Patent Description:
Typical 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.).

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 OFDM with a cyclic prefix (CP) (CP-OFDM) on the downlink (DL), using CP-OFDM and/or SC-FDM (e.g., also known as discrete Fourier transform spread ODFM (DFT-s-OFDM)) on the uplink (UL), as well as supporting beamforming, multiple-input multiple-output (MIMO) antenna technology, and carrier aggregation. International Patent Application Publication No. <CIT> relates to a wireless device, radio network node and methods performed therein. United States Patent Application Publication No. <CIT> relates to a method and apparatus for reporting channel state information in a wireless communication system. "<NPL> discusses DL and UL beam management procedures. United States Patent Application Publication No. <CIT> relates to a method and apparatus for beam allocation in a wireless communication system. "<NPL> considers QCL for UL.

Techniques described herein permit a UE and/or a base station to use downlink reference signals (e.g., channel state information reference signals) to determine an uplink precoder and/or to use uplink reference signals (e.g., sounding reference signals) to determine a downlink precoder when there is reciprocity between downlink channels and uplink channels.

In some aspects, a method of wireless communication is performed by a UE. The method includes receiving an indication of whether to use uplink reference signals or downlink reference signals for uplink precoder determination; selectively transmitting a plurality of uplink reference signals or one or more measurement reports based at least in part on the indication, wherein the one or more measurement reports are associated with a plurality of downlink reference signals; receiving an indication of a precoder, of a plurality of precoders, to be used to precode an uplink communication, wherein the precoder is identified based at least in part on the plurality of uplink reference signals or the one or more measurement reports; and precoding the uplink communication using the precoder.

In some aspects, a UE for wireless communication includes a memory and one or more processors operatively coupled to the memory. The memory and the one or more processors are configured to receive an indication of whether to use uplink reference signals or downlink reference signals for uplink precoder determination; selectively transmit a plurality of uplink reference signals or one or more measurement reports based at least in part on the indication, wherein the one or more measurement reports are associated with a plurality of downlink reference signals; receive an indication of a precoder, of a plurality of precoders, to be used to precode an uplink communication, wherein the precoder is identified based at least in part on the plurality of uplink reference signals or the one or more measurement reports; and precode the uplink communication using the precoder.

Aspects generally include a method, apparatus, system, computer program product, non-transitory computer-readable medium, user equipment, wireless communication device, base station, and processing system as substantially described herein with reference to and as illustrated by the accompanying drawings and specification.

" Any aspect described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over another aspect. These apparatuses and techniques will be described in the following detailed description and illustrated in the accompanying drawings by various blocks, modules, components, circuits, steps, processes, algorithms, etc. (collectively referred to as "elements").

An access point ("AP") may comprise, be implemented as, or known as NodeB, Radio Network Controller ("RNC"), eNodeB (eNB), Base Station Controller ("BSC"), Base Transceiver Station ("BTS"), Base Station ("BS"), Transceiver Function ("TF"), Radio Router, Radio Transceiver, Basic Service Set ("BSS"), Extended Service Set ("ESS"), Radio Base Station ("RBS"), Node B (NB), gNB, <NUM> NB, NR BS, Transmit Receive Point (TRP), or some other terminology.

An access terminal ("AT") may comprise, be implemented as, or be known as an access terminal, a subscriber station, a subscriber unit, a mobile station, a remote station, a remote terminal, a user terminal, a user agent, a user device, user equipment (UE), a user station, a wireless node, or some other terminology. In some aspects, an access terminal may comprise a cellular telephone, a smart phone, a cordless telephone, a Session Initiation Protocol ("SIP") phone, a wireless local loop ("WLL") station, a personal digital assistant ("PDA"), a tablet, a netbook, a smartbook, an ultrabook, a handheld device having wireless connection capability, a Station ("STA"), or some other suitable processing device connected to a wireless modem. Accordingly, one or more aspects taught herein may be incorporated into a phone (e.g., a cellular phone, a smart phone), a computer (e.g., a desktop), a portable communication device, a portable computing device (e.g., a laptop, a personal data assistant, a tablet, a netbook, a smartbook, an ultrabook), wearable device (e.g., smart watch, smart glasses, smart bracelet, smart wristband, smart ring, smart clothing, etc.), medical devices or equipment, biometric sensors/devices, an entertainment device (e.g., music device, video device, satellite radio, gaming device, etc.), a vehicular component or sensor, smart meters/sensors, industrial manufacturing equipment, a global positioning system device, or any other suitable device that is configured to communicate via a wireless or wired medium. In some aspects, the node is a wireless node. A wireless node may provide, for example, connectivity for or to a network (e.g., a wide area network such as the Internet or a cellular network) via a wired or wireless communication link. Some UEs may be considered machine-type communication (MTC) UEs, which may include remote devices that may communicate with a base station, another remote device, or some other entity. Machine type communications (MTC) may refer to communication involving at least one remote device on at least one end of the communication and may include forms of data communication which involve one or more entities that do not necessarily need human interaction. MTC UEs may include UEs that are capable of MTC communications with MTC servers and/or other MTC devices through Public Land Mobile Networks (PLMN), for example. Examples of MTC devices include sensors, meters, location tags, monitors, drones, robots/robotic devices, etc. MTC UEs, as well as other types of UEs, may be implemented as NB-IoT (narrowband internet of things) devices.

A BS is an entity that communicates with user equipment (UEs) and may also be referred to as a base station, a NR BS, a Node B, a gNB, a <NUM> NB, an access point, a TRP, etc. Each BS may provide communication coverage for a particular geographic area.

A relay station may also be referred to as a relay BS, a relay base station, a relay, etc..

Wireless network <NUM> may be a heterogeneous network that includes BSs of different types, e.g., macro BSs, pico BSs, femto BSs, relay BSs, etc. These different types of BSs may have different transmit power levels, different coverage areas, and different impact on interference in wireless network <NUM>.

A UE may also be referred to as an access terminal, a terminal, a mobile station, a subscriber unit, a station, etc. A UE may be a cellular phone (e.g., 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, a camera, a gaming device, a netbook, a smartbook, an ultrabook, medical device or equipment, biometric sensors/devices, wearable devices (smart watches, smart clothing, smart glasses, smart wrist bands, smart jewelry (e.g., smart ring, smart bracelet)), an entertainment device (e.g., a music or video device, or a satellite radio), a vehicular component or sensor, smart meters/sensors, 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 evolved or enhanced machine-type communication (eMTC) UEs. MTC and eMTC UEs include, for example, robots, drones, remote devices, such as sensors, meters, monitors, location tags, etc., that may communicate with a base station, another device (e.g., remote device), or some other entity. Some UEs may be considered Internet-of-Things (IoT) devices.

A dashed line with double arrows indicates potentially interfering transmissions between a UE and a BS.

<FIG> shows a block diagram of a design of base station <NUM> and UE <NUM>, which may be one of the base stations and one of the UEs in <FIG>.

Transmit processor <NUM> may also process system information (e.g., for semi-static resource partitioning information (SRPI), etc.) and control information (e.g., CQI requests, grants, upper layer signaling, etc.) and provide overhead symbols and control symbols. Transmit processor <NUM> may also generate reference symbols for reference signals (e.g., the CRS) and synchronization signals (e.g., the primary synchronization signal (PSS) and secondary synchronization signal (SSS)). According to certain aspects described in more detail below, the synchronization signals can be generated with location encoding to convey additional information.

A channel processor may determine RSRP, RSSI, RSRQ, CQI, etc..

On the uplink, at UE <NUM>, a transmit processor <NUM> may receive and process data from a data source <NUM> and control information (e.g., for reports comprising RSRP, RSSI, RSRQ, CQI, etc.) from controller/processor <NUM>. The symbols from transmit processor <NUM> may be precoded by a TX MIMO processor <NUM> if applicable, further processed by modulators 254a through 254r (e.g., for DFT-s-OFDM, CP-OFDM, etc.), and transmitted to base station <NUM>.

Controllers/processors <NUM> and <NUM> and/or any other component(s) in <FIG> may direct the operation at base station <NUM> and UE <NUM>, respectively, to perform uplink precoder determination using downlink reference signals and/or downlink precoder determination using uplink reference signals. For example, controller/processor <NUM> and/or other processors and modules at UE <NUM>, may perform or direct operations of UE <NUM> to perform uplink precoder determination using downlink reference signals. For example, controller/processor <NUM> and/or other controllers/processors and modules at UE <NUM> may perform or direct operations of, for example, process <NUM> of <FIG> and/or other processes as described herein. In some aspects, one or more of the components shown in <FIG> may be employed to perform example process <NUM>, example process <NUM>, example process <NUM>, and/or other processes for the techniques described herein. Memories <NUM> and <NUM> may store data and program codes for base station <NUM> and UE <NUM>, respectively.

In some aspects, the UE <NUM> may include means for receiving an indication of whether to use uplink reference signals or downlink reference signals for uplink precoder determination; means for selectively transmitting a plurality of uplink reference signals or one or more measurement reports based at least in part on the indication, wherein the one or more measurement reports are determined based at least in part on measuring a plurality of downlink reference signals; means for receiving an indication of a precoder, of a plurality of precoders, to be used to precode an uplink communication, wherein the precoder is identified based at least in part on the plurality of uplink reference signals or the one or more measurement reports; means for precoding the uplink communication using the precoder; and/or the like. Such means may include one or more components of the UE <NUM> described herein in connection with <FIG>.

In some aspects, a base station <NUM> may include means for receiving, from a UE, one or more measurement reports associated with a plurality of downlink reference signals, wherein the plurality of downlink reference signals are measured by the UE using a plurality of precoders; means for identifying a downlink reference signal, of the plurality of downlink reference signals, based at least in part on the one or more measurement reports, wherein the downlink reference signal corresponds to a precoder, of the plurality of precoders, to be used by the UE to precode an uplink communication; means for transmitting, to the UE, an indication of at least one of the downlink reference signal or the precoder; and/or the like. Additionally, or alternatively, the base station <NUM> may include means for determining a degree of reciprocity between one or more downlink beams and one or more corresponding uplink beams that form reciprocal beam pairs with the one or more downlink beams; means for selectively identifying a precoder, of a plurality of precoders, to be used to precode the downlink communication based at least in part on the degree of reciprocity, wherein the precoder is identified based at least in part on measuring a plurality of uplink reference signals using the plurality of precoders or receiving one or more measurement reports associated with one or more downlink reference signals; means for precoding the downlink communication using the precoder; and/or the like. Such means may include one or more components of the base station <NUM> described herein in connection with <FIG>.

<FIG> shows an example frame structure <NUM> for FDD in a telecommunications system (e.g., LTE). The transmission time line 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., <NUM> milliseconds (ms)) and may be partitioned into <NUM> subframes with indices of <NUM> through <NUM>. Each subframe may include two slots. Each radio frame may thus include <NUM> slots with indices of <NUM> through <NUM>. Each slot may include L symbol periods, e.g., seven symbol periods for a normal cyclic prefix (as shown in <FIG>) or six symbol periods for an extended cyclic prefix. The <NUM> symbol periods in each subframe may be assigned indices of <NUM> through <NUM>-<NUM>.

In certain telecommunications (e.g., LTE), a BS may transmit a primary synchronization signal (PSS) and a secondary synchronization signal (SSS) on the downlink in the center of the system bandwidth for each cell supported by the BS. The PSS and SSS may be transmitted in symbol periods <NUM> and <NUM>, respectively, in subframes <NUM> and <NUM> of each radio frame with the normal cyclic prefix, as shown in <FIG>. The BS may transmit a cell-specific reference signal (CRS) across the system bandwidth for each cell supported by the BS. The CRS may be transmitted in certain symbol periods of each subframe and may be used by the UEs to perform channel estimation, channel quality measurement, and/or other functions. The BS may also transmit a physical broadcast channel (PBCH) in symbol periods <NUM> to <NUM> in slot <NUM> of certain radio frames. The PBCH may carry some system information. The BS may transmit other system information such as system information blocks (SIBs) on a physical downlink shared channel (PDSCH) in certain subframes. The BS may transmit control information/data on a physical downlink control channel (PDCCH) in the first B symbol periods of a subframe, where B may be configurable for each subframe. The BS may transmit traffic data and/or other data on the PDSCH in the remaining symbol periods of each subframe.

In other systems (e.g., such NR or <NUM> systems), a Node B may transmit these or other signals in these locations or in different locations of the subframe.

<FIG> shows two example subframe formats <NUM> and <NUM> with the normal cyclic prefix. Each resource block may cover <NUM> subcarriers in one slot and may include a number of resource elements. Each resource element may cover one subcarrier in one symbol period and may be used to send one modulation symbol, which may be a real or complex value.

Subframe format <NUM> may be used for two antennas. A CRS may be transmitted from antennas <NUM> and <NUM> in symbol periods <NUM>, <NUM>, <NUM> and <NUM>. A reference signal is a signal that is known a priori by a transmitter and a receiver and may also be referred to as pilot. A CRS is a reference signal that is specific for a cell, e.g., generated based at least in part on a cell identity (ID). In <FIG>, for a given resource element with label Ra, a modulation symbol may be transmitted on that resource element from antenna a, and no modulation symbols may be transmitted on that resource element from other antennas. Subframe format <NUM> may be used with four antennas. A CRS may be transmitted from antennas <NUM> and <NUM> in symbol periods <NUM>, <NUM>, <NUM> and <NUM> and from antennas <NUM> and <NUM> in symbol periods <NUM> and <NUM>. For both subframe formats <NUM> and <NUM>, a CRS may be transmitted on evenly spaced subcarriers, which may be determined based at least in part on cell ID. CRSs may be transmitted on the same or different subcarriers, depending on their cell IDs. For both subframe formats <NUM> and <NUM>, resource elements not used for the CRS may be used to transmit data (e.g., traffic data, control data, and/or other data).

The PSS, SSS, CRS and PBCH in LTE are described in <NPL>," which is publicly available.

An interlace structure may be used for each of the downlink and uplink for FDD in certain telecommunications systems (e.g., LTE). For example, Q interlaces with indices of <NUM> through Q - <NUM> may be defined, where Q may be equal to <NUM>, <NUM>, <NUM>, <NUM>, or some other value. Each interlace may include subframes that are spaced apart by Q frames. In particular, interlace q may include subframes q, q + Q, q + 2Q, etc., where q ∈ {<NUM>,.

The wireless network may support hybrid automatic retransmission request (HARQ) for data transmission on the downlink and uplink. For HARQ, a transmitter (e.g., a BS) may send one or more transmissions of a packet until the packet is decoded correctly by a receiver (e.g., a UE) or some other termination condition is encountered. For synchronous HARQ, all transmissions of the packet may be sent in subframes of a single interlace. For asynchronous HARQ, each transmission of the packet may be sent in any subframe.

While aspects of the examples described herein may be associated with LTE technologies, aspects of the present disclosure may be applicable with other wireless communication systems, such as NR or <NUM> technologies.

A single component carrier bandwidth of <NUM> may be supported. NR resource blocks may span <NUM> sub-carriers with a sub-carrier bandwidth of <NUM> kilohertz (kHz) over a <NUM> duration. Each radio frame may include <NUM> subframes with a length of <NUM>. Consequently, each subframe may have a length of <NUM>. Each subframe may indicate a link direction (e.g., DL or UL) for data transmission and the link direction for each subframe may be dynamically switched. Each subframe may include DL/UL data as well as DL/UL control data. UL and DL subframes for NR may be as described in more detail below with respect to <FIG>.

The RAN may include a central unit (CU) and distributed units (DUs). A NR BS (e.g., gNB, <NUM> Node B, Node B, transmit receive point (TRP), access point (AP)) may correspond to one or multiple BSs. NR cells can be configured as access cells (ACells) or data only cells (DCells). For example, the RAN (e.g., a central unit or distributed unit) can configure the cells. DCells may be cells used for carrier aggregation or dual connectivity, but not used for initial access, cell selection/reselection, or handover. In some cases, DCells may not transmit synchronization signals-in some case cases DCells may transmit SS. NR BSs may transmit downlink signals to UEs indicating the cell type. Based at least in part on the cell type indication, the UE may communicate with the NR BS. For example, the UE may determine NR BSs to consider for cell selection, access, handover, and/or measurement based at least in part on the indicated cell type.

The PDCP, RLC, MAC protocol may be adaptably placed at the ANC or TRP.

<FIG> is a diagram <NUM> showing an example of a DL-centric subframe or wireless communication structure. In some aspects, the control portion <NUM> may include legacy PDCCH information, shortened PDCCH (sPDCCH) information), a control format indicator (CFI) value (e.g., carried on a physical control format indicator channel (PCFICH)), one or more grants (e.g., downlink grants, uplink grants, etc.), and/or the like.

The DL-centric subframe may also include an UL short burst portion <NUM>. The UL short burst portion <NUM> may sometimes be referred to as an UL burst, an UL burst portion, a common UL burst, a short burst, an UL short burst, a common UL short burst, a common UL short burst portion, and/or various other suitable terms. In some aspects, the UL short burst portion <NUM> may include one or more reference signals. Additionally, or alternatively, the UL short burst portion <NUM> may include feedback information corresponding to various other portions of the DL-centric subframe. For example, the UL short burst portion <NUM> may include feedback information corresponding to the control portion <NUM> and/or the data portion <NUM>. Non-limiting examples of information that may be included in the UL short burst portion <NUM> include an ACK signal (e.g., a PUCCH ACK, a PUSCH ACK, an immediate ACK), a NACK signal (e.g., a PUCCH NACK, a PUSCH NACK, an immediate NACK), a scheduling request (SR), a buffer status report (BSR), a HARQ indicator, a channel state indication (CSI), a channel quality indicator (CQI), a sounding reference signal (SRS), a demodulation reference signal (DMRS), PUSCH data, and/or various other suitable types of information. The UL short burst portion <NUM> may include additional or alternative information, such as information pertaining to random access channel (RACH) procedures, scheduling requests, and various other suitable types of information.

<FIG> is a diagram <NUM> showing an example of an UL-centric subframe or wireless communication structure. The UL-centric subframe may include a control portion <NUM>. The control portion <NUM> may exist in the initial or beginning portion of the UL-centric subframe. The control portion <NUM> in <FIG> may be similar to the control portion <NUM> described above with reference to <FIG>. The UL-centric subframe may also include an UL long burst portion <NUM>. The UL long burst portion <NUM> may sometimes be referred to as the payload of the UL-centric subframe. The UL portion may refer to the communication resources utilized to communicate UL data from the subordinate entity (e.g., UE) to the scheduling entity (e.g., UE or BS). In some configurations, the control portion <NUM> may be a physical DL control channel (PDCCH).

The UL-centric subframe may also include an UL short burst portion <NUM>. The UL short burst portion <NUM> in <FIG> may be similar to the UL short burst portion <NUM> described above with reference to <FIG>, and may include any of the information described above in connection with <FIG>. The foregoing is merely one example of an UL-centric wireless communication structure, and alternative structures having similar features may exist without necessarily deviating from the aspects described herein.

In wireless communication, a precoder may be used by a UE and/or a base station to configure one or more multiple input, multiple output (MIMO) layers and/or one or more antenna beams for improved transmission and reception of wireless communications (e.g., for an improved signal-to-noise ratio and/or the like). Different precoders may be used to apply different weights to values associated with one or more antennas, signals, transmission powers, transmission chains, reception chains, and/or the like.

In some cases, a UE may transmit multiple sounding reference signals (SRS) to a base station, and may use different precoders for transmission of different SRS communications. For example, the UE may be instructed by the base station to transmit different SRS communications using a pre-specified sequence of uplink precoders. The base station may identity a preferred communication channel based on receiving the multiple SRS communications (e.g., a channel with a high channel quality or the best channel quality as compared to other channels). The base station may indicate, to the UE, a precoder to be used for uplink transmissions (e.g., for uplink control on the PUCCH, for uplink data on the PUSCH, and/or the like), such as by transmitting information that identifies the precoder or transmitting information that identifies the SRS communication that corresponds to the precoder. The UE may use the precoder indicated by the base station to improve communication quality. However, this technique may consume significant uplink resources because the UE transmits multiple SRS communications.

Techniques described herein permit a UE and/or a base station to use downlink reference signals to determine an uplink precoder and/or to use uplink reference signals to determine a downlink precoder. In some cases, there may be channel quality reciprocity between an uplink channel and a corresponding downlink channel (e.g., channels associated with reciprocal over-the air-characteristics and/or device characteristics, channels for which the UE and base station perform calibration operations to maintain reciprocity between uplink and downlink signal paths, channels that are part of the same reciprocal beam pair, and/or the like). In this case, downlink reference signals, such as channel state information reference signals (CSI-RS), may be used to estimate uplink channel characteristics, which may then be used for determination of a precoder to be used by the UE. Similarly, uplink reference signals may be used to estimate downlink channel characteristics, which may then be used for determination of a precoder to be used by a base station. In this way, network resources may be conserved by reducing the need to transmit additional uplink and/or downlink reference signals.

<FIG> and <FIG> are diagrams illustrating an example <NUM> of uplink precoder determination using downlink reference signals, in accordance with various aspects of the present disclosure.

As shown in <FIG>, a UE <NUM> may communicate with a base station <NUM>. The UE <NUM> may correspond to, for example, the UE <NUM> of <FIG> and/or the like. The base station <NUM> may correspond to, for example, the base station <NUM> of <FIG> and/or the like.

As shown by reference number <NUM>, the base station <NUM> may transmit a plurality of downlink reference signals to the UE <NUM>. As shown, in some aspects, the plurality of downlink reference signals are a plurality of channel state information reference signals (CSI-RS). A CSI-RS may include, for example, channel quality information (CQI), a precoding matrix indicator (PMI), a precoding type indicator (PTI), a rank indicator (RI), and/or the like. In some aspects, the base station <NUM> may transmit the downlink reference signals according to a schedule (e.g., a periodic schedule or an aperiodic schedule), and may notify the UE <NUM> of the schedule (e.g., in radio resource control (RRC) connection configuration information and/or the like). Different CSI-RS communications may be associated with different weights to control values associated with, for example, a beam direction, a precoder assignment, a transmission power, and/or the like. For example, different CSI-RS communications may be transmitted using different precoders.

As shown by reference number <NUM>, the UE <NUM> may measure the plurality of downlink reference signals using different precoders. For example, the UE <NUM> may tune to a downlink reference signal, and may measure the downlink reference signal. In some aspects, the UE <NUM> may cycle through a plurality of precoders to receive the downlink reference signals. As an example, the UE <NUM> may use a first precoder shown as Precoder A to measure a first downlink reference signal shown as CSI-RS #<NUM>, may use a second precoder shown as Precoder B to measure a second downlink reference signal shown as CSI-RS #<NUM>, and/or the like.

In some aspects, the precoder cycling may occur according to a pattern. In some aspects, the pattern may be a preconfigured pattern negotiated between the UE <NUM> and the base station <NUM> (e.g., during RRC connection configuration). In this case, the base station <NUM> may store information that indicates a correspondence between a precoder and a downlink reference signal. Alternatively, the base station <NUM> may not receive and/or store information that indicates such correspondence, in some aspects.

As shown by reference number <NUM>, the UE <NUM> may transmit, to the base station <NUM>, one or more measurement reports based at least in part on measuring the plurality of downlink reference signals. For example, a CSI-RS measurement report corresponding to CSI-RS #<NUM> may indicate a first CQI value (e.g., CQI #<NUM>), a first PMI value (e.g., PMI #<NUM>), a first RI value (e.g., RI #<NUM>), and/or the like. Similarly, a CSI-RS measurement report corresponding to CSI-RS #<NUM> may indicate a second CQI value (e.g., CQI #<NUM>), a second PMI value (e.g., PMI #<NUM>), a second RI value (e.g., RI #<NUM>), and/or the like.

As shown in <FIG>, and by reference number <NUM>, the base station <NUM> may use the measurement report(s) to identify a preferred communication channel, which may be associated with a precoder. For example, the preferred communication channel may be associated with a better reported channel quality than one or more other measured downlink references signals included in the measurement report(s). In some aspects, the preferred communication channel may be associated with the best reported channel quality as compared to the other measured downlink references signals included in the measurement report(s). As shown, the communication channel associated with CSI-RS #<NUM> may be associated with a better combination of CQI, PMI, and RI values as compared to the communication channels associated with CSI-RS #<NUM>, CSI-RS #N, and/or the like.

In some aspects, the base station <NUM> may further identify the preferred communication channel and/or the precoder based at least in part on one or more scheduling decisions. The base station <NUM> may make a scheduling decision based at least in part on, for example, one or more uplink reference signals received from the UE <NUM> (e.g., one or more SRS communications), an indication of an uplink and/or a downlink channel quality, and/or the like.

As shown by reference number <NUM>, the base station <NUM> may transmit, to the UE <NUM>, an indication of a precoder to be used to precode one or more uplink communications. In some aspects, the indication may include information that identifies the precoder. For example, the base station <NUM> may store information that indicates a correspondence between a precoder and a downlink reference signal, and may identify the precoder based at least in part on the downlink reference signal associated with the preferred communication channel. Additionally, or alternatively, the indication may include information that identifies the downlink reference signal associated with the preferred communication channel, shown as CSI-RS #<NUM>. In this case, the indication may include, for example, an indication of a particular CSI-RS resource in a particular transmission time interval.

In some aspects, the base station <NUM> may transmit the indication of the precoder in downlink cotrol information (DCI). For example, the DCI may identify the precoder to be used to precode the uplink communication, a downlink reference signal corresponding to the precoder, a ranking of the precoder and at least one other precoder, a ranking of the downlink reference signal and at least one other downlink reference signal, and/or the like. Additionally, or alternatively, the DCI may indicate a first precoder to be used for a first uplink channel (e.g., a PUCCH) and a second precoder to be used for a second uplink channel (e.g., a PUSCH). In some aspects, the first precoder for the first uplink channel and/or the second precoder for the second uplink channel may be explicitly indicated in the DCI. In some aspects, the first precoder and/or the second precoder may be indicated using CSI-RS indices.

As shown by reference number <NUM>, the UE <NUM> may identify the precoder indicated by the base station <NUM>. In some aspects, the UE <NUM> may directly identify the precoder if the precoder is identified in the indication from the base station <NUM>. In some aspects, when the indication identifies the downlink reference signal, the UE <NUM> may identify the precoder based at least in part on a correspondence between the precoder and the downlink reference signal identified in the indication. For example, and as shown, the UE <NUM> may store information that indicates a correspondence between different precoders used to measure different downlink reference signals. In example <NUM>, the UE <NUM> receives an indication of CSI-RS #<NUM>, and determines that Precoder B was used to measure CSI-RS #<NUM>.

In some aspects, the UE <NUM> may select and use another precoder to precode one or more uplink communications based at least in part on a determination that the precoder indicated by the base station <NUM> cannot be used. For example, the UE <NUM> may be unable to use the precoder indicated by the base station <NUM> due to hand blocking and/or the like. During hand blocking, there may be an asymmetry between uplink and downlink channel quality since the UE <NUM> can receive signals but will not be able to transmit signals beyond the maximum permissible limit subject to the location of the user's hand in proximity to the UE <NUM>. Such asymmetry may be detectable by the UE <NUM>, but not by the base station <NUM>. In this case, the UE <NUM> may identify another precoder to use. In some aspects, the base station <NUM> may transmit a ranking (e.g., a ranked list) of precoders and/or downlink reference signals, and the UE <NUM> may identify a precoder based at least in part on the ranking (e.g., may first attempt to use a first precoder in the ranked list, then a second precoder in the ranked list, and/or the like).

As shown by reference number <NUM>, the UE <NUM> may precode one or more uplink communications using the identified precoder, shown as Precoder B, and may transmit the one or more uplink communications to the base station <NUM>. In some aspects, a single indication by the base station <NUM> may correspond to multiple precoders to be used by the UE <NUM> for different uplink channels (e.g., a PUSCH, a PUCCH, and/or the like). Additionally, or alternatively, the base station <NUM> may indicate multiple precoders in the indication, and the multiple precoders may correspond to multiple uplink channels. The UE <NUM> may precode uplink communication(s) for the multiple channels using corresponding precoders indicated by the base station <NUM>.

In some aspects, the UE <NUM> may apply a correction factor to precode the uplink communication(s) using the precoder. For example, an uplink channel and a downlink channel may lack true reciprocity, and the UE <NUM> may account for this by applying a correction factor. The correction factor may include, for example, an adjustment to account for an imbalance between a transmission chain of the UE <NUM> (e.g., corresponding to the uplink channel) and a reception chain of the UE <NUM> (e.g., corresponding to the downlink channel). In some aspects, the adjustment may include a modification of one or more weights applied to values associated with one or more antennas, signals, transmission powers, transmission chains, reception chains, and/or the like.

Additionally, or alternatively, the correction factor may account for differences in reciprocity between an uplink channel or beam and a corresponding downlink channel or beam (e.g., where the uplink beam and the downlink beam form a reciprocal beam pair). In some aspects, the UE <NUM> may modify the correction factor as beam conditions change. The UE <NUM> may measure one or more beam conditions and/or may receive an indication of the one or more beam conditions from the base station <NUM>.

In some aspects, a degree of reciprocity between an uplink beam and a corresponding downlink beam may change such that the beams have a low degree of reciprocity (e.g., a parameter indicative of reciprocity does not satisfy a threshold). In this case, the base station <NUM> transmits an indication, to the UE <NUM>, that the UE <NUM> is to transmit uplink reference signals (e.g., SRS) to the base station <NUM>, and the base station <NUM> uses the uplink reference signals to determine an uplink precoder. In this case, the base station <NUM> may stop transmitting downlink reference signals (e.g., CSI-RS), or may reduce a periodicity of downlink reference signal transmission, thereby conserving network resources.

If the degree of reciprocity is high at a different time (e.g., a parameter indicative of reciprocity satisfies a threshold), then the base station <NUM> transmits an indication, to the UE <NUM>, that the UE <NUM> is to transmit the downlink reference signals in one or more measurement reports, and the base station <NUM> uses the downlink reference signals to determine an uplink precoder. In some aspects, the indication may indicate the degree of reciprocity between one or more uplink beams (e.g., an uplink beam to be used for an uplink communication) and one or more corresponding downlink beams (e.g., that form reciprocal beam pairs with the one or more uplink beams). In some aspects, the degree of reciprocity of a reciprocal beam pair may be determined based at least in part on comparing uplink reference signals (e.g., SRS) for an uplink beam and downlink reference signals (e.g., CSI-RS) for a corresponding downlink beam.

In some aspects, the indication of the degree of reciprocity and/or whether to use uplink reference signals or downlink reference signals for uplink precoder determination may be transmitted periodically. Additionally, or alternatively, the indication may be transmitted based at least in part on a determination that the degree of reciprocity has crossed a threshold (e.g., satisfies the threshold or no longer satisfies the threshold). Additionally, or alternatively, the indication may be transmitted based at least in part on a determination that the degree of reciprocity has changed by a threshold amount.

By using downlink reference signals to determine an uplink precoder, the UE <NUM> and the base station <NUM> may conserve network resources by skipping or preventing transmission of one or more uplink references signals, such as SRS communications, that would otherwise be used by the base station <NUM> to identify the precoder to be used for the one or more uplink communications. Is some cases, this may result in a longer periodicity of SRS transmissions as compared to a periodicity of CSI-RS transmissions. In some aspects, SRS transmissions in one or more beam directions may be skipped, thereby conserving network and UE resources.

In some aspects, the base station <NUM> may transmit, to the UE <NUM>, an indication relating to a quantity or a directionality of uplink reference signals (e.g., SRS) to be transmitted by the UE <NUM>. For example, the base station <NUM> may indicate a quantity that is less than a quantity of uplink reference signals that the UE <NUM> would otherwise transmit if the uplink reference signals were used to determine an uplink precoder. Additionally, or alternatively, the base station <NUM> may indicate fewer directions for transmission of uplink reference signals as compared to a quantity of directions in which the UE <NUM> would otherwise transmit uplink reference signals if the uplink reference signals were used to determine an uplink precoder.

In some aspects, the base station <NUM> may determine the quantity and/or directionality of the uplink reference signals based at least in part on a determination of a correspondence between one or more downlink reference signals and one or more uplink reference signals with regard to channel quality. For example, if the uplink reference signals and the downlink reference signals are highly correlated, then this may indicate that the uplink and downlink channels are highly reciprocal, and fewer uplink reference signals would be needed to accurately identify a preferred communication channel and/or uplink precoder using downlink reference signals. Conversely, if the uplink reference signals and the downlink reference signals are not highly correlated, then this may indicate that the uplink and downlink channels share less reciprocity, and more uplink reference signals would be needed to accurately identify a preferred communication channel and/or uplink precoder using downlink reference signals. Thus, the UE <NUM> and the base station <NUM> can conserve uplink resources by adjusting a quantity of uplink reference signals to be transmitted by the UE <NUM> when an uplink precoder can be identified using downlink reference signals.

As indicated above, <FIG> and <FIG> are provided as an example. Other examples are possible and may differ from what was described with respect to <FIG> and <FIG>.

<FIG> is a diagram illustrating an example <NUM> of downlink precoder determination using uplink reference signals, in accordance with various aspects of the present disclosure.

As shown in <FIG>, a UE <NUM> may communicate with a base station <NUM>. The UE <NUM> may correspond to, for example, the UE <NUM> of <FIG>, the UE <NUM> of <FIG>, and/or the like. The base station <NUM> may correspond to, for example, the base station <NUM> of <FIG>, the base station <NUM> of <FIG>, and/or the like.

As shown by reference number <NUM>, the UE <NUM> may transmit a plurality of uplink reference signals to the base station <NUM>. As shown, in some aspects, the plurality of uplink reference signals are a plurality of sounding reference signals (SRS). In some aspects, the UE <NUM> may transmit the uplink reference signals according to a schedule (e.g., a periodic schedule or an aperiodic schedule), which may be negotiated with and/or indicated by the base station <NUM> (e.g., in radio resource control (RRC) connection configuration information and/or the like).

As shown by reference number <NUM>, the base station <NUM> may measure the plurality of uplink reference signals using different precoders. For example, the base station <NUM> may tune to an uplink reference signal, and may measure the uplink reference signal. In some aspects, the base station <NUM> may cycle through a plurality of precoders to receive the uplink reference signals. As an example, the base station <NUM> may use a first precoder shown as Precoder C to measure a first uplink reference signal shown as SRS #<NUM>, may use a second precoder shown as Precoder D to measure a second uplink reference signal shown as SRS #<NUM>, and/or the like.

As shown by reference number <NUM>, the base station <NUM> may use the measured plurality of uplink reference signals to identify a preferred uplink reference signal (e.g., a preferred SRS), which may be associated with a precoder. For example, a preferred uplink reference signal may be associated with a better channel quality than one or more other measured uplink reference signals. In some aspects, the preferred uplink reference signal may be associated with the best channel quality as compared to the other measured uplink references signals (e.g., within a time period). As shown, the uplink reference signal shown as SRS #<NUM> may be associated with a better channel quality as compared to the SRS #<NUM>, SRS #M, and/or the like.

In some aspects, the base station <NUM> may further identify the preferred uplink reference signal and/or the precoder based at least in part on one or more scheduling decisions. The base station <NUM> may make a scheduling decision based at least in part on, for example, one or more measurement reports, associated with downlink reference signals, received from the UE <NUM> (e.g., one or more CSI-RS measurement reports), an indication of an uplink and/or a downlink channel quality, and/or the like.

As further shown, the preferred uplink reference signal may correspond to a precoder, and the base station <NUM> may identify the precoder based at least in part on a stored correspondence between the preferred uplink reference signal and the precoder. For example, and as shown, the base station <NUM> may store information that indicates a correspondence between different precoders used to measure different uplink reference signals. In example <NUM>, the base station <NUM> identifies SRS #<NUM> as having the best channel quality, and determines that Precoder C was used to measure SRS #<NUM>.

As shown by reference number <NUM>, the base station <NUM> may precode one or more downlink communications using the identified precoder, shown as Precoder C, and may transmit the one or more downlink communications to the UE <NUM>.

In some aspects, the base station <NUM> may apply a correction factor to precode the downlink communication(s) using the precoder. For example, an uplink channel and a downlink channel may lack true reciprocity, and the base station <NUM> may account for this by applying a correction factor. In some aspects, the correction factor may include a modification of one or more weights applied to values associated with one or more antennas, signals, transmission powers, transmission chains, reception chains, and/or the like.

By using uplink reference signals to determine a downlink precoder, the UE <NUM> and the base station <NUM> may conserve network resources by skipping or preventing transmission of one or more downlink references signals, such as CSI-RS communications, that would otherwise be used by the UE <NUM> and/or the base station <NUM> to identify the precoder to be used for the one or more downlink communications.

In some aspects, the base station <NUM> may determine a quantity or a directionality of downlink reference signals (e.g., CSI-RS) to be transmitted by the base station <NUM>. For example, the base station <NUM> may determine a quantity that is less than a quantity of downlink reference signals that the base station <NUM> would otherwise transmit if the downlink reference signals were used to determine a downlink precoder. Additionally, or alternatively, the base station <NUM> may determine fewer directions for transmission of downlink reference signals as compared to a quantity of directions in which the base station <NUM> would otherwise transmit downlink reference signals if the downlink reference signals were used to determine a downlink precoder.

In some aspects, the base station <NUM> may determine the quantity and/or directionality of the downlink reference signals based at least in part on a determination of a correspondence between one or more downlink reference signals and one or more uplink reference signals with regard to channel quality, as described above in connection with <FIG>. In this way, the UE <NUM> and the base station <NUM> can conserve downlink resources by adjusting a quantity of downlink reference signals to be transmitted by the base station <NUM> when a downlink precoder can be identified using uplink reference signals.

<FIG> is a diagram illustrating an example process <NUM> performed by a UE, in accordance with various aspects of the present disclosure. Example process <NUM> is an example where a UE (e.g., the UE <NUM> of <FIG>, the UE <NUM> of <FIG>, the UE <NUM> of <FIG>, and/or the like) performs uplink precoder determination using downlink reference signals.

As shown in <FIG>, in some aspects, process <NUM> includes receiving an indication of whether to use uplink reference signals or downlink reference signals for uplink precoder determination (block <NUM>). For example, the UE may receive an indication of whether to use uplink reference signals or downlink reference signals for uplink precoder determination, as described above in connection with <FIG>. In some aspects, the plurality of uplink reference signals are a plurality of sounding reference signals. In some aspects, the plurality of downlink reference signals are a plurality of channel state information reference signals (CSI-RS). In some aspects, the indication may indicate a degree of reciprocity between an uplink beam, via which the uplink communication is to be transmitted, and a corresponding downlink beam that forms a reciprocal beam pair with the uplink beam.

As shown in <FIG>, in some aspects, process <NUM> may include selectively transmitting a plurality of uplink reference signals or one or more measurement reports based at least in part on the indication, wherein the one or more measurement reports are determined based at least in part on measuring a plurality of downlink reference signals (block <NUM>). The UE determines whether to transmit uplink reference signals or measurement reports associated with downlink reference signals based at least in part on the indication, as described above in connection with <FIG>. When the indication indicates that the UE is to transmit uplink reference signals, the UE may transmit the uplink reference signals to the base station. In some aspects, the plurality of uplink reference signals include a quantity of uplink reference signals indicated to the UE by the base station. In some aspects, the plurality of uplink reference signals are transmitted using one or more beams indicated to the UE by the base station.

When the indication indicates that the UE is to transmit measurement reports associated with downlink reference signals, the UE may receive and measure a plurality of downlink reference signals transmitted by a base station, and may transmit one or more measurement reports to the base station based at least in part on receiving and measuring the plurality of downlink reference signals.

As further shown in <FIG>, in some aspects, process <NUM> includes receiving an indication of a precoder, of a plurality of precoders, to be used to precode an uplink communication, wherein the precoder is identified based at least in part on the plurality of uplink reference signals or the one or more measurement reports (block <NUM>). For example, the UE may receive, from the base station, an indication of a precoder to be used to precode an uplink communication. The precoder may be identified based at least in part on the one or more measurement reports or the plurality of uplink reference signals.

In some aspects, the precoder corresponds to a measured downlink reference signal associated with a better channel quality than one or more other measured downlink references signals included in the plurality of downlink reference signals. In some aspects, the precoder is further identified based at least in part on one or more scheduling decisions.

In some aspects, the indication of the precoder is received in downlink control information (DCI). In some aspects, the DCI identifies at least one of: the precoder to be used to precode the uplink communication, a downlink reference signal corresponding to the precoder, a ranking of the precoder and at least one other precoder, or a ranking of the downlink reference signal and at least one other downlink reference signal. In some aspects, the DCI indicates a first precoder to be used for a first uplink channel and a second precoder to be used for a second uplink channel. In some aspects, the first uplink channel is a physical uplink control channel and the second uplink channel is a physical uplink shared channel.

In some aspects, the UE is configured to use another precoder to precode the uplink communication based at least in part on a determination that the precoder cannot be used. Additionally, or alternatively, the UE may be configured to apply a correction factor to precode the uplink communication using the precoder. Additionally, or alternatively, the UE receive (e.g. from the base station) an indication relating to a quantity or a directionality of uplink reference signals to be transmitted based at least in part on a determination of a correspondence between one or more downlink reference signals and one or more uplink reference signals with regard to channel quality.

As further shown in <FIG>, in some aspects, process <NUM> may include precoding the uplink communication using the precoder (block <NUM>). For example, the UE may precode the uplink communication using the precoder, and may transmit the precoded uplink communication to the base station. Additional details regarding example process <NUM> are described above in connection with <FIG> and <FIG>.

<FIG> is a diagram illustrating an example process <NUM> performed, for example, by a base station, in accordance with various aspects of the present disclosure. Example process <NUM> is an example where a base station (e.g., the base station <NUM> of <FIG>, the base station <NUM> of <FIG>, the base station <NUM> of <FIG>, and/or the like) performs uplink precoder determination using downlink reference signals.

As shown in <FIG>, in some aspects, process <NUM> may include receiving, from a UE, one or more measurement reports associated with a plurality of downlink reference signals, wherein the plurality of downlink reference signals are measured by the UE using a plurality of precoders (block <NUM>). For example, the base station may receive, from a UE, one or more measurement reports associated with a plurality of downlink reference signals. The plurality of downlink reference signals may have been previously transmitted by the base station to the UE, and the UE may have measured the plurality of downlink reference signals using a plurality of precoders. In some aspects, the plurality of downlink reference signals are a plurality of channel state information reference signals (CSI-RS).

In some aspects, the one or more measurement reports are received based at least in part on an indication, transmitted to the UE, to use downlink reference signals for uplink precoder determination. In some aspects, the indication indicates a degree of reciprocity between an uplink beam, via which the uplink communication is to be transmitted, and a corresponding downlink beam that forms a reciprocal beam pair with the uplink beam. In some aspects, the base station may transmit an indication to use uplink reference signals instead of downlink reference signals for uplink precoder determination, as described above in connection with <FIG>. In this case, the UE may stop transmitting the measurements reports associated with the downlink reference signals and/or may start transmitting uplink reference signals, as described elsewhere herein. Additionally, or alternatively, the base station may use uplink reference signals, received from the UE, for an uplink precoder determination based at least in part on transmitting the indication to use uplink reference signals for the uplink precoder determination.

As further shown in <FIG>, in some aspects, process <NUM> may include identifying a downlink reference signal, of the plurality of downlink reference signals, based at least in part on the one or more measurement reports, wherein the downlink reference signal corresponds to a precoder, of the plurality of precoders, to be used by the UE to precode an uplink communication (block <NUM>). For example, the base station may identify a downlink reference signal (e.g., a preferred downlink reference signal associated with a preferred communication channel) based at least in part on the one or more measurement reports. The downlink reference signal may correspond to a precoder, of the plurality of precoders, to be used by the UE to precode an uplink communication.

In some aspects, the downlink reference signal is associated with a better signal quality than one or more other measured downlink references signals included in the plurality of downlink reference signals. Additionally, or alternatively, the precoder may be identified based at least in part on one or more scheduling decisions made by the base station.

As further shown in <FIG>, in some aspects, process <NUM> may include transmitting, to the UE, an indication of at least one of the downlink reference signal or the precoder (block <NUM>). For example, the base station may transmit, to the UE, an indication of at least one of the downlink reference signal or the precoder. In some aspects, the indication of at least one of the downlink reference signal or the precoder is transmitted in downlink control information (DCI). In some aspects, the DCI identifies at least one of: the precoder to be used to precode the uplink communication, the downlink reference signal corresponding to the precoder, a ranking of the precoder and at least one other precoder, or a ranking of the downlink reference signal and at least one other downlink reference signal. Additionally, or alternatively, the DCI may indicate a first precoder to be used for a first uplink channel and a second precoder to be used for a second uplink channel.

In some aspects, the base station transmits an indication of a quantity or a directionality of uplink reference signals to be transmitted by the UE based at least in part on a determination of a correspondence between one or more downlink reference signals and one or more uplink reference signals with regard to channel quality. Additional details regarding example process <NUM> are described above in connection with <FIG> and <FIG>.

<FIG> is a diagram illustrating an example process <NUM> performed, for example, by a base station, in accordance with various aspects of the present disclosure. Example process <NUM> is an example where a base station (e.g., the base station <NUM> of <FIG>, the base station <NUM> of <FIG>, the base station <NUM> of <FIG>, and/or the like) performs downlink precoder determination using uplink reference signals.

As shown in <FIG>, in some aspects, process <NUM> may include determining a degree of reciprocity between one or more downlink beams and one or more corresponding uplink beams that form reciprocal beam pairs with the one or more downlink beams (block <NUM>). For example, the base station may determine a degree of reciprocity between downlink beams and corresponding uplink beams, as described elsewhere herein.

As further shown in <FIG>, in some aspects, process <NUM> may include selectively identifying a precoder, of a plurality of precoders, to be used to precode a downlink communication based at least in part on the degree of reciprocity, wherein the precoder is identified based at least in part on measuring the plurality of uplink reference signals using the plurality of precoders or receiving one or more measurement reports associated with one or more downlink reference signals (block <NUM>). For example, the base station may identify a precoder to be used to precode a downlink communication. In some aspects, such as when there is a high degree of reciprocity, the precoder is identified based at least in part on measuring the plurality of uplink reference signals using a plurality of precoders that includes the precoder. In some aspects, the plurality of uplink reference signals are a plurality of sounding reference signals (SRS) transmitted by the UE.

In some aspects, such as when there is a low degree of reciprocity, the precoder is identified based at least in part on receiving one or more measurement reports generated by the UE based at least in part on reception of one or more downlink reference signals transmitted by the base station to the UE.

In some aspects, the precoder is identified based at least in part on measuring the plurality of uplink reference signals when the degree of reciprocity is greater than a threshold. In some aspects, the precoder is identified based at least in part on receiving the plurality of measurement reports associated with the one or more downlink reference signals when the degree of reciprocity is less than a threshold.

As further shown in <FIG>, in some aspects, process <NUM> may include precoding, by the base station, the downlink communication using the precoder (block <NUM>). For example, the base station may precode the downlink communication using the precoder, and may transmit the precoded downlink communication to the UE.

In some aspects, the base station determines a quantity or a directionality of downlink reference signals to be transmitted based at least in part on a determination of a correspondence between one or more downlink reference signals and one or more uplink reference signals with regard to channel quality. In some aspects, the base station transmits downlink reference signals to the UE based at least in part on the determination. Additional details regarding example process <NUM> are described above in connection with <FIG>.

Even though particular combinations of features are recited in the claims and/or disclosed in the specification, these combinations are not intended to limit the disclosure of possible aspects. Although each dependent claim listed below may directly depend on only one claim, the disclosure of possible aspects includes each dependent claim in combination with every other claim in the claim set.

Claim 1:
A method (<NUM>) of wireless communication performed by a user equipment, UE, comprising:
receiving (<NUM>) an indication of whether to use uplink reference signals or downlink reference signals for uplink precoder determination;
selectively transmitting (<NUM>) a plurality of uplink reference signals or one or more measurement reports based at least in part on the indication, wherein the one or more measurement reports are associated with a plurality of downlink reference signals;
receiving (<NUM>) an indication of a precoder, of a plurality of precoders, to be used to precode an uplink communication, wherein the precoder is identified based at least in part on the plurality of uplink reference signals or the one or more measurement reports; and
precoding (<NUM>) the uplink communication using the precoder.