Embodiments of the present application generally relate to wireless communication technology, in particular to methods and apparatuses of a mobility robustness optimization (MRO) mechanism for a conditional handover (CHO) procedure.
A base station (BS) can have some cells (or areas) to provide communication service. When a user equipment (UE) moves from a serving cell of a source BS to a target cell of a target BS, a handover procedure is performed.
When a radio link failure (RLF) or a handover (HO) failure occurs for a UE, the UE may perform a radio resource control (RRC) re-establishment procedure. The UE may access a cell by a successful RRC re-establishment procedure. The accessed network will request UE information including a RLF report of the UE, such that the network can optimize the mobility problem based on the UE information from the UE. Accordingly, the UE will transmit a failure report to the network.
The 3rd Generation Partnership Project (3GPP) 5G system or network adopts a MRO mechanism. However, details regarding a MRO mechanism for a CHO procedure have not been discussed in 3GPP 5G technology yet.
Some embodiments of the present application provide a method, which may be performed by a UE. The method includes: receiving CHO configuration information for a UE, wherein the CHO configuration information is associated with one or more CHO candidate cells and includes a set of execution conditions corresponding to the one or more CHO candidate cells, and wherein the UE is in a RRC connected state; performing a HO procedure associated with a target cell, in response to receiving a handover command from a source cell or performing a CHO procedure associated with a CHO candidate cell, in response to meeting an execution condition of the CHO candidate cell; starting a timer for HO procedure or CHO procedure; and in response to successfully accessing the target cell or the CHO candidate cell, stopping the timer and transmitting assistant information to the target cell or the CHO candidate cell.
Some embodiments of the present application provide a further method, which may be performed by a UE. The method includes: receiving CHO configuration information for a UE, wherein the CHO configuration information is associated with one or more CHO candidate cells and includes a set of execution conditions corresponding to the one or more CHO candidate cells, wherein the UE is in a RRC connected state; in response to an occurrence of a failure, performing a RRC re-establishment procedure, wherein the failure is one of a RLF, a HO failure, and a CHO failure; selecting a first cell; in response to the first cell being configured with CHO configuration information, performing a CHO procedure; and storing information regarding whether an execution condition for each of the one or more CHO candidate cells is met or not.
Some embodiments of the present application also provide an apparatus for wireless communications. The apparatus includes: a non-transitory computer-readable medium having stored thereon computer-executable instructions; a receiving circuitry; a transmitting circuitry; and a processor coupled to the non-transitory computer-readable medium, the receiving circuitry and the transmitting circuitry, wherein the computer-executable instructions cause the processor to implement the above-mentioned method performed by a UE.
The details of one or more examples are set forth in the accompanying drawings and the descriptions below. Other features, objects, and advantages will be apparent from the descriptions and drawings, and from the claims.
In order to describe the manner in which advantages and features of the application can be obtained, a description of the application is rendered by reference to specific embodiments thereof, which are illustrated in the appended drawings. These drawings depict only example embodiments of the application and are not therefore to be considered limiting of its scope.
The detailed description of the appended drawings is intended as a description of preferred embodiments of the present application and is not intended to represent the only form in which the present application may be practiced. It should be understood that the same or equivalent functions may be accomplished by different embodiments that are intended to be encompassed within the spirit and scope of the present application.
Reference will now be made in detail to some embodiments of the present application, examples of which are illustrated in the accompanying drawings. To facilitate understanding, embodiments are provided under specific network architecture and new service scenarios, such as 3GPP 5G, 3GPP LTE Release 8 and so on. It is contemplated that along with developments of network architectures and new service scenarios, all embodiments in the present application are also applicable to similar technical problems; and moreover, the terminologies recited in the present application may change, which should not affect the principle of the present application.
As illustrated and shown in
The UE(s) 101 may include computing devices, such as desktop computers, laptop computers, personal digital assistants (PDAs), tablet computers, smart televisions (e.g., televisions connected to the Internet), set-top boxes, game consoles, security systems (including security cameras), vehicle on-board computers, network devices (e.g., routers, switches, and modems), internet of things (IoT) devices, or the like. According to some embodiments of the present application, the UE(s) 101 may include a portable wireless communication device, a smart phone, a cellular telephone, a flip phone, a device having a subscriber identity module, a personal computer, a selective call receiver, or any other device that is capable of transmitting and receiving communication signals on a wireless network. In some embodiments of the present application, the UE(s) 101 includes wearable devices, such as smart watches, fitness bands, optical head-mounted displays, or the like. Moreover, the UE(s) 101 may be referred to as a subscriber unit, a mobile, a mobile station, a user, a terminal, a mobile terminal, a wireless terminal, a fixed terminal, a subscriber station, a user terminal, or a device, or described using other terminology used in the art. The UE(s) 101 may communicate directly with BSs 102 via uplink (UL) communication signals.
In some embodiments of the present application, each of the UE(s) 101 may be deployed an IoT application, an eMBB application and/or an URLLC application. It is contemplated that the specific type of application(s) deployed in the UE(s) 101 may be varied and not limited.
The BS(s) 102 may be distributed over a geographic region. In certain embodiments of the present application, each of the BS(s) 102 may also be referred to as an access point, an access terminal, a base, a base unit, a macro cell, a Node-B, an evolved Node B (eNB), a gNB, a NG-RAN (Next Generation-Radio Access Network) node, a Home Node-B, a relay node, or a device, or described using other terminology used in the art. The BS(s) 102 is generally a part of a radio access network that may include one or more controllers communicably coupled to one or more corresponding BS(s) 102.
The wireless communication system 100 may be compatible with any type of network that is capable of transmitting and receiving wireless communication signals. For example, the wireless communication system 100 is compatible with a wireless communication network, a cellular telephone network, a Time Division Multiple Access (TDMA)-based network, a Code Division Multiple Access (CDMA)-based network, an Orthogonal Frequency Division Multiple Access (OFDMA)-based network, an LTE network, a 3GPP-based network, a 3GPP 5G network, a satellite communications network, a high altitude platform network, and/or other communications networks.
In some embodiments of the present application, the wireless communication system 100 is compatible with the 5G of the 3GPP protocol, wherein BS(s) 102 transmit data using an OFDM modulation scheme on the downlink (DL) and the UE(s) 101 transmit data on the UL using a single-carrier frequency division multiple access (SC-FDMA) or OFDM scheme. More generally, however, the wireless communication system 100 may implement some other open or proprietary communication protocols, for example, WiMAX, among other protocols.
In some embodiments of the present application, the BS(s) 102 may communicate using other communication protocols, such as the IEEE 802.11 family of wireless communication protocols. Further, in some embodiments of the present application, the BS(s) 102 may communicate over licensed spectrums, whereas in other embodiments, the BS(s) 102 may communicate over unlicensed spectrums. The present application is not intended to be limited to the implementation of any particular wireless communication system architecture or protocol. In yet some embodiments of present application, the BS(s) 102 may communicate with the UE(s) 101 using the 3GPP 5G protocols.
Each BS(s) 102 may include one or more cells. Each UE(s) 101 may perform a cell section procedure between different cell(s) of different BS(s). Each UE(s) 101 may handover from a serving cell of a source BS to a target cell of a target BS. For example, in the wireless communication system 100 as illustrated and shown in
As specified in 3GPP standard documents, CHO is defined as a handover that is executed by a UE when one or more handover execution conditions are met. The UE starts evaluating the execution condition(s) upon receiving the CHO configuration, and stops evaluating the execution condition(s) during the CHO procedure once the execution condition(s) is met.
According to 3GPP standard documents, the following principles are applicable for CHO:
Referring to
In operation 203, the source BS may transmit CHO REQUEST message to one target BS (e.g., BS 102b as illustrated and shown in
In operation 205, based on an admission control result, the target BS or other potential target BS(s) may prepare handover resource(s) for the UE and send CHO REQUEST ACKNOWLEDGE message to the source BS.
In operation 206, the source BS may transmit RRCReconfiguration message to the UE. The RRCReconfiguration message may include configuration information of CHO candidate cell(s) and the corresponding CHO execution condition(s).
In operation 207, the UE may transmit RRCReconfigurationComplete message to the source BS. In operation 208, the UE may evaluate the CHO condition(s). If one of the CHO candidate cells satisfies the CHO execution condition(s), the UE may detach from the source cell and synchronize to the CHO candidate cell which satisfies the CHO execution condition(s).
In operation 209, the UE may transmit a CHO completion message to the target BS or other potential target BS(s). In operation 210, the 5G network may switch the DL data path towards the target BS or other potential target BS(s). Any ongoing data forwarding may continue.
As specified in 3GPP standard documents, MRO is for detecting connection failure(s) that occur due to Too Early or Too Late Handovers, or Handover to Wrong Cell. The general procedure is that after a RLF or a HO failure happens, a UE access a new cell by RRC re-establishment or connection setup. Once the UE enters a RRC connected state, the UE transmits a RLF report and a RACH report to the serving cell. The serving cell will transmit a failure indication including a RLF report to the last serving cell. Finally, the information is used to optimize the mobility.
Regarding the abovementioned function of MRO, the problems of Too Early or Too Late Handovers, or Handover to Wrong Cell are defined as follows:
In the above definitions, the “successful handover” refers to the UE's state, i.e., the successful completion of the radio access (RA) procedure.
Generally, in a UE information procedure, after a RLF or a HO failure occurs, a UE may perform a RRC re-establishment procedure in a cell. The UE will store some information related with the RLF failure and/or the HO failure. The UE stores the latest RLF Report, including both LTE and NR RLF report until the RLF report is fetched by the network or for 48 hours after the connection failure is detected. For analysis of connection failure(s), the UE makes the RLF report available to the network.
As shown in
In a 3GPP 5G system, a failure indication may be initiated after a UE attempts to re-establish the radio link connection at NG-RAN node B (e.g., BS 420 in
The purpose of the failure indication procedure is to transfer information regarding RRC re-establishment attempts, or received RLF reports, between NG-RAN nodes. The signaling takes place from the NG-RAN node at which a re-establishment attempt is made, or a RLF report is received, to an NG-RAN node to which the UE concerned may have previously been attached prior to the connection failure. This may aid the detection of a RLF case or a HO failure case.
As shown in
The following table shows introductions of some timers as specified in 3GPP standard documents, including a starting condition, a stop condition, an operation at expiry, and a possible general name for each of these timers.
In the exemplary method 500 as shown in
In operation 5021, the UE determines whether a handover command is received from a source cell. In operation 5031, if “YES”, i.e., the UE receives a handover command from a source cell, the UE performs a HO procedure associated with a target cell.
In operation 5022, the UE determines whether an execution condition of a CHO candidate cell is met. In operation 5032, if “YES”, i.e., if an execution condition of a CHO candidate cell is met, the UE performs a CHO procedure associated with the CHO candidate cell.
In operation 504, the UE starts a timer for HO procedure or CHO procedure. In operation 505, if the UE successfully accesses the target cell via the HO procedure or if the UE successfully accesses the CHO candidate cell via the CHO procedure, the UE stops the timer for HO procedure or CHO procedure and transmits assistant information to the target cell or the CHO candidate cell.
In an embodiment, after the UE successfully completes the HO procedure or the CHO procedure, the UE transmits an indication to the target cell or the CHO candidate cell, and the indication indicates that a state of the assistant information is available. The indication may also be named as “an indication of an available state of assistant information”. For instance, the indication indicates at least one of:
In an embodiment, after successfully completing of the HO procedure, the UE receives a UE information request message from the target cell and then transmits a UE information response message to the target cell. The UE information response message includes the assistant information.
In a further embodiment, after successfully completing of the CHO procedure, the UE receives a UE information request message from the CHO candidate cell and then transmits a UE information response message to the CHO candidate cell. The UE information response message includes the assistant information.
According to some embodiments, after successfully completing a HO procedure, the UE reports CHO related information to the serving cell. According to some further embodiments, after successfully completing a HO procedure, the UE reports other information not associated with a CHO procedure to the serving cell. According to some other embodiments, after successfully completing a CHO procedure, the UE reports CHO related information or other information not associated with the CHO procedure to the serving cell. The information reported by the UE in all these embodiments may be named as assistant information.
For instance, the assistant information transmitted by the UE may include at least one of following information or a combination thereof.
In an embodiment, the assistant information includes: a set of identity information regarding one or more CHO candidate cells of the UE; and a set of execution conditions corresponding to the one or more CHO candidate cells.
In a further embodiment, if two conditions are configured to one CHO candidate cell within one or more CHO candidate cells of the UE, the assistant information includes an indication to indicate whether one condition within these two conditions is met or whether no condition within these two conditions is met.
For example, following two conditions may be configured to one CHO candidate cell. In this example, the assistant information may include an indication to indicate that “only Event A3 is met”, “only Event A5 is met”, or “neither Event A3 nor Event A5 is met”.
In another embodiment, the assistant information includes: a time to trigger (TTT) value corresponding to an execution condition of each CHO candidate cell of one or more CHO candidate cells.
In yet another embodiment, the assistant information includes a measurement result for each CHO candidate cell of one or more CHO candidate cells.
In yet another embodiment, the assistant information includes:
For example, the handover timer is timer T304 as specified in 3GPP standard documents. The assistant information includes: a time length of timer T304 configured by control signaling from a BS, and an actual duration length of timer T304 from a time instance of starting T304 to a time instance of actually stopping timer T304.
In yet another embodiment, the assistant information includes a time duration between “a time instance of receiving firstly transmitted CHO configuration information associated with one CHO candidate cell within one or more CHO candidate cells” and “a time instance of starting to perform a HO procedure or a CHO procedure”.
In yet another embodiment, the assistant information includes a time duration between “a time instance of receiving lastly transmitted CHO configuration information associated with one CHO candidate cell within one or more CHO candidate cells” and “a time instance of starting to perform a HO procedure or a CHO procedure”.
In yet another embodiment, the assistant information includes a measurement result for each of one or more serving beams of the UE.
In yet another embodiment, the assistant information includes a state of each serving beam of one or more serving beams of the UE during the UE performing the HO procedure or the CHO procedure. The state of each serving beam may be failed or available.
According to some embodiments, a BS of the target cell of the UE transmits a failure indication message to a BS of the source cell, e.g., via Xn interface. According to some other embodiments, a BS of the CHO candidate cell of the UE transmits a failure indication message to a BS of the source cell, e.g., via Xn interface. The failure indication message may include an indication, to indicate “a successful completion of the HO procedure” or “a successful completion of the CHO procedure”. For short, “a successful completion of the HO procedure” may be named as “a successful HO procedure” or the like. For short, “a successful completion of the CHO procedure” may be named as “a successful CHO procedure” or the like.
The following texts describe specific Embodiments 1 and 2 of the method as shown and illustrated in
According to Embodiment 1, a UE (e.g., UE 101, the UE, or UE 310 as shown and illustrated in any of
According to Embodiment 2, a UE (e.g., UE 101, the UE, or UE 310 as shown and illustrated in any of
Details described in all other embodiments of the present application (for example, details of a MRO mechanism for a CHO procedure and the transmitted assistant information) are applicable for the embodiments of
Under some scenarios, if a CHO failure or a HO failure occurs, a UE performs a CHO procedure. This CHO procedure may be named as a CHO recovery procedure to some extents. There may be two cases, one case is that the UE successfully completes the CHO procedure, and the other case is that the UE unsuccessfully completes the CHO procedure. In these two cases, the UE needs to report some related information. Specific examples are described in the embodiments of
In the exemplary method 600 as shown in
In operation 602, upon an occurrence of a failure, the UE initiates a RRC re-establishment procedure. The failure may be one of a RLF, a HO failure, and a CHO failure.
In operation 603, the UE selects a cell, e.g., by performing a cell selection procedure. In operation 604, if the selected cell is configured with CHO configuration information, the UE performs a CHO procedure.
In operation 605, the UE stores information regarding whether an execution condition for each CHO candidate cell within one or more CHO candidate cells is met or not.
In an embodiment, if the UE successfully completes the CHO procedure, the UE transmits, to the selected cell, an indication of an available state of assistant information. The indication may also be named as an assistant information available indication. For instance, the indication may be included in RRCReconfigurationComplete message.
In an example, the UE further receives a UE information request message from the selected cell and transmits a UE information response message to the selected cell. The UE information response message includes the assistant information.
In a further embodiment, if the UE does not successfully complete the CHO procedure, the UE selects another cell. The UE may transmit a RRC re-establishment request to the abovementioned another cell. The UE may further transmit the assistant information available indication to the abovementioned another cell, in response to successful completing the RRC re-establishment procedure which is initiated in the operation 602 as shown and illustrated in
In an example, the UE further receives a UE information request message from the abovementioned another cell and transmits the UE information response message to the abovementioned another cell. The UE information response message includes the assistant information.
In both embodiments that the UE successfully completes the CHO procedure and the UE does not successfully complete the CHO procedure, the assistant information available indication may be at least one of:
According to some embodiments, a BS of the selected cell of the UE transmits a failure indication message to a BS of the source cell, e.g., via Xn interface. According to some other embodiments, a BS of the abovementioned another selected cell of the UE transmits a failure indication message to a BS of the source cell, e.g., via Xn interface. The failure indication message may include an indication, to indicate “a successful CHO procedure after initiating the RRC re-establishment procedure” or “a failed CHO procedure after initiating the RRC re-establishment procedure”. For short, “a successful CHO procedure after initiating the RRC re-establishment procedure” may be named as “a successful CHO recovery procedure” or the like. For short, “a failed CHO procedure after initiating the RRC re-establishment procedure” may be named as “a failed CHO recovery procedure” or the like.
According to some embodiments, the assistant information includes at least one of:
According to some other embodiments, the assistant information includes at least one of:
The following texts describe specific Embodiments 3 and 4 of the method as shown and illustrated in
In Embodiment 3, a UE successfully completes a CHO recovery procedure. According to Embodiment 3, a UE (e.g., UE 101, the UE, or UE 310 as shown and illustrated in any of
In Embodiment 4, a UE does not successfully complete a CHO recovery procedure. According to Embodiment 4, a UE (e.g., UE 101, the UE, or UE 310 as shown and illustrated in any of
Details described in all other embodiments of the present application (for example, details of a MRO mechanism for a CHO procedure and the transmitted assistant information) are applicable for the embodiments of
As shown in
Although in
In some embodiments of the present application, the at least one non-transitory computer-readable medium 706 may have stored thereon computer-executable instructions which are programmed to implement the operations of the methods, for example as described in view of any of
Those having ordinary skills in the art would understand that the operations of a method described in connection with the aspects disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, a hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. Additionally, in some aspects, the operations of a method may reside as one or any combination or set of codes and/or instructions on a non-transitory computer-readable medium, which may be incorporated into a computer program product.
While this disclosure has been described with specific embodiments thereof, it is evident that many alternatives, modifications, and variations may be apparent to those skilled in the art. For example, various components of the embodiments may be interchanged, added, or substituted in the other embodiments. Also, all of the elements of each figure are not necessary for operation of the disclosed embodiments. For example, those having ordinary skills in the art would be enabled to make and use the teachings of the disclosure by simply employing the elements of the independent claims. Accordingly, embodiments of the disclosure as set forth herein are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and scope of the disclosure.
In this document, the terms “includes,” “including,” or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by “a,” “an,” or the like does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that includes the element. Also, the term “another” is defined as at least a second or more. The term “having” and the like, as used herein, are defined as “including.”
Filing Document | Filing Date | Country | Kind |
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PCT/CN2020/117865 | 9/25/2020 | WO |