Trans-zone handover delay in cell mobility

Abstract

A user equipment is disclosed that is configured to evaluate an expected cross-zone handover delay to at least one of a plurality of candidate cells, and to generate and transmit an indication of the cross-zone handover delay to a network node of a serving cell. This allows the network to consider over-zone handover latency when deciding how and whether to perform over-zone handover.

Description

Technical Field

[0001] Various example embodiments relate to wireless communication systems, and more particularly to facilitating mobility within such wireless communication systems. Background Art

[0002] As a user equipment (UE) moves through a wireless communication system, it may move through cells comprising radio coverage areas supported by one or more network access nodes. The ability to maintain effective communication between the UE and the wireless communication system as the UE moves through the radio coverage areas is generally referred to as mobility. There may be delays and potential outages in coverage associated with movement between cells and layer 1 or layer 2 (sometimes referred to as lower layers), and triggered mobility is increasingly being considered to reduce the delays, overhead, and outages associated with UEs moving between different cells. Summary of the invention

[0003] The scope of protection sought by various exemplary embodiments of the present invention is set out in the independent claims. Exemplary embodiments and features described in this specification that do not fall within the scope of the independent claims, if any, are to be construed as examples that aid in understanding the various embodiments of the present invention.

[0004] According to various but not necessarily all example embodiments of the present invention, there is provided an apparatus comprising: at least one processor; and at least one memory storing instructions, wherein when the instructions are executed by the at least one processor, the apparatus is caused to at least perform: evaluating an expected handover delay to at least one of a plurality of candidate cells; generating an indication of the handover delay; and causing the indication to be transmitted to a network node of a serving cell.

[0005] The delay for handover of a device such as a user equipment from a serving cell to a target cell when moving between cells depends on various factors, some of which are specific to the user equipment. The selection of a target cell for handover is typically performed at the network, and the network may not know and may not be able to accurately estimate the handover delay for a particular user equipment. It is desirable for the network to have some visibility into this information so that cells with short delays or at least within acceptable limits can be preferentially selected as target cells. Therefore, various aspects provide for evaluating the expected handover delays for one or more candidate cells, and generating and transmitting an indication of one or more of the handover delays to the network.

[0006] In some example embodiments, the handover delay is used for lower layer triggered mobility LTM or layer 1 / layer 2 L1 / L2 triggered mobility handover. L1 / L2 triggered mobility handover is increasingly used to reduce the overhead and latency associated with handover, so in L1 / L2 mobility, knowing the handover delay associated with a particular UE can be particularly advantageous when performing target cell selection.

[0007] For the purposes of this application, LTM and L1 / L2 triggered mobility handoff are used interchangeably to mean handoff triggered by lower layer measurements.

[0008] In other example embodiments, the handoff delay is for layer 3 triggered handoff. It may also be advantageous to understand the handoff delay in L3 triggered handoff.

[0009] In some example embodiments, the apparatus is configured to perform the evaluating step in response to at least one of: receiving a request from a network node; a predetermined point in a cell handover process; a signal strength measurement status; or detection of one or more cells.

[0010] In some example embodiments, the signal strength measurement status may include completion of a signal strength measurement, and / or a determination that one or more signal strength measurement values ​​are greater than a threshold;

[0011] In some example embodiments, the predetermined point in the cell handover procedure may be a point during which measurements associated with handover are performed prior to receiving the cell handover command (eg, during a timing advance acquisition procedure).

[0012] In some example embodiments, the apparatus is caused to perform the evaluating step in response to receiving a request from the network node, the request being received within at least one of: a message indicating a configuration of the candidate cell; a message indicating that a cell handover is to be performed; or a separate dedicated request.

[0013] The message indicating the configuration of the candidate cell may be a configuration updated after the network node down-selects the candidate cell.

[0014] In some example embodiments, the apparatus is caused to perform the evaluating step in response to receiving a request from the network, the request indicating the at least one candidate cell of the plurality of candidate cells for which the evaluation is to be performed.

[0015] In some example embodiments, the apparatus is configured to perform the evaluation on a subset of the plurality of candidate cells.

[0016] In some example embodiments, the apparatus is configured to: perform the evaluation for a plurality of the plurality of candidate cells, wherein the indication includes a handover delay to each of the plurality of the plurality of candidate cells; and in response to the transmitted indication, receive from the network node a handover command triggering a handover to a target cell among the plurality of the plurality of cells, wherein the target cell is associated with a minimum handover delay included in the indication.

[0017] In some example embodiments, the apparatus is caused to transmit the handover delay indication within at least one of: a UE assistance information message; an L1 measurement report; an L3 measurement report; a message indicating that configuration of a candidate cell is complete; or a response to a cell handover command.

[0018] In some example embodiments, the apparatus is caused to generate the handover delay indication for at least one of: each candidate cell; each candidate cell for which the apparatus has performed measurements; a candidate cell indicated in a request received from the network node; a target cell indicated in a received cell handover command; a candidate cell satisfying at least one predetermined condition, the predetermined condition comprising a handover delay condition or a measurement condition; or at least one candidate cell and a detected cell that is not a candidate cell.

[0019] In some example embodiments, the apparatus is caused to transmit the handoff delay indication for a candidate cell that satisfies at least one predetermined condition, the at least one predetermined condition comprising the handoff delay being less than a threshold.

[0020] In some example embodiments, the handoff delay indication comprises one of: a time delay value; an indication that the delay is within one of a plurality of predetermined value ranges; an indication that the delay meets or does not meet a threshold; an index of an indication value; or an offset value.

[0021] The index may index a table of values ​​known to the network and the UE. The table may be within the configuration of the system, or it may be a dynamic table stored on the network and the UE and updated via reconfiguration messages. The index may be a Boolean value indicating true or false.

[0022] In some example embodiments, the apparatus comprises user equipment.

[0023] According to various but not necessarily all example embodiments of the present invention, according to one aspect, a device is provided, which includes at least one processor; and at least one memory storing instructions, which, when executed by the at least one processor, cause the device to at least perform: transmitting multiple candidate cell configurations to a user equipment, wherein the multiple candidate cells are potential target cells to which the user equipment is to handover; in response to receiving at least one indication of an expected handover delay for at least one of the candidate cells, generating a message about the handover and transmitting it to the user equipment.

[0024] In some example embodiments, the candidate cells include candidate cells for LTM or L1 / L2 handoff.

[0025] In some example embodiments, the message includes at least one of: a modification of the configuration of the multiple candidate cells; an indication for the user equipment to perform a layer 3L3 handover; a cell handover indication; an indication for the user equipment to perform further measurements, or an indication not to perform a handover.

[0026] Examples of further measurements may include layer 1 signal strength measurements and in some cases further delay measurements.The signal strength measurement may be a measurement of signal quality and / or signal power and may be based on a measurement of RSRP received signal to received power.

[0027] The modification may include one of an addition, modification or deletion of a candidate cell configuration, or it may include an updated measurement configuration for the candidate cell.

[0028] In some exemplary embodiments, the cell switching indication indicates a target cell.

[0029] In some example embodiments, the apparatus is caused to perform: comparing the value of the at least one expected handoff delay to a threshold; and generating the message in response to the comparing.

[0030] In some example embodiments, if the comparison indicates that the delay is greater than the threshold for a candidate cell, the apparatus is caused to perform one of: deciding not to trigger a handover to the candidate cell and / or removing the candidate cell from potential candidate cells.

[0031] In some exemplary embodiments, the apparatus is caused to perform: in response to receiving at least one measurement report indicating signal strengths of at least some of the multiple candidate cells, and in response to receiving the evaluation of the handover delay for at least some of the multiple candidate cells, selecting a target cell from the multiple candidate cells based on the handover delay and the measurement report; and generating the cell handover command as the message, the cell handover command indicating one of the candidate cells as a target cell for handover.

[0032] In some example embodiments, the selecting step includes ignoring candidate cells having a handoff delay greater than the threshold.

[0033] In some example embodiments, the selecting step includes: for candidate cells having signal strength measurements above a threshold, selecting one of the cells having a lowest expected handoff delay.

[0034] In some example embodiments, the apparatus is caused, in response to receiving the at least one indication of the expected handoff delay, to: forward the indication to a central unit network node; and generate the message in response to receiving handoff information from the central unit network node.

[0035] In some example embodiments, the apparatus is further caused to forward the at least one measurement report to the central unit network node in response to receiving the at least one measurement report indicating signal strengths of at least some of the plurality of candidate cells.

[0036] In some example embodiments, the network node is a distributed unit network node and is in communication with a central unit which may perform cell selection, and the distributed unit may forward relevant delay and measurement information to the central unit.

[0037] In some example embodiments, the apparatus is caused to generate a message requesting the user equipment to perform an evaluation of a handover delay.

[0038] According to various but not necessarily all example embodiments of the present invention, there is provided an apparatus comprising at least one processor; and at least one memory storing instructions, wherein when the instructions are executed by the at least one processor, the apparatus at least performs: generating a message requesting a user equipment to perform an evaluation of a handover delay.

[0039] In some example embodiments, the message comprises one of: a message indicating configuration of the candidate cell; a message indicating that a cell handover is to be performed; or a separate dedicated request.

[0040] In some example embodiments, the apparatus comprises a network node, such as a gNB or a distributed unit of a base station.

[0041] According to various but not necessarily all example embodiments of the present invention, according to a further aspect, a device includes at least one processor; and at least one memory storing instructions, which, when executed by the at least one processor, causes the device to at least perform: generating handover information in response to at least one indication of an expected handover delay of a user equipment received from a distributed unit network node; and transmitting to the distributed unit network node.

[0042] In some example embodiments, the apparatus is caused to perform: comparing the value of the at least one expected handoff delay to a threshold; and generating the handoff information in response to the comparing.

[0043] In some example embodiments, in response to receiving at least one measurement report indicating signal strength of at least some of the multiple candidate cells and receiving the evaluation of the handover delay for at least some of the multiple candidate cells, the device is caused to perform: selecting a target cell from the multiple candidate cells based on the handover delay and the measurement report; and transmitting an indication of the target cell to the distributed unit as the handover information.

[0044] In some example embodiments, the apparatus is further caused to transmit an indication of the handover to a selected target cell.

[0045] In some example embodiments, the apparatus comprises a network node, such as a central unit network node of a gNB.

[0046] According to various but not necessarily all example embodiments of the present invention, there is provided a network node comprising at least one apparatus according to one aspect comprising a distributed unit of the network node and apparatus according to another aspect comprising a central unit of the network node.

[0047] According to various but not necessarily all example embodiments of the present invention, there is provided a method performed by an apparatus, the method comprising: evaluating an expected handover delay to at least one of a plurality of candidate cells; generating an indication of the handover delay; and transmitting the indication to a network node of a serving cell.

[0048] In some example embodiments, the evaluating step is performed in response to at least one of: receiving a request from a network node; a predetermined point in a cell handover process; a signal strength measurement status; or detection of one or more cells.

[0049] In some example embodiments, the evaluating step is performed in response to receiving a request from the network node, the request being received within at least one of: a message indicating configuration of the candidate cell; a message indicating that a cell handover is to be performed; or a separate dedicated request.

[0050] In some example embodiments, the evaluating step is performed in response to receiving a request from the network, the request indicating the at least one candidate cell of the plurality of candidate cells for which the evaluation is to be performed.

[0051] In some example embodiments, the evaluating step is performed on one of: one, a subset, or all of the plurality of candidate cells.

[0052] In some exemplary embodiments, the evaluating step is performed for multiple of the multiple candidate cells, wherein the indication includes a handover delay to each of the multiple of the multiple candidate cells, and the method includes receiving a handover command from the network node in response to the transmitted indication, the handover command triggering a handover to a target cell in the multiple of the multiple candidate cells, wherein the target cell is associated with a minimum handover delay included in the indication.

[0053] In some example embodiments, the method includes transmitting the handover delay indication in at least one of: a UE assistance information message; an L1 measurement report; an L3 measurement report; a message indicating that configuration of the candidate cell is complete; or a response to a cell handover command.

[0054] In some example embodiments, the method includes generating the handover delay indication for at least one of: each candidate cell; each candidate cell for which the device has performed measurements; a candidate cell indicated in a request received from the network node; a target cell indicated in a received cell handover command; a candidate cell that satisfies at least one predetermined condition, the predetermined condition comprising a handover delay condition or a measurement condition; or a detected cell that is not a candidate cell.

[0055] In some example embodiments, the method includes transmitting the handoff delay indication for candidate cells that satisfy at least one predetermined condition, the at least one predetermined condition including the handoff delay being less than a threshold.

[0056] According to various but not necessarily all example embodiments of the present invention, a method performed by an apparatus is provided, the method comprising transmitting a plurality of candidate cell configurations to a user equipment, the plurality of candidate cells being potential target cells to which the user equipment is to handover; receiving at least one indication of an expected handover delay for at least one of the candidate cells and generating a message regarding the handover; and transmitting the message to the user equipment.

[0057] In some example embodiments, the method includes comparing the value of the at least one expected handoff delay to a threshold; and generating the message in response to the comparing.

[0058] In some example embodiments, the method comprises, if the comparison indicates that the delay for a candidate cell is greater than the threshold, deciding not to trigger a handover to the candidate cell and / or removing the candidate cell from potential candidate cells.

[0059] In some example embodiments, the method includes: receiving at least one measurement report indicating signal strength of at least some of the multiple candidate cells, and receiving the evaluation of the handover delay of at least some of the multiple candidate cells; selecting a target cell from the multiple candidate cells based on the handover delay and the measurement report; and generating the cell switching command as the message, the cell switching command indicating one of the candidate cells as the target cell for handover.

[0060] In some example embodiments, the selecting step includes ignoring candidate cells having a handoff delay greater than the threshold.

[0061] In some example embodiments, the selecting step includes, for candidate cells having signal strength measurements above a threshold, selecting one of the cells having a lowest expected handoff delay.

[0062] In some example embodiments, the method includes: receiving at least one indication of the expected handoff delay and forwarding the indication to a central unit network node; receiving handoff information from the central unit network node and generating the message.

[0063] In some example embodiments, the method comprises receiving at least one measurement report indicating signal strengths of at least some of the plurality of candidate cells, and forwarding the at least one measurement report to the central unit network node.

[0064] In some example embodiments, the method comprises generating a message requesting the user equipment to perform an evaluation of a handoff delay.

[0065] According to various, but not necessarily all, example embodiments of the invention, there is provided a method comprising generating a message requesting a user equipment to perform an evaluation of a handover delay.

[0066] According to various but not necessarily all example embodiments of the present invention, a method performed at an apparatus is provided, the method comprising: receiving at least one indication of an expected handover delay of a user equipment from a distributed unit of a network node; generating handover information and transmitting the handover information to the distributed unit network node.

[0067] In some example embodiments, the method comprises comparing the value of the at least one expected handoff delay to a threshold; and generating the handoff information in response to the comparing.

[0068] In some example embodiments, at least one measurement report indicating signal strength of at least some of the plurality of candidate cells is received, and a target cell is selected from the plurality of candidate cells based on the handoff delay and the measurement report; and an indication of the target cell is transmitted to the distributed unit.

[0069] In some example embodiments, the method includes transmitting an indication of the handoff to a selected target cell.

[0070] According to various but not necessarily all example embodiments of the present invention, there is provided an apparatus comprising: means for evaluating an expected handover delay to at least one of a plurality of candidate cells; means for generating an indication of the handover delay; and means for transmitting the indication to a network node of a serving cell.

[0071] In some example embodiments, the apparatus comprises means for receiving a request from a network node.

[0072] According to various but not necessarily all example embodiments of the present invention, there is provided a device comprising: a device for transmitting a plurality of candidate cell configurations to a user equipment, wherein the plurality of candidate cells are potential target cells to which the user equipment is to handover; a device for receiving at least one indication of an expected handover delay for at least one of the candidate cells; and a device for generating a message regarding the handover for transmission to the user equipment.

[0073] In some example embodiments, the apparatus comprises means for comparing the value of the at least one expected handoff delay to a threshold value.

[0074] In some example embodiments, the apparatus comprises means for selecting a target cell from the plurality of candidate cells based on the handoff delay and the measurement report.

[0075] In some example embodiments, the apparatus comprises means for generating a message requesting the user equipment to perform an evaluation of a handoff delay.

[0076] According to various, but not necessarily all, exemplary embodiments of the present invention, there is provided an apparatus comprising means for generating a message requesting a user equipment to perform an evaluation of a handover delay.

[0077] According to various but not necessarily all example embodiments of the present invention, a device is provided, comprising: a device for receiving at least one indication of an expected handover delay of a user equipment from a distributed unit of a network node, a device for generating handover information, and a device for transmitting the handover information to the distributed unit network node.

[0078] In some example embodiments, the apparatus comprises means for comparing the value of the at least one expected handoff delay to a threshold; and means for generating the handoff information in response to the comparing.

[0079] In some example embodiments, the apparatus includes means for selecting a target cell from the plurality of candidate cells based on the handoff delay and the measurement report; and transmitting an indication of the target cell to the distributed unit.

[0080] The apparatus may perform the optional features set out in relation to the above mentioned devices.

[0081] According to various but not necessarily all example embodiments of the present invention, there is provided an apparatus comprising: a circuit configured to evaluate an expected handover delay to at least one of a plurality of candidate cells; a circuit configured to generate an indication of the handover delay; and a transmitter for transmitting the indication to a network node of a serving cell.

[0082] In some example embodiments, the apparatus comprises a receiver for receiving a request from a network node.

[0083] According to various but not necessarily all example embodiments of the present invention, there is provided an apparatus comprising: a transmitter configured to transmit a plurality of candidate cell configurations to a user equipment, the plurality of candidate cells being potential target cells to which the user equipment is to handover; a receiver configured to receive at least one indication of an expected handover delay for at least one of the candidate cells; and a generating circuit configured to generate a message regarding the handover for transmission to the user equipment.

[0084] In some example embodiments, the apparatus comprises a comparison circuit configured to compare the value of the at least one expected handoff delay with a threshold value.

[0085] In some example embodiments, the apparatus comprises a selection circuit configured to select a target cell from the plurality of candidate cells based on the handoff delay and the measurement report.

[0086] In some example embodiments, the apparatus comprises generating circuitry configured to generate a message requesting a user equipment to perform an evaluation of a handoff delay.

[0087] According to various, but not necessarily all, example embodiments of the present invention, there is provided an apparatus comprising a generating circuit configured to generate a message requesting a user equipment to perform an evaluation of a handover delay.

[0088] According to various but not necessarily all example embodiments of the present invention, a device is provided, comprising: a receiver for receiving at least one indication of an expected handover delay of a user equipment from a distributed unit of a network node, a generating circuit configured to generate handover information, and a transmitter for transmitting the handover information to the distributed unit network node.

[0089] In some example embodiments, the apparatus comprises a comparison circuit configured to compare the value of the at least one expected handoff delay with a threshold; and in response to the comparison, the generation circuit is configured to generate the handoff information.

[0090] In some example embodiments, the apparatus comprises a selection circuit configured to select a target cell from the plurality of candidate cells based on the handoff delay and the measurement report; and the transmitter is configured to transmit an indication of the target cell to the distributed unit.

[0091] The circuitry may be configured to perform the optional features set forth in relation to the above-mentioned apparatus.

[0092] According to various but not necessarily all exemplary embodiments of the present invention, there is provided a computer program comprising computer-readable instructions which, when executed by at least one processor on a device, is operable to control the device to perform at least the following operations: evaluating an expected handover delay to at least one of a plurality of candidate cells; generating an indication of the handover delay; and causing the indication to be transmitted to a network node of a serving cell.

[0093] According to various but not necessarily all example embodiments of the present invention, there is provided a computer program comprising computer-readable instructions, which, when executed by at least one processor on an apparatus, are operable to control the apparatus to perform at least the following operations: transmitting a plurality of candidate cell configurations to a user equipment, the plurality of candidate cells being potential target cells to which the user equipment is to handover; and in response to receiving at least one indication of an expected handover delay for at least one of the candidate cells, generating a message about the handover for transmission to the user equipment.

[0094] According to various but not necessarily all example embodiments of the present invention, there is provided a computer program comprising computer-readable instructions which, when executed by at least one processor on a device, are operable to control the device to perform at least the following operations: generating hand-off information in response to receiving at least one indication of an expected hand-off delay for a user equipment from a distributed unit of a network node; and causing the hand-off information to be transmitted to the distributed unit of the network node.

[0095] According to various but not necessarily all exemplary embodiments of the present invention, there is provided a non-transitory computer-readable medium including program instructions stored thereon for performing at least the following operations:

[0096] An expected handoff delay to at least one of a plurality of candidate cells is evaluated; an indication of the handoff delay is generated; and the indication is caused to be transmitted to a network node of a serving cell.

[0097] According to various but not necessarily all example embodiments of the present invention, there is provided a non-transitory computer-readable medium including program instructions stored thereon, the program instructions being used to perform at least the following operations: transmitting a plurality of candidate cell configurations to a user equipment, the plurality of candidate cells being potential target cells to which the user equipment is to handover; in response to receiving at least one indication of an expected handover delay for at least one of the candidate cells, generating a message regarding the handover for transmission to the user equipment.

[0098] According to various but not necessarily all example embodiments of the present invention, there is provided a non-transitory computer-readable medium including program instructions stored thereon, the program instructions being used to perform at least the following operations: generating hand-off information in response to at least one indication of an expected hand-off delay of a user equipment received from a distributed unit of a network node; and causing the hand-off information to be transmitted to the distributed unit of the network node.

[0099] The instructions may be used to perform the optional features listed with respect to the above-mentioned method.

[0100] Further particular and preferred aspects are set out in the accompanying independent and dependent claims. Features of the dependent claims may be combined with features of the independent claims as appropriate, and in combinations other than those explicitly set out in the claims.

[0101] A computer program product comprises instructions for causing an apparatus to execute any of the methods described above.

[0102] Where an apparatus feature is described as being operable to provide a function, it will be understood that this includes apparatus features that provide that function or that are adapted or configured to provide that function. BRIEF DESCRIPTION OF THE DRAWINGS

[0103] Some exemplary embodiments will now be described with reference to the accompanying drawings, in which:

[0104] Figure 1 Schematically illustrates different components of mobility delay that may cause handover delay;

[0105] Figure 2 Provided Figure 1 Further details of the different components in;

[0106] Figure 3A An example of an index mapping to a handoff delay table according to an example embodiment is provided;

[0107] Figure 3B An example of an enumerated value mapping table according to an example embodiment is provided;

[0108] Figure 4 A signaling diagram of an example embodiment is provided;

[0109] Figure 5 A signaling diagram of another example embodiment is provided;

[0110] Figure 6 A signaling diagram of another example embodiment is provided showing different options for transmitting signaling at a network node; and

[0111] Figure 7 A communication network according to an example embodiment is schematically illustrated. DETAILED DESCRIPTION

[0112] Before discussing example embodiments in further detail, an overview will first be provided.

[0113] During mobility of the user equipment UE, the delay for handover to different candidate cells may vary depending on, for example, whether the target cell is known or whether an intra-frequency or inter-frequency handover is to be performed. Some UEs are also able to perform some steps of handover faster than other UEs.

[0114] RAN4 defines minimum requirements, which take into account the worst case (longest time) requirements. In scenarios where the UE can outperform these requirements, the expected handover delay is invisible to the network before the UE sends the random access preamble on the target cell. In RACH-less L1 / L2 handover, the network does not know when the UE is ready to be scheduled on the target cell, because unlike RACH-based HO where the random access preamble code transmission is defined as the end point for the handover, the handover has no clear end point.

[0115] Many delay components in such handover (such as Figure 1 The cell switching / handover interruption time is not visible to the network, i.e., when the decision to trigger a cell switch / handover occurs, the network may not know exactly the expected handover interruption time.

[0116] Providing a network node with information about expected handoff delays for candidate cells may enable the network node to improve its handoff decisions and potentially reduce handoff latency.

[0117] Compared with the traditional higher layer handover, L1 / L2 triggered mobility has been introduced to reduce delay, and in the case where the estimated expected handover delay for the candidate cell is long, it may be advantageous for the network node not to trigger the handover to the cell or to trigger the L3 handover. Delay assistance information may also be used in the L3 handover process. In the context of this specification, unless otherwise specified, the term "handover" HO is intended to cover both L1 / L2 cell handover and L3 handover. Therefore, the embodiments described herein may be applied to both L3 handover and L1 / L2 cell handover.

[0118] In summary, various embodiments provide expected handoff information to the network, thereby allowing the network to consider the expected handoff delay estimated by the UE as an input to the cell switching / handoff decision.

[0119] In various example embodiments, the following steps may be used:

[0120] 1) The UE estimates the expected handover delay to the candidate cell and signals it to the network.

[0121] This may be done for all candidate cells, or a subset of candidate cells, or even just a single candidate cell.

[0122] 2) Upon receiving the handover indication, the network decides whether to:

[0123] a) Perform cell handover to the indicated cell. If the expected interruption or handover delay is less than a threshold (delay threshold) and the associated signal strength measurement indicates that the signal strength is above another threshold (signal strength threshold), the network triggers the cell handover. For this purpose, according to the prior art, the UE can report the measured signal strength.

[0124] b) Providing candidate cell reconfiguration to the UE, for example, adding, modifying, deleting candidate cells / measurement configuration.

[0125] c) Request more measurements or trigger measurements from the UE.

[0126] The delay assistance information can also be applied to L3 handoff.

[0127] By using the method of each example embodiment, when making a decision to trigger a cell handover / handover, the network may estimate the expected handover interruption or delay time. Based on the expected handover interruption / delay time, the network may decide not to trigger a cell handover / handover if the interruption time is too high, but to add, modify, delete candidate cells / measurement configurations, or request more measurements.

[0128] With this method, L1 / L2 handover is allowed only when the interruption of data transmission is shorter than a certain threshold and the requirement that the interruption of data transmission caused by L1 / L2 handover is shorter than that of traditional L3 handover can be met.

[0129] The UE may perform one or more of the following:

[0130] 1) A request is received from the network to estimate the expected HO delay for all candidate cells or a subset thereof and transmitted to the network.

[0131] 2) Evaluate the expected HO delay to each or a subset of the candidate cells.

[0132] 3) Reporting an indication of the expected HO delay to the network in one or more of: L1 Measurement Report, L3 Measurement Report or another message.

[0133] A network node can perform one or more of the following operations:

[0134] 1) Receive delay information from UE.

[0135] 2) Compare the delay to a threshold. If the delay value is less than, equal to, or greater than the threshold, the network triggers or does not trigger subsequent actions, such as:

[0136] a) The network modifies the candidate cell list based on the indicated delay value and triggers an RRCReconfiguration message to add / modify / delete candidate cells or modify the measurement configuration.

[0137] b) The network decides not to perform a cell handover on the indicated candidate cell, but waits for the UE to transmit a subsequent measurement or HO delay value.

[0138] c) When the delay exceeds the threshold, the network decides to trigger L3 handoff instead of LTM.

[0139] d) The network forwards the delay information to the entity that performs the HO decision.

[0140] e) When the delay is less than or equal to the threshold, the network triggers a cell handover on the candidate cell.

[0141] In current commercially available 3GPP systems, mobility and handover (HO) are performed using RRC signaling. The reason for this is due to the robustness of RRC signaling, which helps ensure that any loss of HO related signaling is minimized or at least reduced, and therefore also minimizes or reduces HO failures due to signaling failures. Traditional HO is based solely on the use of L3 measurements. The results of these measurements are then sent by the UE to the network using RRC signaling in a measurement report. Based on these L3 measurement results sent in the measurement report, the network can decide to HO the UE from one cell to another. One aspect of existing L3 HO solutions is that they are said to sometimes introduce delays, which can lead to some challenges in certain situations.

[0142] As part of the further NR mobility enhancement work item, 3GPP is specifying mechanisms and procedures for L1 / L2-based inter-cell mobility for mobility delay reduction. LTM or L1 / L2-based mobility is the process by which the UE changes cells based on L1 / L2 triggered commands. The UE is configured with multiple candidate cells using RRC configuration. In LTM, the network receives L1 measurement reports from the UE and performs changes to the UE's serving cell through a cell switching command (e.g., MAC control unit, i.e., MAC CE). MAC CE is used to indicate the previously signaled LTM candidate cells (e.g., cell IDs) and the candidate cell configuration associated with a specific cell switching command.

[0143] LTM is currently applied to UEs in NR connected mode. However, the procedure may also be applied to other states and systems such as 6G in the future. The current design of the LTM procedure based on the latest RAN1 and RAN2 protocols can be summarized in the following steps:

[0144] 1. An LTM capable UE is connected to a cell (serving cell) and is performing L3 measurements on one or more neighboring cells.

[0145] 2. The network provides the UE with an LTM candidate cell configuration including one or more LTM candidate cells through an RRC message.

[0146] 3. The UE performs L1 measurements on the configured candidate cells and reports the results to the network.

[0147] 4. Based on the L1 measurement results reported by the UE, the network may configure the UE to activate one or more TCI states using MAC CE for one or more candidate cells before the cell handover command. Alternatively, the TCI state is activated at the cell handover command.

[0148] 5. The network may select one of the LTM candidate cells from one or more activated LTM candidate cells as the target cell, and use a MAC-CE LTM cell handover command to the UE to request the UE to handover the cell, so that the UE performs an LTM handover to the target cell.

[0149] - The cell switching command includes the following (at least):

[0150] - Index of LTM candidate target configuration to be applied to LTM cell handover

[0151] - Indication (and possible activation, if not done before cell handover in step 4) of the DL and UL (or combined) TCI state ID for the LTM target cell

[0152] -DL and UL BWP ID

[0153] 6. The UE detaches from the source cell and completes LTM handover to the target cell.

[0154] Optional / Additional Steps:

[0155] As an additional or optional step, the network may request the UE to prepare for UL synchronization to the potential LTM target cell. This step may be performed between steps 4 and 5 above.

[0156] In order to prepare one or more LTM candidate cells, the network may initiate random access of PDCCH commands on one or more candidate cells before the network requests the actual LTM cell to be handed over to the target cell.

[0157] On a potential LTM target cell, the UE may send a preamble using RACH to enable the network to acquire the UL timing, timing advance (TA) value of the target cell before the cell handover command.

[0158] However, UL synchronization may also be performed after LTM cell switching, for example, if early TA acquisition is not performed by a PDCCH order before the cell switching command.

[0159] Handover delay

[0160] RAN4 has defined the handover delay and its different options for L3 handover in Section 6 of TS 38.133. In the work item for further NR mobility enhancement (RP-223520), 3GPP is defining L1 / L2 based inter-cell mobility (LTM), which is a lower layer based handover, for which RAN4 is defining the LTM HO delay requirement.

[0161] In existing L3 HO requirements, the handover delay may depend on different factors, such as whether the target cell is known or unknown, and whether the HO is to an intra-frequency or inter-frequency target cell. Some of these conditions are visible to the network, but the network does not know, for example, whether the candidate cell is known to the UE, or the current radio conditions potentially leading to different measurement times.

[0162] Furthermore, the HO delay defined in TS 38.133 is a minimum requirement, and some UEs may be able to complete some steps of the delay faster than others. In the L3 HO scenario, this fact is addressed by having the UE transmit a preamble code on the PRACH (Physical Radio Access Channel) in the target cell once it has handed over to the target cell and is ready to transmit. That is, when the UE sends PRACH on the new cell, the network knows that the UE is ready to transmit / receive on the new cell. The network does not know when exactly this happens before sending the PRACH.

[0163] The values ​​of the parameters related to the handover interruption time are defined for different source-target cell combinations and depend, for example, on

[0164] 1. Is the handover an intra-frequency handover or an inter-frequency handover?

[0165] 2. Whether the target cell is known or unknown,

[0166] 3. Whether the source / target cell is in FR1 or FR2 (frequency range 1 / 2),

[0167] Separate requirements are defined for Inter-RAT (Radio Access Handover), NR DAPS (New Radio Dual Access Protocol Stack) handover, NR conditional handover and NR handover with PSCell (primary-secondary cell).

[0168] The latency of LTM handoff has not yet been defined by RAN4, but components of the latency were initially captured by RAN2 in an operational CR (R2-2213332). Although the details of the latency have not yet been agreed upon, the intent may be that LTM handoff will cause a shorter disruption to data transmission than a traditional L3 handoff.

[0169] Figure 1 The different components that may cause handover delays for LTM or L1 / L2 based inter-cell mobility are schematically shown.

[0170] The HO delay or interruption time for L1 / L2 based inter-cell mobility may be considered as the time from when the UE receives the cell switching command to when the UE performs the first DL / UL reception / transmission on the indicated beam of the target cell.

[0171] TRRC is the processing time for RRCReconfiguration carrying candidate configurations.

[0172] Tprocessing,1 / Tpprocessing,2 are the time used for UE processing before and after the cell handover command, respectively.

[0173] Tmeas is the measured delay (from target appearance to cell handover command).

[0174] Tcmd is the time used to process L1 / L2 commands (HARQ - Hybrid Automatic Repeat Request and Parsing).

[0175] Tsearch is the time required to search for the target cell.

[0176] TΔ is the time used for fine tracking and obtaining complete timing information.

[0177] Tmargin is the time used for SSB or CSI-RS post-processing.

[0178] TIU is the interruption uncertainty of acquiring the first available PRACH opportunity in a new cell.

[0179] TRAR is the time for RAR (Random Access Response) delay.

[0180] Tfirst data is the time after RAR for the UE to perform the first DL / UL reception / transmission on the indicated beam of the target cell.

[0181] In some embodiments there may be other sources of delay, such as FFS if TRS tracking after HO and CSI RS measurement should also be included, ie the time when a high performance beam is used.

[0182] Figure 2 A table is shown which describes in more detail Figure 1 The different components of mobility delay and typical time values ​​are shown in .

[0183] The UE may implement a delay (eg, T delay ) evaluation. In one implementation example, the delay association is done in advance. For example, the UE has been configured (by the UE or the network) with a static lookup table that describes the delay association with Tdelay Or any required sub-component (e.g., MAC CE processing), RF re-tuning, baseband re-tuning, cell search time associated delays and conditions. The association may be based on a UE internal process identifier association or a statically known time. For example, when the processing does not have a dynamic component, or when the processing never exceeds a certain value (and in order to obtain the benefit, the value is still less than the value defined in the minimum requirement). The evaluated delay may depend largely on the UE, but in the evaluation, the UE can use, for example, whether the cell is known (detectable, measured...), the number of cells that the UE is currently measuring, and what the radio conditions are, whether the cell is intra-frequency or inter-frequency or a TRP cell. Once the UE or the network triggers the delay request, the UE evaluates the received command, radio conditions and processing conditions, and extracts corresponding values ​​from the lookup table that match the static (e.g., known processing, known memory interaction, delay) dynamic conditions (e.g., values ​​related to dynamic radio conditions or related to processing, memory) in which the UE is.

[0184] For example, the UE has a lookup table that includes an association of each possible MAC CE value with an integer value [{MAC CE cell switch 1, delay 1ms}, {MAC CE cell switch 2, delay 2ms}, ..]. Once MAC CE cell switch 2 is received and once identified, the UE reads the lookup table delay value 2ms and adds it to the total (Tdelay) delay calculation. This delay may be less than or equal to the minimum requirement, and therefore, the indicated total interruption delay may be less than the minimum requirement. Similarly, the different processes associated with the interruption delay and defined by the minimum requirement may be decomposed into values ​​from which the UE collects and sums the total delay value or the decomposed delay values.

[0185] In summary, RAN4’s discussion reached the following consensus on LTM cell handover delay:

[0186] RACH-based cell switching delay T for Pcell / PScell delay Can have the following components:

[0187] T delay =T cmd +Tprocessing / T LTM-processing +T search +T Δ +T margin +T uncertainity / T IU ,in

[0188] T uncertainity / T IU is the uncertainty in obtaining the first available PRACH opportunity in a new cell.

[0189] Note: “ / ” here means “or”.

[0190] The RACH-free cell switching delay for Pcell / PScell ​​may have the following components:

[0191] T delay =T cmd +T processing,2 / T LTM-processing +T search +T Δ +T margin +T uncertainity / T IU ,

[0192] Note: “ / ” here means “or”.

[0193] T cmd Equal to T HARQ +3ms, where T HARQ It is the timing between the cell handover command and the acknowledgement specified in TS 38.213.

[0194] For all except T cmd RAN4#107 has not yet agreed on the values ​​for each parameter in the agreed formula for any other parameters other than , however, it is expected that these values ​​may differ in a similar manner as in the L3 handover requirements, or there may be more variation based on at least the following:

[0195] 1. Frequency range of target cell

[0196] 2. Is the target cell a neighboring cell or the current serving cell?

[0197] 3. Is the target cell an intra-frequency cell or an inter-frequency cell?

[0198] 4. How much of the candidate cell configuration processing has been completed before the cell switching command

[0199] 5. Is TCI state activation done before or at the cell handover command? 6. Is RACH done before or after cell handover?

[0200] The end point of the LTM handover has not yet been agreed upon by RAN4. In a RACH based cell handover, similar to L3 handover, the UE will send PRACH on the target cell at the end of the interruption and it can be assumed that this is the end point of the handover. However, in the no-RACH case, it is unclear when the handover is complete, so the network may not know when it can expect the UE to be ready to be scheduled. RAN4 is still discussing what is defined as the end point for the no-RACH case.

[0201] As described above, the delay for handover to different candidate cells may be different, depending on, for example, whether the target cell is known or whether there is a problem with the intra-frequency or inter-frequency handover. Some UEs may also be able to perform some steps of handover faster than other UEs, so each UE may have different processing capabilities. In addition, radio conditions may affect the delay. Therefore, when estimating the handover delay for the candidate cell, the UE may consider at least some of the following characteristics: whether the candidate cell is known (detected by the UE, measured by the UE), how many candidate cells the UE is currently measuring, radio conditions, whether the handover to the candidate cell is an intra-frequency handover or an inter-frequency handover. For example, depending on the hardware and software configuration and tolerances in production and testing, different UEs may have different handover delays under the same or substantially similar conditions. Therefore, according to the embodiments described herein, each UE may measure the handover delay under different conditions and store them for reporting. RAN4 defines the minimum requirements, which means that the delay takes into account the worst case (longest delay) requirements. Therefore, in case the UE may perform better than required, the expected handoff delay may not be visible to the network until the UE actually sends the random access preamble on the target cell.

[0202] Furthermore, in RACH-less LTM handover, the network does not know when the UE is ready to be scheduled on the target cell, since there is no clear end point for the handover similar to RACH-based HO where the random access preamble transmission is defined as the end point for the handover. The UE only knows and is visible to it the time it takes to perform a cell handover (or handover) to the target cell, depending on the scenario.

[0203] In order to address the issues outlined above and to help achieve visibility of expected handover / cell switching delays to the network, especially in the case of RACH-free handover (but not excluding RACH-based cases), the following is proposed:

[0204] The UE estimates the expected handover delay to the candidate cells and signals it to the network.

[0205] Evaluation and indication of handoff delays can be performed for:

[0206] -All candidate units

[0207] -Candidate cells that the UE has measured (L1 and / or L3 measurements)

[0208] - For a subset of candidate cells based on network request or configuration or some other criteria

[0209] This instruction can be completed by:

[0210] -L1 measurement report

[0211] -L3 measurement report

[0212] - Separate existing or new message (e.g. UE assistance information)

[0213] - Control information, such as MAC CE or UCI

[0214] The indication may be a one-time indication or a dynamic indication sent under specific conditions.

[0215] After receiving the instruction, the network

[0216] - Treat the indicated handoff delay as an input to the handoff decision process

[0217] ° If the handover is L1 / L2 triggered, the DU (distributed unit of the network node gNB) takes the information into account by reading indications (L1 measurements, MAC CE, UCI) or receiving a message from the CU (central unit of the gNB) indicating the UE delay.

[0218] -Then, the network entity that performs the handover decision will

[0219] ° Decide whether to perform a cell handover to the indicated cell

[0220] If the outage delay is less than the delay threshold and the associated signal strength measurement is above the signal strength threshold, the network triggers a cell handover.

[0221] The network may transmit an indication to the target cell indicating a handover delay. This may be done by the decision entity transmitting the signal or by a central entity (e.g., CU). The target entity may then expect the UE to be handed over to a specific cell within the specified delay.

[0222] ° Decide whether to perform candidate cell reconfiguration for the UE

[0223] For example, add, modify, delete candidate units

[0224] For example, add, modify, delete measurement configurations

[0225] ° The decision is to request more measurements from the UE or to trigger measurements.

[0226] In one embodiment, the UE performs an evaluation on certain candidate cells, for example, all candidate cells or a subset of candidate cells. The UE then transmits the handover delay indication for a first subset of these candidate cells that meet at least one predetermined condition. The at least one predetermined condition may include that the handover delay is less than a threshold value, such as a predefined minimum delay. The UE may exclude from the handover delay indication a second subset of these candidate cells that do not meet the predetermined condition that the handover delay is less than the threshold value. The first subset may include multiple indicated candidate cells. As described above, the network entity may then select a target cell for handover from the indicated candidate cells, for example, a candidate cell associated with a minimum handover delay, or a candidate cell associated with a minimum handover delay that also provides a signal strength above a corresponding signal strength threshold.

[0227] In addition to performing evaluation on certain candidate cells, the UE may also perform evaluation on detected cells that are not candidate cells. This may be the case when a cell has been recently detected by the UE but has not yet been indicated as a candidate cell by the network. The UE may transmit a handover delay indication for the detected cell and for one or more candidate cells.

[0228] In the following, LTM handoff is used as an example, but the proposed solution can also be used for other handoff types.

[0229] In various embodiments, handoff and cell handoff may be used interchangeably, since the delay assistance information may also be applicable to L3 handoff.

[0230] In various embodiments, using LTM as the baseline mobility scenario, the following steps may be used:

[0231] 1. In some embodiments: upon / after signaling the LTM candidate cell configuration to the UE, the network requests the UE to estimate the expected handoff delay for all or a subset of the candidate cells and transmit it to the network.

[0232] - The network may send the request in a LTM candidate cell configuration, a cell handover command, or another existing or new message.

[0233] - In an alternative, the network may send the request under certain conditions, for example based on L1 or L3 measurements reported by the UE.

[0234] - The request may consider all or a subset of the candidate cells.

[0235] 2. The UE evaluates the expected HO / LTM cell handover delay to each or a subset of the candidate cells.

[0236] - The evaluation may be performed based on a network request, as a default at a predetermined point in the cell handover procedure, or triggered by certain conditions, such as measurement status (L1 / L3 measurements performed or not performed), measurement results to be reported, etc.

[0237] - The evaluation may be performed before a cell handover command to cover one or more candidate cells, or may be performed based on a cell handover command only for the target cell.

[0238] - The evaluation may be performed on a subset of cells indicated by the network (ie down-selected) or selected by the UE (based on RRC configuration).

[0239] 3. The UE reports the expected HO delay to the network in an L1 measurement report, L3 measurement report or another message:

[0240] a. For each candidate unit

[0241] b. For each candidate cell on which the UE has performed measurements (L1 measurements, L3 measurements)

[0242] c. Based on the network request in step 1

[0243] d. For the target cell in the cell switching command

[0244] e. Further conditions (based on RSRP, based on estimated HO delay, etc.)

[0245] The UE may report the expected HO delay as:

[0246] - Exact value in ms (with appropriate granularity: e.g., 1, 2, 3, 10, 20, 50, 100, 0).

[0247] - A value out of a predefined selection (e.g., less than X milliseconds, less than X+Y milliseconds, etc.)

[0248] - For example, the index of a value or range of values ​​in a table

[0249] -Offset value (e.g. baseline value 20ms, UE indicates + / - x milliseconds delay from this offset)

[0250] - Binary value (eg, inside or outside the range of allowed handoff delays).

[0251] Figure 3A and 3B A table indicating examples of indices that map to delay values ​​in a mapping table is shown. These values ​​may be specified in RRC signaling, or they may be hard-coded system specifications.

[0252] The delay value may be associated with a candidate ID or PCI, or with a value derived from one of the above, or with another cell identifier. For example, delay may be: (candidateId, delay). Similarly, the association may be based on a sorted list, where the delay value corresponds to a cellId in another list.

[0253] Figures 4 to 6 Signaling diagrams are shown. In these signaling diagrams, different possible options for various embodiments are shown. In one case, the UE performs an expected HO delay evaluation based on the candidate cell configuration for all or a subset of the candidate cells. The evaluation may be performed based on a network request or as a default. The steps related to various embodiments are explained below.

[0254] Figure 4 A signaling diagram showing signals sent between a UE, a source or serving network node, and a target network node during an LTM procedure.

[0255] Initially there is a preparation phase, where the UE sends L3 measurements to the serving node. In step 2, the serving node prepares a set of candidate cell configurations that it sends to the UE. In the LTM candidate cell configuration, the network may request the UE to perform an expected HO delay assessment on all or a subset of the candidate cells. This may also / alternatively be done in a separate message, which is not shown in the signaling diagram.

[0256] The UE then performs the evaluation based on the request, or if there is no request, the UE may perform the evaluation by default.

[0257] The signalling diagram then shows a set of options steps 3, 4, 5, 6 of different ways in which the UE may report the result of the HO delay evaluation.

[0258] In these steps, the UE indicates the result of the expected HO delay evaluation for all or a subset of the candidate cells in the following way:

[0259] Option 1 (Step 3): RRC Reconfiguration Complete Message

[0260] Option 2 (Step 4): UE Assistance Information

[0261] Option 3 (Step 5): L1 Measurement Report

[0262] Option 4 (Step 6): L3 Measurement Report

[0263] Option 5 (not shown): MAC CE Control Element

[0264] Option 6 (not shown): Uplink Control Information

[0265] In this signaling diagram, random access is performed after cell switching, but if configured, it can also be performed before the cell switching command based on the PDCCH (Physical Downlink Control Channel) order.

[0266] Figure 5 Another possible option of an example embodiment is shown. In this scenario, the UE performs an expected HO delay evaluation based on the cell handover command only for the indicated target LTM candidate cell. This evaluation can be done based on a network request or as a default. This allows the network to know when to schedule a target cell and may be useful in situations where the network selects a target cell based only on signal strength measurements and the delay varies significantly between cells.

[0267] The steps performed during LTM execution are described below.

[0268] The UE transmits a L1 / L3 measurement report and makes a HO decision at step 4. At step 5, a LTM cell handover command is sent from the network, within which the network may request the UE to perform an expected HO delay assessment on all or a subset of the candidate cells.

[0269] The UE performs the evaluation based on the request, or if there is no request, the UE may perform the evaluation by default upon receiving a cell handover command.

[0270] In step 6: the UE indicates the expected HO delay evaluation result for the target cell and signals it to the network. The handover is then performed and the different time delays for the steps taken during the handover are shown.

[0271] Apart from Figure 4 and Figure 5 In addition to the examples shown, the UE may also evaluate and / or indicate to the network the expected HO delay based on other triggers, such as:

[0272] -When one or more cells are detected

[0273] - When L1 or L3 measurements are completed to report on one or more cells

[0274] - Based on measurement results, such as when RSRP exceeds a threshold or any other existing or new event triggers

[0275] Figure 4The options given in can be used to report the evaluation results.

[0276] Figure 6 An example of network behavior when a HO delay indication is received is shown.

[0277] The network receives the delay information from the UE in the different possible formats mentioned above.

[0278] Initially, the UE performs HO delay evaluation of candidate cells.

[0279] The UE then transmits the HO delay evaluation result (as described above) to the network.

[0280] The network then processes the delay results for each cell

[0281] - For example, the network receives a delay value from the UE and compares the delay with a threshold. Depending on the network entity configuration, if the delay value is less than or greater than (equal to) the threshold, the network triggers or does not trigger subsequent actions.

[0282] Option 1: The network modifies the candidate cell list (candidateId) based on the indicated delay value. When processing the HO delay indication, the network triggers an RRCReconfiguration message to add / modify / delete candidate cells or modify the measurement configuration.

[0283] Option 2: The network decides not to perform a cell handover on a candidate cell indicated by the UE and the network has evaluated that (candidateId, delay) exceeds a threshold. The network may wait for the UE to transmit a subsequent measurement or HO delay value and re-evaluate the decision upon receiving a new delay value.

[0284] Option 3: When delay > threshold, the network decides to trigger L3 handoff instead of LTM. The threshold can be, for example, threshold = 1 / 2 L3 handoff delay, or when the delay is equal to or exceeds the L3 handoff delay.

[0285] Option 4: (not exclusive of others). The network entity receiving the HO message (e.g., via RRC) forwards the delay information to the entity performing the HO decision. This may be done when the receiving entity first evaluates whether the delay value is greater than a threshold. Alternatively, the forwarding may be blind and the decision entity performs the evaluation.

[0286] When the delay <= threshold, the network may trigger a cell handover on the candidate ID. This may also trigger an indication of a target cell carrying the delay as an indication. The target cell may then start a waiting process and wait until a cell handover is triggered and the UE has appeared on the target cell.

[0287] According to different embodiments, the network may use expected delay time in its target cell decision. In some cases where low latency is important, it may determine which candidate cells meet the signal strength requirement from the L1 and / or L3 measurements, and may then select the candidate cell with the lowest expected delay time that meets the requirement. Alternatively, where signal quality is important, it may select a set of potential candidate cells with delay values ​​less than a threshold (e.g., a certain minimum delay), and may then select the candidate cell with the highest signal measurement. Alternatively, both factors may be inputs to the decision, where each factor is weighted according to the circumstances, and a threshold is used to remove candidate cells (with too low signal measurements or too high delays) from the selection process.

[0288] Figure 7 A UE 10, a source network node 20 and a candidate network node 22 are shown according to one embodiment. The network node 20 supports providing radio coverage in a cell 30 and may include a distributed unit of a gNB in ​​communication with a central unit 40. Alternatively, the network node 20 may include a base station or a femto network node ...

[0289] The UE 10 comprises a monitoring circuit 18 for monitoring the power and / or quality of links between the UE 10 and neighbouring candidate cells 32 supported by other network nodes 22. The UE 10 also comprises a data memory 12 for storing candidate cell configuration information received from the network node 20, a delay estimation circuit 14 for estimating an expected handover delay for a particular candidate cell, and a mobility control circuit 17 for controlling handovers between cells.

[0290] Transmit and receive circuitry 16 is also provided for transmitting and receiving messages comprising information and data to the network node 20. These messages may include L1 / L3 measurement reports generated by the monitoring circuitry 18 indicating the quality and / or power of respective links to one or more neighbouring cells, and they may include one or more indications of expected handover delays estimated by the delay estimation circuitry 14.

[0291] The network node 20 comprises a data memory 22, a transmitting and receiving circuit 26 for transmitting and receiving messages with the user equipment 10 and in some cases also with the central unit 40 and the target network node. A determining circuit 24 is provided for determining neighboring cells for which locally triggered mobility may be suitable and for preparing these candidate cells. A message generating circuit 25 generates a message comprising configuration information for a plurality of candidate cells identified by the circuit 24.

[0292] The transmit and receive circuitry 26 transmits these messages to the UE. The transmit and receive circuitry 26 also receives from the UE 10 measurements indicating the signal strength of the different candidate cells and an indication of the handover delay.

[0293] The network includes mobility control circuitry 24, 44 which can determine whether to perform a handover based on the received signal. In some embodiments, this is circuitry 24 within the network node 20, while in other embodiments, such as where the network node 20 is a distributed unit of a gNB, it can be circuitry 44 within the central unit 40.

[0294] The circuit may determine that certain cells with delays above a threshold should be down-selected, or it may decide that the delays are generally high and / or the signal is low and not perform a handoff, or perform more measurements or perform a L3 handoff.

[0295] In case the network decides to perform a handover, the network may use a target cell evaluation circuit 25, 45 to determine a target cell from the candidate cells based on L1 / L3 measurements and delays. Again, this may be a circuit 25 within the network node 20, or in the case where the network node 20 is a distributed unit of a gNB, for example, then it may be a circuit 45 within the central unit 40. The evaluation circuit 25, 45 may be configured to consider only candidate cells with measurements above a threshold and delays below a threshold, and may then select one of them as the target cell based on the shortest delay, the strongest signal, or a combination of both.

[0296] Where the network node has determined that a cell handover is appropriate and has selected a target cell, it may generate a cell handover command and transmit it together with an indication of the target cell to the UE 10. It may also transmit the target cell indication to the target cell 22.

[0297] Those skilled in the art will readily appreciate that the steps of the various methods described above can be performed by programming computers.Herein, some embodiments are also intended to cover program storage devices such as digital data storage media, which are machine or computer readable and machine executable or computer executable programs of encoded instructions, wherein the instructions perform some or all of the steps of the above methods.The program storage device can be, for example, a digital memory, a magnetic storage medium such as a disk and a tape, a hard drive, or an optically readable digital data storage medium.Each embodiment is also intended to cover a computer programmed to perform each of the steps of the above methods.The term "non-transitory" used herein is a restriction on the medium itself (i.e., tangible, rather than a signal), rather than a restriction on data storage persistence (e.g., RAM and ROM).

[0298] As used in this disclosure, the term "circuitry" may refer to one or more or all of the following:

[0299] (a) hardware-only circuit implementations (such as implementations in analog and / or digital circuits only); and

[0300] (b) a combination of hardware circuitry and software such as (where applicable):

[0301] (i) a combination of analog and / or digital hardware circuitry and software / firmware, and

[0302] (ii) any portion of a hardware processor and software (including a digital signal processor), software and memory that work together to enable a device such as a mobile phone or server to perform

[0303] various functions); and

[0304] (c) Hardware circuits and / or processors, such as a microprocessor or portion of a microprocessor, that require software (eg, firmware) to operate, but where the software may not be present, the software may not be required to operate.

[0305] This definition of circuitry applies to all uses of the term in this disclosure, including in any claims. As a further example, as used in this disclosure, the term circuitry also encompasses implementations of only a hardware circuit or processor (or multiple processors) or a portion of a hardware circuit or processor and its (or their) accompanying software and / or firmware. The term circuitry also encompasses, for example and if applicable to the claimed element, a baseband integrated circuit or processor integrated circuit for a mobile device or a similar integrated circuit in a server, cellular network equipment, or other computing or network equipment.

[0306] Although embodiments of the present invention have been described in the preceding paragraphs with reference to various embodiments, it should be appreciated that modifications to the embodiments given can be made without departing from the scope of the invention as claimed.

[0307] Features described in the preceding description may be used in combinations other than the combinations explicitly described.

[0308] Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not.

[0309] Although features have been described with reference to certain embodiments, those features may also be present in other embodiments whether described or not.

[0310] While efforts have been made in the foregoing description to call attention to those features of the present invention which are regarded as particularly important, it should be understood that the applicants claim protection for any patentable feature or combination of features mentioned above and / or shown in the accompanying drawings, whether or not particular emphasis has been placed thereon.

Claims

1. A device for communication, comprising: at least one processor; as well as at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus to at least perform: evaluating an expected handoff delay to at least one of a plurality of candidate cells; generating an indication of the handoff delay; and The indication is caused to be transmitted to a network node of a serving cell.

2. The device according to claim 1, wherein: causing the apparatus to perform the evaluating step in response to at least one of: Receive requests from network nodes; Predetermined points during cell switching; Signal strength measurement status; Detection of one or more cells.

3. The device according to claim 1, wherein: causing the apparatus to perform the evaluating step in response to receiving a request from the network node, the request being received during at least one of: a message indicating configuration of the candidate cell; A message indicating that a cell handover is to be performed; or Separate dedicated request.

4. A device according to any one of the preceding claims, wherein: The apparatus is caused to perform the evaluating step in response to receiving a request from the network, the request indicating that the evaluation is to be performed for the at least one candidate cell of the plurality of candidate cells.

5. An apparatus according to any preceding claim, wherein: The apparatus is caused to perform the evaluation on a subset of the plurality of candidate cells.

6. An apparatus according to any preceding claim, wherein: Make the device: performing said evaluating for a plurality of said plurality of candidate cells, wherein said indication comprises a handoff delay to each of said plurality of said plurality of said candidate cells; as well as In response to the transmitted indication, a handoff command is received from the network node, which triggers a handoff to a target cell of the plurality of the plurality of the candidate cells, wherein the target cell is associated with a minimum handoff delay included in the indication.

7. An apparatus according to any preceding claim, wherein: causing the apparatus to transmit the handoff delay indication within at least one of: UE assistance information message; L1 measurement report; L3 measurement report; A message indicating that configuration of the candidate cell is completed; . Response to cell handover command; MAC CE control element; or Uplink control information.

8. The device according to claim 6 or 7, wherein: causing the apparatus to generate the handoff delay indication for at least one of: Each candidate cell; each candidate cell for which the apparatus has performed measurements; candidate cells indicated in a request received from the network node; the target cell indicated in the received cell handover command; a candidate cell that satisfies at least one predetermined condition, wherein the predetermined condition includes a handover delay condition or a measurement condition; or At least one candidate cell and a detected cell that is not a candidate cell.

9. An apparatus according to any preceding claim, wherein: The apparatus is caused to transmit the handoff delay indication for a candidate cell that satisfies at least one predetermined condition, the at least one predetermined condition comprising the handoff delay being less than a threshold.

10. An apparatus according to any preceding claim, wherein: The handover delay indication includes one of the following: Time delay value; an indication that the delay is within one of a plurality of predetermined value ranges; an indication that the delay meets or does not meet a threshold; The index of the indicated value; Offset value.

11. An apparatus according to any preceding claim, wherein: The apparatus comprises user equipment.

12. An apparatus for communication, comprising at least one processor; and at least one memory storing instructions, the instructions, when executed by the at least one processor, causing the apparatus to at least perform: Transmitting multiple candidate cell configurations to the user equipment, where the multiple candidate cells are potential target cells to be handed over by the user equipment; generating a message regarding the handoff in response to receiving at least one indication of an expected handoff delay for at least one of the candidate cells; as well as The message is caused to be transmitted to the user equipment.

13. The device according to claim 12, wherein: The message includes at least one of the following: Modification of the configuration of the plurality of candidate cells; An instruction for the user equipment to perform a layer 3 L3 handover; Cell switching indication; an instruction for the user equipment to perform further measurements, or The indication of handover is not executed.

14. An apparatus according to claim 12 or 13, causing the apparatus to perform: comparing the value of the at least one expected handoff delay with a threshold; and generating the message in response to the comparison.

15. The apparatus according to claims 13 and 14, causing the apparatus to execute: In response to receiving at least one measurement report indicating signal strengths of at least some of the plurality of candidate cells and receiving the evaluation of the handoff delays of at least some of the plurality of candidate cells, Selecting a target cell from the plurality of candidate cells according to the handover delay and the measurement report; and The cell switching command is generated as the message, and the cell switching command indicates one of the candidate cells as a target cell for handover.

16. The device according to claim 12 or 13, wherein: causing the apparatus, in response to receiving the at least one indication of the expected handoff delay, to: forward the indication to a central unit network node; as well as Generating the message is performed in response to receiving handoff information from the central unit network node.

17. The apparatus according to any one of claims 12 to 16, causing the apparatus to perform: generating a message requesting the user equipment to perform an evaluation of a handover delay; and The message is caused to be transmitted to the user equipment.

18. An apparatus for communication, comprising at least one processor; and at least one memory storing instructions, the instructions, when executed by the at least one processor, causing the apparatus to at least perform: generating handoff information in response to receiving at least one indication of an expected handoff delay for a user equipment from a distributed element network node; and The handoff information is transmitted to a distributed unit network node.

19. The apparatus according to claim 18, causing the apparatus to execute: comparing the value of the at least one expected handoff delay to a threshold; and generating the handoff information in response to the comparing.

20. The device according to claim 18 or 19, wherein: In response to receiving at least one measurement report indicating signal strengths of at least some of the plurality of candidate cells and receiving the evaluation of the handoff delay for at least a portion of the plurality of candidate cells, causing the apparatus to: Selecting a target cell from the plurality of candidate cells according to the handover delay and the measurement report; and An indication of the selected target cell is transmitted to the distributed unit as the handoff information.

21. A method for communication, comprising: evaluating an expected handoff delay to at least one of a plurality of candidate cells; generating an indication of the handoff delay; as well as The indication is caused to be transmitted to a network node of a serving cell.

22. A method for communication, comprising: Transmitting multiple candidate cell configurations to the user equipment, where the multiple candidate cells are potential target cells to be handed over by the user equipment; generating a message regarding the handoff in response to receiving at least one indication of an expected handoff delay for at least one of the candidate cells; as well as The message is caused to be transmitted to the user equipment.

23. A method for communication, comprising: generating handoff information in response to receiving at least one indication of an expected handoff delay of a user equipment from a distributed element network node; as well as The handoff information is transmitted to a distributed unit network node.

24. A computer program product comprising instructions for causing an apparatus to perform at least the method according to any one of claims 21-23.

25. A computer-readable medium comprising instructions for causing an apparatus to perform at least the method according to any one of claims 21-23.

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