Patent Description:
However, as the demand for mobile broadband access continues to increase, there exists a need for further improvements in LTE, NR, and other technologies. These improvements may be applicable to other multiple access technologies and the telecommunication standards that employ these technologies.

<NPL> discusses decoupling DL and UL beam selection and makes the following observations: Observation <NUM>: Both downlink and uplink beam pair links should be able to be determined based on DL RSs. Observation <NUM>: Received L1-RSRP report on configured downlink RS does not reveal UE's possible TX power reduction needed in uplink transmission using the RS as spatial source. Observation <NUM>: Current L1-RSRP reporting scheme could be enhanced by configuring UE to report additional metric like a power headroom calculated on measured downlink RS used for L1-RSRP measurement. Based on received additional metric the gNB would be able to determine which DL RSs are feasible to be configured as source RSs (spatial relation infos) for the uplink. <CIT>, relates to reporting a power limit along with an indication of at least one constraint upon which the power limit is based. In some aspects, the constraint is a radio frequency (RF) exposure constraint. For example, a power headroom limit calculated by a first apparatus may be constrained by a specific absorption rate (SAR) limit or a maximum permissible exposure (MPE) limit. The first apparatus may thus report to a second apparatus the current power headroom limit of the first apparatus along with an indication of whether the power headroom limit is constrained by an SAR limit or an MPE limit (e.g., as opposed to being constrained by a maximum transmit power limit). The second apparatus may then schedule the first apparatus taking into account the power headroom limit and the corresponding constraint (e.g., maximum power or SAR/MPE). <CIT>, relates to managing the transmission of uplink beams. For example, a first apparatus may generate a signal for transmission to a second apparatus. Thereafter, the first apparatus may detect a condition associated with transmitting the signal via a first uplink beam at a first transmission power. The condition may include the first uplink beam exceeding a maximum permissible exposure (MPE) limit. Accordingly, the first apparatus may refrain from transmitting the signal via the first uplink beam based on the at least one condition and transmit the signal to the second apparatus using a second uplink beam different from the first uplink beam.

In some aspect there is provided a method of wireless communication, performed by a user equipment (UE) in accordance with claim <NUM>.

In some aspects, a UE for wireless communication may include memory and one or more processors operatively coupled to the memory. The memory and the one or more processors may be configured to determine, for a candidate UE uplink beam, a transmit power due to a maximum permissible exposure (MPE) constraint; estimate, for the candidate UE uplink beam, a receive power for a base station based at least in part on the transmit power due to the MPE constraint; determine a target receive power for the base station; and select the candidate UE uplink beam as an active UE uplink beam based at least in part on the estimated receive power for the base station and the target receive power for the base station.

In some aspects, a non-transitory computer-readable medium may store one or more instructions for wireless communication. The one or more instructions, when executed by one or more processors of a UE, may cause the one or more processors to determine, for a candidate UE uplink beam, a transmit power due to a maximum permissible exposure (MPE) constraint; estimate, for the candidate UE uplink beam, a receive power for a base station based at least in part on the transmit power due to the MPE constraint; determine a target receive power for the base station; and select the candidate UE uplink beam as an active UE uplink beam based at least in part on the estimated receive power for the base station and the target receive power for the base station.

In some aspects, an apparatus for wireless communication may include means for determining, for a candidate apparatus uplink beam, a transmit power due to a maximum permissible exposure (MPE) constraint; means for estimating, for the candidate apparatus uplink beam, a receive power for a base station based at least in part on the transmit power due to the MPE constraint; means for determining a target receive power for the base station; and means for selecting the candidate apparatus uplink beam as an active apparatus uplink beam based at least in part on the estimated receive power for the base station and the target receive power for the base station.

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

Controller/processor <NUM> of base station <NUM>, controller/processor <NUM> of UE <NUM>, and/or any other component(s) of <FIG> may perform one or more techniques associated with uplink beam selection in millimeter wave subject to maximum permissible exposure constraints, as described in more detail elsewhere herein. For example, controller/processor <NUM> of base station <NUM>, controller/processor <NUM> of UE <NUM>, and/or any other component(s) of <FIG> may perform or direct operations of, for example, process <NUM> of <FIG>, process <NUM> of <FIG>, process <NUM> of <FIG>, and/or other processes as described herein. Memories <NUM> and <NUM> may store data and program codes for base station <NUM> and UE <NUM>, respectively.

In some aspects, UE <NUM> may include means for determining, for a candidate UE uplink beam, a transmit power due to a maximum permissible exposure (MPE) constraint; means for estimating, for the candidate UE uplink beam, a receive power for a base station based at least in part on the transmit power due to the MPE constraint; means for determining a target receive power for the base station; means for selecting the candidate UE uplink beam as an active UE uplink beam based at least in part on the estimated receive power for the base station and the target receive power for the base station; and/or the like. Additionally, or alternatively, UE <NUM> may include means for determining whether to use distinct UE beam pairs for uplink and downlink communications with a base station based at least in part on a sounding reference signal (SRS) configuration for the UE <NUM>; means for selecting one or more UE uplink beams for communicating with the base station based at least in part on determining whether to use the distinct UE beam pairs for uplink and downlink communications; means for transmitting using the one or more UE uplink beams; and/or the like. In some aspects, such means may include one or more components of UE <NUM> described in connection with <FIG>.

In some aspects, base station <NUM> may include means for selecting an active apparatus downlink beam based at least in part on a first metric reported by a user equipment (UE); means for selecting an active apparatus uplink beam based at least in part on a second metric, wherein the second metric is different from the first metric; means for transmitting an indication of the active apparatus downlink beam and the active apparatus uplink beam to the UE, wherein the active apparatus downlink beam and the active apparatus uplink beam are indicated using different spatial references; and/or the like. In some aspects, such means may include one or more components of base station <NUM> described in connection with <FIG>.

<FIG> is a diagram illustrating an example <NUM> relating to uplink beam selection in millimeter wave subject to maximum permissible exposure constraints.

As shown in <FIG>, a UE and a base station may be capable of communicating via one or more beams, and a communication via a beam may take multiple different paths, shown as a cluster of paths, to reach a receiver. In some cases, a beam may be a millimeter wave (mmWave) beam that carries a communication in the mmWave frequency band. When transmitting in the mmWave frequency band, a transmitter may use a higher antenna gain as compared to transmitting in the sub-<NUM> gigahertz (GHz) frequency band. As a result, the effective isotropic radiated power (EIRP), which represents the radiated power in a particular direction (e.g., the direction of the beam), may be higher for mmWave communications as compared to sub-<NUM> communications. To improve safety, some governing bodies have placed restrictions on the peak EIRP that can be directed toward the human body. These restrictions are sometimes referred to as maximum permissible exposure (MPE) limitations, MPE constraints, and/or the like.

As shown by reference number <NUM>, in some aspects, an MPE condition may be due to a hand blocking scenario, where a hand of a user of the UE blocks or obstructs communications to and/or from an antenna subarray of the UE, or is otherwise positioned near the antenna subarray. Additionally, or alternatively, the MPE condition may be due to the position of another body part of the user, such as the user's face, head, ear, leg, and/or the like. When the UE is subject to an MPE condition, a downlink beam of a first cluster <NUM> may be suitable for use by the UE to communicate with the base station, but an uplink beam of the first cluster <NUM> may not be permitted for use due to the MPE condition.

An uplink beam and a downlink beam in the same cluster (e.g., the first cluster <NUM>) may form a reciprocal beam pair, where the uplink beam is used for transmission at the UE and reception at the base station, and the downlink beam is used for transmission at the base station and reception at the UE. In a reciprocal beam pair, the uplink beam and the downlink beam may be in the same direction or path (e.g., with energy radiating in a particular direction or path more than other directions or paths), but communications on the uplink beam may propagate in the opposite direction as communications on the downlink beam. Further, electrical characteristics of an antenna used to transmit and receive communications via a reciprocal beam pair may be the same, such as gain, radiation pattern, impedance, bandwidth, resonant frequency, polarization, and/or the like, regardless of whether the antenna is transmitting or receiving, due to the reciprocity theorem of electromagnetics. As used herein, a reciprocal beam pair may refer to a beam pair having beam correspondence. Similarly, a non-reciprocal beam pair may refer to a beam pair that does not have beam correspondence.

As indicated above, when the UE is subject to an MPE condition, a downlink beam of a reciprocal beam pair may be suitable for use by the UE to receive communications from the base station, and may have better beam conditions (e.g., a stronger beam) as compared to other downlink beams (e.g., in a different or distinct beam pair), but an uplink beam of the reciprocal beam pair may not be permitted for transmission of communications by the UE due to the MPE condition. For example, the downlink beam may not be subject to an MPE constraint because an EIRP level of a transmission by the base station may subside by the time the transmission reaches the UE and/or the user's hand or other body part. However, the uplink beam may be subject to an MPE constraint because an EIRP level of a transmission by the UE may exceed a permitted EIRP level due to the close proximity of the UE and the user's hand or other body part. This is shown by the first cluster <NUM>.

In such a case, it may be beneficial for the UE and/or the base station to use a first beam for uplink communications and a second beam for downlink communications, where the first beam (e.g., a UE uplink beam or a BS uplink beam) does not form a reciprocal beam pair with the second beam (e.g., a UE downlink beam or a BS downlink beam). In other words, the first beam and the second beam may be included in distinct beam pairs (ie. , different beam pairs). In some aspects, the UE may select non-reciprocal (e.g., distinct, different, and/or the like) UE beams to communicate with the base station even if the base station is using reciprocal BS beams to communicate with the UE. For example, the UE uplink beam may be included in a second cluster <NUM> and the UE downlink beam may be included in the first cluster <NUM> (e.g., even if the base station is using a BS uplink beam and a BS downlink beam that are both included in the first cluster <NUM>). The UE uplink beam may form a reciprocal beam pair with a UE downlink beam in the second cluster <NUM> that is weaker than and/or has less suitable beam conditions than the UE downlink beam in the first cluster <NUM>. By choosing distinct UE uplink and UE downlink beams (e.g., a UE uplink beam and a UE downlink beam from different beam pairs), the UE may improve performance while satisfying an MPE constraint.

Additionally, or alternatively, the base station may select non-reciprocal BS beams, such that a UE uplink beam, used to transmit communications to the base station <NUM> (e.g., and received at the base station via a BS uplink beam), has a reduced MPE impact at the UE as compared to a BS uplink beam that forms a reciprocal beam pair with the BS downlink beam that has the best or better performance. In some aspects, the UE may report different metrics to facilitate the selection of the BS uplink beam and/or the BS downlink beam. Additional details regarding beam selection are described below.

However, in some cases, a base station may use uplink communications, such as sounding reference signals (SRS) transmitted by the UE, to perform operations for downlink communications. For example, the base station may use SRS to perform downlink channel estimation, to refine a base station downlink beam (e.g., to perform downlink beam management), and/or the like. These operations may be performed with an assumption that the UE is using the same beam pair (e.g., a single beam pair), at a particular time (e.g., a same symbol, a same slot, and/or the like), for a UE uplink beam (e.g., for transmitting uplink communications) and a UE downlink beam (e.g., for receiving downlink communications). When the UE selects distinct beam pairs for a UE uplink beam and a UE downlink beam, this assumption is not true. As a result, downlink performance may suffer due to inaccurate channel estimation, non-optimal beam refinement, and/or the like that use SRS transmitted on a UE uplink beam that does not correspond to (e.g., is non-reciprocal with, is part of a distinct UE beam pair from, and/or the like) a UE downlink beam being used by the UE.

Some techniques and apparatuses described herein permit a UE to infer whether a base station is using SRS, transmitted by the UE, to perform downlink operations, such as downlink channel estimation and/or downlink beam refinement. In some aspects, if the UE infers that the base station is using the SRS for downlink operations, then the UE may determine not to use distinct beam pairs for uplink and downlink communications (e.g., may use the same beam pair for uplink and downlink communications), thereby improving downlink performance (e.g., as compared to selecting distinct UE beam pairs for uplink and downlink) due to more accurate downlink channel estimation, downlink beam refinement, and/or the like. Additionally, or alternatively, if the UE infers that the base station is not using the SRS for downlink operations, then the UE may determine to use distinct beam pairs for uplink and downlink communications, thereby improving performance while satisfying an MPE constraint, as described above. In some aspects, the UE inference may be based at least in part on an SRS configuration, as described in more detail below.

Furthermore, some techniques and apparatuses described herein permit the UE to select one or more beams (e.g., UE uplink beams, UE downlink beams, and/or the like) based at least in part on determining whether to use distinct UE beam pairs for uplink and downlink beam pairs, based at least in part on the SRS configuration, and/or the like. In some aspects, the UE may use different input parameters for beam selection based at least in part on determining whether to use distinct UE beam pairs for uplink and downlink beam pairs, based at least in part on the SRS configuration, and/or the like, resulting in improved performance. For example, better throughput, fewer decoding errors, a better block error rate, and/or the like may be achieved by better channel estimation. This may conserve network resources (e.g., due to selection of an appropriate modulation and coding scheme, due to fewer retransmissions, and/or the like), and/or may conserve resources (e.g., memory resources, processing resources, battery power, and/or the like) of the UE and/or the base station (e.g., due to processing fewer retransmissions and/or the like). In this way, the UE can implement distinct UE beam pairs as appropriate (e.g., depending on an MPE constraint, an SRS configuration, and/or the like) while permitting the base station to correctly perform channel estimation.

Other examples are possible and may differ from what was described in connection with <FIG>.

<FIG> is a diagram illustrating an example <NUM> of uplink beam selection in millimeter wave subject to maximum permissible exposure constraints, in accordance with various aspects of the present disclosure.

As shown by reference number <NUM>, a UE <NUM> may determine, for a candidate UE uplink beam, a transmit power (e.g., a maximum transmit power) due to a maximum permissible exposure (MPE) constraint (e.g., an MPE limitation, an MPE restriction, and/or the like), shown in <FIG> as an MPE-based maximum power limit. As used herein, the maximum transmit power due to the MPE constraint may be referred to as an MPE-constrained maximum transmit power. In some aspects, the MPE-constrained maximum transmit power for a candidate UE uplink beam may vary over time due to, for example, movement of the UE <NUM>, rotation of the UE <NUM>, and/or the like. Thus, the UE <NUM> may determine the MPE-constrained maximum transmit power for a candidate UE uplink beam at a specific time, for a specific time period, and/or the like. Although some operations are described herein as being performed using a maximum transmit power due to an MPE constraint (e.g., an MPE-constrained maximum transmit power), in some aspects, one or more of these operations may be performed using a transmit power due to an MPE constraint (e.g., an MPE-constrained transmit power), such as a transmit power that is less than the maximum transmit power due to an MPE constraint.

As shown, in some aspects, the MPE-constrained maximum transmit power may be less than a maximum transmit power for the UE <NUM> when not subject to an MPE constraint (e.g., a maximum transmit power due to a class of the UE <NUM>, a specification-mandated maximum transmit power indicated in a wireless communication standard, and/or the like). For example, when the candidate UE uplink beam is subject to an MPE constraint (e.g., due to the candidate UE uplink beam being directed toward a body), then the MPE-constrained maximum transmit power for the candidate UE uplink beam may be less than the maximum transmit power for the UE <NUM>. However, in some aspects, the MPE-constrained maximum transmit power may be equal to a maximum transmit power for the UE <NUM> when not subject to an MPE constraint. For example, when the candidate UE uplink beam is not subject to an MPE constraint (e.g., due to the candidate UE uplink beam not being directed toward a body), then the MPE-constrained maximum transmit power for the candidate UE uplink beam may be equal to the maximum transmit power for the UE <NUM>.

In some aspects, the UE <NUM> may determine the MPE-constrained maximum transmit power for a candidate UE uplink beam based at least in part on an EIRP value for the candidate UE uplink beam, a maximum or peak EIRP value stored by the UE <NUM> (e.g., as dictated by a governing body, as specified in a wireless communication standard, as configured for the UE <NUM>, and/or the like), a determination of whether the candidate UE uplink beam is directed toward a body (e.g., a human body), and/or the like. For example, if the candidate UE uplink beam is not directed toward a body, then the UE <NUM> may set the MPE-constrained maximum transmit power to a maximum transmit power value for the UE <NUM>, which may be stored by the UE <NUM>, may be determined based at least in part on a class of the UE <NUM>, may be specified by a wireless communication standard, and/or the like. However, if the candidate UE uplink beam is directed toward a body, then the UE <NUM> may set the MPE-constrained maximum transmit power based at least in part on a determined EIRP value for the candidate UE uplink beam and/or a maximum permitted EIRP value.

As shown by reference number <NUM>, the UE <NUM> may estimate, for the candidate UE uplink beam, a receive power for a base station (e.g., an estimated BS receive power) based at least in part on the MPE-constrained maximum transmit power. In some aspects, the UE <NUM> may estimate the BS receive power using the MPE-constrained maximum transmit power, a pathloss estimate (e.g., for transmissions from the UE <NUM> to the base station <NUM>), and/or the like. In some aspects, the UE <NUM> may estimate the pathloss after accounting for antenna array gains for the UE <NUM> and/or the base station <NUM> with respect to the candidate UE uplink beam, after accounting for beamforming for the candidate UE uplink beam, and/or the like.

As shown by reference number <NUM>, the UE <NUM> may determine a target receive power for the base station (e.g., a target BS receive power). In some aspects, the UE <NUM> may determine the target BS receive power based at least in part on one or more parameters configured by the base station <NUM> and/or indicated to the UE <NUM> by the base station <NUM>. For example, the UE <NUM> may determine the target BS receive power based at least in part on a configured power parameter per resource block (e.g., shown as a P0_PUSCH parameter), a resource block allocation, a scaling factor associated with the resource block allocation (e.g., a scaling factor that depends on an uplink grant size), a modulation and coding scheme (MCS), a scaling factor associated with the MCS (e.g., a higher power for a higher MCS, a lower power for a lower MCS, and/or the like), and/or the like. In some aspects, the UE <NUM> may determine the target BS receive power based at least in part on an equation stored by the UE <NUM> and/or specified by a wireless communication standard.

As shown by reference number <NUM>, the UE <NUM> may determine a virtual power headroom (VPHR) value for the candidate UE uplink beam. In some aspects, the VPHR value may be determined based at least in part on the estimated receive power for the base station (e.g., the estimated BS receive power) and the target receive power for the base station (e.g., the target BS receive power). For example, the VPHR may be calculated as the difference between estimated receive power for the base station and the target receive power for the base station (e.g., the estimated BS receive power minus the target BS receive power). In some aspects, the difference between the estimated BS receive power and the target BS receive power may be determined by filtering multiple samples (e.g., estimates, targets, and/or the like) over a time period.

Stated another way, the VPHR may be based at least in part on the MPE-constrained maximum transmit power, a pathloss estimate, and the target BS receive power (e.g., the MPE-constrained maximum transmit power minus the pathloss estimate minus the target BS receive power). In some aspects, the VPHR may be represented in units of decibels per milliwatt (e.g., decibel-milliwatts, or dBm).

As shown by reference number <NUM>, the UE <NUM> may select a candidate UE uplink beam, from a plurality of candidate UE uplink beams, based at least in part on respective VPHR values determined for each of the plurality of candidate UE uplink beams. The selected candidate UE uplink beam may be used by the UE <NUM>, as an active UE uplink beam, to communicate with the base station <NUM> (e.g., to transmit information on one or more channels, such as a physical uplink control channel (PUCCH), a physical uplink shared channel (PUSCH), a random access channel (RACH), and/or the like). In some aspects, the UE <NUM> may select the candidate UE uplink beam that has the maximum VPHR value as compared to VPHR values of other candidate UE uplink beams (e.g., all other candidate UE uplink beams). Stated another way, the UE <NUM> may select the candidate UE uplink beam that has the maximum difference between an estimated BS receive power and a target BS receive power as compared to the respective differences determined for other candidate UE uplink beams (e.g., all other candidate UE uplink beams).

For example, in <FIG>, candidate UE uplink beam <NUM> is shown as having a VPHR value of <NUM> dBm, candidate UE uplink beam <NUM> is shown as having a VPHR value of <NUM> dBm, and candidate UE uplink beam <NUM> is shown as having a VPHR value of <NUM> dBm. In this case, the UE <NUM> may select candidate UE uplink beam <NUM> as the active UE uplink beam to be used to transmit communications to the base station <NUM> (e.g., regardless of whether the selected candidate UE uplink beam corresponds to a BS uplink beam being used by the BS to receive communications from the UE <NUM>). In this way, the UE <NUM> may take MPE constraints into account when selecting the candidate UE uplink beam as the active UE uplink beam, thereby selecting the best candidate UE uplink beam that satisfies safety requirements. Furthermore, the UE <NUM> may be capable of maintaining a link for uplink communications despite a scenario with a severe MPE constraint.

In some aspects, the UE <NUM> may account for hysteresis scenarios and/or may prevent or reduce hysteresis when selecting the active UE uplink beam. For example, the UE <NUM> may select a candidate UE uplink beam as the active UE uplink beam based at least in part on a determination that the candidate UE uplink beam has the maximum VPHR value (and/or a maximum difference between an estimated BS receive power and a target BS receive power) for a threshold amount of time. Additionally, or alternatively, the UE <NUM> may wait for a threshold amount of time to elapse after selecting a candidate UE uplink beam as the active UE uplink beam before performing another selection. These techniques may account for time hysteresis and may conserve resources (e.g., computing resources, processing resources, memory resources, network resources, and/or the like) that would otherwise be wasted by switching back and forth between beams.

Additionally, or alternatively, the UE <NUM> may select a candidate UE uplink beam as the active UE uplink beam based at least in part on a determination that the maximum VPHR value (and/or a maximum difference between an estimated BS receive power and a target BS receive power) of the candidate UE uplink beam is greater than other VPHR values (or other differences) determined for the other candidate UE uplink beams by a threshold amount (e.g., is greater than the second highest VPHR value and/or the second highest difference by the threshold amount). This may account for power hysteresis and may conserve resources, as described above.

Additionally, or alternatively, the UE <NUM> may compare a candidate UE uplink beam (e.g., a first candidate UE uplink beam) to another candidate UE uplink beam (e.g., a second candidate UE uplink beam), such as a current active UE uplink beam and/or one or more other candidate UE uplink beams. In this case, the UE <NUM> may select the first candidate UE uplink beam over the second candidate UE uplink beam based at least in part on comparing VPHR values for those beams, comparing a difference between estimated BS receive power and the target BS receive power for those beams, and/or the like. For example, the UE <NUM> may select the first candidate UE uplink beam over the second candidate UE uplink beam based at least in part on a determination that the first candidate UE uplink beam has a greater VPHR value than that of the second candidate UE uplink beam (e.g., by a threshold amount, for a threshold time period, and/or the like), has a greater difference between an estimated BS receive power and a target BS receive power than that of the second candidate UE uplink beam (e.g., by a threshold amount, for a threshold time period, and/or the like), and/or the like.

As described above in connection with <FIG>, in some aspects, the candidate UE uplink beam selected as the active UE uplink beam may not be reciprocal with (e.g., may not form a reciprocal beam pair with) an active UE downlink beam being used by the UE <NUM> to receive downlink communications from the base station <NUM>. For example, the active UE uplink beam may not be in a same direction or path (or may not be in opposite directions or paths) as the active UE downlink beam. Additionally, or alternatively, the active UE uplink beam may radiate energy (e.g., a majority of radiated energy) in a different direction or path than the active UE downlink beam. Additionally, or alternatively, electrical characteristics of an antenna used to transmit communications on the active UE uplink beam may be different from electrical characteristics used to receive communications on the active UE downlink beam. Such electrical characteristics may include one or more of a gain, a radiation pattern, an impedance, a bandwidth, a resonant frequency, a polarization, and/or the like.

In some aspects, the UE <NUM> may determine not to use a distinct pair of beams for the active UE uplink beam and the active UE downlink beam (e.g., may determine not to use a non-reciprocal beam pair, or may determine to use a reciprocal beam pair). For example, if the base station <NUM> uses uplink communications from the UE <NUM> for downlink estimates (e.g., other than sounding reference signals (SRS) designed for such a use), then such downlink estimates may be less accurate if the UE <NUM> does not use a reciprocal beam pair. Thus, the UE <NUM> may determine that the UE <NUM> is not permitted to use a distinct pair of beams based at least in part on a determination that the base station <NUM> uses uplink communications from the UE <NUM> for downlink estimation, and the UE <NUM> may determine not to use a distinct pair of beams in this scenario. In this way, the accuracy of the downlink estimates of the base station <NUM> may be improved or maintained.

Conversely, the UE <NUM> may determine that the UE <NUM> is permitted to use a distinct pair of beams based at least in part on a determination that the base station <NUM> is not configured to use uplink communications from the UE <NUM> for downlink estimation (e.g., other than SRS specifically designed for such use, such as SRS for downlink channel state information (CSI) acquisition, non-codebook SRS, and/or the like). In this case, the UE <NUM> may determine to use a distinct pair of beams (e.g., if a candidate UE uplink beam, selected as the active UE uplink beam using the techniques described herein, is distinct from the active UE downlink beam). Thus, the UE <NUM> may perform one or more operations described herein (e.g., in connection with reference numbers <NUM>-<NUM>, in connection with process <NUM> of <FIG>, and/or the like) based at least in part on a determination that the base station is not configured to use uplink communications for downlink estimation. In this way, the accuracy of the downlink estimates of the base station <NUM> may be maintained, while permitting selection of the best UE uplink beam that does not violate an MPE constraint.

For example, the UE <NUM> may determine to select a candidate UE uplink beam, that is not reciprocal with the active downlink beam, based at least in part on a sound reference signal (SRS) configuration for the UE. In some aspects, the UE <NUM> may determine to select a candidate UE uplink beam, that is not reciprocal with the active downlink beam, based at least in part on a number of SRS resource sets configured for one or more SRS usages, whether an SRS resource is included in multiple SRS resource sets associated with different SRS usages, a time domain configuration indicated by the SRS configuration, a periodicity indicated by the SRS configuration, a spatial reference configuration indicated by the SRS configuration, a determination that SRS resources are not configured for an antenna switching usage and/or a codebook usage, a determination that SRS resources for at least one of an antenna switching usage or a codebook usage are configured with a periodicity that satisfies a threshold, a determination that a first SRS resource set is configured with an antenna switching usage and a second SRS resource set is configured with a codebook usage, and/or the like.

Using the techniques described herein, UE uplink beam selection may depend on a different metric and/or value than UE downlink beam selection. For example, UE uplink beam selection may use VPHR values, while UE downlink beam selection may not. For example, UE downlink beam selection may use a signal to interference plus noise (SINR) value, a reference signal received power (RSRP) value, a spectral efficiency (SPEFF) value, and/or the like.

<FIG> is a diagram illustrating another example <NUM> of uplink beam selection in millimeter wave subject to maximum permissible exposure constraints, in accordance with various aspects of the present disclosure.

As shown by reference number <NUM>, a UE <NUM> may report, and a base station <NUM> may receive, a first metric to be used to select a base station (BS) downlink beam. For example, the first metric may include a reference signal received power (RSRP) value and/or the like.

As shown by reference number <NUM>, the UE <NUM> may report, and the base station <NUM> may receive, a second metric to be used to select a BS uplink beam. In some aspects, the second metric may be different from the first metric. For example, the second metric may not be an RSRP value. For example, the second metric may include a VPHR value, as described above in more detail in connection with <FIG>. Additionally, or alternatively, the second metric may include and/or may be determined based at least in part on a maximum transmit power for the UE due to an MPE constraint (e.g., an MPE-constrained maximum transmit power), a pathloss estimate for the base station and the UE, an estimated receive power for the base station, a target receive power for the base station, and/or the like, as described in more detail above in connection with <FIG>.

In some aspects, the UE <NUM> may report the value of the second metric for one or more uplink beams. Additionally, or alternatively, the UE <NUM> may report an indication of one or more uplink beams identified based at least in part on the second metric. For example, and as shown, the UE <NUM> may report information that identifies multiple uplink beams, shown as beams <NUM>, <NUM>, and <NUM>. In some aspects, the UE <NUM> may determine these beams using the second metric, such as VPHR and/or the like, as described above in connection with <FIG>. In some aspects, the UE <NUM> may rank the uplink beams and/or report a beam ranking, which may be used by the base station <NUM> to select an active BS uplink beam.

Additionally, or alternatively, the UE <NUM> may report multiple values, corresponding to multiple uplink beams, using the second metric. For example, and as shown, the UE <NUM> may report an indication of a VPHR value of <NUM> dBm for beam <NUM>, <NUM> dBm for beam <NUM>, and <NUM> dBm for beam <NUM>. In some aspects, the base station <NUM> may use the multiple values of the second metric, corresponding to the multiple uplink beams, to select an active BS uplink beam.

In some aspects, the UE <NUM> may periodically report values of the second metric and/or uplink beams determined based at least in part on those values. In some aspects, the periodicity for such reporting may be configured by the base station <NUM> (e.g., in an RRC configuration message, a MAC-CE, DCI, and/or the like). Additionally, or alternatively, the base station <NUM> may transmit a request for the UE <NUM> to report such values and/or uplink beams (e.g., aperiodically), and the UE <NUM> may report such values and/or uplink beams based at least in part on the request. Additionally, or alternatively, the UE <NUM> may report such values and/or uplink beams based at least in part on a determination, by the UE, that a reporting condition is satisfied. The reporting condition may include, for example, a change to an MPE constraint at the UE (e.g., by a threshold amount, for a threshold number of uplink beams, and/or the like), a change to a UE-specific constraint (e.g., by a threshold amount), a change to an environmental constraint associated with the UE <NUM> (e.g., by a threshold amount), and/or the like. The UE-specific constraint may include, for example, a thermal constraint (e.g., regarding a temperature measured by the UE <NUM>), a power consumption constraint, and/or the like.

As shown by reference number <NUM>, the base station <NUM> may select an active BS downlink beam based at least in part on the first metric. Additionally, or alternatively, the base station <NUM> may select an active BS uplink beam based at least in part on the second metric. In some aspects, the active BS downlink beam and the active BS uplink beam do not form a reciprocal beam pair.

In some aspects, the base station <NUM> may select the active BS uplink beam from multiple candidate uplink beams reported by the UE <NUM>. For example, the base station <NUM> may select the active BS uplink beam with the best beam conditions at the base station <NUM> and/or with the best reported metric value (e.g., of the second metric). Additionally, or alternatively, the base station <NUM> may select the active BS uplink beam based at least in part on values of second metrics reported by the UE <NUM>. In some aspects, the base station <NUM> may use one or more metrics reported by the UE <NUM> and/or one or more candidate uplink beams reported by the UE <NUM> in combination with one or more factors determined by the base station <NUM>, such as a measurement associated with the candidate uplink beams, a traffic profile associated with the base station <NUM>, a beam capability associated with the base station <NUM>, and/or the like.

As shown by reference number <NUM>, the base station <NUM> may transmit, and the UE <NUM> may receive, an indication of the active BS downlink beam and the active BS uplink beam. In some aspects, the active BS downlink beam and the active BS uplink beam may be indicated using different spatial references. The different spatial references may be for a non-reciprocal beam pair, such as a quasi co-location (QCL) reference or a transmission configuration indicator (TCI) state for the active BS downlink beam, and a spatial reference for the active BS uplink beam that does not share reciprocity with the QCL reference or the TCI state. In some aspects, the indication may be transmitted in an RRC message, DCI, a MAC-CE, and/or the like. The base station <NUM> and the UE <NUM> may communicate using the active BS downlink beam and/or the active BS uplink beam.

As described above, in some aspects, the active BS downlink beam and the active BS uplink beam do not form a reciprocal beam pair. For example, as shown, the base station <NUM> may select and/or indicate downlink beam <NUM> (e.g., which forms a reciprocal beam pair with uplink beam <NUM>) and uplink beam <NUM> (e.g., which forms a reciprocal beam pair with downlink beam <NUM>). By selecting non-reciprocal BS beams, the base station <NUM> may be capable of selecting a BS downlink beam (e.g., an optimal BS downlink beam) and a non-reciprocal BS uplink beam corresponding to a UE uplink beam that has a reduced MPE impact at the UE <NUM> as compared to a UE uplink beam corresponding to a BS uplink beam that forms a reciprocal beam pair with the BS downlink beam. In this way, MPE constraints may be satisfied while still permitting good network performance.

<FIG> is a diagram illustrating an example process <NUM> performed, for example, by a UE, in accordance with various aspects of the present disclosure. Example process <NUM> is an example where a UE (e.g., UE <NUM> and/or the like) performs operations associated with uplink beam selection in millimeter wave subject to maximum permissible exposure constraints.

As shown in <FIG>, in some aspects, process <NUM> may include determining, for a candidate UE uplink beam, a transmit power due to a maximum permissible exposure (MPE) constraint (block <NUM>). For example, the UE (e.g., using controller/processor <NUM> and/or the like) may determine, for a candidate UE uplink beam, a transmit power (e.g., a maximum transmit power) due to an MPE constraint, as described above in connection with <FIG>.

As further shown in <FIG>, in some aspects, process <NUM> may include estimating, for the candidate UE uplink beam, a receive power for a base station based at least in part on the transmit power due to the MPE constraint (block <NUM>). For example, the UE (e.g., using controller/processor <NUM> and/or the like) may estimate, for the candidate UE uplink beam, a receive power for a base station based at least in part on the transmit power due to the MPE constraint, as described above in connection with <FIG>.

As further shown in <FIG>, in some aspects, process <NUM> may include determining a target receive power for the base station (block <NUM>). For example, the UE (e.g., using controller/processor <NUM> and/or the like) may determine a target receive power for the base station, as described above in connection with <FIG>.

As further shown in <FIG>, in some aspects, process <NUM> may include selecting the candidate UE uplink beam as an active UE uplink beam based at least in part on the estimated receive power for the base station and the target receive power for the base station (block <NUM>). For example, the UE (e.g., using controller/processor <NUM> and/or the like) may select the candidate UE uplink beam as an active UE uplink beam based at least in part on the estimated receive power for the base station and the target receive power for the base station, as described above in connection with <FIG>.

In a first aspect, the candidate UE uplink beam is selected as the active UE uplink beam based at least in part on a virtual power headroom value that represents a difference between the estimated receive power for the base station and the target receive power for the base station.

In a second aspect, alone or in combination with the first aspect, the difference is determined based at least in part on multiple samples filtered over a time period.

In a third aspect, alone or in combination with one or more of the first and second aspects, the candidate UE uplink beam is selected as the active UE uplink beam based at least in part on a determination that the candidate UE uplink beam has a maximum virtual power headroom value as compared to other candidate UE uplink beams.

In a fourth aspect, alone or in combination with one or more of the first through third aspects, the candidate UE uplink beam is selected as the active UE uplink beam based at least in part on at least one of: a determination that the candidate UE uplink beam has the maximum virtual power headroom value for a threshold amount of time, a determination that the maximum virtual power headroom value satisfies a threshold as compared to virtual power headroom values of the other candidate UE uplink beams, or a combination thereof.

In a fifth aspect, alone or in combination with one or more of the first through fourth aspects, the candidate UE uplink beam is selected as the active UE uplink beam over another candidate UE uplink beam based at least in part on a determination that the candidate UE uplink beam has a greater virtual power headroom value as compared to the other candidate UE uplink beam.

In a sixth aspect, alone or in combination with one or more of the first through fifth aspects, the candidate UE uplink beam is selected as the active UE uplink beam based at least in part on at least one of: a determination that the candidate UE uplink beam has the greater virtual power headroom value for a threshold amount of time, a determination that the virtual power headroom value for the candidate UE uplink beam is greater than that of the other candidate UE uplink beam by a threshold amount, or a combination thereof.

In a seventh aspect, alone or in combination with one or more of the first through sixth aspects, the candidate UE uplink beam is selected as the active UE uplink beam based at least in part on a determination that the candidate UE uplink beam has a maximum difference between the estimated receive power and the target receive power as compared to other candidate UE uplink beams.

In an eighth aspect, alone or in combination with one or more of the first through seventh aspects, the candidate UE uplink beam is selected as the active UE uplink beam based at least in part on at least one of: a determination that the candidate UE uplink beam has the maximum difference for a threshold amount of time, a determination that the candidate UE uplink beam has the maximum difference by a threshold amount, or a combination thereof.

In a ninth aspect, alone or in combination with one or more of the first through eighth aspects, the candidate UE uplink beam is selected as the active UE uplink beam over another candidate UE uplink beam based at least in part on a determination that the candidate UE uplink beam has a greater difference between the estimated receive power and the target receive power as compared to the other candidate UE uplink beam.

In a tenth aspect, alone or in combination with one or more of the first through ninth aspects, the candidate UE uplink beam is selected as the active UE uplink beam based at least in part on at least one of: a determination that the candidate UE uplink beam has the greater difference for a threshold amount of time, a determination that the candidate UE uplink beam has the greater difference by a threshold amount, or a combination thereof.

In an eleventh aspect, alone or in combination with one or more of the first through tenth aspects, the estimated receive power for the base station is determined based at least in part on a pathloss estimate.

In a twelfth aspect, alone or in combination with one or more of the first through eleventh aspects, the target receive power for the base station is determined based at least in part on at least one of a configured power parameter per resource block, a scaling factor for uplink grant size, or a scaling factor for modulation and coding scheme.

In a thirteenth aspect, alone or in combination with one or more of the first through twelfth aspects, the virtual power headroom value is reported to the base station.

In a fourteenth aspect, alone or in combination with one or more of the first through thirteenth aspects, the candidate UE uplink beam is not reciprocal with an active downlink beam for the UE.

In a fifteenth aspect, alone or in combination with one or more of the first through fourteenth aspects, process <NUM> includes determining to select the candidate UE uplink beam, that is not reciprocal with the active downlink beam, based at least in part on a sound reference signal (SRS) configuration for the UE.

In a sixteenth aspect, alone or in combination with one or more of the first through fifteenth aspects, process <NUM> includes determining to select the candidate UE uplink beam, that is not reciprocal with the active downlink beam, based at least in part on at least one of: a number of SRS resource sets configured for one or more SRS usages, whether an SRS resource is included in multiple SRS resource sets associated with different SRS usages, a time domain configuration indicated by the SRS configuration, a periodicity indicated by the SRS configuration, a spatial reference configuration indicated by the SRS configuration, a determination that SRS resources are not configured for an antenna switching usage, a codebook usage, or a combination thereof, a determination that SRS resources for at least one of an antenna switching usage or a codebook usage are configured with a periodicity that satisfies a threshold, a determination that a first SRS resource set is configured with an antenna switching usage and a second SRS resource set is configured with a codebook usage, or a combination thereof.

In a seventeenth aspect, alone or in combination with one or more of the first through sixteenth aspects, the candidate UE uplink beam is selected as the active UE uplink beam based at least in part on a determination that the base station is not configured to use uplink communications for downlink estimation.

In an eighteenth aspect, alone or in combination with one or more of the first through seventeenth aspects, the candidate UE uplink beam is selected as the active UE uplink beam based at least in part on a different metric than is used for UE downlink beam selection.

In a nineteenth aspect, alone or in combination with one or more of the first through eighteenth aspects, the active UE uplink beam is used to communicate with the base station via one or more antennas of the UE.

In a twentieth aspect, alone or in combination with one or more of the first through nineteenth aspects, process <NUM> includes receiving an indication of an active BS downlink beam and an active BS uplink beam from the base station, wherein the active BS downlink beam and the active BS uplink beam are indicated using different spatial references.

<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., base station <NUM> and/or the like) performs operations associated with uplink beam selection in millimeter wave subject to maximum permissible exposure constraints.

As shown in <FIG>, in some aspects, process <NUM> may include selecting an active base station (BS) downlink beam based at least in part on a first metric reported by a user equipment (UE) (block <NUM>). For example, the base station (e.g., using controller/processor <NUM> and/or the like) may select an active BS downlink beam based at least in part on a first metric reported by a UE, as described above in connection with <FIG>.

As further shown in <FIG>, in some aspects, process <NUM> may include selecting an active BS uplink beam based at least in part on a second metric, wherein the second metric is different from the first metric (block <NUM>). For example, the base station (e.g., using controller/processor <NUM> and/or the like) may select an active BS uplink beam based at least in part on a second metric, as described above in connection with <FIG>. In some aspects, the second metric is different from the first metric.

As further shown in <FIG>, in some aspects, process <NUM> may include transmitting an indication of the active BS downlink beam and the active BS uplink beam to the UE, wherein the active BS downlink beam and the active BS uplink beam are indicated using different spatial references (block <NUM>). For example, the base station (e.g., using controller/processor <NUM>, transmit processor <NUM>, TX MIMO processor <NUM>, MOD <NUM>, antenna <NUM>, and/or the like) may transmit an indication of the active BS downlink beam and the active BS uplink beam to the UE, as described above in connection with <FIG>. In some aspects, the active BS downlink beam and the active BS uplink beam are indicated using different spatial references.

In a first aspect, the active BS downlink beam and the active BS uplink beam do not form a reciprocal beam pair.

In a second aspect, alone or in combination with the first aspect, the first metric is a reference signal receive power (RSRP) value.

In a third aspect, alone or in combination with one or more of the first and second aspects, the second metric is a virtual power headroom value that represents a difference between an estimated receive power for the base station and a target receive power for the base station.

In a fourth aspect, alone or in combination with one or more of the first through third aspects, the second metric includes or is based at least in part on at least one of: a transmit power (e.g., a maximum transmit power) for the UE due to a maximum permissible exposure (MPE) constraint, a pathloss estimate for the base station and the UE, an estimated receive power for the base station, a target receive power for the base station, or a combination thereof.

In a fifth aspect, alone or in combination with one or more of the first through fourth aspects, the active BS uplink beam is selected based at least in part on a plurality of second metrics, corresponding to a plurality of candidate uplink beams, reported to the base station by the UE.

In a sixth aspect, alone or in combination with one or more of the first through fifth aspects, the active BS uplink beam is selected from a plurality of candidate uplink beams, corresponding to a plurality of second metrics, reported to the base station by the UE.

In a seventh aspect, alone or in combination with one or more of the first through sixth aspects, the second metric is reported to the base station by the UE.

In an eighth aspect, alone or in combination with one or more of the first through seventh aspects, the second metric is reported based at least in part on at least one of: a configured periodicity, a request from the base station, a determination that a reporting condition is satisfied, or a combination thereof.

In a ninth aspect, alone or in combination with one or more of the first through eighth aspects, the reporting condition includes at least one of: a change to a maximum permissible exposure (MPE) constraint at the UE, a change to a UE-specific constraint, a change to an environmental constraint associated with the UE, or a combination thereof.

In a tenth aspect, alone or in combination with one or more of the first through ninth aspects, the indication is transmitted in at least one of: a radio resource control (RRC) message, downlink control information, a media access control (MAC) control element (CE), or a combination thereof.

<FIG> is a diagram illustrating an example <NUM> of sounding reference signal (SRS) resource sets, in accordance with various aspects of the present disclosure.

A base station <NUM> may configure a UE <NUM> with one or more SRS resource sets to allocate resources for SRS transmissions by the UE <NUM>. For example, a configuration for SRS resource sets may be indicated in an SRS configuration (sometimes referred to as an SRS resource configuration, an SRS resource set configuration, and/or the like). In some aspects, the SRS configuration may be indicated in a radio resource control (RRC) message (e.g., an RRC configuration message, and RRC reconfiguration message, and/or the like). As shown by reference number <NUM>, an SRS configuration may indicate one or more resources (e.g., shown as SRS resources) that are included in an SRS resource set. The resources may include time resources, frequency resources, spatial resources, and/or the like (e.g., a slot, a symbol, a resource block, a periodicity for the time resources, a beam, a spatial reference, and/or the like).

As shown by reference number <NUM>, an SRS configuration may indicate one or more antenna ports via which an SRS is to be transmitted in an SRS resource (e.g., in a time-frequency resource, a spatial resource, and/or the like). Thus, an SRS configuration for an SRS resource set may indicate one or more resources in which an SRS is to be transmitted, and may indicate one or more antenna ports on which the SRS is to be transmitted in those resources. In some aspects, the SRS configuration for an SRS resource set may indicate a usage (e.g., an SRS usage, sometimes referred to as a use case, which may be indicated in an SRS-SetUse information element) for the SRS resource set. For example, an SRS resource set may have a usage of antenna switching, codebook, non-codebook, beam management (sometimes referred to as uplink beam management), and/or the like. In some aspects, the UE <NUM> may use the same UE uplink beam to transmit SRS for the antenna switching usage and SRS for the codebook usage.

An antenna switching SRS resource set may be used to indicate downlink channel state information (CSI) with reciprocity between an uplink and downlink channel. For example, when there is reciprocity between an uplink channel and a downlink channel, a base station <NUM> may use an antenna switching SRS (e.g., an SRS transmitted using a resource of an antenna switching SRS resource set) to acquire downlink CSI (e.g., to determine a downlink precoder to be used to communicate with the UE <NUM>, to estimate a downlink channel, and/or the like). Thus, in some cases, an antenna switching usage may be referred to as a downlink acquisition usage. As described in more detail elsewhere herein, in some aspects, the UE <NUM> may infer whether the base station <NUM> is using SRS for downlink operations (e.g., downlink channel estimation, BS downlink beam refinement, and/or the like) based at least in part on an SRS configuration for an antenna switching usage because antenna switching SRS are used for downlink acquisition (e.g., to indicate downlink CSI).

A codebook SRS resource set may be used to indicate uplink CSI when a base station <NUM> indicates an uplink precoder to the UE <NUM>. For example, when the base station <NUM> is configured to indicate an uplink precoder to the UE <NUM> (e.g., using a precoder codebook), the base station <NUM> may use a codebook SRS (e.g., an SRS transmitted using a resource of a codebook SRS resource set) to acquire uplink CSI (e.g., to determine an uplink precoder to be indicated to the UE <NUM> and used by the UE <NUM> to communicate with the base station <NUM>, to estimate an uplink channel, and/or the like). As described in more detail elsewhere herein, in some aspects, the UE <NUM> may infer whether the base station <NUM> is using SRS for downlink operations based at least in part on an SRS configuration for a codebook usage.

A non-codebook SRS resource set may be used to indicate uplink CSI when the UE <NUM> selects an uplink precoder (e.g., instead of the base station <NUM> indicating an uplink precoder to be used by the UE <NUM>). For example, when the UE <NUM> is configured to select an uplink precoder, the base station <NUM> may use a non-codebook SRS (e.g., an SRS transmitted using a resource of a non-codebook SRS resource set) to acquire uplink CSI. In this case, the non-codebook SRS may be precoded using a precoder selected by the UE <NUM> (e.g., which may be indicated to the base station <NUM>). The base station <NUM> may use the non-codebook SRS resource set to estimate an uplink channel.

A beam management SRS resource set may be used for indicating CSI for millimeter wave communications. For example, a beam management SRS resource set may be used to beam-sweeping SRS.

As shown in <FIG>, in some aspects, different SRS resource sets indicated to the UE <NUM> (e.g., having different usages) may overlap (e.g., in time, in frequency, and/or the like, such as in the same slot). For example, as shown by reference number <NUM>, a first SRS resource set (e.g., shown as SRS Resource Set <NUM>) is shown as having an antenna switching usage. As shown, this example antenna switching SRS resource set includes a first SRS resource (shown as SRS Resource A) and a second SRS resource (shown as SRS Resource B). Thus, antenna switching SRS may be transmitted in SRS Resource A (e.g., a first time-frequency resource) using antenna port <NUM> and antenna port <NUM>, and may be transmitted in SRS Resource B (e.g., a second time-frequency resource) using antenna port <NUM> and antenna port <NUM>.

As shown by reference number <NUM>, a second SRS resource set (e.g., shown as SRS Resource Set <NUM>) may be a codebook usage. As shown, this example codebook SRS resource set includes only the first SRS resource (shown as SRS Resource A). Thus, codebook SRS may be transmitted in SRS Resource A (e.g., the first time-frequency resource) using antenna port <NUM> and antenna port <NUM>. In this case, the UE <NUM> may not transmit codebook SRS in SRS Resource B (e.g., the second time-frequency resource) using antenna port <NUM> and antenna port <NUM>.

As described in more detail below, the UE <NUM> may use the SRS configuration to determine whether to use distinct beam pairs for uplink and downlink communications (e.g., based at least in part on an inference about whether the base station <NUM> is using SRS for downlink operations). Additionally, or alternatively, the UE <NUM> may use the SRS configuration to select one or more beams (e.g., UE uplink beams, UE downlink beams, and/or the like). In this way, the UE can implement distinct UE beam pairs as appropriate (e.g., to satisfy an MPE constraint) while permitting the base station to correctly perform channel estimation.

<FIG> is a diagram illustrating an example <NUM> of uplink beam selection in millimeter wave using an SRS configuration, in accordance with various aspects of the present disclosure.

As shown by reference number <NUM>, a base station <NUM> may transmit, and a UE <NUM> may receive, an SRS configuration (e.g., which may include information as described above in connection with <FIG>). The SRS configuration may indicate a configuration for the UE <NUM> to transmit SRS. For example, the SRS configuration may identify one or more SRS resource sets to be used to transmit SRS. An SRS resource set may include a set of resources (e.g., time resources, frequency resources, spatial resources, and/or the like) to be used by the UE <NUM> to transmit SRS. Additionally, or alternatively, the SRS configuration may identify a usage for an SRS resource set (e.g., an antenna switching usage, a codebook usage, a non-codebook usage, a beam management usage, and/or the like).

Additionally, or alternatively, the SRS configuration may identify one or more antenna ports to be used for an SRS resource set (e.g., one or more antenna ports via which an SRS is to be transmitted for the SRS resource set). In some aspects, the SRS configuration may indicate a single antenna port for an SRS resource set. In some aspects, the SRS configuration may indicate multiple antenna ports for an SRS resource set (e.g., two antenna ports, three antenna ports, and/or the like). Additionally, or alternatively, the SRS configuration may indicate whether two or more SRS resource sets (e.g., having different usages, such as antenna switching and codebook) overlap (e.g., whether a specific resource, such as a time resource, a frequency resource, and/or the like, is included in multiple SRS resource sets).

In some aspects, the SRS configuration may indicate a number of SRS resource sets configured for the UE <NUM>. Additionally, or alternatively, the SRS configuration may indicate the usages for those SRS resource sets(s), thereby indicating a number of SRS resource sets configured for each specific usage. Additionally, or alternatively, the SRS configuration may indicate a time domain configuration for an SRS resource set, such as whether an SRS resource set is periodic, aperiodic, semi-persistent, and/or the like. Additionally, or alternatively, the SRS configuration may indicate a periodicity for an SRS resource set (e.g., how often SRS are to be transmitted in the time domain for the SRS resource set).

Additionally, or alternatively, the SRS configuration may indicate a spatial reference configuration for an SRS resource set, such as one or more spatial parameters (e.g., spatial domain filter(s), spatial relation(s), precoder(s), beam(s), and/or the like) to be used to transmit SRS for the SRS resource set. In some aspects, the spatial reference configuration may be indicated in an RRC message, in a media access control (MAC) control element (CE) (MAC-CE), in downlink control information (DCI), and/or the like. The SRS configuration may be used by the UE <NUM> to determine whether to use distinct UE beams for uplink and downlink communications and/or to select one or more beams for communicating with the base station <NUM>, as described in more detail below.

As shown by reference number <NUM>, the UE <NUM> may determine whether to use distinct UE beam pairs for uplink and downlink communications (e.g., as described in more detail above in connection with <FIG>) based at least in part on the SRS configuration. In some aspects, the UE <NUM> may use only an SRS configuration for an antenna switching usage and/or a codebook usage (e.g., and not for a non-codebook usage or a beam management usage) to determine whether to use the distinct UE beam pairs. Antenna switching SRS may be used by the base station <NUM> to acquire downlink CSI, and codebook SRS may be used by the base station <NUM> to acquire uplink CSI. Thus, an SRS configuration for one or both of these usages may be used by the UE <NUM> to infer whether the base station <NUM> is using SRS, transmitted by the UE <NUM>, to perform downlink operations (e.g., downlink channel estimation, downlink beam refinement, and/or the like).

For example, the UE <NUM> may determine whether to use distinct UE beam pairs for uplink and downlink communications based at least in part on a number of SRS resource sets configured for one or more SRS usages (e.g., a number of SRS resource sets configured for an antenna switching usage, a number of SRS resource sets configured for a codebook usage, and/or the like), whether an SRS resource is included in multiple SRS resource sets associated with different SRS usages (e.g., an antenna switching usage and a codebook usage), a time domain configuration indicated by the SRS configuration, a periodicity indicated by the SRS configuration (e.g., whether the periodicity for a specific usage, such as an antenna switching usage or a codebook usage, satisfies a threshold), a spatial reference configuration indicated by the SRS configuration, and/or the like.

In some aspects, one or more of these parameters or other parameters of an SRS configuration may be used by the UE <NUM> to infer whether the base station <NUM> is using SRS for downlink operations. In some aspects, if the UE <NUM> infers that the base station <NUM> is using the SRS for downlink operations, then the UE <NUM> may determine not to use distinct beam pairs for uplink and downlink communications (e.g., may use the same beam pair for uplink and downlink communications), thereby improving downlink performance (e.g., as compared to selecting distinct UE beam pairs for uplink and downlink) due to more accurate downlink channel estimation, downlink beam refinement, and/or the like. In some aspects, if the UE <NUM> infers that the base station <NUM> is not using the SRS for downlink operations, then the UE <NUM> may determine to use distinct beam pairs for uplink and downlink communications, thereby improving performance while satisfying an MPE constraint, as described above. Additional details and examples regarding inferring whether the base station <NUM> is using SRS for downlink operations are described below in connection with <FIG>.

As shown by reference number <NUM>, the UE <NUM> may select one or more UE uplink beams, for communicating with the base station <NUM> (e.g., for transmitting one or more SRS to the base station <NUM>), based at least in part on determining whether to use the distinct UE beam pairs for uplink and downlink communications. Additionally, or alternatively, the UE <NUM> may select the one or more UE uplink beams based at least in part on the SRS configuration (e.g., one or more parameters indicated by the SRS configuration).

For example, in some aspects, if the UE <NUM> determines to use distinct UE beam pairs for uplink and downlink communications, then the UE <NUM> may select one or more UE uplink beams using only an uplink metric (e.g., and not a downlink metric) that takes one or more uplink parameters (e.g., a maximum transmit power for the UE <NUM> subject to an MPE constraint, a pathloss estimate, an estimated receive power at the base station <NUM>, a target receive power at the base station <NUM>, a virtual power headroom, and/or the like) into account when selecting the one or more UE uplink beams. Additionally, or alternatively, in some aspects, if the UE <NUM> determines to use the same UE beam pair for uplink and downlink communications, then the UE <NUM> may select one or more UE uplink beams using a joint metric that takes one or more uplink parameters and one or more downlink parameters (e.g., a signal to interference plus noise ratio (SINR) parameter, a reference signal received power (RSRP) parameter, a spectral efficiency parameter, and/or the like) into account when selecting the one or more UE uplink beams. In some aspects, the joint metric may represent a tradeoff between uplink and downlink performance when using the same beam pair for both uplink and downlink communications. In some aspects (as described in more detail below in connection with <FIG>), the UE <NUM> may select the one or more UE uplink beams using only a downlink metric (e.g., and not an uplink metric) that takes into account one or more downlink parameters.

Additionally, or alternatively, the UE <NUM> may select the one or more UE uplink beams for an SRS resource based at least in part on an SRS usage of the SRS resource (e.g., an antenna switching usage, a codebook usage, and/or the like), whether the SRS resource is included in multiple SRS resource sets with different SRS usages, a number of antenna ports configured for the SRS resource, a spatial reference configuration for the SRS resource, a spatial reference configuration for a physical channel (e.g., a physical downlink shared channel (PDSCH), a physical uplink shared channel (PUSCH), a physical downlink control channel (PDCCH), a physical uplink control channel (PUCCH), and/or the like), whether a spatial reference configuration of the SRS resource and the channel are the same, a number of SRS resources included in an SRS resource set that includes the SRS resource, a number of SRS resource sets with a same usage as the SRS resource, and/or the like. Additional details and examples regarding selecting one or more UE uplink beams are described below in connection with <FIG>.

As shown by reference number <NUM>, the UE <NUM> may transmit using the one or more UE uplink beams. For example, the UE <NUM> may transmit information, such as one or more SRS (e.g., according to the SRS configuration), to the base station <NUM> using the one or more UE uplink beams. In some aspects, the UE <NUM> may select a UE uplink beam for an SRS resource based at least in part on an SRS configuration for the SRS resource and/or a determination of whether the UE <NUM> is to use distinct UE beam pairs for uplink and downlink communications, and may transmit SRS on the selected UE uplink beam for the SRS resource.

By determining whether to use distinct UE beam pairs for uplink and downlink communications based at least in part on an inference of whether a base station <NUM> is using SRS to perform downlink operations, the UE <NUM> may allow for accurate downlink channel estimation and/or downlink beam refinement by the base station <NUM> while complying with an MPE constraint. Furthermore, by using different input parameters for UE uplink beam selection based at least in part on determining whether to use distinct UE beam pairs for uplink and downlink beam pairs, the UE <NUM> may also improve performance while complying with the MPE constraint. In this way, the UE <NUM> can implement distinct UE beam pairs as appropriate (e.g., depending on an MPE constraint, an SRS configuration, and/or the like) while permitting the base station <NUM> to correctly perform channel estimation.

Other examples may differ from what was described with respect to <FIG>.

<FIG> shows examples of how a UE <NUM> may use an SRS configuration (e.g., shown as an SRS resource configuration) to infer whether a base station <NUM> is using SRS for downlink operations and/or to determine whether to use distinct UE beam pairs for uplink and downlink communications. In some aspects, the UE <NUM> may implement a single example shown in <FIG>, may implement multiple examples shown in <FIG>, may implement different combinations of examples shown in <FIG> (e.g., in different scenarios), and/or may implement examples other than those shown in <FIG>.

As shown by reference number <NUM>, in some aspects, the UE <NUM> may determine to use distinct UE beam pairs for uplink and downlink communications based at least in part on a determination that SRS resources are not configured for an antenna switching usage and/or that SRS resources are not configured for a codebook usage. For example, if there are not any SRS resources configured for an antenna switching usage, then the base station <NUM> may not be using SRS to acquire downlink CSI. As a result, using distinct beam pairs for uplink and downlink communications will not result in inaccurate downlink channel estimation. Additionally, or alternatively, if there are not any SRS resources configured for a codebook usage, then this may imply that the base station <NUM> is not performing channel estimation (e.g., on the uplink or downlink) for the UE <NUM> using SRS. Thus, the UE <NUM> may use distinct UE beam pairs to improve uplink performance, while complying with an MPE constraint, without negatively impacting downlink performance.

As shown by reference number <NUM>, in some aspects, the UE <NUM> may determine to use distinct UE beam pairs for uplink and downlink communications based at least in part on a determination that SRS resources, configured for an antenna switching usage and/or a codebook usage, are configured with a periodicity that satisfies a threshold. For example, if SRS resources are configured with a long periodicity (e.g., greater than or equal to a threshold, such as <NUM> slots, <NUM> seconds, and/or the like), this may imply that the base station <NUM> is not using SRS for channel estimation because channel estimation using SRS may be unreliable with such a long periodicity for SRS transmissions. Thus, the UE <NUM> may use distinct UE beam pairs to improve uplink performance, while complying with an MPE constraint, without negatively impacting downlink performance.

As shown by reference number <NUM>, in some aspects, the UE <NUM> may determine to use distinct UE beam pairs for uplink and downlink communications based at least in part on a determination that a first SRS resource set is configured with an antenna switching usage and a second SRS resource set is configured with a codebook usage. For example, having SRS configured for both of these usages may imply that the base station <NUM> is not going to use SRS for downlink operations. Thus, the UE <NUM> may use distinct UE beam pairs to improve uplink performance, while complying with an MPE constraint, without negatively impacting downlink performance.

As shown by reference number <NUM>, in some aspects, the UE <NUM> may determine to use the same UE beam pair for uplink and downlink communications if none of the conditions described above (e.g., in connection with reference numbers <NUM>, <NUM>, and <NUM>) are satisfied. For example, the UE <NUM> may determine to use the same UE beam pair for uplink and downlink communications based at least in part on a determination that only a single SRS resource set is configured (e.g., with an antenna switching usage or a codebook usage), based at least in part on a determination that all configured SRS resource sets are configured with the same usage, and/or the like. These SRS configurations may imply that the base station <NUM> uses SRS for downlink operations. Thus, the UE <NUM> may use the same beam pair for uplink and downlink communications to avoid negatively impacting downlink performance.

<FIG> shows examples of how a UE <NUM> may use an SRS configuration and/or a determination of whether to use distinct UE beam pairs for uplink and downlink communications to select one or more UE uplink beams. In some aspects, the UE <NUM> may implement a single example shown in <FIG>, may implement multiple examples shown in <FIG>, may implement different combinations of examples shown in <FIG> (e.g., in different scenarios), and/or may implement examples other than those shown in <FIG>.

As shown by reference number <NUM>, for a codebook SRS resource, the UE <NUM> may use a joint metric (e.g., as described above in connection with <FIG>) to select UE uplink beam(s) based at least in part on a determination that the UE <NUM> is to use a same UE beam pair for uplink and downlink communications. For example, the UE <NUM> may select a single UE beam pair for uplink and downlink communications (e.g., shown as UE beam to denote a single UE uplink beam), or may select multiple UE beam pairs that are each used for both uplink and downlink communications (e.g., shown as UE beam pair to denote two UE uplink beams). In some aspects, the UE <NUM> may select a single UE beam pair for uplink and downlink communications if a single antenna port is configured for the codebook SRS resource (e.g., in a specific time resource). In some aspects, the UE <NUM> may select multiple (e.g., shown as two) UE beam pairs, that are each used for both uplink and downlink communications, if multiple (e.g., shown as two) antenna ports configured for the codebook SRS resource (e.g., in a specific time resource). As further shown, the UE <NUM> may map SRS resources to beams (e.g., an individual UE uplink beam of a pair of UE uplink beams having the same polarization (pol) or different polarizations) based at least in part on a number of SRS resources and/or a number of antenna ports indicated in the SRS configuration.

As shown by reference number <NUM>, for the codebook SRS resource, the UE <NUM> may use an uplink metric (e.g., as described above in connection with <FIG>) to select UE uplink beam(s) based at least in part on a determination that the UE <NUM> is to use distinct UE beam pairs for uplink and downlink communications. As indicated above, the UE <NUM> may select a single UE beam pair for uplink and downlink communications if a single antenna port is configured for the codebook SRS resource, or may select multiple (e.g., shown as two) UE beam pairs, that are each used for both uplink and downlink communications, if multiple (e.g., shown as two) antenna ports configured for the codebook SRS resource. As also indicated above, the UE <NUM> may map SRS resources to beams based at least in part on a number of SRS resources and/or a number of antenna ports indicated in the SRS configuration.

As shown by reference number <NUM>, for an antenna switching SRS resource, the UE <NUM> may select UE uplink beam(s) for SRS as the same UE uplink beam(s) selected for the PDSCH (and/or another channel) if a spatial reference configuration for the SRS resources is the same as a spatial reference configuration for the PDSCH (and/or the other channel). If those spatial references are not the same, then the UE <NUM> may use a downlink metric (e.g., as described above in connection with <FIG>) to select the UE uplink beam(s) for SRS. As described above, the UE <NUM> may map SRS resources to UE uplink beams based at least in part on a number of SRS resources and/or a number of antenna ports indicated in the SRS configuration.

<FIG> is a diagram illustrating an example process <NUM> performed, for example, by a UE, in accordance with various aspects of the present disclosure. Example process <NUM> is an example where a UE (e.g., UE <NUM> and/or the like) performs operations associated with uplink beam selection in millimeter wave using an SRS configuration.

As shown in <FIG>, in some aspects, process <NUM> may include determining whether to use distinct UE beam pairs for uplink and downlink communications with a base station based at least in part on a sounding reference signal (SRS) configuration for the UE (block <NUM>). For example, the UE (e.g., using controller/processor <NUM> and/or the like) may determine whether to use distinct UE beam pairs for uplink and downlink communications with a base station based at least in part on an SRS configuration for the UE, as described above.

As shown in <FIG>, in some aspects, process <NUM> may include selecting one or more UE uplink beams for communicating with the base station based at least in part on determining whether to use the distinct UE beam pairs for uplink and downlink communications (block <NUM>). For example, the UE (e.g., using controller/processor <NUM> and/or the like) may select one or more UE uplink beams for communicating with the base station based at least in part on determining whether to use the distinct UE beam pairs for uplink and downlink communications, as described above.

As shown in <FIG>, in some aspects, process <NUM> may include transmitting using the one or more UE uplink beams (block <NUM>). For example, the UE (e.g., using controller/processor <NUM>, transmit processor <NUM>, TX MIMO processor <NUM>, MOD <NUM>, antenna <NUM>, and/or the like) may transmit using the one or more UE uplink beams, as described above.

Process <NUM> may include additional aspects, such as any single aspect and/or any combination of aspects described below and/or in connection with one or more other processes described elsewhere herein.

In some aspects, the SRS configuration is for at least one of an antenna switching usage, a codebook usage, or a combination thereof. In some aspects, transmitting using the one or more UE uplink beams comprises transmitting SRS using the one or more UE uplink beams based at least in part on the SRS configuration. In some aspects, the determination of whether to use distinct UE beam pairs is based at least in part on at least one of: a number of SRS resource sets configured for one or more SRS usages, whether an SRS resource is included in multiple SRS resource sets associated with different SRS usages, a time domain configuration indicated by the SRS configuration, a periodicity indicated by the SRS configuration, a spatial reference configuration indicated by the SRS configuration, or a combination thereof.

In some aspects, the UE is configured to use the distinct UE beam pairs based at least in part on a determination that SRS resources are not configured for an antenna switching usage, a codebook usage, or a combination thereof. In some aspects, the UE is configured to use the distinct UE beam pairs based at least in part on a determination that SRS resources for at least one of an antenna switching usage or a codebook usage are configured with a periodicity that satisfies a threshold. In some aspects, the UE is configured to use the distinct UE beam pairs based at least in part on a determination that a first SRS resource set is configured with an antenna switching usage and a second SRS resource set is configured with a codebook usage. In some aspects, the UE is configured to use a same UE beam pair for uplink and downlink communications with the base station based at least in part on a determination that: only a single SRS resource set is configured, or all SRS resource sets are configured with a same SRS usage.

In some aspects, the one or more UE uplink beams are selected for an SRS resource based at least in part on the SRS configuration. In some aspects, the one or more UE uplink beams are selected for an SRS resource based at least in part on at least one of: an SRS usage of the SRS resource, whether the SRS resource is included in multiple SRS resource sets with different SRS usages, a number of antenna ports configured for the SRS resource, a spatial reference configuration for the SRS resource, a spatial reference configuration for a physical channel, a number of SRS resources included in an SRS resource set that includes the SRS resource, a number of SRS resource sets with a same usage as the SRS resource, or a combination thereof.

In some aspects, the one or more UE uplink beams are selected for an SRS resource based at least in part on at least one of: only an uplink metric, only a downlink metric, or a joint metric that is based at least in part on one or more uplink parameters and one or more downlink parameters.

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>, <NUM>), of wireless communication performed by a user equipment, UE (<NUM>) comprising:
determining (<NUM>, <NUM>), for a candidate UE uplink beam, a transmit power due to a maximum permissible exposure, MPE, constraint;
estimating (<NUM>, <NUM>), for the candidate UE uplink beam, a receive power for a base station based at least in part on the transmit power due to the MPE constraint;
determining (<NUM>, <NUM>) a target receive power for the base station; and
selecting (<NUM>, <NUM>) the candidate UE uplink beam as an active UE uplink beam based at least in part on the estimated receive power for the base station (<NUM>) and the target receive power for the base station (<NUM>).