WO2020101757A1

WO2020101757A1 - Method and apparatus for determining dynamic beam correspondence for phased array antenna

Info

Publication number: WO2020101757A1
Application number: PCT/US2019/039934
Authority: WO
Inventors: Ping SHI; Xiaoyin He
Original assignee: Huawei Technologies Co., Ltd.
Priority date: 2019-06-28
Filing date: 2019-06-28
Publication date: 2020-05-22
Also published as: CN113316902A; CN113316902B

Abstract

Techniques are provided for dynamically detecting UE beam correspondence when an uplink TX power back off condition occurs. In one example, a UE compares a list of TX beams with a list of RX beams of the base station. If the sort list of TX beams are in the same relative order as the list of RX beams, then the UE may determine that there is UE beam correspondence with respect to the base station. Conversely, if the sort list of TX beams are not in the same relative order as the list of RX beams, then the UE may determine that UE beam correspondence does not exist with respect to the base station. Either way, the result may be indicated by a beam correspondence indication transmitted from the UE to the base station.

Description

METHOD AND APPARATUS FOR DETERMINING DYNAMIC BEAM CORRESPONDENCE FOR

PHASED ARRAY ANTENNA

TECHNICAL FIELD

The present disclosure relates generally to telecommunications, and in particular embodiments, to methods for determining dynamic beam correspondence for phased array antennas.

BACKGROUND

Wireless signals communicated at high carrier frequencies, such as millimeter Wave (mmW) signals, tend to exhibit high free-space path loss. To compensate for high path loss rates, high-frequency communications may use beamforming at both the base station and user equipment (UE). In millimeter wave communication, phased antennas are commonly used to meet the link budget. An antenna array may be configured to have high gain in a certain beam direction. Radio communication in mmWave band may be highly directional. Beam management may be used to align UE antenna beams to base station antenna beam directions both in the uplink and downlink directions. In a time division duplexed (TDD) system, the uplink and downlink channels may be symmetrical. Notably, due to spatial reciprocity, a beam direction used by a device to transmit a signal will generally offer similar levels of spatial performance when used by the device to receive a signal. As used herein, the term“beam direction” refers to a radio antenna pattern, or set of beamforming weights, that is used for directional signal transmission and/or reception. Accordingly, a UE and a base station may use the same beam directions to transmit/receive uplink and downlink signals.

MPE limits have been defined to regulate the electromagnetic radiation radiated to human body. Current MPE limits may generally require that 5G mmWave UE’s back off maximum power when a human body is in close proximity. However, not every beam may be directed toward the human body. Backing off power of some beams, but not others, may cause there to be a lack of beam

correspondence between uplink and downlink in some situations. A multipath environment may provide extra path, and thus recreate the beam correspondence with a different TX/RX beam mapping. Techniques for efficiently detecting beam correspondence and notifying the base station are therefore needed for 5G networks.

SUMMARY

Technical advantages are generally achieved, by embodiments of this disclosure which describe methods for determining dynamic beam correspondence for phased array antennas.

[0001] In accordance with an embodiment, a method for dynamically detecting beam correspondence between transmit (TX) beams and receive (RX) beams of a base station when an uplink TX power back off condition occurs is provided. In this example, the method further includes receiving, by a user equipment (UE), downlink reference signals associated with the TX beams of the base station, and generating, by the UE, a list of the TX beams of the base station based on received signal quality levels of the reference signals, where the list of TX beams ranking the TX beams of the base station in order of received signal quality. The method further includes estimating a list of RX beams of the base station based on at least the received signal quality levels of the reference signals and adjusted TX levels of TX beams of the UE, where the adjusted TX levels of the TX beams of the UE include at least one TX level that is less than a maximum TX level due to the uplink TX power back off condition. The method further includes comparing the list of the TX beams with the list of RX beams, and based thereon transmitting a beam correspondence indication to the base station that indicates whether there is UE beam correspondence for the TX beams and the RX beams of the base station. On one example, the uplink TX power back off condition is triggered by a maximum permissible exposure (MPE) sensor. In another example, the uplink TX power back off condition is triggered by a surface temperature sensor. In any one of the above-mentioned examples, or in a new example, the method further includes receiving a control signal from the base station that indicates a size of at least one of the list of the TX beams and the list of the RX beams. In any one of the above- mentioned examples, or in a new example, comparing the list of the TX beams with the list of RX beams, and transmitting the beam correspondence indication based thereon includes determining that the list of the TX beams matches the list of RX beams, and based thereon transmitting the beam correspondence indication indicating that there is UE beam correspondence for the TX beams and the RX beams of the base station. In any one of the above-mentioned examples, or in a new example, comparing the list of the TX beams with the list of RX beams, and transmitting a beam

correspondence indication based thereon comprises determining that the list of the TX beams does not match the list of RX beams, and based thereon transmitting the beam correspondence indication indicating that there is no UE beam correspondence for the TX beams and the RX beams of the base station. In any one of the above-mentioned examples, or in a new example, the method further includes transmitting the list of the TX beams to the base station. In any one of the above-mentioned examples, or in a new example, the method further includes transmitting the list of the RX beams to the base station. An apparatus for performing this method is also provided. BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of embodiments provided herein, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a diagram of a network for communicating data;

FIG. 2 is a diagram of downlink beamformed transmissions;

FIG. 3 is a diagram of uplink beamformed transmissions;

FIGS. 4A-4H are diagrams of an embodiment beam correspondence detection technique;

FIG. 5 is a protocol diagram of a beam correspondence communications sequence;

FIG. 6 is a flowchart of an embodiment method for dynamically detecting beam correspondence when an uplink TX power back off condition occurs;

FIG. 7 is a flowchart of an embodiment method for remapping uplink beams when UE beam correspondence does not exist;

FIG. 8 is an example of a table maintained for detecting dynamic beam correspondence;

FIG. 9 is another example of a table maintained for detecting dynamic beam correspondence;

FIG. 10 is yet another example of a table maintained for detecting dynamic beam correspondence;

FIG. 11 is yet another example of a table maintained for detecting dynamic beam correspondence;

FIG. 12 is yet another example of a table maintained for detecting dynamic beam correspondence;

FIG. 13 is yet another example of a table maintained for detecting dynamic beam correspondence; FIG. 14 is a flowchart of an embodiment method for dynamically detecting beam correspondence;

FIG. 15 is a block diagram of an embodiment processing system for performing methods described herein; and

FIG. 16 is a block diagram of a transceiver adapted to transmit and receive signaling over a telecommunications network according to example embodiments described herein. DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Various illustrative embodiments are discussed in detail below. It should be appreciated, however, that this disclosure provides many applicable concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative of specific ways to make and use embodiments described herein, and do not limit the scope of the claims.

Due to spatial reciprocity, a beam direction used by a device to transmit a signal will generally offer similar levels of spatial performance when used by the device to receive a signal over the same path. As referred to herein, a device has“beam correspondence” when the device’ s RX beams provide the same relative performance with respect to one another as the device’ s TX beams. By extension, a UE has“UE beam correspondence” when the UE’ s RX beams provide the same relative performance with respect to one another as the UE’s TX beams. As an example, if a UE has two RX beams (RX1, RX2) and two TX beams (TX1, TX2) (where TX1 is mapped to RX1 and TX2 is mapped to RX2), the UE would have“beam correspondence” with respect to a base station when a performance level associated with RX1 exceeds a performance level associated with RX2 AND a performance level associated with TX1 exceeds a performance level associated with TX2. The UE would lack“UE beam correspondence” with respect to the base station when a performance level associated with RX1 exceeds a performance level associated with RX2 AND a performance level associated with TX1 fails to exceed a performance level associated with TX2. It should be appreciated that the relative performance of the UE’s RX beams may be measured during a downlink beam management procedure, and that the relative performance of the UE’ s TX beams may either be measured in an uplink beam management procedure or estimated based on TX power settings and path losses derived from the downlink beam management procedure. When a UE maintains UE beam correspondence, it may generally be acceptable to use whichever UE TX beam corresponds to the UE RX beam that was selected during a downlink beam management procedure, thereby allowing an uplink beam management procedure to be disabled.

In some scenarios, conditions associated with beam calibration and/or TX power adjustments may result in the loss of UE beam correspondence. As an example, a UE may adjust TX power levels for some (but not all) UE TX beams upon detecting an uplink TX power back off condition, which may cause a UE TX beam associated with a higher path loss to produce a higher estimated/measured uplink reference signal received power/quality level than a UE TX beam associated with a lower path loss value due to a disparity in the TX power levels. As another example, the TX and RX beams of a UE may fall out of calibration due to non-ideal performance characteristics, or more specifically to the drifting of said performance characteristics, of analog and/or digital beamforming/ signal - processing components in the UE’s TX and RX chains.

Embodiments of this disclosure provide techniques for dynamically detecting UE beam

correspondence when an uplink TX power back off condition occurs, e.g., a maximum permissible exposure (MPE) condition, a surface temperature condition, etc. In one example, the UE compares a list of TX beams with a list of RX beams of the base station. If the sort list of TX beams are in the same relative order as the list of RX beams (e.g., if all of the TX indices match the corresponding RX indices when the ordered lists are compared), then the UE may determine that there is UE beam correspondence with respect to the base station. Conversely, if the sort list of TX beams are not in the same relative order as the list of RX beams (e.g., if one of the TX indices does not match the corresponding RX indices when the ordered lists are compared), then the UE may determine that UE beam correspondence does not exist with respect to the base station. Either way, the result may be indicated by a beam correspondence indication transmitted from the UE to the base station. In some examples, the UE may also transmit the list of TX beams and/or the list of RX beams to the base station When the beam correspondence indication indicates that the UE has UE beam correspondence with respect to the base station, the base station may send a“quasi-co-located (QCL’d)” indication to the UE to indicate that an uplink beam management procedure has been disabled, in which case the UE may use whichever TX beam is mapped to the RX beam selected during the downlink beam management procedure in lieu of the uplink beam management procedure.

Additionally, embodiments of this disclosure allow a UE to re-map UE TX beams to UE RX beams to maintain and or restore UE beam correspondence. Some devices (e.g., generally base stations) may use the same beam ID for corresponding TX and RX beams of the device. Other devices (e.g., some base stations and most UEs) may use different beam IDs for corresponding TX and RX beams of the device. Embodiments of this disclosure allow those devices to update the table to maintain device beam correspondence. In particular, after determining that a device has lost beam correspondence, the device may update a mapping of TX beam IDs to RX beam IDs to restore the device beam correspondence. It should be appreciated that while much of this disclosure relates to UE beam correspondence, a base station may also maintain or lose“BS beam correspondence” with respect to a UE, and that (like UEs) a base station is generally considered to have“BS beam correspondence” when the base station’s RX beams provide the same relative performance with respect to one another as the base station’s TX beams. These and other details are described in greater detail below.

FIG. 1 is a network 100 for communicating data. The network 100 includes a base station 110 having a coverage area 101, a plurality of UEs 120, and a backhaul network 130. As shown, the base station 110 establishes uplink (dashed line) and or downlink (dotted line) connections with the user equipments (UEs) 120, which serve to carry data from the UEs 120 to the base station 110 and vice- versa. Data carried over the uplink/downlink connections may include data communicated between the UEs 120, as well as data communicated to/from a remote-end (not shown) by way of the backhaul network 130. As used herein, the term“base station” refers to any component (or collection of components) configured to provide wireless access to a network, such as a transmit receive point (TRP), an enhanced Node B (eNB), a next-generation NB (gNB), a macro-cell, a femtocell, a Wi-Fi access point (AP), or other wirelessly enabled devices. The base station 110 may provide wireless access in accordance with one or more wireless communication protocols, e.g., 5th generation new radio (5G_NR), long term evolution (LTE), LTE advanced (LTE-A), High Speed Packet Access (HSPA), Wi-Fi 802.1 la/b/g/n/ac, etc. As used herein, the term“UE” refers to any component (or collection of components) capable of establishing a wireless connection with a base station, such as a mobile device, a mobile station (STA), and other wirelessly enabled devices. In some embodiments, the network 100 may comprise various other wireless devices, such as relays, low power nodes, etc.

As mentioned above, spatial reciprocity dictates that a beam direction used by a device to transmit a signal will generally offer similar levels of spatial performance when used by the device to receive a signal. However, in some situation a UE may be required to reduce their TX power of some beams UE TX beams when a TX power back of condition occurs, which may or may not result in the loss of “UE beam correspondence”.

An uplink TX power back off condition may be triggered by a maximum permissible exposure (MPE) sensor. More specifically, UEs may be required to reduce their transmit (TX) power when they sense that they are in close proximity to a human body in order to comply with maximum permissible exposure (MPE) regulations set forth by the Federal Communications Commission (FCC) and similar other agencies. Fifth generation (5G) devices that utilize mmW signals with directional transmission may selectively reduce the TX power of specific TX beams that are directed toward a human body without reducing the TX power of TX beams that are directed away from the human body, which may improve the performance of TX beams operating at fully TX power. However, reducing the TX power of some TX beams, but not others, may result in a lack of UE beam correspondence with respect to the base station. That is to say, a UE that detects a human body in close proximity to the UE’ s TX antenna array may adjust the TX power of a specific UE TX beam (or group of UE TX beams) directed toward the human body, while maintaining normal (e.g., non-adjusted) power levels for UE TX beams that are directed away from the human body.

An uplink TX power back off condition may also be triggered by a surface temperature sensor. For example, a UE may include a surface temperature sensor that detects when a surface of the device exceeds a threshold temperature (referred to informally as a“high temperature” for ease of explanation), and adjust the power of a TX antenna array that is proximately located to that surface, while continuing to operate other TX antenna array(s) at normal (e.g., non-adjusted) power levels.

FIG. 2 is a diagram 200 of downlink beamformed transmissions from the base station 110 to a UE 120. As shown, the base station 110 transmits reference signals over TX beams 211-213 of the base station 110 (which are referred to as“BS TX beams”). The reference signal transmitted over BS TX beam 211 is associated with a first BS TX beam index (TX1), the reference signal transmitted over BS TX beam 212 is associated with a second BS TX beam index (TX2), and the reference signal transmitted over BS TX beam 213 is associated with a third BS TX beam index (TX3). The beamformed reference signals may carry the corresponding TX beam index. Alternatively, the beamformed reference signals may be communicated over resources associated with the

corresponding TX beam index (e.g., the reference signal transmitted over BS TX beam 211 may be communicated in resources associated with the TX1, etc.). The UE 120 may receive the beamformed reference signals over RX beams 221-223 of the UE (which are referred to as“UE RX beams”)- As is explained in FIGS. 4A-4H, the received signal quality of a given reference signal will largely be determined by the combined spatial performance of the respective BS TX beam and UE RX beam over which the reference signal is transmitted/received.

FIG. 3 is a diagram 300 of uplink beamformed transmissions from the UE 120 to the base station 110. As shown, the base station 110 receives reference signals over RX beams 311-313 of the base station 110 (referred to as“BS RX beams”), which are transmitted by the UE 120 over the TX beams 321- 323 of the UE 120 (referred to as“UE TX beams”). It should be appreciated that in implementation, the base station received signal quality levels of the references may actually be estimated based on path loss information obtained from the measurements of downlink reference signals and TX power levels of the UE. This is explained in greater detail in the descriptions relating to FIGS. 4A-4F.

The reference signal received over BS RX beam 311 is associated with a first BS RX beam index (RX1), the reference signal transmitted over BS RX beam 312 is associated with a second BS RX beam index (RX2), and the reference signal transmitted over BS RX beam 313 is associated with a third BS RX beam index (RX3). The BS RX beam 311 may have similar spatial characteristics as the BS TX beam 211 such that RX1 corresponds to TX1. Likewise, the BS RX beam 312 may have similar spatial characteristics as the BS TX beam 212 such that RX2 corresponds to TX2, and the BS RX beam 313 may have similar spatial characteristics as the BS TX beam 213 such that RX3 corresponds to TX3. Additionally, the UE TX beams 321, 322, 323 may have similar spatial characteristics as the UE RX beams 221, 222, 223, respectively. In some embodiments, TX power levels of one or more of the UE TX beams 321, 322, 323 may be adjusted when a power back off condition is detected.

In some embodiments, a UE may generate a list of TX and RX beams, and compare them to determine whether UE beam correspondence has been maintained. In some examples, the list of TX/RX beams may include a subset of the beams available to the UE and/or base station, and the base station may send the UE a control signal that indicates the number of beams to include in the list of TX/RX beams for purposes of determining UE beam correspondence.

FIGS. 4A-4H are diagrams 401-408 of an embodiment beam correspondence detection technique. FIGS. 4A-4E illustrate a procedure for generating a list of BS TX beams during downlink channel estimation. As shown, downlink reference signals 410, 420, 430 being transmitted from the base station 110 to the UE 120 over the BS TX beams 211-213. Some or all of the downlink reference signals 410-430 may be transmitted over the BS TX beams 211-213 during a common time interval. Alternatively, some or all the downlink reference signals 410-430 may be transmitted over the BS TX beams 211-213 during different time intervals. In this example, downlink reference signal 410 is transmitted over the BS TX beam 211 and is associated with TX1; downlink reference signals 420 is transmitted over the BS TX beam 212 and is associated with TX2, and downlink reference signal 430 is transmitted over the BS TX beam 213 and is associated with TX3. The UE 120 receives the downlink reference signals 410, 420, and 430 over each of the UE RX beams 221, 222, 223, and then measures a received signal quality level of the received downlink reference signals 410-430, which is represented by the thickness of the arrows corresponding to each of the received downlink reference signals 410-430 in FIGS. 4B-4D. FIG. 4E illustrates the cumulative result of the downlink reference signal measurements taken by the UE. In this example, path between the BS TX beam 212 and the UE RX beam 222 provides the best received signal quality, the path between the BS TX beam 213 and the UE RX beam 223 provides the second best received signal quality, and the path between the BS TX beam 211 and the UE RX beam 221 provides the third best received signal quality. Accordingly, in this example, the UE 120 generates a list of the TX beams <TX2, TX3, TX1>.

FIGS. 4F-4H illustrates a procedure for estimating a list of BS RX beams based on path loss information derived from the downlink channel estimation and UE TX power levels. As shown, the UE 210 estimates path losses based on the received downlink reference signals 410430, and then estimates a list of BS RX beams 311-313 based on the path losses and TX levels of UE TX beams 321-323. With beam correspondence, when there is no power back off condition present (as shown in FIG. 4G), the list of BS RX beams <RX2, RX3, RX1> generally matches the list of the TX beams <TX2, TX3, TX1>, since the channel is symmetric between downlink and uplink. . However, when a power back off condition present, the list of BS RX beams may or may not match the list of the TX beams depending on the extent of the TX power adjustment. In the example shown in FIG. 4F, the TX power of the UE TX beam 322 is adjusted enough to affect BS beam correspondence, and the list of BS RX beams <RX3, RX2, RX1> does not match the list of the TX beams <TX2, TX3, TX1>. In other examples, the UE TX beams may not be adjusted in a manner that affects BS beam

correspondence when a power back off condition is present, and the list of BS RX beams <RX2,

RX3, RX1> may nevertheless match the list of the TX beams <TX2, TX3, TX1>.

Embodiments of this disclosure provide a method to determine the UE correspondence based on the UE antenna characteristics, with the information from various sensors from UE and measurement from base station beam management process. A UE may use its build-in sensors to sense the proximity of human body and determine the maximum power back-off for each beam based on this information and antenna characteristics. In a typical beamed communication system, beam management may be required for both uplink and downlink. In a point-to-multipoint system, downlink beam management may be executed, as the multiple UEs are required to monitor the BS. Downlink beam management is preferred as the beam training resource could be shared by multiple UEs, the higher base station power could yield better signal-to-noise ratio at UE for beam selection. Downlink beam management may include measuring the received signal quality of downlink reference signals for different combination of BS TX beams. Downlink reference signals may include any known signal, such as synchronization signal (e.g., primary synchronization signal (PSS), secondary synchronization signal (SSS), etc.), physical broadcast channel (PBCH) signals, and cell specific reference signals (CSI-RS). The UE may then construct lists of BS TX and BS RX beams using the aforementioned information. The length of the lists may be determined according to control signaling received from the base station. The UE may notify the base station that beam correspondence does not exist. If beam correspondence does not exist, an uplink beam management process may be initiated by the base station because uplink beam performance may not be reliably inferred from downlink beam management measurements. Uplink beam management may be similar to downlink beam management, except that the UE may transmit uplink reference signals, such as sounding reference signals, CSI-RS, are other reference signals, which may then be used for uplink beam training.

When beam correspondence is present, downlink beam alignment results may be used to determine uplink beams. If uplink resources are QCL’d with downlink beams, the UE may use the

corresponding beam obtained from RX searching for uplink transmission. Beam correspondence may be achieved through calibration (e.g., adjusting phase/gain of the beams, etc.). Beam correspondence may not be present when uplink power back-off conditions occur.

Without UE beam correspondence, a base station may use different beams for downlink (TX) and uplink (RX) operation for a specific UE. There are scenarios in which matching BS TX and RX beams are used for downlink and uplink transmission and reception by a base station to/from a given UE, while the UE may use non-matching TX and RX beams for uplink and downlink

transmission/reception with the base station. In such scenarios, the UE may use different beams for uplink transmission and downlink reception. A UE may determine a dynamic beam correspondence with respect to BS beams, creating beam correspondence with TX and RX beam mapping, when there exists a dynamic beam correspondence. The UE may update the RX/TX beam mapping for quasi-co located (QCL) uplink beams.

Beam correspondence refers the ordered property between TX beam and RX beam of the same device when a relative performance for TX beams can be inferred from RX beams, and vice versa. In some embodiments, a UE may have UE beam correspondence when the UE is capable of selecting a corresponding TX beam for UL transmission based on DL measurements without participating in an UL beam management procedure. From an implementation perspective, even if the phase shifter is common for UL and DL path, the different matching network on the front-end may cause differences between UL and DL beams. The actual correspondence of beams on UL and DL may be affected by differences in direction and power. Uplink and downlink path characteristics may cause different antenna patterns.

MPE limits have been defined to regulate the electromagnetic radiation radiated to human body. Current MPE limits may generally require that 5G mmWave UE’s back off maximum power when a human body is in close proximity. However, not every beam may be directed toward the human body. Backing off power of some selected beams, but not others, may cause there to be a lack of beam correspondence between uplink and downlink in some situations. For mobile and portable application, multiple antenna array may be placed at different portion of device. Phased array antenna may experience different thermal environment, and selective power back-off due to thermal concern may exist, which will destroy the beam correspondence. A multipath environment may provide extra path, and thus recreate the dynamic beam correspondence with a different TX/RX beam mapping.

Techniques for efficiently detecting dynamic beam correspondence and notifying the base station are therefore needed for 5G networks.

Embodiments of this disclosure provide a method to determine the UE dynamic beam

correspondence based on the UE antenna characteristics, with the information from various sensors from UE and measurement from base station beam management process. A UE may use its build-in sensors to sense the proximity of human body and determine the maximum power back-off for each beam based on this information and antenna characteristics.

FIG. 5 is a protocol diagram 500 of a beam correspondence communications sequence between the UE 120 and the base station 110. The sequence begins when the base station 110 communicates downlink reference signals 510 to the UE 120. The UE 120 then measures a signal quality of the downlink reference signals 510, generate a List of BS TX beams, and estimates path loss values between UE TX beams and BS RX beams. The UE 120 then detects an uplink TX power back off condition, and estimate a list of BS RX beams based on the path loss values and the adjusted UE TX power levels of the UE TX beams. The UE 120 then compares the list of BS RX beams with the list of BS TX beams, and sends a beam correspondence indication 520 to the base station 110 indicating whether UE beam correspondence exists with respect to the BS TX beams and the BS RX beams.

FIG. 6 is a flowchart of an embodiment method 600 for dynamically detecting beam correspondence between BS TX beams and BS RX beams when an uplink TX power back off condition occurs, as may be performed by a UE. At step 610, the UE receives downlink reference signals associated with the TX beams of the base station. At step 620, the UE generates a list of the TX beams of the base station based on received signal quality levels of the reference signals. At step 630, the UE detects uplink TX power back off condition requiring adjustment of TX levels of one or more TX beams of the UE. At step 640, the UE estimates a list of RX beams of the base station based on at least the UE received signal quality levels of the BS reference signals and the adjusted TX levels of the TX beams of the UE. At step 650, the UE compare the list of the TX beams with the list of RX beams to determine beam correspondence between TX and RX beams of the base station. At step 660, the UE transmits a beam correspondence indication to the base station that indicates whether there is UE beam correspondence with respect to the TX and RX beams of the base station.

Although the UE TX/RX characteristics can be calibrated to achieve beam correspondence, the beam correspondence may be lost due to selective power back-off for certain beams, as it is explained previously. In a typical UE implementation, a UE may maintain a table for TX/RX performance of UE beams. A UE may also maintain a table for TX power adjustment settings (e.g., max power back off settings) for each UE beam when uplink power back-off conditions occur. A UE may be able to maintain beam correspondence through calibration when uplink power back-off conditions are not present. A UE may update the TX/RX difference per UE beam based on the sensing information or other software control when uplink power back-off conditions are present.

FIG. 7 is a flowchart of an embodiment method 700 for remapping uplink beams when UE beam correspondence does not exist. At step 710, the UE receives downlink reference signals associated with the TX beams of the base station. At step 720, the UE generates a list of the TX beams of the base station based on received signal quality levels of the reference signals. At step 730, the UE detects uplink TX power back off condition requiring adjustment of TX levels of one or more TX beams of the UE. At step 740, the UE estimates a list of RX beams of the base station based on at least the UE received signal quality levels of the BS reference signals and the adjusted TX levels of the TX beams of the UE. At this point, the UE may determine that UE beam correspondence does not exist based on the current mapping. At step 750, the UE sends the list of the TX beams and the list of RX beams to the base station. At step 760, the UE receives a beam remapping indication from the base station. The beam remapping indication be determined by the base station based on a comparison of the list of TX beams and the list of RX beams. In one example, the beam remapping indication may be an“QCL uplink resource” indication that is determined by comparing the best X TX and RX beams reported by UE, and sending a singling that maps the corresponding the uplink TX and downlink RX resources have a“QCL association” with one another for purposes of beamformed transmissions (meaning that the beams used to transmit uplink and downlink data over the respective resources offer similar spatial performance). . _ At step 770, the UE map at least one UE TX beam to at least one UE RX beam based on the indicated QCL resource[s].

FIGS. 8-13 are examples of tables that may be maintained by the UE for purposes of detecting dynamic beam correspondence. In FIG. 8, beam correspondence has been deemed to exist between BS TX and RX beams, and the table maps UE TX beams to UE RX beam is maintained such that each UE RX beam is associated with a corresponding UE TX beam having the same direction and the same beam ID as the UE RX beam. In FIG. 9, a table is created and updated to track the TX/RX performance difference. For each UE beam, a static TX/RX gain difference is created, reflecting the characteristics of TX/TX performance. This difference may come array gain difference, antenna mismatch difference between TX and RX, PA/LNA difference between beams. This difference could be characterized in the factory, using one beam as the reference beam. In FIG. 10, selected power back-off for each beam is also maintained and updated dynamically, with the total TX/RX difference corresponding to the sum of max power back-off and TX/RX gain difference for each beam.

During a beam alignment procedure, a UE may scan UE beams for each BS beam, and provide BS beam quality based in received signal receive power (RSRP) levels. In addition, a UE may calculate achievable TX signal quality (strength) based on the RX signal quality and the TX/RX difference. FIGS. 11-12 are tables for estimating relative received signal strength at a base station based on the UE received signal strength. For each BS TX beam i, UE measure the signal strength Rij with each available UE beam j. For a link with K BS beams and N UE beams, there will be K x N

measurements. For each BS TX/UE RX beam combination, UE will calculate the reverse link (UE TX/BS RX) signal quality. For each UE beam j and BS beam i, UE estimates available UE TX power at BS receiver using the total TX/RX difference tj and the measured RX signal power with a constant T to adjust the constant offset due to path loss. The calculated available TX power at BS receiver is T + Rij - tj . T is a constant for all UE/BS beams at any beam measurement interval. The calculated available UE TX power at BS receiver reflects the received UE signal quality at BS, which can be used to select UE/BS beams for uplink transmission if BS beam correspondence exists.

A UE may select a number of BS beams from the lists based on the beam measurement results. FIG. 13 is a table of list for each BS beam using measured RSSP and calculated UE available TX power at BS receiver. For each BS beam i, best UE RX beam and TX beam are selected. For a link with K BS beam, there will be K UE RX beam and K UE TX beam. These K UE RX beams and K UE TX beams will be respectively according to the signal quality criteria. The corresponding BS beam ID will be used to create a K BS beam ID list. For example, in a link of K = 4 and N = 3, if the RX measurement are R13, R31, R21, R43, then the BS beam list using RX criteria is BR1, BR3, BR2, B4 ( BS beam 1, 3, 2, 4/UE beam 3, 1, 1, 3). Similarly, if list using calculated TX power for K BS beam are tl2, t33, t21, t22, then the BS beam list using TX criteria is Btl, Bt3, Bt2, Bt4 (BS beam 1, 3, 2, 4 /UE beam 2, 3, 1, 2). If the BS beam lists have the same beams and same beam orders, then the UE may determine that beam correspondence is present. In the above example, BS list from RX criteria is the same as TX criteria (although the corresponding UE list are different), a dynamic beam correspondence with respect to BS beams is determined. The number of beams in list for comparison could be less than the number of available BS beams. For example, if BS has 64 beams, but only configures UE to report 4 best BS beams for beam management purpose, then only the first four BS beams in the list are used to determine if the dynamic beam correspondence exist. If the BS beam lists have different beams or different orders of beams, then the UE may determine that beam correspondence is not present. When beam correspondence exists for a UE, the BS can choose to signal quasi-collocated (QCL) beams, which may generally be a pair of TX and RX beams having the beam ID. When QCL beams are signals, uplink beam management may be disabled, which saves overhead, processing resources, and power. With dynamic beam correspondence, the QCL’d downlink and uplink beams/resources may have different UE RX and TX beams based on a previous measurement. A UE may maintain the mapping between RX UE beam and TX UE beam for each assigned downlink BS beam, and the mapping may be transparent to the BS. In one embodiment, a UE may report the BS beam lists when sending the beam correspondence indication. In one embodiment, a base station may initialize the uplink beam management process to determine best uplink beam pairs. In another embodiment, a base station may use beam correspondence information and the reported BS beam list without triggering an uplink beam management process. If beam correspondence exists, BS may signal the QCL beams for uplink transmission, utilizing reported BS beam list. In another embodiment, when UE reports no beam correspondence, BS may order UE to further report estimated TX signal quality for a number X of BS beams (using TX criteria). UE may select the first X BS beams from the BS beam listing using TX criteria and report to BS. Upon the receiving of the BS beam list using RX criteria and TX criteria, BS may signal the re-QCL BS beam for the specific UE without the uplink beam management. For example, if a UE reports BS beam 1, 3, 4 to BS using RX criteria, and further reports BS beam 2, 3, 1 using TX criteria, upon BS request. BS may select to map beam 1 (BS TX)/ beam 2 (BS RX), beam 3/beam 3, beam 4/ beaml, and signals the QCLed beams to UE. The base station may assume the UE beam correspondence, and notify the UE via downlink control signaling. After receiving BS signaling, a UE may use a wide sense QCL in determining the corresponding UE TX beam for BS RX beams.

FIG. 14 is a flowchart of an embodiment method as may be performed by a UE. At step 1405, the UE enters into an Idle/Connected mode. At 1410, the UE checks for hardware beam correspondence. If hardware beam correspondence does not exist, the UE sends a message indicating no beam correspondence capability to the base station at step 1418.

At step 1415, the UE performs an MPE processing algorithm(or other power back-off algorithm), and determines whether a power back-off condition is reported at step 1425. If so, the UE performs steps 1430-1440, otherwise the UE advances to step 1495.

At step 1430, the UE determines a maximum power back off level for each beam based on, for example, human body proximity information. At step 1435, the UE determines the TX/RX difference for each beam pair, and updates the TX/RX gain differences for each beam at step 1440 using the max power back-off levels.

At step 1445, the UE determines whether in P1/P2 process. If so, the method proceeds to step 1450. Otherwise, the method skips to sept 1495. At step 1450, the UE sweeps each UE beam at each BS beam and corresponding UE beam ID. At step 1455, the UE calculates expected max TX levels based on RSRP and TX/RX gains differences for each BS beam. At step 1460, the UE creates a list of BS beams using RX RSRP quality with UE beam IDs. At step 1465, the UE creates a list of BS beams using calculated TX signal levels with UE beam IDS. At step 1470, the UE determines whether a BS beam list from RX criteria is the same as from TX criteria. If not, the method reverts to step 1418. Otherwise, the method proceeds to step 1475, where the UE selects a BS beam and reports the selected beam to the base station.

At step 1480, the UE determines whether to report beams having the same UE beam ID with RX criteria and TX criteria to the base station. If so, the UE sends an update to the base station that includes beam correspondence capability information at step 1485. Otherwise, the UE simply updates the downlink-uplink beam mapping tables at step 1490, and returns to call processing.

A UE may determine its UE beam reciprocity state and sends a“UE beam reciprocity state” message to a BS, which triggers proper uplink beam management accordingly. The UE beam reciprocity state message can take place when the UE tries to register to the network. Embodiments of this disclosure identify when a multipath environment affects beam correspondence. When dynamic beam correspondence exists, updates to the mapping table between TX beam and RX beams may be performed. Embodiments of this disclosure address the max power back-off due to MPE (or thermal condition), and provide improved performance when uplink power back off conditions occur through better beam tracking (e.g., harness the multipath environment, provide better receiving and transmitting performance, etc.) and lower power consumption (e.g., utilizing the dynamic beam correspondence and reduce the overhead due to uplink beam alignment process).

FIG. 15 illustrates a block diagram of an embodiment processing system 1500 for performing methods described herein, which may be installed in a host device. As shown, the processing system 1500 includes a processor 1504, a memory 1506, interfaces 1510-1512, and one or more sensor(s) 1514, which may (or may not) be arranged as shown in FIG. 15. The processor 1504 may be any component or collection of components adapted to perform computations and/or other processing related tasks, and the memory 1506 may be any component or collection of components adapted to store programming and/or instructions for execution by the processor 1504. A means for configuring a context for a UE may include processor 1504. In an embodiment, the memory 1506 includes a non- transitory computer readable medium. The interfaces 1510, 1512 may be any component or collection of components that allow the processing system 1500 to communicate with other devices/components and/or a user. For example, one or more of the interfaces 1510, 1512 may be adapted to communicate data, control, or management messages from the processor 1504 to applications installed on the host device and/or a remote device. As another example, one or more of the interfaces 1510, 1512 may be adapted to allow a user or user device (e.g., personal computer (PC), etc.) to interact/communicate with the processing system 1500. The sensor(s) 1514 may include any component or collection of components for detecting uplink TX power back off condition. For example, the sensors 1514 include a maximum permissible exposure (MPE) sensor and/or a surface temperature sensor. Other examples are also possible. The processing system 1500 may include additional components not depicted in FIG. 15, such as long term storage (e.g., non-volatile memory, etc.).

In some embodiments, the processing system 1500 is included in a network device that is accessing, or part otherwise of, a telecommunications network. In one example, the processing system 1500 is in a network-side device in a wireless or wireline telecommunications network, such as a network TRP, a relay station, a scheduler, a controller, a gateway, a router, an applications server, or any other device in the telecommunications network. In other embodiments, the processing system 1500 is in a user-side device accessing a wireless or wireline telecommunications network, such as a mobile station, a user equipment (UE), a personal computer (PC), a tablet, a wearable communications device (e.g., a smartwatch, etc.), or any other device adapted to access a telecommunications network.

In some embodiments, one or more of the interfaces 1510, 1512 connects the processing system 1500 to a transceiver adapted to transmit and receive signaling over the telecommunications network. FIG. 16 illustrates a block diagram of a transceiver 1600 adapted to transmit and receive signaling over a telecommunications network. The transceiver 1600 may be installed in a host device. As shown, the transceiver 1600 comprises a network-side interface 1602, a coupler 1604, a transmitter 1606, a receiver 1608, a signal processor 1610, and a device-side interface 1612. The network-side interface 1602 may include any component or collection of components adapted to transmit or receive signaling over a wireless or wireline telecommunications network. The network-side interface 1602 may also include any component or collection of components adapted to transmit or receive signaling over a short-range interface. The network-side interface 1602 may also include any component or collection of components adapted to transmit or receive signaling over a Uu interface. The coupler 1604 may include any component or collection of components adapted to facilitate bi-directional communication over the network-side interface 1602. The transmitter 1606 may include any component or collection of components (e.g., up-converter, power amplifier, etc.) adapted to convert a baseband signal into a modulated carrier signal suitable for transmission over the network-side interface 1602. A means for transmitting an initial message of an access procedure may include transmitter 1606. The receiver 1608 may include any component or collection of components (e.g., down-converter, low noise amplifier, etc.) adapted to convert a carrier signal received over the network-side interface 1602 into a baseband signal. A means for receiving mobile subscriber identifiers, initial downlink messages of access procedures, and forwarded requests to connect to a network may include receiver 1608.

The signal processor 1610 may include any component or collection of components adapted to convert a baseband signal into a data signal suitable for communication over the device-side interface(s) 1612, or vice-versa. The device-side interface(s) 1612 may include any component or collection of components adapted to communicate data-signals between the signal processor 1610 and components within the host device (e.g., the processing system 1500, local area network (LAN) ports, etc.).

The transceiver 1600 may transmit and receive signaling over any type of communications medium.

In some embodiments, the transceiver 1600 transmits and receives signaling over a wireless medium. For example, the transceiver 1600 may be a wireless transceiver adapted to communicate in accordance with a wireless telecommunications protocol, such as a cellular protocol (e.g., long-term evolution (LTE), etc.), a wireless local area network (WLAN) protocol (e.g., Wi-Fi, etc.), or any other type of wireless protocol (e.g., Bluetooth, near field communication (NFC), etc.). In such embodiments, the network-side interface 1602 comprises one or more antenna/radiating elements. For example, the network-side interface 1602 may include a single antenna, multiple separate antennas, or a multi-antenna array configured for multi-layer communication, e.g., single input multiple output (SIMO), multiple input single output (MISO), multiple input multiple output (MIMO), etc. In other embodiments, the transceiver 1600 transmits and receives signaling over a wireline medium, e.g., twisted-pair cable, coaxial cable, optical fiber, etc. Specific processing systems and/or transceivers may utilize all of the components shown, or only a subset of the components, and levels of integration may vary from device to device.

Throughout this disclosure, programming is described as storing instructions for execution by a processor in a device. It should be appreciated that when the instructions are executed by the processor, the processor may cause the device, or otherwise control one or more components within the device, to perform a functional step or process defined by the instruction. For example, when executing an“instruction to receive a signal”, a processor may cause the device to receive the signal or otherwise control circuitry in the device to perform signal processing steps to receive the signal. Likewise, when executing an“instruction to transmit a signal”, a processor may cause the device to transmit the signal or otherwise control circuitry in the device to perform signal processing steps to transmit the signal.

Although the present disclosure has been described with reference to specific features and embodiments, the description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments will be apparent to persons skilled in

-i6- the art upon reference to the description. It is therefore intended that the appended claims encompass any such modifications or embodiments.

Claims

WHAT IS CLAIMED IS:

1. A method for dynamically detecting beam correspondence between transmit (TX) beams and receive (RX) beams of a base station when an uplink TX power back off condition occurs, the method comprising:

receiving, by a user equipment (UE), downlink reference signals associated with the TX beams of the base station;

generating, by the UE, a list of the TX beams of the base station based on received signal quality levels of the reference signals, the list of TX beams ranking the TX beams of the base station in order of received signal quality;

estimating, by the UE, a list of RX beams of the base station based on at least the received signal quality levels of the reference signals and adjusted TX levels of TX beams of the UE, the adjusted TX levels of the TX beams of the UE including at least one TX level that is less than a maximum TX level due to the uplink TX power back off condition; and

comparing, by the UE, the list of the TX beams with the list of RX beams, and based thereon transmitting a beam correspondence indication to the base station that indicates whether there is UE beam correspondence for the TX beams and the RX beams of the base station.

2. The method of claim 1, wherein the uplink TX power back off condition is triggered by a maximum permissible exposure (MPE) sensor.

3. The method of claim 1, wherein the uplink TX power back off condition is triggered by a surface temperature sensor.

4. The method of any of claims 1-3, further comprising receiving a control signal from the base station that indicates a size of at least one of the list of the TX beams and the list of the RX beams.

5. The method of any of claims 1-4, wherein comparing the list of the TX beams with the list of RX beams, and transmitting the beam correspondence indication based thereon comprises:

determining that the list of the TX beams matches the list of RX beams, and based thereon transmitting the beam correspondence indication indicating that there is UE beam correspondence for the TX beams and the RX beams of the base station.

6. The method of any of claims 1-4, wherein comparing the list of the TX beams with the list of RX beams, and transmitting a beam correspondence indication based thereon comprises:

-i8- determining that the list of the TX beams does not match the list of RX beams, and based thereon transmitting the beam correspondence indication indicating that there is no UE beam correspondence for the TX beams and the RX beams of the base station.

7. The method of any of claims 1-6, further comprising transmitting the list of the TX beams to the base station.

8. The method of any of claims 1-7, further comprising transmitting the list of the RX beams to the base station.

9. A user equipment (UE) adapted to dynamically detect beam correspondence between transmit (TX) beams and receive (RX) beams of a base station when an uplink TX power back off condition occurs, the UE comprising:

a processor; and

a non-transitory computer readable storage medium storing programming for execution by the processor, the programming including instructions to:

receive downlink reference signals associated with the TX beams of the base station; generate a list of the TX beams of the base station based on received signal quality levels of the reference signals, the list of TX beams ranking the TX beams of the base station in order of received signal quality;

estimate a list of RX beams of the base station based on at least the received signal quality levels of the reference signals and adjusted TX levels of TX beams of the UE, the adjusted TX levels of the TX beams of the UE including at least one TX level that is less than a maximum TX level due to the uplink TX power back off condition; and

compare the list of the TX beams with the list of RX beams, and based thereon transmit a beam correspondence indication to the base station that indicates whether there is UE beam correspondence for the TX beams and the RX beams of the base station.

10. The UE of claim 9, wherein the uplink TX power back off condition is triggered by a maximum permissible exposure (MPE) sensor.

11. The UE of claim 9, wherein the uplink TX power back off condition is triggered by a surface temperature sensor.

12. The UE of any of claims 9-11, wherein the programming further includes instructions to receive a control signal from the base station that indicates a size of at least one of the list of the TX beams and the list of the RX beams.

13. The UE of any of claims 9-12, wherein the instructions to compare the list of the TX beams with the list of RX beams, and transmit the beam correspondence indication based thereon include instructions to:

determine that the list of the TX beams matches the list of RX beams, and based thereon transmit the beam correspondence indication indicating that there is UE beam correspondence for the TX beams and the RX beams of the base station.

14. The UE of any of claims 9-12, wherein the instructions to compare the list of the TX beams with the list of RX beams, and transmit the beam correspondence indication based thereon include instructions to:

determine that the list of the TX beams does not match the list of RX beams, and based thereon transmit the beam correspondence indication indicating that there is no UE beam correspondence for the TX beams and the RX beams of the base station.

15. The UE of any of claims 9-14, wherein the programming further includes instructions to transmit the list of the TX beams to the base station.

16. The UE of any of claims 9-15, wherein the programming further includes instructions to transmit the list of the RX beams to the base station.

17. A method for remapping uplink beam when UE beam correspondence does not exist, the method comprising:

receiving, by a user equipment (UE), downlink reference signals associated with the TX beams of the base station,

estimating, by the UE, a list of RX beams of the base station based on at least the received signal quality levels of the reference signals and adjusted TX levels of TX beams of the UE, the adjusted TX levels of the TX beams of the UE including at least one TX level that is less than a maximum TX level due to the uplink TX power back off condition; and sending, by the UE, indications of the list of the TX beams and the list of RX beams to the base station; and

receiving, by the UE, a QCL uplink resource indication from the base station, based thereon re-mapping at least one uplink beam to one downlink beam , the QCL uplink resource indication indicating that one uplink resource has a QCL association with at least one downlink resource for purposes of beamformed transmissions.

18. The method of claim 17, further comprising:

mapping, by the UE, at least one UE TX beam to at least one UE RX beam based on the updated QCL resources, wherein beam correspondence is assumed to exist between the mapped at least one UE TX beam and the at least one UE RX beam.

19. A user equipment (UE) comprising:

a processor; and

receive downlink reference signals associated with the TX beams of the base station, generate a list of the TX beams of the base station based on received signal quality levels of the reference signals, the list of TX beams ranking the TX beams of the base station in order of received signal quality;

send indications of the list of the TX beams and the list of RX beams to the base station; and receive a QCL uplink resource indication from the base station, based thereon re-mapping at least one uplink beam to one downlink beam , the QCL uplink resource indication indicating that one uplink resource has a QCL association with at least one downlink resource for purposes of beamformed transmissions.

20. The UE of claim 19, wherein the programming further includes instructions to:

map at least one UE TX beam to at least one UE RX beam based on the updated QCL resources, wherein beam correspondence is assumed to exist between the mapped at least one UE TX beam and the at least one UE RX beam.