Patent Description:
Examples of such multiple-access systems include fourth generation (<NUM>) systems such as a Long Term Evolution (LTE) systems or LTE-Advanced (LTE-A) systems, and fifth generation (<NUM>) systems which may be referred to as New Radio (NR) systems. These systems may employ technologies such as code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), orthogonal frequency division multiple access (OFDMA), or discrete Fourier transform-spread-OFDM (DFT-S-OFDM). HUAWEI ET AL: "Beam management across multiple carriers" discusses beam management across multiple carriers. HUAWEI ET AL: "Cross-carrier beam management" discusses cross-carrier beam management.

The described techniques relate to improved methods, systems, devices, or apparatuses that support cross-band quasi-co-located (QCL) beam determination. Specific embodiments are defined in the dependent claims.

A method of wireless communication is described. The method may include identifying a characteristic of a first beam associated with a first antenna array, determining a second beam associated with a second antenna array as a quasi-co-located beam with respect to the first beam based on the characteristic, and communicating on the first and second beams based on the determining.

An apparatus for wireless communication is described. The apparatus may include a processor, a memory in electronic communication with the processor, and instructions stored in the memory. The instructions may be executable by the processor to cause the apparatus to identify a characteristic of a first beam associated with a first antenna array, determine a second beam associated with a second antenna array as a quasi-co-located beam with respect to the first beam based on the characteristic, and communicate on the first and second beams based on the determining.

A non-transitory computer readable medium storing code for wireless communication is described. The code may include instructions executable by a processor to identify a characteristic of a first beam associated with a first antenna array, determine a second beam associated with a second antenna array as a quasi-co-located beam with respect to the first beam based on the characteristic, and communicate on the first and second beams based on the determining.

Another apparatus for wireless communication is described. The apparatus may include means for identifying a characteristic of a first beam associated with a first antenna array, means for determining a second beam associated with a second antenna array as a quasi-co-located beam with respect to the first beam based on the characteristic, and means for communicating on the first and second beams based on the determining.

In some examples of the method, apparatuses, or non-transitory computer-readable medium described herein, the first antenna array is associated with analog beams and the second antenna array is associated with digital beams. In some instances, the first antenna array is associated with a first frequency band and the second antenna array is associated with a second frequency band. In some instances, the characteristic comprises at least one of a radiation pattern, a peak beam direction, or a received power of the first beam. In some instances, the determining comprises adjusting beam weights of the second beam to substantially match the radiation pattern of the first beam and designating the second beam as a cross-band quasi-co-located beam with respect to the first beam. In some instances, the determining comprises determining the second beam having a phased array beam steering with a steered direction most aligned with the peak beam direction of the first beam relative to other beams associated with the second antenna array and designating the second beam as a cross-band quasi-co-located beam with respect to the first beam. In some cases, the received power is higher than received power of other beams associated with the first antenna array and higher than a threshold power.

In some instances, the determining comprises sending a request on a first frequency band to a base station for a training signal on a second frequency band with a second frequency band transmit beam matching a beam pattern and peak beam direction of a first frequency band transmit beam, receiving the training signal, determining the second beam having a phased array beam steering with a steered direction such that a received power of the second beam is higher than other beams associated with the second antenna array, and designating the second beam as a cross-band quasi-co-located beam with respect to the first beam. Some examples of the method, apparatuses, or non-transitory computer-readable medium described herein may further include processes, features, means, or instructions for iteratively sending requests to at least one different base station for training signals to determine the second beam. Some examples of the method, apparatuses, or non-transitory computer-readable medium described herein may further include processes, features, means, or instructions for determining, for each beam associated with the first antenna array, at least one quasi-co-located beam associated with the second antenna array based on a characteristic of each beam. Some examples of the method, apparatuses, or non-transitory computer-readable medium described herein may further include processes, features, means, or instructions for identifying a change in form factor of a wireless device containing the first and second antenna arrays and determining, for at least one beam associated with the first antenna array, at least one different quasi-co-located beam associated with the second antenna array in response to the change in form factor.

Some examples of the method, apparatuses, or non-transitory computer-readable medium described herein may further include processes, features, means, or instructions for receiving an indicator to measure a reference signal via a quasi-co-located beam with respect to the first beam and measuring the reference signal on the second beam based on the indicator. In some instances, the first beam is a beam having received power that is higher than received power of other beams associated with the first antenna array. Some examples of the method, apparatuses, or non-transitory computer-readable medium described herein may further include processes, features, means, or instructions for receiving a request to report a beam identification of the first beam, reporting the beam identification of the first beam, and receiving an indicator to measure a reference signal on a beam quasi-co-located with respect to the first beam having the beam identification. In some cases, the beam identification comprises an identification number of a synchronization signal block (SSB), a channel state information reference signal (CSI-RS), or a sounding reference signal (SRS). Some examples of the method, apparatuses, or non-transitory computer-readable medium described herein may further include processes, features, means, or instructions for receiving a transmit beam identification indicating a beam used for transmission on a frequency band associated with the first antenna array, identifying the second beam associated with the second antenna array and quasi-co-located with respect to a receive beam corresponding to the transmit beam identification, and measuring a reference signal using the second beam.

A method of wireless communication performed by a base station is described. The method may include identifying a user equipment (UE) searching for a connection with a secondary cell on a second frequency band, wherein the UE is served by the base station on a first frequency band and transmitting an indicator to the UE to inform the UE regarding selection of a particular beam for measuring a reference signal from the secondary cell.

An apparatus for wireless communication is described. The apparatus may include a processor, a memory in electronic communication with the processor, and instructions stored in the memory. The instructions may be executable by the processor to cause the apparatus to identify a user equipment (UE) searching for a connection with a secondary cell on a second frequency band, wherein the UE is served by a base station on a first frequency band and transmit an indicator to the UE to inform the UE regarding selection of a particular beam for measuring a reference signal from the secondary cell.

A non-transitory computer readable medium storing code for wireless communication is described. The code may include instructions executable by a processor to identify a user equipment (UE) searching for a secondary cell connection on a second frequency band, wherein the UE is served by a base station on a first frequency band and transmit an indicator to the UE to inform the UE regarding selection of a particular beam for measuring a reference signal from the secondary cell.

An apparatus for wireless communication is described. The apparatus may include means for identifying a user equipment (UE) searching for a secondary cell connection on a second frequency band, wherein the UE is served by a base station on a first frequency band and means for transmitting an indicator to the UE to inform the UE regarding selection of a particular beam for measuring a reference signal from the secondary cell.

In some instances, the secondary cell is co-located with the base station. Some examples of the method, apparatuses, or non-transitory computer-readable medium described herein may further include processes, features, means, or instructions for signaling the secondary cell to transmit reference signals in a direction aligned with a transmit beam used to transmit the indicator or with the particular beam. In some instances, the indicator comprises an instruction to measure the reference signal in a direction substantially aligned with a receive beam used to receive transmissions from the base station on the first frequency band. In some instances, the indicator comprises a beam identification number of a receive beam used to receive transmissions from the base station on the first frequency band. Some examples of the method, apparatuses, or non-transitory computer-readable medium described herein may further include processes, features, means, or instructions for requesting the UE to report the beam identification number. In some cases, the indicator comprises a beam identification number of a transmit beam used to send transmissions from the base station to the UE on the first frequency band. In some cases, the indicator is included in a reference signal measurement configuration transmission to the UE.

Wireless devices may use multiple antenna arrays for communications on different frequency bands. A user equipment (UE), for example, may dedicate a first antenna array to a frequency band below <NUM> (sub-<NUM> band) and a second antenna array to a different frequency band, such as a millimeter wave (mmW) band (e.g., <NUM>). In some instances, if a base station (e.g., gNB) serving the UE on the frequency band used by the first antenna array is co-located with a second base station serving the UE on the frequency band used by the second antenna array, the UE may benefit from determining which beam(s) associated with antenna(s) in the first antenna array correspond with beam(s) associated with antenna(s) in the second antenna array in terms of similarity in beam pattern and direction. This is known as determination of cross-band quasi-co-located (QCL) beams, and a UE with known cross-band QCL beams may use information related to one set of beams on one frequency band to determine the ideal beams from a second set of beams to use for communications on a second frequency band, resulting in power savings and increased operational efficiency.

In some instances, however, the antenna distribution for different antenna arrays may be distributed differently across the UE. Further, each antenna array may have different numbers of antennas. The arrangement and configuration of antennas in different antenna arrays may be based in part on the type of antennas and the frequency band in which the antenna array is intended to operate. In some examples, antenna elements in a first array that are used for sub-<NUM> communications may be distributed at different locations of the UE and form digital beams (e.g., beam weights are dynamically computed based on certain metrics), while antenna elements in a second array used for mmW communications may form analog beams. Accordingly, the distribution, number, and types of beams formed by antenna arrays for different bands may have different shapes and widths, making it difficult for the UE to determine which beams associated with a first antenna array are cross-band QCL with beams associated with a second antenna array.

In order to determine cross-band QCL beams for two example beam sets, in some instances, for each beam in a first beam set, a corresponding beam pattern is computed for beam(s) of a second beam set that most closely aligns with the beam pattern for each beam in the first beam set. In another example, for each beam in the first beam set, a corresponding peak beam direction is computed for beam(s) of the second beam set that most closely aligns with the peak beam direction for each beam in the first beam set. In some instances, a UE and base station may coordinate efforts to determine cross-band QCL beam sets at the UE, such as by the UE requesting the base station to send training signals on one frequency band using particular beams that are most likely to align with an ideal predetermined beam on a different frequency band. The cross-band QCL beam determination may further be refined, such as by performing the training operations with multiple base stations to filter out variations that may be a function of the propagation environment. The training operations may also be dynamically repeated in response to changes in antenna arrangement, such as changes in form-factor configurations (e.g., bendable or folding devices).

The determination of cross-band QCL beams for a UE may have benefits including improved operational efficiency, extended range, and reduced power consumption. In one example, a UE may typically perform a beam sweeping procedure where it turns on multiple receive beams in all directions in order to receive reference signals from a base station, especially if the UE is not aware of the arrival angle of the reference signals. Likewise, the base station may need to send reference signals in multiple directions if it does not know the direction at which the UE will receive the reference signals. As described further herein, the base station and UE may use information gathered from beam management procedures regarding ideal transmit and receive beams for a frequency band associated with one base station to coordinate beam patterns and directions for reference signals sent by a co-located base station on other frequency bands. The coordination of reference signal via certain beams may reduce beam sweep overhead and allow for extended range with narrower beams in a particular direction.

Aspects of the disclosure are initially described in the context of a wireless communications system. Aspects of the disclosure are further illustrated by and described with reference to apparatus diagrams, system diagrams, and flowcharts that relate to cross-band QCL determination and application, including for initial beam selection. The detailed description set forth below, in connection with the appended drawings and appendix, is intended as a description of various configurations and is not intended to limit the scope of the disclosure. Rather, the detailed description includes specific details for the purpose of providing a thorough understanding of the present disclosure.

This disclosure relates generally to determining cross-band QCL beams from different sets of beams where the different beam sets may be used for communication on different frequency bands with co-located base stations. In various embodiments, the techniques and apparatus may be used for wireless communication networks such as code division multiple access (CDMA) networks, time division multiple access (TDMA) networks, frequency division multiple access (FDMA) networks, orthogonal FDMA (OFDMA) networks, single-carrier FDMA (SC-FDMA) networks, LTE networks, GSM networks, as well as other communications networks. As described herein, the terms "networks" and "systems" may be used interchangeably.

3GPP Long Term Evolution (LTE) is a 3GPP project which was aimed at improving the universal mobile telecommunications system (UMTS) mobile phone standard. The present disclosure is concerned with the evolution of wireless technologies from LTE, <NUM>, <NUM>, and beyond with shared access to wireless spectrum between networks using a collection of new and different radio access technologies or radio air interfaces.

In particular, <NUM> networks contemplate diverse deployments, diverse spectrum, and diverse services and devices that may be implemented using an OFDM-based unified, air interface. In order to achieve these goals, further enhancements to LTE and LTE-A are considered in addition to development of a new radio (NR) technology. The <NUM> NR will be capable of scaling to provide coverage (<NUM>) to a massive Internet of things (IoTs) with an ultra-high density (e.g., ~<NUM> nodes/km2), ultra-low complexity (e.g., ~<NUM> of bits/sec), ultra-low energy (e.g., -<NUM>+ years of battery life), and deep coverage with the capability to reach challenging locations; (<NUM>) including mission-critical control with strong security to safeguard sensitive personal, financial, or classified information, ultra-high reliability (e.g., -<NUM>% reliability), ultra-low latency (e.g., ∼ <NUM>), and users with wide ranges of mobility or lack thereof; and (<NUM>) with enhanced mobile broadband including extreme high capacity (e.g., ∼ <NUM> Tbps/km2), extreme data rates (e.g., multi-Gbps rate, <NUM>+ Mbps user experienced rates), and deep awareness with advanced discovery and optimizations.

The <NUM> NR may be implemented to use optimized OFDM-based waveforms with scalable numerology and transmission time interval (TTI); having a common, flexible framework to efficiently multiplex services and features with a dynamic, low-latency time division duplex (TDD)/frequency division duplex (FDD) design; and with advanced wireless technologies, such as massive multiple input, multiple output (MIMO), robust millimeter wave (mmWave) transmissions, advanced channel coding, and device-centric mobility. Scalability of the numerology in <NUM> NR, with scaling of subcarrier spacing, may efficiently address operating diverse services across diverse spectrum and diverse deployments. For example, in various outdoor and macro coverage deployments of less than <NUM> FDD/TDD implementations, subcarrier spacing may occur with <NUM>, for example over <NUM>, <NUM>, <NUM>, <NUM>, and the like bandwidth. For other various outdoor and small cell coverage deployments of TDD greater than <NUM>, subcarrier spacing may occur with <NUM> over <NUM>/<NUM> bandwidth, for example. For other various indoor wideband implementations, using a TDD over the unlicensed portion of the <NUM> band, the subcarrier spacing may occur with <NUM> over a <NUM> bandwidth, for example. Finally, for various deployments transmitting with mmWave components at a TDD of <NUM>, subcarrier spacing may occur with <NUM> over a <NUM> bandwidth, for example. Other deployments of different subcarrier spacing over different bandwidths are also within the scope of the present disclosure.

The scalable numerology of <NUM> NR facilitates scalable TTI for diverse latency and quality of service (QoS) requirements. The efficient multiplexing of long and short TTIs may allow transmissions to start on symbol boundaries.

<FIG> illustrates an example of a wireless communications system <NUM> that supports cross-band QCL determination and application in accordance with various aspects of the present disclosure. The wireless communications system <NUM> includes base stations <NUM>, UEs <NUM>, and a core network <NUM>. In some examples, the wireless communications system <NUM> may be a Long Term Evolution (LTE) network, an LTE-Advanced (LTE-A) network, or a New Radio (NR) network. In some cases, wireless communications system <NUM> may support enhanced broadband communications, ultra-reliable (e.g., mission critical) communications, low latency communications, or communications with low-cost and low-complexity devices.

The wireless communications system <NUM> may include, for example, a heterogeneous LTE/LTE-A or NR network in which different types of base stations <NUM> provide coverage for various geographic coverage areas <NUM>.

In some cases, this may facilitate use of antenna arrays within a UE <NUM> (e.g., for multiple-input multiple-output (MIMO) operations such as spatial multiplexing, or for directional beamforming).

For example, wireless communications system <NUM> may employ LTE License Assisted Access (LTE-LAA) or LTE-Unlicensed (LTE-U) radio access technology or NR technology in an unlicensed band such as the <NUM> ISM band. In some cases, operations in unlicensed bands may be based on a CA configuration in conjunction with CCs operating in a licensed band.

In some cases, the antennas of a base station <NUM> or UE <NUM> may be located within one or more antennas or antenna arrays, which may support MIMO operations such as spatial multiplexing, or transmit or receive beamforming. The UE <NUM> may use beams associated with a first antenna array for communications on a first frequency band and beams associated with a second antenna array for communications on a second frequency band. Determining which beams associated with the first antenna array are cross-band QCL with respect to beams associated with the second antenna array may improve communication efficiency and power consumption when the base stations <NUM> serving the UE <NUM> for the two frequency bands are co-located.

MIMO wireless systems use a transmission scheme between a transmitting device (e.g., a base station <NUM>) and a receiving device (e.g., a UE <NUM>), where both transmitting device and the receiving device are equipped with multiple antennas. MIMO communications may employ multipath signal propagation to increase the utilization of a radio frequency spectrum band by transmitting or receiving different signals via different spatial paths, which may be referred to as spatial multiplexing. The different signals may, for example, be transmitted by the transmitting device via different antennas or different combinations of antennas. Likewise, the different signals may be received by the receiving device via different antennas or different combinations of antennas. Each of the different signals may be referred to as a separate spatial stream, and the different antennas or different combinations of antennas at a given device (e.g., the orthogonal resource of the device associated with the spatial dimension) may be referred to as spatial layers.

Beamforming, which may also be referred to as spatial filtering, directional transmission, or directional reception, is a signal processing technique that may be used at a transmitting device or a receiving device (e.g., a base station <NUM> or a UE <NUM>) to shape or steer an antenna beam (e.g., a transmit beam or receive beam) along a direction between the transmitting device and the receiving device. The adjustment of signals communicated via the antenna elements may include a transmitting device or a receiving device applying certain phase offset, timing advance/delay, or amplitude adjustment to signals carried via each of the antenna elements associated with the device.

In one example, a base station <NUM> may multiple use antennas or antenna arrays to conduct beamforming operations for directional communications with a UE <NUM>. For instance, signals may be transmitted multiple times in different directions, which may include a signal being transmitted according to different beamforming weight sets associated with different directions of transmission. A receiving device (e.g., a UE <NUM>, which may be an example of a mmW receiving device) may try multiple receive beams when receiving various signals from the base station <NUM>, such as synchronization signals or other control signals.

Time intervals of a communications resource may be organized according to radio frames each having a duration of <NUM> milliseconds (Tf = <NUM> * Ts). Each frame may include ten subframes numbered from <NUM> to <NUM>, and each subframe may have a duration of <NUM> millisecond. A subframe may be further divided into two slots each having a duration of <NUM> milliseconds, and each slot may contain <NUM> or <NUM> modulation symbol periods (e.g., depending on the length of the cyclic prefix prepended to each symbol period). In some cases a subframe may be the smallest scheduling unit of the wireless communications system <NUM>, and may be referred to as a transmission time interval (TTI).

In some wireless communications systems, a slot may further be divided into multiple mini-slots containing one or more symbols and in some instances, a symbol of a mini-slot or a mini-slot may be the smallest unit of scheduling. Some wireless communications systems may implement slot aggregation in which multiple slots or mini-slots may be aggregated together for communication between a UE <NUM> and a base station <NUM>.

A resource element may consist of one symbol period (e.g., a duration of one modulation symbol) and one subcarrier (e.g., a <NUM> frequency range). A resource block may contain <NUM> consecutive subcarriers in the frequency domain (e.g., collectively forming a "carrier") and, for a normal cyclic prefix in each orthogonal frequency-division multiplexing (OFDM) symbol, <NUM> consecutive OFDM symbol periods in the time domain (<NUM> slot), or <NUM> total resource elements across the frequency and time domains. The number of bits carried by each resource element may depend on the modulation scheme (the configuration of modulation symbols that may be applied during each symbol period). Thus, the more resource elements that a UE <NUM> receives and the higher the modulation scheme (e.g., the higher the number of bits that may be represented by a modulation symbol according to a given modulation scheme), the higher the data rate may be for the UE <NUM>. In MIMO systems, a wireless communications resource may refer to a combination of a radio frequency spectrum band resource, a time resource, and a spatial resource (e.g., spatial layers), and the use of multiple spatial layers may further increase the data rate for communications with a UE <NUM>.

The term "carrier" refers to a set of radio frequency spectrum resources having a defined organizational structure for supporting uplink or downlink communications over a communication link <NUM>. For example, a carrier of a communication link <NUM> may include a portion of a radio frequency spectrum band that may also be referred to as a frequency channel. In some examples a carrier may be made up of multiple sub-carriers (e.g., waveform signals of multiple different frequencies). A carrier may be organized to include multiple physical channels, where each physical channel may carry user data, control information, or other signaling.

The organizational structure of the carriers may be different for different radio access technologies (e.g., LTE, LTE-A, NR, etc.).

For example, the carrier bandwidth may be one of a number of predetermined bandwidths for carriers of a particular radio access technology (e.g., <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM>). In some examples the system bandwidth may refer to a minimum bandwidth unit for scheduling communications between a base station <NUM> and a UE <NUM>. In other examples a base station <NUM> or a UE <NUM> may also support communications over carriers having a smaller bandwidth than the system bandwidth. In such examples, the system bandwidth may be referred to as "wideband" bandwidth and the smaller bandwidth may be referred to as a "narrowband" bandwidth. In some examples of the wireless communications system <NUM>, wideband communications may be performed according to a <NUM> carrier bandwidth and narrowband communications may be performed according to a <NUM> carrier bandwidth.

Devices of the wireless communications system <NUM> (e.g., base stations or UEs <NUM>) may have a hardware configuration that supports communications over a particular carrier bandwidth, or may be configurable to support communications over one of a set of carrier bandwidths. For example, base stations <NUM> or UEs <NUM> may perform some communications according to a system bandwidth (e.g., wideband communications), and may perform some communications according to a smaller bandwidth (e.g., narrowband communications). In some examples, the wireless communications system <NUM> may include base stations <NUM> and/or UEs that can support simultaneous communications via carriers associated with more than one different bandwidth.

Wireless communications systems such as an NR system may use a combination of licensed, shared, and unlicensed spectrum bands, among others. The flexibility of eCC symbol duration and subcarrier spacing may allow for the use of eCC across multiple spectrums. In some examples, NR shared spectrum may increase spectrum utilization and spectral efficiency, specifically through dynamic vertical (e.g., across frequency) and horizontal (e.g., across time) sharing of resources.

As depicted in <FIG>, a UE <NUM> may communicate over wireless communication links <NUM> with multiple gNBs <NUM> using different frequency bands. For example, the UE <NUM> may communicate on a sub-<NUM> band using digital beams from a first antenna array and on a mmW band using analog beams from a second antenna array. In some instances, the gNB <NUM> serving the UE <NUM> on the sub-<NUM> band is co-located with the gNB <NUM> serving the UE <NUM> on the mmW band. The UE <NUM> may determine the beams for the sub-<NUM> band that are cross-band QCL with beams for the mmW band using beam management procedures described further herein. In some instances, the UE <NUM> may send a request across communication link <NUM> to the gNB <NUM> for the gNB <NUM> to send training signals to assist the UE <NUM> in determination of cross-band QCL beams. Other procedures are also described herein for determining and applying cross-band QCL beams.

<FIG> illustrates a wireless communication system <NUM> that supports determination and application of cross-band QCL beams in accordance with various aspects of the present disclosure. As seen in <FIG>, gNB <NUM>-A may use multiple transmit and/or receive beams <NUM> to communicate with UEs <NUM> within its geographical coverage area <NUM>-A. The UEs <NUM> may similarly use multiple transmit/receive beams <NUM> to communicate with the gNB <NUM>-A. In some cases, each of the transmit beams <NUM> sent by gNB <NUM>-A may be in a different direction. Accordingly, certain beams (e.g., <NUM>-A and <NUM>-B) sent by the gNB <NUM>-A will be more suited for one UE <NUM>-A while other beams (e.g., <NUM>-C and <NUM>-D) sent by the gNB <NUM>-A will be better suited for another UE <NUM>-B, depending on the direction of the transmit beams and the location of the receiving UE <NUM> relative to those beams. Further, each UE <NUM> may use different receive beams <NUM> to receive transmissions from the gNB <NUM>-A. The receive beams <NUM> that are more closely aligned with the direction of the transmit beams <NUM> from the gNB <NUM>-A will be more ideal for receiving those transmissions. For example, a UE <NUM>-B may determine that beam <NUM>-D is most ideal for receiving transmit beam <NUM>-D based on determining that the received power on receive beam <NUM>-D is greater than received power on other receive beams at the UE <NUM>-B.

The UE <NUM>-B and gNB <NUM>-A may perform training procedures to determine the appropriate transmit/receive beams <NUM> and <NUM> for communication between UE <NUM>-B and gNB <NUM>-A. In some instances, the UE <NUM>-B may use a second set of beams <NUM> for communication on a different frequency band with a different gNB <NUM>-B. Here, the UE <NUM>-B may need to perform beam training procedures similar to those used for the first set of beams <NUM> to determine which of the second set of beams <NUM> is ideally used for communication with gNB <NUM>-B. Likewise, gNB <NUM>-B may need to perform beam sweeping procedures to send synchronization signals and the like in multiple directions to cover UEs <NUM> within its geographical coverage area, and/or perform beam training procedures to locate the ideal beams for communication with known UEs <NUM>.

In some instances, however, gNB <NUM>-B may be co-located with gNB <NUM>-A. Accordingly, the transmit and receive beams used by the gNBs <NUM> for communication with a particular UE <NUM> may have similar angle of arrival, signal strength, and other similar characteristics. As such, the UE <NUM> may determine which beams from the first set of beams <NUM> are cross-band QCL with respect to beams from the second set of beams <NUM>, as described in further detail herein, to reduce overhead signaling and beam training resources.

<FIG> shows an example antenna configuration <NUM> of a wireless device <NUM> that supports cross-band QCL determination in accordance with aspects of the present disclosure. The wireless device <NUM> may be a UE <NUM> or a base station <NUM> with multiple antenna arrays. The wireless device <NUM> may use different antenna arrays for communications on different frequency bands. For example, the wireless device <NUM> may have a first antenna array 310A that is used for communications on a sub-<NUM> band while a second antenna array 310B is used for communications on a mmW band. The antenna elements for the antenna arrays <NUM> may be distributed at different locations throughout the wireless device <NUM>, and the first antenna array 310A may have different number of antennas compared to the second antenna array 310B. Further, communications on different frequency bands may, in some instances, require different types of beams. For example, the first antenna array 310A for communication on the sub-<NUM> band may form digital beams, where the beam weights arc dynamically computed based on certain metrics. The second antenna array 310B for communication on the mmW band, however, may form analog beams, where the beam weights are preconfigured and common across the operation band. Various limitations associated with communications on the mmW band may mean analog beams are better suited for mmW communications. Accordingly, the formed beams associated with the first antenna array 310A may have different shapes and widths compared to formed beams associated with the second antenna array 310B.

<FIG> depicts example sets of beams <NUM> formed by different antenna arrays <NUM> of a wireless device such as UE <NUM> or base station <NUM>. As seen in <FIG>, a wireless device <NUM> may use a first antenna array 405A to communicate on a sub-<NUM> frequency band and a second antenna array 405B to communicate on a mmW frequency band. In the illustrated example, the first antenna array 405A may form digital beams 410A-480A for communication on the sub-<NUM> band. The second antenna array 405B may form analog beams 410B-480B for communication on the mmW band. Although <FIG> shows antenna arrays 405A and 405B having a same number of beams allowing a one-to-one cross-band QCL mapping between the beam sets, different numbers of beams for the two antenna arrays 405A and 405B are also possible. Further, the two beam sets may be used for communication on different bands within the same frequency range (e.g., both beam sets operating in sub-<NUM> bands or in mmW bands).

The wireless device <NUM> may determine which beams from the first beam set 400A are cross-band QCL with respect to beams from the second beam set 400B. The cross-band QCL mapping may help determine which beams from the two beam sets 400A and 400B are most ideal for communication on different frequency bands if the arriving or transmitted signal have similar angle of arrival or transmission. In the illustrated example, for a given analog beam set 400B, the wireless device <NUM> may determine a mapping with digital beam set 400A such that the best beam in set 400B can indicate the best beam in set 400A for arriving signals having the same arrival angle, and vice versa. For example, the wireless device <NUM> may be a UE <NUM> that receives a signal 401B on the mmW band with a particular angle of arrival as shown in <FIG>. If the UE <NUM> has determined the cross-band QCL mapping between the beam sets 400A and 400B, the incoming signal 401B received via beam 430B may indicate the appropriate beam 460A to use for receiving an incoming signal 401A having a similar angle of arrival on the sub-<NUM> band, if the signals 401A and 401B are transmitted by co-located base stations. Accordingly, the UE <NUM> may reduce beam training overhead and power consumption with the cross-band QCL mapping.

Various procedures for determining cross-band QCL mapping are within the scope of the present disclosure. In some instances, the wireless device <NUM> may determine and configure cross-band QCL beams based on matching beam patterns. In the illustrated example, for each analog beam in beam set 400B of UE <NUM>, a corresponding digital beam pattern may be computed that most closely matches the analog beam pattern. The computed digital beams that substantially match different analog beams in beam set 400B will form beam set 400A. In some instances, the radiation pattern of a given analog beam is measured, e.g., in a chamber. The beam weights of the digital beam are adjusted such that the radiation pattern of the digital beam substantially match the analog beam pattern, e.g., by minimizing the maximum gap between the analog and beam patterns. The analog beam and the digital beam having a beam pattern that most closely matches the pattern of the analog beam are then recorded or designated as cross-band QCL mapped.

Alternatively, or in addition, the cross-band QCL mapping may be determined based on peak beam directions. In the illustrated example, for each analog beam in beam set 400B of UE <NUM>, a corresponding digital beam having a peak direction that substantially aligns with that of the analog beam is determined. In some instances, the radiation pattern of a given analog beam is measured, and the peak beam direction of the beam is identified. The phased array beam steering with the steered direction aligned with the analog beam is the corresponding digital beam. The analog beam and the digital beam having peak beam direction most aligned with the peak beam direction of the analog beam are then recorded or designated as cross-band QCL mapped.

In some instances, a base station <NUM> and UE <NUM> may coordinate efforts to determine cross-band QCL beams, such as through over-the-air procedures without the need of offline calibration. For example, a UE <NUM> may request a base station <NUM> to assist the UE <NUM> in computing a digital beam that most closely matches an analog beam, as illustrated in <FIG>.

<FIG> illustrate example procedures for coordination between a UE <NUM> and base station <NUM> for determining cross-band QCL beams. In <FIG>, a UE <NUM> identifies a downlink signal <NUM> on a mmW frequency band sent by a mmW base station 105B on a transmission beam 530B that results in a highly directional beam as received at the UE <NUM>. The highly directional nature of the signal <NUM> may be identified if the received analog beam 430B captures significant power compared to remaining analog beams from antenna array 405B. Based on the highly directional nature of the received signal <NUM>, the UE <NUM> may determine that the analog beam 430B on which the signal <NUM> is received is suitable for determining a cross-band QCL digital beam associated with a sub-<NUM> antenna array 405A.

In response to identification of the highly directional analog beam transmission <NUM>, the UE <NUM> may request a sub-<NUM> base station 105A to send a training signal on the sub-<NUM> band with a digital downlink beam that most closely matches the analog downlink beam 530B used by the mmW base station 105B. As seen in <FIG>, the co-located base stations <NUM> may coordinate to determine a digital transmission beam 530A from base station 105A that has the same peak beam direction and closest beam pattern compared to the analog beam 530B used by base station 105B for transmission of downlink signal <NUM> to the UE <NUM>. Accordingly, both downlink signals <NUM> and <NUM> from the mmW base station 105B and sub-<NUM> base station 105A will arrive at the UE <NUM> having similar angles of arrival to assist the UE <NUM> in beam training procedures.

As seen in <FIG>, having received the highly directional downlink signal <NUM>, the UE <NUM> may compute a receive digital beam 430A on the sub-<NUM> band having a highest receive power or receive power above a threshold. For example, the receive digital beam 430A may be computed based on phased array beam steering with the steered direction matching the angle of arrival of the signal <NUM> on the sub-<NUM> band. The receive beam 430A having greatest receive power relative to other beams or power above a threshold may be designated as the most ideal beam for receiving signals on the sub-<NUM> frequency band from base station 105B. The UE <NUM> can then record or designate the receive analog beam 430B on the mmW band and the receive digital beam 430A on the sub-<NUM> band as cross-band QCL beams. The UE <NUM> can similarly repeatedly perform the beam training procedures in coordination with base station <NUM> to map remaining beams at the UE <NUM>.

The coordinated training procedures between UE <NUM> and base stations <NUM> described with respect to <FIG> ensures that the transmission beams 530A and 530B from the base stations <NUM> have similar transmission radiation pattern for the sub-<NUM> and mmW bands. In some instances, however, the received radiation patterns at the UE <NUM> may differ for sub-<NUM> and mmW frequency bands depending on the propagation environment. Accordingly, the UE <NUM> may repeat the operations described in <FIG> in coordination with other base stations (not shown) or different base station beams. The results from performing cross-band QCL mapping using different base stations or transmission beams may be used to confirm or determine an average cross-band QCL mapping for the beams at the UE <NUM>. For example, if the resulting cross-band QCL pairings are independent of which base station <NUM> or which particular transmission beam is used, the UE <NUM> may have more confidence that the pairing is not a function of channel conditions and accurately captures the UE receive beam shape alignment across the sub-<NUM> and mmW frequency bands.

Although the cross-band QCL mapping procedures described in the examples above are in reference to determining cross-band QCL digital beams in a sub-<NUM> band based on corresponding analog beams in a mmW band, other bands, beam types, procedures, and factors are within the scope of the present disclosure. For example, the operations described above for cross-band QCL determination may be used for band combinations other than sub-<NUM> or mmW frequency bands. The operations described above may also be used between beam sets having the same type, such as between two analog beam sets (e.g., an analog beam set on <NUM> with cross-band QCL mapping to an analog beam set on <NUM>). The operations described above may also be applied to determining cross-band QCL mapping for both transmission beams as well as receive beams using similar techniques as disclosed herein. Further, the operations described above with respect to <FIG>, for example, may be applied by first connecting to a sub-<NUM> base station 105A and then requesting the co-located mmW base station 105B to send training signals for determining cross-band QCL analog beams based on the initially received sub-<NUM> beams.

Still further, the operations described above may be repeated upon changes in environment or physical form-factor changes to the wireless device, for example. In some instances, for example, a UE <NUM> may have variable form-factor configurations such as bendable phones or folding laptops. Here, the UE <NUM> may index the cross-band QCL pairings for the current form-factor configuration and then repeat the operations for determining cross-band QCL mapping if the configuration changes. In some cases, the UE <NUM> may use sensor information, or perform self-calibration, to identify the form-factor configuration at the UE <NUM>. Self-calibration may involve assistance from the network by receiving dummy grants to allow the UE to transmit from some resources while receiving the same signal on other signals.

By determining cross-band QCL mapping for different beam sets, a wireless device may avoid having to perform unnecessary operations associated with beam training or uncertainty as to location of a receiving device. <FIG> illustrate an example application of cross-band QCL determination for improving communication efficiency during initial beam selection. As illustrated in <FIG>, a UE <NUM> is connected to a primary cell (PCell) 105A on sub-<NUM> frequency band and searches for a potential secondary cell (SCell) 105B on a mmW band for carrier aggregation. A potential SCell 105B is co-located with the PCell 105A and sends reference signals (RS) <NUM>, e.g., SSB/CSI-RS, on different beams 630A for initial beam selection by the UE <NUM>. As shown in <FIG>, without knowledge of the location of the UE <NUM>, the SCell 105B may need to send reference signals <NUM> in all directions across multiple beams 630B, and the full beam sweep procedure may require high overhead. Likewise, without a cross-band QCL determination of its mmW beams 430B, the UE <NUM> may not have knowledge in this instance of the mmW reference signal <NUM> arrival angle and may thus need to simultaneously turn on multiple receive beams 430B in all directions to correctly receive the mmW reference signal <NUM>. Further, the UE <NUM> may be beyond the range of reference signal <NUM> sent via beam sweep procedures.

In the illustrated example, if the UE <NUM> and PCell 105A have previously identified, via beam management procedures, an ideal receive beam 430A and transmit beam 630A for communications between the PCell 105A and UE <NUM> on the sub-<NUM> band, the PCell 105A may coordinate with the co-located SCell 105B to aid in beam selection at the UE <NUM>. In particular, as seen in <FIG>, the SCell 105B may send reference signals via beam(s) 630B in a direction similar to the direction of the sub-<NUM> beam 630A used by the PCell 105A for transmissions to the UE <NUM>. In some instances, the PCell 105A may send an instruction to the UE <NUM> to measure the reference signals <NUM> of the SCell 105B along mmW beam 430B having similar direction as the receive beam 430A used by the UE <NUM> for receiving communications from the PCell 105A on the sub-<NUM> band. The cross-band QCL aided beam selection may reduce the beam sweep overhead at the SCell 105B, since the SCell 105B may no longer need to transmit reference signals <NUM> across all beams in all directions. The UE <NUM> may benefit with power savings due to avoiding using all receive beams 430B on the mmW frequency band. Further, the range of the mmW transmissions by the SCell 105B may be increased by using narrower beams 630B having a shared direction with the beams 630A and 430A of the PCell 105A communications on the sub-<NUM> band.

In the illustrated example, various options for signaling the UE <NUM> to measure reference signals <NUM> via particular beams 430B in the mmW band are within the scope of the present disclosure. In one option, the PCell 105A may send an indicator to instruct the UE <NUM> to measure reference signals <NUM> on the mmW band using a beam 430B having direction similar to the current receive beam 430A used for receiving transmissions on the sub-<NUM> band from the PCell 105A. The indicator may be sent in reference signal measurement configuration messages to the UE <NUM>, for example. The UE <NUM> may then determine the appropriate mmW receive beam(s) based on determination of cross-band QCL beams as described above with reference to <FIG>, <FIG>.

In some instances, the PCell 105A may signal a receive beam identification (ID) on the sub-<NUM> band to the UE <NUM> and instruct the UE <NUM> to measure reference signals <NUM> on the mmW band using beam(s) having a direction similar to the receive beam ID. The receive beam ID may be an identification assigned to a particular beam at the UE <NUM> to distinguish the beam from other possible beams. As used in the present disclosure, a receive beam ID may include different identification forms for particular beams. For example, a synchronization signal block (SSB) ID may be associated with each SSB transmitted by a base station on a particular beam. The base station may transmit one SSB on each beam, and each SSB may be associated with a unique SSB ID. Accordingly, the SSB ID may be used as one form of indicating UE beam ID under these circumstances, e.g. UE should use the same beam as that for receiving the SSB with the indicated SSB ID. Similarly, channel state information reference signal (CSI-RS) resource indicator or ID and sounding reference signal (SRS) resource ID may also be used as a form of indicating the UE beam ID in some instances, e.g. UE should use the same beam as that for receiving the CSI-RS with indicated CSI-RS ID, or as that for transmitting SRS with indicated SRS resource ID. Returning to the illustrated example, the PCell 105A may request the UE <NUM> to report the beam ID of the ideal beam 430B used by the UE <NUM> to receive sub-<NUM> communications from the PCell 105A. In response, the PCell 105A may send this receive beam ID to the UE <NUM> in a reference signal measurement configuration when the PCell 105A instructs the UE <NUM> to measure mmW reference signals on a beam based on the receive beam ID.

In certain instances, the PCell 105A may alternatively or additionally signal a transmit beam ID (e.g., in reference signal measurement configuration) on the sub-<NUM> band to the UE <NUM> and instruct the UE <NUM> to measure reference signals <NUM> on the mmW band using beam(s) having a direction similar to the ideal UE receive beam for receiving communications from PCell 105A, where the ideal UE receive beam is the receive beam corresponding to the transmit beam ID. In the illustrated example, the transmit beam ID is an identification of the particular transmit beam 630A used by the PCell 105A to communicate with the UE <NUM> on the sub-<NUM> band. Since the UE <NUM> has previously identified the ideal beam(s) for receiving sub-<NUM> communications from the PCell 105A, the UE <NUM> may determine that the receive beam that corresponds to the transmit beam ID is receive beam 430A. The UE <NUM> may then identify a mmW receive beam 430B that is cross-band QCL with respect to receive beam 430A and use the receive beam 430B for receiving mmW reference signals <NUM> from SCell 105B. In addition, besides the indicator identifying the cross-band QCLed beam, the PCell may also signal the source and target bands, e.g. sub-<NUM> and mmW, where the indicated reference beam and its respective cross-band QCL beam are located.

<FIG> shows a flowchart illustrating a process <NUM> for determining cross-band QCL mapping in accordance with various aspects of the present disclosure. The operations of process <NUM> may be implemented by a wireless device such as a base station or its components, or a user equipment or its components, as described with reference to <FIG> and <FIG>. For example, the operations of process <NUM> may be performed by the processor <NUM> or <NUM>, either alone or in combination with other components, as described herein. In some examples, the base station <NUM> or UE <NUM> may execute a set of codes to control the functional elements of the device to perform the functions described below. Additionally or alternatively, the base station <NUM> or UE <NUM> may perform aspects of the functions described below using special-purpose hardware.

At <NUM>, the wireless device identifies a characteristic of a first beam associated with a first antenna array. At <NUM>, the wireless device determines a second beam associated with a second antenna array as a quasi-co-located beam with respect to the first beam based on the characteristic. At <NUM>, the wireless device communicates on the first and second beams based on the determining.

<FIG> shows a flowchart illustrating a process <NUM> performed by a base station for assisting a user equipment with initial beam selection based on a cross-band QCL mapping in accordance with various aspects of the present disclosure. The operations of process <NUM> may be implemented by a base station or its components, as described with reference to <FIG> and <FIG>. For example, the operations of process <NUM> may be performed by the processor <NUM>, either alone or in combination with other components, as described herein. In some examples, the base station <NUM> may execute a set of codes to control the functional elements of the device to perform the functions described below. Additionally or alternatively, the base station <NUM> may perform aspects of the functions described below using special-purpose hardware.

At <NUM>, the base station <NUM> identifies a user equipment (UE) searching for a secondary cell connection on a second frequency band, wherein the UE is served by a base station on a first frequency band. At <NUM>, the base station <NUM> transmits an indicator to the UE to inform the UE regarding selection of a particular beam for measuring a reference signal from the secondary cell. In some instances, the indicator may comprise an instruction to measure the reference signal in a direction substantially aligned with a receive beam used to receive transmissions from the base station on the first frequency band, a beam identification number of a receive beam used to receive transmissions from the base station on the first frequency band, or a beam identification number of a transmit beam used to send transmissions from the base station to the UE on the first frequency band.

<FIG> shows a block diagram <NUM> of a design of a base station/eNB <NUM> and a UE <NUM>, which may be one of the base stations/eNBs and one of the UEs in <FIG>. At the eNB <NUM>, a transmit processor <NUM> may receive data from a data source <NUM> and control information from a controller/processor <NUM>. The control information may be for various control channels such as the PBCH, PCFICH, PHICH, PDCCH, EPDCCH, MPDCCH etc. The data may be for the PDSCH, etc. The transmit processor <NUM> may process (e.g., encode and symbol map) the data and control information to obtain data symbols and control symbols, respectively. The transmit processor <NUM> may also generate reference symbols, e.g., for the PSS, SSS, and cell-specific reference signal. A transmit (TX) multiple-input multiple-output (MIMO) processor <NUM> may perform spatial processing (e.g., precoding) on the data symbols, the control symbols, and/or the reference symbols, if applicable, and may provide output symbol streams to the modulators (MODs) 932a through 932t. Downlink signals from modulators 932a through 932t may be transmitted via the antennas 934a through 934t, respectively. The downlink signals may include training signals or a highly direction signal to assist the UE <NUM> to determine cross-band QCL beams, such as those described with reference to <FIG>, or the indicator to the UE <NUM> to inform the UE <NUM> regarding selection of beam(s) for measuring reference signals, as described with reference to <FIG>. The antennas 934a through 934t may, for example, comprise multiple antenna arrays, where each antenna array may be used for communications on different frequency bands, as described herein. The beams associated with a first antenna array may be mapped to beams associated with a second antenna array based on cross-band QCL determination operations described above with reference to <FIG>, for example.

At the UE <NUM>, the antennas 952a through 952r may receive the downlink signals from the eNB <NUM> and may provide received signals to the demodulators (DEMODs) 954a through 954r, respectively. A MIMO detector <NUM> may obtain received symbols from all the demodulators 954a through 954r, perform MIMO detection on the received symbols if applicable, and provide detected symbols.

On the uplink, at the UE <NUM>, a transmit processor <NUM> may receive and process data (e.g., for the PUSCH) from a data source <NUM> and control information (e.g., for the PUCCH) from the controller/processor <NUM>. The symbols from the transmit processor <NUM> may be precoded by a TX MIMO processor <NUM> if applicable, further processed by the modulators 954a through 954r (e.g., for SC-FDM, etc.), and transmitted to the eNB <NUM>. The transmissions to the eNB <NUM> may include requests for training signals to assist in identifying cross-band QCL beams, such as described in reference to <FIG>, for example, or reporting a receive beam ID to the eNB <NUM> for assistance with initial beam selection, as described with reference to <FIG>. At the eNB <NUM>, the uplink signals from the UE <NUM> may be received by the antennas <NUM>, processed by the demodulators <NUM>, detected by a MIMO detector <NUM> if applicable, and further processed by a receive processor <NUM> to obtain decoded data and control information sent by the UE <NUM>. The processor <NUM> may provide the decoded data to a data sink <NUM> and the decoded control information to the controller/processor <NUM>.

The controllers/processors <NUM> and <NUM> may direct the operation at the eNB <NUM> and the UE <NUM>, respectively. The controller/processor <NUM> and/or other processors and modules at the eNB <NUM> may perform or direct the execution of the functional blocks illustrated in <FIG>, and/or other various processes for the techniques described herein. The controllers/processor <NUM> and/or other processors and modules at the UE <NUM> may also perform or direct the execution of the functional blocks illustrated in <FIG>, and/or other processes for the techniques described herein. The memories <NUM> and <NUM> may store data and program codes for the eNB <NUM> and the UE <NUM>, respectively. For example, memory <NUM> may store instructions that, when performed by the processor <NUM> or other processors depicted in <FIG>, cause the base station <NUM> to perform operations described with respect to <FIG>. Similarly, memory <NUM> may store instructions that, when performed by processor <NUM> or other processors depicted in <FIG> cause the UE <NUM> to perform operations described with respect to <FIG>.

While blocks in <FIG> are illustrated as distinct components, the functions described above with respect to the blocks may be implemented in a single hardware, software, firmware, or combination component or in various combinations of components. For example, the functions described with respect to the transmit processor <NUM>, the receive processor <NUM>, or the TX MIMO processor <NUM> may be performed by or under the control of processor <NUM>.

Claim 1:
A method (<NUM>) for wireless communication, characterised by:
identifying (<NUM>), by a wireless device (<NUM>, <NUM>), a characteristic of a first beam from a set of analog beams associated with a first antenna array;
determining (<NUM>), by the wireless device (<NUM>, <NUM>), a second beam associated from a set of digital beams with a second antenna array as a quasi-co-located beam with respect to the first beam based on the characteristic, wherein the characteristic comprises at least a radiation pattern and wherein the determining comprises
adjusting beam weights of the second beam to substantially match the radiation pattern of the first beam; and
designating the second beam as a cross-band quasi-co-located beam with respect to the first beam; and
communicating (<NUM>), by the wireless device (<NUM>, <NUM>), on the first and second beams based on the determining.