WO2022099671A1

WO2022099671A1 - Indicating channel state information reference signal pattern for sparse channel estimation

Info

Publication number: WO2022099671A1
Application number: PCT/CN2020/128958
Authority: WO
Inventors: Rui Hu; Liangming WU; Yu Zhang; Chenxi HAO; Wei XI; Hao Xu; Qiaoyu Li; Min Huang; Kangqi LIU; Chao Wei
Original assignee: Qualcomm Incorporated
Priority date: 2020-11-16
Filing date: 2020-11-16
Publication date: 2022-05-19

Abstract

Certain aspects of the present disclosure provide techniques for indicating a channel state information reference signal pattern for sparse channel estimation. A method that may be performed by a user equipment (UE) includes receiving, in a bandwidth from a base station (BS), channel state information (CSI) reference signals (CSI-RSs) transmitted using a CSI-RS pattern determined based on an indication of a channel sparsity condition of the bandwidth; and transmitting, to the BS, a CSI report determined based on the CSI-RSs.

Description

INDICATING CHANNEL STATE INFORMATION REFERENCE SIGNAL PATTERN FOR SPARSE CHANNEL ESTIMATION

BACKGROUND

Field of the Disclosure

Aspects of the present disclosure relate to wireless communications, and more particularly, to techniques for indicating a channel state information (CSI) reference signal (CSI-RS) pattern for wideband sparse channel estimation.

Description of Related Art

Wireless communication systems are widely deployed to provide various telecommunication services such as telephony, video, data, messaging, broadcasts, etc. These wireless communication systems may employ multiple-access technologies capable of supporting communication with multiple users by sharing available system resources (e.g., bandwidth, transmit power, etc. ) . Examples of such multiple-access systems include 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) systems, LTE Advanced (LTE-A) systems, code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, orthogonal frequency division multiple access (OFDMA) systems, single-carrier frequency division multiple access (SC-FDMA) systems, and time division synchronous code division multiple access (TD-SCDMA) systems, to name a few.

These multiple access technologies have been adopted in various telecommunication standards to provide a common protocol that enables different wireless devices to communicate on a municipal, national, regional, and even global level. New radio (e.g., 5G NR) is an example of an emerging telecommunication standard. NR is a set of enhancements to the LTE mobile standard promulgated by 3GPP. NR is designed to better support mobile broadband Internet access by improving spectral efficiency, lowering costs, improving services, making use of new spectrum, and better integrating with other open standards using OFDMA with a cyclic prefix (CP) on the downlink (DL) and on the uplink (UL) . To these ends, NR supports beamforming, multiple-input multiple-output (MIMO) antenna technology, and carrier aggregation.

However, as the demand for mobile broadband access continues to increase, there exists a need for further improvements in NR and LTE technology. Preferably, these improvements should be applicable to other multi-access technologies and the telecommunication standards that employ these technologies.

SUMMARY

The systems, methods, and devices of the disclosure each have several aspects, no single one of which is solely responsible for its desirable attributes. Without limiting the scope of this disclosure as expressed by the claims which follow, some features will now be discussed briefly. After considering this discussion, and particularly after reading the section entitled “Detailed Description” one will understand how the features of this disclosure provide advantages that include improved frequency domain resource utilization.

Certain aspects of the subject matter described in this disclosure can be implemented in a method for wireless communication by a user equipment (UE) . The method generally includes receiving, in a bandwidth from a base station (BS) , channel state information (CSI) reference signals (CSI-RSs) transmitted using a CSI-RS pattern determined based on an indication of a channel sparsity condition of the bandwidth; and transmitting, to the BS, a CSI report determined based on the CSI-RSs.

Certain aspects of the subject matter described in this disclosure can be implemented in a method for wireless communication by a base station (BS) . The method generally includes transmitting, in a bandwidth, channel state information (CSI) reference signals (CSI-RSs) using a CSI-RS pattern determined based on an indication of a channel sparsity condition of the bandwidth; and receiving, from a user equipment (UE) , a CSI report determined based on the CSI-RSs.

Certain aspects of the subject matter described in this disclosure can be implemented in an apparatus in a wireless communication system. The apparatus generally includes: a memory: and a processor coupled to the memory and configured to: transmit, in a bandwidth, channel state information (CSI) reference signals (CSI-RSs) using a CSI-RS pattern determined based on an indication of a channel sparsity condition of the bandwidth; and receive, from a user equipment (UE) , a CSI report determined based on the CSI-RSs.

Certain aspects of the subject matter described in this disclosure can be implemented in an apparatus in a wireless communication system. The apparatus generally includes: a memory; and a processor coupled to the memory and configured to: receive, in a bandwidth from a base station (BS) , channel state information (CSI) reference signals (CSI-RSs) transmitted using a CSI-RS pattern determined based on an indication of a channel sparsity condition of the bandwidth; and transmit, to the BS, a CSI report determined based on the CSI-RSs.

Certain aspects of the subject matter described in this disclosure can be implemented in an apparatus in a wireless communication system. The apparatus generally includes: means for transmitting, in a bandwidth, channel state information (CSI) reference signals (CSI-RSs) using a CSI-RS pattern determined based on an indication of a channel sparsity condition of the bandwidth; and means for receiving, from a user equipment (UE) , a CSI report determined based on the CSI-RSs.

Certain aspects of the subject matter described in this disclosure can be implemented in an apparatus in a wireless communication system. The apparatus generally includes: means for receiving, in a bandwidth from a base station (BS) , channel state information (CSI) reference signals (CSI-RSs) transmitted using a CSI-RS pattern determined based on an indication of a channel sparsity condition of the bandwidth; and means for transmitting, to the BS, a CSI report determined based on the CSI-RSs.

Certain aspects of the subject matter described in this disclosure can be implemented in a computer readable medium storing computer executable code that, when executed by a processing system, cause the processing system to perform operations generally including: transmitting, in a bandwidth, channel state information (CSI) reference signals (CSI-RSs) using a CSI-RS pattern determined based on an indication of a channel sparsity condition of the bandwidth; and receiving, from a user equipment (UE) , a CSI report determined based on the CSI-RSs.

Certain aspects of the subject matter described in this disclosure can be implemented in a computer readable medium storing computer executable code that, when executed by a processing system, cause the processing system to perform operations generally including: receiving, in a bandwidth from a base station (BS) , channel state information (CSI) reference signals (CSI-RSs) transmitted using a CSI-RS pattern determined based on an indication of a channel sparsity condition of the bandwidth; and transmitting, to the BS, a CSI report determined based on the CSI-RSs.

To the accomplishment of the foregoing and related ends, the one or more aspects comprise the features hereinafter fully described and particularly pointed out in the claims. The following description and the appended drawings set forth in detail certain illustrative features of the one or more aspects. These features are indicative, however, of but a few of the various ways in which the principles of various aspects may be employed.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above-recited features of the present disclosure can be understood in detail, a more particular description, briefly summarized above, may be had by reference to aspects, some of which are illustrated in the drawings. It is to be noted, however, that the appended drawings illustrate only certain typical aspects of this disclosure and are therefore not to be considered limiting of its scope, for the description may admit to other equally effective aspects.

FIG. 1 is a block diagram conceptually illustrating an example wireless communication network, in accordance with certain aspects of the present disclosure.

FIG. 2 is a block diagram conceptually illustrating a design of an example a base station (BS) and user equipment (UE) , in accordance with certain aspects of the present disclosure.

FIG. 3 is an example frame format for certain wireless communication systems (e.g., new radio (NR) ) , in accordance with certain aspects of the present disclosure.

FIGs. 4A &4B are graphs illustrating example sparsity in wideband channels, according to aspects of the present disclosure.

FIG. 5 is a call flow diagram illustrating example signaling for determining a CSI-RS pattern that is designed to leverage a channel sparse characteristic, in accordance with certain aspects of the present disclosure.

FIG. 6 is a call flow diagram illustrating example signaling for determining a CSI-RS pattern based on sounding reference signals (SRS) , in accordance with certain aspects of the present disclosure.

FIG. 7 is a flow diagram illustrating example operations for wireless communication by a UE, in accordance with certain aspects of the present disclosure.

FIG. 8 is a flow diagram illustrating example operations for wireless communication by a BS, in accordance with certain aspects of the present disclosure.

FIG. 9 illustrates a communications device that may include various components configured to perform the operations illustrated in FIG. 7, in accordance with aspects of the present disclosure.

FIG. 10 illustrates a communications device that may include various components configured to perform the operations illustrated in FIG. 8, in accordance with aspects of the present disclosure.

To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one aspect may be beneficially utilized on other aspects without specific recitation.

DETAILED DESCRIPTION

Aspects of the present disclosure provide apparatus, methods, processing systems, and computer readable mediums for determining a CSI-RS pattern that is designed to leverage a channel sparse characteristic for use when transmitting CSI-RS to a device (e.g., a UE) that is to report CSI based on the CSI-RS and for indicating the CSI-RS pattern to the device. According to aspects of the present disclosure, some wideband channels exhibit sparsity in the delay domain. That is, the channel delay spread may be large due to a large time difference between an earliest arriving path and a latest arriving path, so the channel impulse response (CIR) length of the channel may be long. However, the number of significant paths may be small, because there may be a limited number of significant scatters between the earliest arriving path and latest arriving path. In aspects of the present disclosure, CSI-RS patterns may be designed to leverage a channel sparsity characteristic in the delay domain. The CSI-RS patterns that leverage the channel sparsity characteristic may, for example, not be uniformly spaced, and may utilize frequency densities other than the currently known densities of 1 or 0.5 per resource block (RB) .

According to aspects of the present disclosure, CSI-RS patterns that leverage the channel sparsity characteristic may have improved (e.g., reduced) frequency domain resource consumption as compared to previously known techniques, when the delay spread of a channel is large.

In aspects of the present disclosure, a UE reporting CSI may have difficulty processing CSI-RS when the CSI-RS are transmitted using a pattern that leverages a channel sparsity characteristic and the UE has not been informed of the pattern.

Accordingly, the present disclosure provides techniques and apparatus for indicating (e.g., signaling) a CSI-RS pattern that is designed to leverage channel sparse characteristic to a device (e.g., a UE) that is to report CSI based on the CSI-RS.

The following description provides examples of indicating a CSI-RS pattern for sparse channel estimation in communication systems, and is not limiting of the scope, applicability, or examples set forth in the claims. Changes may be made in the function and arrangement of elements discussed without departing from the scope of the disclosure. Various examples may omit, substitute, or add various procedures or components as appropriate. For instance, the methods described may be performed in an order different from that described, and various steps may be added, omitted, or combined. Also, features described with respect to some examples may be combined in some other examples. For example, an apparatus may be implemented or a method may be practiced using any number of the aspects set forth herein. In addition, the scope of the disclosure is intended to cover such an apparatus or method which is practiced using other structure, functionality, or structure and functionality in addition to, or other than, the various aspects of the disclosure set forth herein. It should be understood that any aspect of the disclosure disclosed herein may be embodied by one or more elements of a claim. The word “exemplary” is used herein to mean “serving as an example, instance, or illustration. ” Any aspect described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects.

In general, any number of wireless networks may be deployed in a given geographic area. Each wireless network may support a particular radio access technology (RAT) and may operate on one or more frequencies. A RAT may also be referred to as a radio technology, an air interface, etc. A frequency may also be referred to as a carrier, a subcarrier, a frequency channel, a tone, a subband, etc. Each frequency may support a single RAT in a given geographic area in order to avoid interference between wireless networks of different RATs.

The techniques described herein may be used for various wireless networks and radio technologies. While aspects may be described herein using terminology commonly associated with 3G, 4G, and/or new radio (e.g., 5G NR) wireless technologies, aspects of the present disclosure can be applied in other generation-based communication systems.

NR access may support various wireless communication services, such as enhanced mobile broadband (eMBB) targeting wide bandwidth, millimeter wave mmW, massive machine type communications MTC (mMTC) targeting non-backward compatible MTC techniques, and/or mission critical targeting ultra-reliable low-latency communications (URLLC) . These services may include latency and reliability requirements. These services may also have different transmission time intervals (TTI) to meet respective quality of service (QoS) requirements. In addition, these services may co-exist in the same subframe.

NR supports beamforming and beam direction may be dynamically configured. MIMO transmissions with precoding may also be supported. MIMO configurations in the DL may support up to 8 transmit antennas with multi-layer DL transmissions up to 8 streams and up to 2 streams per UE. Multi-layer transmissions with up to 2 streams per UE may be supported. Aggregation of multiple cells may be supported with up to 8 serving cells.

FIG. 1 illustrates an example wireless communication network 100 in which aspects of the present disclosure may be performed. For example, the wireless communication network 100 may be an NR system (e.g., a 5G NR network) . As shown in FIG. 1, the wireless communication network 100 may be in communication with a core network 132. The core network 132 may in communication with one or more base station (BSs) 110a-z (each also individually referred to herein as BS 110 or collectively as BSs 110) and/or user equipment (UE) 120a-y (each also individually referred to herein as UE 120 or collectively as UEs 120) in the wireless communication network 100 via one or more interfaces.

According to certain aspects, the BSs 110 and UEs 120 may be configured for indicating a CSI-RS pattern for sparse channel estimation. As shown in FIG. 1, the BS 110a includes a CSI-RS manager 112 that transmits, in a bandwidth, channel state information (CSI) reference signals (CSI-RSs) using a CSI-RS pattern determined based on an indication of a channel sparsity condition of the bandwidth; and receives, from a user equipment (UE) , a CSI report determined based on the CSI-RSs, in accordance with aspects of the present disclosure. The UE 120a includes a CSI manager 122 that receives, in a bandwidth from a base station (BS) , channel state information (CSI) reference signals (CSI-RSs) transmitted using a CSI-RS pattern determined based on an indication of a channel sparsity condition of the bandwidth; and transmits, to the BS, a CSI report determined based on the CSI-RSs, in accordance with aspects of the present disclosure.

A BS 110 may provide communication coverage for a particular geographic area, sometimes referred to as a “cell” , which may be stationary or may move according to the location of a mobile BS 110. In some examples, the BSs 110 may be interconnected to one another and/or to one or more other BSs or network nodes (not shown) in wireless communication network 100 through various types of backhaul interfaces (e.g., a direct physical connection, a wireless connection, a virtual network, or the like) using any suitable transport network. In the example shown in FIG. 1, the

BSs

110a, 110b and 110c may be macro BSs for the

macro cells

102a, 102b and 102c, respectively. The BS 110x may be a pico BS for a pico cell 102x. The BSs 110y and 110z may be femto BSs for the

femto cells

102y and 102z, respectively. A BS may support one or multiple cells.

The BSs 110 communicate with UEs 120 in the wireless communication network 100. The UEs 120 (e.g., 120x, 120y, etc. ) may be dispersed throughout the wireless communication network 100, and each UE 120 may be stationary or mobile. Wireless communication network 100 may also include relay stations (e.g., relay station 110r) , also referred to as relays or the like, that receive a transmission of data and/or other information from an upstream station (e.g., a BS 110a or a UE 120r) and sends a transmission of the data and/or other information to a downstream station (e.g., a UE 120 or a BS 110) , or that relays transmissions between UEs 120, to facilitate communication between devices.

A network controller 130 may be in communication with a set of BSs 110 and provide coordination and control for these BSs 110 (e.g., via a backhaul) . In aspects, the network controller 130 may be in communication with a core network 132 (e.g., a 5G Core Network (5GC) ) , which provides various network functions such as Access and Mobility Management, Session Management, User Plane Function, Policy Control Function, Authentication Server Function, Unified Data Management, Application Function, Network Exposure Function, Network Repository Function, Network Slice Selection Function, etc.

FIG. 2 illustrates example components of BS 110a and UE 120a (e.g., the wireless communication network 100 of FIG. 1) , which may be used to implement aspects of the present disclosure.

At the BS 110a, a transmit processor 220 may receive data from a data source 212 and control information from a controller/processor 240. The control information may be for the physical broadcast channel (PBCH) , physical control format indicator channel (PCFICH) , physical hybrid ARQ indicator channel (PHICH) , physical downlink control channel (PDCCH) , group common PDCCH (GC PDCCH) , etc. The data may be for the physical downlink shared channel (PDSCH) , etc. A medium access control (MAC) -control element (MAC-CE) is a MAC layer communication structure that may be used for control command exchange between wireless nodes. The MAC-CE may be carried in a shared channel such as a physical downlink shared channel (PDSCH) , a physical uplink shared channel (PUSCH) , or a physical sidelink shared channel (PSSCH) .

The processor 220 may process (e.g., encode and symbol map) the data and control information to obtain data symbols and control symbols, respectively. The transmit processor 220 may also generate reference symbols, such as for the primary synchronization signal (PSS) , secondary synchronization signal (SSS) , PBCH demodulation reference signal (DMRS) , and channel state information reference signal (CSI-RS) . A transmit (TX) multiple-input multiple-output (MIMO) processor 230 may perform spatial processing (e.g., precoding) on the data symbols, the control symbols, and/or the reference symbols, if applicable, and may provide output symbol streams to the modulators (MODs) in transceivers 232a-232t. Each modulator in transceivers 232a-232t may process a respective output symbol stream (e.g., for OFDM, etc. ) to obtain an output sample stream. Each modulator may further process (e.g., convert to analog, amplify, filter, and upconvert) the output sample stream to obtain a downlink signal. Downlink signals from the modulators in transceivers 232a-232t may be transmitted via the antennas 234a-234t, respectively.

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

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

The

memories

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

Antennas 252,

processors

266, 258, 264, and/or controller/processor 280 of the UE 120a and/or antennas 234,

processors

220, 230, 238, and/or controller/processor 240 of the BS 110a may be used to perform the various techniques and methods described herein. For example, as shown in FIG. 2, the controller/processor 240 of the BS 110a has a CSI-RS manager 241 that transmits, in a bandwidth, channel state information (CSI) reference signals (CSI-RSs) using a CSI-RS pattern determined based on an indication of a channel sparsity condition of the bandwidth; and receives, from a user equipment (UE) , a CSI report determined based on the CSI-RSs, according to aspects described herein. As shown in FIG. 2, the controller/processor 280 of the UE 120a has a CSI manager 281 that transmits, in a bandwidth, channel state information (CSI) reference signals (CSI-RSs) using a CSI-RS pattern determined based on an indication of a channel sparsity condition of the bandwidth; and receives, from a user equipment (UE) , a CSI report determined based on the CSI-RSs, according to aspects described herein. Although shown at the controller/processor, other components of the UE 120a and BS 110a may be used to perform the operations described herein.

NR may utilize orthogonal frequency division multiplexing (OFDM) with a cyclic prefix (CP) on the uplink and downlink. NR may support half-duplex operation using time division duplexing (TDD) . OFDM and single-carrier frequency division multiplexing (SC-FDM) partition the system bandwidth into multiple orthogonal subcarriers, which are also commonly referred to as tones, bins, etc. Each subcarrier may be modulated with data. Modulation symbols may be sent in the frequency domain with OFDM and in the time domain with SC-FDM. The spacing between adjacent subcarriers may be fixed, and the total number of subcarriers may be dependent on the system bandwidth. The minimum resource allocation, called a resource block (RB) , may be 12 consecutive subcarriers. The system bandwidth may also be partitioned into subbands. For example, a subband may cover multiple RBs. NR may support a base subcarrier spacing (SCS) of 15 KHz and other SCS may be defined with respect to the base SCS (e.g., 30 kHz, 60 kHz, 120 kHz, 240 kHz, etc. ) .

FIG. 3 is a diagram showing an example of a frame format 300 for NR. The transmission timeline for each of the downlink and uplink may be partitioned into units of radio frames. Each radio frame may have a predetermined duration (e.g., 10 ms) and may be partitioned into 10 subframes, each of 1 ms, with indices of 0 through 9. Each subframe may include a variable number of slots (e.g., 1, 2, 4, 8, 16, …slots) depending on the SCS. Each slot may include a variable number of symbol periods (e.g., 7, 12, or 14 symbols) depending on the SCS. The symbol periods in each slot may be assigned indices. A sub-slot structure may refer to a transmit time interval having a duration less than a slot (e.g., 2, 3, or 4 symbols) . Each symbol in a slot may be configured for a link direction (e.g., DL, UL, or flexible) for data transmission and the link direction for each subframe may be dynamically switched. The link directions may be based on the slot format. Each slot may include DL/UL data as well as DL/UL control information.

In NR, a synchronization signal block (SSB) is transmitted. In certain aspects, SSBs may be transmitted in a burst where each SSB in the burst corresponds to a different beam direction for UE-side beam management (e.g., including beam selection and/or beam refinement) . The SSB includes a PSS, a SSS, and a two symbol PBCH. The SSB can be transmitted in a fixed slot location, such as the symbols 0-3 as shown in FIG. 3. The PSS and SSS may be used by UEs for cell search and acquisition. The PSS may provide half-frame timing, the SS may provide the CP length and frame timing. The PSS and SSS may provide the cell identity. The PBCH carries some basic system information, such as downlink system bandwidth, timing information within radio frame, SS burst set periodicity, system frame number, etc. The SSBs may be organized into SS bursts to support beam sweeping. Further system information such as, remaining minimum system information (RMSI) , system information blocks (SIBs) , other system information (OSI) can be transmitted on a physical downlink shared channel (PDSCH) in certain subframes. The SSB can be transmitted up to sixty-four times, for example, with up to sixty-four different beam directions for mmWave. The multiple transmissions of the SSB are referred to as a SS burst set. SSBs in an SS burst set may be transmitted in the same frequency region, while SSBs in different SS bursts sets can be transmitted at different frequency regions.

According to aspects of the present disclosure, some wideband channels exhibit sparsity in the delay domain. That is, the channel delay spread may be large due to a large time difference between an earliest arriving path and a latest arriving path, so the channel impulse response (CIR) length of the channel may be long. However, the number of significant paths may be small, because there may be a limited number of significant scatters between the earliest arriving path and latest arriving path.

FIGs. 4A &4B are

graphs

400 and 450 illustrating example sparsity in wideband channels, according to aspects of the present disclosure. In graph 400, amplitudes of significant paths are shown in an exemplary wideband channel experiencing 1 microsecond (μs) delay spread as the cluster delay line (CDL) . As illustrated, the exemplary channel has a channel impulse response length L of approximately 60, and a number of significant paths having amplitude larger than 0.05, for example (approximately 20 paths) that is smaller than 60. In graph 450, amplitudes of significant paths are shown in an exemplary wideband channel experiencing 5 microsecond (μs) delay spread as the CDL. As illustrated, the exemplary channel has a channel impulse response length L of approximately 320, and a number of significant paths having amplitude larger than 0.1, for example (approximately 12 paths) that is much smaller.

In aspects of the present disclosure, CSI-RS patterns may be designed to leverage a channel sparsity characteristic in the delay domain. The CSI-RS patterns that leverage the channel sparsity characteristic may, for example, not be uniformly spaced, and may utilize frequency densities other than the currently known densities of 1 or 0.5 per resource block (RB) .

Accordingly, it is desirable to develop techniques and apparatus for indicating (e.g., signaling) a CSI-RS pattern that is designed to leverage channel sparse characteristic to a device (e.g., a UE) that is to report CSI based on the CSI-RS.

Example Indicating Channel State Information Reference Signal Pattern for Sparse Channel Estimation

Aspects of the present disclosure provide techniques and apparatus for determining a CSI-RS pattern that is designed to leverage a channel sparse characteristic for use when transmitting CSI-RS to a device (e.g., a UE) that is to report CSI based on the CSI-RS and for indicating the CSI-RS pattern to the device.

In aspects of the present disclosure, a BS (e.g., a gNB) may configure a CSI-RS pattern based on a sparsity property of a channel. The sparsity property of the channel may be determined and reported by the UE to the BS, or the sparsity property of the channel may be inferred by the BS based on the estimated uplink channel (e.g., treating the UL and DL channels as having reciprocity) .

According to aspects of the present disclosure, a BS may configure a wideband CSI-RS (e.g., a CSI-RS transmission in a wide bandwidth that does not use a pattern based on a sparsity property) for a UE to process in order for the UE to estimate the wideband channel condition. The triggering of the wideband CSI-RS by the BS may be less frequent than CSI-RS transmitted using a pattern based on the sparsity property of the channel. The wideband CSI-RS may be periodic or aperiodic.

In aspects of the present disclosure, upon processing a wideband CSI-RS, a UE may report (e.g., signal) the estimated channel sparsity condition to the BS. Then, the BS may determine a CSI-RS pattern based on the UE feedback (that is, based on the channel sparsity condition) . The BS may then dynamically configure a CSI-RS pattern and transmit the CSI-RS using the pattern.

FIG. 5 is an exemplary call flow 500 of a UE 120 and BS 110, according to aspects of the present disclosure. At 502, the BS configures and transmits a wideband CSI-RS. As previously described, the BS may transmit the wideband CSI-RS periodically or aperiodically. At 504, the UE performs wideband channel estimation in response to detecting that the current CSI-RS (e.g., the CSI-RS at 502) is a wideband CSI-RS. In performing the wideband channel estimation, the UE may estimate the CIR length, L, of the channel and the minimum number of pilot tones, K. At 506, the UE feeds back the channel sparsity condition to the BS. In one option for feeding back the channel sparsity condition, the UE may feed back L and K. In this option, the UE and the BS use the same CSI-RS pattern generation technique (e.g., a formula) , and the CSI-RS pattern may be determined based on {L, N _p, N} , where L≥N _p=ceil (αK) with α＞1, N _p is the number of pilot tones, and N is the size of a fast Fourier transform (FFT) used by the BS in transmitting the CSI-RS. N _p may be determined by the BS based on K, where if K=L, then the channel is considered not sparse and the BS may determine not to transmit CSI-RS using a pattern based on the channel sparsity condition. In another option for feeding back the channel sparsity condition, the UE may indicate a set of one or more CSI-RS pattern indexes to the BS. In this option, different CSI-RS patterns are indexed (e.g., in a codebook) and are known to both the BS and the UE. The index of the CSI-RS pattern may be determined by the UE based on {K, L, N} . At 510, the BS determines the CSI-RS pattern based on the UE feedback (e.g., based on L and K or based on the set of pattern indexes sent by the UE) and signals to the UE the pattern the BS is using in transmitting CSI-RS. In one option for signaling the pattern, the BS indicates the CSI-RS pattern by signaling {L, N _p, N} or {N _p, N} to the UE. In another option for signaling the pattern, the BS indicates the selected CSI-RS pattern by signaling the corresponding CSI-RS pattern index to the UE. At 512, the BS transmits CSI-RS using the selected CSI-RS pattern. At 514, the UE estimates CSI for the channel based on the CSI-RS transmitted at 512 and the pattern. The UE transmits the CSI report to the BS at 516.

FIG. 6 is an exemplary call flow 600 of a UE 120 and BS 110, according to aspects of the present disclosure. At 602, the UE transmits a sounding reference signal (SRS) . At 604, the BS estimates the channel sparse condition based on the SRS. In estimating the channel sparse condition, the BS may estimate the CIR length, L, of the channel and the minimum number of pilot tones, K. At 606, the BS determines the CSI-RS pattern based on the estimate of the channel sparse condition. At 608, the BS signals to the UE the pattern the BS is using in transmitting CSI-RS. In one option for signaling the pattern, the BS indicates the CSI-RS pattern by signaling {L, N _p, N} or {N _p, N} to the UE. In another option for signaling the pattern, the BS indicates the selected CSI-RS pattern by signaling a CSI-RS pattern index to the UE. At 610, the BS transmits CSI-RS using the selected CSI-RS pattern. At 612, the UE estimates CSI for the channel based on the CSI-RS transmitted at 610 and the pattern. The UE transmits the CSI report to the BS at 614.

FIG. 7 is a flow diagram illustrating example operations 700 for wireless communication, in accordance with certain aspects of the present disclosure. The operations 700 may be performed, for example, by a UE (e.g., such as the UE 120a in the wireless communication network 100) . The operations 700 may be implemented as software components that are executed and run on one or more processors (e.g., controller/processor 280 of FIG. 2) . Further, the transmission and reception of signals by the UE in operations 700 may be enabled, for example, by one or more antennas (e.g., antennas 252 of FIG. 2) . In certain aspects, the transmission and/or reception of signals by the UE may be implemented via a bus interface of one or more processors (e.g., controller/processor 280) obtaining and/or outputting signals.

The operations 700 may begin, at block 702, by receiving, in a bandwidth from a base station (BS) , channel state information (CSI) reference signals (CSI-RSs) transmitted using a CSI-RS pattern determined based on an indication of a channel sparsity condition of the bandwidth. For example, UE 120a (shown in FIGs. 1-2) receives in a bandwidth from BS 110a (shown in FIGs. 1-2) , CSI-RSs (e.g., the CSI-RS transmitted at 512 in FIG. 5 or at 610 in FIG. 6) transmitted using a CSI-RS pattern determined based on an indication (e.g., the feedback of the channel sparsity condition at 506 in FIG. 5 or the estimate of the channel sparsity condition at 604 in FIG. 6) of a channel sparsity condition of the bandwidth.

Operations 700 may continue, at block 704, by transmitting, to the BS, a CSI report determined based on the CSI-RSs. Continuing the example from above, the UE 120a transmits, to the BS 110a, a CSI report (e.g., the CSI report transmitted at 516 in FIG. 5 or at 614 in FIG. 6) determined based on the CSI-RSs.

Operations 700 may optionally include, at block 706, transmitting to the BS the indication of the channel sparsity condition (e.g., before the BS transmits the CSI-RSs of block 702) . Still in the example from above, the UE 120a transmits (e.g., feeds back) to the BS 110a the indication of the channel sparsity condition, as shown at 506 in FIG. 5.

FIG. 8 is a flow diagram illustrating example operations 800 for wireless communication, in accordance with certain aspects of the present disclosure. The operations 800 may be performed, for example, by a BS (e.g., such as the BS 110a in the wireless communication network 100) . The operations 800 may be complementary to the operations 700 performed by the UE. The operations 800 may be implemented as software components that are executed and run on one or more processors (e.g., controller/processor 240 of FIG. 2) . Further, the transmission and reception of signals by the BS in operations 800 may be enabled, for example, by one or more antennas (e.g., antennas 234 of FIG. 2) . In certain aspects, the transmission and/or reception of signals by the BS may be implemented via a bus interface of one or more processors (e.g., controller/processor 240) obtaining and/or outputting signals.

The operations 800 may begin, at block 802, by transmitting, in a bandwidth, channel state information (CSI) reference signals (CSI-RSs) using a CSI-RS pattern determined based on an indication of a channel sparsity condition of the bandwidth. For example, BS 110a (shown in FIGs. 1-2) transmits, in a bandwidth, CSI-RSs (e.g., the CSI-RS transmitted at 512 in FIG. 5 or at 610 in FIG. 6) transmitted using a CSI-RS pattern determined based on an indication (e.g., the feedback of the channel sparsity condition at 506 in FIG. 5 or the estimate of the channel sparsity condition at 604 in FIG. 6) of a channel sparsity condition of the bandwidth.

Operations 800 may continue, at block 804, by receiving, from a user equipment (UE) , a CSI report determined based on the CSI-RSs. Continuing the example from above, the BS 110a receives, from the UE 120a, a CSI report (e.g., the CSI report received at 516 in FIG. 5 or at 614 in FIG. 6) determined based on the CSI-RSs.

Operations 800 may optionally include, at block 806, receiving, from the UE, the indication of the channel sparsity condition (e.g., before transmitting the CSI-RSs of block 802) . Still in the example from above, the BS 110a receives from the UE 120a the indication of the channel sparsity condition, as shown at 506 in FIG. 5.

FIG. 9 illustrates a communications device 900 that may include various components (e.g., corresponding to means-plus-function components) configured to perform operations for the techniques disclosed herein, such as the operations illustrated in FIG. 7. The communications device 900 includes a processing system 902 coupled to a transceiver 908 (e.g., a transmitter and/or a receiver) . The transceiver 908 is configured to transmit and receive signals for the communications device 900 via an antenna 910, such as the various signals as described herein. The processing system 902 may be configured to perform processing functions for the communications device 900, including processing signals received and/or to be transmitted by the communications device 900.

The processing system 902 includes a processor 904 coupled to a computer-readable medium/memory 912 via a bus 906. In certain aspects, the computer-readable medium/memory 912 is configured to store instructions (e.g., computer-executable code) that when executed by the processor 904, cause the processor 904 to perform the operations illustrated in FIG. 7, or other operations for performing the various techniques discussed herein for indicating a CSI-RS pattern for sparse channel estimation. In certain aspects, computer-readable medium/memory 912 stores code 914 for receiving, in a bandwidth from a base station (BS) , channel state information (CSI) reference signals (CSI-RSs) transmitted using a CSI-RS pattern determined based on an indication of a channel sparsity condition of the bandwidth; code 916 for transmitting, to the BS, a CSI report determined based on the CSI-RSs; and optional code 918 for transmitting to the BS the indication of the channel sparsity condition. In certain aspects, the processor 904 has circuitry configured to implement the code stored in the computer-readable medium/memory 912. The processor 904 includes circuitry 924 for receiving, in a bandwidth from a base station (BS) , channel state information (CSI) reference signals (CSI-RSs) transmitted using a CSI-RS pattern determined based on an indication of a channel sparsity condition of the bandwidth; circuitry 926 for transmitting, to the BS, a CSI report determined based on the CSI-RSs; and optional circuitry 928 for transmitting to the BS the indication of the channel sparsity condition.

FIG. 10 illustrates a communications device 1000 that may include various components (e.g., corresponding to means-plus-function components) configured to perform operations for the techniques disclosed herein, such as the operations illustrated in FIG. 8. The communications device 1000 includes a processing system 1002 coupled to a transceiver 1008 (e.g., a transmitter and/or a receiver) . The transceiver 1008 is configured to transmit and receive signals for the communications device 1000 via an antenna 1010, such as the various signals as described herein. The processing system 1002 may be configured to perform processing functions for the communications device 1000, including processing signals received and/or to be transmitted by the communications device 1000.

The processing system 1002 includes a processor 1004 coupled to a computer-readable medium/memory 1012 via a bus 1006. In certain aspects, the computer-readable medium/memory 1012 is configured to store instructions (e.g., computer-executable code) that when executed by the processor 1004, cause the processor 1004 to perform the operations illustrated in FIG. 8, or other operations for performing the various techniques discussed herein for indicating a CSI-RS pattern for sparse channel estimation. In certain aspects, computer-readable medium/memory 1012 stores code 1014 for transmitting, in a bandwidth, channel state information (CSI) reference signals (CSI-RSs) using a CSI-RS pattern determined based on an indication of a channel sparsity condition of the bandwidth; code 1016 for receiving, from a user equipment (UE) , a CSI report determined based on the CSI-RSs; and optional code 1018 for receiving, from the UE, the indication of the channel sparsity condition. In certain aspects, the processor 1004 has circuitry configured to implement the code stored in the computer-readable medium/memory 1012. The processor 1004 includes circuitry 1024 for transmitting, in a bandwidth, channel state information (CSI) reference signals (CSI-RSs) using a CSI-RS pattern determined based on an indication of a channel sparsity condition of the bandwidth; circuitry 1026 for receiving, from a user equipment (UE) , a CSI report determined based on the CSI-RSs; and optional circuitry for receiving, from the UE, the indication of the channel sparsity condition.

Example Aspects

In a first aspect, a method for wireless communication by a base station (BS) , includes: transmitting, in a bandwidth, channel state information (CSI) reference signals (CSI-RSs) using a CSI-RS pattern determined based on an indication of a channel sparsity condition of the bandwidth; and receiving, from a user equipment (UE) , a CSI report determined based on the CSI-RSs.

In a second aspect, in combination with the first aspect, the method includes receiving, from the UE, the indication of the channel sparsity condition.

In a third aspect, in combination with one or more of the first and second aspects, the method includes transmitting wideband CSI-RSs, wherein the indication of the channel sparsity condition of the bandwidth is determined based on the wideband CSI-RSs.

In a fourth aspect, in combination with one or more of the first through third aspects, the method includes: receiving, from the UE, a sounding reference signal (SRS) ; and determining the indication of the channel sparsity condition based on the SRS.

In a fifth aspect, in combination with one or more of the first through fourth aspects, the indication of the channel sparsity condition comprises: an estimate of channel impulse response (CIR) length of the bandwidth; and a minimum number of pilot tones.

In a sixth aspect, in combination with the fifth aspect, the method includes determining a number of pilot tones based on the minimum number of pilot tones; and determining the CSI-RS pattern based on the estimate of the CIR length, the number of pilot tones, and a fast Fourier transform (FFT) size used by the BS in transmitting the CSI-RSs using the pattern.

In a seventh aspect, in combination with the sixth aspect, the method includes transmitting to the UE the number of pilot tones and the FFT size prior to transmitting the CSI-RSs using the CSI-RS pattern.

In an eighth aspect, in combination with the seventh aspect, the method includes transmitting to the UE the estimate of the CIR length prior to transmitting the CSI-RSs using the CSI-RS pattern.

In a ninth aspect, in combination with one or more of the first through eighth aspects, the indication of the channel sparsity condition comprises an index corresponding to the CSI-RS pattern in a set of CSI-RS patterns.

In a tenth aspect, in combination with the ninth aspect, the method includes transmitting to the UE the index corresponding to the CSI-RS pattern prior to transmitting the CSI-RSs using the CSI-RS pattern.

In an eleventh aspect, in combination with one or more of the first through tenth aspects, the method includes transmitting to the UE an indication of the CSI-RS pattern prior to transmitting the CSI-RSs using the CSI-RS pattern.

In a twelfth aspect, a method for wireless communication by a user equipment (UE) , includes: receiving, in a bandwidth from a base station (BS) , channel state information (CSI) reference signals (CSI-RSs) transmitted using a CSI-RS pattern determined based on an indication of a channel sparsity condition of the bandwidth; and transmitting, to the BS, a CSI report determined based on the CSI-RSs.

In a thirteenth aspect, in combination with the twelfth aspect, the method includes transmitting to the BS the indication of the channel sparsity condition.

In a fourteenth aspect, in combination with one or more of the twelfth and thirteenth aspects, the method includes: processing wideband CSI-RSs transmitted by the BS; and determining the indication of the channel sparsity condition of the bandwidth based on the wideband CSI-RSs.

In a fifteenth aspect, in combination with one or more of the twelfth through fourteenth aspects, the method includes transmitting a sounding reference signal (SRS) , wherein the indication of the channel sparsity condition is determined based on the SRS.

In a sixteenth aspect, in combination with one or more of the twelfth through fifteenth aspects, the indication of the channel sparsity condition comprises: an estimate of channel impulse response (CIR) length of the bandwidth; and a minimum number of pilot tones.

In a seventeenth aspect, in combination with the sixteenth aspect, a number of pilot tones is determined based on the minimum number of pilot tones, and the method includes determining the CSI-RS pattern based on the estimate of the CIR length, the number of pilot tones, and a fast Fourier transform (FFT) size used by the BS in transmitting the CSI-RSs using the pattern.

In an eighteenth aspect, in combination with the seventeenth aspect, the method includes receiving from the BS the number of pilot tones and the FFT size prior to receiving the CSI-RSs using the CSI-RS pattern.

In a nineteenth aspect, in combination with the eighteenth aspect, the method includes receiving from the BS the estimate of the CIR length prior to receiving the CSI-RSs using the CSI-RS pattern.

In a twentieth aspect, in combination with one or more of the twelfth through nineteenth aspects, the indication of the channel sparsity condition comprises an index corresponding to the CSI-RS pattern in a set of CSI-RS patterns.

In a twenty-first aspect, in combination with the twentieth aspect, the method includes receiving from the BS the index corresponding to the CSI-RS pattern prior to receiving the CSI-RSs using the CSI-RS pattern.

In a twenty-second aspect, in combination with one or more of the twelfth through twenty-first aspects, the method includes receiving from the BS an indication of the CSI-RS pattern prior to receiving the CSI-RSs using the CSI-RS pattern.

In a twenty-third aspect, in a wireless communications system, an apparatus includes a memory; and a processor coupled to the memory and configured to: transmit, in a bandwidth, channel state information (CSI) reference signals (CSI-RSs) using a CSI-RS pattern determined based on an indication of a channel sparsity condition of the bandwidth; and receive, from a user equipment (UE) , a CSI report determined based on the CSI-RSs.

In a twenty-fourth aspect, in combination with the twenty-third aspect, the processor is further configured to: receive, from the UE, the indication of the channel sparsity condition.

In a twenty-fifth aspect, in combination with one or more of the twenty-third and twenty-fourth aspects, the processor is further configured to: transmit wideband CSI-RSs, wherein the indication of the channel sparsity condition of the bandwidth is determined based on the wideband CSI-RSs.

In a twenty-sixth aspect, in combination with one or more of the twenty-third through the twenty-fifth aspects, the processor is further configured to: receive, from the UE, a sounding reference signal (SRS) ; and determine the indication of the channel sparsity condition based on the SRS.

In a twenty-seventh aspect, in combination with one or more of the twenty-third through twenty-sixth aspects, the indication of the channel sparsity condition comprises: an estimate of channel impulse response (CIR) length of the bandwidth; and a minimum number of pilot tones.

In a twenty-eighth aspect, in combination with the twenty-seventh aspect, the processor is further configured to: determine a number of pilot tones based on the minimum number of pilot tones; and determine the CSI-RS pattern based on the estimate of the CIR length, the number of pilot tones, and a fast Fourier transform (FFT) size used by the BS in transmitting the CSI-RSs using the pattern.

In a twenty-ninth aspect, in combination with the twenty-eighth aspect, the processor is further configured to: transmit to the UE the number of pilot tones and the FFT size prior to transmitting the CSI-RSs using the CSI-RS pattern.

In a thirtieth aspect, in combination with the twenty-ninth aspect, the processor is further configured to: transmit to the UE the estimate of the CIR length prior to transmitting the CSI-RSs using the CSI-RS pattern.

In a thirty-first aspect, in combination with one or more of the twenty-third through thirtieth aspects, the indication of the channel sparsity condition comprises an index corresponding to the CSI-RS pattern in a set of CSI-RS patterns.

In a thirty-second aspect, in combination with the thirty-first aspect, the processor is further configured to: transmit to the UE the index corresponding to the CSI-RS pattern prior to transmitting the CSI-RSs using the CSI-RS pattern.

In a thirty-third aspect, in combination with one or more of the twenty-third through thirty-second aspects, the processor is further configured to: transmit to the UE an indication of the CSI-RS pattern prior to transmitting the CSI-RSs using the CSI-RS pattern.

In a thirty-fourth aspect, in a wireless communications system, an apparatus includes a memory; and a processor coupled to the memory and configured to: receive, in a bandwidth from a base station (BS) , channel state information (CSI) reference signals (CSI-RSs) transmitted using a CSI-RS pattern determined based on an indication of a channel sparsity condition of the bandwidth; and transmit, to the BS, a CSI report determined based on the CSI-RSs.

In a thirty-fifth aspect, in combination with the thirty-fourth aspect, the processor is further configured to: transmit to the BS the indication of the channel sparsity condition.

In a thirty-sixth aspect, in combination with one or more of the thirty-fourth and thirty-fifth aspects, the processor is further configured to: process wideband CSI-RSs transmitted by the BS; and determine the indication of the channel sparsity condition of the bandwidth based on the wideband CSI-RSs.

In a thirty-seventh aspect, in combination with one or more of the thirty-fourth through thirty-sixth aspects, the processor is further configured to: transmit a sounding reference signal (SRS) , wherein the indication of the channel sparsity condition is determined based on the SRS.

In a thirty-eighth aspect, in combination with one or more of the thirty-fourth through thirty-seventh aspects, the indication of the channel sparsity condition comprises: an estimate of channel impulse response (CIR) length of the bandwidth; and a minimum number of pilot tones.

In a thirty-ninth aspect, in combination with the thirty-eighth aspect, a number of pilot tones is determined based on the minimum number of pilot tones, and the processor is further configured to: determine the CSI-RS pattern based on the estimate of the CIR length, the number of pilot tones, and a fast Fourier transform (FFT) size used by the BS in transmitting the CSI-RSs using the pattern.

In a fortieth aspect, in combination with the thirty-ninth aspect, the processor is further configured to: receive from the BS the number of pilot tones and the FFT size prior to receiving the CSI-RSs using the CSI-RS pattern.

In a forty-first aspect, in combination with the fortieth aspect, the processor is further configured to: receive from the BS the estimate of the CIR length prior to receiving the CSI-RSs using the CSI-RS pattern.

In a forty-second aspect, in combination with one or more of the thirty-fourth through forty-first aspects, the indication of the channel sparsity condition comprises an index corresponding to the CSI-RS pattern in a set of CSI-RS patterns.

In a forty-third aspect, in combination with the forty-second aspect, the processor is further configured to: receive from the BS the index corresponding to the CSI-RS pattern prior to receiving the CSI-RSs using the CSI-RS pattern.

In a forty-fourth aspect, in combination with one or more of the thirty-fourth through forty-third aspects, the processor is further configured to: receive from the BS an indication of the CSI-RS pattern prior to receiving the CSI-RSs using the CSI-RS pattern.

In a forty-fifth aspect, an apparatus for wireless communication includes: means for transmitting, in a bandwidth, channel state information (CSI) reference signals (CSI-RSs) using a CSI-RS pattern determined based on an indication of a channel sparsity condition of the bandwidth; and means for receiving, from a user equipment (UE) , a CSI report determined based on the CSI-RSs.

In a forty-sixth aspect, in combination with the forty-fifth aspect, the apparatus includes means for receiving, from the UE, the indication of the channel sparsity condition.

In a forty-seventh aspect, in combination with one or more of the forty-fifth and forty-sixth aspects, the apparatus includes means for transmitting wideband CSI-RSs, wherein the indication of the channel sparsity condition of the bandwidth is determined based on the wideband CSI-RSs.

In a forty-eighth aspect, in combination with one or more of the forty-fifth through forty-seventh aspects, the apparatus includes: means for receiving, from the UE, a sounding reference signal (SRS) ; and means for determining the indication of the channel sparsity condition based on the SRS.

In a forty-ninth aspect, in combination with one or more of the forty-fifth through forty-eighth aspects, the indication of the channel sparsity condition comprises: an estimate of channel impulse response (CIR) length of the bandwidth; and a minimum number of pilot tones.

In a fiftieth aspect, in combination with the forty-ninth aspect, the apparatus includes: means for determining a number of pilot tones based on the minimum number of pilot tones; and determining the CSI-RS pattern based on the estimate of the CIR length, the number of pilot tones, and a fast Fourier transform (FFT) size used by the BS in transmitting the CSI-RSs using the pattern.

In a fifty-first aspect, in combination with the fiftieth aspect, the apparatus includes means for transmitting to the UE the number of pilot tones and the FFT size prior to transmitting the CSI-RSs using the CSI-RS pattern.

In a fifty-second aspect, in combination with the fiftieth-first aspect, the apparatus includes means for transmitting to the UE the estimate of the CIR length prior to transmitting the CSI-RSs using the CSI-RS pattern.

In a fifty-third aspect, in combination with one or more of the forty-fifth through fifty-second aspects, the indication of the channel sparsity condition comprises an index corresponding to the CSI-RS pattern in a set of CSI-RS patterns.

In a fifty-fourth aspect, in combination with the fifty-third aspect, the apparatus includes means for transmitting to the UE the index corresponding to the CSI-RS pattern prior to transmitting the CSI-RSs using the CSI-RS pattern.

In an fifty-fifth aspect, in combination with one or more of the forty-fifth through fifty-fourth aspects, the apparatus includes means for transmitting to the UE an indication of the CSI-RS pattern prior to transmitting the CSI-RSs using the CSI-RS pattern.

In a fifty-sixth aspect, an apparatus for wireless communication includes: means for receiving, in a bandwidth from a base station (BS) , channel state information (CSI) reference signals (CSI-RSs) transmitted using a CSI-RS pattern determined based on an indication of a channel sparsity condition of the bandwidth; and means for transmitting, to the BS, a CSI report determined based on the CSI-RSs.

In a fifty-seventh aspect, in combination with the fifty-sixth aspect, the apparatus includes means for transmitting to the BS the indication of the channel sparsity condition.

In a fifty-eighth aspect, in combination with one or more of the fifty-sixth and fifty-seventh aspects, the apparatus includes: means for processing wideband CSI-RSs transmitted by the BS; and means for determining the indication of the channel sparsity condition of the bandwidth based on the wideband CSI-RSs.

In a fifty-ninth aspect, in combination with one or more of the fifty-sixth through fifty-eighth aspects, the apparatus includes means for transmitting a sounding reference signal (SRS) , wherein the indication of the channel sparsity condition is determined based on the SRS.

In a sixtieth aspect, in combination with one or more of the fifty-sixth through fifty-ninth aspects, the indication of the channel sparsity condition comprises: an estimate of channel impulse response (CIR) length of the bandwidth; and a minimum number of pilot tones.

In a sixty-first aspect, in combination with the sixtieth aspect, a number of pilot tones is determined based on the minimum number of pilot tones, and the apparatus includes means for determining the CSI-RS pattern based on the estimate of the CIR length, the number of pilot tones, and a fast Fourier transform (FFT) size used by the BS in transmitting the CSI-RSs using the pattern.

In a sixty-second aspect, in combination with the sixty-first aspect, the apparatus includes means for receiving from the BS the number of pilot tones and the FFT size prior to receiving the CSI-RSs using the CSI-RS pattern.

In a sixty-third aspect, in combination with the sixty-second aspect, the apparatus includes means for receiving from the BS the estimate of the CIR length prior to receiving the CSI-RSs using the CSI-RS pattern.

In a sixty-fourth aspect, in combination with one or more of the fifty-sixth through sixty-third aspects, the indication of the channel sparsity condition comprises an index corresponding to the CSI-RS pattern in a set of CSI-RS patterns.

In a sixty-fifth aspect, in combination with the sixty-fourth aspect, the apparatus includes means for receiving from the BS the index corresponding to the CSI-RS pattern prior to receiving the CSI-RSs using the CSI-RS pattern.

In a sixty-sixth aspect, in combination with one or more of the fifty-sixth through sixty-fifth aspects, the apparatus includes means for receiving from the BS an indication of the CSI-RS pattern prior to receiving the CSI-RSs using the CSI-RS pattern.

The techniques described herein may be used for various wireless communication technologies, such as NR (e.g., 5G NR) , 3GPP Long Term Evolution (LTE) , LTE-Advanced (LTE-A) , code division multiple access (CDMA) , time division multiple access (TDMA) , frequency division multiple access (FDMA) , orthogonal frequency division multiple access (OFDMA) , single-carrier frequency division multiple access (SC-FDMA) , time division synchronous code division multiple access (TD-SCDMA) , and other networks. The terms “network” and “system” are often used interchangeably. A CDMA network may implement a radio technology such as Universal Terrestrial Radio Access (UTRA) , cdma2000, etc. UTRA includes Wideband CDMA (WCDMA) and other variants of CDMA. cdma2000 covers IS-2000, IS-95 and IS-856 standards. A TDMA network may implement a radio technology such as Global System for Mobile Communications (GSM) . An OFDMA network may implement a radio technology such as NR (e.g. 5G RA) , Evolved UTRA (E-UTRA) , Ultra Mobile Broadband (UMB) , IEEE 802.11 (Wi-Fi) , IEEE 802.16 (WiMAX) , IEEE 802.20, Flash-OFDMA, etc. UTRA and E-UTRA are part of Universal Mobile Telecommunication System (UMTS) . LTE and LTE-A are releases of UMTS that use E-UTRA. UTRA, E-UTRA, UMTS, LTE, LTE-A and GSM are described in documents from an organization named “3rd Generation Partnership Project” (3GPP) . cdma2000 and UMB are described in documents from an organization named “3rd Generation Partnership Project 2” (3GPP2) . NR is an emerging wireless communications technology under development.

In 3GPP, the term “cell” can refer to a coverage area of a Node B (NB) and/or a NB subsystem serving this coverage area, depending on the context in which the term is used. In NR systems, the term “cell” and BS, next generation NodeB (gNB or gNodeB) , access point (AP) , distributed unit (DU) , carrier, or transmission reception point (TRP) may be used interchangeably. A BS may provide communication coverage for a macro cell, a pico cell, a femto cell, and/or other types of cells. A macro cell may cover a relatively large geographic area (e.g., several kilometers in radius) and may allow unrestricted access by UEs with service subscription. A pico cell may cover a relatively small geographic area and may allow unrestricted access by UEs with service subscription. A femto cell may cover a relatively small geographic area (e.g., a home) and may allow restricted access by UEs having an association with the femto cell (e.g., UEs in a Closed Subscriber Group (CSG) , UEs for users in the home, etc. ) . A BS for a macro cell may be referred to as a macro BS. A BS for a pico cell may be referred to as a pico BS. A BS for a femto cell may be referred to as a femto BS or a home BS.

A UE may also be referred to as a mobile station, a terminal, an access terminal, a subscriber unit, a station, a Customer Premises Equipment (CPE) , a cellular phone, a smart phone, a personal digital assistant (PDA) , a wireless modem, a wireless communication device, a handheld device, a laptop computer, a cordless phone, a wireless local loop (WLL) station, a tablet computer, a camera, a gaming device, a netbook, a smartbook, an ultrabook, an appliance, a medical device or medical equipment, a biometric sensor/device, a wearable device such as a smart watch, smart clothing, smart glasses, a smart wrist band, smart jewelry (e.g., a smart ring, a smart bracelet, etc. ) , an entertainment device (e.g., a music device, a video device, a satellite radio, etc. ) , a vehicular component or sensor, a smart meter/sensor, industrial manufacturing equipment, a global positioning system device, or any other suitable device that is configured to communicate via a wireless or wired medium. Some UEs may be considered machine-type communication (MTC) devices or evolved MTC (eMTC) devices. MTC and eMTC UEs include, for example, robots, drones, remote devices, sensors, meters, monitors, location tags, etc., that may communicate with a BS, another device (e.g., remote device) , or some other entity. A wireless node may provide, for example, connectivity for or to a network (e.g., a wide area network such as Internet or a cellular network) via a wired or wireless communication link. Some UEs may be considered Internet-of-Things (IoT) devices, which may be narrowband IoT (NB-IoT) devices.

In some examples, access to the air interface may be scheduled. A scheduling entity (e.g., a BS) allocates resources for communication among some or all devices and equipment within its service area or cell. The scheduling entity may be responsible for scheduling, assigning, reconfiguring, and releasing resources for one or more subordinate entities. That is, for scheduled communication, subordinate entities utilize resources allocated by the scheduling entity. Base stations are not the only entities that may function as a scheduling entity. In some examples, a UE may function as a scheduling entity and may schedule resources for one or more subordinate entities (e.g., one or more other UEs) , and the other UEs may utilize the resources scheduled by the UE for wireless communication. In some examples, a UE may function as a scheduling entity in a peer-to-peer (P2P) network, and/or in a mesh network. In a mesh network example, UEs may communicate directly with one another in addition to communicating with a scheduling entity.

The methods disclosed herein comprise one or more steps or actions for achieving the methods. The method steps and/or actions may be interchanged with one another without departing from the scope of the claims. In other words, unless a specific order of steps or actions is specified, the order and/or use of specific steps and/or actions may be modified without departing from the scope of the claims.

As used herein, a phrase referring to “at least one of” a list of items refers to any combination of those items, including single members. As an example, “at least one of: a, b, or c” is intended to cover a, b, c, a-b, a-c, b-c, and a-b-c, as well as any combination with multiples of the same element (e.g., a-a, a-a-a, a-a-b, a-a-c, a-b-b, a-c-c, b-b, b-b-b, b-b-c, c-c, and c-c-c or any other ordering of a, b, and c) .

As used herein, the term “determining” encompasses a wide variety of actions. For example, “determining” may include calculating, computing, processing, deriving, investigating, looking up (e.g., looking up in a table, a database or another data structure) , ascertaining and the like. Also, “determining” may include receiving (e.g., receiving information) , accessing (e.g., accessing data in a memory) and the like. Also, “determining” may include resolving, selecting, choosing, establishing and the like.

The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein, but is to be accorded the full scope consistent with the language of the claims, wherein reference to an element in the singular is not intended to mean “one and only one” unless specifically so stated, but rather “one or more. ” Unless specifically stated otherwise, the term “some” refers to one or more. All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. No claim element is to be construed under the provisions of 35 U.S.C. §112 (f) unless the element is expressly recited using the phrase “means for” or, in the case of a method claim, the element is recited using the phrase “step for. ”

The various operations of methods described above may be performed by any suitable means capable of performing the corresponding functions. The means may include various hardware and/or software component (s) and/or module (s) , including, but not limited to a circuit, a digital signal processor (DSP) , an application specific integrated circuit (ASIC) , or a processor (e.g., a general purpose or specifically programmed processor) . Generally, where there are operations illustrated in figures, those operations may have corresponding counterpart means-plus-function components with similar numbering.

The various illustrative logical blocks, modules and circuits described in connection with the present disclosure may be implemented or performed with a general purpose processor, a DSP, an ASIC, a field programmable gate array (FPGA) or other programmable logic device (PLD) , 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 commercially available processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

If implemented in hardware, an example hardware configuration may comprise a processing system in a wireless node. The processing system may be implemented with a bus architecture. The bus may include any number of interconnecting buses and bridges depending on the specific application of the processing system and the overall design constraints. The bus may link together various circuits including a processor, machine-readable media, and a bus interface. The bus interface may be used to connect a network adapter, among other things, to the processing system via the bus. The network adapter may be used to implement the signal processing functions of the PHY layer. In the case of a user terminal (see FIG. 1) , a user interface (e.g., keypad, display, mouse, joystick, etc. ) may also be connected to the bus. The bus may also link various other circuits such as timing sources, peripherals, voltage regulators, power management circuits, and the like, which are well known in the art, and therefore, will not be described any further. The processor may be implemented with one or more general-purpose and/or special-purpose processors. Examples include microprocessors, microcontrollers, DSP processors, and other circuitry that can execute software. Those skilled in the art will recognize how best to implement the described functionality for the processing system depending on the particular application and the overall design constraints imposed on the overall system.

If implemented in software, the functions may be stored or transmitted over as one or more instructions or code on a computer readable medium. Software shall be construed broadly to mean instructions, data, or any combination thereof, whether referred to as software, firmware, middleware, microcode, hardware description language, or otherwise. Computer-readable media include both computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. The processor may be responsible for managing the bus and general processing, including the execution of software modules stored on the machine-readable storage media. A computer-readable storage medium may be coupled to a processor such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. By way of example, the machine-readable media may include a transmission line, a carrier wave modulated by data, and/or a computer readable storage medium with instructions stored thereon separate from the wireless node, all of which may be accessed by the processor through the bus interface. Alternatively, or in addition, the machine-readable media, or any portion thereof, may be integrated into the processor, such as the case may be with cache and/or general register files. Examples of machine-readable storage media may include, by way of example, RAM (Random Access Memory) , flash memory, ROM (Read Only Memory) , PROM (Programmable Read-Only Memory) , EPROM (Erasable Programmable Read-Only Memory) , EEPROM (Electrically Erasable Programmable Read-Only Memory) , registers, magnetic disks, optical disks, hard drives, or any other suitable storage medium, or any combination thereof. The machine-readable media may be embodied in a computer-program product.

A software module may comprise a single instruction, or many instructions, and may be distributed over several different code segments, among different programs, and across multiple storage media. The computer-readable media may comprise a number of software modules. The software modules include instructions that, when executed by an apparatus such as a processor, cause the processing system to perform various functions. The software modules may include a transmission module and a receiving module. Each software module may reside in a single storage device or be distributed across multiple storage devices. By way of example, a software module may be loaded into RAM from a hard drive when a triggering event occurs. During execution of the software module, the processor may load some of the instructions into cache to increase access speed. One or more cache lines may then be loaded into a general register file for execution by the processor. When referring to the functionality of a software module below, it will be understood that such functionality is implemented by the processor when executing instructions from that software module.

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 (IR) , 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 medium. Disk and disc, as used herein, include compact disc (CD) , laser disc, optical disc, digital versatile disc (DVD) , floppy disk, and

disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Thus, in some aspects computer-readable media may comprise non-transitory computer-readable media (e.g., tangible media) . In addition, for other aspects computer-readable media may comprise transitory computer-readable media (e.g., a signal) . Combinations of the above should also be included within the scope of computer-readable media.

Thus, certain aspects may comprise a computer program product for performing the operations presented herein. For example, such a computer program product may comprise a computer-readable medium having instructions stored (and/or encoded) thereon, the instructions being executable by one or more processors to perform the operations described herein, for example, instructions for performing the operations described herein and illustrated in FIG. 7 and/or FIG. 8.

Further, it should be appreciated that modules and/or other appropriate means for performing the methods and techniques described herein can be downloaded and/or otherwise obtained by a user terminal and/or base station as applicable. For example, such a device can be coupled to a server to facilitate the transfer of means for performing the methods described herein. Alternatively, various methods described herein can be provided via storage means (e.g., RAM, ROM, a physical storage medium such as a compact disc (CD) or floppy disk, etc. ) , such that a user terminal and/or base station can obtain the various methods upon coupling or providing the storage means to the device. Moreover, any other suitable technique for providing the methods and techniques described herein to a device can be utilized.

It is to be understood that the claims are not limited to the precise configuration and components illustrated above. Various modifications, changes and variations may be made in the arrangement, operation and details of the methods and apparatus described above without departing from the scope of the claims.

Claims

A method for wireless communications by a base station (BS) , comprising:

transmitting, in a bandwidth, channel state information (CSI) reference signals (CSI-RSs) using a CSI-RS pattern determined based on an indication of a channel sparsity condition of the bandwidth; and

receiving, from a user equipment (UE) , a CSI report determined based on the CSI-RSs.
The method of claim 1, further comprising receiving, from the UE, the indication of the channel sparsity condition.
The method of claim 1, further comprising transmitting wideband CSI-RSs, wherein the indication of the channel sparsity condition of the bandwidth is determined based on the wideband CSI-RSs.
The method of claim 1, further comprising:

receiving, from the UE, a sounding reference signal (SRS) ; and

determining the indication of the channel sparsity condition based on the SRS.
The method of claim 1, wherein the indication of the channel sparsity condition comprises:

an estimate of channel impulse response (CIR) length of the bandwidth; and

a minimum number of pilot tones.
The method of claim 5, further comprising:

determining a number of pilot tones based on the minimum number of pilot tones; and

determining the CSI-RS pattern based on the estimate of the CIR length, the number of pilot tones, and a fast Fourier transform (FFT) size used by the BS in transmitting the CSI-RSs using the pattern.
The method of claim 6, further comprising transmitting to the UE the number of pilot tones and the FFT size prior to transmitting the CSI-RSs using the CSI-RS pattern.
The method of claim 7, further comprising transmitting to the UE the estimate of the CIR length prior to transmitting the CSI-RSs using the CSI-RS pattern.
The method of claim 1, wherein the indication of the channel sparsity condition comprises an index corresponding to the CSI-RS pattern in a set of CSI-RS patterns.
The method of claim 9, further comprising transmitting to the UE the index corresponding to the CSI-RS pattern prior to transmitting the CSI-RSs using the CSI-RS pattern.
The method of claim 1, further comprising transmitting to the UE an indication of the CSI-RS pattern prior to transmitting the CSI-RSs using the CSI-RS pattern.
A method for wireless communications by a user equipment (UE) , comprising:

receiving, in a bandwidth from a base station (BS) , channel state information (CSI) reference signals (CSI-RSs) transmitted using a CSI-RS pattern determined based on an indication of a channel sparsity condition of the bandwidth; and

transmitting, to the BS, a CSI report determined based on the CSI-RSs.
The method of claim 12, further comprising transmitting to the BS the indication of the channel sparsity condition.
The method of claim 12, further comprising:

processing wideband CSI-RSs transmitted by the BS; and

determining the indication of the channel sparsity condition of the bandwidth based on the wideband CSI-RSs.
The method of claim 12, further comprising:

transmitting a sounding reference signal (SRS) , wherein the indication of the channel sparsity condition is determined based on the SRS.
The method of claim 12, wherein the indication of the channel sparsity condition comprises:

an estimate of channel impulse response (CIR) length of the bandwidth; and

a minimum number of pilot tones.
The method of claim 16, wherein a number of pilot tones is determined based on the minimum number of pilot tones, and the method further comprises determining the CSI-RS pattern based on the estimate of the CIR length, the number of pilot tones, and a fast Fourier transform (FFT) size used by the BS in transmitting the CSI-RSs using the pattern.
The method of claim 17, further comprising receiving from the BS the number of pilot tones and the FFT size prior to receiving the CSI-RSs using the CSI-RS pattern.
The method of claim 18, further comprising receiving from the BS the estimate of the CIR length prior to receiving the CSI-RSs using the CSI-RS pattern.
The method of claim 12, wherein the indication of the channel sparsity condition comprises an index corresponding to the CSI-RS pattern in a set of CSI-RS patterns.
The method of claim 20, further comprising receiving from the BS the index corresponding to the CSI-RS pattern prior to receiving the CSI-RSs using the CSI-RS pattern.
The method of claim 12, further comprising receiving from the BS an indication of the CSI-RS pattern prior to receiving the CSI-RSs using the CSI-RS pattern.
In a wireless communications system, an apparatus comprising:

a memory; and

a processor coupled to the memory and configured to:

transmit, in a bandwidth, channel state information (CSI) reference signals (CSI-RSs) using a CSI-RS pattern determined based on an indication of a channel sparsity condition of the bandwidth; and

receive, from a user equipment (UE) , a CSI report determined based on the CSI-RSs.
The apparatus of claim 23, wherein the processor is further configured to receive, from the UE, the indication of the channel sparsity condition.
The apparatus of claim 23, wherein the processor is further configured to transmit wideband CSI-RSs, wherein the indication of the channel sparsity condition of the bandwidth is determined based on the wideband CSI-RSs.
The apparatus of claim 23, wherein the processor is further configured to:

receive from the UE, a sounding reference signal (SRS) ; and

determine the indication of the channel sparsity condition based on the SRS.
In a wireless communications system, an apparatus comprising:

a memory; and

a processor coupled to the memory and configured to:

receive, in a bandwidth from a base station (BS) , channel state information (CSI) reference signals (CSI-RSs) transmitted using a CSI-RS pattern determined based on an indication of a channel sparsity condition of the bandwidth; and

transmit, to the BS, a CSI report determined based on the CSI-RSs.
The apparatus of claim 27, wherein the processor is further configured to transmit to the BS the indication of the channel sparsity condition.
The apparatus of claim 27, wherein the processor is further configured to:

process wideband CSI-RSs transmitted by the BS; and

determine the indication of the channel sparsity condition of the bandwidth based on the wideband CSI-RSs.
The apparatus of claim 27, wherein the processor is further configured to:

transmit a sounding reference signal (SRS) , wherein the indication of the channel sparsity condition is determined based on the SRS.