UE-Assisted Data Forwarding in Conditional Handover

Abstract

A method for use by a communication device, wherein the method comprises the following steps: receiving (S20) a switching command from one of a plurality of network cells providing communication services for the communication device, creating (S21) measurement data after receiving the switching command, logging (S22) the measurement data and the end of the measurement after the execution condition of switching to another of the plurality of network cells is met, and sending (S23) the measurement data logged to another of the plurality of network cells.

Description

Technical Field

[0001] At least some example embodiments relate to mobility in cellular and mobile communication systems such as Long Term Evolution (LTE) or New Radio (NR). In particular, 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.

[0002] List of Abbreviations / Acronyms

[0003] 3GPP Third Generation Partnership Project

[0004] ARQ Automatic Repeat Request

[0005] BS Base Station

[0006] CHO Conditional Switch

[0007] CQI Channel Quality Indicator

[0008] eMBB Enhanced Mobile Broadband

[0009] eNB Evolved NodeB

[0010] gNB Next Generation NodeB

[0011] HARQ Hybrid Automatic Repeat Request

[0012] HO Handover

[0013] ID Identifier

[0014] LTE Long Term Evolution

[0015] NR New Radio

[0016] OFDM Orthogonal Frequency Division Multiplexing

[0017] PCI Physical Cell ID

[0018] PRACH Physical Random Access Channel

[0019] RACH Random Access Channel

[0020] RAN Radio Access Network

[0021] RRC Radio Resource Control

[0022] RRM Radio Resource Management

[0023] SI International System of Units

[0024] UE User Equipment

[0025] Xn The interface between gNBs as defined in 3GPP TS 38.423 Background Art

[0026] In the case where a mobile terminal such as a user equipment (UE) (hereinafter also referred to as a "communication device") is assigned to a serving node (or "cell") within a (cellular) communication network (which is currently serving and / or associated to the mobile terminal), a handover (HO) will be performed to another node (or "cell"), which will then serve the terminal in the case of a handover condition. Common handover conditions occur in the case where the mobile terminal is moving across the geographical coverage of the corresponding node within the cellular communication network. However, the same geographical coverage may be served by multiple nodes or cells and also in such a situation, a handover condition may occur. For example, a (single) node may define different cells (e.g., distinguishable by different physical resources associated therewith) and a handover may therefore occur at the same node but in connection with a handover from cell to cell. Various handover procedures are known, and among those, one handover procedure is a conditional handover (CHO).

[0027] Conditional HO (CHO):

[0028] The CHO process is similar to a conventional handover. The message sequence diagram of the (common and known) CHO process is shown in Figure 1 middle.

[0029] The entities involved in the signaling are illustrated in a horizontal arrangement as a terminal or user equipment (UE), a source gNB (currently serving / associated to the UE), and a target gNB (subsequently serving / associated to the UE) to which a handover or conditional handover CHO is (to be) performed. The source and target gNBs communicate via an interface Xn (not illustrated as such). 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 temporal sequence of the messages is from "top to bottom" in the figure.

[0030] The first steps (represented by S1 to S8 in "Phase 1") are largely the same as for a conventional handover. The source gNB performs measurement control for the UE (S1). A configured event (S2) triggers the UE to send a measurement report to the serving gNB (S3). Based on the report, the source gNB typically prepares the target gNB for handover (handover request from source gNB to target gNB in ​​S4) and receives a handover request confirmation (from the target gNB in ​​S5) and then a handover command to the UE (S6). The command typically 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.

[0031] For conventional 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 an additional CHO execution condition expires. This condition is typically configured by the source gNB during the HO command in S6, for example.

[0032] 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 risking access in the target cell and the stability of its radio link.

[0033] The HO command is generated by the target cell and included into the "Handover Request Confirm" before the source forwards it to the UE via Radio Resource Control (RRC) signaling.

[0034] The "actual" HO is performed in the CHO execution phase (phase 2, see steps S9 to S13). After the CHO execution conditions are 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. Thereafter, 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 Confirm message in step S12. In the subsequent step / phase S13, the UE and the source gNB will adapt to the scope for which the "old" (i.e. previous) preparations or settings are no longer valid for them. In this scope, after the (HO or) CHO completion, the target gNB will become the new source gNB.

[0035] In CHO, since there may be a significant time delay between HO preparation and the actual HO execution, the situation at the target cell may potentially change during this time.

[0036] In addition, if Figure 1 As shown, after receiving the handover command, the UE will not immediately perform a handover to the target cell but instead wait until the CHO execution condition is met, 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 data forwarding from the source to the target cell.

[0037] In the baseline handover scheme of NR Rel.15, the source cell starts forwarding UE packets after sending a handover command to the UE.

[0038] This is useful because the UE is expected to access the target cell immediately after receiving the handover command.

[0039] However, in CHO, the source cell does not know the moment when the UE detaches from the source cell and therefore it does not have any information for triggering data forwarding in time (ie when the UE has detached from the source cell or has just recently detached).

[0040] In the prior art, several approaches have been proposed to deal with this problem.

[0041] Method 1: Similar to baseline handover, the source cell can start data forwarding after sending a handover command to the UE.

[0042] This may result in unnecessary forwarding of many UE data packets (consuming resources over the Xn interface) while the UE is still transmitting and receiving from the source cell. The impact is even higher when multiple targets are prepared for CHO.

[0043] Method 2: The source cell starts data forwarding when it receives an indication from the target cell that the RACH access is completed by the UE.

[0044] This scheme does not cause unnecessary forwarding of data packets, however, it may cause service interruption if the UE connects to the target cell before the user packets are already in the target BS.

[0045] This is particularly relevant to contention-based random access, where the target BS may send an indication only upon receiving the third message (also referred to as "Msg3") in the random access procedure from the UE.

[0046] However, the source cell can roughly estimate the time when CHO is performed from the time when it receives the indication from the target cell.

[0047] However, this estimation suffers from errors caused by RACH retransmissions, guessing the target cell's Physical Random Access Channel (PRACH) opportunity periodicity without the source cell's knowledge, UE and target cell processing delays, delays through the Xn interface, and so on.

[0048] Method 3: The source cell may 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 some time that the missing CQI, HARQ / ARQ feedback report is lost because the UE has detached and not due to a temporary and instantaneous change in the channel (a "false alarm"), which again creates uncertainty about the CHO execution time.

[0049] Method 4: The UE may attempt to notify the source cell by means of RRC signaling (also referred to as a "bye" message) when the CHO execution conditions are met.

[0050] This method is not considered a priority in 3GPP discussions because the indication sent by the UE may not be received at the time the UE performs access to the target cell.

[0051] Method 5: During CHO completion, the source cell obtains an indication from the target cell that the UE has accessed the target cell (eg, HO completed). Based on this, the source cell can roughly determine when the execution condition has been triggered, and thus when forwarding should have occurred.

[0052] However, similar to method 2, this information is very coarse, as the time between triggering of the execution condition and receiving the indication from the target cell is unknown and can be significant (involving RACH procedures and Xn signaling). Summary of the invention

[0053] It is an aim of at least some of the example embodiments to improve upon the prior art.

[0054] This object is achieved by a method, an apparatus and a non-transitory storage medium as specified in the accompanying claims.

[0055] Furthermore, a computer program product is provided, comprising a computer executable code, which when executed by a processor performs the method according to any one of the method aspects.

[0056] According to at least some example embodiments, at least one of the following advantages is achieved:

[0057] • The source cell obtains reliable and accurate statistics from the handed-over UE, which the source cell can utilize for a more timely triggering of data forwarding, which results in a better trade-off between interruption through late forwarding and unnecessary forwarding through early forwarding.

[0058] The proposed solution also allows to consider different mobility scenarios for different cell borders, such as for 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 grouping of UEs depending on their moving speed.

[0059] • The source cell does not have to wait or rely on unreliable information (e.g. missing CQI or HARQ acknowledgement), it is only used and considered as a replacement for custom CHO signaling and its absence may also have other reasons than HO to another cell (e.g. very deep fade events).

[0060] • The statistical nature of the logged measurement data allows decisions to be made about different reliability levels (e.g. based on percentiles) to suit the needs of different data services allowing for more conservative or more liberal strategies respectively.

[0061] • Ultimately, this supports and improves user quality of experience due to increased service continuity.

[0062] Additional advantages will become apparent from the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] Additional details, features, objects and advantages will become apparent from the following detailed description of example embodiments of at least some aspects which is to be read in conjunction with the accompanying drawings, in which:

[0064] Figure 1 A signaling diagram illustrating the steps of the CHO preparation and execution process is shown.

[0065] Figure 2 A flow chart illustrating an example method according to at least some embodiments is shown.

[0066] Figure 3 A flow chart illustrating an example method according to at least some embodiments is shown.

[0067] Figure 4 A signaling diagram is shown illustrating steps of an example of a CHO preparation process and a CHO execution process with collecting, logging, and exchanging CHO related measurement data according to at least some embodiments.

[0068] Figure 5 Shown is a schematic block diagram illustrating a configuration of a control unit in which at least some example embodiments may be implemented. DETAILED DESCRIPTION

[0069] In the following, certain 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 can be freely combined with each other. However, it is to be clearly understood that the description of certain example embodiments / aspects is given by way of example only, and it is not intended to be understood as limiting the application to the disclosed details.

[0070] It should be understood that any of the modifications mentioned may be applied alone or in combination with the corresponding aspects to which they relate, unless they are explicitly stated to exclude alternatives.

[0071] 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.

[0072] According to at least some example embodiments, a communication device (also referred to as "user equipment (UE)") creates measurement data, for example, once it receives a HO command from a source cell (also referred to hereinafter as "a cell of the plurality of cells"). If an execution condition is met, 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 referred to hereinafter as "another cell of the plurality of cells"). The collected measurement data is sent to the target cell.

[0073] exist Figure 2 In the embodiment, a method according to at least some example embodiments is illustrated. A communication device receives (S20) a HO command from a cell in a 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 an execution condition is met, a HO to another cell in the plurality of cells is performed. In addition, the collected measurement data is logged (S22) and sent (S23) to another cell in the plurality of cells.

[0074] According to an example implementation, the communications device indicates the availability of logged information (e.g., logged measurement data) to the target cell after the execution condition is met and the end of the measurement is logged. According to an example implementation, the indication of the availability of the logged measurement data is sent after the handover and RACH access between the communications device and the target cell is completed.

[0075] 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.

[0076] 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 about different moments and elapsed times:

[0077] For example, the logged measurement data contains information about the times at which the CHO conditions are met.

[0078] For example, the measurement data recorded in the log includes data on the elapsed time between the reception of the CHO command and the time when the CHO execution condition is satisfied.

[0079] For example, the measurement data recorded in the log includes data on the elapsed time between the time when the transmission of the measurement report for CHO configuration from the communication device to the source cell was triggered and the time when the CHO execution condition was satisfied.

[0080] • For example, the logged measurement data additionally includes a cell identifier (PCI) of the source and / or target cell.

[0081] According to an example implementation, the sending of the logged measurement data is performed directly after the completion of the HO execution or during the completion of the HO execution.

[0082] In at least some of the above mentioned cases, the notion of "elapsed time" may be measured in common SI units of seconds and milliseconds and / or in the elapsed number of radio frames, subframes, time slots, or Orthogonal Frequency Division Multiplexing (OFDM) symbols.

[0083] According to at least some example embodiments, a network entity, such as a target cell (also referred to as "a network cell among the plurality of network cells"), receives logged measurement data from a UE. The logged measurement data includes data collected by the UE at least during the time it received a HO command from its source cell (also referred to as "another network cell among the plurality of network cells") and the time when the execution condition was met. The target cell then sends the logged measurement data to the source cell.

[0084] exist Figure 3 In the method according to at least some example embodiments, at least one cell of the plurality of cells receives (S30) measurement data created in response to a HO command from another cell of the plurality of cells and logged after an execution condition is satisfied. In addition, the received logged measurement data is sent (S31) to another cell of the plurality of cells.

[0085] According to an example implementation, the indication of the availability of the logged information is received by the target cell before it actually receives the logged measurement data.

[0086] According to an example implementation, the target cell sends a request to the UE to report logged measurement data already after receiving the indication of the availability of the logged information but before it actually receives the logged measurement data.

[0087] According to an example implementation, the execution condition is a CHO condition, which is sent from the source cell as part of the HO command.

[0088] According to an example implementation, the measurement data further includes data about a time. For example, the logged measurement data includes data about a time when the CHO condition is met. In another example, the logged measurement data includes data about an elapsed time between 1) acceptance of a handover command or sending of a measurement report that triggered a CHO configuration and 2) a time when the CHO execution condition is met.

[0089] Additionally, according to an example implementation, the time instant is represented by a timestamp or alternatively by the number / index of the radio frame and subframe / time slot / OFDM symbol when the CHO execution condition is met.

[0090] According to an example implementation, the source cell logs the time at which it sends a HO command to the UE or receives a measurement report from the UE. In addition, for example, the time is represented by a timestamp or alternatively by the number / index of the radio frame and subframe / time slot / OFDM symbol when the HO command has been sent or the measurement report has been received.

[0091] According to an example implementation, the target cell forwards the logged measurement data to the source cell via the Xn interface to improve future handling of CHO by the source cell.

[0092] Using this information, the source cell can collect statistics about the duration between a sent HO command and the time the associated CHO condition is met. This allows better decisions to be made about the moment when the source cell should stop forwarding data to the target cell.

[0093] For example, if all durations between a sent HO command and the time when the associated CHO conditions are met are greater than X ms, the source cell may not trigger any data forwarding for the handed over UE until a certain duration T less than X ms has expired.

[0094] Another example would be that if the statistics reveal a spike at Y ms with little standard deviation, then the source cell should not wait until an indication is received from the target cell (which is the baseline approach as discussed above). Typically, these statistics can be used by a machine learning algorithm running at the source cell to determine the moment to trigger data forwarding for a specific target cell, i.e., the machine learning algorithm is implementation specific.

[0095] Figure 4 A signaling diagram of a CHO process according to an example implementation is shown. Figure 1 Likewise, the entities involved in the signaling are illustrated in a horizontal arrangement as a user equipment (UE), a serving BS (e.g., a source gNB, BS currently serving / associated to the UE), and a target BS to which a handover or conditional handover HO is (to be) performed (e.g., a target gNB, BS subsequently serving / associated to the UE). The serving and target BSs 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 temporal sequence of messages is from "top to bottom" in the figure.

[0096] At the beginning of the relevant process, the serving BS (source cell) sends a measurement control message to the UE (S410). The UE then sends a measurement report to the source cell (S411), which triggers a HO request from the source cell to the target BS (target cell) (S412). The request is confirmed by a HO request confirmation (S413) from the target cell to the source cell. After this, the source cell distributes a HO command to the UE (S414). 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 time (S417). Next, RACH access occurs and the HO is completed (S418). In a subsequent step, the UE sends an indication of the measurement data recorded in the log to the target cell (S419), which contains information about the time when the CHO execution condition is met. The target cell signals its interest in the information by requesting to report the measurement data recorded in the log (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).

[0097] Understandably, Figure 2 and Figure 3 The steps are also reflected in Figure 4 In the example process of FIG. 4 , the receiving of the HO command in step S20 corresponds to step S414 , in which the source cell distributes the HO command to the UE. In step S21 , measurement data is created, which is also created in steps S415 and S416 . Figure 4 In the example embodiment of . As long as the execution condition is met, the measurement data is recorded in the log (respectively, steps S22, S417). Then, the measurement data is sent from the UE and received at the target cell (respectively, steps S23, S421, S30). Finally, the measurement data recorded in the log is sent by the target cell to the source cell in steps S31, S422, respectively.

[0098] Figure 5 Control units 10, 20 and 30 are depicted, each including processing resources (e.g., processing circuitry) 11, 21, 31, memory resources (e.g., memory circuitry) 12, 22, 32, and interfaces (e.g., interface circuitry) 13, 23, 33. In at least one exemplary embodiment, the control unit 10 is configured to be implemented in and / or used by a UE, such as a communication device and / or as described above. Figure 4 UE shown in FIG. 1 , the control unit 20 is configured to be implemented in and / or used by a serving BS, such as a serving BS. Figure 4The source cell and / or serving BS shown in FIG. 1 , and the control unit 30 is configured to be implemented in and / or used by the target BS, such as the target BS Figure 4 4. In addition, each control unit has its own bus system 14, 24, 34, which connects the above resources so that data can be exchanged between the three components of the unit. In addition, the control units 10 and 20 and the control units 10 and 30 can be connected wirelessly via links 41, 42. The control unit 20 and the control unit 30 also have an additional Xn interface 40, which realizes the connection between the respective units and their resources.

[0099] The terms "connected," "coupled," or any variation thereof, mean any connection or coupling (direct or indirect) between two or more elements, and may include the presence of one or more intermediate elements between two elements that are "connected" or "coupled" together. The coupling or connection between elements may be physical, logical, or a combination thereof. As employed herein, two elements may be considered to be "connected" or "coupled" together by use of one or more wires, cables, and printed electrical connections, as well as by use of electromagnetic energy, such as, as non-limiting examples, electromagnetic energy having wavelengths in the radio frequency region, the microwave region, and the optical (both visible and invisible) region.

[0100] 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 are also applicable to some example embodiments.

[0101] A piece of information may be sent from one entity to another in one or more messages. Each of these messages may include another (different) piece of information.

[0102] The names of network elements, protocols and methods are based on current standards. In other versions or other technologies, the names of these network elements and / or protocols and / or methods may be different, as long as they provide corresponding functions.

[0103] If not stated otherwise 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.

[0104] From the above description, it should therefore be apparent that the example embodiments provide, for example, a base station such as a gNB or components thereof, an apparatus embodying the same, a method for controlling and / or operating the same, (multiple) computer programs for controlling and / or operating the same, and a medium that carries (multiple) such computer programs and forms (multiple) computer program products.

[0105] In general, various embodiments of a UE may include, but are not limited to, a mobile station, a cell phone, a personal digital assistant (PDA) with wireless communication capabilities, a portable computer with wireless communication capabilities, an image capture device such as a digital camera with wireless communication capabilities, a gaming device with wireless communication capabilities, a music storage and playback appliance with wireless communication capabilities, an Internet appliance allowing wireless Internet access and browsing, and a portable unit or terminal incorporating a combination of such functionality.

[0106] Implementation of any of the above described blocks, apparatus, systems, techniques, or methods includes, as non-limiting examples, implementation as hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controllers or other computing devices, or some combination thereof.

[0107] Additionally, as used in this application, the term "circuitry" refers to one or more or all of the following:

[0108] (a) Hardware circuit implementation only (such as implementation with analog and / or digital circuitry only)

[0109] (b) a combination of circuitry and software (and / or firmware), such as (where applicable): (i) a combination of processor(s) or (ii) portions of processor(s) / software (including digital signal processor(s)), software and memory(s) that work together to enable a device such as a mobile phone or server to perform various functions, and

[0110] (c) Circuitry, such as microprocessor(s) or portion of microprocessor(s), that requires software or firmware for operation even if the software or firmware is not physically present.

[0111] This definition of "circuitry" applies to this application, including all uses of this term in any claim. As another example, as used in this application, the term "circuitry" would also cover an implementation of only a processor (or multiple processors) or a portion 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" would also cover a baseband integrated circuit or an application processor integrated circuit for a mobile phone or a similar integrated circuit in a server, cell network device, or other network device.

[0112] According to at least some example embodiments, an apparatus for use by a communication device is provided. For example, the apparatus includes Figure 5 According to another example implementation or in addition, the device is configured to perform Figure 2 Method 1 as shown in FIG.

[0113] The apparatus includes: a component for receiving a switching command from one of a plurality of network cells providing communication services for a communication device, a component for creating measurement data after receiving the switching command, a component for recording the measurement data and the end of the measurement in a log after an execution condition for performing a switching to another of the plurality of network cells is met, and a component for sending the measurement data recorded in the log to another of the plurality of network cells.

[0114] According to an example implementation, the apparatus further comprises a component for logging the measurement data and, after the end of the measurement, sending an indication of the availability of the measurement data recorded in the log to another network cell among the multiple network cells providing communication services.

[0115] According to an example implementation, the apparatus further comprises a component for receiving a request to report measurement data recorded with logging from another network cell among the multiple network cells providing communication services after sending an indication of availability of measurement data recorded with logging to another network cell among the multiple network cells providing communication services.

[0116] In an example implementation, the execution condition is a condition for conditionally switching CHO.

[0117] In an example implementation, the sending of the logged measurement data is performed immediately after or during completion of the handover execution.

[0118] In an example implementation, sending the indication of the availability of the logged measurement data is performed after handover and random access channel (RACH) access between the communication device and another network cell of the plurality of network cells is completed.

[0119] In an example implementation, the logged measurement data includes data related to the times at which the CHO condition is met.

[0120] In an example implementation, the information related to the time when the CHO condition is satisfied includes at least one of the time when the CHO execution condition is satisfied and the elapsed time between the acceptance of the handover command and the time when the CHO execution condition is satisfied.

[0121] In an example implementation, the information related to the time at which the CHO condition is satisfied includes an elapsed time between the sending of the measurement report triggering the CHO configuration and the time at which the CHO execution condition is satisfied.

[0122] In example implementations, elapsed time is indicated in seconds or milliseconds.

[0123] In an example implementation, the elapsed time is indicated by an elapsed number of at least one of: a radio frame, a subframe, a time slot, or an Orthogonal Frequency Division Multiplexing (OFDM) symbol.

[0124] In an example implementation, the logged measurement data includes a physical cell identifier PCI of at least one of the network cells providing the communication service.

[0125] In an example implementation, the plurality of network cells providing communication services include a target cell and a source cell.

[0126] According to at least some example embodiments, there is provided an apparatus for use by at least one network cell of a plurality of network cells providing communication services to a communication device. For example, the apparatus is part of a target cell and includes Figure 5 According to another example implementation or in addition, the device is configured to perform Figure 3 Method 2 as shown in the figure.

[0127] The apparatus includes: a component for receiving measurement data for logging from a communication device, wherein the measurement data for logging is created in response to the communication device receiving a switching command from another network cell among a plurality of network cells and is logged after an execution condition for switching to one of the plurality of network cells is met; and a component for sending the measurement data for logging to another network cell among the plurality of network cells.

[0128] According to an example implementation, the apparatus further comprises means for receiving an indication of availability of the logged measurement data before the logged measurement data is received.

[0129] According to an example implementation, the apparatus further comprises means for sending a request to the communication device to report the logged measurement data upon receiving the indication of the availability of the logged measurement data.

[0130] In an example implementation, the execution condition is a condition for a conditional switch (CHO).

[0131] In an example implementation, the logged measurement data includes data related to the times at which the CHO condition is met.

[0132] According to an example implementation, the apparatus further comprises means for obtaining the logged measurement data and means for forwarding the logged measurement data to another network cell of the plurality of network cells via the Xn interface.

[0133] According to another example, the apparatus is part of a serving cell and comprises Figure 5 According to another example implementation or in addition, the device is configured to perform Figure 3 Method 2 shown in the figure.

[0134] In an example implementation, the apparatus further includes means for logging a time at which a handover command is sent to the communication device or a measurement report is received from the communication device.

[0135] In an example implementation, the time instant includes a radio frame where the execution condition is satisfied and at least one of a number or an index or at least one of a timestamp of at least one of: a subframe, or a time slot, or an OFDM symbol.

[0136] According to an example implementation, the apparatus further comprises means for collecting statistical data from the logged measurement data.

[0137] It should be understood that the above description is what is currently considered to be the preferred exemplary embodiment of the present invention. However, it should be noted that the description of the preferred exemplary embodiment 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 use by a communication device, the method comprising: receiving a conditional handover command from a source cell, the conditional handover command comprising an instruction for the communication device to record information about a time at which a conditional handover execution condition is satisfied, creating measurement data after receiving the conditional switching command, logging the measurement data and the end of the measurement after a conditional handover execution condition for executing a handover to a target cell is satisfied, and sending measurement data recorded in the log to the target cell, wherein the measurement data recorded in the log includes data related to the moment when the conditional handover execution condition is met, including the elapsed time between the receipt of the conditional handover command and the moment when the conditional handover execution condition is met, and the measurement data recorded in the log is sent to the source cell.

2. The method according to claim 1, further comprising: After logging the measurement data and the end of the measurement after the conditional handover execution condition for executing the handover to the target cell is satisfied, an indication of availability of the logged measurement data is sent to the target cell providing a communication service.

3. The method according to claim 1 or 2, further comprising: After sending an indication of availability of the logged measurement data to a target cell providing the communication service, a request to report the logged measurement data is received from the target cell providing the communication service. 4 . The method according to claim 1 , wherein the sending of the logged measurement data is performed directly after the completion of the handover execution or during the completion of the handover execution. 5 .

5. The method according to claim 1 or 2, wherein the sending of the indication of the availability of the logged measurement data is performed after the handover and the completion of a random access channel (RACH) access between the communication device and the target cell.

6. A method according to claim 1, wherein the information related to the moment when the conditional switching condition is met includes at least one of the following: the moment when the conditional switching execution condition is met, and the elapsed time between the receipt of the conditional switching command and the moment when the conditional switching execution condition is met.

7. The method according to claim 1, wherein the information related to the moment when the conditional handover condition is met comprises the elapsed time between the sending of the measurement report that triggers the conditional handover configuration and the moment when the conditional handover execution condition is met.

8. The method according to claim 6 or 7, wherein the elapsed time is indicated in seconds or milliseconds.

9. The method according to claim 7 or 8, wherein the elapsed time is indicated by an elapsed number of at least one of: a radio frame, a subframe, a time slot or an Orthogonal Frequency Division Multiplexing (OFDM) symbol.

10. The method according to claim 1 or 2, wherein the measurement data recorded in the log includes a physical cell identifier (PCI) of at least one network cell among network cells providing communication services.

11. A method for use by at least one network cell of a plurality of network cells, the method comprising: Receiving, by one of the plurality of network cells providing communication services for the communication device, measurement data recorded in a log from the communication device, wherein the measurement data recorded in the log is created in response to the communication device receiving a conditional handover command from another network cell of the plurality of network cells and is logged after an execution condition for performing a handover to the one of the plurality of network cells is satisfied, and the measurement data recorded in the log includes data related to a moment when the execution condition is satisfied, including an elapsed time between receipt of the conditional handover command and the moment when the execution condition is satisfied, and The logged measurement data is sent to the another network cell of the plurality of network cells.

12. The method according to claim 11, further comprising: An indication of availability of logged measurement data is received by the one of the plurality of network cells before the logged measurement data is received.

13. The method according to claim 11 or 12, further comprising: A request to report logged measurement data is sent by the one of the plurality of network cells upon receiving an indication of availability of logged measurement data. The method according to claim 11 , wherein the execution condition is a condition for conditional switching.

15. The method according to claim 11 or 12, wherein the logged measurement data comprises data relating to the time at which the conditional switching condition is met.

16. The method according to claim 11 or 12, wherein the one of the plurality of network cells is a target cell, and the another of the plurality of network cells is a source cell, and wherein the method further comprises: The source cell records in a log the time when it sends the conditional handover command to the communication device or when it receives a measurement report from the communication device.

17. The method according to claim 16, wherein the time instant comprises a radio frame in which the execution condition is satisfied and at least one of the number or index of at least one of the following or at least one of the timestamps: a subframe, a time slot, or an OFDM symbol.

18. The method according to claim 11 or 12, further comprising: The measurement data recorded in the log is obtained by the one network cell among the multiple network cells and the measurement data recorded in the log is forwarded to the another network cell among the multiple network cells via an Xn interface, wherein the one network cell among the multiple network cells is a target cell and the another network cell among the multiple network cells is a source cell.

19. The method according to claim 11 or 12, further comprising: Statistics are collected from the logged measurement data.

20. A non-transitory computer-readable storage medium storing a program comprising software code portions that, when executed on a processor of a communication device, cause the processor to perform: receiving a conditional handover command from a source cell, the conditional handover command comprising an instruction for the communication device to record information about a time at which a conditional handover execution condition is satisfied, creating measurement data after receiving the conditional switching command, logging the measurement data and the end of the measurement after a conditional handover execution condition for executing a handover to a target cell is satisfied, and sending measurement data recorded in the log to the target cell, wherein the measurement data recorded in the log includes data related to the moment when the conditional handover execution condition is met, including the elapsed time between the receipt of the conditional handover command and the moment when the conditional handover execution condition is met, and the measurement data recorded in the log is sent to the source cell.

21. A non-transitory computer-readable storage medium storing a program comprising software code portions that, when executed on a processor of at least one of a plurality of network cells providing communication services to a communication device, cause the processor to perform: Receiving measurement data recorded in a log from the communication device by one of the plurality of network cells providing communication services for the communication device, wherein the measurement data recorded in the log is created in response to the communication device receiving a conditional switching command from another network cell of the plurality of network cells and is recorded in the log after an execution condition for performing a switching to the one of the plurality of network cells is satisfied, and the measurement data recorded in the log includes data related to a moment when the execution condition is satisfied, including an elapsed time between receipt of the conditional switching command and the moment when the execution condition is satisfied, and The logged measurement data is sent to the another network cell of the plurality of network cells.

22. An apparatus for use by a communication device, the apparatus comprising at least one processor and at least one memory, the at least one memory comprising computer program code, the at least one memory and the computer program code being configured to, with the at least one processor, cause the apparatus to at least perform: receiving a conditional handover command from a source cell, the conditional handover command comprising an instruction for the communication device to record information about a time at which a conditional handover execution condition is satisfied, creating measurement data after receiving the conditional switching command, logging the measurement data and the end of the measurement after a conditional handover execution condition for executing a handover to a target cell is satisfied, and sending measurement data recorded in the log to the target cell, wherein the measurement data recorded in the log includes data related to the moment when the conditional handover execution condition is met, including the elapsed time between the receipt of the conditional handover command and the moment when the conditional handover execution condition is met, and the measurement data recorded in the log is sent to the source cell.

23. The apparatus of claim 22, wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to further perform: After logging the measurement data and end of measurement after the conditional handover execution condition for executing handover to the target cell is satisfied, an indication of availability of the logged measurement data is sent to the target cell providing a communication service.

24. The apparatus according to claim 22 or 23, wherein the at least one memory and the computer program code are configured to, together with the at least one processor, cause the apparatus to further perform: After sending an indication of availability of the logged measurement data to the target cell providing the communication service, a request to report the logged measurement data is received from the target cell providing the communication service.

25. The apparatus of claim 22 or 23, wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to further perform: The logged measurement data is sent directly after completion of the handover execution or during the completion of the handover execution.

26. The apparatus of claim 22 or 23, wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to further perform: The indication of availability of logged measurement data is sent after completion of the handover and a random access channel (RACH) access between the communication device and the target cell.

27. An apparatus according to claim 23 or 24, wherein the information related to the moment when the conditional switching condition is met includes at least one of the following: the moment when the conditional switching execution condition is met, and the elapsed time between the receipt of the conditional switching command and the moment when the conditional switching execution condition is met.

28. The apparatus according to claim 23 or 24, wherein the information related to the moment when the conditional handover condition is met comprises the elapsed time between the sending of the measurement report that triggers the conditional handover configuration and the moment when the conditional handover execution condition is met.

29. The apparatus of claim 27, wherein the elapsed time is indicated in seconds or milliseconds.

30. The apparatus of claim 27, wherein the elapsed time is indicated by an elapsed number of at least one of: a radio frame, a subframe, a time slot, or an Orthogonal Frequency Division Multiplexing (OFDM) symbol.

31. The apparatus according to any one of claims 22 or 23, wherein the logged measurement data includes a physical cell identifier (PCI) of at least one network cell among network cells providing communication services.

32. An apparatus for use by at least one network cell of a plurality of network cells providing communication services to a communication device, the apparatus comprising at least one processor and at least one memory, the at least one memory comprising computer program code, the at least one memory and the computer program code being configured to, together with the at least one processor, cause the apparatus to at least perform: receiving logged measurement data from the communication device, wherein the logged measurement data is created in response to the communication device receiving a conditional handover command from another of the plurality of network cells and is logged after an execution condition for performing a handover to the one of the plurality of network cells is satisfied, and the logged measurement data includes data related to a moment when the execution condition is satisfied, including an elapsed time between receipt of the conditional handover command and the moment when the execution condition is satisfied, and The logged measurement data is sent to the another network cell of the plurality of network cells.

33. The apparatus of claim 32, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus to further perform: An indication of availability of logged measurement data is received before the logged measurement data is received.

34. The apparatus of claim 32 or 33, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus to further perform: A request to report the logged measurement data is sent to the communication device upon receiving an indication of the availability of the logged measurement data.

35. The apparatus of claim 32, wherein the execution condition is a condition for conditional switching.

36. An apparatus as claimed in claim 32 or 33, wherein the logged measurement data comprises data relating to the time at which the conditional switching condition is met.

37. The apparatus of claim 32 or 33, wherein the one of the plurality of network cells is a target cell and the another of the plurality of network cells is a source cell, wherein the apparatus is used by the source cell, and wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus to further perform: The time when it sends the conditional handover command to the communication device or when it receives a measurement report from the communication device is recorded in a log.

38. The apparatus of claim 37, wherein the time instant comprises a radio frame in which the execution condition is satisfied and at least one of a number or an index of at least one of the following or at least one of a timestamp: a subframe, or a time slot, or an OFDM symbol.

39. The apparatus of claim 32 or 33, wherein the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus to further perform: The logged measurement data is obtained and forwarded to the another network cell among the multiple network cells via an Xn interface, wherein the one network cell among the multiple network cells is a target cell and the another network cell among the multiple network cells is a source cell.

40. The apparatus of claim 32 or 33, wherein the at least one memory and the computer program code are configured, with the at least one processor, to cause the apparatus to further perform: Statistics are collected from the logged measurement data.

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