WO2018135986A1

WO2018135986A1 - Beam management using suplink reference signals

Info

Publication number: WO2018135986A1
Application number: PCT/SE2017/051188
Authority: WO
Inventors: Niclas Wiberg; Håkan ANDERSSON; Johan FURUSKOG; Johan KÅREDAL; Mattias Frenne; Tomas Sundin; John SKÖRDEMAN; Qiang Zhang
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2017-01-19
Filing date: 2017-11-29
Publication date: 2018-07-26

Abstract

An event-triggered mechanism for causing a UE to perform a transmission burst as a result of detecting a need to support a BPL during a transition in the transmission environment. An advantage of such an event-triggered mechanism is that beam tracking of a BPL that requires UL transmissions to maintain the tracking can be supported by a transmission burst without the need for either semi-statically configured SRS, which is too slow to control, or PDCCH based scheduling for every transmission, which may prove unreliable and wasteful of control-channel resources.

Description

BEAM MANAGEMENT

TECHNICAL FIELD

[001] Disclosed are embodiments for beam management.

BACKGROUND

[002] The next generation mobile wireless communication system, which is referred to as "5G," will support a diverse set of use cases and a diverse set of deployment scenarios. 5G will encompass an evolution of today's 4G networks and the addition of a new, globally standardized radio-access technology known as "New Radio" (NR).

[003] The diverse set of deployment scenarios includes deployment at both low frequencies (100s of MHz), similar to LTE today, and very high frequencies (mm waves in the tens of GHz). At high frequencies, propagation characteristics make achieving good coverage challenging. One solution to the coverage issue is to employ beamforming (e.g., high-gain beamforming) to achieve satisfactory link budget.

[004] Beamforming is an important technology in future radio communication systems.

It can improve performance both by increasing the received signal strength, thereby improving the coverage, and by reducing unwanted interference, thereby improving the capacity.

Beamforming can be applied both in a transmitter and a receiver.

[005] In a transmitter, beamforming involves configuring the transmitter to transmit a signal in a specific direction (or a few directions) and not in other directions. In a receiver, beamforming involves configuring the receiver to receive signals from a certain direction (or a few directions) and not from other directions. When beamforming is applied in both the transmitter and the receiver for a given communication link, the combination of the beam used by the transmitter to transmit a signal to the receiver and the beam used by the receiver to receive the signal is referred to as a beam-pair link (BPL). Generally, the beamforming gains are related to the widths of the used beams: a relatively narrow beam provides more gain than a wider beam.

[006] For a more specific description of beamforming, one typically talks about beamforming weights rather than beams. On the transmission side, the signal to be transmitted is multiplied with beamforming weights (e.g., complex constants) before being distributed to the individual antenna elements. There is a separate beamforming weight for each antenna element, which allows maximum freedom in shaping the transmission beam given the fixed antenna array. Correspondingly, on the receiving side, the received signal from each antenna element is multiplied separately with the beamforming weights before the signals are combined. However, in the context of the present text, the description is easier to follow if the somewhat simplified notion of beams, pointing in certain physical directions, is adopted.

[007] Beamforming generally requires some form of beam management, such as beam search, beam refinement, and/or beam tracking, to determine what transmit (TX) and receive (RX) beams to use for communication between two communication units. Typically, the two communication units are a Transmission and Reception Point (TRP) (e.g., a base station) and a user equipment (UE) (e.g., a device, such as, for example, a smartphone, a sensor, an appliance, etc., that is capable of wireless communication).

[008] Beam search can involve the transmitter sweeping a signal across several beams

(i.e., transmitting a signal, such as a reference signal, multiple times using different TX beams), to allow a receiver in an unknown direction to receive the signal. Beam search can also involve the receiver scanning across several receive beams, thereby being able to receive a signal from an initially unknown direction. Beam search typically also involves the receiver sending a message to a transmitter to indicate which transmit beam or beams are best suited for

transmission to that receiver.

[009] Beam refinement is applied when a working beam or beam pair is already selected. Beam refinement is to improve an already selected beam, for instance changing its beamforming weights to obtain a narrower beam that provides a better gain.

[0010] Beam tracking is process that is used to update the selected beams, i.e., to replace the TX or RX beam in an existing BPL when the conditions change (e.g., due to mobility). Beam refinement and tracking are typically performed by temporarily evaluating a different beam than the one that is currently used for communication, and switching to that beam if it is deemed better than the current beam.

[0011] Beam search can take a considerable amount time when there are many beams to search for on both the transmitter and receiver side, and communication is typically not possible during this search time. Beam refinement and tracking, on the other hand, are usually ongoing activities that cause little or no disturbance to ongoing communication. SUMMARY

[0012] Networks often transmit periodic or continuous reference signals to support beam management (e.g. by sweeping across several transmit beams as describe above). Such transmissions are here referred to as beam reference signals (BRS). Some aspects of beam management can be performed by a UE with little or no explicit involvement from the network, since the UE can assume that the network is transmitting the BRS periodically or continuously. For instance, UEs typically perform beam search as part of the system-acquisition procedure, resulting in the selection of a UE RX beam such that by using this RX beam the UE can sufficiently well receive BRS transmitted on a certain network beam. Then the UE performs a random-access transmission using a selected UE TX beam and using a transmission resource (time and/or frequency) where the UE expects the network to be able to receive random-access transmissions using that beam. UEs often continue to receive BRS even when communication is ongoing - this facilitates beam search, beam refinement and beam tracking.

[0013] Many radio communication systems include some kind of radio-link supervision, whereby the quality of the communication link is regularly checked, and some action is taken in case the quality is unacceptable or the communication is lost. Radio-link supervision often involves a receiver checking the presence and/or quality of a sync signal or a reference signal. It can also involve monitoring the number of retransmissions in a retransmission protocol, and monitoring the time it takes to receive a response to an earlier transmitted request message. In case any of these checks indicate a severe problem, the device often declares a radio-link failure and initiates some action. In case of a network node having lost communication with a UE, the action can involve releasing some or all network resources related to that UE. In case of a UE having lost communication with a network, the action can involve searching for sync and reference signals from the network and, in case such signals are found, attempting to access the network again. In a beamforming system, this typically involves beam search.

[0014] In addition, networks schedule and transmit UE specific reference signals that, among other things, can be used for beam searching, beam tracking, and beam refinement. Such signals are referred to here as beam refinement reference signals (BRRS). Another example of a UE specific reference signal is the channel state information reference signal (CSI-RS). This is a reference signal scheduled by the network for one (or possibly, several) specific UE (or UEs) with the intention of providing measurement opportunities in the UE such that more detailed channel knowledge may be obtained and reported back to the network.

[0015] Further, networks (e.g., TRPs) may configure UEs to periodically transmit uplink

(UL) reference signals, which are known as sounding reference signals (SRS).

[0016] To sustain a transmission link between the network and the UE over time-varying conditions (e.g. due to mobility), UEs typically consider several possible BPLs for which the beams are tracked and refined. Such BPLs that are identified jointly by the network and the UE are here referred to as monitored BPLs.

[0017] Out of the monitored BPLs, the network and UE agree to use at least one BPL for data and control channel reception and transmission (here referred to as the "active" BPL). Depending on its capabilities, a UE can support one or more active BPLs.

[0018] Tracking a BPL implies beam tracking and/or refinement at the network as well as the UE. To track a monitored BPL (active or non-active) there must be some transmissions on which to measure and evaluate the link quality. In DL, the always-on BRS enables tracking of the DL TX beam and, more slowly, of the DL RX beam. For faster DL RX beam tracking scheduled BRRS can be used. In the event of DL/UL reciprocity, the BRS may then suffice to track a BPL and no UL transmissions are needed. In a scenario where DL/UL reciprocity does not hold, the BPL tracking requires UL transmissions (e.g., SRSs) to maintain the BPL for the UL.

[0019] The main-candidate duplex scheme envisioned for NR is dynamic time-division duplex (TDD), meaning that the transmission direction, whether it is DL or UL, is dynamically scheduled. This makes the use of periodically scheduled reference signals less dependable since they can only be transmitted if the direction of the duplex scheme happens to agree with the scheduled reference signal for a given subframe.

[0020] A problem with existing solutions is that the SRS is semi-statically configured for periodic transmission. That is not suitable in the envisioned NR where the main candidate duplex scheme is dynamic TDD, meaning that the transmission direction, whether it is DL or UL, is dynamically scheduled.

[0021] A more flexible solution has been proposed for NR, which is an SRS that is explicitly scheduled for every transmission. However, in a beam-based system such as NR, that is not always suitable. During an event such as switching of the TX and/or RX beam, there is likely a need for UL transmissions in conjunction with UL beam tracking. The switching will be in progress for some duration during which it is ineffective to occupy the DL control channel (PDCCH) with a scheduling grant for every wanted SRS transmission. Additionally, using the PDCCH during the whole switching procedure may be unreliable in case the PDCCH

transmission relies on this particular BPL.

[0022] Conversely, a periodic transmission of SRS, such as what semi-persistent scheduling could yield, will be wasteful since the UL transmission is only necessary for a limited (rather brief) time to track the beam transition. Semi-persistent scheduling can in principle be turned on, and then off again. However, this requires RRC signaling which is too slow for beam tracking purposes.

[0023] In short, there is currently no solution to dynamically initiate a burst (i.e., a plurality) of UL transmissions in a short amount of time when there are events, such as changes in the transmission environment, causing updates to the BPL. Such a burst could make a beam tracking more stable.

[0024] Accordingly, this disclosure proposes an event-triggered mechanism for causing a

UE to perform a transmission burst as a result of detecting a need to support a BPL during a transition in the transmission environment.

[0025] An advantage of such an event-triggered mechanism is that beam tracking of a

BPL that requires UL transmissions to maintain the tracking can be supported by a

transmission burst without the need for either semi- statically configured SRS, which is too slow to control, or PDCCH based scheduling for every transmission, which may prove unreliable and wasteful of control-channel resources. Hence, the proposed mechanism solves the need of event-triggered short-duration bursts of UL transmissions in a resource-efficient way.

[0026] An additional advantage of using UL transmissions (e.g., SRSs) to track a BPL is the possibility that the SRS transmission is received by another network node than the intended one. The network may then be able to continue tracking the BPL from this network node. This scenario does not have a reciprocal counterpart since in the case of DL transmission, the signal used to track the BPL is only transmitted from one node. [0027] Hence, in one aspect, there is provided a method for beam management. In some embodiments the method includes: a transmission and reception point (TRP), detecting the occurrence of a beam management event; and in response to detecting the occurrence of the beam management event, the TRP triggering a UE to perform a plurality of RS transmissions comprising a first transmission of a first RS and a second transmission of a second RS. In another embodiment, the method includes: the TRP receiving a beam management message transmitted by the UE, wherein the beam management message comprises information indicating that the UE will perform a plurality of RS transmissions comprising a first transmission of a first RS and a second transmission of a second RS; the TRP using a first RX beam to receive the first RS transmission; and the TRP using a second RX beam to receive the second RS transmission. In another embodiment, the method includes: the UE detecting the occurrence of a beam management event; and in response to detecting the occurrence of the beam management event, the UE performing a plurality of RS transmissions comprising transmitting a first RS during a first subframe and transmitting a second RS during a second subframe.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The accompanying drawings, which are incorporated herein and form part of the specification, illustrate various embodiments.

[0029] FIG. 1 illustrate the use of monitored (e.g., active and non-active) BPLs for communications between a TRP and a UE.

[0030] FIG. 2 is a flow chart illustrating a process according to one embodiment.

[0031] FIG. 3 is a flow chart illustrating a process according to one embodiment.

[0032] FIG. 4 is a flow chart illustrating a process according to one embodiment.

[0033] FIG. 5 is a block diagram of TRP according to some embodiments.

[0034] FIG. 6 is a block diagram of a UE according to some embodiments.

[0035] FIG. 7 is a diagram showing functional modules of an TRP according to some embodiments.

[0036] FIG. 8 is a diagram showing functional modules of an TRP according to some embodiments.

[0037] FIG. 9 is a diagram showing functional modules of an UE according to some embodiments. DETAILED DESCRIPTION

[0038] In FIG. 1 there is shown a TRP 150 (e.g., a base station) utilizing a TRP TX beam

102 to transmit signals to a UE 101 (e.g., control signaling and/or user data), and further showing UE 101 using a UE RX beam 106 to receive signals transmitted by TRP 150. While FIG. 1 illustrates a single TRP communicating with UE 101, in other embodiments two or more TRPs may be communicating with UE 101, wherein one of the TRPs uses the active BPL to communicate with UE 101 and another of the TRPs uses a non-active BPL to communicate with UE 101.

[0039] As mentioned above, when TRP 150 switches a TX and/or an RX beam for communicating with UE 101, there is likely a need for TRP 150 to receive from UE 101 SRSs. The beam switching will be in progress for some duration during which it is ineffective to use the DL control channel (PDCCH) to transmit to UE 101 a scheduling grant for every needed SRS transmission. Additionally, using the PDCCH during the whole switching procedure may be unreliable. One solution is to have UE 101 perform SRS transmission on a continuous basis (e.g., have the UE perform an SRS transmission every nth subframe), such as what semi- persistent scheduling could yield, but such continuous transmissions are wasteful since the UL transmission is only necessary for a limited (rather brief) time to track the beam transition. In principle, such semi-persistent scheduling can be turned on, and then off again, but this requires RRC- signaling, which is too slow for beam tracking purposes.

[0040] Accordingly, this disclosure describes embodiments in which a burst of UL transmissions is initiated when an event occurs that triggers the need to support a BPL during a transition in the transmission environment, e.g. a beam change. That is, for example, when a need for a beam change is detected, UE 101 will perform an UL transmission burst (i.e., transmit a signal n times (n > 1) (e.g., n > 50) within a short duration (e.g., between 50 and 200 milliseconds (ms)). The signal utilized may be the SRS or any other predefined UL reference signal. In one embodiment, the UL transmission burst consists of periodic transmissions of the UL reference signal (RS) - e.g., the UL RS is transmitted say every t subframes (e.g., t=5 or t=10) in a total period of x subframes (e.g., x = 500) for a total of x/t transmissions within the period. In some embodiments, the burst is cancelled when a second event occurs. For example, when the second event occurs TRP 150 may send to UE 101 a Downlink Control Information (DCI) message, which is carried by the PDCCH, comprising a command to stop the burst. In another embodiment, the command to stop the burst is transmitted to UE 101 using a MAC Control Element (MAC CE). The burst parameters, such as x and t, and also including necessary parameters to configure the UL reference signal itself, may be configured in UE 101 using higher-layer signaling.

[0041] The network (e.g., TRP 150) may initiate the UL transmission burst. For example, in some embodiments, TRP 150 causes UE 101 to perform the UL transmission burst by transmitting to UE 101 a single triggering message (e.g., a single scheduling message). In some embodiments, TRP 150 transmits the triggering message to UE 101 by transmitting to UE 101 a DCI that comprises the triggering message or a MAC CE that comprises the triggering message.

[0042] TRP 150, in some embodiments, transmits the triggering message in response to detecting any one or more of the following: a BPL is about to be activated/deactivated; a beam change is needed; a BBU, cell or TRP handover is about to happen; the BPL quality, reflected in different reports from UE 101, such as RSRP or CQI reports, and DL HARQ feedback, has dropped below a threshold or the change rate of the quality has exceeded a threshold; a certain event or combination of events (based on beam tracking, UE position, throughput, BLER, etc.) have previously led to abrupt changes in beam tracking that might be aided by an UL beam- reference signal transmission. These events can. e.g., be recognized through machine learning of such patterns; and a need to measure UE 101-to-UE interference for dynamic TDD-scheduling with different directions in neighboring nodes.

[0043] In some embodiments, UE 101 may initiate the UL transmission burst when any one or more of these events occur: when initiating a beam- switch procedure and,

correspondingly, stop the UL transmission when finished with the beam-switch procedure; when the BPL quality drops below a threshold (measured via RSRP, BLER, etc.) and, correspondingly, stop the UL transmission when detecting a DCI; and when declaring link failure according to a link-monitoring procedure that can be based on e.g., the quality of a reference signal or a timer.

[0044] Additionally, in some embodiments, UE 101 transmits a notification message to

TRP 150 prior to performing the UL transmission burst to notify TRP 150 that the UL transmission burst is imminent. The notification message may take the form of a scheduling request on the physical layer.

[0045] FIG. 2 is a flow chart illustrating a process 200, according to some embodiments.

Process 200 may begin in step 202 in which TRP 150 detects the occurrence of a beam management event for UE 101. In some embodiments, detecting the occurrence of the beam management event comprises TRP 150 detecting at least one of: the activation of a BPL; the deactivation of a BPL; a drop in the quality of a BPL (e.g., a quality measure for the BPL has fallen below a threshold or the rate of change of the quality measure has exceeded a threshold); a need to switch to a new RX beam; and a need to measure UE-to-UE interference for dynamic TDD scheduling with different directions in neighboring nodes.

[0046] Next (step 204), in response to detecting the occurrence of the beam management event, TRP 150 triggers UE 101 to perform a plurality of RS transmissions (i.e., an RS transmission burst) comprising a first transmission of a first RS and a second transmission of a second RS. In some embodiments, the first RS is an SRS and the second RS is the SRS. In some embodiments, the TRP triggers UE 101 to perform the plurality RS transmissions within a short duration (e.g., 100 ms). In some embodiments, as a result of being triggered by TRP 150 to perform the plurality RS transmissions, UE 101 transmits the first RS during a first subframe and transmit the second RS during a second subframe, wherein there are t subframes between the first subframe and the second subframe, wherein t > 0.

[0047] In some embodiments, TRP 150 triggers UE 101 to perform the plurality of RS transmissions by transmitting a triggering message to UE 101. For example, TRP 150 may transmit to UE 101 DCI comprising the triggering message or TRP 150 may transmit to UE 101 a MAC Control Element comprising the triggering message.

[0048] In some embodiments, TRP 150 also causes UE 101 to cease performing the RS transmissions. For example, TRP 150 may transmit to UE 101 a command to cease the RS transmissions, wherein transmitting the command to the UE comprises one of: i) transmitting to the UE DCI comprising the command and ii) transmitting to the UE a MAC Control Element comprising the command. [0049] In some embodiments, process 200 further includes TRP 150 using a first RX beam to receive the first RS transmission (step 206) and using a second RX beam to receive the second RS transmission (step 208).

[0050] FIG. 3 is a flow chart illustrating a process 300, according to some embodiments.

Process 300 may begin in step 302 in which TRP 150 receives a beam management message transmitted by UE 101, wherein the beam management message comprises information indicating that the UE will perform a plurality of RS transmissions (i.e., an RS transmission burst) comprising a first transmission of a first RS and a second transmission of a second RS.

[0051] In step 304, TRP 150 uses a first receive, RX, beam to receive the first RS transmission. And in step 306, TRP 150 uses a second RX beam to receive the second RS transmission. In some embodiments, process 300 further includes TRP 150 comparing the performance of the first RX beam with respect to receiving the first RS transmission to the performance of the second RX beam with respect to receiving the second RS transmission (step 308), and, based on the comparison, TRP 150 selecting one of the first RX beam and the second RX beam for use in receiving signals transmitted by UE 101 (step 310).

[0052] FIG. 4 is a flow chart illustrating a process 400, according to some embodiments.

Process 400 may begin in step 402 in which UE 101 detects the occurrence of a beam

management event. In some embodiments, UE 101 detects the occurrence of the beam management event by detecting at least one of: activation of a BPL; deactivation of a BPL; a drop in the quality of a BPL (e.g., a quality measure for the BPL has fallen below a threshold or the rate of change of the quality measure has exceeded a threshold); an initiation of a beam- switch procedure; and a link failure. In other embodiments, UE 101 detects the occurrence of the beam management event by receiving a triggering message transmitted by TRP 150.

[0053] In step 404, in response to detecting the occurrence of the beam management event, UE 101 performs a plurality of RS transmissions (i.e., an RS transmission burst) comprising transmitting a first RS during a first subframe and transmitting a second RS during a second subframe (there may be some number of subframes (e.g., 5 or 10) separating the first subframe from the second subframe in which UE 101 does not transmit any SRS). In some embodiments, the first RS is an SRS and the second RS is the SRS. In some embodiments, UE 101 performs the RS transmission burst within a short duration (e.g. less than 200 ms). [0054] In some embodiments, process 400 further includes UE 101, prior to performing the plurality of RS transmissions, transmitting to TRP 150 a beam management message for informing TRP 150 that UE 101 will perform the plurality of RS transmissions, wherein UE 101 transmits the beam management message in response to detecting the occurrence of the beam management event (step 403).

[0055] FIG. 5 is a block diagram of TRP 150 according to some embodiments. As shown in FIG. 5, TRP 150 may comprise: a data processing system (DPS) 502, which may include one or more processors (P) 555 (e.g., a general-purpose microprocessor and/or one or more other processors, such as an application- specific integrated circuit (ASIC), field- programmable gate arrays (FPGAs), and the like); a transmitter 505 and a receiver 506 coupled to an antenna 522 for use in wirelessly communicating with a UE; a network interface 548 for use in connecting TRP 150 to a network 110 (e.g., an Internet Protocol (IP) network) so that TRP 150 can communicate with other devices connected to network 110; and local storage unit (a.k.a., "data storage system") 508, which may include one or more non-volatile storage devices and/or one or more volatile storage devices (e.g., random-access memory (RAM)). In embodiments where TRP 150 includes a general-purpose microprocessor, a computer program product (CPP) 541 may be provided. CPP 541 includes a computer-readable medium (CRM) 542 storing a computer program (CP) 543 comprising computer-readable instructions (CRI) 544. CRM 542 may be a non-transitory computer-readable medium, such as, but not limited, to magnetic media (e.g., a hard disk), optical media (e.g., a DVD), memory devices (e.g., random- access memory), and the like. In some embodiments, the CRI 544 of computer program 543 is configured such that when executed by data processing system 502, the CRI causes TRP 150 to perform steps described above (e.g., steps described above with reference to the flow charts). In other embodiments, TRP 150 may be configured to perform steps described herein without the need for code. That is, for example, data processing system 502 may consist merely of one or more ASICs. Hence, the features of the embodiments described herein may be implemented in hardware and/or software.

[0056] FIG. 6 is a block diagram of a UE 101 according to some embodiments. As shown in FIG. 6, UE 101 may comprise: a data processing system (DPS) 602, which may include one or more processors 655 (e.g., a general-purpose microprocessor and/or one or more other processors, such as an application-specific integrated circuit (ASIC), field-programmable gate arrays (FPGAs), and the like); a transmitter 605 and a receiver 606 coupled to an antenna 622 for use in wirelessly communicating with a radio-access network (RAN) node (e.g., a TRP); and local storage unit (a.k.a., "data storage system") 612, which may include one or more nonvolatile storage devices and/or one or more volatile storage devices (e.g., random-access memory (RAM)). In embodiments where UE 101 includes a general-purpose microprocessor, a computer program product (CPP) 641 may be provided. CPP 641 includes a computer-readable medium (CRM) 642 storing a computer program (CP) 643 comprising computer-readable instructions (CRI) 644. CRM 642 may be a non-transitory computer-readable medium, such as, but not limited, to magnetic media (e.g., a hard disk), optical media (e.g., a DVD), memory devices (e.g., random-access memory), and the like. In some embodiments, the CRI 644 of computer program 643 is configured such that when executed by data processing system 602, the CRI causes UE 101 to perform steps described above (e.g., steps described above with reference to the flow charts). In other embodiments, UE 101 may be configured to perform steps described herein without the need for code. That is, for example, data processing system 602 may consist merely of one or more ASICs. Hence, the features of the embodiments described herein may be implemented in hardware and/or software.

[0057] FIG. 7 is a diagram showing functional modules of TRP 150 according to some embodiments. In the embodiment shown, TRP 150 includes: a beam management detection module 702 configured to detect the occurrence of a beam management event; and an RS transmission burst triggering module 704 that is configured such that, in response to the beam management detection module detecting the occurrence of the beam management event, the RS transmission burst triggering module triggers UE 101 to perform a plurality of RS transmissions comprising a first transmission of a first RS and a second transmission of a second RS.

[0058] FIG. 8 is a diagram showing functional modules of TRP 150 according to some embodiments. In the embodiment shown, TRP 150 includes: a message processing module 802 for processing a received beam management message transmitted by UE 101, wherein the received beam management message comprises information indicating that the UE will perform a plurality of RS transmissions (i.e., an RS transmission burst) comprising a first transmission of a first RS and a second transmission of a second RS; and a beam module 804 configured to i) use a first receive, RX, beam to receive the first RS transmission and ii) use a second RX beam to receive the second RS transmission.

[0059] FIG. 9 is a diagram showing functional modules of UE 101 according to some embodiments. In the embodiment shown, UE 101 includes: a beam management detection module 902 configured to detect the occurrence of a beam management event; and an RS transmission burst module 904 configured such that, in response to the beam management module detecting the occurrence of the beam management event, the RS transmission burst module employs a transmitter to perform a plurality of RS transmissions (i.e., an RS

transmission burst) comprising transmitting a first RS during a first subframe and transmitting a second RS during a second subframe.

[0060] While various embodiments of the present disclosure are described herein

(including the appendices, if any), it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of the present disclosure should not be limited by any of the above-described exemplary embodiments. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the disclosure unless otherwise indicated herein or otherwise clearly contradicted by context.

[0061] Additionally, while the processes described above and illustrated in the drawings are shown as a sequence of steps, this was done solely for the sake of illustration. Accordingly, it is contemplated that some steps may be added, some steps may be omitted, the order of the steps may be re-arranged, and some steps may be performed in parallel.

[0062] ABBREVIATIONS

[0063] 5G Fifth-Generation Mobile Radio Access

[0064] BBU Base-Band Unit

[0065] BLER Block-Error Rate

[0066] BPL Beam-Pair Link

[0067] BRRS Beam-Refinement Reference Signal

[0068] BRS Beam-Reference Signal

[0069] CE Control Element

[0070] CSI-RS Channel- State Information Reference Signal

[0071] DCI Downlink Control Information (message) [0072] eNB enhanced Node B (i.e., Base Station)

[0073] HARQ Hybrid Automatic Repeat reQuest

[0074] LTE Long-Term Evolution

[0075] MAC Medium- Access Control

[0076] NR New Radio

[0077] PDCCH Physical Downlink Control Channel

[0078] RRC Radio-Resource Control

[0079] RSRP Reference Signal Received Power

[0080] Rx Receiver

[0081] SRS Sounding Reference Signal

[0082] Tx Transmitter

[0083] TRP Transmission and Reception Point

Claims

1. A method for beam management, the method comprising:

a transmission and reception point, TRP (150), detecting the occurrence of a beam management event; and

in response to detecting the occurrence of the beam management event, the TRP (150) triggering a user equipment, UE (101), to perform a plurality of reference signal, RS, transmissions comprising a first transmission of a first RS and a second transmission of a second RS.

2. The method of claim 1, further comprising:

the TRP (150) using a first receive, RX, beam to receive the first RS transmission; and the TRP (150) using a second RX beam to receive the second RS transmission.

3. The method of claim 1 or 2, wherein the first RS is a Sounding Reference Signal, SRS, and the second RS is the SRS.

4. The method of any one of claims 1-3, wherein triggering the UE (101) to perform the plurality RS transmissions comprises triggering the UE (101) to perform the plurality of transmission within a short duration.

5. The method of any one of claims 1-4, wherein triggering the UE (101) to perform the plurality RS transmissions comprises triggering the UE (101) to transmit the first RS during a first subframe and transmit the second RS during a second subframe, wherein there are t subframes between the first subframe and the second subframe, wherein t > 0.

6. The method of any one of claims 1-5, wherein triggering the UE (101) to perform the plurality of RS transmissions consists of transmitting a triggering message to the UE (101).

7. The method of claim 6, wherein transmitting the triggering message to the UE (101) comprises one of: i) transmitting to the UE (101) Downlink Control Information (DCI) comprising the triggering message and ii) transmitting to the UE (101) a MAC Control Element comprising the triggering message.

8. The method of any one of claims 1-7, further comprising causing the UE (101) to cease performing the RS transmissions.

9. The method of any one of claims 1-8, wherein causing the UE (101) to cease performing the RS transmissions comprises transmitting to the UE (101) a command to cease the RS transmissions, wherein transmitting command to the UE (101) comprises one of: i) transmitting to the UE (101) Downlink Control Information (DCI) comprising the command and ii) transmitting to the UE (101) a MAC Control Element comprising the command.

10. The method of any one of claims 1-9, wherein detecting the occurrence of the beam management event comprises detecting at least one of:

the activation of a beam pair link, BPL,

the deactivation of a BPL,

a drop in the quality of a BPL,

a need to switch to a new RX beam, and

a need to measure UE-to-UE interference for dynamic TDD scheduling with different directions in neighboring nodes.

11. The method of claim 2, further comprising:

the TRP (150) comparing the performance of the first RX beam with respect to receiving the first RS transmission to the performance of the second RX beam with respect to receiving the second RS transmission; and

based on the comparison selecting one of the first RX beam and the second RX beam for use in receiving signals transmitted by the UE (101).

12. A transmission and reception point, TRP (150), the TRP (150) being adapted to: detect the occurrence of a beam management event; and

in response to detecting the occurrence of the beam management event, trigger a user equipment, UE (101), to perform a plurality of reference signal, RS, transmissions comprising a first transmission of a first RS and a second transmission of a second RS.

13. A transmission and reception point, TRP (150), the TRP (150) comprising:

a beam management detection module (702) configured to detect the occurrence of a beam management event; and

an RS transmission burst triggering module (704) that is configured such that, in response to the beam management detection module detecting the occurrence of the beam management event, the RS transmission burst triggering module triggers a user equipment, UE (101), to perform a plurality of RS transmissions comprising a first transmission of a first RS and a second transmission of a second RS.

14. The TRP (150) of claim 12 or 13, wherein:

the TRP (150) is configured to use a first receive, RX, beam to receive the first RS transmission; and

the TRP (150) is configured to use a second RX beam to receive the second RS transmission.

15. The TRP of claim 14, wherein:

the TRP (150) is configured to compare the performance of the first RX beam with respect to receiving the first RS transmission to the performance of the second RX beam with respect to receiving the second RS transmission; and

the TRP (150) is configured to select one of the first RX beam and the second RX beam for use in receiving signals transmitted by the UE (101) based on the comparison.

16. The TRP (150) of any one of claims 12-15, wherein the TRP (150) is configured to trigger the UE (101) to perform the plurality RS transmissions within a short duration.

17. The TRP (150) of any one of claims 12-16, wherein

the TRP (150) is configured to trigger the UE (101) to perform the plurality of RS transmissions by transmitting a triggering message to the UE (101), and

transmitting the triggering message to the UE (101) comprises one of: i) transmitting to the UE (101) Downlink Control Information, DCI, comprising the triggering message and ii) transmitting to the UE (101) a MAC Control Element comprising the triggering message.

18. The TRP (150) of any one of claims 12-17, wherein

the TRP (150) is further configured to transmit to the UE (101) a command to cause the UE (101) to cease the RS transmissions, and

the TRP (150) is configured to transmit the command by i) transmitting to the UE (101) Downlink Control Information, DCI, comprising the command or ii) transmitting to the UE (101) a MAC Control Element comprising the command.

19. The TRP (150) of any one of claims 12-18, wherein detecting the occurrence of the beam management event comprises detecting at least one of:

the activation of a beam pair link, BPL,

the deactivation of a BPL,

a drop in the quality of a BPL,

a need to switch to a new RX beam, and

20. A method for beam management, comprising:

a transmission and reception point, TRP (150), receiving a beam management message transmitted by a user equipment, UE (101), wherein the beam management message comprises information indicating that the UE (101) will perform a plurality of reference signal, RS, transmissions comprising a first transmission of a first RS and a second transmission of a second RS;

21. The method of claim 20, further comprising:

22. A transmission and reception point, TRP (150), the TRP (150) being adapted to: receive a beam management message transmitted by a user equipment, UE (101), wherein the beam management message comprises information indicating that the UE (101) will perform a plurality of reference signal, RS, transmissions comprising a first transmission of a first RS and a second transmission of a second RS;

use a first receive, RX, beam to receive the first RS transmission; and

use a second RX beam to receive the second RS transmission.

23. A transmission and reception point, TRP (150), comprising:

a message processing module (802) for processing a received beam management message transmitted by a user equipment, UE (101), wherein the received beam management message comprises information indicating that the UE (101) will perform a plurality of reference signal, RS, transmissions comprising a first transmission of a first RS and a second transmission of a second RS;

a beam module (804) configured to i) use a first receive, RX, beam to receive the first RS transmission and ii) use a second RX beam to receive the second RS transmission.

24. The TRP (150) of claim 22 or 23, wherein:

the TRP (150) is configured to compare the performance of the first RX beam with respect to receiving the first RS transmission to the performance of the second RX beam with respect to receiving the second RS transmission; and the TRP (150) is further configured such that, based on the comparison, the TRP (150) selects one of the first RX beam and the second RX beam for use in receiving signals transmitted by the UE (101).

25. A method for beam management, comprising:

a user equipment, UE (101), detecting the occurrence of a beam management event; and in response to detecting the occurrence of the beam management event, the UE (101) performing a plurality of reference signal, RS, transmissions comprising transmitting a first RS during a first subframe and transmitting a second RS during a second subframe.

26. The method of claim 25, wherein performing the plurality RS transmissions comprises performing the plurality of transmission within a duration less than or about equal to 100 milliseconds.

27. The method of claim 25 or 26, wherein

there are t subframes between the first subframe and the second subframe, wherein t > 0, and

during each of the t subframes the UE (101) does not transmit an SRS.

28. The method of any one of claims 25-27, further comprising:

prior to performing the plurality of RS transmissions, the UE (101) transmitting to a TRP (150) a beam management message for informing the TRP (150) that the UE (101) will perform the plurality of RS transmissions, wherein the UE (101) transmits the beam management message in response to detecting the occurrence of the beam management event.

29. The method of any one of claim 25-28, wherein detecting the occurrence of the beam management event comprises detecting at least one of:

the activation of a beam pair link, BPL,

the deactivation of a BPL,

a drop in the quality of a BPL, an initiation of a beam- switch procedure,

a link failure, and

a triggering message transmitted by a TRP (150).

30. A user equipment, UE (101), the UE (101) being adapted to:

detect the occurrence of a beam management event; and

in response to detecting the occurrence of the beam management event, perform a plurality of reference signal, RS, transmissions comprising transmitting a first RS during a first subframe and transmitting a second RS during a second subframe.

31. A user equipment, UE (101), the UE (101) comprising:

a beam management detection module (902) configured to detect the occurrence of a beam management event; and

an RS transmission burst module (904) configured such that, in response to the beam management module detecting the occurrence of the beam management event, the RS transmission burst module employs a transmitter to perform a plurality of reference signal, RS, transmissions comprising transmitting a first RS during a first subframe and transmitting a second RS during a second subframe.

32. The UE (101) of claim 30 or 31, wherein the UE (101) is configured to perform the plurality RS transmissions within a duration of less than or about equal to 100 milliseconds.