Method and device for implementing cell selection or cell reselection process

Abstract

A method for operating a user equipment UE (10) in a wireless communication network is disclosed. The method comprises the steps of: obtaining (S1) broadcast information comprising redirection information; and performing (S2) a cell selection or cell reselection procedure based on the obtained broadcast information. A corresponding UE and a computer program are also disclosed. A method for operating a network node (20) that serves a user equipment UE (10) in a wireless communication network is also disclosed. The method comprises the step of: broadcasting (S10) information that comprises redirection information enabling the UE to perform a cell selection or cell reselection procedure. A corresponding network node and a computer program are also disclosed.

Description

Technical Field

[0001] The proposed technology generally relates to user equipment and network nodes in a wireless communication network and methods performed by them. More specifically, it relates to methods and devices for implementing a cell selection or cell reselection process with reduced signaling requirements. Background Art

[0002] Release with redirection and resume with redirection are two processes in a Long-Term Evolution (LTE) network and New Radio (NR), where a cell can release a user equipment (UE) in an active mode or deny service to a UE that is accessing the cell, instead directing the UE to another cell or frequency for it to establish a new connection. Information related to release with redirection and resume with redirection is sent from the network (e.g., from a network node) to the UE in a unicast message. This unicast message provides specific details about the cell that the UE should access and / or the relevant frequency to be used by the UE, i.e., system information. In Long-Term Evolution (LTE), New Radio (NR), and other mobile networks, such system information is sent in the Master Information Block (MIB) and different System Information Blocks (SIBs). The MIB includes a limited number of the most necessary and frequently sent parameters that are required to obtain additional information from the cell. A UE in an idle mode reads the system information included in the MIB and SIBs to know how to move between different cells, i.e., how to perform a cell selection or cell reselection process. The parameters read by the UE are related to, for example, the identification of the network and the cell, cell blocking, signal level thresholds, quality level thresholds, frequency channels, and priorities. Specific information about the general process is given in the appendix.

[0003] However, this general process is prone to some drawbacks. In particular, it requires a large amount of signaling between the network node and the UE. That is, the UE needs to first perform a random access process, followed by sending an RRC resume request or an RRC establishment request message, and in addition, it also needs to wait for an RRC release with redirection information. All such signaling may be affected by signaling delays, which in turn may cause the UE to remain at the cell for an unnecessary long time. The proposed technology aims to at least mitigate some of the problems associated with the cell selection or cell reselection process. Summary of the Invention

[0004] The general objective is to provide a mechanism that can perform an effective cell selection or cell reselection process in a wireless communication network.

[0005] A specific objective is to provide a method for operating a user equipment (UE) that can perform an effective cell selection or cell reselection process in a cellular wireless communication network.

[0006] Another objective is to provide a user equipment UE that utilizes a method for operating the user equipment UE, which is capable of performing an effective cell selection or cell reselection process in a cellular radio communication network.

[0007] Yet another objective is to provide a method for operating a network node, which enables a user equipment UE to perform an effective cell selection or cell reselection process in a cellular radio communication network.

[0008] Still another objective is to provide a network node that utilizes a method enabling a user equipment UE to perform an effective cell selection or cell reselection process in a cellular radio communication network.

[0009] A specific objective is to provide a computer program for controlling a user equipment UE and a network node to execute the methods disclosed herein.

[0010] These and other objectives are met by embodiments of the proposed technology.

[0011] According to a first aspect, there is provided a method for operating a user equipment UE in a wireless communication network. The method includes the steps of obtaining broadcast information including redirection information and performing a cell selection or cell reselection process based on the obtained broadcast information.

[0012] According to a second aspect, there is provided a method for operating a network node that serves a user equipment UE in a wireless communication network. The method includes the step of broadcasting information including redirection information that enables the UE to perform a cell selection or cell reselection process.

[0013] According to a third aspect, there is provided a user equipment UE in a wireless communication system. The UE includes: a communication circuit configured to obtain broadcast system information, and a processing circuit configured to perform a cell selection or cell reselection process based on the obtained broadcast information.

[0014] According to a fourth aspect, there is provided a network node that serves a user equipment UE in a wireless communication network. The network node includes: a communication circuit configured to broadcast information including redirection information that enables the UE to perform a cell selection or cell reselection process.

[0015] According to a fifth aspect, there is provided a computer program for controlling a user equipment in a wireless communication network. The computer program includes instructions that, when executed by at least one processor, cause the at least one processor to read the obtained broadcast information including redirection information and initiate a cell selection or cell reselection process based on the read obtained broadcast information.

[0016] According to a sixth aspect, there is provided a computer program for controlling a network node that serves a user equipment (UE) in a wireless communication network. The computer program comprises instructions which, when executed by at least one processor, cause the at least one processor to initiate a broadcast of information comprising redirection information that enables the UE to perform a cell selection or cell reselection procedure.

[0017] Embodiments of the proposed technology implement a more time - efficient cell selection or cell reselection procedure for a user equipment (UE). It also achieves an improvement in latency.

[0018] Other advantages will be appreciated when reading the detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Embodiments and their further objects and advantages can best be understood by reference to the following description in conjunction with the drawings, in which:

[0020] Figure 1 is a schematic diagram showing a network node that serves a plurality of user equipments in a wireless communication network.

[0021] Figure 2A is a schematic flow chart showing a method for operating a user equipment according to the proposed technology.

[0022] Figure 2B is a schematic flow chart showing a method for operating a network node according to the proposed technology.

[0023] Figure 3 is a schematic signaling diagram showing how a UE according to the proposed technology can interact with a network node and an access stratum.

[0024] Figure 4 is a schematic block diagram showing a specific embodiment of a UE according to the proposed technology.

[0025] Figure 5 is a schematic block diagram showing a specific embodiment of a network node according to the proposed technology.

[0026] Figure 6 is a schematic diagram showing the implementation of a computer program according to the proposed technology. DETAILED DESCRIPTION

[0027] In all the figures, the same reference numerals are used for similar or corresponding elements.

[0028] In general, unless explicitly stated otherwise and / or implied from the context, all terms used herein will be interpreted according to their ordinary meaning in the relevant technical field. Unless otherwise explicitly stated, all references to "an / a / element, device, component, apparatus, step, etc." should be interpreted liberally as referring to at least one instance of the element, device, component, apparatus, step, etc. Unless a step is explicitly described as after or before another step and / or implicitly a step must be after or before another step, the steps of any method disclosed herein need not be performed in the exact order disclosed. In appropriate cases, any feature of any embodiment disclosed herein can be applied to any other embodiment. Similarly, any advantage of any embodiment can be applied to any other embodiment, and vice versa. Other objects, features, and advantages of the appended embodiments will be apparent from the following description.

[0029] To better understand the proposed technology, it may be helpful to start with a brief analysis of the technical problem. Consider Figure 1 the schematic diagram of a wireless communication network given in. Network node 20 serves a plurality of UEs 10 in cell 1. As described in the background section of the present disclosure, release with redirection and resume with redirection are two procedures in LTE and NR, where a cell can release an active-mode UE 10 or deny service to a UE 10 that is accessing the cell, instead directing the UE to another cell or frequency. Release with redirection and resume with redirection are sent from the network (i.e., from network node 20) to UE 10 in a unicast message. The unicast message is shown by an arrow in Figure 1 . A particular problem associated with this method concerns the signaling delay in the cell when the UE is redirected to another cell. Such signaling delay may deteriorate the latency and keep the UE poorly connected for an unnecessarily long time.

[0030] The proposed technology aims to provide a mechanism that at least partially addresses the problems caused by signaling delay. The proposed approach is based on the insight that redirection information can be broadcast in the cell rather than unicast. The redirection information used herein can generally be regarded as a list of services that a particular network or network node can support. For example, voice, video, etc. Such redirection information is latency-sensitive and provided / supported at a particular frequency. In particular, the redirection information can include rules for redirecting the UE.

[0031] According to the proposed technique, a mechanism is provided that allows a network node to interact with a UE in an efficient manner, in which redirection information is broadcast by the network node and acquired by the UE so that the UE can make an informed decision on whether to initiate a cell selection or cell reselection process. This very important mechanism is based on two complementary approaches: an approach performed by the UE and an approach performed by the network node. The approach performed by the UE will be described below. The approach performed by the network node will be described in a later section.

[0032] To this end, the proposed technique provides a method for operating a user equipment UE 10 in a wireless communication network. The method includes: a step S1 of acquiring broadcast information including redirection information, and a step S2 of performing a cell selection or cell reselection process based on the acquired broadcast information. Figure 2A A schematic flowchart showing the method is provided.

[0033] This particular method can be compared with existing processes, in which, in the case where the network or a network node does not support a certain service or one or several UEs that wish to camp on it are redirected to another radio access technology RAT or network node (e.g., during service-based load balancing), the network or the network node has to wait until these UEs execute a request. This process will require uplink UL signaling and downlink DL signaling in the random access channel and the channel carrying RRC signaling to be able to redirect the UE. This has to happen even if the network or the network node already has clear rules regarding redirecting UEs that request a given service when camping on a given frequency / RAT.

[0034] However, the proposed technique provides a mechanism by which the network or a network node can indicate redirection information in a broadcast message. This is very beneficial for reducing latency during the start of a particular service, and it also reduces the amount of air interface signaling between the UE and the target network node when the UE attempts to establish or resume a connection. This is due to the fact that, due to the broadcast information, the UE already knows that it needs to be redirected to another RAT / cell / frequency without having to first perform a random access (which requires at least 4 messages), followed by sending an RRC resume request or an RRC establishment request message and waiting for an RRC release with redirection information.

[0035] Some embodiments contemplated herein will now be described in more detail. However, other embodiments are included within the scope of the subject matter disclosed herein, and the disclosed subject matter should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided only as examples to convey the scope of the subject matter to those skilled in the art.

[0036] According to a specific embodiment of the proposed technique, a method is provided in which a cell selection or cell reselection process is performed based on a predetermined criterion to be satisfied according to redirection information. As already mentioned, the redirection information may include rules specifying how the UE should move between cells / frequencies or RATs. Thus, when the UE has obtained the redirection information by broadcast, the UE can be preconfigured to infer how it should move based on the content. Specific examples of such a predetermined criterion will be given below.

[0037] According to another embodiment of the proposed technique, a method is provided in which step S2 of performing a cell selection or cell reselection process is initiated during a connection recovery process when the UE10 is in an inactive state or during a connection establishment process when the UE 10 is in an idle state. This embodiment enables the UE to utilize the earlier obtained redirection information when initiating a connection establishment process. For example, it may obtain the redirection information at time t = 0 and then use this information at a later time t = t* (when initiating a connection recovery process). Since the UE can use the information that has been obtained, the amount of dedicated signaling during this process will be reduced.

[0038] According to an alternative embodiment of the proposed technique, a method is provided in which step S2 of performing a cell selection or cell reselection process is initiated during a connection recovery process, and the predetermined criterion to be satisfied includes:

[0039] · The recovery cause of a possible connection recovery process is included in the redirection information; and / or

[0040] · The access category of a possible connection recovery process is included in the redirection information.

[0041] This is an alternative version of the above version related to the connection establishment process. By determining that the redirection information includes the recovery cause and / or the access category, the UE can initiate a cell selection or cell reselection process with a reduced amount of dedicated signaling.

[0042] According to yet another embodiment of the proposed technique, the obtained broadcast information further includes a mapping between the recovery cause and / or the access category and at least one of the following: redirection to a target radio access technology (i.e., target RAT), redirection to a target serving cell, and redirection to a target frequency. The UE can advantageously use such a mapping to find a suitable new connection.

[0043] For example, the proposed technique provides a method in which step S2 of performing a cell selection or cell reselection process is initiated during a connection establishment process, and the predetermined criterion to be satisfied includes:

[0044] · The establishment reasons for possible connection establishment procedures are included in the redirection information, and / or

[0045] · The access category of possible connection establishment procedures is included in the redirection information.

[0046] This particular embodiment deals with the scenario where the UE aims to establish a connection rather than resume a connection as described previously. The same benefits are achieved in this case, for example, a reduction in the amount of dedicated signaling.

[0047] An alternative embodiment of the proposed technique provides a method in which the obtained broadcast information further includes a mapping between the establishment reason and / or access category and at least one of the following:

[0048] · Redirection to a target radio access technology, i.e., target RAT,

[0049] · Redirection to a target serving cell, and

[0050] · Redirection to a target frequency.

[0051] Above, we have described the content of redirection information in various versions that enables the UE to effectively select or reselect a cell. The redirection information is obtained from the broadcast of a network node. There are several specific methods for incorporating the redirection information into the broadcast. According to a possible embodiment of the proposed technique, a method is provided in which the redirection information is included in the system information block SIB of the broadcast.

[0052] A particular version of the above embodiment provides a method in which the redirection information is included in an information element added to an existing SIB.

[0053] According to another aspect of the proposed technique, as described previously, a complementary method performed by a network node is also provided. By broadcasting relevant redirection information (which can be used by the UE as a basis for the cell selection or cell reselection process as described above), this complementary method will enable the user equipment to perform a time-efficient cell reselection or cell selection process. To this end, a method for operating a network node 20 that serves a user equipment UE 10 in a wireless communication network is provided. The method includes a step S10 of broadcasting information that includes redirection information enabling the UE to perform a cell selection or cell reselection process. The method is schematically illustrated by the flowchart in Figure 2B and is shown schematically in the flowchart of

[0054] Some embodiments related to network operation methods will now be described in more detail. However, other embodiments are included within the scope of the subject matter disclosed herein, and the disclosed subject matter should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided only as examples to convey the scope of the subject matter to those skilled in the art.

[0055] A particular embodiment of the proposed network operation method provides a method in which the redirection information includes at least one of the following:

[0056] · The recovery reason for a possible connection recovery procedure for UE 10;

[0057] · The access category for a possible connection recovery procedure for UE 10;

[0058] · The establishment reason for a possible connection establishment procedure for UE 10; and

[0059] · The access category for a possible connection establishment procedure for UE 10.

[0060] The provision of information of this nature enables the UE to effectively control the connection recovery procedure or the connection establishment procedure. This will in turn ensure a reduction in the amount of signaling and also avoid any signaling delays associated therewith.

[0061] Another embodiment of the present invention provides a network operation method in which the redirection information further includes a mapping between the recovery reason, the establishment reason, and / or the access category and at least one of the following:

[0062] · Redirection to a target radio access technology, i.e., target RAT,

[0063] · Redirection to a target serving cell, and

[0064] · Redirection to a target frequency.

[0065] The network node can also use different modes to send the redirection information. Several possibilities are described below, although none of the proposed modes are mandatory.

[0066] An alternative embodiment of the proposed network operation method provides a method in which step S10 of broadcasting information includes broadcasting a system information block SIB that includes the redirection information.

[0067] According to this transmission mode, broadcast messages can be provided through system information blocks (e.g., SIB2, SIB4, or SIB5). Since the information in some scenarios may be sensitive from a pure security perspective, it is possible to encrypt the SIB so that it can be decrypted by inactive / idle UEs and the node responsible for broadcasting the message. For example, it is also possible to send redirection information in the form of SIB2, SIB4, and SIB5 sequentially, corresponding to the serving frequency, inter-frequency, and inter-RAT frequency, respectively, as follows:

[0068] When it is only related to serving frequency cell reselection, that is, when providing information about the serving frequency in the serving cell for cell reselection, it is sent in SIB2. This information can be mapped to the serving frequency in the cell reselection priority list.

[0069] When it is only related to inter-frequency cell reselection, that is, when providing information about neighboring cells on other frequencies in the same RAT for cell reselection, it is sent in SIB4. This information can be mapped one-to-one to the corresponding frequency in the cell reselection priority list.

[0070] When it is only related to inter-RAT frequency cell reselection, that is, when providing information about neighboring cells on other RAT frequencies for cell reselection, it is sent in SIB5. This information can be mapped one-to-one to the corresponding frequency in the cell reselection priority list.

[0071] A specific version of the above embodiment provides a method in which the redirection information is included in an information element IE added to the existing SIB. For example, we can define an IE that can be added to the existing SIBs for inter-frequency, intra-frequency, and inter-RAT frequencies.

[0072] In addition to this version, it is also possible to send the redirection information in an aggregated message in one of the SIBs or in a new SIB defined for this purpose and dedicated to this purpose.

[0073] Some of the embodiments related to both the method of operating a user equipment and the complementary method of operating a network node have been described. Below, we will provide some specific examples of how these methods can cooperate to achieve an effective cell selection or cell reselection process. These examples are provided only to help understand the concepts presented by the proposed technology and should not be construed as a limitation.

[0074] As a first example, consider the scenario where a UE is camped on a cell. It is also assumed that the network node broadcasts redirection information related to the camped UE. The UE can now obtain the broadcast redirection information, for example, by receiving and decoding the SIB. Based on the content of the redirection information, the UE can determine whether to access or attempt to resume the connection in the cell on which the UE is camped, or whether to access another cell (optionally, on another frequency). The specific decision made in this regard will be based on whether the information obtained actually includes redirection information.

[0075] As another example, again consider a wireless communication network in which a UE is served by a network node in a cell. The proposed technique can now be used to achieve a fast redirection of the UE to another cell / frequency and / or RAT. To achieve this, the network node broadcasts redirection information associated with such frequency and / or RAT. The UE then obtains the redirection information from the broadcast message (e.g., system information). The redirection information can be used, for example, in the following scenarios:

[0076] i) If the UE obtains a request to initiate a resume / establishment procedure from the access stratum (AS) or the upper layer. The UE should determine whether the broadcast message (e.g., system information) in the cell on which the obtained UE is camped contains relevant redirection information.

[0077] ii) If the obtained broadcast message (e.g., system information block) contains redirection information, the UE performs cell selection according to the indicated target frequency and / or target RAT (which is configured in the redirection information).

[0078] iii) If the obtained broadcast message (e.g., system information block) does not contain redirection information, the UE can continue with the establishment and resume procedure, i.e., in the cell / frequency / RAT in which it is currently camped.

[0079] Figure 3It is a schematic signaling diagram showing a possible scenario of the proposed technology. The network node 20 broadcasts redirection information, which is acquired by the UE. At a later stage, the UE obtains an instruction to initiate a resume / establish connection procedure from, for example, the access stratum AS. The UE can initiate a cell selection or cell reselection procedure based on the redirection information provided in the broadcast message (e.g., in the form of a target frequency or a target RAT). For example, it can use this information to resume the connection with the network node 20, but it can also be directed to establish a new connection with another network node 21, which spans a different cell. By utilizing the proposed mechanism, if the network node 21 is within the RAN notification area RNA of the UE, the UE can also resume to the network node 21. In particular, it can be used to control the UE to select a network node to resume to within the network nodes present in the RNA. The UE can be configured, for example, to check the network nodes within its RNA and determine a suitable network node from these network nodes based on the acquired redirection information. The RNA is an area that allows the UE to move without notifying the network. When an inactive UE moves to a cell that is not part of its RNA list, it performs a location update procedure. The RNA list is typically provided to the UE in the RRCRelease / SuspendConfig message.

[0080] According to the proposed technology, the redirection information can include information that may be related to and dependent on several different possible scenarios. As a first example, consider the case of resume when the UE is in an inactive state. For such a scenario, the relevant redirection information can include at least one of the following mappings:

[0081] · A mapping between the resume reason and the target frequency and possible RAT to which the UE is redirected when it obtains a request to resume the connection due to this resume reason from the upper layer or the AS,

[0082] · A mapping between the resume reason and the target cell in a given RAT and frequency to which the UE is redirected when it obtains a request to resume the connection due to this resume reason from the upper layer or the AS,

[0083] · A mapping between the resume reason and the target RAT to which the UE is redirected when it obtains a request to resume the connection due to this resume reason from the upper layer or the AS.

[0084] Thus, the network node can be provided with such a mapping.

[0085] In the case of establishment for an inactive UE, the relevant redirection information can instead include at least one of the following mappings:

[0086] · Establish a mapping between the establishment cause and the target frequency and RAT to which the UE is redirected when obtaining a request to establish a connection based on the specific establishment cause from the upper layer or the AS.

[0087] · Establish a mapping between the establishment cause and the target cell among the given RAT and frequency to which the UE is redirected when obtaining a request to establish a connection based on the specific establishment cause from the upper layer or the AS.

[0088] · Establish a mapping between the establishment cause and the target RAT to which the UE is redirected when obtaining a request to establish a connection based on the specific establishment cause from the upper layer or the AS.

[0089] Therefore, network nodes can be provided with such a mapping or generate such a mapping and broadcast them in the form of redirection information. The redirection information is then obtained (e.g., received and decoded) by the relevant UE. The UE can then use the obtained information as a basis for initiating the cell selection and cell reselection processes.

[0090] Network nodes can also use different modes to send redirection information. Several possibilities are described below, although none of the proposed modes are mandatory.

[0091] According to the first transmission mode, the broadcast message can be provided through a system information block (e.g., SIB2, SIB4, or SIB5). Since the information in some scenarios may be sensitive from a pure security perspective, one possible mode is that the SIB should be encrypted using a security key, which can be a public key that can be calculated by an inactive / idle UE and by the node responsible for broadcasting the message.

[0092] In another alternative version, the redirection information can be sent in an aggregated message of new information elements IE in one of the SIBs or in a new SIB defined for and dedicated to this purpose.

[0093] The alternative methods disclosed herein have been described in detail. Hereinafter, we describe the devices that can utilize the proposed methods. All the advantages associated with the corresponding methods mentioned are equally valid for the devices to be described and will not be repeated.

[0094] According to a specific aspect of the proposed technology, a user equipment UE 10 configured to operate in a wireless communication system is provided. The UE includes a communication circuit 100 configured to obtain broadcast system information including redirection information. The UE further includes a processing circuit 110 configured to perform a cell selection or cell reselection process based on the obtained broadcast information.

[0095] As used herein, the non - limiting term "user equipment (UE)" may refer to a mobile phone, cellular phone, personal digital assistant (PDA) equipped with radio communication capabilities, smart phone, laptop computer or personal computer (PC) equipped with an internal or external mobile broadband modem, tablet computer with radio communication capabilities, target device, machine - to - machine (M2M) device, machine - type communication (MTC) device, Internet of Things (IoT) device, device - to - device (D2D) UE, machine - type UE or UE capable of machine - to - machine communication, customer premise equipment (CPE), laptop embedded device (LEE), laptop - mounted device (LME), USB dongle, portable electronic radio communication device, and / or sensor device, meter, vehicle, household appliance, medical device, camera, television, radio, lighting device, etc. equipped with wireless communication capabilities. Specifically, the term UE should be construed as a non - limiting term that includes any type of wireless device that communicates with a network node in a wireless communication system and / or any type of wireless device that may communicate directly with another wireless communication device. In other words, a wireless communication device can be any device equipped with circuitry for wireless communication according to any relevant communication standard.

[0096] According to a particular embodiment of the proposed technology, a user equipment UE 10 is provided, wherein the processing circuit 110 is configured to perform a cell selection or cell reselection process based on a predetermined criterion to be satisfied by redirection information.

[0097] According to another embodiment of the proposed technology, a user equipment UE 10 is provided, wherein the processing circuit 110 is configured to initiate a cell selection or cell reselection process during a connection recovery process when the UE 10 is in an inactive state or during a connection establishment process when the UE 10 is in an idle state.

[0098] According to yet another embodiment of the proposed technology, a user equipment UE10 is provided, wherein the processing circuit 110 is configured to initiate a cell selection or cell reselection process during a connection recovery process and is configured to perform a cell selection or cell reselection process in the following cases:

[0099] - If the recovery reason of a possible connection recovery process is included in the redirection information; and / or

[0100] - If the access category of a possible connection recovery process is included in the redirection information.

[0101] According to yet another embodiment of the proposed technology, a user equipment UE 10 is provided, wherein the communication circuit 100 is configured to obtain broadcast information that further includes a mapping between the recovery reason and / or access category and at least one of the following:

[0102] - Redirection to a target radio access technology, i.e., target RAT;

[0103] - Redirection to a target serving cell; and

[0104] - Redirection to a target frequency.

[0105] For example, the proposed technique provides a user equipment UE 10, wherein the processing circuit 110 is configured to initiate a cell selection or cell reselection process during a connection establishment procedure, and is configured to perform the cell selection or cell reselection process when:

[0106] - If the establishment cause of a possible connection establishment procedure is included in the redirection information; and / or

[0107] - If the access category of a possible connection establishment procedure is included in the redirection information.

[0108] An alternative embodiment of the proposed technique provides a user equipment UE10, wherein the communication circuit 100 is configured to obtain broadcast information, which also includes a mapping between the establishment cause and / or access category and at least one of the following:

[0109] - Redirection to a target radio access technology, i.e., target RAT;

[0110] - Redirection to a target serving cell; and

[0111] - Redirection to a target frequency.

[0112] A specific embodiment of the proposed technique provides a user equipment UE 10, wherein the communication circuit 110 is configured to obtain redirection information included in a broadcast system information block SIB.

[0113] A specific version of the above embodiment provides a user equipment UE 10, wherein the redirection information is included in an information element added to an existing SIB.

[0114] According to another aspect of the proposed technique, there is provided a network node 20, which is configured to: serve a user equipment UE 10 in a wireless communication network. The network node includes a communication circuit 200, which is configured to broadcast information, and the information includes redirection information that enables the UE to perform a cell selection or cell reselection process.

[0115] As used herein, the non-limiting term "network node" may refer to a base station, an access point, a network control node, etc., such as a network controller, a radio network controller, a base station controller, an access controller, etc. Specifically, the term "base station" may include different types of radio base stations (which include standard base station functions, such as Node B or evolved Node B (eNB), gNodeB), and may also include macro / micro / pico radio base stations, home base stations (also known as femto base stations), relay nodes, repeaters, radio access points, base transceiver stations (BTS), and even radio control nodes that control one or more remote radio units (RRUs), etc.

[0116] A particular embodiment of the proposed technology provides a network node 20, wherein the redirection information includes at least one of the following:

[0117] · A recovery reason for a possible connection recovery procedure for UE 10,

[0118] · An access category for a possible connection recovery procedure for UE 10,

[0119] · A setup reason for a possible connection setup procedure for UE10, and

[0120] · An access category for a possible connection setup procedure for UE10.

[0121] Another particular embodiment of the proposed technology provides a network node 20, wherein the redirection information further includes a mapping between the recovery reason, the setup reason, and / or the access category and at least one of the following:

[0122] · A redirection to a target radio access technology, i.e., a target RAT,

[0123] · A redirection to a target serving cell, and

[0124] · A redirection to a target frequency.

[0125] Yet another particular embodiment of the proposed technology provides a network node 20, wherein the communication circuit 200 is configured to broadcast information that includes the redirection information in a system information block SIB.

[0126] A particular version of the above embodiment provides a network node 20, wherein the redirection information is included in an information element added to an existing SIB.

[0127] It should be understood that the methods and apparatuses described herein can be implemented, combined, and rearranged in various ways.

[0128] For example, an embodiment may be implemented in hardware, or in software executed by appropriate processing circuitry, or a combination thereof.

[0129] The steps, functions, processes, modules, and / or blocks described herein can be implemented in hardware using any conventional techniques, such as using discrete circuit or integrated circuit technology, including both general-purpose electronic circuits and application-specific circuits.

[0130] Alternatively, at least some of the steps, functions, processes, modules, and / or blocks described herein can be implemented in software, such as a computer program run by a suitable processing circuitry (e.g., one or more processors or processing units).

[0131] Examples of processing circuitry include, but are not limited to: one or more microprocessors, one or more digital signal processors (DSPs), one or more central processing units (CPUs), video acceleration hardware, and / or any suitable programmable logic circuitry, such as one or more field-programmable gate arrays (FPGAs) or one or more programmable logic controllers (PLCs).

[0132] It should also be understood that the general processing capabilities of any conventional device or unit implementing the proposed technology can be reused. For example, existing software can also be reused by reprogramming the existing software or by adding new software components.

[0133] Figure 4 FIG. is a schematic block diagram showing an example of a UE / network node 10; 20 based on a processor-memory implementation according to an embodiment. In this particular example, the UE / network node 10; 20 includes a processor 110; 210 and a memory 120; 220, and the memory 120; 200 includes instructions executable by the processor 110; 210, whereby the processor operably controls the UE / network node 10; 20. The UE / network node 10; 20 also includes a communication circuit 130; 230. The communication circuit 130; 230 may include functions for wired and / or wireless communication with other devices and / or network nodes in the network. In a specific example, the communication circuit 130; 230 may be based on radio circuitry for communicating with one or more other nodes (including sending and / or receiving information). The communication circuit 130; 230 may be interconnected with the processor 110; 210 and / or the memory 120; 220. The communication circuit 130; 230 may be interconnected with hardware circuitry and / or REG / MEM. By way of example, the communication circuit 130; 230 may include any one of the following: a receiver, a transmitter, a transceiver, an input / output (I / O) circuit, an input port, and / or an output port.

[0134] Figure 5FIG. 0 is a schematic block diagram showing another example of a UE / network node 10; 20 implemented based on a hardware circuit according to an embodiment. Specific examples of suitable hardware circuits 110; 210 include: one or more appropriately configured or possibly reconfigurable electronic circuits (e.g., application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs)) or any other hardware logic, such as circuits based on interconnected discrete logic gates and / or flip-flops for performing dedicated functions together with suitable registers (REG) and / or memory units (MEM) 120; 220.

[0135] Solutions can also be provided based on a combination of hardware and software. The actual hardware-software partitioning can be determined by the system designer based on numerous factors, including processing speed, implementation cost, and other requirements.

[0136] Thus, a processing circuit including one or more processors is configured to: perform well-defined processing tasks such as those described herein when running a computer program. The processing circuit does not have to be dedicated to only performing the above steps, functions, processes, and / or blocks, but can also perform other tasks.

[0137] The proposed technology also provides computer programs 125; 135 for controlling a user equipment in a wireless communication network. The computer program includes instructions that, when executed by at least one processor, cause the at least one processor to read the acquired broadcast information including redirection information and initiate a cell selection or cell reselection process based on the read acquired broadcast information.

[0138] The proposed technology also provides a computer program product including a computer-readable medium 330 in which the computer programs 125; 135 of the above aspects are carried or stored.

[0139] The proposed technology also provides computer programs 225; 235 for controlling a network node 20 that serves a user equipment UE 10 in a wireless communication network. The computer program includes instructions that, when executed by at least one processor, cause the at least one processor to initiate a broadcast of information including redirection information that enables the UE to perform a cell selection or cell reselection process.

[0140] The proposed technology also provides a computer program product including a computer-readable medium 330 in which the computer programs 225; 235 of the above aspects are carried or stored.

[0141] By way of example, the above software or computer program can be implemented as a computer program product 330, which is typically carried or stored on a computer-readable medium (specifically, a non-volatile medium). The computer-readable medium can include one or more removable or non-removable storage devices, including (but not limited to): read-only memory (ROM), random access memory (RAM), compact disc (CD), digital versatile disc (DVD), Blu-ray disc, universal serial bus (USB) memory, hard disk drive (HDD) storage device, flash memory, magnetic tape, or any other conventional storage device. The computer program can thus be loaded into the operating memory of a computer or equivalent processing device for execution by its processing circuitry.

[0142] The proposed technology also provides a carrier comprising any one of the computer programs described above, wherein the carrier is one of an electrical signal, an optical signal, an electromagnetic signal, a magnetic signal, an electronic signal, a radio signal, a microwave signal, or a computer-readable storage medium.

[0143] Figure 6 is a schematic diagram showing an example of a computer implementation according to an embodiment. In this particular example, at least some of the steps, functions, processes, modules, and / or blocks described herein are implemented as computer programs 125; 135; 225; 235, which are loaded into memories 120; 220 for execution by a processing circuitry including one or more processors 110; 210. The processors 110; 210 and the memories 120; 200 are interconnected with each other to enable normal software execution. Optional input / output devices 140; 240 can also be interconnected with the processors 110; 210 and / or the memories 120; 200 to enable the input and / or output of relevant data (such as input parameters and / or resulting input parameters).

[0144] The term "processor" should be construed in a general sense as any system or device capable of executing program code or computer program instructions to perform a specific processing, determination, or computational task.

[0145] Thus, a processing circuitry including one or more processors is configured to: perform well-defined processing tasks such as those described herein when running a computer program. The processing circuitry does not have to be dedicated to only executing the above steps, functions, processes, and / or blocks, but can also perform other tasks.

[0146] Appendix

[0147] In this appendix, we provide some information about the general procedure during cell redirection of the UE. Additional information can be found in section 5.2.4.2 of technical specification TS 38.331 of 3GPP and section 5.2 of technical specification TS 38.304 of 3GPP.

[0148] As mentioned in the background art, cell redirection is typically controlled by using certain parameters via the MIB and SIBs. The specific SIBs and parameters depend on the relevant RAT. We will describe this below.

[0149] In NR, the threshold parameters available in different SIBs are as follows:

[0150] - SIB1 contains information on whether the UE can access the cell and scheduling information for other SIBs, as well as configuration information common to all UEs. Therefore, the threshold parameters in SIB1 are related to the serving cell and specify the conditions for allowing the UE to camp on that cell. Some of the relevant parameters are: RRC - q-RxLevMin, which is the parameter specifying the minimum signal level required in the cell (referred to as RSRP).

[0151] - q-RxLevMinOffset, which specifies the offset relative to q-RxLevMin (i.e., the RSRP threshold). This parameter is optional but is typically used to achieve better cell selection decisions.

[0152] - q-QualMin, which is the parameter specifying the minimum quality level required in the cell (referred to as RSRQ).

[0153] - q-QualMinOffset, which is the offset relative to q-QualMin.

[0154] - connEstFailOffset, which is used to configure the parameter for connection establishment failure control. Below, it is referred to as Qoffsettemp.

[0155] The specific system information block called SIB2 contains cell reselection information common to intra-frequency, inter-frequency, and / or inter-RAT cell reselection. Some of the parameters related to common terms are as follows:

[0156] - q-Hyst: The signal level of the neighboring cell is reduced by this hysteresis value to avoid ping-pong effects.

[0157] - q-Hyst: The signal level of the neighboring cell is reduced by this hysteresis value to avoid ping-pong effects. That is, avoid sending the UE back and forth between serving cells.

[0158] -s-NonIntraSearchP, which is the threshold Srxlev value of the serving cell and is used to determine whether the UE should search for a new cell.

[0159] -s-NonIntraSearchQ, which is the threshold Squal value of the serving cell and is used to determine whether the UE should search for a new cell.

[0160] -q-RxLevMin, which is the minimum signal level of an adjacent cell.

[0161] -q-QualMin, which specifies the minimum quality level (in dB) required in the cell for co-frequency adjacent cells.

[0162] -s-IntraSearchP, which indicates the receiver level threshold, i.e., the Rx level threshold. The UE performs co-frequency measurements only when the SrxLev of the serving cell is less than or equal to s-IntraSearchP.

[0163] -s-IntraSearchQ, which indicates the quality level threshold. The UE performs co-frequency measurements only when the Squal of the serving cell is less than or equal to s-IntraSearchQ.

[0164] -t-ReselectionNR, which is the time required to meet the threshold conditions before reselection can be completed.

[0165] -p-Max, which is the maximum power from the UE and is used to calculate Pcompensation used below.

[0166] -threshServingLowP, which is the Srlev threshold (given in decibels (dB)) used by the UE on the serving cell when reselecting to a lower priority RAT / frequency.

[0167] -threshServingLowQ, which is the Squal threshold used by the UE on the serving cell when reselecting to a lower priority RAT / frequency.

[0168] The specific system information block called SIB3 contains information related only to co-frequency cell reselection. The threshold parameters related to common terms are as follows:

[0169] -intraFreqNeighCellList, a list of co-frequency adjacent cells with specific cell reselection parameters given below:

[0170] -physCellId, which represents the physical cell ID of an adjacent cell.

[0171] -q-OffsetCell, which represents a specific Rx offset between the serving cell and an adjacent cell.

[0172] -q-RxLevMinOffsetCell, which represents a cell-specific Rx level offset (in dB) relative to Qrxlevmin.

[0173] -q-QualMinOffsetCell, which represents a cell-specific quality level offset (in dB) relative to Qqualmin.

[0174] The specific system information block called SIB4 contains information related only to inter-frequency cell reselection. This means that each parameter set can be used for the corresponding adjacent frequency band. The relevant threshold parameters are:

[0175] -q-RxLevMin, which represents the minimum signal level of an adjacent cell.

[0176] -q-QualMin, which represents the minimum quality level of an adjacent cell.

[0177] -p-Max, which is the maximum power from the UE and is used to calculate Pcompensation used below.

[0178] -t-ReselectionNR, which represents the time interval for evaluating reselection criteria before reselection can be completed.

[0179] -qOffsetFreq, which represents the offset of equal-priority NR frequencies.

[0180] -q-RxLevMinOffsetCell, which represents a cell-specific Rx level offset (in dB) relative to q-RxLevMin.

[0181] -threshX-HighP, which represents the Srxlev threshold (in dB) used by the UE when reselecting to a frequency with a higher priority than the current serving frequency. Each frequency of NR may have a specific threshold.

[0182] -threshX-LowP, which represents the Srxlev threshold (in dB) used by the UE when reselecting to a frequency with a lower priority than the current serving frequency. Each frequency of NR may have a specific threshold.

[0183] The specific system information block called SIB5 contains information related only to E-UTRA frequency and inter-RAT cell reselection information for neighboring cells. The threshold levels in SIB5 are unique for each E-UTRA frequency. The relevant parameters are:

[0184] -t-ReselectionEUTRA

[0185] -q-RxLevMin

[0186] -q-QualMin

[0187] -p-MaxEUTRA, which is the maximum power from the UE and is used to calculate Pcompensation used in the following part.

[0188] -q-RxLevMinOffsetCell, which represents the cell-specific Rx level offset (in dB) relative to q-RxLevMin.

[0189] -threshX-HighP, which represents the Srxlev threshold (in dB) used by the UE when reselecting to a RAT with a higher priority than the current serving frequency. Each frequency of E-UTRAN may have a specific threshold.

[0190] -threshX-LowP, which represents the Srxlev threshold (in dB) used by the UE when reselecting to a RAT with a lower priority than the current serving frequency. Each frequency of E-UTRAN may have a specific threshold.

[0191] In LTE, the equivalent parameters are arranged in the SIBs in a similar way. In this scenario, the parameters in SIB1, SIB3, SIB5, and SIB24 are of interest.

[0192] SIB1 contains information relevant when evaluating whether to allow the UE to access the cell and defines the scheduling of other system information, i.e., it contains threshold parameters equivalent to SIB1 in NR.

[0193] The relevant threshold parameters are:

[0194] -q-RxLevMin

[0195] -q-RxLevMinOffset

[0196] -p-Max

[0197] -a-QualMin-r9

[0198] -q-QualMinOffset-r9

[0199] SIB3 then contains cell reselection information that is common for intra-frequency, inter-frequency and / or inter-RAT cell reselection (i.e., applicable to more than one type of cell reselection but not necessarily to all cell reselections), and intra-frequency cell reselection information other than the intra-frequency cell reselection information related to neighboring cells, i.e., it contains threshold parameters equivalent to those in SIB2 in NR. The relevant threshold parameters are:

[0200] -q-Hyst

[0201] -s-NonIntraSearch / s-NonIntraSearchP-r9

[0202] -s-NonIntraSearchQ-r9

[0203] -q-RxLevMin

[0204] -q-QualMin-r9

[0205] -s-IntraSearch / s-IntraSerachP-r9

[0206] -s-IntraSearchQ-r9

[0207] -t-ReselectionEUTRA

[0208] -p-Max

[0209] -threshServingLow.

[0210] The specific system information block called SIB5 contains information related only to inter-frequency cell reselection. That is, information about other EUTRA frequencies and inter-frequency neighboring cells related to cell reselection. This IE It includes cell reselection parameters common for a frequency and cell-specific reselection parameters, i.e., it contains threshold parameters equivalent to those in SIB4 in NR. The relevant threshold parameters are:

[0211] -q-RxLevMin

[0212] -q-QualMin-r9

[0213] -p-Max

[0214] -t-ReselectionEUTRA

[0215] -qOffsetFreq

[0216] -threshX-High

[0217] -threshX-Low

[0218] A specific system information block called SIB24 contains information related only to inter-RAT cell reselection, i.e., information about NR frequencies and NR neighboring cells related to cell reselection. That is, it contains threshold parameters equivalent to SIB5 in NR. The relevant threshold parameters are:

[0219] -t-ReselectionNR-r15

[0220] -q-RxLevMin-r15

[0221] -p-MaxNR-r15

[0222] -q-QualMin-r15

[0223] -threshX-High-r15

[0224] -threshX-Low-r15

[0225] Having introduced the relevant parameters, we continue and describe the various scenarios in which these parameters are used. To this end, we first describe the mobility management in the idle mode RRC_IDLE. For a UE in RRC_IDLE, mobility is handled via the cell selection / reselection process. The UE wakes up only once in each DRX cycle to monitor the paging messages of the network and perform measurements related to the reference signal received power RSRP and the reference signal received quality RSRQ for the serving cell, and if necessary, perform measurements on some other target cells in order to be able to decide whether it can still camp on the serving cell or whether it needs to find a better cell. As briefly explained above, the network NW indicates to the UE via the parameter sets incorporated in the MIB and SIBs by broadcast how to quantify the serving cell measurements and the other target cell measurements. More specifically, for each cell, the received RSRP level represented by Srxlev and the received RSRQ level represented by Squal are calculated using the following formulas:

[0226] Srxlev = Qrxlevmeas - (Qrxlevmin + Qrxlevminoffset) - Pcompensation - Qoffsettemp Squal = Qqualmeas - (Qqualmin + Qqualminoffset) - Qoffsettemp,

[0227] Among them, Qrxlevmeas and Qqualmeas are the cell RSRP and RSRQ measurements performed by the UE, and among them, other parameters are provided to the UE via system information. In NR, the serving cell parameters are broadcast in SIB1, the same-frequency parameters are broadcast in SIB2, the different-frequency parameters are broadcast in SIB4, and the different RAT parameters are broadcast in SIB5. The following table shows the detailed descriptions of Qrxlevmin, Qqualmin, Qrxlevminoffsetcell, and Qqualvminoffsetcell defined in Technical Specification TS 38.304.

[0228]

[0229]

[0230]

[0231] The parameter Qrxlevminoffsetcell specifies the cell-specific Rx level offset and the cell-specific quality level offset.

[0232] Srxlev The cell selection RX level value, in dB.

[0233] Squal The cell selection quality value, in dB.

[0234] Qoffsettemp The offset applied to the cell temporarily, in dB.

[0235] Qrxlevmeas The measured cell RX level value RSRP.

[0236] Qqualmeas The measured cell quality value RSRQ.

[0237] Qrxlevminoffset: The offset relative to the signaled Qrxlevmin considered in the Srxlev evaluation as a result of periodically searching for higher-priority PLMNs while normally camped on the VPLMN.

[0238] Qqualminoffset: The offset relative to the signaled Qqualmin considered in the Squal evaluation as a result of periodically searching for higher-priority PLMNs while normally camped on the VPLMN.

[0239] Pcompensation:

[0240] In the case where the UE supports additionalPmax in the NS-PmaxList in SIB1:

[0241] max(Pmax - PPowerClass, 0) - (min(PAdditionalPmax, PPowerClass) - min(Pmax, PPowerClass));

[0242] In other cases:

[0243] max(Pmax - PPowerClass, 0) (dB).

[0244] Qrxlevmin The minimum required RX level in the cell, in dBm.

[0245] Qrxlevmin is obtained from q-RxLevMin in SIB1, SIB2, and SIB4. Additionally, if there is a Qrxlevminoffsetcell for the relevant cell in SIB3, SIB4, and SIB5, the cell-specific offset is added to the corresponding Qrxlevmin to obtain the minimum required RX level in the relevant cell.

[0246] Qqualmin The minimum required quality level in the cell, in dB. Additionally, if the Qqualminoffsetcell for the relevant cell is signaled, the cell-specific offset is added to obtain the minimum required quality level in the relevant cell.

[0247] Qrxlevminoffsetcell This specifies the cell-specific Rx level offset relative to Qrxlevmin, in dB.

[0248] Qqualvminoffsetcell This specifies the cell-specific quality level offset relative to Qqualmin, in dB. In Technical Specification 38.331, this is q-QualMinOffsetCell in SIB3, SIB4, and SIB5.

[0249] Qoffset For co-frequency, Qoffset has a valid value of <>0 dB.

[0250] -Qoffset = 0 dB.

[0251] For inter-frequency with equal priority:

[0252] -Qoffset + Qoffsetfrequency, if Qoffset has a valid value of <>0 dB.

[0253] -Qoffsetfrequency.

[0254] -Qhyst hysteresis parameter.

[0255] A cell is considered a suitable cell for UE to camp on when at least the following cell selection criteria are met: Srxlev > 0; Squal > 0.

[0256] The UE needs to perform measurements on higher priority inter-frequency and inter-RAT frequencies. The UE performs cell reselection to an inter-frequency or inter-RAT frequency cell according to criteria based on absolute priority. For intra-frequency and equal priority inter-frequency cell reselection, it is based on the cell ranking criteria defined in TS 38.304 and the criteria based on the number of good beams. The UE ranks the cells that meet the cell selection criteria.

[0257] To limit UE measurements on different target cells, the following rules are applied:

[0258] · If the UE measurements on the serving cell satisfy Srxlev > SIntraSearchP and Squal > SIntraSearchQ, the UE does not need to perform measurements on any intra-frequency cells.

[0259] · If the measurements on the serving cell satisfy Srxlev > SnonIntraSearchP and Squal > SnonIntraSearchQ, the UE does not need to perform measurements on any inter-frequency or inter-RAT cells.

[0260] · If Srxlev < SIntraSearchP or Squal < SIntraSearchQ, the UE performs intra-frequency cell measurements and ranking according to Section 5.2.4.6 of TS 38.331, and if the reselection criteria are met during the time interval TreselectionRAT, it reselects to the highest priority cell. If Srxlev < SnonIntraSearchP or Squal < SnonIntraSearchQ, the UE only performs inter-frequency and / or inter-RAT measurements on the cells indicated in the system information and for which the UE has a provided priority, as described in Section 5.2.4.2 of TS 38.331.

[0261] Now we continue and describe the specific cell reselection priorities. In NR, an idle or inactive UE camped on a cell can receive them (e.g., common for intra-frequency / inter-frequency in SIB2 in NR, for inter-frequency in SIB4, and for inter-Rat in SIB5 in NR) via system information. The absolute priorities of different NR frequencies or inter-RAT frequencies can be provided to the UE in the following ways: in system information, in the RRCRelease message, or inherited from another RAT in the case of inter-RAT cell selection or reselection. In the case of system information, the NR frequencies or inter-RAT frequencies can be listed without providing priorities, i.e., there is no field cellReselectionPriority for that frequency.

[0262] The IE CellReselectionPriority relates to the absolute priority of the associated carrier frequency, such as the absolute priority of the carrier frequency used in the cell reselection process. Corresponds to the parameter "priority" in TS38.304

[20] . A value of 0 represents the lowest priority. The UE behavior in the case where this field does not exist is specified in TS 38.304 (if applicable).

[0263] CellReselectionPriority information element (IE)

[0264] --ASN1START

[0265] --TAG-CELLRESELECTIONPRIORITY-START

[0266] CellReselectionPriority ::= INTEGER(0..7)

[0267] --TAG-CELLRESELECTIONPRIORITY-STOP

[0268] --ASN1STOP

[0269] Also, according to TS 38.304, via system information, the priority indication for each frequency (intra-RAT or inter-RAT) can be configured for the UE. First, the UE performs cell reselection evaluations only for the NR frequencies and inter-RAT frequencies that are given in the system information and for which the UE has a provided priority.

[0270] 2.1.3.1 Intra-frequency reselection

[0271] If the network is using a single carrier frequency, intra-frequency reselection shall be performed under the following conditions. The UE camps on the serving cell as long as the following conditions are met:

[0272] · Srxlev > SIntraSearchP, the RSRP of adjacent measurement is not lower than the threshold value

[0273] · Squal > SIntraSearchQ, the RSRQ of adjacent measurement is not lower than the threshold value.

[0274] Among them,

[0275] · The SIntraSearchP parameter is the threshold value announced by the serving cell as part of SIB2, i.e., the s-IntraSearchP IE.

[0276] · The SIntraSearchQ parameter is the threshold value announced by the serving cell as part of SIB2, i.e., the s-IntraSearchQ IE.

[0277] · Srxlev = Qrxlevmeas - (Qrxlevmin + Qrxlevminoffset) - Pcompensation - Qoffsettemp

[0278] · Squal = Qqualmeas - (Qqualmin + Qqualminoffset) - Qoffsettemp

[0279] When the above conditions are not met, the UE switches to the cell with the best rank under the following conditions:

[0280] · The UE must have camped on the serving cell for at least 1 second.

[0281] · During the time interval t-ReselectionNR, the new cell must have a better rank than the serving cell.

[0282] For cells that meet the cell selection criteria Srxlev > 0 and Squal > 0, if it is the serving cell, it is ranked to Rs, and if it is an adjacent cell, it is ranked to Rn, which are defined as follows:

[0283] · Rs = Qmeas,s + Qhyst

[0284] · Rn = Qmeas,n - Qoffset.

[0285] Now we continue and describe the inter-frequency reselection. If the network uses more than one carrier frequency, the serving cell announces other carriers as part of SIB4. If another carrier is involved, the priority of this frequency compared to the serving frequency will be considered.

[0286] The UE shall perform measurements on NR inter-frequency cells with a reselection priority equal to, higher than, or lower than that of the serving NR frequency under the following conditions:

[0287] Srxlev < SnonIntraSearchP or Squal < SnonIntraSearchQ

[0288] Wherein,

[0289] · The SnonIntraSearchP parameter is the threshold value that the serving cell advertises as part of SIB2, i.e., the s-NonIntraSearchP IE.

[0290] · The SnonIntraSearchQ parameter is the threshold value that the serving cell advertises as part of SIB2, i.e., the s-NonIntraSearchQ IE.

[0291] Next, we will describe the mechanism for reselection to equal priority. Reselection to an NR frequency with the same priority as the serving cell is based on the ranking for intra-frequency cell reselection.

[0292] First, consider the case of reselection to a higher priority. Reselection to an NR frequency with a higher priority than the serving cell is performed under the following conditions:

[0293] · The UE must have camped on the serving cell for at least 1 second.

[0294] · The new cell satisfies: in the case where threshServingLowQ has been broadcast in SIB2, Squal > ThreshX, HighQ condition during the time interval L-ReselectionNR.

[0295] · The new cell satisfies: in the case where threshServingLowQ has not been broadcast in SIB2, Srxlev > ThreshX, HighP condition during the time interval t-ReselectionNR.

[0296] Wherein,

[0297] · ThreshServingLowQ and t-ReselectionNR are advertised in SIB2.

[0298] · ThreshX, HighQ and ThreshX, HighP are advertised in SIB4.

[0299] Now, instead, consider reselection to a lower priority. Reselection to an NR frequency with a lower priority than the serving cell is performed under the following conditions:

[0300] · The UE must have camped on the serving cell for at least 1 second.

[0301] · The new cell meets the LowQ condition that during the time interval t-ReselectionNR, Squal > ThreshX, when threshServingLowQ has been broadcast in SIB2 and Squal < ThreshServingLowQ.

[0302] · The new cell meets the LowP condition that during the time interval t-ReselectionNR, Squal > ThreshX, when threshServingLowQ has been broadcast in SIB2 and Srxlev < ThreshServingLowP.

[0303] Where,

[0304] · ThreshServingLowQ, ThreshServingLowP, and t-ReselectionNR are advertised in SIB2.

[0305] · ThreshX,LowQ and ThreshX,LowP are advertised in SIB4.

[0306] In this case, the UE cannot find a cell with an equal or higher priority NR frequency to which it can reselect.

[0307] Next, we describe inter-RAT frequency reselection. The UE shall perform measurements on inter-RAT frequencies with a reselection priority higher or lower than that of the serving NR frequency under the following conditions:

[0308] Srxlev < SnonIntraSearchP or Squal < SnonIntraSearchQ

[0309] Where,

[0310] · The SnonIntraSearchP parameter is the threshold that the serving cell advertises as part of SIB2, i.e., the s-NonIntraSearchP IE.

[0311] · The SnonIntraSearchQ parameter is the threshold that the serving cell advertises as part of SIB2, i.e., the s-NonIntraSearchQ IE.

[0312] Re-selection to an equal priority scenario between RATs is not supported. This means that there is no equal priority between the NR frequency in the serving cell and the EUTRA frequency in the neighboring cell. Re-selection to a higher priority (i.e., higher than the serving cell) EUTRA frequency is performed under the following conditions:

[0313] · The UE must have camped on the serving cell for at least 1 second.

[0314] · The new cell satisfies: when threshServingLowQ has been broadcast in SIB2, Squal > ThreshX,HighQ condition is satisfied during the time interval t-ReselectionEUTRA.

[0315] · The new cell satisfies: when threshServingLowQ has not been broadcast in SIB2, Srxlev > ThreshX,HighP condition is satisfied during the time interval t-ReselectionEUTRA.

[0316] Where,

[0317] · ThreshServingLowQ is advertised in SIB2.

[0318] · t-ReselectionEUTRA, ThreshX,HighQ and ThreshX,HighP are advertised in SIB5.

[0319] Re-selection to a lower priority (i.e., lower than the serving cell) EUTRA frequency is performed under the following conditions:

[0320] · The UE must have camped on the serving cell for at least 1 second.

[0321] · The new cell satisfies: when threshServingLowQ has been broadcast in SIB2 and Squal < ThreshServingLowQ, Squal > ThreshX,LowQ condition is satisfied during the time interval t-ReselectionEUTRA.

[0322] · The new cell satisfies: when threshServingLowQ has not been broadcast in SIB2 and Srxlev < ThreshServingLowP, Srxlev > ThreshX,LowP condition is satisfied during the time interval t-ReselectionEUTRA.

[0323] Where,

[0324] ·ThreshServingLowQ and ThreshServingLowP are advertised in SIB2.

[0325] ·t-ReselectionEUTRA, ThreshX, LowP and ThreshX, LowQ are advertised in SIB5.

[0326] In this section, we will describe the mechanism behind release with redirection. In LTE, the release and redirection features are used to release an RRC_CONNECTED UE to RRC_IDLE and redirect it to another frequency, whether in the same RAT or not.

[0327] The message of the RRC connection release type may include release cause information, redirection carrier frequency, and idle mode mobility control information.

[0328] In LTE, NR, and other mobile networks, system information is broadcast in the Master Information Block (MIB) and different System Information Blocks (SIBs). The MIB includes a limited number of the most important and frequently transmitted parameters (which are required to obtain other information from the cell) and is transmitted on the BCH in the idle mode. A UE in the idle mode (RRC_IDLE) reads the system information from the MIB and SIBs to know how to move between different cells, i.e., how to perform cell selection / reselection. The parameters read by the UE are related to, for example, the identification of the network and the cell, cell blocking, signal level thresholds, quality level thresholds, frequency channels, and priorities.

[0329] In NR, the threshold parameters available in different SIBs are as follows:

[0330] ·SIB1 contains information on whether the UE can access the cell, scheduling information for other SIBs, and RRC configuration information common to all UEs. Therefore, the threshold parameters in SIB1 are related to the serving cell and the situations in which the UE can camp on that serving cell.

[0331] The relevant parameters are:

[0332] -q-RxLevMin, which specifies the minimum required signal level (RSRP) in the cell.

[0333] -q-RxLevMinOffset, which is an offset relative to q-RxLevMin (RSRP threshold). It is optional but is used to make a better cell selection decision (it is added to the serving cell signal level value).

[0334] -q-QualMin, which specifies the minimum required quality level in the cell, i.e., the RSRQ level.

[0335] -q-QualMinOffset, which is the offset relative to q-QualMin.

[0336] -connEstFailOffset, which is used to configure the parameters for connection establishment failure control. In the following sections, it is referred to as Qoffsettemp.

[0337] ·SIB2 contains cell reselection information common to intra-frequency, inter-frequency, and / or inter-RAT cell reselection (excluding intra-frequency cell reselection related to neighboring cells). The relevant parameters are:

[0338] -q-Hyst: The signal level of the neighboring cell is reduced by this hysteresis value to avoid ping-pong effects.

[0339] -s-NonIntraSearchP, which is the threshold Srxlev value of the serving cell to determine whether the UE should search for new cells.

[0340] -s-NonIntraSearchQ, which is the threshold Squal value of the serving cell to determine whether the UE should search for new cells.

[0341] -q-RxLevMin, which is the lowest signal level of the neighboring cell.

[0342] -q-QualMin, which specifies the lowest quality level (in dB) required in the cell for intra-frequency neighboring cells.

[0343] -s-IntraSearchP, which indicates the Rx level threshold. The UE performs intra-frequency measurements only when SrxLev of the serving cell <= SintraSearch.

[0344] -s-IntraSearchQ, which indicates the quality level threshold. The UE performs intra-frequency measurements only when Squal of the serving cell <= SintraSearchQ.

[0345] -t-ReselectionNR, which is the time required to meet the threshold conditions before reselection can be completed.

[0346] -p-Max, which is the maximum power from the UE and is used to calculate Pcompensation used in the following sections.

[0347] -threshServingLowP, which is the Srlev threshold (in dB) used by the UE on the serving cell when reselecting to a lower priority RAT / frequency (ThreshServing, LowP in 38.304).

[0348] -threshServingLowQ, which is the Squal threshold used by the UE on the serving cell when reselecting to a lower priority RAT / frequency (ThreshServing, LowQ in 38.304).

[0349] SIB3 contains information related only to intra-frequency cell reselection. The relevant threshold parameters are:

[0350] -intraFreqNeighCellList, a list of the sizes (1... maxCellIntra) of intra-frequency neighboring cells with specific cell reselection parameters:

[0351] -physCellId, which represents the physical cell ID of the neighboring cell

[0352] -q-OffsetCell (Qoffsets, n in 38.304), which represents a specific Rx offset between the serving cell and the neighboring cell

[0353] -q-RxLevMinOffsetCell (Qrxlevminoffsetcell in 38.304), which represents the cell-specific Rx level offset (in dB) relative to Qrxlevmin

[0354] -q-QualMinOffsetCell (Qqualminoffsetcell in 38.304), which represents the cell-specific quality level offset (in dB) relative to Qqualmin.

[0355] SIB4 contains information related only to inter-frequency cell reselection. This means that each parameter set can be used for the corresponding neighboring frequency band. The relevant threshold parameters are:

[0356] -q-RxLevMin, which represents the lowest signal level of the neighboring cell.

[0357] -q-QualMin, which represents the lowest quality level of the neighboring cell.

[0358] -p-Max, which is the maximum power from the UE and is used to calculate Pcompensation used in the following part.

[0359] -t-ReselectionNR, which represents the time interval for evaluating reselection criteria before reselection can be completed.

[0360] -qOffsetFreq, which represents the offset of equal priority NR frequencies.

[0361] -q-RxLevMinOffsetCell, which represents the cell-specific Rx level offset (in dB) relative to q-RxLevMin.

[0362] -threshX-HighP, which represents the Srxlev threshold (in dB) used by the UE when reselecting to a frequency with a higher priority than the current serving frequency. Each frequency of NR may have a specific threshold.

[0363] -threshX-LowP, which represents the Srxlev threshold (in dB) used by the UE when reselecting to a frequency with a lower priority than the current serving frequency. Each frequency of NR may have a specific threshold.

[0364] SIB5 contains information related only to inter-RAT cell reselection information regarding E-UTRA frequencies and neighboring cells. The threshold levels in SIB5 are unique for each E-UTRA frequency. The relevant parameters are:

[0365] -t-ReselectionEUTRA

[0366] -q-RxLevMin

[0367] -q-QualMin

[0368] -p-MaxEUTRA, which is the maximum power from the UE and is used to calculate Pcompensation used in the following sections.

[0369] -q-RxLevMinOffsetCell, which represents the cell-specific Rx level offset (in dB) relative to q-RxLevMin.

[0370] -threshX-HighP, which represents the Srxlev threshold (in dB) used by the UE when reselecting to a RAT with a higher priority than the current serving frequency. Each frequency of E-UTRAN may have a specific threshold.

[0371] -threshX-LowP, which represents the Srxlev threshold (in dB) used by the UE when reselecting to a RAT with a lower priority than the current serving frequency. Each frequency of E-UTRAN may have a specific threshold.

[0372] In LTE, equivalent parameters are arranged in the SIBs in a similar manner. Here, the parameters in SIB1, SIB3, SIB5, and SIB24 are of interest.

[0373] SIB1 contains information relevant when evaluating whether to allow a UE to access the cell and defines the scheduling of other system information (i.e., it contains threshold parameters equivalent to SIB1 in NR). The relevant threshold parameters are:

[0374] -q-RxLevMin

[0375] -q-RxLevMinOffset

[0376] -p-Max

[0377] -q-QualMin-r9

[0378] -q-QualMinOffset-r9.

[0379] SIB3 contains cell reselection information that is common for intra-frequency, inter-frequency, and / or inter-RAT cell reselection (i.e., applicable to more than one type of cell reselection but not necessarily to all cell reselections), as well as intra-frequency cell reselection information other than that related to intra-frequency cell reselection for adjacent cells, i.e., it contains threshold parameters equivalent to SIB2 in NR. The relevant threshold parameters are:

[0380] -q-Hyst

[0381] -s-NonIntraSearch / s-NonIntraSearchP-r9

[0382] -s-NonIntraSearchQ-r9

[0383] -q-RxLevMin

[0384] -q-QualMin-r9

[0385] -s-IntraSearch / s-IntraSerachP-r9

[0386] -s-IntraSearchQ-r9

[0387] -t-ReselectionEUTRA

[0388] -p-Max

[0389] -threshServingLow.

[0390] SIB5 contains information related only to inter-frequency cell reselection, i.e., information related to cell reselection about other EUTRA frequencies and inter-frequency neighboring cells. This IE includes cell reselection parameters common to a frequency and cell-specific reselection parameters (i.e., it contains threshold parameters equivalent to SIB4 in NR). The relevant threshold parameters are:

[0391] -q-RxLevMin

[0392] -q-QualMin-r9

[0393] -p-Max

[0394] -t-ReselectionEUTRA

[0395] -qOffsetFreq

[0396] -threshX-High

[0397] -threshX-Low.

[0398] SIB24 contains information related only to inter-RAT cell reselection, i.e., information related to cell reselection about NR frequencies and NR neighboring cells (i.e., it contains threshold parameters equivalent to SIB5 in NR). The relevant threshold parameters are:

[0399] -t-ReselectionNR-r15

[0400] -q-RxLevMin-r15

[0401] -p-MaxNR-r15

[0402] -q-QualMin-r15

[0403] -threshX-High-r15

[0404] -threshX-Low-r15.

[0405] For a UE in RRC_IDLE, mobility is handled via the cell selection / reselection process. Specifically, the UE wakes up only once in each DRX cycle to monitor the paging messages of the network and perform reference signal received power (RSRP) / reference signal received quality (RSRQ) measurements for the serving cell, and if necessary, perform RSRP / RSRQ measurements for some other target cells to decide whether it can still camp on the serving cell or whether it needs to find a better cell.

[0406] As briefly described above, NW indicates to the UE how to quantify serving cell and other target cell measurements via a parameter set broadcast in the MIB and SIBs. More precisely, for each cell, the received RSRP level represented by Srxlev and the received RSRQ level represented by Squal are calculated by using the following formulas:

[0407] Srxlev = Qrxlevmeas - (Qrxlevmin + Qrxlevminoffset) - Pcompensation - QoffsettempSqual = Qqualmeas - (Qqualmin + Qqualminoffset)QoffsettemD

[0408] Where Qrxlevmeas and Qqualmeas are the cell RSRP and RSRQ measurements made by the UE, respectively, and the other parameters are provided to the UE via system information. In NR, serving cell parameters are broadcast in SIB1, co-frequency parameters are broadcast in SIB2, inter-frequency parameters are broadcast in SIB4, and inter-RAT parameters are broadcast in SIB5.

[0409] The following table shows a detailed description of Qrxlevmin, Qqualmin, Qrxlevminoffsetcell, and Qqualvminoffsetcell defined in TS 38.304. The parameters Qrxlevminoffsetcell and Qqualvminoffsetcell introduced in Rel-15 specify a cell-specific Rx level offset and a cell-specific quality level offset.

[0410] Srxlev Cell selection RX level value (dB)

[0411] Squal Cell selection quality value (dB)

[0412] Qoffsettemp Offset applied to the cell temporarily as specified in [3] (dB)

[0413] Qrxlevmeas Measured cell RX level value RSRP

[0414] Qqualmeas Measured cell quality value RSRQ

[0415] Qrxlevminoffset Offset relative to the signaled Qrxlevmin considered in the Srxlev evaluation as a result of periodically searching for a higher priority PLMN when normally resident in the VPLMN

[0416] Qqualminoffset is the offset relative to the signaled Qqualmin considered in the Squal assessment as a result of the UE regularly searching for higher priority PLMNs while normally resident in the VPLMN.

[0417] Pcompensation

[0418] If the UE supports additionalPmax in the NS-PmaxList (if present) in SIB1:

[0419] max(Pmax - PPowerClass, 0) - (min(PAdditionalPmax, PPowerClass) - min(Pmax, PPowerClass)) (dB);

[0420] Otherwise:

[0421] max(Pmax - PPowerClass, 0) (dB)

[0422] Qrxlevmin is the minimum required RX level in the cell (dBm).

[0423] Qrxlevmin is obtained from q-RxLevMin in SIB1, SIB2, and SIB4. Additionally, if there is a Qrxlevminoffsetcell for the relevant cell in SIB3, SIB4, and SIB5, the cell-specific offset is added to the corresponding Qrxlevmin to obtain the minimum required RX level in the relevant cell.

[0424] Qqualmin is the minimum required quality level in the cell (dB). Additionally, if a Qqualminoffsetcell for the relevant cell is signaled, the cell-specific offset is added to obtain the minimum required quality level in the relevant cell.

[0425] Qrxlevminoffsetcell This specifies the cell-specific Rx level offset relative to Qrxlevmin, in dB. In 38.331, this is q-RxLevMinOffsetCell in SIB3, SIB4, and SIB5.

[0426] Qqualvminoffsetcell This specifies the cell-specific quality level offset relative to Qqualmin, in dB. In 38.331, this is q-QualMinOffsetCell in SIB3, SIB4, and SIB5.

[0427] Qoffset

[0428] For the same frequency:

[0429] -Qoffset has a valid value of <> dB.

[0430] -Qoffset = 0 dB.

[0431] For different frequencies with equal priorities:

[0432] -Qoffset + Qoffsetfrequency, if Qoffset has a valid value of <> 0 dB.

[0433] -Qoffsetfrequency.

[0434] Qhyst hysteresis parameter.

[0435] To avoid ping-pong effects during signal level fluctuations. It is announced in SIB2.

[0436] When at least the following cell selection criteria are met, the cell is considered a cell suitable for UE to camp on: Srxlev > 0; Squal > 0.

[0437] The UE needs to perform measurements on higher-priority different-frequency and different-RAT frequencies. The UE performs cell reselection to different-frequency or different-RAT frequency cells according to criteria based on absolute priorities. For same-frequency and different-frequency cell reselection with equal priorities, it is based on the cell ranking criteria defined in TS 38.304 and the criteria based on the number of good beams. The UE ranks the cells that meet the cell selection criteria.

[0438] To limit UE measurements on different target cells, we have the following rules:

[0439] · If the UE measurements on the serving cell satisfy Srxlev > SIntraSearchP and Squal > SIntraSearchQ, the UE does not need to perform measurements on any same-frequency cells.

[0440] · If the measurements on the serving cell satisfy Srxlev > SnonIntraSearchP and Squal > SnonIntraSearchQ, the UE does not need to perform measurements on any different-frequency or different-RAT cells.

[0441] If Srxlev < SIntraSearchP or Squal < SIntraSearchQ, the UE performs intra-frequency cell measurements and ranking according to Section 5.2.4.6 of TS 38.331, and if the reselection criteria are met during the time interval TreselectionRAT, it reselects to the highest priority cell. If Srxlev < SnonIntraSearchP or Squal < SnonIntraSearchQ, the UE performs inter-frequency and / or inter-RAT measurements only for the cells indicated in the system information and for which the UE has a provided priority, as described in Section 5.2.4.2 of TS 38.331.

[0442] In NR, an idle or inactive UE camped on a cell can receive (e.g., common for intra-frequency / inter-frequency in SIB2 in NR, inter-frequency in SIB4, and inter-Rat in SIB5 in NR) via the system information. The absolute priorities of different NR frequencies or inter-RAT frequencies can be provided to the UE in the following ways: in the system information, in the RRCRelease message, or inherited from another RAT in the case of inter-RAT cell (re)selection. In the case of the system information, the NR frequencies or inter-RAT frequencies can be listed without providing a priority, i.e., there is no field cellReselectionPriority for that frequency.

[0443] -CellReselectionPriority

[0444] The IE CellReselectionPriority relates to the absolute priority of the relevant carrier frequency, such as the absolute priority of the carrier frequency used in the cell reselection process. Corresponds to the parameter "priority" in TS38.304

[20] . The value 0 represents the lowest priority. The UE behavior in the case where this field does not exist is specified in TS 38.304 (if applicable).

[0445] CellReselectionPriority information element

[0446] --ASN1START

[0447] --TAG-CELLRESELECTIONPRIORITY-START

[0448] CellReselectionPriority ::= INTEGER(0..7)

[0449] --TAG-CELLRESELECTIONPRIORITY-STOP

[0450] --ASN1STOP

[0451] Via system information, the priority indication for each frequency (same RAT or different RAT) can be configured for the UE. First, the UE only performs cell reselection evaluation for NR frequencies and different RAT frequencies that are given in the system information and for which the UE has a provided priority.

[0452] If the network is using a single-carrier frequency, intra-frequency reselection shall be performed under the following conditions. As long as the following conditions are met, the UE stays on the serving cell:

[0453] · Srxlev > SIntraSearchP, the adjacent measured RSRP is not lower than the threshold

[0454] · Squal > SIntraSearchQ, the adjacent measured RSRQ is not lower than the threshold.

[0455] Wherein,

[0456] · The SIntraSearchP parameter is the threshold that the serving cell advertises as part of SIB2, i.e., the s-IntraSearchP IE.

[0457] · The SIntraSearchQ parameter is the threshold that the serving cell advertises as part of SIB2, i.e., the s-IntraSearchQ IE.

[0458] · Srxlev = Qrxlevmeas - (Qrxlevmin + Qrxlevminorfset) - Pcompensation - Qoffsettemp

[0459] · Squal = Qqualmeas - (Qqualmin + Qqualminoffset) - Qoffsettemp

[0460] When the above conditions are not met, the UE switches to the best-ranked cell under the following conditions:

[0461] · The UE must have stayed on the serving cell for at least 1 second.

[0462] · During the time interval t-ReselectionNR, the new cell must have a better rank than the serving cell.

[0463] Cells that meet the cell selection criteria Srxlev > 0 and Squal > 0, if they are serving cells, are ranked as Rs, and if they are adjacent cells, are ranked as Rn, which are defined as follows:

[0464] · Rs = Qmeas,s + Qhyst

[0465] · Rn = Qmeas,n - Qoffset

[0466] If the network uses more than one carrier frequency, the serving cell advertises the other carriers as part of SIB4. If another carrier is involved, the priority of that frequency compared to the serving frequency will be considered.

[0467] The UE shall perform measurements on NR inter-frequencies with a reselection priority equal to, higher than, or lower than that of the serving NR frequency under the following conditions:

[0468] Srxlev < SnonIntraSearchP or Squal < SnonIntraSearchQ

[0469] where,

[0470] · The SnonIntraSearchP parameter is the threshold that the serving cell advertises as part of SIB2, i.e., the s-NonIntraSearchP IE.

[0471] · The SnonIntraSearchQ parameter is the threshold that the serving cell advertises as part of SIB2, i.e., the s-NonIntraSearchQ IE.

[0472] Reselection to an NR frequency with the same priority as the serving cell is based on the ranking for intra-frequency cell reselection.

[0473] Reselection to an NR frequency with a higher priority than the serving cell is performed under the following conditions:

[0474] · The UE must have camped on the serving cell for at least 1 second.

[0475] · The new cell satisfies: in the case where threshServingLowQ has been broadcast in SIB2, Squal > ThreshX,HighQ condition during the time interval t-ReselectionNR.

[0476] · The new cell satisfies: in the case where threshServingLowQ has not been broadcast in SIB2, Srxlev > ThreshX,HighP condition during the time interval t-ReselectionNR.

[0477] where,

[0478] · ThreshServingLowQ and t-ReselectionNR are advertised in SIB2.

[0479] · ThreshX, HighQ and ThreshX, HighP are broadcast in SIB4.

[0480] Perform reselection to a lower priority NR frequency than the serving cell under the following conditions:

[0481] · The UE must have camped on the serving cell for at least 1 second.

[0482] · The new cell meets the condition that during the time interval t-ReselectionNR, Squal > ThreshX, LowQ when threshServingLowQ has been broadcast in SIB2 and Squal < ThreshServingLowQ.

[0483] · The new cell meets the condition that during the time interval t-ReselectionNR, Squa] > ThreshX, LowP when threshServingLowQ has been broadcast in SIB2 and Srxlev < ThreshServingLowP.

[0484] Where

[0485] · ThreshServingLowQ, ThreshServingLowP, t-ReselectionNR are broadcast in SIB2.

[0486] · ThreshX, LowQ and ThreshX, LowP are broadcast in SIB4.

[0487] In this case, the UE cannot find a cell with an equal or higher priority NR frequency to which it can reselect.

[0488] The UE shall perform measurements on an inter-RAT frequency with a reselection priority higher or lower than that of the serving NR frequency under the following conditions:

[0489] Srxlev < SnonIntraSearchP or Squal < SnonIntraSearchQ

[0490] Where

[0491] · The SnonIntraSearchP parameter is the threshold that the serving cell broadcasts as part of SIB2, i.e., the s-NonIntraSearchP IE.

[0492] · The SnonIntraSearchQ parameter is the threshold that the serving cell advertises as part of SIB2, i.e., the s-NonIntraSearchQ IE.

[0493] Equal priorities between RATs are not supported. This means that there is no equal priority between the NR frequency in the serving cell and the EUTRA frequency in the neighboring cell.

[0494] Reselection to a higher priority EUTRA frequency than the serving cell is performed under the following conditions:

[0495] · The UE must have camped on the serving cell for at least 1 second.

[0496] · The new cell satisfies the Squal>ThreshX, HighQ condition during the time interval t-ReselectionEUTRA when threshServingLowQ has been broadcast in SIB2.

[0497] · The new cell satisfies the Srxlev>ThreshX, HighP condition during the time interval t-ReselectionEUTRA when threshServingLowQ has not been broadcast in SIB2.

[0498] Where,

[0499] · ThreshServingLowQ is advertised in SIB2.

[0500] · t-ReselectionEUTRA, ThreshX, HighQ, and ThreshX, HighP are advertised in SIB5.

[0501] Reselection to a lower priority EUTRA frequency than the serving cell is performed under the following conditions:

[0502] · The UE must have camped on the serving cell for at least 1 second.

[0503] · The new cell satisfies the Squal>ThreshX, LowQ condition during the time interval t-ReselectionEUTRA when threshServingLowQ has been broadcast in SIB2 and Squal<ThreshServingLowQ.

[0504] ·The new cell meets the condition that when threshServingLowQ is not broadcast in SIB2 and Srxlev < ThreshServingLowP, Srxlev > ThreshX,LowP is satisfied during the time interval t-ReselectionEUTRA.

[0505] Among them,

[0506] ·ThreshServingLowQ and ThreshServingLowP are announced in SIB2.

[0507] ·t-ReselectionEUTRA, ThreshX,LowP and ThreshX,LowQ are announced in SIB5.

[0508] Release with redirection to an NR frequency for an incoming UE in RRC_INACTIVE

[0509] Compared with the case where the UE comes from RRC_IDLE, the delay of release and redirection can be shorter because the security has been activated. When sending the secure RRCRelease message, the network can move the UE to RRC_IDLE or RRC_INACTIVE. Since the network redirects the UE to another NR frequency, typically, the network moves the UE to RRC_INACTIVE in order to also speed up the recovery of the connection on the target frequency and further reduce the total delay, as shown below:

[0510] As shown above, if an RRC_INACTIVE UE attempts to resume the RRC connection, and after entering RRC_CONNECTED, the UE pauses to RRC_INACTIVE and has information about redirection to an NR frequency, the delay can be improved. At the target cell, the UE attempts to resume the connection.

[0511] The delay in this case is 2*RTT_nr (RRCResumeRequest, RRCResume, RRCResumeComplete, RRCRelease) + RTT_Xn (network delay obtained from context in the source) + RTT_5gc (signaling between the CN and the source path switch) + 1.5*RTT_nr (RRCResumeRequest, RRCResume, RRCResumeComplete) + RTT_Xn (network delay obtained from context in the target) + RTT_5gc (signaling between the CN and the source path switch) = 3.5*RTT_nr + 2*RTT_Xn + 2*RTT_5gc.

[0512] However, there are performance issues in terms of latency for an incoming UE that attempts to resume or establish a connection for a specific service (such as VoIP, video call, etc.) that is not supported by the target cell. In the case of an RRC_IDLE UE, the UE will need to trigger the RRC establishment process, enter RRC_CONNECTED, perform initial security activation, and then receive the protected redirection information. This will also involve some core network signaling as follows:

[0513] The problem solved by the present invention relates to the latency of the existing release with redirection process.

[0514] In the two-step release and redirection, with context relocation, the RRC_INACTIVE UE attempts to resume the RRC connection, and the UE pauses at RRC_INACTIVE without entering RRC_CONNECTED and has information for redirection to the NR frequency. At the target cell, the UE attempts to resume the connection.

[0515] Compared with the baseline case where the UE first enters RRC_CONNECTED and then is released, two messages (RRCResume and RRCResumeComplete) between the UE and the target cell can be skipped.

[0516] The latency in the two-step case with context relocation is 2*RTT_nr (RRCResumeRequest, RRCResume, RRCResumeComplete, RRCRelease) + RTT_Xn (network latency from context acquisition in the source) + RTT_5gc (signaling between the CN and the source path switch) + 1.5*RTT_nr (RRCResumeRequest, RRCResume, RRCResumeComplete) + RTT_Xn (network latency from context acquisition in the target) + RTT_5gc (signaling between the CN and the source path switch) = 2.5*RTT_nr + 3*RTT_Xn + 2*RTT_5gc.

Claims

1. A method for operating a user equipment (UE) in a wireless communication network, the method comprising the steps of: - Obtaining broadcast system information including redirection information; and - performing a cell selection or cell reselection process based on the acquired broadcast system information, wherein the steps of performing the cell selection or cell reselection process are initiated during a connection recovery process when the UE is in an inactive state, wherein, performing the cell selection or cell reselection process based on a predetermined criterion to be satisfied according to the redirection information, wherein the predetermined criterion to be satisfied includes: - the recovery reason of a possible connection recovery process is included in the redirection information; and / or - the access category of a possible connection recovery process is included in the redirection information.

2. The method according to claim 1, wherein, The acquired broadcast system information further includes a mapping between the recovery reason and / or the access category and at least one of the following: - redirection to a target radio access technology, i.e., target RAT; - redirection to a target serving cell; and - redirection to a target frequency.

3. The method according to claim 1, wherein, The redirection information is included in a broadcast system information block SIB.

4. The method according to claim 3, wherein, The redirection information is included in an information element added to an existing SIB.

5. A method performed by a network node serving a user equipment (UE) in a wireless communication network, wherein, The method includes the steps of: - broadcasting system information, the system information including redirection information enabling the UE to perform a cell selection or cell reselection process, wherein the redirection information includes at least one of the following: - the recovery reason of a possible connection recovery process for the UE; - the access category of a possible connection recovery process for the UE.

6. The method according to claim 5, wherein, The redirection information further includes a mapping between the recovery reason and / or the access category and at least one of the following: - redirection to a target radio access technology, i.e., target RAT; - redirection to a target serving cell; and - redirection to a target frequency.

7. The method according to claim 5, wherein, The step of broadcasting system information includes: broadcasting a system information block SIB including the redirection information.

8. The method according to claim 7, wherein, The redirection information is included in an information element added to an existing SIB.

9. A user equipment (UE) in a wireless communication system, wherein, The UE includes: - a communication circuit configured to acquire broadcast system information including redirection information; and - a processing circuit configured to perform a cell selection process or a cell reselection process based on the acquired broadcast system information, wherein the processing circuit is configured to: initiate the cell selection or cell reselection process during a connection recovery process when the UE is in an inactive state, wherein the processing circuit is configured to: perform the cell selection or cell reselection process based on a predetermined criterion to be satisfied according to the redirection information, wherein the processing circuit is configured to perform the cell selection or cell reselection process in the following cases: - if the recovery reason of a possible connection recovery process is included in the redirection information; and / or - if the access category of a possible connection recovery process is included in the redirection information.

10. The user equipment UE according to claim 9, wherein, The broadcast system information further includes a mapping between the recovery reason and / or the access category and at least one of the following: - redirection to a target radio access technology, i.e., target RAT; - redirection to a target serving cell; and - redirection to a target frequency.

11. The user equipment UE according to claim 9, wherein, The communication circuit is configured to obtain redirection information included in a broadcast system information block SIB.

12. A network node for serving a user equipment UE in a wireless communication network, wherein, The network node includes: - A communication circuit configured to broadcast system information, the system information including redirection information that enables the UE to perform a cell selection or cell reselection process, wherein the redirection information includes at least one of the following: - A recovery reason for a possible connection recovery process for the UE; - An access category for a possible connection recovery process for the UE.

13. The network node according to claim 12, wherein, The redirection information further includes a mapping between the recovery reason and / or the access category and at least one of the following: - A redirection to a target radio access technology, i.e., a target RAT; - A redirection to a target serving cell; and - A redirection to a target frequency.

14. The network node according to claim 12, wherein, The communication circuit (200) is configured to broadcast information including the redirection information in a system information block SIB.

15. The network node according to claim 14, wherein, The redirection information is included in an information element added to an existing SIB.

16. A computer program product comprising instructions which, when executed by at least one processor, cause the at least one processor to perform the method according to any one of claims 1 - 4.

17. A computer program product comprising instructions which, when executed by at least one processor, cause the at least one processor to perform the method according to any one of claims 5 - 8.

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