CHANNEL STATE INFORMATION (CSI) REFERENCE SIGNAL (RS) (CSI-RS) REPETITION CONFIGURATIONS FOR HIGH DOPPLER SYSTEMS

Aspects of the present disclosure relate to wireless communications, and more particularly, to techniques for configuring CSI-RS repetitions for CSI measurement in high Doppler scenarios. An example method generally includes receiving, from a network entity, a configuration identifying channel state information (CSI) reference signal (RS) (CSI-RS) repetitions over which a CSI report is to be generated, receiving CSI-RS repetitions according to the configuration, measuring CSI based on the received CSI-RS repetitions, and transmitting the CSI report including the measured CSI to the network entity.

TECHNICAL FIELD

Aspects of the present disclosure relate to wireless communications, and more particularly, to techniques for configuring channel state information (CSI) reference signal (RS) (CSI-RS) repetitions for measurement in high Doppler systems.

BACKGROUND

SUMMARY

One innovative aspect 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, from a network entity, a configuration identifying channel state information (CSI) reference signal (RS) (CSI-RS) repetitions over which a CSI report is to be generated, receiving CSI-RS repetitions according to the configuration, measuring CSI based on the received CSI-RS repetitions, and transmitting the CSI report including the measured CSI to the network entity.

One innovative aspect of the subject matter described in this disclosure can be implemented in a method for wireless communication by a network entity. The method generally includes transmitting, to a user equipment (UE), a configuration identifying channel state information (CSI) reference signal (RS) (CSIRS) repetitions over which a CSI report is to be generated, transmitting CSI-RS repetitions according to the configuration, receiving a CSI report from the UE based on the transmitted CSI-RS repetitions, determining one or more parameters for communicating with the UE based on the received CSI report, and transmitting the determined parameters to the UE.

Aspects of the present disclosure provide means for, apparatus, processors, and computer-readable mediums for performing the methods described herein.

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 some 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.

DETAILED DESCRIPTION

Aspects of the present disclosure relate to wireless communications, and more particularly, to mobility techniques that allow for configuring channel state information (CSI) reference signal (RS) (CSI-RS) repetitions for measurement in high Doppler systems.

FIG.1illustrates an example wireless communication network100in which aspects of the present disclosure may be performed. For example, as shown inFIG.1, UE120amay include a CSI measurement configuration module122that may be configured to perform (or cause UE120ato perform) operations500ofFIG.5. Similarly, a BS120amay include a CSI measurement configuration module112that may be configured to perform (or cause BS110ato perform) operations600ofFIG.6.

NR access (for example, 5G NR) may support various wireless communication services, such as enhanced mobile broadband (eMBB) targeting wide bandwidth (for example, 80 MHz or beyond), millimeter wave (mmWave) targeting high carrier frequency (for example, 25 GHz or beyond), massive machine type communications MTC (mMTC) targeting non-backward compatible MTC techniques, or mission critical services 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 time-domain resource (for example, a slot or subframe) or frequency-domain resource (for example, component carrier).

Wireless communication network100may also include relay stations (for example, relay station110r), also referred to as relays or the like, that receive a transmission of data or other information from an upstream station (for example, a BS110aor a UE120r) and sends a transmission of the data or other information to a downstream station (for example, a UE120or a BS110), or that relays transmissions between UEs120, to facilitate communication between devices.

A network controller130may couple to a set of BSs110and provide coordination and control for these BSs110. The network controller130may communicate with the BSs110via a backhaul. The BSs110may also communicate with one another (for example, directly or indirectly) via wireless or wireline backhaul.

FIG.2shows a block diagram illustrating an example base station (BS) and an example user equipment (UE) in accordance with some aspects of the present disclosure.

At the BS110, a transmit processor220may receive data from a data source212and control information from a controller/processor240. 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. The processor220may process (for example, encode and symbol map) the data and control information to obtain data symbols and control symbols, respectively. The transmit processor220may also generate reference symbols, such as for the primary synchronization signal (PSS), secondary synchronization signal (SSS), and cell-specific reference signal (CRS). A transmit (TX) multiple-input multiple-output (MIMO) processor230may perform spatial processing (for example, precoding) on the data symbols, the control symbols, or the reference symbols, if applicable, and may provide output symbol streams to the modulators (MODs)232a-232t. Each modulator232may process a respective output symbol stream (for example, for OFDM, etc.) to obtain an output sample stream. Each modulator may further process (for example, convert to analog, amplify, filter, and upconvert) the output sample stream to obtain a downlink signal. Downlink signals from modulators232a-232tmay be transmitted via the antennas234a-234t, respectively.

The memories242and282may store data and program codes for BS110and UE120, respectively. A scheduler244may schedule UEs for data transmission on the downlink or uplink.

The controller/processor280or other processors and modules at the UE120may perform or direct the execution of processes for the techniques described herein. As shown inFIG.2, the controller/processor280of the UE120has a CSI measurement configuration module122that may be configured to perform (or cause UE120to perform) operations500ofFIG.5. Similarly, the BS120amay include a CSI measurement configuration module112that may be configured to perform (or cause BS110ato perform) operations600ofFIG.6.

FIG.3Ais a diagram showing an example of a frame format300for 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 depending on the subcarrier spacing. Each slot may include a variable number of symbol periods (e.g., 7 or 14 symbols) depending on the subcarrier spacing. The symbol periods in each slot may be assigned indices. A mini-slot, which may be referred to as a sub-slot structure, refers to a transmit time interval having a duration less than a slot (e.g., 2, 3, or 4 symbols).

In NR, a synchronization signal (SS) block is transmitted. The SS block includes a PSS, a SSS, and a two symbol PBCH. The SS block can be transmitted in a fixed slot location, such as the symbols 0-3 as shown inFIG.3A. 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 SS blocks 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 SS block can be transmitted up to sixty-four times, for example, with up to sixty-four different beam directions for mmW. The up to sixty-four transmissions of the SS block are referred to as the SS burst set. SS blocks in an SS burst set are transmitted in the same frequency region, while SS blocks in different SS bursts sets can be transmitted at different frequency locations.

As shown inFIG.3B, the SS blocks may be organized into SS burst sets to support beam sweeping. As shown, each SSB within a burst set may be transmitted using a different beam, which may help a UE quickly acquire both transmit (Tx) and receive (Rx) beams (particular for mmW applications). A physical cell identity (PCI) may still decoded from the PSS and SSS of the SSB.

A control resource set (CORESET) for systems, such as an NR and LTE systems, may comprise one or more control resource (e.g., time and frequency resources) sets, configured for conveying PDCCH, within the system bandwidth. Within each CORESET, one or more search spaces (e.g., common search space (CSS), UE-specific search space (USS), etc.) may be defined for a given UE. According to aspects of the present disclosure, a CORESET is a set of time and frequency domain resources, defined in units of resource element groups (REGs). Each REG may comprise a fixed number (e.g., twelve) tones in one symbol period (e.g., a symbol period of a slot), where one tone in one symbol period is referred to as a resource element (RE). A fixed number of REGs may be included in a control channel element (CCE). Sets of CCEs may be used to transmit new radio PDCCHs (NR-PDCCHs), with different numbers of CCEs in the sets used to transmit NR-PDCCHs using differing aggregation levels. Multiple sets of CCEs may be defined as search spaces for UEs, and thus a NodeB or other base station may transmit an NR-PDCCH to a UE by transmitting the NR-PDCCH in a set of CCEs that is defined as a decoding candidate within a search space for the UE, and the UE may receive the NR-PDCCH by searching in search spaces for the UE and decoding the NR-PDCCH transmitted by the NodeB.

Example Methods for Configuring Channel State Measurement (CSI) Reference Signal (RS) (CSI-RS) Repetitions for Measurement in High Doppler Systems

Aspects of the present disclosure relate to wireless communications, and more particularly, to configuring channel state information (CSI) reference signal (RS) (CSI-RS) repetitions for measurement in high Doppler systems. As will be described in greater detail below, CSI-RS repetitions may be configured and transmitted from a network entity to a user equipment (UE) to allow for CSI measurement reports to be generated over a period of time such that the CSI measurement reports and adjustments to communication parameters based on the CSI measurement reports take into account UE movement in high speed/high Doppler environments.

FIG.4illustrates an example scenario in which a channel state information (CSI) report becomes outdated in a high Doppler scenario. As illustrated, a network entity may be configured to transmit a CSI-RS periodically according to configuration410, in which a CSI-RS is transmitted every four slots, which may be a minimum interval for transmitting CSI-RSs to a UE for measurement. For each of these CSI-RSs, as illustrated in timeline400, a UE may perform a CSI measurement and report CSI (e.g., a rank indicator (RI), precoding matrix indicator (PMI), and/or channel quality indicator (CQI)) to a serving network entity. In response, the serving network entity may transmit a downlink control information (DCI) including transmission parameters for downlink transmissions to the UE, such as a rank and a modulation and coding scheme (MCS). However, by the time the network entity performs a subsequent downlink transmission (e.g., on PDSCH), the rank and/or MCS may be outdated and thus inappropriate for the current channel conditions at the UE.

For aperiodic CSI reports using aperiodic CSI-RS resources, a CSI report may be based on an instantaneous observation of a single CSI resource. In scenarios where a UE is stationary or moving slowly, an instantaneous observation of a single CSI resource may provide sufficiently accurate information regarding the condition of a channel; however, in high Doppler scenarios, the reported CSI (e.g., RI/PMI/CQO) may be inaccurate because the channel may vary rapidly due to the UE being in a high Doppler scenario.

For CSI reports using periodic or semipersistently scheduled CSI-RS resources, a UE can perform time domain filtering over multiple channel observations and report a CQI based on averaged channel observations. However, quasi-colocation (QCL) assumptions may not be defined for different CSI-RS observations, which may make CQI calculation assumptions unclear or uncertain. For example, a UE may not be aware of time domain precoder cycling, which may be introduced for performance gains in high Doppler scenarios, for different CSI-RSs. Further, because CSI-RSs may be transmitted periodically over a number of slots, filtering over multiple channel observations may introduce a delay in capturing time variation in channel conditions.

To account for high Doppler scenarios in measuring CSI, aspects of the present disclosure may provide for various CSI-RS resource repetitions that can be used to allow for accurate measurement of rapidly changing channel conditions in high Doppler scenarios.

FIG.5illustrates example operations500that may be performed by a user equipment (UE) to report CSI based on a CSI-RS resource repetition configuration for measuring CSI in high Doppler scenarios, according to certain aspects of the present disclosure. Operations500may be performed, for example, by a UE120illustrated inFIG.1.

Operations500begin, at502, where the UE receives, from a network entity, a configuration identifying channel state information (CSI) reference signal (RS) (CSI-RS) repetitions over which a CSI report is to be generated.

At504, the UE receives CSI-RS repetitions according to the configuration.

At506, the UE measures CSI based on the received CSI-RS repetitions.

At508, the UE transmits the CSI report including the measured CSI to the network entity.

FIG.6illustrates example operations600that may considered complementary to operations500ofFIG.5. For example, operations600may be performed by a network entity (e.g., a gNB DU/CU) to configure a UE (performing operations500ofFIG.5) to measure CSI based on a CSI-RS configuration identifying CSI-RS repetitions over which a CSI report is to be generated.

Operations600begin, at602, where the network entity transmits, to a user equipment (UE), a configuration identifying channel state information (CSI) reference signal (RS) (CSI-RS) repetitions over which a CSI report is to be generated.

At604, the network entity transmits CSI-RS repetitions to the UE according to the configuration.

At606, the network entity receives a CSI report from the UE based on the transmitted CSI repetitions.

At608, the network entity determines one or more parameters for communicating with the UE based on the received CSI report and transmits the determined parameters to the UE.

In some embodiments, the CSI-RS repetitions may be defined as an intra-slot or inter-slot repetition over which a CSI measurement is performed (e.g., averaged over time, etc.) and reported to a network entity.FIG.7illustrates an example of an intra-slot CSI-RS repetition700in which CSI-RS resources are repeated in the time domain. A number of the repeated CSI-RS resources may be used for associated CSI reports, and the CSI reports generated from the CSI-RS repetitions may include one or more of a rank indicator (RI), precoding matrix indicator (PMI), or channel quality indicator (CQI).

Repetition and measurement of CSI-RS repetitions in the time domain may be activated, in some embodiments, if an NZP-CSI-RS-ResourceSet is configured with both the Repetition-On and trs-info parameters enabled (e.g., repetition enabled and tracking reference signal (TRS) information enabled). There may be no restrictions on the CSI-RS patterns (e.g., a number of ports, pattern density, etc.). A UE may assume the same or different QCL references for the different CSI-RS resources. For example, a UE need not assume the same QCL-TypeD reference for each of the CSI-RS resources. The report may include additional information beyond physical layer reference signal received power (L1-RSRP) measurements; for example, as discussed above, the report may include RI, PMI, and/or CQI. In some aspects, if the NZP-CSI-RS-ResourceSet includes periodic CSI-RSs (e.g., includes a periodicity parameter for the CSI-RSs), the NZP-CSI-RS-ResourceSet may be associated with a CSI report configuration, and the CSI report configuration may be configured with a time restriction for channel measurements.

In some aspects, a time domain repetition periodicity may include a one-slot periodicity. CSI-RS repetitions may be configured on an intra-slot or joint inter-slot and intra-slot basis. For example, a CSI-RS repetition configuration may specify that CSI-RSs are repeated n times within a slot, with a periodicity of m slots.

FIGS.8A-8Cillustrate example CSI-RS patterns for CSI-RS resource repetition. Generally, when CSI-RS resource repetition is enabled for CSI reporting, as discussed above, various patterns may be considered with repetition across different physical resource blocks.

FIG.8Aillustrates an example CSI-RS pattern800A in which a total number of configured CSI-RS ports span multiple PRBs in the frequency domain. In this example, six CSI-RSs may be defined according to different frequency resources for a given time resource. Unlike a configuration in which CSI-RSs are distributed within a single PRB, example CSI-RS pattern800A may spread CSI-RS resources across different PRBs so that additional frequency intervals may be enabled between adjacent CSI-RS components. The number of interval resource elements may be defined based on a number of CSI-RS resource repetitions.

FIG.8Billustrates an example CSI-RS pattern800B in which time domain multiplexed CSI-RS components within a single PRB are frequency multiplexed across different PRBs. For example, in Release 15/Release 16 CSI-RS configurations, a number of CSI-RS resources may be time multiplexed on a same frequency resource (e.g., such that two CSI-RS resources for different CSI-RS ports are adjacent to each other in the time domain and use the same frequency resources). In CSI-RS pattern800B, CSI-RS resources for different CSI-RS ports may be frequency multiplexed across different PRBs such that each CSI-RS port is associated with a specific, unique set of frequency resources. Further, as illustrated, a plurality of CSI-RS resource repetitions may be defined in the time domain, and each CSI-RS port may use a same frequency resource for each CSI-RS repetition.

FIG.8Cillustrates an example of PRB-level combs for CSI-RS repetitions. In example800C, a higher number of PRB-level combs (e.g., comb-r or comb-6) may be configured for CSI-RS repetitions based on the number of CSI-RS resource repetitions.

Generally, by frequency division multiplexing CSI-RS resources, the overall CSI-RS density may be minimized when CSI-RS resource repetition is disabled. Further, enabling frequency division multiplexed CSI-RS resource repetition may provide for improvements in measuring CSI in high Doppler scenarios, and in high Doppler scenarios with low or medium delay spread, previously defined time division multiplexed CSI-RS repetitions for different CSI-RS ports may still be used.

FIGS.9A-9Billustrate an example of CSI-RS patterns for CSI-RS resource repetition in which CSI-RS resources are staggered across repetitions. As illustrated in example900A, a number of CSI-RS resources may be spread across multiple PRBs (similar to the example illustrated inFIG.8A). In each CSI-RS resource repetition, however, a resource element or resource block offset for the CSI-RS resources can be configured such that the CSI-RS resources for a given CSI-RS port are transmitted using different frequency resources for each repetition. Similarly, as illustrated in example900B, inter-slot repetitions may also be defined in terms of a PRB offset such that CSI-RS repetitions are transmitted in different PRBs in the time domain. Generally, by staggering a CSI-RS repetition pattern across CSI-RS resource repetition instances, aspects described herein can compensate for time domain losses introduced by a reduced density of CSI-RS transmissions from spreading CSI-RS resources at a given time out in the frequency domain across different PRBs.

FIG.10illustrates an example CSI-RS pattern1000in which same or different quasi-colocation (QCL) references may be assumed for different CSI-RS repetitions. Generally, repeated CSI-RS resources may, but need not, be associated with a same QCL reference (e.g., a same QCL Type-A/B/C/D reference). A subset of CSI-RS resource repetitions may be configured to be associated with a same QCL reference, and different subsets of CSI-RS resource repetitions may be configured to be associated with different QCL references.

For a CSI report associated with repeated CSI-RS resources, an associated CSI reference resource may be defined and used by the UE to calculate CSI (e.g., to calculate or otherwise determine a rank indicator (RI), precoding matrix indicator (PMI), and/or channel quality indicator (CQI). The CSI reference resource may be defined in relation to a frequency domain resource assignment or a time domain resource assignment for the CSI-RS repetitions. CSI-RS resources may be defined, for example, in relation to the slot or symbol in which the CSI-RS reference resource is carried. For example, the CSI-RS repetitions from which a CSI report is generated may be defined as the repetitions that are scheduled no later than a last slot or symbol of the CSI reference resource or the repetitions that are scheduled no later than a first slot or symbol of the CSI reference resource.

In some aspects, when calculating CQI, symbols overlapping with and after a first CSI-RS resource repetition and before a next CSI-RS resource associated with a different QCL reference may be assumed to use the same precoding as the precoding measured in the symbols associated with the first CSI-RS repetition.

In some aspects, a UE may refrain from reporting CSI for a specific symbol of a CSI-RS resource. For example, the UE may refrain from reporting CSI for these symbols due to overlaps between the CSI-RS resource and uplink symbols, synchronization signal blocks, resources associated with a control resource set (CORESET), etc. In some aspects, a channel quality indicator (CQI) calculation may assume that resources after the symbol for which the UE refrained from reporting CSI are not included in the calculation. In some aspects, the CQI calculation may be performed based on an assumption that resources after the symbol for which the UE refrained from reporting CSI are associated with a previous CSI-RS for which the UE did not refrain from reporting CSI, if applicable. In some aspects, when a UE refrains from reporting CSI for a specific symbol of a CSI-RS resource, the UE need not generate a CSI report.

FIG.11illustrates an example CSI-RS repetition pattern1100in which CSI-RS repetitions are configured as a sequence of CSI-RSs in a transfer domain. As illustrated, a UE may be configured with a CSI-RS sequence R(m) in a transfer domain, such as the sequence

1≤m≤M in the Doppler domain.

CSI-RS patterns repeated in the time domain may be configured such that the CSI-RS pattern comprises CSI-RS sequences with time domain spreading. REs in the same location of the same CSI-RS component in different time domain resource assignment instances may be formed into a time domain sequence r(n), 1≤n≤N, and the time domain sequence may be generated by spreading the transfer domain CSI-RS sequence into the time domain. N may represent the number of repeated CSI-RS components in the time domain. In some aspects, the transfer domain may be a discrete Fourier transform (DFT)-basis domain.

In some aspects, the spreading may be performed as a linear operation, such as an inverse DFT operation. For example, the spreading can be performed according to the equation r=F×R, where r and R are the vectors formed by the time domain sequence r(n) and transfer domain sequence R(m), respectively, and F is an N×M matrix comprised by rows of DFT bases. The spreading may be an underdetermined spreading in which N<M, a determined spreading in which N=M, or an overdetermined spreading in which N>M. Generally an underdetermined spreading may allow for further reductions in tie domain resources for measuring Doppler spreads by using a precoding with higher spectral efficiency than the repetition codes.

In some aspects, when time domain spreading for CSI-RS resources is considered, when calculating CQI, the associated CSI reference resource may also be assumed to use time domain spreading techniques for PDSCH transmission. Modulated symbols may be defined in a transfer domain and spread into the time domain. Similar QCL reference assumptions may be used as those described above. Generally, if a transmission of a symbol of a CSI-RS resource is refrained (e.g., due to an overlap with an uplink symbol, an SSB, or symbols in a CORESET), the UE may refrain from generating and transmitting a CSI report.

In some aspects, time restrictions for channel measurements may be adjusted to account for CSI-RS resource repetition. If a CSI-RS resource repetition-based CSI report in which RI/PMI/CQI is used, a UE configured with the higher layer parameter timeRestrictionForChannelMeasurements in a CSI report configuration can derive channel measurements for computing CSI based on a most recent occasion of a non-zero-power (NZP) CSI-RS no later than the CSI reference resources identified by the parameter CSI-RS-ResourceSet associated with the CSI report.

The techniques described herein may be used for the wireless networks and radio technologies mentioned above as well as other wireless networks and radio technologies. For clarity, while aspects may be described herein using terminology commonly associated with 3G, 4G, or 5G wireless technologies, aspects of the present disclosure can be applied in other generation-based communication systems.

NR may utilize OFDM with a CP on the uplink and downlink and include support for half-duplex operation using TDD. In NR, a subframe is still 1 ms, but the basic TTI is referred to as a slot. A subframe contains a variable number of slots (for example, 1, 2, 4, 8, 16, . . . slots) depending on the subcarrier spacing. The NR RB is 12 consecutive frequency subcarriers. NR may support a base subcarrier spacing of 15 KHz and other subcarrier spacing may be defined with respect to the base subcarrier spacing, for example, 30 kHz, 60 kHz, 120 kHz, 240 kHz, etc. The symbol and slot lengths scale with the subcarrier spacing. The CP length also depends on the subcarrier spacing. Beamforming may be supported and beam direction may be dynamically configured. MIMO transmissions with precoding may also be supported. In some examples, 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. In some examples, 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.

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

As used herein, “or” is used intended to be interpreted in the inclusive sense, unless otherwise explicitly indicated. For example, “a or b” may include a only, b only, or a combination of a and b. As used herein, a phrase referring to “at least one of” or “one or more of” a list of items refers to any combination of those items, including single members. For example, “at least one of: a, b, or c” is intended to cover the possibilities of: a only, b only, c only, a combination of a and b, a combination of a and c, a combination of b and c, and a combination of a and b and c.