CSI-RS measurement

Abstract

Example embodiments of the present disclosure provide a solution for channel state information reference signal (CSI-RS) measurement, especially for enabling CSI- RS measurement for a layer 1 (L1) / layer 2 (L2)-triggered mobility (LTM) procedure. In an example method, a first network device receives a configuration of at least one CSI- RS of a second network device. The first network device determines, based on a measurement report from a user equipment (UE) and the configuration, to enable use of the at least one CSI-RS of the second network device. The first network device transmits a first request for enabling use of the at least one CSI-RS of the second network device. In this way, CSI-RS measurement for the LTM procedure can be supported.

Description

CSI-RS MEASUREMENTFIELD

[0001] Various example embodiments relate to the field of communication, and in particular, to devices, methods, apparatuses, and a computer readable medium for channel state information reference signal (CSI-RS) measurement, especially for enabling CSI- RS measurement for a layer 1 (Ll) / layer 2 (L2)-triggered mobility (LTM) procedure.BACKGROUND

[0002] A communication network can be seen as a facility that enables communications between two or more communication devices, or provides communication devices access to a data network. A mobile or wireless communication network is one example of a communication network.

[0003] Such communication networks operate in accordance with standards, such as those promulgated by 3GPP (Third Generation Partnership Project) or ETSI (European Telecommunications Standards Institute). Examples of such standards include the so- called 5G (5th Generation) standard or other standards promulgated by 3GPP.SUMMARY

[0004] In general, example embodiments of the present disclosure provide a solution for CSI-RS measurement, for instance, for enabling LTM reporting using candidate cell CSI-RS of a candidate cell.

[0005] In a first aspect, there is provided a first network device. The first network device comprises at least one processor and at least one memory storing instructions that, when executed by the at least one processor, cause the first network device at least to: receive a configuration of at least one channel state information reference signal (CSI-RS) of a second network device; determine, based on a measurement report from a user equipment (UE) and the configuration, to enable use of the at least one CSI-RS of the second network device; and transmit a first request for enabling use of the at least one CSI-RS of the second network device.

[0006] In a second aspect, there is provided a second network device. The second network device comprises at least one processor and at least one memory storinginstructions that, when executed by the at least one processor, cause the second network device at least to: transmit a configuration of at least one channel state information reference signal (CSI-RS) of the second network device; receive a second request for enabling use of the at least one CSI-RS; and transmit the at least one CSI-RS.

[0007] In a third aspect, there is provided a third network device. The third network device comprises at least one processor and at least one memory storing instructions that, when executed by the at least one processor, cause the third network device at least to: receive, from a first network device, a first request for enabling use of channel state information reference signal (CSI-RS) of a second network device; and transmit, to the second network device, a second request for enabling use of the CSI-RS of the second network device.

[0008] In a fourth aspect, there is provided a first network device. The first network device comprises at least one processor and at least one memory storing instructions that, when executed by the at least one processor, cause the first network device at least to: receive a configuration of at least one channel state information reference signal (CSI- RS) of a second network device; receive a second indication related to activating the at least one CSI-RS of the second network device; and trigger at least one UE served by the first network device to measure the activated at least one CSI-RS.

[0009] In a fifth aspect, there is provided a second network device. The second network device comprises at least one processor and at least one memory storing instructions that, when executed by the at least one processor, cause the second network device at least to: transmit a configuration of at least one channel state information reference signal (CSI- RS) for at least one user equipment (UE) served by a second network device; determine to activate the at least one CSI-RS for the at least one UE served by the second network device; and transmit a first indication related to activating the at least one CSI-RS.

[0010] In a sixth aspect, there is provided a third network device. The third network device comprises at least one processor and at least one memory storing instructions that, when executed by the at least one processor, cause the third network device at least to: receive, from a second network device, a first indication related to activating channel state information reference signal (CSI-RS) of the second network device, wherein the second indication is based on a decision to activate the CSI-RS for at least one user equipment (UE) served by the second network device; and transmit, to the first network device, a second indication related to activating CSI-RS for at least one user equipment (UE) servedby the second network device.

[0011] In a seventh aspect, there is provided a method. The method comprises: receiving a configuration of at least one channel state information reference signal (CSI-RS) of a second network device; determining, based on a measurement report from a user equipment (UE) and the configuration, to enable use of the at least one CSI-RS of the second network device; and transmitting a first request for enabling use of the at least one CSI-RS of the second network device.

[0012] In an eighth aspect, there is provided a method. The method comprises: transmitting a configuration of at least one channel state information reference signal (CSI-RS) of the second network device; receiving a second request for enabling use of the at least one CSI-RS; and transmitting the at least one CSI-RS.

[0013] In a ninth aspect, there is provided a method. The method comprises: receiving, from a first network device, a first request for enabling use of channel state information reference signal (CSI-RS) of a second network device; and transmitting, to the second network device, a second request for enabling use of the CSI-RS of the second network device.

[0014] In a tenth aspect, there is provided a method. The method comprises: receiving a configuration of at least one channel state information reference signal (CSI-RS) of a second network device; receiving a second indication related to activating the at least one CSI-RS of the second network device; and triggering at least one UE served by the first network device to measure the activated at least one CSI-RS.

[0015] In an eleventh aspect, there is provided a method. The method comprises: transmitting a configuration of at least one channel state information reference signal (CSI-RS) for at least one user equipment (UE) served by a second network device; determining to activate the at least one CSI-RS for the at least one UE served by the second network device; and transmitting a first indication related to activating the at least one CSI-RS.

[0016] In a twelfth aspect, there is provided a method. The method comprises: receiving, from a second network device, a first indication related to activating channel state information reference signal (CSI-RS) of the second network device, wherein the second indication is based on a decision to activate the SP CSI-RS for at least one user equipment (UE) served by the second network device; and transmitting, to a first network device, a second indication related to activating SP CSI-RS of the second network device.

[0017] In a thirteenth aspect, there is provided an apparatus. The apparatus comprises: means for receiving a configuration of at least one channel state information reference signal (CSI-RS) of a second network device; means for determining, based on a measurement report from a user equipment (UE), to enable use of the at least one CSI- RS of the second network device; and means for transmitting a first request for enabling use of the at least one CSI-RS of the second network device.

[0018] In a fourteenth aspect, there is provided an apparatus. The apparatus comprises: means for transmitting a configuration of at least one channel state information reference signal (CSI-RS) of the second network device; means for receiving a second request for enabling use of the at least one CSI-RS; and means for transmitting the at least one CSI- RS.

[0019] In a fifteenth aspect, there is provided an apparatus. The apparatus comprises: means for receiving, from a first network device, a first request for enabling use of channel state information reference signal (CSI-RS) of a second network device; and means for transmitting, to the second network device, a second request for enabling use of the CSI-RS of the second network device.

[0020] In a sixteenth aspect, there is provided an apparatus. The apparatus comprises: means for receiving a configuration of at least one channel state information reference signal (CSI-RS) of a second network device; means for receiving a second indication related to activating the at least one CSI-RS of the second network device; and means for triggering at least one UE served by the first network device to measure the activated at least one CSI-RS.

[0021] In a seventeenth aspect, there is provided an apparatus. The apparatus comprises: means for transmitting a configuration of at least one channel state information reference signal (CSI-RS) for at least one user equipment (UE) served by a second network device; means for determining to activate the at least one CSI-RS for the at least one UE served by the second network device; and means for transmitting a first indication related to activating the at least one CSI-RS.

[0022] In an eighteenth aspect, there is provided an apparatus. The apparatus comprises: means for receiving, from a second network device, a first indication related to activating channel state information reference signal (CSI-RS) of the second network device, wherein the second indication is based on a decision to activate the SP CSI-RS for at least one user equipment (UE) served by the second network device; and means fortransmitting, to a first network device, a second indication related to activating SP CSI- RS of the second network device.

[0023] In a nineteenth aspect, there is provided a non-transitory computer readable medium comprising program instructions for causing an apparatus to perform at least the method of any one of the above seventh to twelfth aspect.

[0024] In a twentieth aspect, there is provided a computer program comprising instructions, which, when executed by an apparatus, cause the apparatus to perform at least the method of any one of the above seventh to twelfth aspect.

[0025] In a twenty-first aspect, there is provided a first network device. The first network device comprises: receiving circuitry configured to receive a configuration of at least one channel state information reference signal (CSI-RS) of a second network device; determining circuitry configured to determining, based on a measurement report from a user equipment (UE) and the configuration, to enable use of the at least one CSI-RS of the second network device; and transmitting circuitry configured to transmitting a first request for enabling use of the at least one CSI-RS of the second network device.

[0026] In a twenty-second aspect, there is provided a second network device. The second network device comprises: first transmitting circuitry configured to transmit a configuration of at least one channel state information reference signal (CSI-RS) of the second network device; receiving circuitry configured to receive a second request for enabling use of the at least one CSI-RS; and second transmitting circuitry configured to transmit the at least one CSI-RS.

[0027] In a twenty-third aspect, there is provided a third network device. The third network device comprises: receiving circuitry configured to receive, from a first network device, a first request for enabling use of channel state information reference signal (CSI- RS) of a second network device; and transmitting circuitry configured to transmit, to the second network device, a second request for enabling use of the CSI-RS of the second network device.

[0028] In a twenty-fourth aspect, there is provided a fourth network device. The fourth network device comprises: first receiving circuitry configured to receive a configuration of at least one channel state information reference signal (CSI-RS) of a second network device; second receiving circuitry configured to receive a second indication related to activating the at least one CSI-RS of the second network device; and triggering circuitry configured to trigger at least one UE served by the first network device to measure theactivated at least one CSI-RS.

[0029] In a twenty-fifth aspect, there is provided a fifth network device. The fifth network device comprises: first transmitting circuitry configured to transmit a configuration of at least one channel state information reference signal (CSI-RS) for at least one user equipment (UE) served by a second network device; determining circuitry configured to determine to activate the at least one CSI-RS for the at least one UE served by the second network device; and second transmitting circuitry configured to transmit a first indication related to activating the at least one CSI-RS.

[0030] In a twenty-sixth aspect, there is provided a sixth network device. The sixth network device comprises: receiving circuitry configured to receive, from a second network device, a first indication related to activating channel state information reference signal (CSI-RS) of the second network device, wherein the second indication is based on a decision to activate the SP CSI-RS for at least one user equipment (UE) served by the second network device; and transmitting circuitry configured to transmit, to a first network device, a second indication related to activating SP CSI-RS of the second network device.

[0031] It is to be understood that the summary section is not intended to identify key or essential features of embodiments of the present disclosure, nor is it intended to be used to limit the scope of the present disclosure. Other features of the present disclosure will become easily comprehensible through the following description.BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Some example embodiments will now be described with reference to the accompanying drawings, in which:

[0033] FIG. 1 illustrates an example communication network in which embodiments of the present disclosure may be implemented;

[0034] FIG. 2 illustrates a first example of a process flow in accordance with some example embodiments of the present disclosure;

[0035] FIG. 3 illustrates a second example of a process flow in accordance with some example embodiments of the present disclosure;

[0036] FIG. 4 illustrates a third example of a process flow in accordance with some example embodiments of the present disclosure;

[0037] FIG. 5 illustrates a fourth example of a process flow in accordance with some example embodiments of the present disclosure;

[0038] FIG. 6 illustrates an example intra-centralized unit (CU) LTM procedure in accordance with some example embodiments of the present disclosure;

[0039] FIGS. 7A-7B illustrate an example inter-CU LTM procedure in accordance with some example embodiments of the present disclosure;

[0040] FIG. 8 illustrates another example intra-CU LTM procedure in accordance with some example embodiments of the present disclosure;

[0041] FIGS. 9A-9B illustrate another example inter-CU LTM procedure in accordance with some example embodiments of the present disclosure;

[0042] FIG. 10 illustrates a flowchart of an example method implemented at a first network device in accordance with some embodiments of the present disclosure;

[0043] FIG. 11 illustrates a flowchart of an example method implemented at a second network device in accordance with some embodiments of the present disclosure;

[0044] FIG. 12 illustrates a flowchart of an example method implemented at a third network device in accordance with some embodiments of the present disclosure;

[0045] FIG. 13 illustrates a flowchart of another example method implemented at a first network device in accordance with some embodiments of the present disclosure;

[0046] FIG. 14 illustrates a flowchart of another example method implemented at a second network device in accordance with some embodiments of the present disclosure;

[0047] FIG. 15 illustrates a flowchart of another example method implemented at a third network device in accordance with some embodiments of the present disclosure;

[0048] FIG. 16 illustrates a simplified block diagram of a device that is suitable for implementing some example embodiments of the present disclosure; and

[0049] FIG. 17 illustrates a block diagram of an example of a computer-readable medium in accordance with some example embodiments of the present disclosure.

[0050] Throughout the drawings, the same or similar reference numerals represent the same or similar elements.DETAILED DESCRIPTION

[0051] Principles of the present disclosure will now be described with reference to some example embodiments. It is to be understood that these embodiments are described only for the purpose of illustration and help those skilled in the art to understand and implement the present disclosure, without suggesting any limitation as to the scope of the disclosure. The disclosure described herein can be implemented in various manners other than the ones described below.

[0052] In the following description and claims, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skills in the art to which this disclosure belongs.

[0053] References in the present disclosure to “one embodiment,” “an embodiment,” “an example embodiment,” and the like indicate that the embodiment described may include a particular feature, structure, or characteristic, but it is not necessary that every embodiment includes the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

[0054] It shall be understood that although the terms “first” and “second” etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and similarly, a second element could be termed a first element, without departing from the scope of example embodiments. As used herein, the term “and / or” includes any and all combinations of one or more of the listed terms.

[0055] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises”, “comprising”, “has”, “having”, “includes” and / or “including”, when used herein, specify the presence of stated features, elements, and / or components etc., but do not preclude the presence or addition of one or more other features, elements,components and / or combinations thereof. As used herein, “at least one of the following: ” and “at least one of ” and similar wording, where the list of two or more elements are joined by “and” or “or”, mean at least any one of the elements, or at least any two or more of the elements, or at least all the elements.

[0056] As used in this application, the term “circuitry” may refer to one or more or all of the following:(a) hardware-only circuit implementations (such as implementations in only analog and / or digital circuitry) and(b) combinations of hardware circuits and software, such as (as applicable):(i) a combination of analog and / or digital hardware circuit(s) with software / firmware and(ii) any portions of hardware processor(s) with software (including digital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as a mobile phone or server, to perform various functions) and(c) hardware circuit(s) and or processor(s), such as a microprocessor(s) or a portion of a microprocessor(s), that requires software (for example, firmware) for operation, but the software may not be present when it is not needed for operation.

[0057] This definition of circuitry applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term circuitry also covers an implementation of merely a hardware circuit or processor (or multiple processors) or portion of a hardware circuit or processor and its (or their) accompanying software and / or firmware. The term circuitry also covers, for example and if applicable to the particular claim element, a baseband integrated circuit or processor integrated circuit for a mobile device or a similar integrated circuit in server, a cellular network device, or other computing or network device.

[0058] As used herein, the term “network”, “communication network” or “data network” refers to a network following any suitable communication standards, such as long term evolution (LTE), LTE-advanced (LTE-A), wideband code division multiple access (WCDMA), high-speed packet access (HSPA), narrow band Internet of things (NB-IoT), wireless fidelity (Wi-Fi) and so on. Furthermore, the communications between a terminaldevice and a network device / element in the communication network may be performed according to any suitable generation communication protocols, including, but not limited to, the fourth generation (4G), 4.5G, the future fifth generation (5G), IEEE 802.11 communication protocols, and / or any other protocols either currently known or to be developed in the future. Embodiments of the present disclosure may be applied in various communication systems. Given the rapid development in communications, there will of course also be future type communication technologies and systems with which the present disclosure may be embodied. It should not be seen as limiting the scope of the present disclosure to only the aforementioned system.

[0059] As used herein, the term “network device” refers to a node in a communication network via which a terminal device receives services (e.g., positioning services) therefrom. The network device may refer to a core network device or access network device, such as base station (BS) or an access point (AP) or a transmission and reception point (TRP), for example, a node B (NodeB or NB), an evolved NodeB (eNodeB or eNB), a NR NB (also referred to as a gNB), a remote radio unit (RRU), a radio header (RH), a remote radio head (RRH), a WiFi device, a relay, a low power node such as a femto, a pico, and so forth, depending on the applied terminology and technology. In the following description, the terms “network device”, “AP device”, “AP” and “access point” may be used interchangeably.

[0060] The term “terminal device” refers to any end device that may be capable of wireless communication. By way of example rather than limitation, a terminal device may also be referred to as a communication device, user equipment (UE), a Subscriber Station (SS), a Portable Subscriber Station, a Mobile Station (MS), a station (STA) or station device, or an Access Terminal (AT). The terminal device may include, but not limited to, a mobile phone, a cellular phone, a smart phone, voice over IP (VoIP) phones, wireless local loop phones, a tablet, a wearable terminal device, a personal digital assistant (PDA), portable computers, desktop computer, image capture terminal devices such as digital cameras, gaming terminal devices, music storage and playback appliances, vehiclemounted wireless terminal devices, wireless endpoints, mobile stations, laptop-embedded equipment (LEE), laptop-mounted equipment (LME), USB dongles, smart devices, wireless customer-premises equipment (CPE), an Internet of Things (loT) device, a watch or other wearable, a head-mounted display (HMD), a vehicle, a drone, a medical device and applications (for example, remote surgery), an industrial device and applications (for example, a robot and / or other wireless devices operating in an industrial and / or anautomated processing chain contexts), a consumer electronics device, a device operating on commercial and / or industrial wireless networks, and the like. In the following description, the terms “station”, “station device”, “STA”, “terminal device”, “communication device”, “terminal”, “user equipment” and “UE” may be used interchangeably.

[0061] Principles and embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. Reference is first made to FIG. 1, which illustrates an example communication system 100 in which embodiments of the present disclosure may be implemented. The system 100 includes a plurality of network devices, such as a network device 111 and a network device 112. The network devices 111, 112 serve respective areas 101 and 102 (also called as cells 101 and 102) using different frequency bands in both DL and UL. Such a frequency band may also be referred to as an operating frequency band of the corresponding network device.

[0062] The system 100 also includes one or more terminal devices, such as terminal devices 120, 121, 122. The terminal devices 120, 121, 122 are capable of connecting and communicating in an UL and DL with either or both of the network devices 111, 112 as long as the terminal devices located within the corresponding cells. In communication systems, an UL refers to a link in a direction from a terminal device to a network device, and a DL refers to a link in a direction from the network device to the terminal device. In addition to communicating the terminal devices 120, 121, 122, the network devices 111, 112 may also communicate with each other, for example, via a backhaul link.

[0063] It is to be understood that the number of network devices and terminal devices is only for the purpose of illustration without suggesting any limitations. The system 100 may include any suitable number of network devices and terminal devices adapted for implementing embodiments of the present disclosure. Although not shown, it would be appreciated that one or more terminal devices may be located in the cell 101 or 102.

[0064] Communications in the communication system 100 may be implemented according to any proper communication protocol(s), comprising, but not limited to, cellular communication protocols of the first generation (1G), the second generation (2G), the third generation (3G), the fourth generation (4G) and the fifth generation (5G) and on the like, wireless local network communication protocols such as Institute for Electrical and Electronics Engineers (IEEE) 802.11 and the like, and / or any other protocols currently known or to be developed in the future. Moreover, the communication mayutilize any proper wireless communication technology, comprising but not limited to: Code Division Multiple Access (CDMA), Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Frequency Division Duplex (FDD), Time Division Duplex (TDD), Multiple-Input Multiple-Output (MIMO), Orthogonal Frequency Division Multiple (OFDM), Discrete Fourier Transform spread OFDM (DFT- s-OFDM) and / or any other technologies currently known or to be developed in the future.

[0065] The coverage ranges of the cells 102, 104 of the network devices 111 is tightly related to the operating frequency bands of the network devices 111, 112. FIG. 1 shows an example where the operating frequency bands of the network devices 111, 113 are different, with the operating frequency band of the network device 111 higher than the operating frequency band of the network device 112. It is very possible that the coverage range of the cell 101 is smaller than that of the cell 102, due to a more serious path-loss situation in the high frequency band system. In the shown example, the cell 101 is overlapped with the cell 102. The large cell 102 may sometimes be referred to as a macro cell and the network device 112 may be referred to as a macro base station, while the relatively small cell 101 may sometimes be referred to as a small cell and the network device 111 may be referred to as a small base station. As a specific example, the network device 111 may be operating at sub6GHz, such as 3.5 GHz, while the network device 112 may be operating at a millimetre-wave (mmW) frequency band, such as at 28 GHz. It is to be understood that other operating frequency bands are also possible for the network devices 111, 112.

[0066] In some scenarios, the cell 101 and / or the cell 102 may have an asymmetric UL and DL budget. Such asymmetric budget easily happens in a cell with a high frequency band. For example, in a case of operating at the mmW frequency band, the different budget between the UL and DL may be up to 25 dB. FIG. 1 shows that the asymmetric UL and DL in the cell 101. For example, the cell 101 includes an UL coverage area 103 and a DL coverage area that is the same as the range of the cell 101. The UL coverage area 103 is smaller than the DL coverage area. For example, up to 25 dB budget difference may lead to a situation where the UL coverage area is only about 1 / 4 of the DL coverage area. The main reasons are the small UL transmission power of terminal devices and / or smaller UL transmission beamforming gain, as compared with the DL case.

[0067] Due to the UL / DL coverage asymmetry in the cell 101, there may be a situation where a terminal device is still communicating with the network device 101 in a DL with a high quality while the UL from that terminal device to the network device 101 is worse.For example, the terminal device 120 was previously in the coverage area 103 and had both UL and DL connections with the network device 111. After movement, the terminal device 120 is still in the cell 101 of the network device 111 and can work in the DL with the network device 111. However, at this time, the UL quality from the terminal device 120 to the network device 111 is decreased. For the terminal device 121 within the coverage area 103, the UL and DL with the network device 111 both works well. For the terminal device 122 outside the cell 101 but within the cell 102, it may establish a connection with the network device 112 in both UL and DL. To enable UL communication of the terminal device 120, as mentioned above, in embodiments of the present disclosure, the terminal device 120 is allowed to switch only its UL to the network device 112 and still maintain its DL with the network device 111.

[0068] It would be appreciated that although the frequency band of the network device 111 has been described as being higher than that of the network device 112, in some other cases, the frequency band of the network device 112 may be higher than or equal to that of the network device 111. In these cases, there may also occur when a terminal device has a good DL and a worse UL with one of the network devices 111, 112 and may thus switch the UL to the other one of the network devices 111, 112.

[0069] Generally, there are three types of time-variant reference resources, namely, periodic, semi-persistent (SP), and aperiodic (AP) reference resources. Channel state information reference signal (CSLRS) is a kind of resource that can be triggered by these three different time variants, unlike synchronization signal block (SSB) which is always periodic. Similarly, reporting of the measurement is also supported in the above three time-variants. The time relation between resources and reporting holds as in the following table.

[0070] It is specified that periodic CSI-RS could be reported by periodic reporting, semi persistent report, and aperiodic report. SP CSI-RS could be reported by semi persistent report and aperiodic report, while aperiodic CSI-RS could only be reported by aperiodic report. Among them, periodic CSI-RS are configured and activated by radio resource control (RRC). SP CSI-RS is configured by RRC but activated / deactivated by a media access control (MAC)-control element (CE). Aperiodic CSI-RS is configured by RRC, but activated by a downlink control information (DCI).

[0071] In some scenarios, SSB based LTM can be supported, and CSI-RS based LTM may need to be supported as well. For SSB based LTM, the measurement of SSB from other cells are performed in the serving cell and then are reported to next generation node B (gNB) which in turn is used to decide the target cell for cell switch.

[0072] Similarly, measurements of CSLRSs from other cells are performed in the serving cell and are reported to gNB which would be used to decide the target cell. The difference between these two types of reference signal is that SSB is a broadcast always- on signal sent with wide gNB beam; while CSI-RS is a reference signal transmitted with narrow gNB beam, larger bandwidth, and shorter periodicity as compared to SSB based measurement. CSI-RS is typically configured for specific UE(s) within a cell. This difference results in a more dynamic nature of CSI-RS from the candidate cells, which is not in control of the serving cell.

[0073] Layer 1 (Ll) / layer 2 (L2)-triggered mobility (LTM) is a cell switch procedure, where UE’s serving cell (primary cell (PCell) or primary secondary cell (PCell)) is switched by the network by sending an LTM cell switch command. The LTM switch command is currently assumed as delivered by MAC signaling using a MAC CE. Hence, the LTM switch command does not use RRC signaling as a L3 based handover, which is one of the current methods for changing between cells.

[0074] Moreover, LTM cell switch decision is based on LI measurements, which are performed and reported using LI measurement reports by the UE. Measurements and reports are based on LTM candidate cell configuration provided by the network for one or more LTM candidate cells. A LTM candidate cell may be a neighboring cell or a UE’s current serving cell (e.g., SCell).

[0075] In some situations, LTM measurements on a neighboring candidate cell are performed using SSBs transmitted by the candidate cell for which the SSB configurationis provided to the UE. Before the cell switch, the network may optionally activate one or more transmission configuration indication (TCI) state(s) for one or more candidate cells. Once the TCI state(s) of the candidate cell is activated, the UE may start tracking the time / frequency synchronization using the reference signals associated with the activated TCI state(s). The UE may also perform early UL synchronization before the cell switch if it is requested by the network.

[0076] LTM can offer improvements in handover latency and interruption time as compared to layer 3 (L3) based mobility. Moreover, CSI-RS measurement for LTM procedure may need to be supported.

[0077] Generally, CSI-RS may occupy wider bandwidth than SSB. Since periodic CSI- RS is predictable, there may be enough time for the candidate cell to communicate it to other cells, however at the expense of bandwidth. Semi-persistent (SP) and aperiodic CSL RSs have their advantage in terms of saving bandwidth for data, and some short duration measurement. All three types of CSI-RS can be used to facilitate LTM, though periodic CSI-RS has higher favor over the others due to its predictability.

[0078] Nevertheless, on the other hand, due to the dynamic nature of CSI-RS, currently, it might be difficult to support the update of CSI-RS from candidate cells for LTM measurement. When the candidate cells update the periodicity or activate SP CSI-RS or AP CSI-RS fortheir own cell usage, the source cell (i.e., the current serving cell) may not aware of it.

[0079] Therefore, some embodiments of the present disclosure propose a solution for channel state information reference signal (CSI-RS) measurement, especially enabling CSI-RS measurement for LTM procedure. In this solution, a first network device receives a configuration of at least one channel state information reference signal (CSI-RS) of a second network device. Also, the first network device determines, based on a measurement report from a user equipment (UE) and the configuration, to enable use of the at least one CSI-RS of the second network device. In addition, the first network device transmits a first request for enabling use of the at least one CSI-RS of the second network device. In other words, the first network device transmits the first request to start transmission of the at least one CSI-RS of the second network device. By implementing the example embodiments of the present disclosure, CSI-RS measurement for LTM procedure can be supported.

[0080] For illustrative purposes, principles and example embodiments of the presentdisclosure will be described below with reference to FIG. 1 to FIG. 17. However, it is to be noted that these embodiments are given to enable the skilled in the art to understand inventive concepts of the present disclosure and implement the solution as proposed herein, and not intended to limit scope of the present application in any way.

[0081] FIG. 2 illustrates a first example of a process flow 200 in accordance with some example embodiments of the present disclosure. For ease of understanding, the process flow 200 will be described with reference to FIG. 1. It would be appreciated that although the process flow 200 has been described referring to the communication network 100 of FIG. 1, this process flow 200 may be likewise applied to other similar communication scenarios.

[0082] As shown in FIG. 2, at 220, a second network device 204 may transmit a configuration 222 of at least one channel state information reference signal (CSI-RS) of the second network device 204. Accordingly, at 230, a first network device 202 may receive a configuration 228 of at least one CSI-RS of the second network device 204.

[0083] In some embodiments, the configuration 222 may be received by a third network device 206 from the second network device 204 at 224, and the configuration 228 may be transmitted by the third network device 206 to the first network device at 226. Additionally or alternatively, in some implementations, the configuration 222 may be received by the first network device 202 from the second network device 204 directly.

[0084] Thereafter, at 240, the first network device 202 may determine, based on a measurement report from a user equipment (UE) and the configuration, to enable use of the at least one CSI-RS of the second network device. In some embodiments, the measurement report from the UE may be layer 1 (LI) measurement reports. Additionally or alternatively, in some embodiments, the measurement report from the UE may be layer 3 (L3) measurement reports.

[0085] At 250, the first network device 202 may transmit a first request 252 for enabling use of the at least one CSI-RS of the second network device. Accordingly, at 254, the third network device 206 may receive, from the first network device, the first request for enabling use of CSI-RS of a second network device. Thereafter, at 256, the third network device 206 may transmit, to the second network device 204, a second request 258 for enabling use of the CSI-RS of the second network device.

[0086] In some embodiments, the request for enabling the use of at one CSI-RS comprises indication of at least one of semi-persistent (SP) CSI-RS or aperiodic (AP)CSI-RS. The indication may contain the identifier of the CSI-RS(s) to be activated. The information of CSI-RS resource identifier is given in the configuration of CSI-RS sent by the second network device. In some embodiments, the configuration may contain the indication of which CSI-RSs can be used to request for activation. The configuration may further contain CSI-RSs which the second device may activate for its own purpose but may not be used by the other network device to make request to activate them. The configuration may contain indication information of which CSI-RSs can be used for by other network devices to make request to activate them. The configuration may contain indication information of which CSI-RSs cannot be used for by other network devices to request to activate them.

[0087] In some embodiments, the first network device may further receive a first acknowledgement to the first request. In some embodiments, the CSI-RS comprises at least one of semi-persistent (SP) CSI-RS or aperiodic (AP) CSI-RS, and the first request and the second request comprise at least one CSI-RS resource identifier, at least one CSI- RS resource set identifier, or both. In some embodiments, the first network device may receive a negative acknowledgement to the first request. In some embodiments, the first network device may receive information of updated configuration of the requested CSI- RS to the first request.

[0088] In some embodiments, in the case that the CSI-RS comprises the SP CSI-RS, the first request and the second request comprise a flag to indicate to activate the CSI-RS, and when transmitting the first request for enabling use of the at least one CSI-RS, the first network device may transmit an activation request with an activation time duration. Accordingly, when receiving the first request for enabling use of the at least one CSI-RS, the third network device may receive the activation request with the activation time duration. Accordingly, when receiving the second request for enabling use of the at least one CSI-RS comprises, the second network device may receive an activation request with the activation time duration.

[0089] Additionally or alternatively, in some embodiments, in the case that the CSI-RS comprises the SP CSI-RS, the first request and the second request comprise a flag to indicate to activate the CSI-RS, and when transmitting the first request for enabling use of the at least one CSI-RS, the first network device may transmit the first request to activate the CSI-RS. Accordingly, when receiving the first request for enabling use of the at least one CSI-RS, the third network device may receive the first request to activate the CSI-RS. Accordingly, when receiving the second request for enabling use of the at leastone CSI-RS comprises, the second network device may receive the second request to activate the CSI-RS.

[0090] At 260, the second network device 204 may receive the second request for enabling use of the at least one CSI-RS. Thereafter, at 270, the second network device 204 may transmit the at least one CSI-RS.

[0091] In some embodiments, the second network device may further transmit a second acknowledgement to the second request. In some embodiments, the second network device may transmit a negative acknowledgement to the second request when the second device determines to not activate and transmit the requested CSI-RSs. In some embodiments, the second network device may transmit an updated configuration of the requested CSI-RS to the second request when the second device determines update some configuration of the requested CSI-RSs and then activate and transmit based on the updated configuration. Accordingly, in some embodiments, the third network device may further receive, from the second network device, the second acknowledgement or negative acknowledgement or updated configuration to the second request, and the third network device may transmit, to the first network device, a first acknowledgement or negative acknowledgement or updated configuration to the first request.

[0092] In some embodiments, when the first network device determines to stop the measurements on at least one activated CSI-RS, the first network device may further transmit a third request to deactivate the (activated) CSI-RS to indicate the no further use of activated CSI-RS, the third request comprises a flag to indicate to deactivate the CSI- RS, and the third request further comprises at least one CSI-RS resource identifier, at least one CSI-RS resource set identifier, or both.

[0093] Accordingly, in some embodiments, the third network device may further receive, from the first network device, the third request to deactivate the CSI-RS, the third network device may further transmit, to the second network device, a fourth request to deactivate the CSI-RS, the fourth request comprises a flag to indicate to deactivate the CSI-RS, and the fourth request further comprises at least one CSI-RS resource identifier, at least one CSI-RS resource set identifier, or both.

[0094] Accordingly, in some embodiments, the second network device may further receive the fourth request to deactivate the CSI-RS. In some embodiments, the second network device may decide to stop or not stop the transmission of the activated CSI-RS after the reception of the request to deactivate the CSI-RS. In some embodiments, thesecond network device may further transmit a fourth acknowledgement to the fourth request. In some embodiments, when the second network device decides not stop the transmission of the CSI-RS, the acknowledgement message may contain an indication of continuing the transmission of activated CSI-RS. Accordingly, in some embodiments, the third network device may receive, from the second network device, the fourth acknowledgement to the fourth request, and the third network device may transmit, to the first network device, a third acknowledgement to the third request. Accordingly, in some embodiments, the first network device may receive the third acknowledgement to the third request.

[0095] In some embodiments, the first network device and the second network device are associated with same base station, the first network device comprises a source distributed unit (DU) of the base station, the second network device comprises a target DU of the base station, and the third network device comprises a centralized unit (CU) of the base station.

[0096] In some embodiments, the first network device and the second network device are associated with different base station, the first network device comprises a source distributed unit (DU) of the source base station, and the second network device comprises a target DU of the target base station. The request from the source DU is transmitted to a source CU (CU of the source base station), and then the source CU forwards the request to the target CU (CU of the target base station) which further forwards the request to the target DU. Similarly, when a message (e.g., configuration or acknowledgement) is transmitted by the target DU to the source DU, it is transmitted from the target DU to the target CU, then the target CU forwards that to the source CU and the source CU forward that to the source DU.

[0097] Additionally or alternatively, in some embodiments, in the case that the CSI-RS comprises the AP CSI-RS, when transmitting the first request for enabling use of the at least one CSI-RS, the first network device may transmit the first request to trigger the CSI-RS. Accordingly, when receiving the first request for enabling use of the at least one CSI-RS, the third network device may receive the first request to trigger the CSI-RS. Accordingly, when receiving the second request for enabling use of the at least one CSI- RS, the second network device may receive the second request to trigger the CSI-RS.

[0098] In some embodiments, the first acknowledgement to the first request comprises at least one field for indicating an upcoming time instant for a transmission of the CSI-RS from the second network device, and the at least one field comprises a system frame number or a slot number.

[0099] FIG. 3 illustrates a second example of a process flow 300 in accordance with some example embodiments of the present disclosure. For ease of understanding, the process flow 300 will be described with reference to FIG. 1. It would be appreciated that although the process flow 300 has been described referring to the communication network 100 of FIG. 1, this process flow 300 may be likewise applied to other similar communication scenarios.

[0100] As shown in FIG. 3, at 320, a second network device 304 may transmit a configuration 322 of at least one channel state information reference signal (CSI-RS) of the second network device 304. Accordingly, at 324, a first network device 302 may receive a configuration 322 of at least one CSI-RS of the second network device 304. Thereafter, at 340, the first network device 302 may determine, based on a measurement report from a user equipment (UE) and the configuration, to enable use of the at least one CSI-RS of the second network device.

[0101] At 350, the first network device 302 may transmit a first request 352 for enabling use of the at least one CSI-RS of the second network device. Accordingly, at 354, the second network device 304 may receive, from the first network device, the first request for enabling use of CSI-RS of a second network device. In some embodiments, the first network device may further receive a first acknowledgement to the first request. In some embodiments, the CSI-RS comprises at least one of semi-persistent (SP) CSI-RS or aperiodic (AP) CSI-RS, and the first request comprises at least one CSI-RS resource identifier, at least one CSI-RS resource set identifier, or both.

[0102] In some embodiments, in the case that the CSI-RS comprises the SP CSI-RS, the first request comprises a flag to indicate to activate the CSI-RS, and when transmitting the first request for enabling use of the at least one CSI-RS, the first network device may transmit an activation request with an activation time duration. Accordingly, when receiving the first request for enabling use of the at least one CSI-RS, the second network device may receive the activation request with the activation time duration.

[0103] Additionally or alternatively, in some embodiments, in the case that the CSI-RS comprises the SP CSI-RS, the first request comprises a flag to indicate to activate the CSI-RS, and when transmitting the first request for enabling use of the at least one CSI- RS, the first network device may transmit the first request to activate the CSI-RS.Accordingly, when receiving the first request for enabling use of the at least one CSI-RS, the third network device may receive the first request to activate the CSI-RS.

[0104] Thereafter, at 370, the second network device 304 may transmit the at least one CSI-RS. Accordingly, in some embodiments, the second network device may transmit, to the first network device, a first acknowledgement to the first request. In some embodiments, the first network device may further transmit a third request to deactivate the CSI-RS, the third request comprises a flag to indicate to deactivate the CSI-RS, and the third request further comprises at least one CSI-RS resource identifier, at least one CSI-RS resource set identifier, or both.

[0105] Accordingly, in some embodiments, the second network device may further receive, from the first network device, the third request to deactivate the CSI-RS. Accordingly, in some embodiments, the second network device may transmit, to the first network device, a third acknowledgement to the third request. Accordingly, in some embodiments, the first network device may receive the third acknowledgement to the third request. In some embodiments, the first network device and the second network device are associated with different base stations, the first network device comprises a source base station, and the second network device comprises a target base station.

[0106] Additionally or alternatively, in some embodiments, in the case that the CSI-RS comprises the AP CSI-RS, when transmitting the first request for enabling use of the at least one CSI-RS, the first network device may transmit the first request to trigger the CSI-RS. Accordingly, when receiving the first request for enabling use of the at least one CSI-RS, the second network device may receive the first request to trigger the CSI-RS.

[0107] In some embodiments, the first acknowledgement to the first request comprises at least one field for indicating an upcoming time instant for a transmission of the CSI- RS from the second network device, and the at least one field comprises a system frame number or a slot number.

[0108] FIG. 4 illustrates a third example of a process flow 400 in accordance with some example embodiments of the present disclosure. For ease of understanding, the process flow 400 will be described with reference to FIG. 1. It would be appreciated that although the process flow 400 has been described referring to the communication network 100 of FIG. 1, this process flow 400 may be likewise applied to other similar communication scenarios.

[0109] As shown in FIG. 4, at 420, a second network device 404 may transmit aconfiguration 422 of at least one channel state information reference signal (CSI-RS) for at least one user equipment (UE) served by the second network device 404. Accordingly, at 430, a first network device 402 may receive a configuration 428 of at least one CSI-RS of the second network device 404.

[0110] In some embodiments, the configuration 422 may be received by a third network device 406 from the second network device 404 at 424, and the configuration 428 may be transmitted by the third network device 406 to the first network device 402 at 426. Additionally or alternatively, in some implementations, the configuration 422 may be received by the first network device 402 from the second network device directly.

[0111] Thereafter, at 440, the second network device 202 may determine to activate the at least one CSI-RS for the at least one UE served by the second network device. At 450, the third network device 406 may transmit a first indication 452 related to activating the at least one CSI-RS. Accordingly, at 454, the third network device 406 may receive, from the second network device, the first indication related to activating CSI-RS of the second network device. Thereafter, at 456, the third network device 406 may transmit, to the first network device 402, a second indication 458 related to activating CSI-RS for at least one user equipment (UE) served by the second network device.

[0112] In some embodiments, the second network device may further receive a first acknowledgement to the first indication. In some embodiments, the CSI-RS comprises semi-persistent (SP) CSI-RS, the first indication and the second indication comprise a flag to indicate to activate the CSI-RS, and the first indication and the second indication comprise at least one CSI-RS resource identifier, at least one CSI-RS resource set identifier, or both. In some embodiments, the indication may contain an activation indication with an activation time duration.

[0113] At 460, the first network device 402 may receive the second indication related to activating the at least one CSI-RS of the second network device. Thereafter, at 470, the first network device 402 may trigger at least one UE served by the first network device to measure the activated at least one CSI-RS. In other words, the first network device 402 may send a command (L2 MAC, e.g. MAC-CE or LI DCI) to the UE indicating the activation of a CSI-RS and may further send a command to trigger the UE to report at least one measurement associated with the activated CSI-RS. In some embodiments, the first network device may further transmit a second acknowledgement to the second indication.

[0114] Accordingly, in some embodiments, the third network device may further receive, from the first network device, the second acknowledgement to the second indication, and the third network device may transmit, to second first network device, a first acknowledgement to the first indication.

[0115] In some embodiments, when the second network device decides to stop the transmission of an CSI-RS for which an activation indication was sent earlier to the first network device, the second network device may further transmit a third indication related to deactivating the CSI-RS, the third indication comprises a flag to indicate to deactivate the CSI-RS, and the third indication further comprises at least one CSI-RS resource identifier, at least one CSI-RS resource set identifier, or both.

[0116] Accordingly, in some embodiments, the third network device may further receive, from the second network device, the third indication related to deactivating the CSI-RS, the third network device may further transmit, to the first network device, a fourth indication related to deactivating the CSI-RS, the fourth indication comprises a flag to indicate to deactivate the CSI-RS, and the fourth indication further comprises at least one CSI-RS resource identifier, at least one CSI-RS resource set identifier, or both.

[0117] Accordingly, in some embodiments, the first network device may further receive the fourth indication related to deactivating the CSI-RS, and the first network device may further transmit a fourth acknowledgement to the fourth indication.

[0118] Accordingly, in some embodiments, the first network device may trigger at least one UE served by the first network device to stop measure the deactivated at least one CSI-RS. In other words, the first network device may send a command (L2 MAC, e.g. MAC-CE or LI DCI) to the UE indicating the deactivation of a CSI-RS. The first network device may further send a command (L2 MAC, e.g. MAC-CE or LI DCI) to trigger the UE to stop reporting or deactivating the reporting associated with the deactivated CSI-RS

[0119] Accordingly, in some embodiments, the third network device may receive, from the first network device, the fourth acknowledgement to the fourth indication, and the third network device may transmit, to the second network device, a third acknowledgement to the third indication. Accordingly, in some embodiments, the second network device may receive the third acknowledgement to the third indication.

[0120] In some embodiments, the first network device and the second network device are associated with same base station, the first network device comprises a source distributed unit (DU) of the base station, the second network device comprises a targetDU of the base station, and the third network device comprises a centralized unit (CU) of the base station.

[0121] In some embodiments, the first network device and the second network device are associated with different base station, the first network device comprises a source distributed unit (DU) of the source base station, and the second network device comprises a target DU of the target base station. The indication from the target DU is transmitted to a target CU (CU of the target base station), and then the target CU forwards the indication to the source CU (CU of the source base station) which further forwards the indication to the source DU. Similarly, when a message (e.g., acknowledgement) is transmitted by the source DU to the target DU, it is transmitted from the source DU to the source CU, then the source CU forwards that to the target CU and the target CU forward that to the target DU.

[0122] FIG. 5 illustrates a fourth example of a process flow 500 in accordance with some example embodiments of the present disclosure. For ease of understanding, the process flow 500 will be described with reference to FIG. 1. It would be appreciated that although the process flow 500 has been described referring to the communication network 100 of FIG. 1, this process flow 500 may be likewise applied to other similar communication scenarios.

[0123] As shown in FIG. 5, at 520, a second network device 504 may transmit a configuration 522 of at least one channel state information reference signal (CSI-RS) for at least one user equipment (UE) served by a second network device 504. Accordingly, at 524, a first network device 502 may receive the configuration 522 of at least one CSI- RS of the second network device 504.

[0124] Thereafter, at 540, the second network device 504 may determine to activate the at least one CSI-RS for the at least one UE served by the second network device. At 550, the second network device 504 may transmit a first indication 552 related to activating the at least one CSI-RS. Accordingly, at 554, the first network device 502 may receive, from the second network device, the first indication related to activating the at least one CSI-RS of the second network device.

[0125] In some embodiments, the first network device may further transmit a first acknowledgement to the first indication. In some embodiments, the CSI-RS comprises semi-persistent (SP) CSI-RS, the first indication comprises a flag to indicate to activate the CSI-RS, and the first indication comprises at least one CSI-RS resource identifier, atleast one CSI-RS resource set identifier, or both.

[0126] Thereafter, at 570, the first network device 502 may trigger at least one UE served by the first network device to measure the activated at least one CSI-RS. Accordingly, in some embodiments, the first network device may transmit, to the second network device, a first acknowledgement to the first indication.

[0127] In some embodiments, the second network device may further transmit a third indication related to deactivating the CSI-RS, the third indication comprises a flag to indicate to deactivate the CSI-RS, and the third indication further comprises at least one CSI-RS resource identifier, at least one CSI-RS resource set identifier, or both.

[0128] Accordingly, in some embodiments, the first network device may further receive, from the second network device, the third indication related to deactivating the CSI-RS. Accordingly, in some embodiments, the first network device may transmit, to the second network device, a third acknowledgement to the third indication. Accordingly, in some embodiments, the second network device may receive the third acknowledgement to the third indication.

[0129] In some embodiments, the first network device and the second network device are associated with different base stations, the first network device comprises a source base station, and the second network device comprises a target base station.

[0130] In some implementations of this disclosure, several example methods for enabling source cell / DU (i.e., the current serving cell) to request or be aware of the update of CSI-RS from candidate cells / DUs for LTM measurement. For a first option, the source cell may request the target cell to activate / deactivate SP CSI-RS s or trigger AP CSI-RS.

[0131] For example, the serving cell may request the candidate cell to trigger the transmission of selected AP / SP CSI-RSs. Based on the LI measurements (e.g., based on SSBs or / and periodic CSI-RSs of the candidate cell), the serving cell may decide to trigger additional CSI-RSs which are configured as semi-persistent or aperiodic type. For example, when a received candidate cell SSB measurement is above a certain quality, the serving cell may determine to activate measurements on CSI-RSs which are quasi colocated with the SSB if such CSI-RSs are not activated already and configured as SP CSI- RS.

[0132] The serving cell may request the target cell to activate selected SP or AP CSI- RSs. The serving cell may send the identifier of the selected SP or AP CSI-RSs or SP / APresource set(s).

[0133] For SP CSI-RSs (or a SP CSI-RS resource set), either two independent requests, one for activation and one for deactivation, or a single activation request with an activation time duration may be used. The candidate cell may acknowledge the request via Fl or Xn signaling. And the candidate cell may deny or update the configuration parameters of the requested CSI-RSs.

[0134] After the acknowledgment, the candidate cell is supposed to start the transmission of acknowledged CSI-RSs. In one example, the AP CSI-RS acknowledgement may comprise at least one field indicating an upcoming time instant for the AP CSI-RS transmission by the candidate cell (e.g. system frame number, or slot number). After receiving the acknowledgment from the candidate cell, the serving cell may trigger the UE to measure SP or AP CSI-RSs of the selected candidate cell and report the measurements.

[0135] For a second option, the candidate cell may inform the serving cell about the activation / deactivation of SP CSI-RS. For example, when the candidate cell activates a SP CSI-RS (or a SP CSI-RS resource set) for its own UEs, it can also inform other candidates who are interested in monitoring these resources.

[0136] The serving cell may provide the assistance information in terms of candidate SSB beams for which the serving cell is interested in receiving notification for activation of SP CSI-RS resource set. Based on the information about the activation of SP CSI-RS, the serving cell may trigger the UE to measure the selected SP CSI-RSs of the candidate cell and report the measurements.

[0137] Similar procedure can be used when the candidate cell deactivates an activated SP CSI-RS (or a SP CSI-RS resource set). Moreover, the above procedure can be used by a candidate cell when the candidate cell determines to transmit AP CSI-RSs.

[0138] Additionally, with regard to the differentiation of SP CSI-RSs of candidate cell for LTM-TRIGGERED-SP-Activation (the first option) and SP-Activation-Indication- For-LTM (the second option), for both the above options the candidate cell indicates which SP CSI-RSs are configured for activation from the source cell (the first option) and which of the SP CSI-RSs the candidate cell intends to activate for its own beam management purpose (the second option).

[0139] For the first option, the serving cell can request for activation only for the SPCSI-RSs that are dedicated for LTM purpose. Moreover, the candidate cell may control other SP CSI-RSs that are activated for its own beam management purpose. The candidate cell may inform this event to DUs which are interested in this event or to source DU. It is up to the source cell to make use of this information. Additionally, the candidate cell (DU) may also notify the release (or deactivation) of SP CSI-RSs to enable the serving DU to trigger command towards UE to stop the measurement report.

[0140] FIG. 6 illustrates an example intra-centralized unit (CU) LTM procedure in accordance with some example embodiments of the present disclosure. For example, the example intra-CU LTM procedure relates to the first option mentioned above.

[0141] The signaling flow of FIG. 6 shows an example of source cell generated request to activate and / or deactivated SP CSI-RSs of a candidate cell (represented as a target DU 684 in FIG. 6). Note that the example is shown only for intra-CU scenarios, but it may also be applied for inter-CU scenarios, where signaling from the source CU to the target DU will be done via the target CU (CU where the target DU belongs).

[0142] At 601-602, the UE 681 sends measurement report containing the cell quality measurements of serving and neighboring cells. The UE 681 can be configured by the serving cell to send measurement report early when it still has a good connection to the serving cell. Using the reported cell quality measurements, the CU 686 can identify a potential set of candidate target cells to which the UE can be handed over to which may belong to the same DU or different ones - as shown in the current example.

[0143] At 603, the CU 686 decides about the preparation of new cells. At 604, the CU 686 requests the preparation of candidate target cell(s) controlled by target DU 684 by sending UE Context Setup Request message. At 605, the target DU 684 provides the configuration of the UE in UE Context Setup Response message containing a container from DU to CU. Here the target DU 684 would include P / SP / AP CSLRS which is intended for its own UE in the configuration. At 606-607, the CU 686 requests UE context modification from the source DU 682 and the source DU 682 respond to it.

[0144] Having received the UE configurations for the candidate target cell(s), the CU 686 generates an RRC Reconfiguration that is sent to the UE at 608. Among other information, the RRC Reconfiguration message contains: measurement reporting configuration for L1 / L2 handover, configuration information of CSLRS of candidate cells including the configuration of SP or / and AP CSI-RSs, and / or configuration of the prepared candidate cell(s) which the UE needs to execute when it receives a MAC CEcommand to change the serving cell (perform handover).

[0145] At 609, the CU 686 provides source DU 682 about the RRC configuration message. At 610, the source DU 682 forwards the RRCReconfiguration message to the UE 681. At 611-612, the UE 681 informs source DU 682 RRCReconfigurationComplete. The UE 681 performs LI measurement. At 613, the UE 681 send the LI measurement report to the source DU 682.

[0146] At 620, based on the measurements, the serving DU determines to activate SP CSLRSs of target DU 684. At 622-624, the source DU 682 requests the activation of SP CSLRS. The request may contain the IDs of SP CSLRS resources / resource-set and a flag to indicate whether to activate. At 626-628, the target DU 684 responds to the request by an acknowledgement.

[0147] Alternatively, at 622, there could be a one-way message called “CSLRS Activation Indication”, and at 628, there could be a one-way message called “CSLRS Activation Confirmation”. At 630, target DU 684 starts (if activation request is received) the transmission of the requested CSLRSs. At 632, the serving DU sends a MAC Control Element (MAC CE) or a LI message to trigger UE to measure the activated CSLRS from the candidate cells.

[0148] The UE 681 performs LI measurement. At 634, the UE 681 send the LI measurement reports to the source DU 682. At 636, the serving DU determines to deactivate (if already activated) SP CSLRSs of target DU 684. At 638-640, the source DU 682 requests the deactivation of already activated SP CSLRS. The request may contain the IDs of SP CSLRS resources / resource-set and a flag to indicate whether to activate or deactivate. At 642-644, the target DU 684 responds to the request by an acknowledgement. 642 and 644 could be optional when there is no feedback (acknowledgement) required from the target DU 684 for the deactivation request. Also, 646 could also be optional because in some cases the target DU 684 may determine not to stop the transmission of CSLRSs. Alternatively, at 638, there could be a one-way message called “CSLRS Deactivation Indication”, and at 644, there could be a one-way message called “CSLRS Deactivation Confirmation”.

[0149] At 646, the target DU 684 stops (if deactivation request is received) the transmission of the requested CSLRSs. At 660, based on the measurement, the source DU 660 decides a target cell. At 662, the source DU 660 sends the MAC-CE for cell switch. At 664, the cell switch completion procedure will be carried out.

[0150] FIGS. 7A-7B illustrate an example inter-CU LTM procedure in accordance with some example embodiments of the present disclosure. For example, the example inter- CU LTM procedure relates to the first option mentioned above.

[0151] At 701, the source gNB 782 configures the UE measurement procedures and the UE 781 reports according to the measurement configuration (L3 measurement reports). At 702, the source gNB 782 decides to handover the UE (LTM decision). At 703a-703b, the source gNB 782 issues Handover Request message(s) to the target gNB(s) 784 and 784-1 to prepare the handover at the target side.

[0152] At 704a-704b, admission control may be performed by the target gNB(s) 784 and 784-1. At 705a-705b, the target gNB(s) 784 and 784-1 prepare the handover with L1 / L2 and sends the HANDOVER REQUEST ACKNOWLEDGE to the source gNB 782. At 706, the source gNB 782 sends the RRCReconfiguration message to the UE 781.

[0153] At 707, the UE 781 informs the source gNB 782 RRCReconfigurationComplete. The UE 781 performs LI measurement. At 708, the UE 781 sends the LI measurement report to the source gNB 782. At 720, based on the measurements, the serving gNB 782 determines to activate SP CSLRSs of target gNB 784.

[0154] At 722, the source gNB 782 requests the activation of SP CSLRS. The request may contain the IDs of SP CSLRS resources / resource-set and a flag to indicate whether to activate or deactivate. At 724, the target gNB 784 starts (if activation request is received) the transmission of the requested CSLRSs. At 726, the target gNB 784 responds to the request by an acknowledgement. Alternatively, at 722, there could be a message called “CSLRS Activation Indication”, and at 726, there could be a message called “CSLRS Activation Confirmation”.

[0155] At 728, the serving gNB 782 sends a MAC Control Element (MAC CE) or a LI message to trigger UE to measure the activated CSLRS from the candidate cells. The UE 781 performs LI measurement. At 730, the UE 781 sends the LI measurement reports to the source gNB 782. At 732, the serving gNB 782 determines to deactivate (if already activated) SP CSLRSs of target gNB 784.

[0156] At 734, the source gNB 782 requests the deactivation of already activated SP CSLRS. The request may contain the IDs of SP CSLRS resources / resource-set and a flag to indicate whether to activate or deactivate. At 736, the target gNB 784 stops (if deactivation request is received) the transmission of the requested CSLRSs. At 738, the target gNB 784 responds to the request by an acknowledgement. 736 could be optionalbecause in some cases the target gNB 784 may determine not to stop the transmission of CSI-RSs. 738 could be optional when there is no feedback (acknowledgement) required from the target gNB 784 for the deactivation request. Alternatively, at 734, there could be a message called “CSI-RS Deactivation Indication”, and at 738, there could be a message called “CSI-RS Deactivation Confirmation”.

[0157] At 760, the source gNB 782 triggers cell switch (LTM trigger). At 762, the source gNB 782 sends the MAC-CE for LTM cell switch (LTM cell switch command). At 764, the source gNB 782 sends the SN STATUS TRANSFER message. At 764, the LTM handover completion will be carried out.

[0158] Continued with FIG. 7B. At 770, the UE 781 synchronizes to the target gNB 784 and completes the RRC handover procedure by sending RRCReconfigurationComplete message to the target gNB 784.

[0159] At 771, the target gNB 784 sends the HANDOVER SUCCESS message to the source gNB 782. At 772, the source gNB 782 sends the HANDOVER CANCEL message. At 773, the target gNB 784 sends a PATH SWITCH REQUEST message to AMF 787. At 774, the DL data path is switched towards the target gNB 784. The UPF 788 sends one or more “end marker” packets on the old path to the source gNB 782 per PDU session / tunnel and then can release any U-plane / TNL resources towards the source gNB 784. At 775, the AMF 787 confirms the PATH SWITCH REQUEST message with the PATH SWITCH REQUEST ACKNOWLEDGE message.

[0160] At 776, upon reception of the PATH SWITCH REQUEST ACKNOWLEDGE message from the AMF 787, the target gNB 784 sends the UE CONTEXT RELEASE to inform the source gNB 782 about the success of the handover. The source gNB 782 can then release radio and C-plane related resources associated to the UE context. Any ongoing data forwarding may continue.

[0161] FIG. 8 illustrates another example intra-CU LTM procedure in accordance with some example embodiments of the present disclosure. For example, the example intra- CU LTM procedure relates to the second option mentioned above.

[0162] The signaling flow of FIG. 8 shows an example of target cell initiating the request to inform the source cell about activating or deactivating SP CSI-RSs of its own. Note that the example is shown for only intra-CU scenarios, but this may be applied for inter-CU scenarios, where signaling from the source CU to the target DU will be done via the target CU (CU where the target DU belongs).

[0163] At 801-802, the UE 881 sends measurement report containing the cell quality measurements of serving and neighboring cells. The UE 881 can be configured by the serving cell to send measurement report early when it still has a good connection to the serving cell. Using the reported cell quality measurements, the CU 886 can identify a potential set of candidate target cells to which the UE can be handed over to which may belong to the same DU or different ones - as shown in the current example.

[0164] At 803, the CU 886 decides about the preparation of new cells. At 804, the CU 886 requests the preparation of candidate target cell(s) controlled by target DU 884 by sending UE Context Setup Request message. At 805, the target DU 884 provides the configuration of the UE in UE Context Setup Response message containing a container from DU to CU. Here the target DU 884 would include P / SP / AP CSI-RS which is intended for its own UE in the configuration. At 806-807, the CU 886 requests UE context modification from the source DU 882 and the source DU 882 respond to it.

[0165] Having received the UE configurations for the candidate target cell(s), the CU 886 generates an RRC Reconfiguration that is sent to the UE at 808. Among other information, the RRC Reconfiguration message contains: measurement reporting configuration for L1 / L2 handover, configuration information of CSI-RS of candidate cells including the configuration of SP or / and AP CSI-RSs, and / or configuration of the prepared candidate cell(s) which the UE needs to execute when it receives a MAC CE command to change the serving cell (perform handover).

[0166] At 809, the CU 886 provides source DU 882 about the RRC configuration message. At 810, the source DU 882 forwards the RRCReconfiguration message to the UE 881. At 811-812, the UE 881 informs the source DU 882 RRCReconfigurationComplete. The UE 881 performs LI measurement. At 813, the UE 881 send the LI measurement report to the source DU 882.

[0167] At 820, the candidate cell decides to activate a SP CSI-RS (or a SP CSI-RS resource set) for its own UEs. At 822 and 826, the candidate cell indicates the activation of SP CSI-RSs to the source CU 886. The indication may contain the IDs of SP CSI-RS resources / resource-set and a flag to indicate whether to activate. At 824, the candidate cell starts the transmission of the indicated CSI-RSs. At 828 and 830, the source DU 882 confirms the notification of activation of SP CSI-RS. 828 and 830 could be optional when there is no feedback (acknowledgement) required from the source DU 882 for the activation indication. Alternatively, at 826, there could be a one-way message called“CSI-RS Activation Indication”; and at 822, there could be a one-way message called “CSI-RS Activation Confirmation”.

[0168] At 832, the serving DU sends a MAC Control Element (MAC CE) or a LI message to trigger UE to measure the activated CSI-RS from the candidate cells. The UE 881 performs LI measurement. At 834, the UE 881 send the LI measurement reports to the source DU 882. At 836, the candidate cell decides to deactivate already activated SP CSLRSs for which the activation indication was sent to other cells earlier for its own UEs. At 838 and 842, the candidate cell indicates the deactivation of SP CSLRSs to the source CU 886 (if already activated). The indication may contain the IDs of SP CSI-RS resources / resource-set and a flag to indicate whether to activate or deactivate.

[0169] At 840, the candidate cell stops (if deactivation) the transmission of the indicated CSLRSs. At 844 and 846, the source DU 882 confirms the notification of deactivation of SP CSLRS. 844 and 846 could be optional when there is no feedback (acknowledgement) required from the source DU 882 for the deactivation indication. Alternatively, at 842, there could be a one-way message called “CSLRS Activation Indication”; and at 838, there could be a one-way message called “CSLRS Activation Confirmation”.

[0170] At 860, based on the measurement, the source DU 882 decides a target cell. At 862, the source DU 882 sends the MAC-CE for cell switch. At 864, the cell switch completion procedure will be carried out.

[0171] FIGS. 9A-9B illustrate an example inter-CU LTM procedure in accordance with some example embodiments of the present disclosure. For example, the example inter- CU LTM procedure relates to the second option mentioned above.

[0172] At 901, the source gNB 982 configures the UE measurement procedures and the UE 981 reports according to the measurement configuration (L3 measurement reports). At 902, the source gNB 982 decides to handover the UE (LTM decision). At 903a-903b, the source gNB 982 issues Handover Request message(s) to the target gNB(s) 984 and 984-1 to prepare the handover at the target side. At 904a-904b, admission control may be performed by the target gNB(s) 984 and 984-1.

[0173] At 905a-905b, the target gNB(s) 984 and 984-1 prepare the handover with L1 / L2 and sends the HANDOVER REQUEST ACKNOWLEDGE to the source gNB 982. At 906, the source gNB 982 sends the RRCReconfiguration message to the UE 981. At 907, the UE 981 informs the source gNB 982 RRCReconfigurationComplete. The UE 981 performs LI measurement. At 908, the UE 981 sends the LI measurement report to thesource gNB 982.

[0174] At 920, the target gNB 984 determines to activate SP CSI-RSs. At 922, the target gNB 984 indicates the activation of SP CSI-RS to the source gNB 982. The indication may contain the IDs of SP CSI-RS resources / resource-set and a flag to indicate whether to activate or deactivate. At 924, the source gNB 982 confirms the notification of activation of SP CSI-RS. 924 could be optional when there is no feedback (acknowledgement) required from the source gNB 982 for the activation indication. Alternatively, at 922, there could be a one-way message called “CSI-RS Activation Indication”.

[0175] At 926, the serving gNB 982 sends a MAC Control Element (MAC CE) or a LI message to trigger UE to measure the activated CSI-RS from the candidate cells. The UE 981 performs LI measurement. At 928, the UE 981 sends the LI measurement reports to the source gNB 982. At 930, the target gNB 984 determines to deactivate already activated SP CSI-RSs. At 932, the target gNB 984 indicates the deactivation of SP CSI- RSs to the source gNB 982 (if already activated). The indication may contain the IDs of SP CSI-RS resources / resource-set and a flag to indicate whether to activate or deactivate.

[0176] At 934, the source gNB 982 confirms the notification of deactivation of SP CSI- RS. 934 could be optional when there is no feedback (acknowledgement) required from the source gNB 982 for the deactivation indication. Alternatively, at 932, there could be a one-way message called “CSI-RS Deactivation Indication”. At 960, the source gNB 982 triggers cell switch (LTM trigger). At 962, the source gNB 982 sends the MAC-CE for LTM cell switch (LTM cell switch command). At 964, the source gNB 982 sends the SN STATUS TRANSFER message. At 966, the LTM handover completion will be carried out.

[0177] Continued with FIG. 9B. At 970, the UE 981 synchronizes to the target gNB 984 and completes the RRC handover procedure by sending RRCReconfigurationComplete message to the target gNB 984.

[0178] At 971, the target gNB 984 sends the HANDOVER SUCCESS message to the source gNB 982. At 972, the source gNB 982 sends the HANDOVER CANCEL message. At 973, the target gNB 984 sends a PATH SWITCH REQUEST message to AMF 987. At 974, the DL data path is switched towards the target gNB 984. The UPF 988 sends one or more “end marker” packets on the old path to the source gNB 982 per PDU session / tunnel and then can release any U-plane / TNL resources towards the source gNB984. At 975, the AMF 987 confirms the PATH SWITCH REQUEST message with the PATH SWITCH REQUEST ACKNOWLEDGE message.

[0179] At 976, upon reception of the PATH SWITCH REQUEST ACKNOWLEDGE message from the AMF 987, the target gNB 984 sends the UE CONTEXT RELEASE to inform the source gNB 982 about the success of the handover. The source gNB 982 can then release radio and C-plane related resources associated to the UE context. Any ongoing data forwarding may continue.

[0180] FIG. 10 illustrates a flowchart of an example method 1000 implemented at a first network device in accordance with some embodiments of the present disclosure. For ease of understanding, the method 1000 will be described from the perspective of the first network device 202 with reference to FIG. 2 and from the perspective of the first network device 302 with reference to FIG. 3.

[0181] At block 1010, the first network device may receive a configuration of at least one channel state information reference signal (CSLRS) of a second network device. At block 1020, the first network device may determine, based on a measurement report from a user equipment (UE) and the configuration, to enable use of the at least one CSLRS of the second network device. At block 1030, the first network device may transmit a first request for enabling use of the at least one CSLRS of the second network device.

[0182] In some embodiments, the CSLRS comprises at least one of semi-persistent (SP) CSLRS or aperiodic (AP) CSLRS, and the first request comprises at least one of the following: at least one CSLRS resource identifier, or at least one CSLRS resource set identifier.

[0183] In some embodiments, the first network device may further receive a first acknowledgement to the first request.

[0184] In some embodiments, the CSLRS comprises the SP CSLRS, the first request comprises a flag to indicate to activate the CSLRS, and wherein transmitting the first request for enabling use of the at least one CSLRS comprises: transmitting an activation request with an activation time duration.

[0185] Additionally or alternatively, in some implementations, the CSLRS comprises the SP CSLRS, the first request comprises a flag to indicate to activate the CSLRS, and wherein transmitting the first request for enabling use of the at least one CSLRS comprises: transmitting the first request to activate the CSLRS.

[0186] Additionally or alternatively, in some implementations, the first network device may further transmit a third request to deactivate the CSI-RS, wherein the third request comprises a flag to indicate to deactivate the CSI-RS, and the third request further comprises at least one of the following: at least one CSI-RS resource identifier, or at least one CSI-RS resource set identifier; and receive a third acknowledgement to the third request.

[0187] In some embodiments, in the case that the first network device and the second network device are associated with same base station, the first network device comprises a source distributed unit (DU) of a base station, and the second network device comprises a target DU of the base station.

[0188] In some embodiments, in the case that the first network device and the second network device are associated with different base stations, the first network device comprises a source base station, and the second network device comprises a target base station.

[0189] Additionally or alternatively, in some implementations, in the case that the CSI- RS comprises the AP CSI-RS, transmitting the first request for enabling use of the at least one CSI-RS comprises transmitting the first request to trigger the CSI-RS, and the first acknowledgement to the first request comprises at least one field for indicating an upcoming time instant for a transmission of the CSI-RS from the second network device, wherein the at least one field comprises a system frame number or a slot number.

[0190] FIG. 11 illustrates a flowchart of an example method 1100 implemented at a second network device in accordance with some embodiments of the present disclosure. For ease of understanding, the method 1100 will be described from the perspective of the second network device 204 with reference to FIG. 2 and from the perspective of the second network device 304 with reference to FIG. 3.

[0191] At block 1110, the second network device may transmit a configuration of at least one channel state information reference signal (CSI-RS) of the second network device. At block 1120, the second network device may receive a second request for enabling use of the at least one CSI-RS. At block 1130, the second network device may transmit the at least one CSI-RS.

[0192] In some embodiments, and the CSI-RS comprises at least one of semi-persistent (SP) CSI-RS or aperiodic (AP) CSI-RS, and the second request comprises at least one of the following: at least one CSI-RS resource identifier, or at least one CSI-RS resource setidentifier.

[0193] In some embodiments, the second network device may further transmit a second acknowledgement to the second request.

[0194] In some embodiments, the CSI-RS comprises the SP CSI-RS, the second request comprises a flag to indicate to activate the CSI-RS, and wherein receiving the second request for enabling use of the at least one CSI-RS comprises: receiving an activation request with an activation time duration.

[0195] Additionally or alternatively, in some implementations, the CSI-RS comprises the SP CSI-RS, the second request comprises a flag to indicate to activate the CSI-RS, and wherein receiving the second request for enabling use of the at least one CSI-RS comprises: receiving the second request to activate the CSI-RS.

[0196] Additionally or alternatively, in some implementations, the second network device may further receive a fourth request to deactivate the CSI-RS, wherein the fourth request comprises a flag to indicate to deactivate the CSI-RS, and the fourth request further comprises at least one of the following: at least one CSI-RS resource identifier, or at least one CSI-RS resource set identifier; and transmit a fourth acknowledgement to the fourth request.

[0197] In some embodiments, in the case that the first network device and the second network device are associated with same base station, the first network device comprises a source distributed unit (DU) of a base station, and the second network device comprises a target DU of the base station.

[0198] In some embodiments, in the case that the first network device and the second network device are associated with different base stations, the first network device comprises a source base station, and the second network device comprises a target base station.

[0199] Additionally or alternatively, in some implementations, in the case that the CSI- RS comprises the AP CSI-RS, receiving the second request for enabling use of the at least one CSI-RS comprises receiving the second request to trigger the CSI-RS, and the second acknowledgement to the second request comprises at least one field for indicating an upcoming time instant for a transmission of the CSI-RS, wherein the at least one field comprises a system frame number or a slot number.

[0200] FIG. 12 illustrates a flowchart of an example method 1200 implemented at athird network device in accordance with some embodiments of the present disclosure. For ease of understanding, the method 1200 will be described from the perspective of the third network device 206 with reference to FIG. 2.

[0201] At block 1210, the third network device may receive, from a first network device, a first request for enabling use of channel state information reference signal (CSI-RS) of a second network device. At block 1220, the third network device may transmit, to the second network device, a second request for enabling use of the CSI-RS of the second network device.

[0202] In some embodiments, the third network device may further receive, from the second network device, a second acknowledgement to the second request and transmit, to the first network device, a first acknowledgement to the first request, and the CSI-RS comprises at least one of semi-persistent (SP) CSI-RS or aperiodic (AP) CSI-RS, and the first request and the second request comprise at least one of the following: at least one CSI-RS resource identifier, or at least one CSI-RS resource set identifier.

[0203] In some embodiments, the CSI-RS comprises the SP CSI-RS, the first request and the second request comprise a flag to indicate to activate the CSI-RS, and wherein receiving the first request for enabling use of the CSI-RS comprises: receiving an activation request with an activation time duration.

[0204] Additionally or alternatively, in some embodiments, the CSI-RS comprises the SP CSI-RS, the first request and the second request comprise a flag to indicate to activate the CSI-RS, and wherein receiving the first request for enabling use of the CSI-RS comprises: receiving the first request to activate the CSI-RS.

[0205] Additionally or alternatively, in some implementations, the third network device may further: receive, from the first network device, a third request to deactivate the CSI- RS; transmit, to the second network device, a fourth request to deactivate the CSI-RS, wherein the third request and the fourth request comprise a flag to indicate to deactivate the CSI-RS, and the third request and the fourth request further comprise at least one of the following: at least one CSI-RS resource identifier, or at least one CSI-RS resource set identifier; receive, from the second network device, a fourth acknowledgement to the fourth request; and transmit, to the first network device, a third acknowledgement to the third request.

[0206] In some embodiments, the first network device comprises a source distributed unit (DU) of a base station, the second network device comprises a target DU of the basestation, and the third network device comprises a centralized unit (CU) of the base station.

[0207] FIG. 13 illustrates a flowchart of an example method 1300 implemented at a first network device in accordance with some embodiments of the present disclosure. For ease of understanding, the method 1300 will be described from the perspective of the first network device 402 with reference to FIG. 4 and from the perspective of the first network device 502 with reference to FIG. 5.

[0208] At block 1310, the first network device may receive a configuration of at least one channel state information reference signal (CSI-RS) of a second network device. At block 1320, the first network device may receive a second indication related to activating the at least one CSI-RS of the second network device. At block 1330, the first network device may trigger at least one UE served by the first network device to measure the activated at least one CSI-RS.

[0209] In some embodiments, the CSI-RS comprises semi -persistent (SP) CSI-RS, and the second indication comprises a flag to indicate to activate the CSI-RS, and the first indication further comprises at least one of the following: at least one CSI-RS resource identifier, or at least one CSI-RS resource set identifier.

[0210] Additionally or alternatively, in some implementations, the first network device may further transmit an acknowledgement to the second indication.

[0211] In some embodiments, the CSI-RS comprises the SP CSI-RS, the indication comprises a flag to indicate to activate the CSI-RS with an activation time duration.

[0212] Additionally or alternatively, in some implementations, the first network device further: receive a fourth indication related to deactivating the CSI-RS, wherein the fourth indication comprises a flag to indicate to deactivate the CSI-RS, and the fourth indication further comprises at least one of the following: at least one CSI-RS resource identifier, or at least one CSI-RS resource set identifier.

[0213] Additionally or alternatively, in some implementations, the first network device may further transmit a fourth acknowledgement to the fourth indication.

[0214] In some embodiments, in the case that the first network device and the second network device are associated with same base station, the first network device comprises a source distributed unit (DU) of a base station, and the second network device comprises a target DU of the base station.

[0215] In some embodiments, in the case that the first network device and the secondnetwork device are associated with different base stations, the first network device comprises a source base station, and the second network device comprises a target base station.

[0216] FIG. 14 illustrates a flowchart of an example method 1400 implemented at a second network device in accordance with some embodiments of the present disclosure. For ease of understanding, the method 1400 will be described from the perspective of the second network device 404 with reference to FIG. 4 and from the perspective of the first network device 504 with reference to FIG. 5.

[0217] At block 1410, the second network device may transmit a configuration of at least one channel state information reference signal (CSI-RS) for at least one user equipment (UE) served by a second network device. At block 1420, the second network device may determine to activate the at least one CSI-RS for the at least one UE served by the second network device. At block 1430, the second network device may transmit a first indication related to activating the at least one CSI-RS.

[0218] In some embodiments, the CSI-RS comprises semi-persistent (SP) CSI-RS, the first indication comprises a flag to indicate to activate the CSI-RS, and the first indication further comprises at least one of the following: at least one CSI-RS resource identifier, or at least one CSI-RS resource set identifier.

[0219] Additionally or alternatively, in some implementations, wherein the second network device may further receive an acknowledgement to the first indication.

[0220] In some embodiments, the CSI-RS comprises the SP CSI-RS, the indication comprises a flag to indicate to activate the CSI-RS with an activation time duration.

[0221] Additionally or alternatively, in some implementations, wherein the second network device may further transmit: a third indication related to deactivating the CSI- RS, wherein the third indication comprises a flag to indicate to deactivate the CSI-RS, and the third indication further comprises at least one of the following: at least one CSI- RS resource identifier, or at least one CSI-RS resource set identifier;

[0222] Additionally or alternatively, in some implementations, wherein the second network device may further receive a third acknowledgement to the third indication.

[0223] In some embodiments, in the case that the first network device and the second network device are associated with same base station, the first network device comprises a source distributed unit (DU) of a base station, and the second network device comprisesa target DU of the base station.

[0224] In some embodiments, in the case that the first network device and the second network device are associated with different base stations, the first network device comprises a source base station, and the second network device comprises a target base station.

[0225] FIG. 15 illustrates a flowchart of an example method 1500 implemented at a third network device in accordance with some embodiments of the present disclosure. For ease of understanding, the method 1500 will be described from the perspective of the third network device 406 with reference to FIG. 4.

[0226] At block 1502, the third network device may receive, from a second network device, a first indication related to activating channel state information reference signal (CSI-RS) of the second network device, wherein the second indication is based on a decision to activate the CSI-RS for at least one user equipment (UE) served by the second network device. At block 1504, the third network device may transmit, to the first network device, a second indication related to activating CSI-RS for at least one user equipment (UE) served by the second network device.

[0227] In some embodiments, the CSI-RS comprises semi-persistent (SP) CSI-RS, the first indication and the second indication comprise a flag to indicate to activate the CSI- RS, and the first indication and the second indication comprise at least one of the following: at least one CSI-RS resource identifier, or at least one CSI-RS resource set identifier.

[0228] Additionally or alternatively, in some implementations, the third network device may further: receive, from the second network device, a third indication related to deactivating the CSI-RS; transmit, to the first network device, a fourth indication related to deactivating the CSI-RS, wherein the third indication and the fourth indication comprise a flag to indicate to deactivate the CSI-RS, and the third indication and the fourth indication further comprise at least one of the following: at least one CSI-RS resource identifier, or at least one CSI-RS resource set identifier; receive, from the first network device, a fourth acknowledgement to the fourth indication; and transmit, to the second network device, a third acknowledgement to the third indication.

[0229] In some embodiments, the first network device comprises a source distributed unit (DU) of a base station, the second network device comprises a target DU of the base station, and the third network device comprises a centralized unit (CU) of the base station.

[0230] In some embodiments, an apparatus capable of performing any of the method 1000 (for example, the first network device 202 or the first network device 302) may comprise means for performing the respective steps of the method 1000. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module.

[0231] In some embodiments, the apparatus comprises means for receiving a configuration of at least one channel state information reference signal (CSI-RS) of a second network device; means for determining, based on a measurement report from a user equipment (UE) and the configuration, to enable use of the at least one CSI-RS of the second network device; and means for transmitting a first request for enabling use of the at least one CSI-RS of the second network device.

[0232] In some embodiments, the apparatus further comprises means for receiving a first acknowledgement to the first request, and the CSI-RS comprises at least one of semi- persistent (SP) CSI-RS or aperiodic (AP) CSI-RS, and the first request comprises at least one of the following: at least one CSI-RS resource identifier, or at least one CSI-RS resource set identifier.

[0233] In some embodiments, the CSI-RS comprises the SP CSI-RS, the first request comprises a flag to indicate to activate the CSI-RS, and wherein the means for transmitting the first request for enabling use of the at least one CSI-RS comprises: means for transmitting an activation request with an activation time duration.

[0234] Additionally or alternatively, in some implementations, the CSI-RS comprises the SP CSI-RS, the first request comprises a flag to indicate to activate the CSI-RS, and the means for transmitting the first request for enabling use of the at least one CSI-RS comprises: means for transmitting the first request to activate the CSI-RS.

[0235] Additionally or alternatively, in some implementations, the apparatus further comprises means for transmitting a third request to deactivate the CSI-RS, wherein the third request comprises a flag to indicate to deactivate the CSI-RS, and the third request further comprises at least one of the following: at least one CSI-RS resource identifier, or at least one CSI-RS resource set identifier; and means for receiving a third acknowledgement to the third request.

[0236] In some embodiments, in the case that the first network device and the second network device are associated with same base station, the first network device comprises a source distributed unit (DU) of a base station, and the second network device comprisesa target DU of the base station.

[0237] In some embodiments, in the case that the first network device and the second network device are associated with different base stations, the first network device comprises a source base station, and the second network device comprises a target base station.

[0238] Additionally or alternatively, in some implementations, in the case that the CSI- RS comprises the AP CSI-RS, the means for transmitting the first request for enabling use of the at least one CSI-RS comprises means for transmitting the first request to trigger the CSI-RS, and the first acknowledgement to the first request comprises at least one field for indicating an upcoming time instant for a transmission of the CSI-RS from the second network device, wherein the at least one field comprises a system frame number or a slot number.

[0239] In some embodiments, an apparatus capable of performing any of the method 1100 (for example, the second network device 204 or the second network device 304) may comprise means for performing the respective steps of the method 1100. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module.

[0240] In some embodiments, the apparatus comprises the means for transmitting a configuration of at least one channel state information reference signal (CSI-RS) of the second network device; means for receiving a second request for enabling use of the at least one CSI-RS; and means for transmitting the at least one CSI-RS.

[0241] In some embodiments, the apparatus further comprises means for transmitting a second acknowledgement to the second request, and the CSI-RS comprises at least one of semi-persistent (SP) CSI-RS or aperiodic (AP) CSI-RS, and the second request comprises at least one of the following: at least one CSI-RS resource identifier, or at least one CSI-RS resource set identifier.

[0242] In some embodiments, the CSI-RS comprises the SP CSI-RS, the second request comprises a flag to indicate to activate the CSI-RS, and wherein the means for receiving the second request for enabling use of the at least one CSI-RS comprises: means for receiving an activation request with an activation time duration.

[0243] Additionally or alternatively, in some implementations, the CSI-RS comprises the SP CSI-RS, the second request comprises a flag to indicate to activate the CSI-RS,and wherein the means for receiving the second request for enabling use of the at least one CSI-RS comprises: means for receiving the second request to activate the CSI-RS.

[0244] Additionally or alternatively, in some implementations, the apparatus may further comprise means for receiving a fourth request to deactivate the CSI-RS, wherein the fourth request comprises a flag to indicate to deactivate the CSI-RS, and the fourth request further comprises at least one of the following: at least one CSI-RS resource identifier, or at least one CSI-RS resource set identifier; and means for transmitting a fourth acknowledgement to the fourth request.

[0245] In some embodiments, in the case that the first network device and the second network device are associated with same base station, the first network device comprises a source distributed unit (DU) of a base station, and the second network device comprises a target DU of the base station.

[0246] In some embodiments, in the case that the first network device and the second network device are associated with different base stations, the first network device comprises a source base station, and the second network device comprises a target base station.

[0247] Additionally or alternatively, in some implementations, in the case that the CSI- RS comprises the AP CSI-RS, the means for receiving the second request for enabling use of the at least one CSI-RS comprises means for receiving the second request to trigger the CSI-RS, and the second acknowledgement to the second request comprises at least one field for indicating an upcoming time instant for a transmission of the CSI-RS, wherein the at least one field comprises a system frame number or a slot number.

[0248] In some embodiments, an apparatus capable of performing any of the method 1200 (for example, the third network device 206) may comprise means for performing the respective steps of the method 1200. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module.

[0249] In some embodiments, the apparatus comprises means for receiving, from a first network device, a first request for enabling use of channel state information reference signal (CSI-RS) of a second network device; and means for transmitting, to the second network device, a second request for enabling use of the CSI-RS of the second network device.

[0250] In some embodiments, the apparatus further comprises means for receiving, fromthe second network device, a second acknowledgement to the second request and transmit, to the first network device, a first acknowledgement to the first request, and the CSI-RS comprises at least one of semi-persistent (SP) CSI-RS or aperiodic (AP) CSI-RS, and the first request and the second request comprise at least one of the following: at least one CSI-RS resource identifier, or at least one CSI-RS resource set identifier.

[0251] In some embodiments, the CSI-RS comprises the SP CSI-RS, the first request and the second request comprise a flag to indicate to activate the CSI-RS, and wherein means for receiving the first request for enabling use of the CSI-RS comprises: means for receiving an activation request with an activation time duration.

[0252] Additionally or alternatively, in some embodiments, the CSI-RS comprises the SP CSI-RS, the first request and the second request comprise a flag to indicate to activate the CSI-RS, and wherein means for receiving the first request for enabling use of the CSI- RS comprises: means for receiving the first request to activate the CSI-RS.

[0253] Additionally or alternatively, in some implementations, the apparatus may further comprises means for receiving, from the first network device, a third request to deactivate the CSI-RS; means for transmitting, to the second network device, a fourth request to deactivate the CSI-RS, wherein the third request and the fourth request comprise a flag to indicate to deactivate the CSI-RS, and the third request and the fourth request further comprise at least one of the following: at least one CSI-RS resource identifier, or at least one CSI-RS resource set identifier; means for receiving, from the second network device, a fourth acknowledgement to the fourth request; and means for transmitting, to the first network device, a third acknowledgement to the third request.

[0254] In some embodiments, the first network device comprises a source distributed unit (DU) of a base station, the second network device comprises a target DU of the base station, and the third network device comprises a centralized unit (CU) of the base station.

[0255] In some embodiments, an apparatus capable of performing any of the method 1300 (for example, the first network device 202 or the first network device 302) may comprise means for performing the respective steps of the method 1300. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module.

[0256] In some embodiments, the apparatus comprise means for receiving a configuration of at least one channel state information reference signal (CSI-RS) of a second network device; means for receive a second indication related to activating the atleast one CSI-RS of the second network device; and means for triggering at least one UE served by the first network device to measure the activated at least one CSI-RS.

[0257] In some embodiments, the CSI-RS comprises semi -persistent (SP) CSI-RS, and the second indication comprises a flag to indicate to activate the CSI-RS, and the first indication further comprises at least one of the following: at least one CSI-RS resource identifier, or at least one CSI-RS resource set identifier.

[0258] Additionally or alternatively, in some implementations, the apparatus further comprises: means for receiving a fourth indication related to deactivating the CSI-RS, wherein the fourth indication comprises a flag to indicate to deactivate the CSI-RS, and the fourth indication further comprises at least one of the following: at least one CSI-RS resource identifier, or at least one CSI-RS resource set identifier; and means for transmitting a fourth acknowledgement to the fourth indication.

[0259] In some embodiments, in the case that the first network device and the second network device are associated with same base station, the first network device comprises a source distributed unit (DU) of a base station, and the second network device comprises a target DU of the base station.

[0260] In some embodiments, in the case that the first network device and the second network device are associated with different base stations, the first network device comprises a source base station, and the second network device comprises a target base station.

[0261] In some embodiments, an apparatus capable of performing any of the method 1400 (for example, the second network device 404 or the second network device 504) may comprise means for performing the respective steps of the method 1400. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module.

[0262] In some embodiments, the apparatus comprises the means for transmitting a configuration of at least one channel state information reference signal (CSI-RS) for at least one user equipment (UE) served by a second network device; means for determining to activate the at least one CSI-RS for the at least one UE served by the second network device; and means for transmitting a first indication related to activating the at least one CSI-RS.

[0263] In some embodiments, the CSI-RS comprises semi-persistent (SP) CSI-RS, thefirst indication comprises a flag to indicate to activate the CSI-RS, and the first indication further comprises at least one of the following: at least one CSI-RS resource identifier, or at least one CSI-RS resource set identifier.

[0264] Additionally or alternatively, in some implementations, wherein the apparatus may further comprises means for transmitting for a third indication related to deactivating the CSI-RS, wherein the third indication comprises a flag to indicate to deactivate the CSI-RS, and the third indication further comprises at least one of the following: at least one CSI-RS resource identifier, or at least one CSI-RS resource set identifier; and means for receiving a third acknowledgement to the third indication.

[0265] In some embodiments, in the case that the first network device and the second network device are associated with same base station, the first network device comprises a source distributed unit (DU) of a base station, and the second network device comprises a target DU of the base station.

[0266] In some embodiments, in the case that the first network device and the second network device are associated with different base stations, the first network device comprises a source base station, and the second network device comprises a target base station.

[0267] In some embodiments, an apparatus capable of performing any of the method 1500 (for example, the third network device 406) may comprise means for performing the respective steps of the method 1500. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module.

[0268] In some embodiments, the apparatus comprises means for receiving, from a second network device, a first indication related to activating channel state information reference signal (CSI-RS) of the second network device, wherein the second indication is based on a decision to activate the CSI-RS for at least one user equipment (UE) served by the second network device; and means for transmitting, to the first network device, a second indication related to activating CSI-RS for at least one user equipment (UE) served by the second network device.

[0269] In some embodiments, the CSI-RS comprises semi-persistent (SP) CSI-RS, the first indication and the second indication comprise a flag to indicate to activate the CSI- RS, and the first indication and the second indication comprise at least one of the following: at least one CSI-RS resource identifier, or at least one CSI-RS resource set identifier.

[0270] Additionally or alternatively, in some implementations, the apparatus further comprises means for receiving, from the second network device, a third indication related to deactivating the CSI-RS; means for transmitting, to the first network device, a fourth indication related to deactivating the CSI-RS, wherein the third indication and the fourth indication comprise a flag to indicate to deactivate the CSI-RS, and the third indication and the fourth indication further comprise at least one of the following: at least one CSI- RS resource identifier, or at least one CSI-RS resource set identifier; means for receiving, from the first network device, a fourth acknowledgement to the fourth indication; and means for transmitting, to the second network device, a third acknowledgement to the third indication.

[0271] In some embodiments, the first network device comprises a source distributed unit (DU) of a base station, the second network device comprises a target DU of the base station, and the third network device comprises a centralized unit (CU) of the base station.

[0272] FIG. 16 illustrates a simplified block diagram of a device 1600 that is suitable for implementing some example embodiments of the present disclosure. The device 1600 may be provided to implement a communication device, for example, the first network device 202, the second network device 204, or the third network device 206 as shown in FIG. 2. As shown, the device 1600 includes one or more processors 1610, one or more memories 1620 coupled to the processor 1610, and one or more communication modules 1640 coupled to the processor 610.

[0273] The communication module 1640 is for bidirectional communications. The communication module 1640 has at least one antenna to facilitate communication. The communication interface may represent any interface that is necessary for communication with other network elements.

[0274] The processor 1610 may be of any type suitable to the local technical network and may include one or more of the following: general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on multicore processor architecture, as non-limiting examples. The device 1600 may have multiple processors, such as an application specific integrated circuit chip that is slaved in time to a clock which synchronizes the main processor.

[0275] The memory 1620 may include one or more non-volatile memories and one or more volatile memories. Examples of the non-volatile memories include, but are not limited to, a Read Only Memory (ROM) 1624, an electrically programmable read onlymemory (EPROM), a flash memory, a hard disk, a compact disc (CD), a digital video disk (DVD), and other magnetic storage and / or optical storage. Examples of the volatile memories include, but are not limited to, a random access memory (RAM) 622 and other volatile memories that will not last in the power-down duration.

[0276] A computer program 1630 includes computer executable instructions that are executed by the associated processor 1610. The program 1630 may be stored in the ROM 1624. The processor 1610 may perform any suitable actions and processing by loading the program 1630 into the RAM 1622.

[0277] The embodiments of the present disclosure may be implemented by means of the program 1630 so that the device 1600 may perform any process of the disclosure as discussed with reference to FIGS. 10-15. The embodiments of the present disclosure may also be implemented by hardware or by a combination of software and hardware.

[0278] In some example embodiments, the program 1630 may be tangibly contained in a computer-readable medium which may be included in the device 1600 (such as in the memory 1620) or other storage devices that are accessible by the device 1600. The device 1600 may load the program 1630 from the computer-readable medium to the RAM 1622 for execution. The computer-readable medium may include any types of tangible nonvolatile storage, such as ROM, EPROM, a flash memory, a hard disk, CD, DVD, and the like.

[0279] FIG. 17 illustrates a block diagram of an example of a computer-readable medium 1700 in accordance with some example embodiments of the present disclosure. The computer-readable medium 1700 has the program 1730 stored thereon. It is noted that although the computer-readable medium 1700 is depicted in form of CD or DVD in FIG. 17, the computer-readable medium 1700 may be in any other form suitable for carry or hold the program 1730.

[0280] Generally, various embodiments of the present disclosure may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. Some aspects may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device. While various aspects of embodiments of the present disclosure are illustrated and described as block diagrams, flowcharts, or using some other pictorial representations, it is to be understood that the block, apparatus, system, technique or method described herein may be implemented in, as non-limiting examples, hardware,software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

[0281] The present disclosure also provides at least one computer program product tangibly stored on a non-transitory computer-readable storage medium. The computer program product includes computer-executable instructions, such as those included in program modules, being executed in a device on a target real or virtual processor, to carry out any one of the methods 1000-1500 as described above with reference to FIGS. 10-15. Generally, program modules include routines, programs, libraries, objects, classes, components, data structures, or the like that perform particular tasks or implement particular abstract data types. The functionality of the program modules may be combined or split between program modules as desired in various embodiments. Machineexecutable instructions for program modules may be executed within a local or distributed device. In a distributed device, program modules may be located in both local and remote storage media.

[0282] Program code for carrying out methods of the present disclosure may be written in any combination of one or more programming languages. These program codes may be provided to a processor or controller of a general purpose computer, special purpose computer, or other programmable data processing apparatus, such that the program codes, when executed by the processor or controller, cause the functions / operations specified in the flowcharts and / or block diagrams to be implemented. The program code may execute entirely on a machine, partly on the machine, as a stand-alone software package, partly on the machine and partly on a remote machine or entirely on the remote machine or server.

[0283] In the context of the present disclosure, the computer program codes or related data may be carried by any suitable carrier to enable the device, apparatus or processor to perform various processes and operations as described above. Examples of the carrier include a signal, computer-readable medium, and the like.

[0284] The computer-readable medium may be a computer-readable signal medium or a computer-readable storage medium. A computer-readable medium may include but not limited to an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples of the computer-readable storage medium would include an electrical connection having one or more wires, a portable computer diskette, a hard disk, a randomaccess memory (RAM), a read-only memory (ROM), an erasable programmable readonly memory (EPROM or Flash memory), an optical fiber, a portable compact disc readonly memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing. The term “non-transitory,” as used herein, is a limitation of the medium itself (i.e., tangible, not a signal) as opposed to a limitation on data storage persistency (e.g., RAM vs. ROM).

[0285] Further, while operations are depicted in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Likewise, while several specific implementation details are contained in the above discussions, these should not be construed as limitations on the scope of the present disclosure, but rather as descriptions of features that may be specific to particular embodiments. Certain features that are described in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment may also be implemented in multiple embodiments separately or in any suitable sub-combination.

[0286] Although the present disclosure has been described in languages specific to structural features and / or methodological acts, it is to be understood that the present disclosure defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.

Claims

WE CLAIM:

1. A first network device comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the first network device at least to: receive a configuration of at least one channel state information reference signal (CSI-RS) of a second network device; determine, based on a measurement report from a user equipment (UE) and the configuration, to enable use of the at least one CSI-RS of the second network device; and transmit a first request for enabling use of the at least one CSI-RS of the second network device.

2. The first network device of claim 1, wherein the first network device is further caused to receive a first acknowledgement to the first request, and the CSI-RS comprises at least one of semi-persistent (SP) CSI-RS or aperiodic (AP) CSI-RS, and the first request comprises at least one of the following: at least one CSI-RS resource identifier, or at least one CSI-RS resource set identifier.

3. The first network device of claim 2, wherein the CSI-RS comprises the SP CSI- RS, the first request comprises a flag to indicate to activate the CSI-RS, and wherein transmitting the first request for enabling use of the at least one CSI-RS comprises: transmitting an activation request with an activation time duration.

4. The first network device of claim 2, wherein the CSI-RS comprises the SP CSI- RS, the first request comprises a flag to indicate to activate the CSI-RS, and wherein transmitting the first request for enabling use of the at least one CSI-RS comprises: transmitting the first request to activate the CSI-RS.

5. The first network device of claim 4, wherein the first network device is further caused to: transmit a third request to deactivate the CSI-RS, wherein the third request comprises a flag to indicate to deactivate the CSI-RS, and the third request furthercomprises at least one of the following: at least one CSI-RS resource identifier, or at least one CSI-RS resource set identifier.

6. The first network device of claim 4 or 5, wherein in the case that the first network device and the second network device are associated with same base station, the first network device comprises a source distributed unit (DU) of a base station, and the second network device comprises a target DU of the base station.

7. The first network device of claim 4 or 5, wherein in the case that the first network device and the second network device are associated with different base stations, the first network device comprises a source base station, and the second network device comprises a target base station.

8. The first network device of claim 2, wherein the CSI-RS comprises the AP CSI- RS: transmitting the first request for enabling use of the at least one CSI-RS comprises: transmitting the first request to trigger the CSI-RS, and the first acknowledgement to the first request comprises at least one field for indicating an upcoming time instant for a transmission of the CSI-RS from the second network device, wherein the at least one field comprises a system frame number or a slot number.

9. A second network device comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the second network device at least to: transmit a configuration of at least one channel state information reference signal (CSI-RS) of the second network device; receive a second request for enabling use of the at least one CSI-RS; and transmit the at least one CSI-RS.

10. The second network device of claim 9, wherein the second network device is further caused to transmit a second acknowledgement to the second request, andthe CSI-RS comprises at least one of semi-persistent (SP) CSI-RS or aperiodic (AP) CSI-RS, and the second request comprises at least one of the following: at least one CSI-RS resource identifier, or at least one CSI-RS resource set identifier.

11. The second network device of claim 10, wherein the CSI-RS comprises the SP CSI-RS, the second request comprises a flag to indicate to activate the CSI-RS, and wherein receiving the second request for enabling use of the at least one CSI-RS comprises: receiving an activation request with an activation time duration.

12. The second network device of claim 10, wherein the CSI-RS comprises the SP CSI-RS, the second request comprises a flag to indicate to activate the CSI-RS, and wherein receiving the second request for enabling use of the at least one CSI-RS comprises: receiving the second request to activate the CSI-RS.

13. The second network device of claim 12, wherein the second network device is further caused to: receive a fourth request to deactivate the CSI-RS, wherein the fourth request comprises a flag to indicate to deactivate the CSI-RS, and the fourth request further comprises at least one of the following: at least one CSI-RS resource identifier, or at least one CSI-RS resource set identifier; and stop transmitting the at least one CSI-RS.

14. The second network device of claim 12 or 13, wherein in the case that the first network device and the second network device are associated with same base station, the first network device comprises a source distributed unit (DU) of a base station, and the second network device comprises a target DU of the base station.

15. The second network device of claim 12 or 13, in the case that the first network device and the second network device are associated with different base stations, the first network device comprises a source base station, and the second network device comprises a target base station.

16. The second network device of claim 10, wherein the CSI-RS comprises the AP CSI-RS: receiving the second request for enabling use of the at least one CSI-RS comprises: receiving the second request to trigger the CSI-RS, and the second acknowledgement to the second request comprises at least one field for indicating an upcoming time instant for a transmission of the CSI-RS, wherein the at least one field comprises a system frame number or a slot number.

17. A third network device comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the third network device at least to: receive, from a first network device, a first request for enabling use of channel state information reference signal (CSI-RS) of a second network device; and transmit, to the second network device, a second request for enabling use of the CSI-RS of the second network device.

18. The third network device of claim 17, wherein the third network device is further configured to: receive, from the second network device, a second acknowledgement to the second request; and transmit, to the first network device, a first acknowledgement to the first request, and the CSI-RS comprises at least one of semi-persistent (SP) CSI-RS or aperiodic (AP) CSI-RS, and the first request and the second request comprise at least one of the following: at least one CSI-RS resource identifier, or at least one CSI-RS resource set identifier.

19. The third network device of claim 18, wherein the CSI-RS comprises the SP CSI-RS, the first request and the second request comprise a flag to indicate to activate the CSI-RS, andwherein receiving the first request for enabling use of the CSI-RS comprises: receiving an activation request with an activation time duration.

20. The third network device of claim 18, wherein the CSI-RS comprises the SP CSI-RS, the first request and the second request comprise a flag to indicate to activate the CSI-RS, and wherein receiving the first request for enabling use of the CSI-RS comprises: receiving the first request to activate the CSI-RS.

21. The third network device of claim 20, wherein the third network device is further caused to: receive, from the first network device, a third request to deactivate the CSI-RS; transmit, to the second network device, a fourth request to deactivate the CSI-RS, wherein the third request and the fourth request comprise a flag to indicate to deactivate the CSI-RS, and the third request and the fourth request further comprise at least one of the following: at least one CSI-RS resource identifier, or at least one CSI-RS resource set identifier.

22. The third network device of claim 20 or 21, wherein the first network device comprises a source distributed unit (DU) of a base station, the second network device comprises a target DU of the base station, and the third network device comprises a centralized unit (CU) of the base station.

23. The third network device of claim 18, wherein the CSI-RS comprises the AP CSI-RS: receiving the first request for enabling use of the CSI-RS comprises: receiving the first request to trigger the CSI-RS, and the first acknowledgement to the first request comprises at least one field for indicating an upcoming time instant for a transmission of the CSI-RS, wherein the at least one field comprises a system frame number or a slot number.

24. A first network device comprising: at least one processor; andat least one memory storing instructions that, when executed by the at least one processor, cause the first network device at least to: receive a configuration of at least one channel state information reference signal (CSI-RS) of a second network device; receive a second indication related to activating the at least one CSI-RS of the second network device; and trigger at least one UE served by the first network device to measure the activated at least one CSI-RS.

25. The first network device of claim 24, wherein the CSI-RS comprises semi- persistent (SP) CSI-RS, and the second indication comprises a flag to indicate to activate the CSI-RS, and the first indication further comprises at least one of the following: at least one CSI-RS resource identifier, or at least one CSI-RS resource set identifier.

26. The first network device of claim 25, wherein the first network device is further caused to: receive a fourth indication related to deactivating the CSI-RS, wherein the fourth indication comprises a flag to indicate to deactivate the CSI-RS, and the fourth indication further comprises at least one of the following: at least one CSI-RS resource identifier, or at least one CSI-RS resource set identifier; and trigger at least one UE served by the first network device to stop measure the deactivated at least one CSI-RS.

27. The first network device of claim 25 or 26, wherein in the case that the first network device and the second network device are associated with same base station, the first network device comprises a source distributed unit (DU) of a base station, and the second network device comprises a target DU of the base station.

28. The first network device of claim 25 or 26, wherein in the case that the first network device and the second network device are associated with different base stations, the first network device comprises a source base station, and the second network device comprises a target base station.

29. A second network device comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the second network device at least to: transmit a configuration of at least one channel state information reference signal (CSI-RS) for at least one user equipment (UE) served by a second network device; determine to activate the at least one CSI-RS for the at least one UE served by the second network device; and transmit a first indication related to activating the at least one CSI-RS.

30. The second network device of claim 29, wherein the CSI-RS comprises semi- persistent (SP) CSI-RS, the first indication comprises a flag to indicate to activate the CSI-RS, and the first indication further comprises at least one of the following: at least one CSI-RS resource identifier, or at least one CSI-RS resource set identifier.

31. The second network device of claim 29, wherein the second network device is further caused to: determine to deactivate the at least one activated CSI-RS for the at least one UE served by the second network device; and transmit a third indication related to deactivating the CSI-RS, wherein the third indication comprises a flag to indicate to deactivate the CSI-RS, and the third indication further comprises at least one of the following: at least one CSI-RS resource identifier, or at least one CSI-RS resource set identifier.

32. The second network device of claim 30 or 31, wherein in the case that the first network device and the second network device are associated with same base station, the first network device comprises a source distributed unit (DU) of a base station, and the second network device comprises a target DU of the base station.

33. The second network device of claim 30 or 31, wherein in the case that the first network device and the second network device are associated with different base stations, the first network device comprises a source base station, and the second network device comprises a target base station.

34. A third network device comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the third network device at least to: receive, from a second network device, a first indication related to activating channel state information reference signal (CSI-RS) of the second network device, wherein the second indication is based on a decision to activate the CSI-RS for at least one user equipment (UE) served by the second network device; and transmit, to the first network device, a second indication related to activating CSI-RS for at least one user equipment (UE) served by the second network device.

35. The third network device of claim 34, wherein the CSI-RS comprises semi- persistent (SP) CSI-RS, the first indication and the second indication comprise a flag to indicate to activate the CSI-RS, and the first indication and the second indication comprise at least one of the following: at least one CSI-RS resource identifier, or at least one CSI-RS resource set identifier.

36. The third network device of claim 35, wherein the third network device is further caused to: receive, from the second network device, a third indication related to deactivating the CSI-RS; transmit, to the first network device, a fourth indication related to deactivating the CSI-RS, wherein the third indication and the fourth indication comprise a flag to indicate to deactivate the CSI-RS, and the third indication and the fourth indication further comprise at least one of the following: at least one CSI-RS resource identifier, or at least one CSI-RS resource set identifier.

37. The third network device of claim 35 or 36, wherein the first network device comprises a source distributed unit (DU) of a base station, the second network devicecomprises a target DU of the base station, and the third network device comprises a centralized unit (CU) of the base station.

38. A method comprising: receiving a configuration of at least one channel state information reference signal (CSI-RS) of a second network device; determining, based on a measurement report from a user equipment (UE) and the configuration, to enable use of the at least one CSI-RS of the second network device; and transmitting a first request for enabling use of the at least one CSI-RS of the second network device.

39. A method comprising: transmitting a configuration of at least one channel state information reference signal (CSI-RS) of the second network device; receiving a second request for enabling use of the at least one CSI-RS; and transmitting the at least one CSI-RS.

40. A method comprising: receiving, from a first network device, a first request for enabling use of channel state information reference signal (CSI-RS) of a second network device; and transmitting, to the second network device, a second request for enabling use of the CSI-RS of the second network device.

41. A method comprising: receiving a configuration of at least one channel state information reference signal (CSI-RS) of a second network device; receiving a second indication related to activating the at least one CSI-RS of the second network device; and triggering at least one UE served by the first network device to measure the activated at least one CSI-RS.

42. A method comprising: transmitting a configuration of at least one channel state information reference signal (CSI-RS) for at least one user equipment (UE) served by a second network device;determining to activate the at least one CSI-RS for the at least one UE served by the second network device; and transmitting a first indication related to activating the at least one CSI-RS.

43. A method comprising: receiving, from a second network device, a first indication related to activating channel state information reference signal (CSI-RS) of the second network device, wherein the second indication is based on a decision to activate the SP CSI-RS for at least one user equipment (UE) served by the second network device; and transmitting, to a first network device, a second indication related to activating SP CSI-RS of the second network device.

44. An apparatus comprising: means for receiving a configuration of at least one channel state information reference signal (CSI-RS) of a second network device; means for determining, based on a measurement report from a user equipment (UE), to enable use of the at least one CSI-RS of the second network device; and means for transmitting a first request for enabling use of the at least one CSI-RS of the second network device.

45. An apparatus comprising: means for transmitting a configuration of at least one channel state information reference signal (CSI-RS) of the second network device; means for receiving a second request for enabling use of the at least one CSI-RS; and means for transmitting the at least one CSI-RS.

46. An apparatus comprising: means for receiving, from a first network device, a first request for enabling use of channel state information reference signal (CSI-RS) of a second network device; and means for transmitting, to the second network device, a second request for enabling use of the CSI-RS of the second network device.

47. An apparatus comprising:means for receiving a configuration of at least one channel state information reference signal (CSI-RS) of a second network device; means for receiving a second indication related to activating the at least one CSI- RS of the second network device; and means for triggering at least one UE served by the first network device to measure the activated at least one CSI-RS.

48. An apparatus comprising: means for transmitting a configuration of at least one channel state information reference signal (CSI-RS) for at least one user equipment (UE) served by a second network device; means for determining to activate the at least one CSI-RS for the at least one UE served by the second network device; and means for transmitting a first indication related to activating the at least one CSI- RS.

49. An apparatus comprising: means for receiving, from a second network device, a first indication related to activating channel state information reference signal (CSI-RS) of the second network device, wherein the second indication is based on a decision to activate the SP CSI-RS for at least one user equipment (UE) served by the second network device; and means for transmitting, to a first network device, a second indication related to activating SP CSI-RS of the second network device.

50. A non-transitory computer readable medium comprising program instructions for causing an apparatus to perform at least method of any of claims 38-43.

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