Method and apparatus for UE assisted data forwarding in conditional handover

Abstract

The invention relates to a method and apparatus for UE assisted data forwarding in conditional handover. An embodiment of the present disclosure provides a method for use by a communication device wherein the method comprises the steps of: receiving (S20) a handover command from one of a plurality of network cells providing a communication service for the communication device, creating (S21) measurement data upon receiving the handover command, after an execution condition for executing a handover to another one of the plurality of network cells is satisfied, the measurement data and the end of the measurement are logged (S22), and the logged measurement data are transmitted (S23) to another one of the plurality of network cells.

Description

[0001] This application is a divisional application of a Chinese patent application with an application date of July 30, 2019, an application number of 201980098952.2, and an invention title of "UE-Assisted Data Forwarding in Conditional Handover". Technical Field

[0002] At least some example embodiments relate to mobility in cellular and mobile communication systems such as Long-Term Evolution (LTE) or New Radio (NR). Specifically, at least some example embodiments relate to User Equipment (UE)-assisted data forwarding in so-called "Conditional Handover" (CHO), which aims to improve mobility robustness.

[0003] List of Acronyms / Abbreviations

[0004] 3GPP Third Generation Partnership Project

[0005] ARQ Automatic Repeat reQuest

[0006] BS Base Station

[0007] CHO Conditional Handover

[0008] CQI Channel Quality Indicator

[0009] eMBB Enhanced Mobile Broadband

[0010] eNB evolved Node B

[0011] gNB next-generation Node B

[0012] HARQ Hybrid Automatic Repeat reQuest

[0013] HO Handover

[0014] ID Identifier

[0015] LTE Long-Term Evolution

[0016] NR New Radio

[0017] OFDM Orthogonal Frequency Division Multiplexing

[0018] PCI Physical Cell ID

[0019] PRACH Physical Random Access Channel

[0020] RACH Random Access Channel

[0021] RAN Radio Access Network

[0022] RRC Radio Resource Control

[0023] RRM Radio Resource Management

[0024] SI International System of Units

[0025] UE User Equipment

[0026] Xn Interface between gNB and gNB as defined in 3GPP TS 38.423 Background Art

[0027] In a situation where a mobile terminal such as a User Equipment (UE) (also hereinafter referred to as a "communication device") is assigned to a serving node (or "cell") (which is currently serving and / or associated with the mobile terminal) within a (cellular) communication network, a handover (HO) will be performed to another node (or "cell"), which will then serve the terminal in case of handover conditions. Common handover conditions occur when the mobile terminal is moving across the geographical coverage of the corresponding nodes within the cellular communication network. However, the same geographical coverage can be served by multiple nodes or cells and also in such a situation, handover conditions can occur. For example, a (single) node can define different cells (e.g., distinguishable by different physical resources associated therewith) and handover can thus occur at the same node but related to a handover from cell to cell. Various handover procedures are known and among those, one handover procedure is Conditional Handover (CHO).

[0028] Conditional HO (CHO):

[0029] The CHO process is similar to traditional handover. The message sequence diagram of the (common and known) CHO process is shown in Figure 1 in.

[0030] The entities involved in the signaling are illustrated horizontally as the terminal or User Equipment (UE), the source gNB (currently serving / associated with the UE) and the target gNB to which the handover or conditional handover CHO (is to) be performed (subsequently serving / associated with the UE). The source and target gNB communicate via the interface Xn (not so illustrated). The messages exchanged between such entities are illustrated as arrows and the actions / processing of the messages at the entities are illustrated as boxes / circles. The time sequence of the messages is "top - down" in this figure.

[0031] The first step (represented by S1 to S8 in "Phase 1") is generally the same as a traditional handover. The source gNB performs measurement control on the UE (S1). The configured event (S2) triggers the UE to send a measurement report to the serving gNB (S3). Based on this report, the source gNB generally prepares the target gNB for handover (handover request from the source gNB to the target gNB in S4) and receives a handover request confirmation (from the target gNB in S5) and then sends a handover command to the UE (S6). This command generally includes a list of cells or resources prepared for the handover. The target gNB in step S7 prepares the corresponding reservation of the resources (cells) confirmed in S5, and the UE confirms the HO command to the source gNB in step S8.

[0032] For traditional HO, the UE will immediately access the target cell / target gNB to complete the handover. Instead, for CHO, the UE will only access the target gNB once the additional CHO execution conditions expire. This condition is generally configured by the source gNB, for example, during the HO command in S6.

[0033] The advantage of CHO is that the HO command (in S6) can be sent very early in the so-called preparation phase (Phase 1) when the UE is still safe in the source cell, without the risk of access in the target cell and the stability of its radio link.

[0034] The HO command is generated by the target cell and included in the "handover request confirmation" before being forwarded to the UE by the source via radio resource control (RRC) signaling.

[0035] The "actual" HO is performed in the CHO execution phase (Phase 2, see steps S9 to S13). After the CHO execution condition is met, i.e., the CHO execution event occurs, see S9, the UE performs synchronization and random access with / towards the target gNB in step S10. Subsequently, a handover complete message is sent from the UE to the target gNB in S11, and the target gNB confirms this to the source gNB in a handover complete confirmation message in step S12. In the subsequent step / phase S13, the UE and the source gNB will adapt the scope where the "old" (i.e., previous) preparation or settings are no longer valid. In this scope, after (HO or) CHO completion, the target gNB will become the new source gNB.

[0036] In CHO, since there can be a significant time delay between HO preparation and actual HO execution, the situation at the target cell may potentially change during this time.

[0037] In addition, as Figure 1As shown, after receiving the handover command, the UE will not immediately perform the handover to the target cell but instead wait until the CHO execution condition is satisfied, which may take some time. Therefore, the source cell does not know the moment when the UE detaches from the source cell and performs a random access channel (RACH) access to the target cell, which affects the data forwarding from the source to the target cell.

[0038] In the baseline handover scheme of NR Rel.15, the source cell starts the forwarding of UE packets after sending the handover command to the UE.

[0039] This is useful because the UE is expected to access the target cell immediately after receiving the handover command.

[0040] However, in CHO, the source cell does not know the moment when the UE detaches from the source cell and thus it does not have any information for triggering data forwarding in a timely manner (i.e., when the UE has detached or recently detached from the source cell).

[0041] In the prior art, several methods have been proposed to handle this problem.

[0042] Method 1: Similar to the baseline handover, the source cell can start data forwarding after sending the handover command to the UE.

[0043] This can cause unnecessary forwarding of many UE data packets (consuming resources through the Xn interface) when the UE is still sending and receiving from the source cell. This impact is even higher when preparing multiple targets for CHO.

[0044] Method 2: The source cell starts data forwarding when it receives an indication from the target cell that the UE has completed RACH access.

[0045] This scheme does not cause unnecessary forwarding of data packets. However, it can cause service interruption in the case where the user packets are already in the target BS before the UE connects to the target cell.

[0046] This is especially relevant to contention-based random access, where the target BS can send an indication only when it receives the third message in the random access procedure from the UE (also called "Msg3").

[0047] However, the source cell can roughly estimate the moment of CHO execution from the moment it receives the indication from the target cell.

[0048] However, this estimate suffers from errors caused by RACH retransmissions, guessing the periodicity of the physical random access channel (PRACH) timing of the target cell without the source cell knowing, UE and target cell processing delays, delays through the Xn interface, etc.

[0049] Method 3: The source cell can estimate when the UE has detached based on the lack of, for example, a Channel Quality Indicator (CQI) or Hybrid Automatic Repeat reQuest / Automatic Repeat reQuest (HARQ / ARQ) feedback report. To make this process reliable, the source cell should wait and check for the lack of CQI, HARQ / ARQ feedback reports missing for some time, since the UE has detached and not due to a temporary and instantaneous change in the channel (“false alarm”), which again creates uncertainty about the CHO execution moment.

[0050] Method 4: The UE can attempt to inform the source cell by means of an RRC signaling (also known as “bye” message) when the CHO execution condition is met.

[0051] This method is not preferred in 3GPP discussions because the indication sent by the UE may not be received at the moment when the UE performs the access to the target cell.

[0052] Method 5: During CHO completion, the source cell obtains an indication from the target cell that the UE has accessed the target cell (e.g., HO completion). Based on this, the source cell can roughly determine when the execution condition has been triggered and thus when the forwarding should have occurred.

[0053] However, similar to Method 2, this information is very rough because the time between the triggering of the execution condition and the receipt of the indication from the target cell is unknown and can be significant (involving the RACH procedure and Xn signaling). SUMMARY OF THE INVENTION

[0054] The aim of at least some of the example embodiments in the example embodiments is to improve the prior art.

[0055] This aim is achieved by a method, an apparatus, and a non-transitory storage medium as specified in the appended claims.

[0056] Additionally, a computer program product is provided, including computer-executable code that, when executed by a processor, performs the method according to any one of the method aspects.

[0057] According to at least some example embodiments, at least one of the following advantages is achieved:

[0058] ● The source cell obtains reliable and accurate statistics from the handover UE, which the source cell can utilize for a more timely triggering of data forwarding, which results in a better trade-off between interruptions by late forwarding and unnecessary forwarding by early forwarding.

[0059] ● The proposed solution also allows for considering different mobility scenarios for different cell boundaries, e.g., HO from source cell A to target cell B (e.g., low-speed mobility) or from source cell A to target cell C (e.g., high-speed mobility). Thus, it enables the grouping of UEs depending on their speed of movement.

[0060] ● The source cell does not have to wait for or rely on unreliable information (e.g., missing CQI or HARQ acknowledgments), which is merely used and considered as an alternative for customized CHO signaling and the lack of which can also have other reasons than HO to another cell (e.g., very deep fading events).

[0061] ● The statistical nature of the logged measurement data allows for making decisions on different reliability levels (e.g., based on percentiles) to accommodate the needs of different data services that respectively allow for more conservative or more liberal strategies.

[0062] ● Ultimately, due to the increased service continuity, this supports and improves the quality of the user experience.

[0063] Additional advantages become apparent from the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Additional details, features, objectives, and advantages become apparent from the following detailed description of example embodiments of at least some aspects to be understood in conjunction with the drawings, wherein:

[0065] Figure 1 A signaling diagram is shown that illustrates the steps of a CHO preparation and execution process.

[0066] Figure 2 A flowchart is shown that illustrates an example method according to at least some embodiments.

[0067] Figure 3 A flowchart is shown that illustrates an example method according to at least some embodiments.

[0068] Figure 4 A signaling diagram is shown that illustrates the steps of an example of a CHO preparation process and a CHO execution process with collection, logging, and exchange of CHO-related measurement data according to at least some embodiments.

[0069] Figure 5 A schematic block diagram is shown that illustrates the configuration of a control unit in which at least some example embodiments can be implemented. DETAILED DESCRIPTION

[0070] In the following, some aspects are illustrated by at least some embodiments described in detail with reference to the accompanying drawings. Unless otherwise described, the features of the example embodiments may be freely combined with each other. However, it should be clearly understood that the description of certain example embodiments / aspects is given by way of example only and is not intended to be construed as limiting the present application to the disclosed details.

[0071] It should be understood that any of the modifications mentioned can be applied either individually or in combination with the corresponding aspects to which they relate, unless they are explicitly stated as excluding alternatives.

[0072] Furthermore, it should be understood that the apparatus is configured to perform the corresponding method, although in some cases only the apparatus or only the method is described.

[0073] According to at least some example embodiments, a communication device (also referred to as a "user equipment (UE)") creates measurement data, e.g., once it receives a HO command from a source cell (also hereinafter referred to as "one of the plurality of cells"). If an execution condition is satisfied, then the communication device logs the end of the measurement and stops creating measurement data in order to perform a HO to a target cell (also hereinafter referred to as "another of the plurality of cells"). The collected measurement data is sent to the target cell.

[0074] In Figure 2 a method according to at least some example embodiments is illustrated. The communication device receives (S20) a HO command from one of the plurality of cells. Each of the plurality of cells provides a communication service for the communication device. Subsequently, the communication device collects (S21) measurement data. If the execution condition is satisfied, then a HO to another of the plurality of cells is performed. Additionally, the collected measurement data is logged (S22) and sent (S23) to another of the plurality of cells.

[0075] According to an example implementation, the communication device indicates the availability of the logged information (e.g., the logged measurement data) to the target cell after the execution condition is satisfied and the end of the measurement is logged. According to an example implementation, the indication regarding the availability of the logged measurement data is sent after the handover and the completion of the RACH access between the communication device and the target cell.

[0076] Additionally, according to an example implementation, after the previously mentioned indication has been received by the target cell, the user equipment receives a request to report the logged measurement data from the target cell.

[0077] According to an example implementation, the execution condition is a CHO condition, which is sent from the source cell as part of the HO request. According to an example implementation, the measurement data also contains data regarding different instants of time and elapsed time:

[0078] ● For example, the measurement data logged contains information about the moment when the CHO condition is satisfied.

[0079] ● For example, the measurement data logged contains data about the elapsed time between the reception of the CHO command and the moment when the CHO execution condition is satisfied.

[0080] ● For example, the measurement data logged contains data about the elapsed time between the triggering of the transmission of the measurement report of the CHO configuration from the communication device to the source cell and the moment when the CHO execution condition is satisfied.

[0081] ● Additionally, for example, the measurement data logged includes the cell identifier (PCI) of the source and / or target cell.

[0082] According to an example implementation, the transmission of the measurement data logged is performed directly after the completion of the HO execution or during the completion of the HO execution.

[0083] In at least some of the above-mentioned cases, the concept of "elapsed time" can be measured in the common SI units of seconds and milliseconds and / or in terms of the number of elapsed wireless frames, sub-frames, time slots or orthogonal frequency division multiplexing (OFDM) symbols.

[0084] According to at least some example embodiments, a network entity, such as a target cell (also referred to as "one network cell among a plurality of network cells"), receives the measurement data logged from the UE. The measurement data logged includes data collected by the UE at least during the time when it receives the HO command from its source cell (also referred to as "another network cell among a plurality of network cells") and the moment when the execution condition is satisfied. The target cell then sends the measurement data logged to the source cell.

[0085] In Figure 3 a method according to at least some example embodiments is illustrated. At least one cell among a plurality of cells receives (S30) measurement data logged that is created in response to an HO command from another cell among the plurality of cells and is logged after the execution condition is satisfied. Additionally, the received measurement data logged is sent (S31) to another cell among the plurality of cells.

[0086] According to an example implementation, an indication of the availability of the logged information is received by the target cell before it actually receives the measurement data logged.

[0087] According to an example implementation, the target cell has sent a request to the UE to report the measurement data logged after receiving the indication of the availability of the logged information and before it actually receives the measurement data logged.

[0088] According to an example implementation, the execution condition is the CHO condition, which is sent from the source cell as part of the HO command.

[0089] According to an example implementation, the measurement data also includes data about the time instance. For example, the logged measurement data includes data about the time instance when the CHO condition is satisfied. In another example, the logged measurement data includes data about the elapsed time between 1) the acceptance of the handover command or the transmission of the measurement report that triggered the CHO configuration and 2) the time instance when the CHO execution condition is satisfied.

[0090] Additionally, according to an example implementation, the time instance is represented by a timestamp or alternatively by the number / index of radio frames and subframes / slots / OFDM symbols when the CHO execution condition is satisfied.

[0091] According to an example implementation, the source cell logs the time instance when it sends the HO command to the UE or receives the measurement report from the UE. Additionally, for example, the time instance is represented by a timestamp or alternatively by the number / index of radio frames and subframes / slots / OFDM symbols when the HO command has been sent or the measurement report has been received.

[0092] According to an example implementation, the target cell forwards the logged measurement data to the source cell via the Xn interface to improve the source cell's future handling of CHO.

[0093] Using this information, the source cell can collect statistical data about the duration between the sent HO command and the time when the associated CHO condition is satisfied. This allows for better decisions about the time instance when the source cell should stop forwarding data to the target cell.

[0094] For example, if all durations between the sent HO command and the time when the associated CHO condition is satisfied are greater than X ms, then the source cell may not trigger any data forwarding for the UE for handover until a certain duration T less than X ms has expired.

[0095] Another example would be if the statistical data exposes a spike at Y ms with a low standard deviation, then the source cell should not wait until it receives an indication from the target cell (which is the baseline method as discussed above). Generally, these statistical data can be used by a machine learning algorithm running at the source cell for determining the time instance to trigger data forwarding for a specific target cell, i.e., the machine learning algorithm is implementation-specific.

[0096] Figure 4 A signaling diagram of the CHO process according to an example implementation is shown. As Figure 1Similarly, the entities involved in the signaling are illustrated in a horizontal layout as a User Equipment (UE), a serving BS (e.g., a source gNB, BS that is currently serving / associated with the UE), and a target BS (e.g., a target gNB, BS to which a handover or conditional handover HO (to be) performed is to be made). The serving and target BS communicate via an interface Xn (not illustrated as such). Messages exchanged between such entities are illustrated as arrows, and the actions / processing of the messages at the entities are illustrated as boxes / circles. The time sequence of the messages is "top - down" in this figure.

[0097] At the start of the relevant process, the serving BS (source cell) sends a measurement control message (S410) to the UE. The UE then sends a measurement report (S411) to the source cell, which triggers a HO request (S412) from the source cell to the target BS (target cell). This request is confirmed by a HO request acknowledgement (S413) from the target cell to the source cell. After this, the source cell distributes a HO command (S414) to the UE. After receiving the HO command, the UE starts time measurement (S415) and waits until the CHO execution condition is met (S416). Once the corresponding CHO execution condition is met, the UE logs the corresponding elapsed duration or moment (S417). Next, RACH access occurs and HO is completed (S418). In a subsequent step, the UE sends an indication (S419) to the target cell about the logged measurement data, which contains information about the moment when the CHO execution condition was met. The target cell signals its interest in this information by requesting the logged measurement data (S420) and the UE sends it accordingly (S421). Finally, the target cell forwards the logged measurement data to the source cell for future use (S422).

[0098] It can be understood that Figure 2 and Figure 3 the steps of Figure 4 are also reflected in the Figure 4 example process. Receiving the HO command in step S20 corresponds to step S414, where the source cell distributes the HO command to the UE. In step S21, measurement data is created, which is also created in steps S415, S416 in the Figure 4 example embodiment. As long as the execution condition is met, the measurement data is logged (correspondingly, steps S22, S417). Then, the measurement data is sent from the UE and received at the target cell (correspondingly, steps S23, S421, S30). Finally, the logged measurement data is sent by the target cell to the source cell in steps S31, S422 accordingly.

[0099] Figure 5Depicts control units 10, 20, and 30, each including a processing resource (e.g., processing circuitry) 11, 21, 31, a memory resource (e.g., memory circuitry) 12, 22, 32, and an interface (e.g., interface circuitry) 13, 23, 33. In at least one exemplary embodiment, control unit 10 is configured to be implemented in and / or used by a UE, such as the communication device as described above and / or Figure 4 the UE shown in, control unit 20 is configured to be implemented in and / or used by a serving BS, such as the serving BS being Figure 4 the source cell and / or serving BS shown in, and control unit 30 is configured to be implemented in and / or used by a target BS, such as the target BS being Figure 4 the target cell and / or target BS shown in. Additionally, each control unit has its own bus system 14, 24, 34 that connects the above resources such that data can be exchanged between the three components of the unit. Additionally, control units 10 and 20 and control units 10 and 30 can be wirelessly connected via links 41, 42. Control unit 20 and control unit 30 also have an additional Xn interface 40 that implements the connection between the corresponding unit and its resources.

[0100] The terms "connected", "coupled", or any variation thereof mean any connection or coupling (direct or indirect) between two or more elements, and can include the presence of one or more intermediate elements between the two elements "connected" or "coupled" together. The coupling or connection between elements can be physical, logical, or a combination thereof. As used herein, two elements can be considered to be "connected" or "coupled" together by using one or more wires, cables, and printed electrical connections, and by using electromagnetic energy, as non-limiting examples, electromagnetic energy such as electromagnetic energy having wavelengths in the radio frequency region, microwave region, and optical (both visible and invisible) regions.

[0101] The definitions indicated in this specification are based on the current 3GPP standards. However, they are not restrictive. Other definitions based on the same or corresponding concepts also apply to some example embodiments.

[0102] A piece of information can be sent from one entity to another entity in one or more messages. Each of these messages can include additional (different) pieces of information.

[0103] The names of network elements, protocols, and methods are based on the current standards. In other versions or other technologies, the names of these network elements and / or protocols and / or methods can be different, as long as they provide the corresponding functions.

[0104] Unless otherwise stated or otherwise clear from the context, a statement that two entities are different means that they perform different functions. It does not necessarily mean that they are based on different hardware. That is, each of the entities described in this specification may be based on different hardware, or some or all of the entities may be based on the same hardware. It does not necessarily mean that they are based on different software. That is, each of the entities described in this specification may be based on different software, or some or all of the entities may be based on the same software. Each of the entities described in this specification may be embodied in the cloud.

[0105] In view of the above description, it should thus be apparent that the example embodiments provide, for example, a base station such as a gNB or a component thereof, an apparatus embodying the same, a method for controlling and / or operating the same, one or more computer programs for controlling and / or operating the same, and a medium carrying the one or more computer programs and forming one or more computer program products.

[0106] In general, various embodiments of a UE may include, but are not limited to, a mobile station, a cellular phone, a personal digital assistant (PDA) having wireless communication capabilities, a portable computer having wireless communication capabilities, an image capture device such as a digital camera having wireless communication capabilities, a gaming device having wireless communication capabilities, a music storage and playback appliance having wireless communication capabilities, an Internet appliance allowing wireless Internet access and browsing, and a portable unit or terminal incorporating a combination of such functions.

[0107] The implementation of any of the blocks, apparatuses, systems, techniques, or methods described above includes, by way of non-limiting example, implementation as hardware, software, firmware, a special-purpose circuit or logic, general-purpose hardware or a controller or other computing device, or a particular combination thereof.

[0108] In addition, as used in this application, the term "circuitry" refers to one or more or all of the following:

[0109] (a) only hardware circuit implementations (such as an implementation in only analog and / or digital circuitry)

[0110] (b) a combination of circuitry and software (and / or firmware), such as, if applicable: (i) a combination of one or more processors or (ii) one or more processors / software (including one or more digital signal processors), software, and portions of one or more memories that work together to cause an apparatus such as a mobile phone or a server to perform various functions, and

[0111] (c) circuitry, such as one or more microprocessors or a portion of one or more microprocessors, that requires software or firmware for operation, even if the software or firmware is not physically present.

[0112] This definition of "circuitry" applies in this application, including all uses of the term in any claim. As another example, as used in this application, the term "circuitry" will also cover implementations that are only a processor (or processors) or a part of a processor and its (or their) accompanying software and / or firmware. For example and if applicable to a particular claim element, the term "circuitry" will also cover a baseband integrated circuit for a mobile phone or an application processor integrated circuit or a similar integrated circuit in a server, a cell network device, or other network devices.

[0113] According to at least some example embodiments, an apparatus for use by a communication device is provided. For example, the apparatus includes Figure 5 the control unit 10 shown in. According to another example implementation or additionally, the apparatus is configured to perform Figure 2 the method 1 illustrated in.

[0114] The apparatus includes: components for receiving a handover command from one of a plurality of network cells providing communication services for the communication device, components for creating measurement data after receiving the handover command, components for logging the measurement data and the end of the measurement after an execution condition for performing a handover to another one of the plurality of network cells is satisfied, and components for sending the logged measurement data to another one of the plurality of network cells.

[0115] According to an example implementation, the apparatus further includes components for logging an indication of the availability of the logged measurement data to another one of the plurality of network cells providing communication services after logging the measurement data and the end of the measurement after the execution condition for performing a handover to another one of the plurality of network cells is satisfied.

[0116] According to an example implementation, the apparatus further includes components for receiving a request to report the logged measurement data from another one of the plurality of network cells providing communication services after logging and sending the indication of the availability of the logged measurement data to another one of the plurality of network cells providing communication services.

[0117] In an example implementation, the execution condition is a condition for conditional handover CHO.

[0118] In an example implementation, the sending of the logged measurement data is performed immediately or during the completion of the handover execution.

[0119] In an example implementation, after completion of random access channel (RACH) access between a handover and communication device and another network cell among a plurality of network cells, transmission of an indication regarding the availability of logged measurement data is performed.

[0120] In an example implementation, the logged measurement data includes data related to a moment when a CHO condition is satisfied.

[0121] In an example implementation, the information related to the moment when a CHO condition is satisfied includes at least one of a moment when a CHO execution condition is satisfied and an elapsed time between acceptance of a handover command and a moment when the CHO execution condition is satisfied.

[0122] In an example implementation, the information related to the moment when a CHO condition is satisfied includes an elapsed time between transmission of a measurement report that triggers CHO configuration and a moment when the CHO execution condition is satisfied.

[0123] In an example implementation, the elapsed time is indicated in seconds or milliseconds.

[0124] In an example implementation, the elapsed time is indicated by a number of elapsed ones of at least one of: radio frames, subframes, time slots, or orthogonal frequency division multiplexing (OFDM) symbols.

[0125] In an example implementation, the logged measurement data includes a physical cell identifier (PCI) of at least one network cell among network cells that provide a communication service.

[0126] In an example implementation, the plurality of network cells that provide a communication service includes a target cell and a source cell.

[0127] According to at least some example embodiments, an apparatus for use by at least one network cell among a plurality of network cells that provide a communication service for a communication device is provided. For example, the apparatus is part of a target cell and includes Figure 5 the control unit 30 shown in. According to another example implementation or additionally, the apparatus is configured to perform Figure 3 method 2 illustrated in.

[0128] The apparatus includes: means for receiving logged measurement data from a communication device, where the logged measurement data is created in response to the communication device receiving a handover command from another network cell among a plurality of network cells and is logged after an execution condition for performing a handover to one of the plurality of network cells is satisfied; and means for logging and transmitting the logged measurement data to another network cell among the plurality of network cells.

[0129] According to an example implementation, the apparatus further includes components for receiving an indication of the availability of measurement data logged with a log before the measurement data logged with the log is received.

[0130] According to an example implementation, the apparatus further includes components for sending a request for reporting measurement data logged with a log to a communication device after receiving an indication of the availability of measurement data logged with a log.

[0131] In an example implementation, the execution condition is a condition for conditional handover (CHO).

[0132] In an example implementation, the measurement data logged with a log includes data related to the moment when the CHO condition is satisfied.

[0133] According to an example implementation, the apparatus further includes components for acquiring measurement data logged with a log and components for forwarding the measurement data logged with a log to another network cell among a plurality of network cells via an Xn interface.

[0134] According to another example, the apparatus is part of a serving cell and includes Figure 5 the control unit 20 shown in. According to another example implementation or additionally, the apparatus is configured to execute Figure 3 the method 2 illustrated in.

[0135] In an example implementation, the apparatus further includes components for logging the moment when a handover command is sent to a communication device or a measurement report is received from the communication device.

[0136] In an example implementation, the moment includes at least one of the number or index of radio frames when the execution condition is satisfied and at least one of the following: subframes, or time slots, or OFDM symbols, or a timestamp.

[0137] According to an example implementation, the apparatus further includes components for collecting statistical data from the measurement data logged with a log.

[0138] It should be understood that the above description is of what is currently considered to be the preferred example embodiments of the present invention. However, it should be noted that the description of the preferred example embodiments is given by way of example only and various modifications can be made without departing from the scope of the present invention as defined by the appended claims.

Claims

1. A method for a communication device, the method comprises: receiving a conditional handover command via a source cell provided by a cellular communication network; determining an elapsed time between the reception of the conditional handover command and the moment when the execution condition for the conditional handover is satisfied for a target cell; and sending the determined elapsed time towards the cellular communication network.

2. The method according to claim 1, wherein the method further comprises: creating measurement data after receiving the conditional handover command; recording the measurement data and the end of the measurement after the execution condition for switching to the target cell is satisfied; and sending the recorded measurement data to the target cell, wherein the recorded measurement data includes: data related to the moment when the conditional handover condition is satisfied.

3. The method according to claim 2, wherein the method further comprises: after sending an indication of the availability of the recorded measurement data to the target cell, receiving a request to report the recorded measurement data from the target cell.

4. The method according to claim 1, wherein the method further comprises: sending the determined elapsed time towards the cellular communication network includes at least one of: sending the determined elapsed time towards the source cell, towards the target cell, towards another cell.

5. The method according to claim 1, wherein determining the elapsed time comprises: determining an elapsed time between the reception of the conditional handover command and the moment when the execution condition of the conditional handover is satisfied and the handover to the target cell is executed.

6. The method according to claim 1, wherein the conditional handover command is received from the source cell via radio resource control (RRC) signaling.

7. The method according to claim 1, wherein the conditional handover command is generated by the target cell.

8. The method according to claim 1, wherein the method further comprises: receiving a request to report the determined elapsed time.

9. The method according to claim 1, wherein the method further comprises: after sending an indication of the availability of the determined elapsed time to the target cell, receiving a request to report the determined elapsed time from the target cell.

10. An apparatus, comprises: at least one processor; and at least one memory storing instructions which, when executed by the at least one processor, cause the apparatus to at least: receive a conditional handover command via a source cell provided by a cellular communication network; determine an elapsed time between the reception of the conditional handover command and the moment when the execution condition for the conditional handover is satisfied for a target cell; and send the determined elapsed time towards the cellular communication network.

11. The apparatus according to claim 10, wherein the at least one memory stores instructions which, when executed by the at least one processor, cause the apparatus to at least: After receiving the conditional handover command, create measurement data; After the execution condition for switching to the target cell is satisfied, record the measurement data and the end of the measurement; And Send the recorded measurement data to the target cell, Wherein the recorded measurement data includes: data related to the moment when the conditional handover condition is satisfied.

12. The apparatus according to claim 11, wherein the at least one memory stores instructions that, when executed by the at least one processor, cause the apparatus to at least: After sending an indication of the availability of the recorded measurement data to the target cell, receive a request from the target cell to report the recorded measurement data.

13. The apparatus according to claim 10, wherein the at least one memory stores instructions that, when executed by the at least one processor, cause the apparatus to at least: Sending the determined elapsed time towards the cellular communication network includes at least one of: sending the determined elapsed time towards the source cell, towards the target cell, towards another cell.

14. The apparatus according to claim 10, wherein determining the elapsed time Comprises: Determine an elapsed time that is between the receipt of the conditional handover command and the moment when the execution condition for the conditional handover is satisfied and the handover to the target cell is executed.

15. The apparatus according to claim 10, wherein the conditional handover command is received from the source cell via radio resource control (RRC) signaling.

16. The apparatus according to claim 10, wherein the conditional handover command is generated by the target cell.

17. The apparatus according to claim 10, wherein the at least one memory stores instructions that, when executed by the at least one processor, cause the apparatus to at least: Receive a request to report the determined elapsed time.

18. The apparatus according to claim 10, wherein the at least one memory stores instructions that, when executed by the at least one processor, cause the apparatus to at least: After sending an indication of the availability of the determined elapsed time to the target cell, receive a request from the target cell to report the determined elapsed time.

19. The apparatus according to claim 10, wherein the at least one memory stores instructions that, when executed by the at least one processor, cause the apparatus to at least: After receiving the conditional handover command, create measurement data; After the execution condition for switching to the target cell is satisfied, record the measurement data and the end of the measurement; And Send the recorded measurement data to the target cell, Wherein the recorded measurement data includes: data related to the moment when the conditional handover condition is satisfied.

20. The apparatus according to claim 10, wherein the at least one memory stores instructions that, when executed by the at least one processor, cause the apparatus to at least: After sending an indication of the availability of the recorded measurement data to the target cell, a request to report the recorded measurement data is received from the target cell.

21. The apparatus according to claim 10, wherein the at least one memory stores instructions which, when executed by the at least one processor, cause the apparatus to at least: Sending the determined elapsed time towards the cellular communication network comprises at least one of: sending the determined elapsed time towards the source cell, towards the target cell, towards another cell.

22. The apparatus according to claim 10, wherein the at least one memory stores instructions which, when executed by the at least one processor, cause the apparatus to at least: Determine an elapsed time between the reception of the conditional handover command and the moment when the execution condition of the conditional handover is met and the handover to the target cell is executed.

23. An apparatus, comprising: at least one processor; and at least one memory, the at least one memory storing instructions which, when executed by the at least one processor, cause the apparatus to at least: Send a conditional handover command via a source cell provided by a cellular communication network, wherein an elapsed time is determined between the reception of the conditional handover command and the moment when the execution condition of the conditional handover is met for a target cell; and Receive the determined elapsed time towards the cellular communication network.

Images