI report to the base station 105.

The described techniques may reduce overhead at the UE 115 and the base station 105, reduce bit error rates, improve efficiencies, improve coding rates, decrease system latency, and improve user experience. The described techniques may improve CSI-RS overhead.

FIG. 2 illustrates an example of a swim diagram of a wireless communications system 200 that supports port specific CSI-RS FDD for FDD reciprocity CSI reporting in accordance with aspects of the present disclosure. In some examples, the wireless communications system 200 may implement aspects of wireless communications system 100. In some examples, the wireless communications system 200 may implement aspects of wireless communications system 100, the base station 105-a may be an example of aspects of a base station 105, and the UE 115-a may be an example of aspects of a UE 115.

At 205, the UE 115-a may send an SRS to the base station 105-a over an uplink channel. The base station 105-a may use the SRS to estimate the wireless channel between the base station 105-a and the UE 115-a at 210. From the channel estimate, the base station 105-a may generate spatial and frequency domain decoders at 215. The spatial domain and frequency domain precoders will be discussed further with respect to FIGs. 3 and 4.

At 225, the base station 105-a may estimate the density of the CSI-RS ports based at least in part on reciprocity and the spatial and frequency domain decoders.

At 230, the base station 105-a may send a configuration signal to the UE 115-a that indicates one or more FDDs for one or more CSI-RS ports at the UE 115-a. The UE 115-may determine the FDDs for the one or more CSI-RS ports based at least in part on the configuration signal. The FDDs informs the UE 115-a of what frequency domain density to measure the CSI at each relevant CSI-RS port.

At 240, the base station 105-a may send a CSI-RS signal. The CSI-RS signal may correspond to a plurality of antenna ports at the UE 115-a (e.g., a multi-port CSI-RS) or a single antenna port CSI-RS (e.g., a per-antenna-port CSI-RS) . The UE 115-a may receive the CSI-RS signal and measure channel state information based at least in part on the CSI-RS signal and the frequency domain densities at the one or more CSI-RS ports.

The UE 115-a may generate a CSI report based on the measurements, and forward the CSI report to the base station 105-a at 250. The CSI report may include one or several of the following: a rank indicator (RI) , which indicates a transmission rank (e.g., a suitable number of transmission layers for downlink transmissions) ; a PMI that indicates a suitable precoder matrix based on the selected transmission rank; and a CQI that indicates a suitable channel-coding rate and modulation scheme based at least in part on the selected precoder matrix. The CSI report may also include one or more of a CSI-RS resource indicator (CRI) , an SS/PBCH Block Resource indicator (SSBRI) , and a layer indicator (LI) .

FIG. 3 illustrates an example of a block diagram 300 that supports port specific CSI-RS FDD for FDD reciprocity CSI reporting in accordance with aspects of the present disclosure. In some examples,

wireless communications systems

100 and 200 may implement aspects of the block diagram 300.

The block diagram 300 illustrates a spatial domain and frequency domain precoded CSI-RS. A base station, such as a base station 105, may precode CSI-RS for transmitting it to a UE 115 for channel sounding. The base station 105 may use a precoder matrix to precode the CSI-RS. The precoder may be a type I or a type II precoder, or another type of precoder. A type II precoder may be used with a type 2 based codebook. For example, for a particular subband, the precoder can be formulated such that the base station precodes beams with feedback of the linear combination coefficients (e.g., c _i, m) on the frequency domain basis. In some examples, the spatial line frequency domain coefficients are precoded at the base station. As a result, the UE only has to feedback the linear combination coefficients. The UE may save overhead computing the coefficients.

An example type II precoder is provided in Equation 1:

The term b _i is defined as a spatial domain basis vector (e.g., the i ^th column of the precoder matrix W ₁) . The term

is the frequency domain basis (e.g., the element at the m ^th row, n ^th column of

) and the term c _i, m defines the linear combination coefficients. In Equation 1, b _i corresponds to what the base station precodes and

corresponds to UE feedback.

Another example of a type II precoder is provided in Equation 2:

In Equation 2,

corresponds to what the base station precodes and c _i, m corresponds to UE feedback.

FIG. 3 shows a first set of resource blocks (e.g., RB0, RB1, …RB N ₃-1) per CSI-RS ports (e.g., Port 0, Port 1) at 310 that are precoded following Equation 1. A second set of resource blocks (e.g., RB0, RB1, …RB N ₃-1) per CSI-RS ports (e.g., Port 0, Port 1, Port 2, and Port 3) at 320 that are precoded following Equation 2. The additional precoding at the base station saves overhead at the UE.

FIG. 4 illustrates an example of a block diagram 400 that supports port specific CSI-RS FDD for FDD reciprocity CSI reporting in accordance with aspects of the present disclosure. In some examples,

wireless communications systems

100 and 200 may implement aspects of the block diagram 400. Block diagram 400 illustrates flexible port emulation at a base station.

The block diagram 400 illustrates a joint spatial domain and frequency domain port emulation. A base station, such as a base station 105, may precode CSI-RS. A first set of resource blocks (e.g., RB0, RB1, …, RB N ₃-1) per CSI-RS ports (e.g., Port 0, …, Port 2L-1) at 410 are precoded following Equation 1. The ports correspond to the number of spatial linear beams constraint at 2L and the number of frequency domain basis constraint at M.

Another example of a type II precoder is provided in Equation 3:

The set of resource blocks (e.g., RB0, RB1, …, RB N ₃-1) per CSI-RS ports (e.g., Port 0, …, Port K-1) at 420 are precoded following Equation 3, which corresponds to the number of joint spatial domain and frequency domain linear combination coefficients constraint at K ports. Providing different frequency domain density for different CSI-RS ports will reduce overhead costs.

FIG. 5 illustrates an example of a block diagram 500 that supports port specific CSI-RS FDD for FDD reciprocity CSI reporting in accordance with aspects of the present disclosure. In some examples, block diagram 500 may implement aspects of wireless communications system 100. Block diagram 500 illustrates channel pruning or channel shortening which can be used in generating precoders and determining FDD for CSI-RS ports.

Block diagram 500 illustrates that wideband linear combination coefficients may be obtained via channel pruning to obtain wideband channel and singular value decomposition (SVD) . Block diagram 500 shows a set of resource blocks (e.g., RB0, RB1, …, RB N ₃-1) per CSI-RS ports (e.g., Port 0, Port 1, …, Port K-1) over a set of receive antennas at a first instance 510, a second instance 520, and a third instance 530.

The first instance 510 illustrates a kind of N _r x K x N ₃ subband level channel. For example, the first dimension may be the number of R _x receive antennas, and for each of the R _x receive antennas K ports by N ₃ RB subbands are received. At 515, an averaging is performed which functions as a channel shortening. The channel shortening can follow Equation 4, for example:

Equation 4 may average out the subband and transform the N _r x K x N ₃ subband level channel to an N _r x K wideband channel. This channel pruning may function as a low pass filter that is applied to the subband channels. The longer the filtering taps, the more improved the performance is to achieve DC-tone power. As shown here, the frequency domain precoding granularity of CSI-RS can be port specific, to save CSI-RS overhead. For those CSI-RS ports (after FD precoding) that have strong DC tone power (e.g., less frequency domain fluctuation) , a lower FDD can be applied. Otherwise, a higher FDD may be needed for a CSI-RS port.

The second instance 520 shows the subbands averaged from

to

The channel shortening can reduce the amount of overhead and computation necessary to generate the precoder coefficients. At 525, a wideband singular value decomposition is applied, which generates layers of wideband SVD N _r x K precoder coefficients.

In some examples, a UE may perform channel pruning in order to obtain wideband linear combination coefficients. Channel pruning, or channel shortening, may be considered a low pass filter that is applied to the subband channels. The longer the filtering taps of the channel pruning, the better the performance will be to achieve DC-tone power. If the UE applied shorter filter taps, comparatively worse performance will be achieved than with the longer filter taps. However, the FDP granularity of the CSI-RS can be port specific in order to save CSI-RS overhead. After frequency domain precoding, CSI-RS that have stronger DC tone power can be measured at a lower frequency domain density. Stronger DC tone power means there are less frequency domain fluctuations at the CSI-RS port from the point of view of a frequency domain waveform. Otherwise, if the DC tone power is weaker at a CSI-RS port, a higher frequency domain may be needed.

As FIG. 5 illustrates, the base station can estimate the FDD for the CSI-RS ports based on reciprocity. That is, the base station may estimate the reciprocal channel from an SRS. The base station then generates the spatial and frequency domain precoders for CSI-RS and estimate the required FDD for different CSI-RS ports. The base station may configure the CSI-RS with different FD density to the UE. For example, in a CSI-report configuration signal, two CSI-RS resources for channel measurement may be associated, one with FDD of 0.5 and another of FDD density of 1. In other examples, other FDDs and number of CSI-RS ports may be used. However, in order to enable the CQI measurements at the UE, the FDD may be no smaller than the inverse of the subband size.

FIG. 6 illustrates an example of block diagram 600 that shows CSI reporting configuration for two CSI-RS ports with different frequency domain densities in accordance with aspects of the present disclosure. In some examples, the

wireless communications systems

100 and 200 may implement the block diagram 600. The block diagram shows a set of resource blocks 610 for a first CSI-RS port (e.g., CSI-RS resource A) and a second set of resource blocks 620 for a second CSI-RS port (e.g., CSI-RS resource B) .

Each resource blocks, such as RB/slot block 615 (e.g., RB 0) , shows twelve subcarriers by a time slot broken into fourteen parts. Each resource element corresponds to one subcarrier at a particular time slot. A single-port CSI-RS may occupy a single RB/slot block.

The example of FIG. 6 corresponds to an instance where the CSI-report configuration signal indicated a first CSI-RS port is to have an FDD of 0.5 and a second CSI-RS port is to have an FDD density of 1. In some examples, the two CSI-RS resources may have overlapped bandwidth allocations.

Here, the first CSI-RS resource A 610 has an FDD of 0.5 and the second CSI-RS resource B 620 has an FDD of 1. The first CSI-RS resource A 610 is thus measured for every other resource block (shown as RB0, RB2, …, RB 2M) while the second CSI-RS resource B 620 is measured every resource block (shown as RB0, RB1, …, RB 2M) . This reduction of not measuring the first CSI-RS resource A at every resource block may save overhead costs.

In some examples, a table which indicates CSI-RS patters with different numbers of CSI-RS ports may be used, such as Table 1. Table 1 shows row numbers and densities, which can be configured via an RRC signal. Example densities may include 1 (e.g., each PRB comprises a CSI-RS pattern) and 0.5 (e.g., each PRB-level comb-2 link such CSI-RS pattern) . In other examples, other tables may be used.

Row #	X (#ports)	Density [RE/RB/port]	N	(Y, Z)	CDM
1	1	3	1	(1, 1)	No CDM

2	1	1, 0.5	1	(1, 1)	No CDM
3	2	1, 0.5	1	(2, 1)	FD-CDM2
4	4	1	1	(2, 1)	FD-CDM2
5	4	1	2	(2, 2)	FD-CDM2
7	8	1	1	(2, 1)	FD-CDM2
8	8	1	2	(2, 1)	FD-CDM2
9	8	1	2	(2, 2)	CDM4 (FD2, TD2)
10	12	1	1	(2, 1)	FD-CDM2
11	12	1	2	(2, 2)	CDM4 (FD2, TD2)
12	16	1, 0.5	2	(2, 1)	FD-CDM2
13	16	1, 0.5	2	(2, 2)	CDM4 (FD2, TD2)
14	24	1, 0.5	4	(2, 1)	FD-CDM2
15	24	1, 0.5	4	(2, 2)	CDM4 (FD2, TD2)
16	24	1, 0.5	4	(2, 4)	CDM8 (FD2, TD4)
17	32	1, 0.5	4	(2, 1)	FD-CDM2
18	32	1, 0.5	4	(2, 2)	CDM4 (FD2, TD2)
19	32	1, 0.5	4	(2, 4)	CDM8 (FD2, TD4)

Table 1

FIG. 7 shows a block diagram 700 of a device 705 that supports port specific CSI-RS FDD for FDD reciprocity CSI reporting in accordance with aspects of the present disclosure. The device 705 may be an example of aspects of a UE 115 as described herein. The device 705 may include a receiver 710, a UE communications manager 715, and a transmitter 720. The device 705 may also include a processor. Each of these components may be in communication with one another (e.g., via one or more buses) .

The receiver 710 may receive information such as packets, user data, or control information associated with various information channels (e.g., control channels, data channels, and information related to port specific CSI-RS FDD for FDD reciprocity CSI reporting, etc. ) . Information may be passed on to other components of the device 705. The receiver 710 may receive a configuration signal from a base station that indicates a FDD for one or more CSI-RS ports and pass it to the UE communications manager 715. The receiver 710 may be an example of aspects of the transceiver 1020 described with reference to FIG. 10. The receiver 710 may utilize a single antenna or a set of antennas.

The UE communications manager 715 may process the configuration signal received at the receiver 710. The UE communications manager 715 may transmit the CSI report to the base station, perform CSI-RS measurements for the one or more CSI-RS ports based on the indicated FDD, and generate a CSI report using the one or more CSI-RS ports based on the CSI-RS measurements. The UE communications manager 715 may be an example of aspects of the

UE communications manager

160 and 1010 described herein.

The UE communications manager 715, or its sub-components, may be implemented in hardware, code (e.g., software or firmware) executed by a processor, or any combination thereof. If implemented in code executed by a processor, the functions of the UE communications manager 715, or its sub-components may be executed by 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 in the present disclosure.

The UE communications manager 715, or its sub-components, may be physically located at various positions, including being distributed such that portions of functions are implemented at different physical locations by one or more physical components. In some examples, the UE communications manager 715, or its sub-components, may be a separate and distinct component in accordance with various aspects of the present disclosure. In some examples, the UE communications manager 715, or its sub-components, may be combined with one or more other hardware components, including but not limited to an input/output (I/O) component, a transceiver, a network server, another computing device, one or more other components described in the present disclosure, or a combination thereof in accordance with various aspects of the present disclosure.

The transmitter 720 may transmit signals generated by other components of the device 705. For example, the transmitter 720 may transmit the CSI report generated by the UE communications manager 715. In some examples, the transmitter 720 may be collocated with a receiver 710 in a transceiver module. For example, the transmitter 720 may be an example of aspects of the transceiver 1020 described with reference to FIG. 10. The transmitter 720 may utilize a single antenna or a set of antennas.

FIG. 8 shows a block diagram 800 of a device 805 that supports port specific CSI-RS FDD for FDD reciprocity CSI reporting in accordance with aspects of the present disclosure. The device 805 may be an example of aspects of a device 705, or a UE 115 as described herein. The device 805 may include a receiver 810, a UE communications manager 815, and a transmitter 835. The device 805 may also include a processor. Each of these components may be in communication with one another (e.g., via one or more buses) .

The receiver 810 may receive information such as packets, user data, or control information associated with various information channels (e.g., control channels, data channels, and information related to port specific CSI-RS FDD for FDD reciprocity CSI reporting, etc. ) . Information may be passed on to other components of the device 805. The receiver 810 may receive a configuration signal from a base station that indicates a FDD for one or more CSI-RS ports and transmit the CSI report to the base station. The receiver 810 may be an example of aspects of the transceiver 1020 described with reference to FIG. 10. The receiver 810 may utilize a single antenna or a set of antennas.

The UE communications manager 815 may be an example of aspects of the UE communications manager 715 and UE communications manager 160 as described herein. The UE communications manager 815 may include a CSI-RS manager 825 and a CSI report manager 830. The UE communications manager 815 may be an example of aspects of the UE communications manager 1010 described herein.

The CSI-RS manager 825 may perform CSI-RS measurements for the one or more CSI-RS ports based at least in part on the indicated FDD.

The CSI report manager 830 may generate a CSI report using the one or more CSI-RS ports based on the CSI-RS measurements.

The transmitter 835 may transmit signals generated by other components of the device 805. In some examples, the transmitter 835 may be collocated with a receiver 810 in a transceiver module. For example, the transmitter 835 may be an example of aspects of the transceiver 1020 described with reference to FIG. 10. The transmitter 835 may utilize a single antenna or a set of antennas.

FIG. 9 shows a block diagram 900 of a communications manager 905 that supports port specific CSI-RS FDD for FDD reciprocity CSI reporting in accordance with aspects of the present disclosure. The communications manager 905 may be an example of aspects of a UE communications manager 715, a UE communications manager 815, or a UE communications manager 1010 described herein. The communications manager 905 may include an UE communication manager 910, a CSI-RS manager 915, a CSI report manager 920, and a precoder manager 925. Each of these modules may communicate, directly or indirectly, with one another (e.g., via one or more buses) .

The CSI-RS manager 915 may receive a configuration signal from a base station that indicates a FDD for one or more CSI-RS ports. The CSI-RS manager 915 may perform CSI-RS measurements for the one or more CSI-RS ports based on the indicated FDD. In some cases, the FDD for each of the one or more CSI-RS ports is based on a subband size associated with communications between the base station and the UE. In some examples, the CSI-RS manager 915 may measure a CQI for one or more resource blocks that overlap at the first CSI-RS port and the second CSI-RS port.

In some examples, the CSI-RS manager 915 may receive a first FDD for a first CSI-RS port of the one or more CSI-RS ports. In some examples, the CSI-RS manager 915 may receive a second FDD for a second CSI-RS port of the one or more CSI-RS ports, where the second FDD is different than the first FDD.

In some examples, the CSI report manager 920 may transmit the CSI report to the base station. The CSI report manager 920 may generate a CSI report using the one or more CSI-RS ports based on the CSI-RS measurements. In some examples, the CSI report manager 920 may limit CQI measurement to overlapping resource blocks associated with CSI-RS ports having different frequency domain densities.

The precoder manager 925 may generate a precoding matrix indicator based on the CSI-RS measurements for the one or more CSI-RS ports, where the CSI report includes the precoding matrix indicator. In some cases, the precoding matrix indicator includes a wideband precoding matrix indicator. In some examples, the precoder manager 925 may perform channel pruning to obtain wideband linear combination coefficients.

In some cases, a total number of CSI-RS ports associated with the precoding matrix indicator is based on a combination of CSI-RS resource blocks according to the indicated FDD for the one or more CSI-RS ports.

FIG. 10 shows a diagram of a system 1000 including a device 1005 that supports port specific CSI-RS FDD for FDD reciprocity CSI reporting in accordance with aspects of the present disclosure. The device 1005 may be an example of or include the components of device 705, device 805, or a UE 115 as described herein. The device 1005 may include components for bi-directional voice and data communications including components for transmitting and receiving communications, including a UE communications manager 1010, an I/O controller 1015, a transceiver 1020, an antenna 1025, memory 1030, and a processor 1040. These components may be in electronic communication via one or more buses (e.g., bus 1045) .

The UE communications manager 1010 may receive a configuration signal from a base station that indicates a FDD for one or more CSI-RS ports, transmit the CSI report to the base station, perform CSI-RS measurements for the one or more CSI-RS ports based on the indicated FDD, and generate a CSI report using the one or more CSI-RS ports based on the CSI-RS measurements.

The I/O controller 1015 may manage input and output signals for the device 1005. The I/O controller 1015 may also manage peripherals not integrated into the device 1005. In some cases, the I/O controller 1015 may represent a physical connection or port to an external peripheral. In some cases, the I/O controller 1015 may utilize an operating system such as

or another known operating system. In other cases, the I/O controller 1015 may represent or interact with a modem, a keyboard, a mouse, a touchscreen, or a similar device. In some cases, the I/O controller 1015 may be implemented as part of a processor. In some cases, a user may interact with the device 1005 via the I/O controller 1015 or via hardware components controlled by the I/O controller 1015.

The transceiver 1020 may communicate bi-directionally, via one or more antennas, wired, or wireless links as described above. For example, the transceiver 1020 may represent a wireless transceiver and may communicate bi-directionally with another wireless transceiver. The transceiver 1020 may also include a modem to modulate the packets and provide the modulated packets to the antennas for transmission, and to demodulate packets received from the antennas.

In some cases, the wireless device may include a single antenna 1025. However, in some cases the device may have more than one antenna 1025, which may be capable of concurrently transmitting or receiving multiple wireless transmissions.

The memory 1030 may include RAM and ROM. The memory 1030 may store computer-readable, computer-executable code 1035 including instructions that, when executed, cause the processor to perform various functions described herein. In some cases, the memory 1030 may contain, among other things, a BIOS which may control basic hardware or software operation such as the interaction with peripheral components or devices.

The processor 1040 may include an intelligent hardware device, (e.g., a general-purpose processor, a DSP, a CPU, a microcontroller, an ASIC, an FPGA, a programmable logic device, a discrete gate or transistor logic component, a discrete hardware component, or any combination thereof) . In some cases, the processor 1040 may be configured to operate a memory array using a memory controller. In other cases, a memory controller may be integrated into the processor 1040. The processor 1040 may be configured to execute computer-readable instructions stored in a memory (e.g., the memory 1030) to cause the device 1005 to perform various functions (e.g., functions or tasks supporting port specific CSI-RS FDD for FDD reciprocity CSI reporting) .

The code 1035 may include instructions to implement aspects of the present disclosure, including instructions to support wireless communications. The code 1035 may be stored in a non-transitory computer-readable medium such as system memory or other type of memory. In some cases, the code 1035 may not be directly executable by the processor 1040 but may cause a computer (e.g., when compiled and executed) to perform functions described herein.

FIG. 11 shows a block diagram 1100 of a device 1105 that supports port specific CSI-RS FDD for FDD reciprocity CSI reporting in accordance with aspects of the present disclosure. The device 1105 may be an example of aspects of a base station 105 as described herein. The device 1105 may include a receiver 1110, a base station communications manager 1115, and a transmitter 1120. The device 1105 may also include a processor. Each of these components may be in communication with one another (e.g., via one or more buses) .

The receiver 1110 may receive information such as packets, user data, or control information associated with various information channels (e.g., control channels, data channels, and information related to port specific CSI-RS FDD for FDD reciprocity CSI reporting, etc. ) . Information may be passed on to other components of the device 1105. The receiver 1110 may be an example of aspects of the transceiver 1420 described with reference to FIG. 14. The receiver 1110 may utilize a single antenna or a set of antennas.

The base station communications manager 1115 may perform channel measurements on a wireless channel between the base station and a UE, determine a FDD for one or more CSI-RS ports at the UE based on the channel measurements, and send a configuration signal to the UE that indicates a frequency domain density for the one or more CSI-RS ports at the UE. The base station communications manager 1115 may be an example of aspects of the base station communications manager 1410 described herein.

The base station communications manager 1115, or its sub-components, may be implemented in hardware, code (e.g., software or firmware) executed by a processor, or any combination thereof. If implemented in code executed by a processor, the functions of the base station communications manager 1115, or its sub-components may be executed by a general-purpose processor, a DSP, an ASIC, a FPGA or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described in the present disclosure.

The base station communications manager 1115, or its sub-components, may be physically located at various positions, including being distributed such that portions of functions are implemented at different physical locations by one or more physical components. In some examples, the base station communications manager 1115, or its sub-components, may be a separate and distinct component in accordance with various aspects of the present disclosure. In some examples, the base station communications manager 1115, or its sub-components, may be combined with one or more other hardware components, including but not limited to an I/O component, a transceiver, a network server, another computing device, one or more other components described in the present disclosure, or a combination thereof in accordance with various aspects of the present disclosure.

The transmitter 1120 may transmit signals generated by other components of the device 1105. In some examples, the transmitter 1120 may be collocated with a receiver 1110 in a transceiver module. For example, the transmitter 1120 may be an example of aspects of the transceiver 1420 described with reference to FIG. 14. The transmitter 1120 may utilize a single antenna or a set of antennas.

FIG. 12 shows a block diagram 1200 of a device 1205 that supports port specific CSI-RS FDD for FDD reciprocity CSI reporting in accordance with aspects of the present disclosure. The device 1205 may be an example of aspects of a device 1105, or a base station 105 as described herein. The device 1205 may include a receiver 1210, a base station communications manager 1215, and a transmitter 1235. The device 1205 may also include a processor. Each of these components may be in communication with one another (e.g., via one or more buses) .

The receiver 1210 may receive information such as packets, user data, or control information associated with various information channels (e.g., control channels, data channels, and information related to port specific CSI-RS FDD for FDD reciprocity CSI reporting, etc. ) . Information may be passed on to other components of the device 1205. The receiver 1210 may be an example of aspects of the transceiver 1420 described with reference to FIG. 14. The receiver 1210 may utilize a single antenna or a set of antennas.

The base station communications manager 1215 may be an example of aspects of the base station communications manager 1115 and the base station communications manager 165 as described herein. The base station communications manager 1215 may include a channel sounding manager 1220 and an FDD manager 1225. The base station communications manager 1215 may be an example of aspects of the base station communications manager 1410 described herein.

The channel sounding manager 1220 may perform channel measurements on a wireless channel between the base station and a UE.

The FDD manager 1225 may determine a FDD for one or more CSI-RS ports at the UE based on the channel measurements. The FDD manager 1225 may send a configuration signal to the UE that indicates a frequency domain density for the one or more CSI-RS ports at the UE.

The transmitter 1235 may transmit signals generated by other components of the device 1205. In some examples, the transmitter 1235 may be collocated with a receiver 1210 in a transceiver module. For example, the transmitter 1235 may be an example of aspects of the transceiver 1420 described with reference to FIG. 14. The transmitter 1235 may utilize a single antenna or a set of antennas.

FIG. 13 shows a block diagram 1300 of a base station communications manager 1305 that supports port specific CSI-RS FDD for FDD reciprocity CSI reporting in accordance with aspects of the present disclosure. The base station communications manager 1305 may be an example of aspects of a base station communications manager 165, a base station communications manager 1115, a base station communications manager 1215, or a base station communications manager 1410 described herein. The base station communications manager 1305 may include a channel sounding manager 1310, a FDD manager 1315, a precoder manager 1325, and a CSI report manager 1330. Each of these modules may communicate, directly or indirectly, with one another (e.g., via one or more buses) .

The channel sounding manager 1310 may perform channel measurements on a wireless channel between the base station and a UE.

The FDD manager 1315 may determine a FDD for one or more CSI-RS ports at the UE based on the channel measurements. In some examples, the FDD manager 1315 may estimate the FDD for the one or more CSI-RS ports based on the channel measurements. In some examples, the FDD manager 1315 may determine a first FDD for a first CSI-RS port of the one or more CSI-RS ports.

In some examples, the FDD manager 1315 may determine a second FDD for a second CSI-RS port of the one or more CSI-RS ports, where the second FDD is different than the first FDD and where the configuration signal indicates the first FDD and the second FDD. In some examples, the FDD manager 1315 may provide multiple density levels for different CSI-RS ports. In some examples, the FDD manager 1315 may compare a first frequency domain fluctuation at a first CSI-RS port with a second frequency domain fluctuation at a second CSI-RS port. In some examples, the CSI-RS resources with different frequency domain densities are configured in CSI report settings.

In some examples, the FDD manager 1315 may set a first FDD for the first CSI-RS port to be larger than a second FDD for the second CSI-RS port when the first frequency domain fluctuation is higher than the second frequency domain fluctuation. In some examples, the FDD manager 1315 may set the first FDD for the first CSI-RS port to be smaller than the second FDD for the second CSI-RS port when the first frequency domain fluctuation is lower than the second frequency domain fluctuation. The FDD manager 1315 may send a configuration signal to the UE that indicates a frequency domain density for the one or more CSI-RS ports at the UE.

In some cases, the FDD for each of the one or more CSI-RS ports is based on a subband size associated with communications between the base station and the UE.

The precoder manager 1325 may determine precoders for one or more CSI-RSs based on the channel measurements for each subband of a sounding reference signal.

In some examples, the precoder manager 1325 may receive the sounding reference signal over the wireless channel. In some examples, the precoder manager 1325 may apply a type II precoder to each subband of the sounding reference signal.

The CSI report manager 1330 may receive a CSI report from the UE, where the CSI report is based on the configuration signal. In some cases, the CSI report is limited to overlapping resource blocks associated with CSI-RS ports having different frequency domain densities.

In some cases, the precoding matrix indicator includes a wideband precoding matrix indicator. In some cases, a total number of CSI-RS ports associated with the precoding matrix indicator is based on a combination of CSI-RS resource blocks according to the FDD for the one or more CSI-RS ports. In some cases, the CSI report includes a precoding matrix indicator based on CSI-RS measurements for the one or more CSI-RS ports.

FIG. 14 shows a diagram of a system 1400 including a device 1405 that supports port specific CSI-RS FDD for FDD reciprocity CSI reporting in accordance with aspects of the present disclosure. The device 1405 may be an example of or include the components of device 1105, device 1205, or a base station 105 as described herein. The device 1405 may include components for bi-directional voice and data communications including components for transmitting and receiving communications, including a base station communications manager 1410, a network communications manager 1415, a transceiver 1420, an antenna 1425, memory 1430, a processor 1440, and an inter-station communications manager 1445. These components may be in electronic communication via one or more buses (e.g., bus 1450) .

The base station communications manager 1410 may perform channel measurements on a wireless channel between the base station and a UE, determine a FDD for one or more CSI-RS ports at the UE based on the channel measurements, and send a configuration signal to the UE that indicates a frequency domain density for the one or more CSI-RS ports at the UE.

The network communications manager 1415 may manage communications with the core network (e.g., via one or more wired backhaul links) . For example, the network communications manager 1415 may manage the transfer of data communications for client devices, such as one or more UEs 115.

The transceiver 1420 may communicate bi-directionally, via one or more antennas, wired, or wireless links as described above. For example, the transceiver 1420 may represent a wireless transceiver and may communicate bi-directionally with another wireless transceiver. The transceiver 1420 may also include a modem to modulate the packets and provide the modulated packets to the antennas for transmission, and to demodulate packets received from the antennas.

In some cases, the wireless device may include a single antenna 1425. However, in some cases the device may have more than one antenna 1425, which may be capable of concurrently transmitting or receiving multiple wireless transmissions.

The memory 1430 may include RAM, ROM, or a combination thereof. The memory 1430 may store computer-readable code 1435 including instructions that, when executed by a processor (e.g., the processor 1440) cause the device to perform various functions described herein. In some cases, the memory 1430 may contain, among other things, a BIOS which may control basic hardware or software operation such as the interaction with peripheral components or devices.

The processor 1440 may include an intelligent hardware device, (e.g., a general-purpose processor, a DSP, a CPU, a microcontroller, an ASIC, an FPGA, a programmable logic device, a discrete gate or transistor logic component, a discrete hardware component, or any combination thereof) . In some cases, the processor 1440 may be configured to operate a memory array using a memory controller. In some cases, a memory controller may be integrated into processor 1440. The processor 1440 may be configured to execute computer-readable instructions stored in a memory (e.g., the memory 1430) to cause the device 1405 to perform various functions (e.g., functions or tasks supporting port specific CSI-RS FDD for FDD reciprocity CSI reporting) .

The inter-station communications manager 1445 may manage communications with other base station 105, and may include a controller or scheduler for controlling communications with UEs 115 in cooperation with other base stations 105. For example, the inter-station communications manager 1445 may coordinate scheduling for transmissions to UEs 115 for various interference mitigation techniques such as beamforming or joint transmission. In some examples, the inter-station communications manager 1445 may provide an X2 interface within an LTE/LTE-A wireless communication network technology to provide communication between base stations 105.

The code 1435 may include instructions to implement aspects of the present disclosure, including instructions to support wireless communications. The code 1435 may be stored in a non-transitory computer-readable medium such as system memory or other type of memory. In some cases, the code 1435 may not be directly executable by the processor 1440 but may cause a computer (e.g., when compiled and executed) to perform functions described herein.

FIG. 15 shows a flowchart illustrating a method 1500 that supports port specific CSI-RS FDD for FDD reciprocity CSI reporting in accordance with aspects of the present disclosure. The operations of method 1500 may be implemented by a UE 115 or its components as described herein. For example, the operations of method 1500 may be performed by a communications manager as described with reference to FIGs. 7 through 10. In some examples, a UE may execute a set of instructions to control the functional elements of the UE to perform the functions described below. Additionally or alternatively, a UE may perform aspects of the functions described below using special-purpose hardware.

At 1505, the UE may receive a configuration signal from a base station that indicates a FDD for one or more CSI-RS ports. The operations of 1505 may be performed according to the methods described herein. In some examples, aspects of the operations of 1505 may be performed by a UE communication manager as described with reference to FIGs. 7 through 10.

At 1510, the UE may perform CSI-RS measurements for the one or more CSI-RS ports based on the indicated FDD. The operations of 1510 may be performed according to the methods described herein. In some examples, aspects of the operations of 1510 may be performed by a CSI-RS manager as described with reference to FIGs. 7 through 10.

At 1515, the UE may generate a CSI report using the one or more CSI-RS ports based on the CSI-RS measurements. The operations of 1515 may be performed according to the methods described herein. In some examples, aspects of the operations of 1515 may be performed by a CSI report manager as described with reference to FIGs. 7 through 10.

At 1520, the UE may transmit the CSI report to the base station. The operations of 1520 may be performed according to the methods described herein. In some examples, aspects of the operations of 1520 may be performed by a UE communication manager as described with reference to FIGs. 7 through 10.

FIG. 16 shows a flowchart illustrating a method 1600 that supports port specific CSI-RS FDD for FDD reciprocity CSI reporting in accordance with aspects of the present disclosure. The operations of method 1600 may be implemented by a UE 115 or its components as described herein. For example, the operations of method 1600 may be performed by a communications manager as described with reference to FIGs. 7 through 10. In some examples, a UE may execute a set of instructions to control the functional elements of the UE to perform the functions described below. Additionally or alternatively, a UE may perform aspects of the functions described below using special-purpose hardware.

At 1605, the UE may receive a configuration signal from a base station that indicates a FDD for one or more CSI-RS ports. The operations of 1605 may be performed according to the methods described herein. In some examples, aspects of the operations of 1605 may be performed by an UE communication manager as described with reference to FIGs. 7 through 10.

At 1610, the UE may perform CSI-RS measurements for the one or more CSI-RS ports based on the indicated FDD. The operations of 1610 may be performed according to the methods described herein. In some examples, aspects of the operations of 1610 may be performed by a CSI-RS manager as described with reference to FIGs. 7 through 10.

At 1615, the UE may receive a first FDD for a first CSI-RS port of the one or more CSI-RS ports. In some examples, the UE may receive an indication of multiple density levels for different CSI-RS ports. The operations of 1615 may be performed according to the methods described herein. In some examples, aspects of the operations of 1615 may be performed by a UE communication manager as described with reference to FIGs. 7 through 10.

At 1623, the UE may receive a second FDD for a second CSI-RS port of the one or more CSI-RS ports, where the second FDD is different than the first FDD. The operations of 1623 may be performed according to the methods described herein. In some examples, aspects of the operations of 1623 may be performed by a UE communication manager as described with reference to FIGs. 7 through 10.

At 1625, the UE may generate a CSI report using the one or more CSI-RS ports based on the CSI-RS measurements. The operations of 1625 may be performed according to the methods described herein. In some examples, aspects of the operations of 1625 may be performed by a CSI report manager as described with reference to FIGs. 7 through 10.

At 1630, the UE may transmit the CSI report to the base station. The operations of 1630 may be performed according to the methods described herein. In some examples, aspects of the operations of 1630 may be performed by a UE communication manager as described with reference to FIGs. 7 through 10.

FIG. 17 shows a flowchart illustrating a method 1700 that supports port specific CSI-RS FDD for FDD reciprocity CSI reporting in accordance with aspects of the present disclosure. The operations of method 1700 may be implemented by a base station 105 or its components as described herein. For example, the operations of method 1700 may be performed by a communications manager as described with reference to FIGs. 11 through 14. In some examples, a base station may execute a set of instructions to control the functional elements of the base station to perform the functions described below. Additionally or alternatively, a base station may perform aspects of the functions described below using special-purpose hardware.

At 1705, the base station may perform channel measurements on a wireless channel between the base station and a UE. The operations of 1705 may be performed according to the methods described herein. In some examples, aspects of the operations of 1705 may be performed by a channel sounding manager as described with reference to FIGs. 11 through 14.

At 1710, the base station may determine a FDD for one or more CSI-RS ports at the UE based on the channel measurements. The operations of 1710 may be performed according to the methods described herein. In some examples, aspects of the operations of 1710 may be performed by a FDD manager as described with reference to FIGs. 11 through 14.

At 1715, the base station may send a configuration signal to the UE that indicates a frequency domain density for the one or more CSI-RS ports at the UE. The operations of 1715 may be performed according to the methods described herein. In some examples, aspects of the operations of 1715 may be performed by a base station communication manager as described with reference to FIGs. 11 through 14.

FIG. 18 shows a flowchart illustrating a method 1800 that supports port specific CSI-RS FDD for FDD reciprocity CSI reporting in accordance with aspects of the present disclosure. The operations of method 1800 may be implemented by a base station 105 or its components as described herein. For example, the operations of method 1800 may be performed by a communications manager as described with reference to FIGs. 11 through 14. In some examples, a base station may execute a set of instructions to control the functional elements of the base station to perform the functions described below. Additionally or alternatively, a base station may perform aspects of the functions described below using special-purpose hardware.

At 1805, the base station may perform channel measurements on a wireless channel between the base station and a UE. The operations of 1805 may be performed according to the methods described herein. In some examples, aspects of the operations of 1805 may be performed by a channel sounding manager as described with reference to FIGs. 11 through 14.

At 1810, the base station may determine a FDD for one or more CSI-RS ports at the UE based on the channel measurements. The operations of 1810 may be performed according to the methods described herein. In some examples, aspects of the operations of 1810 may be performed by a FDD manager as described with reference to FIGs. 11 through 14.

At 1815, the base station may determine precoders for one or more CSI-RSs based on the channel measurements for each subband of a sounding reference signal. The operations of 1815 may be performed according to the methods described herein. In some examples, aspects of the operations of 1815 may be performed by a precoder manager as described with reference to FIGs. 11 through 14.

At 1820, the base station may send a configuration signal to the UE that indicates a frequency domain density for the one or more CSI-RS ports at the UE. The operations of 1820 may be performed according to the methods described herein. In some examples, aspects of the operations of 1820 may be performed by a base station communication manager as described with reference to FIGs. 11 through 14.

It should be noted that the methods described herein describe possible implementations, and that the operations and the steps may be rearranged or otherwise modified and that other implementations are possible. Further, aspects from two or more of the methods may be combined.

Although aspects of an LTE, LTE-A, LTE-A Pro, or NR system may be described for purposes of example, and LTE, LTE-A, LTE-A Pro, or NR terminology may be used in much of the description, the techniques described herein are applicable beyond LTE, LTE-A, LTE-A Pro, or NR networks. For example, the described techniques may be applicable to various other wireless communications systems such as Ultra Mobile Broadband (UMB) , Institute of Electrical and Electronics Engineers (IEEE) 802.11 (Wi-Fi) , IEEE 802.16 (WiMAX) , IEEE 802.20, Flash-OFDM, as well as other systems and radio technologies not explicitly mentioned herein.

Information and signals described herein 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 description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

The various illustrative blocks and components described in connection with the disclosure herein may be implemented or performed with a general-purpose processor, a DSP, an ASIC, a CPU, an 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 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, multiple microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration) .

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 herein may 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.

Computer-readable media includes both non-transitory computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. A non-transitory storage medium may be any available medium that may be accessed by a general-purpose or special purpose computer. By way of example, and not limitation, non-transitory computer-readable media may include random-access memory (RAM) , read-only memory (ROM) , electrically erasable programmable ROM (EEPROM) , flash memory, compact disk (CD) ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other non-transitory medium that may be used to carry or store desired program code means in the form of instructions or data structures and that may be accessed by a general-purpose or special-purpose computer, or a general-purpose or special-purpose processor. Also, any connection is 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, digital subscriber line (DSL) , or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of computer-readable medium. Disk and disc, as used herein, include 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 are also included within the scope of computer-readable media.

As used herein, including in the claims, “or” as used in a list of items (e.g., 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) . Also, as used herein, the phrase “based on” shall not be construed as a reference to a closed set of conditions. For example, an example step that is described as “based on condition A” may be based on both a condition A and a condition B without departing from the scope of the present disclosure. In other words, as used herein, the phrase “based on” shall be construed in the same manner as the phrase “based at least in part on. ”

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, or other subsequent reference label.

The description set forth herein, in connection with the appended drawings, describes example configurations and does not represent all the examples that may be implemented or that are within the scope of the claims. The term “example” used herein means “serving as an example, instance, or illustration, ” and not “preferred” or “advantageous over other examples. ” The detailed description includes specific details for the purpose of providing an understanding of the described techniques. These techniques, however, may be practiced without these specific details. In some instances, known structures and devices are shown in block diagram form in order to avoid obscuring the concepts of the described examples.

The description herein is provided to enable a person having ordinary skill in the art to make or use the disclosure. Various modifications to the disclosure will be apparent to a person having ordinary skill in the art, and the generic principles defined herein may be applied to other variations without departing from the scope of the disclosure. Thus, the disclosure is not limited to the examples and designs described herein, but is to be accorded the broadest scope consistent with the principles and novel features disclosed herein.

Claims

A method for wireless communication at a user equipment (UE) , comprising:

receiving a configuration signal from a base station that indicates a frequency domain density for one or more channel state information reference signal (CSI-RS) ports;

performing CSI-RS measurements for the one or more CSI-RS ports based at least in part on the indicated frequency domain density;

generating a channel state information report using the one or more CSI-RS ports based at least in part on the CSI-RS measurements; and

transmitting the CSI report to the base station.
The method of claim 1, wherein receiving the configuration signal from the base station comprises:

receiving a first frequency domain density for a first CSI-RS port of the one or more CSI-RS ports; and

receiving a second frequency domain density for a second CSI-RS port of the one or more CSI-RS ports, wherein the second frequency domain density is different than the first frequency domain density.
The method of claim 2, wherein performing CSI-RS measurements for the one or more CSI-RS ports further comprises:

measuring a channel quality indicator (CQI) for one or more resource blocks that overlap at the first CSI-RS port and the second CSI-RS port.
The method of claim 3, further comprising:

limiting CQI measurement to overlapping resource blocks associated with CSI-RS ports having different frequency domain densities.
The method of claim 1, wherein the frequency domain density for each of the one or more CSI-RS ports is based at least in part on a subband size associated with communications between the base station and the UE.
The method of claim 1, wherein generating the CSI report using the one or more CSI-RS ports comprises:

generating a precoding matrix indicator based at least in part on the CSI-RS measurements for the one or more CSI-RS ports, wherein the CSI report comprises the precoding matrix indicator.
The method of claim 6, wherein the precoding matrix indicator comprises a wideband precoding matrix indicator.
The method of claim 6, wherein a total number of CSI-RS ports associated with the precoding matrix indicator is based at least in part on a combination of CSI-RS resource blocks according to the indicated frequency domain density for the one or more CSI-RS ports.
A method for wireless communication at a base station, comprising:

performing channel measurements on a wireless channel between the base station and a user equipment (UE) ;

determining a frequency domain density for one or more channel state information reference signal (CSI-RS) ports at the UE based at least in part on the channel measurements; and

sending a configuration signal to the UE that indicates a frequency domain density for the one or more CSI-RS ports at the UE.
The method of claim 9, further comprising:

determining precoders for one or more CSI-RSs based at least in part on the channel measurements for each subband of a sounding reference signal.
The method of claim 9, wherein determining the frequency domain density for the one or more CSI-RS ports further comprises:

estimating the frequency domain density for the one or more CSI-RS ports based at least in part on the channel measurements.
The method of claim 9, wherein the frequency domain density for each of the one or more CSI-RS ports is based at least in part on a subband size associated with communications between the base station and the UE.
The method of claim 9, wherein determining the frequency domain density for the one or more CSI-RS ports further comprises:

determining a first frequency domain density for a first CSI-RS port of the one or more CSI-RS ports; and

determining a second frequency domain density for a second CSI-RS port of the one or more CSI-RS ports, wherein the second frequency domain density is different than the first frequency domain density and wherein the configuration signal indicates the first frequency domain density and the second frequency domain density.
The method of claim 9, wherein determining the frequency domain density for the one or more CSI-RS ports further comprises:

comparing a first frequency domain fluctuation at a first CSI-RS port with a second frequency domain fluctuation at a second CSI-RS port;

setting a first frequency domain density for the first CSI-RS port to be larger than a second frequency domain density for the second CSI-RS port when the first frequency domain fluctuation is higher than the second frequency domain fluctuation; and

setting the first frequency domain density for the first CSI-RS port to be smaller than the second frequency domain density for the second CSI-RS port when the first frequency domain fluctuation is lower than the second frequency domain fluctuation.
The method of claim 9, further comprising:

receiving a CSI report from the UE, wherein the CSI report is based at least in part on the configuration signal.
The method of claim 15, wherein the CSI report is limited to overlapping resource blocks associated with CSI-RS ports having different frequency domain densities.
The method of claim 16, wherein the precoding matrix indicator comprises a wideband precoding matrix indicator.
The method of claim 16, wherein a total number of CSI-RS ports associated with the precoding matrix indicator is based at least in part on a combination of CSI-RS resource blocks according to the frequency domain density for the one or more CSI-RS ports.
The method of claim 15, wherein the CSI report includes a precoding matrix indicator based at least in part on CSI-RS measurements for the one or more CSI-RS ports.
An apparatus for wireless communication at a user equipment (UE) , comprising:

a processor,

memory in electronic communication with the processor; and

instructions stored in the memory, wherein the instructions are executable by the processor to:

receive a configuration signal from a base station that indicates a frequency domain density for one or more channel state information reference signal (CSI-RS) ports;

perform CSI-RS measurements for the one or more CSI-RS ports based at least in part on the indicated frequency domain density;

generate a channel state information report using the one or more CSI-RS ports based at least in part on the CSI-RS measurements; and

transmit the CSI report to the base station.
The apparatus of claim 20, wherein the instructions executable by the processor to receive the configuration signal from the base station comprise instructions executable by the processor to:

receive a first frequency domain density for a first CSI-RS port of the one or more CSI-RS ports; and

receive a second frequency domain density for a second CSI-RS port of the one or more CSI-RS ports, wherein the second frequency domain density is different than the first frequency domain density.
The apparatus of claim 21, wherein the instructions executable by the processor to perform CSI-RS measurements for the one or more CSI-RS ports comprise instructions executable by the processor to:

measure a channel quality indicator (CQI) for one or more resource blocks that overlap at the first CSI-RS port and the second CSI-RS port.
The apparatus of claim 22, wherein the instructions executable by the processor are further executable to:

limit CQI measurement to overlapping resource blocks associated with CSI-RS ports having different frequency domain densities.
The apparatus of claim 20, wherein the frequency domain density for each of the one or more CSI-RS ports is based at least in part on a subband size associated with communications between the base station and the UE.
The apparatus of claim 20, wherein the instructions executable by the processor to generate the CSI report using the one or more CSI-RS ports comprise instructions executable by the processor to:

generate a precoding matrix indicator based at least in part on the CSI-RS measurements for the one or more CSI-RS ports, wherein the CSI report comprises the precoding matrix indicator.
The apparatus of claim 25, wherein the precoding matrix indicator comprises a wideband precoding matrix indicator.
The apparatus of claim 25, wherein a total number of CSI-RS ports associated with the precoding matrix indicator is based at least in part on a combination of CSI-RS resource blocks according to the indicated frequency domain density for the one or more CSI-RS ports.
An apparatus for wireless communication at a base station, comprising:

a processor,

memory in electronic communication with the processor; and

instructions stored in the memory, wherein the instructions are executable by the processor to:

perform channel measurements on a wireless channel between the base station and a user equipment (UE) ;

determine a frequency domain density for one or more channel state information reference signal (CSI-RS) ports at the UE based at least in part on the channel measurements; and

send a configuration signal to the UE that indicates a frequency domain density for the one or more CSI-RS ports at the UE.
The apparatus of claim 28, wherein the instructions are further executable by the processor to:

determine precoders for one or more CSI-RSs based at least in part on the channel measurements for each subband of a sounding reference signal.
The apparatus of claim 28, wherein the instructions executable by the processor to determine the frequency domain density for the one or more CSI-RS ports comprise instructions executable by the processor to:

estimate the frequency domain density for the one or more CSI-RS ports based at least in part on the channel measurements.
The apparatus of claim 28, wherein the frequency domain density for each of the one or more CSI-RS ports is based at least in part on a subband size associated with communications between the base station and the UE.
The apparatus of claim 28, wherein the instructions executable by the processor to determine the frequency domain density for the one or more CSI-RS ports comprise instructions executable by the processor to:

determine a first frequency domain density for a first CSI-RS port of the one or more CSI-RS ports; and

determine a second frequency domain density for a second CSI-RS port of the one or more CSI-RS ports, wherein the second frequency domain density is different than the first frequency domain density and wherein the configuration signal indicates the first frequency domain density and the second frequency domain density.
The apparatus of claim 28, wherein the instructions executable by the processor to determine the frequency domain density for the one or more CSI-RS ports comprise instructions executable by the processor to:

compare a first frequency domain fluctuation at a first CSI-RS port with a second frequency domain fluctuation at a second CSI-RS port;

set a first frequency domain density for the first CSI-RS port to be larger than a second frequency domain density for the second CSI-RS port when the first frequency domain fluctuation is higher than the second frequency domain fluctuation; and

set the first frequency domain density for the first CSI-RS port to be smaller than the second frequency domain density for the second CSI-RS port when the first frequency domain fluctuation is lower than the second frequency domain fluctuation.
The apparatus of claim 28, wherein the instructions are further executable by the processor to:

receive a CSI report from the UE, wherein the CSI report is based at least in part on the configuration signal.
The apparatus of claim 34, wherein the CSI report is limited to overlapping resource blocks associated with CSI-RS ports having different frequency domain densities.
The apparatus of claim 35, wherein the precoding matrix indicator comprises a wideband precoding matrix indicator.
The apparatus of claim 35, wherein a total number of CSI-RS ports associated with the precoding matrix indicator is based at least in part on a combination of CSI-RS resource blocks according to the frequency domain density for the one or more CSI-RS ports.
The apparatus of claim 34, wherein the CSI report includes a precoding matrix indicator based at least in part on CSI-RS measurements for the one or more CSI-RS ports.
An apparatus for wireless communication at a user equipment (UE) , comprising:

means for receiving a configuration signal from a base station that indicates a frequency domain density for one or more channel state information reference signal (CSI-RS) ports;

means for performing CSI-RS measurements for the one or more CSI-RS ports based at least in part on the indicated frequency domain density;

means for generating a channel state information report using the one or more CSI-RS ports based at least in part on the CSI-RS measurements; and

means for transmitting the CSI report to the base station.
The apparatus of claim 39, wherein the means for receiving the configuration signal from the base station comprises:

means for receiving a first frequency domain density for a first CSI-RS port of the one or more CSI-RS ports; and

means for receiving a second frequency domain density for a second CSI-RS port of the one or more CSI-RS ports, wherein the second frequency domain density is different than the first frequency domain density.
The apparatus of claim 40, wherein the means for performing CSI-RS measurements for the one or more CSI-RS ports further comprises:

means for measuring a channel quality indicator (CQI) for one or more resource blocks that overlap at the first CSI-RS port and the second CSI-RS port.
The apparatus of claim 41, further comprising:

means for limiting CQI measurement to overlapping resource blocks associated with CSI-RS ports having different frequency domain densities.
The apparatus of claim 39, wherein the frequency domain density for each of the one or more CSI-RS ports is based at least in part on a subband size associated with communications between the base station and the UE.
The apparatus of claim 39, wherein the means for generating the CSI report using the one or more CSI-RS ports comprises:

means for generating a precoding matrix indicator based at least in part on the CSI-RS measurements for the one or more CSI-RS ports, wherein the CSI report comprises the precoding matrix indicator.
The apparatus of claim 44, wherein the precoding matrix indicator comprises a wideband precoding matrix indicator.
The apparatus of claim 44, wherein a total number of CSI-RS ports associated with the precoding matrix indicator is based at least in part on a combination of CSI-RS resource blocks according to the indicated frequency domain density for the one or more CSI-RS ports.
An apparatus for wireless communication at a base station, comprising:

means for performing channel measurements on a wireless channel between the base station and a user equipment (UE) ;

means for determining a frequency domain density for one or more channel state information reference signal (CSI-RS) ports at the UE based at least in part on the channel measurements; and

means for sending a configuration signal to the UE that indicates a frequency domain density for the one or more CSI-RS ports at the UE.
The apparatus of claim 47, further comprising:

means for determining precoders for one or more CSI-RSs based at least in part on the channel measurements for each subband of a sounding reference signal.
The apparatus of claim 47, wherein the means for determining the frequency domain density for the one or more CSI-RS ports further comprises:

means for estimating the frequency domain density for the one or more CSI-RS ports based at least in part on the channel measurements.
The apparatus of claim 47, wherein the frequency domain density for each of the one or more CSI-RS ports is based at least in part on a subband size associated with communications between the base station and the UE.
The apparatus of claim 47, wherein the means for determining the frequency domain density for the one or more CSI-RS ports further comprises:

means for determining a first frequency domain density for a first CSI-RS port of the one or more CSI-RS ports; and

means for determining a second frequency domain density for a second CSI-RS port of the one or more CSI-RS ports, wherein the second frequency domain density is different than the first frequency domain density and wherein the configuration signal indicates the first frequency domain density and the second frequency domain density.
The apparatus of claim 47, wherein the means for determining the frequency domain density for the one or more CSI-RS ports further comprises:

means for comparing a first frequency domain fluctuation at a first CSI-RS port with a second frequency domain fluctuation at a second CSI-RS port;

means for setting a first frequency domain density for the first CSI-RS port to be larger than a second frequency domain density for the second CSI-RS port when the first frequency domain fluctuation is higher than the second frequency domain fluctuation; and

means for setting the first frequency domain density for the first CSI-RS port to be smaller than the second frequency domain density for the second CSI-RS port when the first frequency domain fluctuation is lower than the second frequency domain fluctuation.
The apparatus of claim 47, further comprising:

means for receiving a CSI report from the UE, wherein the CSI report is based at least in part on the configuration signal.
The apparatus of claim 53, wherein the CSI report is limited to overlapping resource blocks associated with CSI-RS ports having different frequency domain densities.
The apparatus of claim 54, wherein the precoding matrix indicator comprises a wideband precoding matrix indicator.
The apparatus of claim 54, wherein a total number of CSI-RS ports associated with the precoding matrix indicator is based at least in part on a combination of CSI-RS resource blocks according to the frequency domain density for the one or more CSI-RS ports.
The apparatus of claim 53, wherein the CSI report includes a precoding matrix indicator based at least in part on CSI-RS measurements for the one or more CSI-RS ports.
A non-transitory computer-readable medium storing code for wireless communication at a user equipment (UE) , the code comprising instructions executable to:

receive a configuration signal from a base station that indicates a frequency domain density for one or more channel state information reference signal (CSI-RS) ports;

perform CSI-RS measurements for the one or more CSI-RS ports based at least in part on the indicated frequency domain density;

generate a channel state information report using the one or more CSI-RS ports based at least in part on the CSI-RS measurements; and

transmit the CSI report to the base station.
The non-transitory computer-readable medium of claim 58, wherein the instructions to receive the configuration signal from the base station are executable to:

receive a first frequency domain density for a first CSI-RS port of the one or more CSI-RS ports; and

receive a second frequency domain density for a second CSI-RS port of the one or more CSI-RS ports, wherein the second frequency domain density is different than the first frequency domain density.
The non-transitory computer-readable medium of claim 59, wherein the instructions to perform CSI-RS measurements for the one or more CSI-RS ports further are executable to:

measure a channel quality indicator (CQI) for one or more resource blocks that overlap at the first CSI-RS port and the second CSI-RS port.
The non-transitory computer-readable medium of claim 60, wherein the instructions are further executable to:

limit CQI measurement to overlapping resource blocks associated with CSI-RS ports having different frequency domain densities.
The non-transitory computer-readable medium of claim 58, wherein the frequency domain density for each of the one or more CSI-RS ports is based at least in part on a subband size associated with communications between the base station and the UE.
The non-transitory computer-readable medium of claim 58, wherein the instructions to generate the CSI report using the one or more CSI-RS ports are executable to:

generate a precoding matrix indicator based at least in part on the CSI-RS measurements for the one or more CSI-RS ports, wherein the CSI report comprises the precoding matrix indicator.
The non-transitory computer-readable medium of claim 63, wherein the precoding matrix indicator comprises a wideband precoding matrix indicator.
The non-transitory computer-readable medium of claim 63, wherein a total number of CSI-RS ports associated with the precoding matrix indicator is based at least in part on a combination of CSI-RS resource blocks according to the indicated frequency domain density for the one or more CSI-RS ports.
A non-transitory computer-readable medium storing code for wireless communication at a base station, the code comprising instructions executable to:

perform channel measurements on a wireless channel between the base station and a user equipment (UE) ;

determine a frequency domain density for one or more channel state information reference signal (CSI-RS) ports at the UE based at least in part on the channel measurements; and

send a configuration signal to the UE that indicates a frequency domain density for the one or more CSI-RS ports at the UE.
The non-transitory computer-readable medium of claim 66, wherein the instructions are further executable to:

determine precoders for one or more CSI-RSs based at least in part on the channel measurements for each subband of a sounding reference signal.
The non-transitory computer-readable medium of claim 66, wherein the instructions to determine the frequency domain density for the one or more CSI-RS ports further are executable to:

estimate the frequency domain density for the one or more CSI-RS ports based at least in part on the channel measurements.
The non-transitory computer-readable medium of claim 66, wherein the frequency domain density for each of the one or more CSI-RS ports is based at least in part on a subband size associated with communications between the base station and the UE.
The non-transitory computer-readable medium of claim 66, wherein the instructions to determine the frequency domain density for the one or more CSI-RS ports further are executable to:

determine a first frequency domain density for a first CSI-RS port of the one or more CSI-RS ports; and

determine a second frequency domain density for a second CSI-RS port of the one or more CSI-RS ports, wherein the second frequency domain density is different than the first frequency domain density and wherein the configuration signal indicates the first frequency domain density and the second frequency domain density.
The non-transitory computer-readable medium of claim 66, wherein the instructions to determine the frequency domain density for the one or more CSI-RS ports further are executable to:

compare a first frequency domain fluctuation at a first CSI-RS port with a second frequency domain fluctuation at a second CSI-RS port;

set a first frequency domain density for the first CSI-RS port to be larger than a second frequency domain density for the second CSI-RS port when the first frequency domain fluctuation is higher than the second frequency domain fluctuation; and

set the first frequency domain density for the first CSI-RS port to be smaller than the second frequency domain density for the second CSI-RS port when the first frequency domain fluctuation is lower than the second frequency domain fluctuation.
The non-transitory computer-readable medium of claim 66, wherein the instructions are further executable to:

receive a CSI report from the UE, wherein the CSI report is based at least in part on the configuration signal.
The non-transitory computer-readable medium of claim 72, wherein the CSI report is limited to overlapping resource blocks associated with CSI-RS ports having different frequency domain densities.
The non-transitory computer-readable medium of claim 73, wherein the precoding matrix indicator comprises a wideband precoding matrix indicator.
The non-transitory computer-readable medium of claim 73, wherein a total number of CSI-RS ports associated with the precoding matrix indicator is based at least in part on a combination of CSI-RS resource blocks according to the frequency domain density for the one or more CSI-RS ports.
The non-transitory computer-readable medium of claim 72, wherein the CSI report includes a precoding matrix indicator based at least in part on CSI-RS measurements for the one or more CSI-RS ports.