Communication method, apparatus, and system

Abstract

The present application relates to the technical field of communications, and provides a communication method, an apparatus, and a system. In the method, a terminal can preferentially select a first RAT with the highest priority (or referred to as an RAT with the highest technology level ) among RATs supported by the terminal, and attempt to camp on a PLMN using the first RAT. In this way, the terminal can camp on a network using an RAT with higher technology level, thereby improving the communication performance of the terminal.

Description

Communication methods, devices and systems

[0001] This application claims priority to Chinese Patent Application No. 202510353308.2, filed on March 24, 2025, entitled "Communication Method, Apparatus and System", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of communications, and more particularly to a communication method, apparatus, and system. Background Technology

[0003] The terminal can select the appropriate public land mobile network (PLMN) based on manual mode and automatic mode. Manual mode means that the terminal accesses the network based on the PLMN selected by the user, while automatic mode means that the terminal selects and accesses the PLMN based on a predefined PLMN selection process.

[0004] Specifically, when a terminal selects a PLMN in automatic mode, it can do so based on predefined PLMN priorities. However, with the development of wireless communication technology, terminals can support multiple radio access technologies (RATs). Using the current PLMN selection method, there is a possibility that the terminal may choose a PLMN from among several PLMNs that does not provide better communication performance for the terminal. Summary of the Invention

[0005] This application provides a communication method, apparatus, and system to improve the communication performance of a terminal.

[0006] Firstly, a communication method is provided, which can be executed by a terminal or by a unit / module / component (such as a chip, chip system, logic circuit, or software) configurable in (or usable in) the terminal. The following explanation uses the execution of this method by a terminal as an example.

[0007] The method includes: the terminal searching for a Public Land Mobile Network (PLMN) employing a first Radio Access Technology (RAT), wherein the first RAT is the highest priority RAT supported by the terminal and has not been selected before; if a PLMN employing the first RAT exists, the terminal selects the first RAT. Further, the terminal attempts to camp on the PLMN employing the first RAT.

[0008] According to the above scheme, the terminal can preferentially select the highest priority RAT (or the RAT with the highest standardization) among the RATs supported by the terminal, and attempt to camp on the PLMN using the highest priority RAT. This helps the terminal camp on a network using a higher standardization RAT, thus improving the terminal's communication performance.

[0009] In some cases, if the terminal determines through a search that a PLMN using the first RAT does not exist, the terminal searches for a PLMN using the second RAT, which is the highest priority RAT supported by the terminal and has not been selected before. For example, if the terminal supports RATs 1, 2, and 3, and the priority levels of these three RATs are from highest to lowest, then if the terminal determines through a search that a PLMN using RAT 1 (i.e., the first RAT) does not exist, the terminal can search for a PLMN using RAT 2 (i.e., the second RAT).

[0010] For details on how the specific terminal determines whether a PLMN using a certain RAT standard exists through a search, please refer to the relevant description corresponding to the embodiment in Figure 3 below. For the sake of brevity, it will not be elaborated here.

[0011] In conjunction with the first aspect, in some implementations of the first aspect, the terminal's attempt to reside in a PLMN using the first RAT can specifically be an attempt to reside in a first PLMN, which is the highest priority PLMN among the candidate PLMNs using the first RAT that the terminal has not attempted to reside in.

[0012] The candidate PLMN set may include at least one PLMN that adopts a first RAT, and each PLMN among the at least one PLMN that adopts the first RAT has a priority.

[0013] In a possible implementation, the terminal can determine the candidate PLMN set based on at least one of the following: the user-configured PLMN priority set, the pre-configured PLMN priority set, or the PLMN set obtained by searching the PLMN of the first RAT (i.e., the APLMN set), and network coverage information.

[0014] The specific implementation details of the user-configured PLMN priority set, the pre-configured PLMN priority set, or the PLMN set obtained by searching the PLMN of the first RAT (i.e., the APLMN set), network coverage, and how the terminal determines the candidate PLMN set can be found in the relevant descriptions corresponding to the embodiments in Figure 3 below. For the sake of brevity, these details will not be elaborated here.

[0015] According to the above scheme, the terminal can preferentially select the highest priority RAT among the RATs supported by the terminal, and can attempt to camp on a higher priority PLMN based on the priority of each PLMN using the first RAT included in the candidate PLMN set. This helps the terminal camp on networks with higher standard RATs and higher priority PLMNs, thus improving the terminal's communication performance.

[0016] If the terminal successfully camps on the first PLMN, the first PLMN can provide network services to the terminal, such as data transmission and voice calls. However, if the terminal fails to camp on the first PLMN—for example, due to a failure to register with the first PLMN, loss of wireless coverage on the first PLMN, or other situations where the first PLMN cannot provide voice calls or data transmission services—then the terminal can attempt to camp on a second PLMN. This second PLMN is the highest priority PLMN among the candidate PLMNs that the terminal has not yet attempted to camp on.

[0017] For example, the candidate PLMN set may include PLMN1, PLMN2, and PLMN3, with their priorities ranked from highest to lowest as PLMN1, PLMN2, and PLMN3. If the terminal fails to camp on PLMN1 (i.e., the first PLMN), it may attempt to camp on PLMN2 (i.e., the second PLMN).

[0018] According to the above scheme, when the terminal fails to camp on the first PLMN using the first RAT, the terminal can select the next priority PLMN supported by the terminal. This helps the terminal to camp on a network with a higher standard RAT and a higher priority PLMN, thereby improving the terminal's communication performance.

[0019] In some cases, the terminal may fail to camp on a PLMN that uses the first RAT. That is, the terminal fails to camp on any of the PLMNs in the candidate PLMN set corresponding to the first RAT (or the terminal fails to use the network services provided by each PLMN in the candidate PLMN set corresponding to the first RAT). In this case, the terminal searches for a PLMN that uses the second RAT, which is the highest priority RAT that the terminal supports and has not been selected.

[0020] According to the above scheme, when a terminal fails to camp on a PLMN using the first RAT, it can select a RAT of the next standard level that it supports and attempt to camp on a PLMN using that next standard level. This helps the terminal select a higher standard level RAT and improves its communication performance.

[0021] Optionally, the above implementation can be used when there is no available home PLMN and an equivalent PLMN of the home network. Specifically, when there is no available home PLMN and an equivalent PLMN of the home network (or understood as the terminal not being within the coverage area of ​​the available home PLMN and an equivalent PLMN of the home network, such as when the terminal is in an international roaming scenario), the terminal searches for the PLMN of the first RAT.

[0022] According to the above scheme, when roaming tariffs do not differentiate between PLMN types (such as in international roaming scenarios), the terminal can choose to use a network with a higher standard level (or higher priority) of RAT, which helps improve the terminal's communication performance. When roaming tariffs may differentiate between different PLMN types (such as in domestic roaming scenarios), the terminal can still select and attempt to camp on a certain network based on the PLMN's priority level, which helps improve the flexibility of PLMN selection and improves the terminal's communication performance without affecting the roaming tariffs incurred.

[0023] In conjunction with the first aspect, in some implementations of the first aspect, the method further includes: when the network selection mode is automatic, the terminal searches for the PLMN of the first RAT.

[0024] According to the above scheme, when the network selection mode is in automatic mode, the terminal can search for PLMNs using the first RAT and attempt to camp. When the network selection mode is in manual mode, this implementation method can be disabled (or not started). That is, the method provided by this application does not affect the situation where the user actively selects a PLMN. The user can actively specify a target PLMN from the list of available PLMNs and attempt to camp.

[0025] In conjunction with the first aspect, in some implementations of the first aspect, the method further includes: the terminal searching for a PLMN employing a first RAT based on configuration parameters stored in a non-volatile (NV) memory, the configuration parameters being used to control network selection with priority of the RAT.

[0026] Optionally, the configuration parameter used to control whether to select the network (PLMN) based on RAT priority can be a Boolean parameter. Specific implementation details of this configuration parameter can be found in the relevant description below, and will not be elaborated upon here for the sake of brevity.

[0027] According to the above scheme, when the terminal powers on (or searches for a network), it can read the configuration parameters stored in the NV memory. If the configuration parameters indicate that the function of selecting a network with RAT priority is enabled (or activated, started), the terminal can prioritize selecting a network with RAT priority. Conversely, if the configuration parameters indicate that the function of selecting a network with RAT priority is disabled (or deactivated, disabled), the terminal can still select a network with PLMN priority. This improves the terminal's flexibility in selecting the PLMN, and when the configuration parameters indicate that network selection with RAT priority is enabled, it can improve the terminal's communication performance.

[0028] In a second aspect, a communication device is provided. In one design, the device may include modules corresponding to the methods / operations / steps / actions described in the first aspect or any embodiment thereof. These modules may be hardware circuits, software, or a combination of hardware circuits and software. In one design, the device includes a processing unit configured to search for a Public Land Mobile Network (PLMN) employing a first Radio Access Technology (RAT), wherein the first RAT is the highest priority RAT supported by the terminal and not yet selected. If a PLMN employing the first RAT exists, the processing unit is further configured to select that first RAT. Further, the processing unit is also configured to attempt to camp on the PLMN employing the first RAT.

[0029] Thirdly, a communication device is provided, including a processor. The processor can implement the methods described in the first aspect and any possible implementation thereof. Optionally, the communication device further includes a memory, and the processor is coupled to the memory and can be used to execute instructions in the memory to implement the methods described in the first aspect and any possible implementation thereof. Optionally, the communication device further includes a communication interface, and the processor is coupled to the communication interface. In the embodiments of this application, the communication interface may be a transceiver, a pin, a circuit, a bus, a module, or other types of communication interface, and is not limited thereto.

[0030] In one implementation, the communication device is a communication equipment (such as a terminal device). When the communication device is a communication equipment, the communication interface can be a transceiver, or an input / output interface.

[0031] In another implementation, the communication device is a chip configured within a communication device. When the communication device is a chip configured within a communication device, the communication interface can be an input / output interface.

[0032] Optionally, the transceiver can be a transceiver circuit. Optionally, the input / output interface can be an input / output circuit.

[0033] Fourthly, a processor is provided, comprising: an input circuit, an output circuit, and a processing circuit. The processing circuit is configured to receive signals through the input circuit and transmit signals through the output circuit, causing the processor to execute the methods described in the first aspect and any possible implementation thereof.

[0034] In specific implementation, the processor can be one or more chips, the input circuit can be input pins, the output circuit can be output pins, and the processing circuit can be transistors, gate circuits, flip-flops, and various logic circuits. The input signal received by the input circuit can be received and input by, for example, but not limited to, a receiver, and the signal output by the output circuit can be, for example, but not limited to, output to and transmitted by a transmitter. Furthermore, the input circuit and the output circuit can be the same circuit, which is used as both the input circuit and the output circuit at different times. This application does not limit the specific implementation of the processor and various circuits.

[0035] Fifthly, a computer program product is provided, comprising: a computer program (also referred to as code or instructions) that, when run, causes a computer to perform the methods described in the first aspect and any possible implementation thereof.

[0036] In a sixth aspect, a computer-readable storage medium is provided that stores a computer program (also referred to as code or instructions) that, when executed on a computer, causes the computer to perform the methods described in the first aspect and any possible implementation thereof.

[0037] In a seventh aspect, a chip system is provided, which is applied to an electronic device. The chip system includes one or more processors, which are configured to invoke computer instructions to cause the electronic device to perform the methods described in the first aspect and any possible implementation thereof.

[0038] Eighthly, a communication system is provided, comprising at least one network device and at least one terminal as described above.

[0039] It should be understood that the beneficial effects of the features corresponding to the first aspect in the second to eighth aspects can be referred to the relevant description of the first aspect above, and will not be repeated here. Attached Figure Description

[0040] Figure 1 is a schematic diagram of the architecture of the communication system provided in an embodiment of this application;

[0041] Figure 2 is a schematic diagram of an application scenario provided by an embodiment of this application;

[0042] Figure 3 is a schematic flowchart of the first communication method provided in this application;

[0043] Figure 4 is a schematic flowchart of the second communication method provided in this application;

[0044] Figure 5 is a schematic flowchart of the third communication method provided in this application;

[0045] Figure 6 is a schematic block diagram of an example of a communication device provided in an embodiment of this application;

[0046] Figure 7 is a schematic structural diagram of another example of the communication device provided in the embodiments of this application. Detailed Implementation

[0047] To facilitate understanding of the embodiments of this application, the following points will be explained first:

[0048] In the embodiments of this application, "instruction" may include direct instruction, indirect instruction, explicit instruction, and implicit instruction. When describing a certain instruction information for indicating A, it can be understood that the instruction information carries A, directly indicates A, or indirectly indicates A.

[0049] In the embodiments of this application, " / " can indicate that the objects before and after are in an "or" relationship. For example, A / B can mean A or B. "And / or" can be used to describe three relationships between the associated objects. For example, A and / or B can mean: A exists alone, A and B exist simultaneously, and B exists alone. A and B can be singular or plural.

[0050] In the embodiments of this application, "at least one" refers to one or more, and "more than one" refers to two or more, such as three, four or more. Similar expressions (such as at least one, at least one, etc.) are used in the same way. "At least one of the following," "one or more of the following," or similar expressions refer to any combination of these items, which may include only a single item or a combination of multiple items. For example, at least one of a, b, or c can represent: a, or b, or c; a and b; or a and c; or b and c; or a, b, and c. Where a, b, and c can be single or multiple.

[0051] In the embodiments of this application, in order to facilitate the description of the technical solutions of the embodiments of this application, the terms "first" and "second" may be used for distinction. The terms "first" and "second" do not limit the quantity or execution order, and the terms "first" and "second" are not necessarily different.

[0052] In the embodiments of this application, the words "exemplary," "example," or "for example" are used to indicate examples, illustrations, or descriptions. Any embodiment or design described as "exemplary," "example," or "for example" should not be construed as being more preferred or advantageous than other embodiments or designs. The use of the words "exemplary," "example," or "for example" is intended to present the relevant concepts in a specific manner to facilitate understanding.

[0053] In the embodiments of this application, "sending information / data" only indicates the direction of information / data transmission, including direct transmission through the device's communication interface (such as an air interface, or simply air interface). "Sending" can also be understood as the "output" of the module interface. "Sending" can include indirect transmission by the processing unit through the communication interface, that is, after the processing unit outputs information / data through the module interface, it is transmitted to the device's communication interface and then sent out. "Receiving information / data" only indicates the direction of information / data transmission, including direct reception through the communication interface. "Receiving" can also be understood as the "input" of the module interface. "Receiving information / data" can include indirect reception by the processing unit through the communication interface, that is, after the communication interface receives information / data, it is transmitted to the module interface of the processing unit and then input to the processing unit through the module interface. "Sending information / data to... (such as a terminal)" can be understood as the destination of the information being the terminal. It can include sending information / data directly or indirectly to the terminal. "Receiving information / data from... (such as a terminal)" can be understood as the source of the information being the terminal, and can include receiving information / data directly or indirectly from the terminal. Information / data may undergo necessary processing, such as format changes, between the source and destination, but the destination can understand the valid information / data from the source. Similar statements in the embodiments of this application can be understood in a similar way, and will not be repeated here.

[0054] The technical solutions of this application can be applied to various communication systems, such as: Long Term Evolution (LTE) systems, 5th Generation (5G) communication systems, satellite communication systems, Wireless Fidelity (WiFi) systems, and the solutions provided in this application can also be applied to future communication systems or other communication systems. This application does not limit these applications.

[0055] Figure 1 is a schematic diagram of the architecture of a communication system applicable to the communication method provided in the embodiments of this application. Figure 1 shows a schematic diagram of a possible, non-limiting system architecture. As shown in Figure 1, the communication system 100 includes a radio access network (RAN) 10 and a core network (CN) 20. Optionally, the communication system 100 also includes an Internet 30. The RAN 10 includes at least one RAN node (110a and 110b in Figure 1, collectively referred to as 110) and at least one terminal (120a-120j in Figure 1, collectively referred to as 120). The RAN 10 may also include other RAN nodes, such as wireless relay devices and / or wireless backhaul devices (not shown in Figure 1). The terminal 120 is wirelessly connected to the RAN node 110. The RAN node 110 is wirelessly or wiredly connected to the core network 20. The core network devices in the core network 20 and the RAN node 110 in the RAN 10 can be different physical devices, or they can be the same physical device integrating core network logical functions and radio access network logical functions.

[0056] RAN 10 can be a cellular system related to the 3rd Generation Partnership Project (3GPP), such as 4G, 5G mobile communication systems, or future-oriented evolution systems. RAN 10 can also be an open access network (O-RAN or ORAN), a cloud radio access network (CRAN), or a wireless fidelity (Wi-Fi) system. RAN 10 can also be a communication system that integrates two or more of the above systems.

[0057] RAN node 110, sometimes also referred to as access network equipment, RAN entity, or access node, is part of the communication system and is used to help terminals achieve wireless access. Multiple RAN nodes 110 in communication system 100 can be of the same type or different types. In some scenarios, the roles of RAN node 110 and terminal 120 are relative. For example, network element 120i in Figure 1 can be a helicopter or drone, which can be configured as a mobile base station. For terminals 120j accessing RAN 10 through network element 120i, network element 120i is a base station; but for base station 110a, network element 120i is a terminal. RAN node 110 and terminal 120 are sometimes both referred to as communication devices. For example, network elements 110a and 110b in Figure 1 can be understood as communication devices with base station functions, and network elements 120a-120j can be understood as communication devices with terminal functions.

[0058] In one possible scenario, a RAN node can be a base station, an evolved NodeB (eNodeB), an access point (AP), a transmission reception point (TRP), a next-generation NodeB (gNB), a next-generation base station in a 6G mobile communication system, a base station in a future mobile communication system, or an access node in a WiFi system. A RAN node can be a macro base station (as shown in Figure 1, 110a), a micro base station or indoor station (as shown in Figure 1, 110b), a relay node or donor node, or a radio controller in a CRAN scenario. Optionally, a RAN node can also be a server, wearable device, vehicle, or in-vehicle equipment. For example, the access network equipment in vehicle-to-everything (V2X) technology can be a roadside unit (RSU).

[0059] In another possible scenario, multiple RAN nodes collaborate to assist the terminal in achieving wireless access, with each RAN node performing a portion of the base station's functions. For example, RAN nodes can be central units (CUs), distributed units (DUs), CU-control plane (CPs), CU-user plane (UPs), or radio units (RUs), etc. CUs and DUs can be separate entities or included in the same network element, such as a baseband unit (BBU). RUs can be included in radio frequency equipment or radio frequency units, such as remote radio units (RRUs), active antenna units (AAUs), or remote radio heads (RRHs).

[0060] In different systems, CU (or CU-CP and CU-UP), DU, or RU may have different names, but those skilled in the art will understand their meaning. For example, in an ORAN system, CU can also be called O-CU (open CU), DU can also be called O-DU, CU-CP can also be called O-CU-CP, CU-UP can also be called O-CU-UP, and RU can also be called O-RU. For ease of description, this application uses CU, CU-CP, CU-UP, DU, and RU as examples in its embodiments. Any of the units among CU (or CU-CP, CU-UP), DU, and RU in the embodiments of this application can be implemented through software modules, hardware modules, or a combination of software modules and hardware modules.

[0061] A terminal can also be called a terminal device, user equipment (UE), mobile station, mobile terminal, etc. Terminals can be widely used in various scenarios, such as device-to-device (D2D), vehicle-to-everything (V2X) communication, machine-type communication (MTC), Internet of Things (IoT), virtual reality, augmented reality, industrial control, autonomous driving, telemedicine, smart grids, smart furniture, smart offices, smart wearables, smart transportation, smart cities, etc. Terminals can be mobile phones, tablets, computers with wireless transceiver capabilities, wearable devices, vehicles, drones, helicopters, airplanes, ships, robots, robotic arms, smart home devices, etc.

[0062] In this application embodiment, the terminal and network device can be hardware devices, or software functions running on dedicated hardware, or software functions running on general-purpose hardware, such as virtualization functions instantiated on a platform (e.g., cloud platform), or entities that include dedicated or general-purpose hardware devices and software functions. This application embodiment does not limit the specific form of the terminal and network device.

[0063] To better understand the methods provided in the embodiments of this application, the relevant technologies and terms involved in the embodiments of this application will be briefly explained below.

[0064] 1. Subscriber Identity Module (SIM)

[0065] A SIM card, also known as a user identification card or smart card, is used to store user authentication information and parameters required for network access. Terminals using this SIM card can then connect to wireless communication networks.

[0066] Optionally, the SIM card in this application embodiment may also be an embedded SIM (eSIM), or may be replaced with other modules that enable the terminal to access the network. This application embodiment does not limit this.

[0067] 2. Public Land Mobile Network (PLMN)

[0068] A PLMN, also known as a mobile communication network or simply a network, is used to provide wireless communication services such as voice and data transmission to terminals. A PLMN is uniquely identified by its Mobile Country Code (MCC) and Mobile Network Code (MNC), allowing different PLMNs to distinguish between different operators or networks.

[0069] The same geographical location may be covered by multiple PLMNs, which may be networks of different operators or different networks of the same operator. In some scenarios, when the terminal is in a state of not being connected to the network, such as when the terminal is powered on (including the terminal's first startup or restart) or when the network currently connected to the terminal is unavailable (or offline, such as when entering an area with no signal or encountering a network failure), the terminal can select an available PLMN from at least one PLMN covering its geographical location to access network services.

[0070] Optionally, PLMNs are divided into several types, and different types of PLMNs may have different priorities. That is, multiple PLMNs covering the same geographical location may have different priorities. The terminal can maintain multiple types of PLMN lists, and each PLMN list can contain at least one PLMN. For ease of understanding, the various types of PLMN lists are explained below.

[0071] (1) Registered PLMN (RPLMN) refers to the PLMN that the terminal registered before it was last powered off or disconnected from the network.

[0072] (2) Home PLMN (HPLMN): HPLMN, also known as local network, is the user's primary network. HPLMN is the network provided by the network operator to which the user's SIM card is registered. HPLMN can be uniquely identified by the Mobile Country Code (MCC) and Mobile Network Code (MNC) in the International Mobile Subscriber Identity (IMSI) stored in the SIM card.

[0073] (3) Equivalent Home Network (EHPLMN), also known as Equivalent Local Network or Equivalent PLMN of Home Network, stores networks with special agreements with the operator to which the HPLMN belongs. EHPLMN and HPLMN have the same service rights.

[0074] (4) User-controlled PLMN (UPLMN) refers to a list of PLMNs that the user manually selects and saves. This UPLMN can be stored, for example, in a file on the SIM card (e.g., a file called "User-controlled PLMN Selector with Access Technology").

[0075] (5) Operator-controlled PLMN (OPLMN): A network pre-installed by the operator in the SIM card or terminal. The OPLMN can be stored in a file on the SIM card (e.g., a file called "Operator-controlled PLMN Selector with Access Technology").

[0076] (6) Available PLMN (APLMN) refers to other PLMNs that the terminal can detect in the current environment but are not included in the above PLMN list (HPLMN / EHPLMN / UPLMN / OPLMN).

[0077] Optionally, when a terminal needs to select a PLMN, it can search based on the maintained list of various types of PLMNs. For example, the terminal can search the maintained list of PLMNs in order of priority and attempt to camp (or access) the network. The priorities of different types of PLMNs can be predefined by the protocol or pre-configured on the terminal; this embodiment does not impose any restrictions on this. For ease of understanding, the following description uses RPLMN, EHPLMN, HPLMN, UPLMN, OPLMN, and APLMN as examples of priorities from high to low to illustrate the process of terminal PLMN selection.

[0078] S1, the terminal starts up from the power-off state and uses the SIM card.

[0079] Optionally, the terminal can check the SIM card status. If, after switching on, the terminal displays "no SIM," it may be because the SIM card is unavailable, for example, due to a damaged SIM card or the use of an invalid SIM card. In this case, the terminal will not perform PLMN selection until the SIM card becomes available.

[0080] Optionally, after the terminal is started, it can read relevant information from at least one of the PLMN lists, namely RPLMN, HPLMMN, EHPLMN, UPLMN, or OPLMN. The relevant information of these networks may be stored in the terminal's memory or in the SIM card. This application embodiment does not limit this.

[0081] Furthermore, the terminal can begin PLMN selection, such as by executing S2.

[0082] S2, the terminal determines whether there is an available RPLMN based on the read RPLMN list.

[0083] If no RPLMN is currently available, the terminal can reselect a PLMN, for example, the terminal can execute S3.

[0084] Specifically, if the terminal performs a frequency scan on all supported frequency bands but still cannot receive broadcast signals related to the RPLMN, the terminal confirms that its current location is not within the coverage area of ​​the RPLMN, and the RPLMN is unavailable. However, it should be understood that the embodiments of this application are not limited to this. If the network information of the RPLMN read by the terminal is invalid (e.g., the current time has exceeded the validity period of the network information), the RPLMN can also be considered unavailable, and a new PLMN needs to be selected.

[0085] If an RPLMN is available, the terminal selects that RPLMN and attempts to connect to it (or attempts to reside there).

[0086] Specifically, after the terminal reads the network information of the most recently successfully registered PLMN (i.e., RPLMN), the terminal can use a frequency scan operation to confirm whether its current location is still within the coverage area of ​​that RPLMN. If the current location is still within the coverage area of ​​that RPLMN and the RPLMN is detected as available (valid), the terminal selects that RPLMN and attempts to connect to (or attempts to camp on) that RPLMN. It should be understood that the method for determining whether an RPLMN is valid can be predefined by the protocol. For example, if the terminal detects that the RPLMN signal strength is greater than a preset threshold of 1 and the signal is stable, then the RPLMN is considered available (valid). This application embodiment does not limit this.

[0087] Furthermore, the terminal can register with the RPLMN. Registration refers to the process by which the terminal establishes a connection with the selected PLMN (such as the RPLMN) and completes authentication and location updates. The terminal can obtain network services through registration. Specifically, the registration process may include the terminal sending an authentication request to the selected PLMN (such as the RPLMN). The authentication request may include, for example, the IMSI and other authentication information (the specific information included in the authentication request may be predefined by the protocol, and this embodiment does not limit this). Further, the selected PLMN (such as the RPLMN) uses the IMSI and authentication key stored in the core network to authenticate the terminal. If authentication is successful, the terminal will be allowed to access the network. After successful authentication, the terminal can send a registration request to the PLMN to complete network registration. Correspondingly, if the PLMN confirms that the terminal's registration request is valid and legitimate, the PLMN can send a registration acceptance message to the terminal, which indicates that the terminal is allowed to access the network and begin using the services. It should be understood that the registration process shown is merely an illustrative example to facilitate understanding of the embodiments of this application, and is not intended to limit the specific embodiments of this application. In practical applications, the registration process may include other steps, and the specific steps included in the registration process may be predefined by the protocol. This application does not limit this.

[0088] If registration is successful, the terminal executes S21.

[0089] S21, the terminal indicates the selected PLMN.

[0090] Specifically, the terminal can indicate its currently selected PLMN to the network. Correspondingly, after receiving the indication from the terminal, the network can decide how to allocate channel resources or perform load balancing based on the PLMN the terminal is in. At this point, the terminal can be understood as having completed the PLMN selection process and successfully camped on and accessed the selected PLMN (ON PLMN state). However, even in the ON PLMN state, situations may arise where the terminal cannot access the network, requiring a reselection of a PLMN. These situations may include, but are not limited to, the following:

[0091] Scenario 1: The terminal can initiate location registration with the network to activate services (such as data transmission and voice calls). For example, the terminal can send a location update request (LR) to the network. If the network accepts the location update request, the terminal can access the network to use services such as data transmission and voice calls. If the network rejects the location update request, the terminal can reselect a PLMN, i.e., the terminal executes S3.

[0092] Case 2: Loss of radio coverage of the selected PLMN. For example, if the PLMN currently hosted by the terminal cannot maintain the connection due to signal loss or quality deterioration, the terminal can reselect a PLMN, that is, the terminal executes S3.

[0093] If registration fails, for example, if the current RPLMN is too overloaded and cannot receive the terminal's registration request, or if the current RPLMN is temporarily malfunctioning or under maintenance, making it impossible to complete the terminal's registration, or if the terminal fails to connect (or try to reside) with the RPLMN, then the terminal can reselect a PLMN, that is, the terminal executes S3.

[0094] S3, the terminal determines whether there is an available network based on the read EHPLMN list / HPLMN list. Specifically, if the EHPLMN list exists, the terminal selects the highest priority available EHPLMN in the list and attempts to access or register. The specific implementation of the terminal's attempt to access or register can be found in the process of the terminal attempting to access or register with the RPLMN shown above, and will not be repeated here. If the terminal fails to access or register with the highest priority EHPLMN and cannot use data transmission, voice calls, or other services by accessing the highest priority EHPLMN, the terminal can select the second highest priority available EHPLMN in the list and attempt to access or register. This continues until the terminal fails to achieve data transmission or voice calls based on multiple EHPLMNs in the EHPLMN list. Finally, the terminal can select an available HPLMN in the HPLMN list and attempt to access or register.

[0095] Alternatively, if the EHPLMN list is nonexistent or empty, the terminal can select an available HPLMN from the HPLMN list and attempt to access or register. If the terminal determines, based on the read EHPLMN / HPLMN list, that there is currently no available EHPLMN or HPLMN, the terminal can reselect a PLMN, i.e., the terminal executes S4.

[0096] S4, the terminal determines whether there is an available network based on the read UPLMN list.

[0097] Optionally, the UPLMN list may contain multiple UPLMN entries. The terminal can attempt to access and register with these UPLMNs sequentially based on their priority order. For example, if the UPLMN list includes networks with priority levels from high to low as UPLMN1, UPLMN2, and UPLMN3, the terminal can attempt to access and register with the UPLMNs in the list sequentially according to this priority order. If the registration is successful, the terminal can use the services provided by the UPLMN. If the registration fails, the terminal can continue to try the next UPLMN with a lower priority level.

[0098] It should be understood that the terminal determines whether an RPLMN in the UPLMN list is available or whether a PLMN needs to be reselected. For details on determining whether an RPLMN is available or whether a PLMN needs to be reselected, please refer to the relevant description shown in S2 above. It will not be repeated here.

[0099] If all UPLMN entries in the UPLMN list have been tried but none have been successfully registered, or services such as data transmission or voice calls have been used, the terminal can reselect a PLMN, i.e., the terminal executes S5.

[0100] S5, the terminal determines whether there is an available network based on the OPLMN list it reads.

[0101] Similar to the UPLMN list, the OPLMN list may contain multiple OPLMN entries. The terminal can try to access and register with these OPLMNs in order of priority. If all OPLMN entries in the OPLMN list have been tried but registration has failed, or if services such as data transmission or voice calls have failed to be used, the terminal can reselect a PLMN, that is, the terminal executes S6.

[0102] S6: The terminal determines whether there is an available network based on the APLMN list.

[0103] Optionally, the APLMN list is dynamically generated by the terminal through a frequency scanning operation, containing multiple detectable available PLMNs and their related information. The terminal can sequentially attempt to connect to and register with each APLMN according to the order in the APLMN list until it successfully accesses or registers with the PLMN and uses the service, or after trying all APLMN entries. It should be understood that the PLMN selection process shown above is only an exemplary description for the purpose of understanding the embodiments of this application, and is not a specific limitation on the embodiments of this application. In practical applications, PLMN selection can be implemented based on other processes. For example, the terminal can access the network based on a PLMN selection implementation method predefined by the protocol, and the embodiments of this application do not limit this. In addition, the priority order of different types of PLMN lists can also be predefined by the protocol, and the embodiments of this application do not limit this.

[0104] It should also be understood that the PLMN selection process shown above is the PLMN selection process in automatic mode, but the embodiments of this application are not limited to this. In actual application, users can also control the terminal to manually select the PLMN that can be accessed, and the embodiments of this application do not limit this.

[0105] With the development of wireless communication technology, the types of radio access technologies (RATs) that a PLMN can support are also increasing. These RAT types can include, for example, New Radio (NR) technology for 5G communication systems, LTE technology for 4G communication systems, Wideband Code Division Multiple Access (WCDMA) technology for 3rd generation (3G) communication systems, or Global System for Mobile Communications (GSM) technology for 2nd generation (2G) communication systems. Based on the priority-based selection of PLMN access networks according to PLMN type, for each PLMN, the terminal can also select a RAT access network from the RAT types supported by the PLMN. If all RATs of the current PLMN cannot be registered, the terminal can reselect a PLMN.

[0106] Optionally, the combination of each PLMN and its supported RAT can be stored in the terminal or SIM card. For example, the combination of UPLMN and its supported RAT can be stored in the "User-Controlled PLMN Selector and Access Technology" file on the SIM card. Assuming the terminal accesses the network in the following order of PLMN priority from high to low: HPLMN1 (corresponding to RAT1), HPLMN2 (corresponding to RAT2), UPLMN1 (corresponding to RAT1), UPLMN2 (corresponding to RAT2), OPLMN1 (corresponding to RAT1), OPLMN2 (corresponding to RAT2), APLMN1 (corresponding to RAT1), APLMN2 (corresponding to RAT2), where the RAT in parentheses represents the RAT supported by the PLMN read by the terminal, then during the PLMN selection process, the network search will proceed in the following order:

[0107] HPLMN1+RAT1→HPLMN2+RAT2→UPLMN1+RAT1→UPLMN2+RAT2→OPLMN1+RAT1→OPLMN2+RAT2→APLMN1+RAT1→APLMN2+RAT2.

[0108] According to the PLMN selection process described above, the terminal can select a higher-priority PLMN to access the network based on the priority level of each PLMN type. Specifically, the terminal prioritizes connecting to an RPLMN, allowing it to quickly return to a familiar network environment. If an RPLMN is unavailable, the terminal can try other high-priority networks (such as HPLMN or EHPLMN) in sequence. In other words, the terminal prioritizes its home network or equivalent home network when selecting a network, thus reducing additional costs incurred due to roaming.

[0109] If there is no available HPLMN or EHPLMN for the terminal (i.e., the terminal is not within the coverage area of ​​an HPLMN or EHPLMN), the terminal is most likely in an international roaming scenario. The terminal can select a suitable visited PLMN (VPLMN) from the UPLMN or OPLMN list to connect to according to priority. The VPLMN can be understood as a network with a roaming protocol to the HPLMN of the SIM card used by the terminal. When the terminal is abroad or not within the coverage area of ​​its home network, the VPLMN can provide temporary communication services for the terminal, allowing the user to continue to use services such as voice calls or data transmission while roaming.

[0110] In international roaming scenarios, since the terminal is not within the coverage area of ​​the HPLMN or EHPLMN, the PLMN type that the terminal can choose when selecting a PLMN is UPLMN, OPLMN, or APLMN. In other words, the terminal selects a PLMN based on a priority list of UPLMN, OPLMN, or APLMN. However, it should be understood that in this scenario, the PLMN tariff used by the terminal is determined by the roaming agreement between the home network (HPLMN) operator and the roaming location (i.e., the terminal's current location) operator. Different types of PLMNs do not affect the tariff. That is, in international roaming scenarios, roaming tariffs do not distinguish between the selected UPLMN, OPLMN, or APLMN type.

[0111] Therefore, in this situation, the choice of RAT level is more important for the terminal. This is because, compared to lower-standard RATs, higher-standard RATs can provide the terminal with higher data transmission rates, lower transmission latency, or higher spectrum efficiency. Under the same tariff standard, users are more likely to expect the terminal to register on a higher-standard RAT network in order to obtain services such as higher voice clarity or smoother data transmission.

[0112] However, in international roaming scenarios, a terminal may simultaneously be connected to both a high-priority PLMN but a low-standard RAT network and a low-priority PLMN but a high-standard RAT network. Since roaming tariffs do not differentiate between UPLMN, OPLMN, and APLMN, users are highly likely to expect the terminal to select a PLMN with a higher-standard RAT network. However, if the terminal still selects the network based on PLMN priority, it may end up connecting to a high-priority PLMN but a low-standard RAT network even when a higher-standard RAT network is available, thus preventing the terminal from obtaining network services with better communication performance.

[0113] For example, Figure 2 is a schematic diagram of an application scenario provided by an embodiment of this application. As shown in Figure 2, assuming the terminal is in an international roaming scenario (i.e., not within the coverage area of ​​HPLMN or EPLMN), the terminal is currently within the coverage area of ​​the high-priority UPLMN1, which supports the RAT GSM, and the terminal is also within the coverage area of ​​the low-priority OPLMN1, which supports the RAT NR. It can be understood that compared to GSM, NR has a higher data transmission rate, lower transmission latency, and higher spectrum efficiency. That is, if the terminal chooses to access the network with the OPLMN1+NR combination, it can obtain higher communication performance. However, if the terminal still chooses to access the network according to the priority level of the PLMN, the terminal will most likely access the network with the UPLMN1+GSM combination, which provides lower communication performance to the terminal compared to the network with the OPLMN1+NR combination.

[0114] Based on this, embodiments of this application propose that the terminal can prioritize RAT priority and select the highest priority RAT (or the RAT with the highest standardization) among the RATs supported by the terminal. Furthermore, after selecting the first RAT, the terminal can attempt to camp on a PLMN with a higher priority level based on the priority of each PLMN using the first RAT. This helps the terminal camp on networks with higher standard RATs and higher PLMN priority, thus improving the terminal's communication performance.

[0115] The methods provided in the embodiments of this application will now be described in detail with reference to the accompanying drawings.

[0116] The communication method provided in this application can be executed by a communication device, which can be a terminal, or it can be a module (such as a chip, logic circuit, or chip system) configurable in (or usable in) a terminal. In this application, the communication method provided in this application is described in detail using a terminal executing the communication method provided in this application as an example; it should be understood that this application is not limited thereto.

[0117] Figure 3 is a schematic flowchart of a communication method provided in an embodiment of this application. This method may include, but is not limited to, steps S301, S302, and S303 below. Each step is described in detail below.

[0118] S301, the terminal searches for a public land mobile network (PLMN) that uses a first radio access technology (RAT), which is the highest priority RAT supported by the terminal and has not been selected.

[0119] The RATs supported by the terminal can also be understood as RATs that the terminal can use, such as NR, LTE, WCDMA, and / or GSM. Optionally, these RATs supported by the terminal can be pre-configured in the terminal, for example, they can be stored in the terminal's firmware or configuration file. In addition, the priority of the RATs supported by the terminal can be predefined by the protocol, or it can be pre-configured in the terminal; this application embodiment does not impose any limitations on this.

[0120] S302, if there is a PLMN that uses the first RAT, the terminal selects the first RAT.

[0121] Taking a terminal that supports RATs including NR, LTE, WCDMA, and GSM as an example, assuming the priority levels of these RATs from highest to lowest are NR, LTE, WCDMA, and GSM, and assuming that PLMNs using NR, LTE, WCDMA, and GSM have not been searched by the terminal, then the terminal can prioritize searching for PLMNs using NR, meaning the first RAT is NR. As another example, if the terminal supports RATs including NR, LTE, WCDMA, and GSM, but a PLMN using NR has already been selected by the terminal, then the terminal can select the highest priority RAT (i.e., LTE) from among the RATs it supports that have not been selected (i.e., among LTE, WCDMA, and GSM) for searching.

[0122] It should be understood that the at least one RAT supported by the terminals shown is NR, LTE, WCDMA and / or GSM, which is merely an exemplary description for ease of understanding of the embodiments of this application and is not a specific limitation on the embodiments of this application. In practical applications, the RAT supported by the terminal may also include other standard levels of RAT, which can be determined based on the terminal's capabilities. The embodiments of this application do not impose any limitations on this, such as including RATs corresponding to future communication systems. Further, if the terminal can find a PLMN using the first RAT, the terminal can select the first RAT. Alternatively, it can be understood that if the terminal's current geographical location is within the coverage area of ​​a PLMN using the first RAT, the terminal can select the first RAT.

[0123] In this embodiment of the application, in the current PLMN selection process, "RAT has been selected by the terminal" means that the terminal has selected the RAT and attempted to access all PLMNs using the RAT.

[0124] Optionally, the terminal may search for a PLMN using the first RAT (Range Access Target) when the network selection mode is set to automatic. The network selection mode refers to the strategy adopted by the terminal when accessing a network (PLMN), and may include automatic mode (or automatic selection mode) and manual mode (or manual selection mode). In automatic mode, the terminal can automatically select and register a more suitable PLMN based on preset rules (such as priority lists, signal strength, and pricing policies). In manual mode, the user can actively specify a target PLMN from the list of available PLMNs, and the terminal then attempts to access and register with the user-selected PLMN.

[0125] In other words, in the embodiments of this application, the terminal can perform network search in automatic mode (i.e., perform the above search for PLMN using the first RAT), and in manual mode, the terminal can attempt to stay on or access the target PLMN selected by the user.

[0126] It should also be understood that in the absence of an available home PLMN and an equivalent PLMN (or equivalent home PLMN) for the home network, the terminal is not within the coverage area of ​​the HPLMN or EHPLMN, and the terminal is highly likely to be in an international roaming scenario. As mentioned above, in international roaming scenarios, roaming tariffs do not distinguish between the selected UPLMN, OPLMN, or APLMN type of PLMN. To enable the terminal to select a higher-standard RAT and obtain higher communication performance in international roaming scenarios, in this embodiment, the terminal's search for a PLMN using the first RAT can be performed even when no available home PLMN and an equivalent PLMN for the home network exist.

[0127] The specific terminal may determine whether there is a PLMN using the first RAT (or whether to select the first RAT) in the following ways, including but not limited to the following methods 1 and 2.

[0128] Method 1: If the terminal or SIM card stores (or configures) at least one PLMN using the first RAT, the terminal can search for that at least one PLMN using the first RAT. If the terminal confirms that one of the at least one PLMN using the first RAT exists, the terminal can consider that a PLMN using the first RAT exists. If the terminal confirms that none of the PLMNs using the first RAT exist, and the terminal still cannot find a PLMN using the first RAT using other methods (such as Method 2 below), the terminal can consider that a PLMN using the first RAT does not exist.

[0129] It should be noted that the SIM card mentioned in this application embodiment can also be an eSIM, that is, it can achieve all or part of the functions of a physical SIM card without physical insertion, or it can be replaced with other modules that enable the terminal to access the network. This application embodiment does not limit this.

[0130] For example, if the terminal or SIM card stores (or can obtain) a set of PLMNs corresponding to the first RAT, and this set of PLMNs includes PLMN1 and PLMN2 using the first RAT, the terminal can search for PLMN1 or PLMN2 to confirm whether a PLMN using the first RAT exists. If the terminal finds that one of PLMN1 or PLMN2 exists, the terminal can consider that a PLMN using the first RAT exists, and the terminal can select that first RAT. If the terminal determines through the search that neither PLMN1 nor PLMN2 exists (i.e., the terminal's geographical location is not within the coverage area of ​​PLMN1 or PLMN2), and the terminal still cannot find a PLMN using the first RAT using other methods (such as method 2 below), the terminal can consider that a PLMN using the first RAT does not exist, and the terminal does not select that first RAT.

[0131] Optionally, for one of the at least one PLMNs using the first RAT (taking PLMN1 as an example), the implementation method for the terminal to confirm the existence of PLMN1 may include, but is not limited to: the terminal can read the relevant information of PLMN1. Further, the terminal can perform a frequency sweep operation on its supported frequency bands. If the terminal can receive a broadcast signal related to PLMN1, the terminal confirms that its current location is within the coverage area of ​​the corresponding PLMN1, that is, the terminal confirms the existence of PLMN1. Conversely, if the terminal cannot receive a broadcast signal related to PLMN1, the terminal can determine that its current location is likely not within the coverage area of ​​the corresponding PLMN1, and the terminal can consider that PLMN1 does not exist.

[0132] Method 2: The terminal can search for (discover) a PLMN using a first RAT (such as NR) in its current geographical location by frequency scanning. The frequency scanning range of the terminal can be, for example, the frequency bands supported by the first RAT (such as the NR band). It should be understood that the frequency bands used by different regions or different operators may be different, and the specific frequency band range for frequency scanning by the terminal can be determined according to the actual situation. This application embodiment does not limit this.

[0133] Specifically, after determining the frequency scanning range, the terminal can scan for possible frequency points on the frequency band supported by the first RAT. For each frequency point, the terminal can attempt to find a base station broadcasting system information (SI) and obtain the PLMN to which that base station belongs. Taking NR as an example, the terminal can search for the synchronization signal (such as the synchronization signal block (SSB)) of a base station on the NR band. If the terminal finds the SSB of a certain base station, it can parse the SSB to obtain the corresponding physical broadcast channel (PBCH). Further, the terminal can read the master information block (MIB) carried by the PBCH. By parsing the MIB, the terminal can further read system information blocks (SIBs), which contain the PLMN to which the base station belongs, thus enabling the terminal to search for the PLMN using NR.

[0134] If, based on method 2, the terminal can find a PLMN using the first RAT, it can be understood that a PLMN using the first RAT exists, and the terminal can select that first RAT. If, based on method 2, the terminal cannot find a PLMN using the first RAT, and the terminal still cannot find a PLMN using the first RAT using other methods (such as method 1 above), it can be understood that a PLMN using the first RAT does not exist.

[0135] According to method 1 or method 2 described above, the terminal can confirm whether a PLMN using the first RAT exists. The specific method used can be predefined by the protocol or pre-configured on the terminal; this embodiment does not limit this. Optionally, method 1 and method 2 can also be used in combination to search for PLMNs using the first RAT as much as possible, thereby helping the terminal access higher-standard RATs and improving the terminal's communication performance.

[0136] It should be understood that the above-described embodiments of method 1, method 2, or a combination of both are merely exemplary descriptions for the purpose of understanding the embodiments of this application, and are not specific limitations on the embodiments of this application. In practical applications, the terminal may also confirm the existence of the PLMN of the first RAT through other means.

[0137] Additionally, if the terminal confirms that no PLMN using the first RAT exists, the terminal can search for a PLMN using the second RAT. Specifically, the second RAT can be the highest priority RAT supported by the terminal, other than the first RAT, that has not yet been selected. For example, if the terminal supports RATs including NR, LTE, WCDMA, and GSM, but a PLMN using NR has already been selected by the terminal, the terminal can select the highest priority RAT (i.e., LTE) from among the RATs it supports that have not yet been selected (i.e., among LTE, WCDMA, and GSM) for the search.

[0138] Furthermore, after the terminal selects the first RAT, the terminal can execute S303.

[0139] S303, the terminal attempts to reside on the PLMN using the first RAT.

[0140] Here, "camping" refers to the process of a terminal successfully connecting to a cell and maintaining communication. Attempting to camp can be understood as the terminal attempting to select a cell with good signal quality or that meets specific conditions (such as the S criterion) from one or more cells covered by the PLMN of the first RAT to establish a connection and maintain communication. Optionally, the terminal's attempt to camp on the PLMN using the first RAT can also be described as the terminal executing (or initiating) a camping procedure to camp on the PLMN using the first RAT, or it can be described as the terminal initializing a camping procedure to camp on the PLMN using the first RAT, or it can be replaced with other descriptive methods. This application embodiment does not limit this.

[0141] Optionally, the terminal's attempt to camp on the PLMN using the first RAT can also be understood as the terminal's attempt to camp on the cell corresponding to the PLMN of the first RAT. For example, it may include the terminal accessing the target cell through a random access channel (RACH) and establishing a radio resource control (RRC) connection with the base station managing the target cell, or it may also include the terminal authenticating and registering with the PLMN. This application embodiment does not limit this.

[0142] Optionally, the terminal may attempt to camp on the highest-priority PLMN (hereinafter referred to as the first PLMN) among the candidate PLMNs of the first RAT that the terminal has not yet attempted to camp on. That is, after the terminal selects the first RAT, the terminal will preferentially attempt to camp on the first PLMN. In other words, after the terminal selects the first RAT based on the RAT priority, the terminal may attempt to camp on the PLMN using the first RAT based on the priority order of the PLMNs.

[0143] The candidate PLMN set may include at least one PLMN that adopts the first RAT. Specific implementation methods for a terminal to obtain the candidate PLMN set may include, but are not limited to, the following implementation methods.

[0144] Optionally, the terminal determines the candidate PLMN set based on at least one of the following: the user-configured PLMN priority set, the pre-configured PLMN priority set, or the PLMN set obtained by searching the PLMN of the first RAT (i.e., the APLMN set), and network coverage information.

[0145] The user-configured PLMN priority set may include at least one PLMN manually selected and saved by the user. The priority level of the user-selected and saved PLMN can be user-configured, and this embodiment does not impose any restrictions on this. Optionally, the user-configured PLMN priority set may also be called the UPLMN priority set. The user-configured PLMN priority set may include, for example, UPLMN1 and UPLMN2, and the user can configure UPLMN1 to have a higher priority than UPLMN2.

[0146] The pre-configured PLMN priority set may include at least one PLMN pre-configured on the terminal. Optionally, the pre-configured PLMN priority set may be one pre-configured on the terminal by the operator, and this embodiment of the application is not limited thereto. Optionally, the pre-configured PLMN priority set may also be referred to as the OPLMN priority set. The pre-configured PLMN priority set may include, for example, OPLMN1 and OPLMN2, and the operator may pre-configure that the priority of OPLMN1 is higher than that of OPLMN2.

[0147] The PLMN set (i.e., APLMN set) obtained by searching the PLMN of the first RAT can be detectable by the terminal in the current environment. This APLMN set can be stored in the terminal in the form of a list, that is, the APLMN set can also be an APLMN list. For details on how the terminal obtains this APLMN set, please refer to the relevant description of the APLMN list above, which will not be repeated here.

[0148] Optionally, the aforementioned UPLMN priority set, OPLMN priority set, or APLMN set can be stored in the terminal or SIM card in the form of a list, and this application embodiment does not impose any restrictions on this.

[0149] Network coverage can be assessed, for example, by the signal strength or network quality of the PLMN at the terminal's current geographical location. Optionally, if the signal strength or network quality of a PLMN at the terminal's current geographical location is greater than (or equivalent to greater than or equal to) a threshold A, the terminal can configure that PLMN as a candidate PLMN. If the signal strength or network quality of a PLMN at the terminal's current geographical location is less than (or equivalent to less than or equal to) a threshold B, then that PLMN cannot be considered a candidate PLMN. Optionally, whether the network coverage is assessed by signal strength, network quality, or other parameters used to indicate network coverage can be predefined by the protocol or pre-configured on the terminal; this embodiment does not impose any limitations on this.

[0150] To facilitate understanding, the following example illustrates how a terminal determines a candidate PLMN set based on the UPLMN priority set, OPLMN priority set, and APLMN set.

[0151] Assuming the UPLMN set includes UPLMN1 and UPLMN2 (UPLMN1 has higher priority than UPLMN2), the OPLMN set includes OPLMN1 and OPLMN2 (OPLMN1 has higher priority than OPLMN2), and the APLMN set includes APLMN1 and APLMN2 (APLMN1 has higher priority than APLMN2), then the candidate PLMN set can contain the UPLMN set, OPLMN set, or APLMN set. That is, the candidate PLMN set can include UPLMN1, UPLMN2, OPLMN1, OPLMN2, APLMN1, and APLMN2. Optionally, assuming the priority levels are UPLMN, OPLMN, and APLMN in descending order, the candidate PLMN set includes at least one PLMN in descending order of priority: UPLMN1, UPLMN2, OPLMN1, OPLMN2, APLMN1, and APLMN2.

[0152] For example, based on the above example, if the terminal also determines the candidate PLMN set according to the network coverage, assuming that the signal strength (or network quality) of UPLMN1, OPLMN1, APLMN1 and APLMN2 among the above multiple PLMNs is greater than (or replaced by greater than or equal to) threshold A, and the signal strength or network quality of UPLMN2 and OPLMN2 is less than (or replaced by less than or equal to) threshold B, then the candidate PLMN set may include UPLMN1, OPLMN1, APLMN1 and APLMN2.

[0153] When a terminal attempts to camp on a PLMN that uses the first RAT, it will prioritize camping on the first PLMN. The first PLMN is the highest priority PLMN among the candidate PLMNs that the terminal has not attempted to camp on in the set of candidate PLMNs that use the first RAT. For example, if the first PLMN is UPLMN1 in the above example, the terminal can attempt to camp on UPLMN1.

[0154] If the attempt to reside in the first PLMN is successful, the first PLMN can provide network services to the terminal, such as data transmission and voice calls.

[0155] If the attempt to camp on the first PLMN fails, the terminal can continue to try to camp on the second PLMN. The second PLMN can be understood as the highest priority PLMN among the PLMNs in the candidate PLMN set that the terminal has not tried to camp on. For example, in the above example, the second PLMN is UPLMN2, and the terminal can try to camp on UPLMN2. And so on. If the terminal fails to camp on UPLMN2, the terminal can continue to try OPLMN1, OPLMN2, APLMN1, or APLMN2 until the terminal successfully camps on a PLMN in the candidate PLMN set. A PLMN in the candidate PLMN set can then provide the terminal with services such as data transmission and voice calls.

[0156] According to the above scheme, the terminal can preferentially select the highest priority RAT (or the RAT with the highest standard) among the RATs supported by the terminal, and attempt to camp on the PLMN using the first RAT. Furthermore, after selecting the first RAT, the terminal can attempt to camp on a PLMN with a higher priority level based on the priority of each PLMN using the first RAT. This helps the terminal camp on networks with higher standard RATs and higher priority PLMNs, thus improving the terminal's communication performance.

[0157] Correspondingly, if the terminal fails to camp on a PLMN that uses the first RAT, that is, until the terminal fails to camp on the PLMN with the lowest priority level in the candidate PLMN set corresponding to the first RAT (such as APLMN2 in the example above), the terminal can search for a PLMN that uses the second RAT. The second RAT is the highest priority RAT that the terminal supports and has not been selected. For details, please refer to the relevant description of the second RAT above, which will not be repeated here.

[0158] Furthermore, if the terminal confirms through a search that a PLMN using the second RAT exists at the current geographical location, the terminal selects the second RAT. It should be understood that the implementation method for the terminal to confirm the existence of a PLMN using the second RAT is similar to the implementation method for the terminal to confirm the existence of a PLMN using the first RAT described above, and can be referred to the description above for details, which will not be repeated here.

[0159] It is understandable that if a PLMN adopting the second RAT exists, the terminal selects the second RAT. Further, the terminal attempts to reside in the PLMN adopting the second RAT. Specifically, the terminal may attempt to reside in the highest priority PLMN among the candidate PLMNs of the second RAT that the terminal has not yet attempted to reside in. The implementation method for the terminal to obtain the candidate PLMN set of the second RAT is similar to the implementation method for the terminal to obtain the candidate PLMN set of the first RAT, as described above, and will not be repeated here.

[0160] If the terminal successfully camps on the PLMN that uses the second RAT, the PLMN can provide network services to the terminal, such as data transmission and voice calls.

[0161] If the terminal fails to camp on a PLMN using the second RAT, or if the terminal confirms through a search that no PLMN using the second RAT exists, the terminal can select a PLMN of the next standard level (such as the third RAT). Specifically, the terminal can search for a PLMN using the third RAT. If a PLMN using the third RAT exists, the terminal can select that third PLMN and attempt to camp on it.

[0162] According to the above scheme, when a terminal fails to camp on a PLMN using the first RAT, it can select a RAT of the next standard level that it supports and attempt to camp on a PLMN using that next standard level. This helps the terminal select a higher standard level RAT and improves its communication performance.

[0163] To improve the flexibility of terminal selection of PLMN, embodiments of this application also propose that the terminal can search for PLMNs using a first RAT based on configuration parameters stored in non-volatile (NV) memory. These configuration parameters are used to control the selection of networks with RAT priority.

[0164] In one implementation, the configuration parameter used to control whether to select a network (PLMN) using RAT priority is a Boolean parameter. Specifically, the Boolean parameter can be used to indicate whether the implementation of RAT priority selection is enabled (or activated, started) or disabled (or deactivated, disabled). For example, if the Boolean parameter is set to true, it indicates that RAT priority selection is enabled, or that the RAT priority selection function is active, or that the RAT priority selection function is started, or that the RAT priority selection function is activated. If the Boolean parameter is set to false, it indicates that RAT priority selection is disabled, or that the RAT priority selection function is inactive, or that the RAT priority selection function is disabled, or that the RAT priority selection function is not activated.

[0165] In another implementation, the configuration parameter stored in the NV memory, specifically whether it is set to enable (or activate, start) or disable (or deactivate, disable) network selection based on RAT priority, can be pre-configured on the terminal. Alternatively, it can be manually configured by the user; for example, if the configuration parameter is set to disable (or deactivate, disable) network selection based on RAT priority, the user can set the configuration parameter to true, thereby enabling the function of selecting the network based on RAT priority.

[0166] Specifically, when the terminal powers on, it can read the configuration parameters stored in the NV memory. If the configuration parameters are used to enable (or activate, start) the function of selecting the network with RAT priority, the terminal can prioritize selecting the network with RAT priority. Conversely, if the configuration parameters are used to disable (or deactivate, disable) the function of selecting the network with RAT priority, the terminal can still select the network with PLMN priority.

[0167] It should be noted that the configuration parameters for controlling whether to select a network based on RAT priority, as shown above, are Boolean parameters only for illustrative purposes to facilitate understanding of the embodiments of this application, and are not specific limitations on the embodiments of this application. In practical applications, the configuration parameters for controlling whether to select a network based on RAT priority can also be other types of configuration parameters. Specifically, they can be predefined by the protocol and can be used to distinguish whether to enable (or activate, start) or deactivate (or deactivate, disable) the selection of a network based on RAT priority. The embodiments of this application do not impose any limitations on this.

[0168] Figure 4 is a specific example of the embodiment shown in Figure 3. The parts in Figure 4 that are the same as those in the embodiment shown in Figure 3 can be referred to the description in the embodiment shown in Figure 3, and will not be repeated here.

[0169] S401, the terminal is powered on in a roaming scenario.

[0170] S402, the terminal searches the current environment for a PLMN that supports the highest standard level (or highest priority) RAT (such as the first RAT mentioned above).

[0171] If the current environment has a PLMN that uses the highest RAT standard supported by the terminal, then the terminal executes S404.

[0172] If the current environment does not have a PLMN of the highest RAT standard supported by the terminal, the terminal executes S403.

[0173] S403, The terminal searches the current environment for the existence of a RAT (such as the second RAT mentioned above) that uses the highest system level (or highest priority) that is supported by the terminal and has not been selected.

[0174] If a RAT with the highest system level (or highest priority) that is supported by the terminal and has not been selected exists in the current environment, the terminal executes S404.

[0175] If there is no RAT in the current environment that uses the highest-level (or highest-priority) standard that the terminal supports and has not been selected, the terminal will exit the network search (i.e., the terminal loses the network).

[0176] S404, the list of PLMNs that can be searched on the RAT with the highest terminal build standard level (or highest priority) (i.e., the set of candidate PLMNs for terminal builds mentioned above).

[0177] Optionally, the implementation method for the terminal to construct the PLMN list can be referred to the relevant description of constructing the candidate PLMN set in the embodiment of Figure 3, which will not be repeated here.

[0178] S405, The terminal attempts to reside on the highest priority PLMN in the list of PLMNs that it has not attempted to reside on before.

[0179] If a terminal successfully resides on the highest-priority PLMN in the constructed PLMN list, then the highest-priority PLMN can provide services such as data transmission and voice calls to the terminal PLMN.

[0180] If the terminal fails to reside on the highest priority PLMN in the constructed PLMN list, the terminal can execute S406.

[0181] S406, the terminal determines whether there is a PLMN in the PLMN list corresponding to the selected RAT that has not been attempted to reside in.

[0182] If there is a PLMN in the PLMN list corresponding to the RAT selected by the terminal that has not been attempted to reside on, the terminal executes S405, that is, the terminal attempts to reside on the PLMN of the next priority level that uses the selected RAT.

[0183] If the PLMN list corresponding to the RAT selected by the terminal does not contain a PLMN that has not been attempted to reside on, the terminal executes S402, that is, through S402, the terminal reselects the next standard level RAT and attempts to reside on the PLMN that adopts the next standard level RAT.

[0184] According to the above scheme, the terminal can preferentially attempt to camp on a PLMN that uses a RAT with a higher priority level (or standard level) supported by the terminal, and attempt to camp on a PLMN with a higher priority level among the PLMNs corresponding to the selected RAT. This helps to improve the communication performance of the terminal.

[0185] Optionally, the communication method provided in this application embodiment can also be used in conjunction with a method where the terminal prioritizes the network selection based on the PLMN's priority level. Specifically, in domestic roaming scenarios, the terminal prioritizes attempting to camp on an HPLMN or EHPLMN. In international roaming scenarios (i.e., when the terminal is not within the coverage area of ​​an HPLMN or EHPLMN), the terminal attempts to camp on a network using the highest priority RAT supported by the terminal and not previously selected by the terminal. A detailed explanation follows with reference to Figure 5.

[0186] Figure 5 is another specific example of the embodiment shown in Figure 3. The parts in Figure 5 that are the same as those in the embodiment shown in Figure 3 can be referred to the description in the embodiment shown in Figure 3, and will not be repeated here.

[0187] S501, the terminal starts up from the power-off state and uses the SIM card.

[0188] S502, the terminal determines whether an HPLMN or EHPLMN exists (or whether it is within the coverage area of ​​an HPLMN or EHPLMN).

[0189] If HPLMN or EHPLMN exists, the terminal can execute S503.

[0190] If neither HPLMN nor EHPLMN exists, the terminal can perform the network search process.

[0191] S503, the terminal attempts to reside in this HPLMN or EHPLMN.

[0192] Optionally, after a terminal resides on the HPLMN or EHPLMN, it can register, that is, the terminal establishes a connection with the HPLMN or EHPLMN and completes authentication and location updates in order to obtain the network services of the HPLMN or EHPLMN.

[0193] If the terminal successfully registers on an HPLMN or EHPLMN, it enters the ON PLMN state. This ON PLMN state indicates that the terminal has successfully registered with a PLMN and can use the voice call, data transmission, and other services provided by that PLMN. The specific steps involved in registration can be found in the relevant descriptions above and will not be repeated here.

[0194] If the terminal fails to register on HPLMN or EHPLMN, the terminal will proceed with the network search process.

[0195] In other words, if a terminal is registered with the HPLMN or EHPLMN but registration fails, the terminal will be unable to obtain network services such as voice calls or data transmission. In this case, the terminal can search for networks again and try to register with a new PLMN.

[0196] The network search process can be the process described in the embodiment of Figure 3 above, where the terminal attempts to camp on a network with a higher-standard RAT and a higher priority PLMN. Specifically, if no available HPLMN (Home PLMN) or EHPLMN (Equivalent Home PLMN) exists, the terminal searches for a PLMN using a first RAT, where the PLMN using the first RAT can be at least one of UPLMN, OPLMN, or APLMN. For a detailed description of the process of the terminal attempting to camp on a network with a higher-standard RAT and a higher priority PLMN, please refer to the relevant description in the embodiment of Figure 3, which will not be repeated here.

[0197] S504 If the terminal successfully searches for a network (i.e., the terminal successfully resides on a PLMN through the network search process), then attempt to reside on a PLMN that uses a certain RAT selected through the network search process.

[0198] Furthermore, the terminal can register with the PLMN. If registration is successful, the terminal can use the PLMN's services such as voice calls and data transmission. Conversely, if registration fails, the terminal will restart the network search process.

[0199] S505: If the terminal fails to search for a network (e.g., there is no available network), the terminal will exit the network search (the terminal loses network access).

[0200] According to the above scheme, in domestic roaming scenarios, the terminal can preferentially attempt to camp on an HPLMN or EHPLMN. In international roaming scenarios (i.e., when the terminal is not within the coverage area of ​​an HPLMN or EHPLMN), the terminal can attempt to camp on a network using the highest priority RAT that the terminal supports and has not yet selected. This helps the terminal camp on networks with higher-standard RATs and higher PLMN priority, thus improving the terminal's communication performance.

[0201] It is understood that, in order to achieve the functions in the above embodiments, the terminal includes hardware structures and / or software modules corresponding to the execution of each function. Those skilled in the art should readily recognize that, based on the units and method steps described in conjunction with the embodiments disclosed in this application, the embodiments of this application can be implemented in hardware or a combination of hardware and computer software. Whether a function is executed by hardware or by computer software driving hardware depends on the specific application scenario and design constraints of the technical solution.

[0202] Figures 6 and 7 are schematic diagrams illustrating possible communication devices provided in embodiments of this application. These communication devices can be used to implement the functions of the terminal in the above method embodiments, and thus can also achieve the beneficial effects of the above method embodiments. In the embodiments of this application, the communication device can be one of the terminals 120a-120j shown in Figure 1, or it can be a network device 110a or 110b shown in Figure 1, or it can be a module (such as a chip or chip system) applied to a terminal or network device.

[0203] The communication device 600 includes a transceiver unit 620, which can be used to receive or send information. The communication device 600 may also include a processing unit 610, which can be used to process instructions or data to achieve corresponding operations.

[0204] It should be understood that when the communication device 600 is a chip configured in (or used in) a communication device, the transceiver unit 620 in the communication device 600 can be the input / output interface or circuit of the chip, and the processing unit 610 in the communication device 600 can be the processor in the chip.

[0205] Optionally, the communication device 600 may further include a storage unit 630, which can be used to store instructions or data. The processing unit 610 can execute the instructions or data stored in the storage unit to enable the communication device to perform corresponding operations.

[0206] The communication device 600 can be used to implement the functions of the terminal in the method embodiment shown in FIG3 above.

[0207] When the communication device 600 is used to implement the functions of the terminal in the method embodiment shown in FIG3: the processing unit 610 is used to search for a Public Land Mobile Network (PLMN) employing a first Radio Access Technology (RAT), wherein the first RAT is the highest priority RAT supported by the terminal and has not been selected before. If a PLMN employing the first RAT exists, the processing unit 610 is also used to select the first RAT. Further, the processing unit 610 is also used to attempt to camp on the PLMN employing the first RAT.

[0208] Optionally, the processing unit 610 is further configured to attempt to reside in a first PLMN, which is the highest priority PLMN among the candidate PLMNs in the set of candidate PLMNs using the first RAT that the terminal has not attempted to reside in.

[0209] Optionally, the processing unit 610 is further configured to attempt to reside in a second PLMN if the attempt to reside in the first PLMN fails, the second PLMN being the highest priority PLMN among the PLMNs in the candidate PLMN set that the terminal has not attempted to reside in.

[0210] Optionally, the processing unit 610 is further configured to determine a candidate PLMN set based on at least one of the following: a user-configured PLMN priority set, a pre-configured PLMN priority set, or a PLMN set obtained by searching the PLMN of the first RAT, and network coverage information.

[0211] Optionally, if no PLMN using the first RAT exists, the processing unit 610 is further configured to search for a PLMN using the second RAT; or, if it fails to successfully reside in a PLMN using the first RAT, the processing unit 610 is further configured to search for a PLMN using the second RAT, wherein the second RAT is the highest priority RAT supported by the terminal and has not been selected.

[0212] Optionally, if a PLMN using a second RAT exists, the processing unit 610 is also configured to select the second RAT; further, the processing unit 610 is also configured to attempt to reside in the PLMN using the second RAT.

[0213] Optionally, the processing unit 610 is also configured to search for a PLMN employing the first RAT in the absence of an available home PLMN and an equivalent PLMN of the home network.

[0214] Optionally, the processing unit 610 is also configured to search for a PLMN employing the first RAT when the network selection mode is set to automatic mode.

[0215] Optionally, the processing unit 610 is also configured to search for a PLMN employing a first RAT based on configuration parameters stored in a non-volatile NV memory, the configuration parameters being used to control network selection with RAT priority.

[0216] It should also be understood that the specific processes by which each unit performs the corresponding steps described above have been detailed in the above method, and will not be repeated here for the sake of brevity. It should be understood that the transceiver unit 620 in the communication device 600 can be implemented through a communication interface (such as a transceiver, transceiver circuit, input / output interface, or pins, etc.). When the communication interface is a transceiver, the transceiver can consist of a receiver and / or a transmitter. The processing unit 610 in the communication device 600 can be implemented through at least one processor, or it can be implemented through at least one logic circuit. Optionally, the communication device 600 also includes a storage unit, which can be implemented using a memory.

[0217] As shown in Figure 7, the communication device 700 includes a processor 710 and an interface circuit 720. The processor 710 and the interface circuit 720 are coupled to each other. It is understood that the interface circuit 720 can be a transceiver or an input / output interface. Optionally, the communication device 700 may further include a memory 730 for storing instructions executed by the processor 710, or storing input data required by the processor 710 to execute instructions, or storing data generated after the processor 710 executes instructions.

[0218] In one implementation, the memory 730 may be integrated into the processor 710 or independent of the processor 710.

[0219] When the communication device 700 is used to implement the method shown in FIG3, the processor 710 is used to implement the function of the processing unit 610, and the interface circuit 720 is used to implement the function of the transceiver unit 620.

[0220] When the aforementioned communication device is a chip applied to a terminal device, the terminal device chip can implement the functions of the terminal in the above method embodiments. The terminal device chip receives information from other modules (such as an RF module or antenna) in the terminal device, the information being sent to the terminal device by the network device; or, the terminal device chip sends information to other modules (such as an RF module or antenna) in the terminal device, the information being sent to the network device by the terminal device.

[0221] When the aforementioned communication device is a module applied to a network device, the network device module can implement the functions of the network device in the above method embodiments. The network device module receives information from other modules (such as radio frequency modules or antennas) in the network device, which is information sent from the terminal device to the network device; or, the network device module sends information to other modules (such as radio frequency modules or antennas) in the network device, which is information sent from the network device to the terminal device. Here, the network device module can be the baseband chip of the network device, or it can be a DU or other modules. The DU here can be a DU under an open radio access network (O-RAN) architecture.

[0222] It is understood that the processor in the embodiments of this application can be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, transistor logic devices, hardware components, or any combination thereof. A general-purpose processor can be a microprocessor or any conventional processor.

[0223] The method steps in the embodiments of this application can be implemented in hardware or in software instructions executable by a processor. The software instructions can consist of corresponding software modules, which can be stored in random access memory, flash memory, read-only memory, programmable read-only memory, erasable programmable read-only memory, electrically erasable programmable read-only memory, registers, hard disks, portable hard disks, CD-ROMs, or any other form of storage medium known in the art. An exemplary storage medium is coupled to a processor, enabling the processor to read information from and write information to the storage medium. The storage medium can also be a component of the processor. The processor and storage medium can reside in an ASIC. Alternatively, the ASIC can reside in an access network device or a terminal device. The processor and storage medium can also exist as discrete components in the access network device or terminal device.

[0224] According to the method provided in the application embodiments, this application embodiment also provides a computer program product, which includes: computer program code, which, when executed by one or more processors, causes a device including the processor to perform the method shown in FIG3.

[0225] In the above embodiments, implementation can be achieved entirely or partially through software, hardware, firmware, or any combination thereof. When implemented using software, it can be implemented entirely or partially in the form of a computer program product. This computer program product includes one or more computer programs or instructions. When the computer program or instructions are loaded and executed on a computer, the processes or functions described in the embodiments of this application are performed, in whole or in part. The computer can be a general-purpose computer, a special-purpose computer, a computer network, network equipment, user equipment, or other programmable device.

[0226] According to the method provided in the embodiments of this application, the embodiments of this application also provide a computer-readable storage medium that stores the above-mentioned computer program or instructions. When the computer program or instructions are run by one or more processors, the apparatus including the processor performs the method shown in FIG3.

[0227] As described above, computer programs or instructions can be stored in or transferred from one computer-readable storage medium to another. For example, the computer programs or instructions can be transferred from one website, computer, server, or data center to another website, computer, server, or data center via wired or wireless means. The computer-readable storage medium can be any available medium accessible to a computer or a data storage device such as a server or data center that integrates one or more available media. The available medium can be a magnetic medium, such as a floppy disk, hard disk, or magnetic tape; it can also be an optical medium, such as a digital video optical disc; or it can be a semiconductor medium, such as a solid-state drive. The computer-readable storage medium can be a volatile or non-volatile storage medium, or it can include both volatile and non-volatile types of storage media.

[0228] According to the method provided in the embodiments of this application, the embodiments of this application also provide a communication system, including one or more of the aforementioned network devices. The system may further include one or more of the aforementioned first terminals.

[0229] In the embodiments provided in this application, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. For example, the apparatus described above is merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between apparatuses or units may be electrical, mechanical, or other forms.

[0230] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this solution according to actual needs.

[0231] In the various embodiments of this application, unless otherwise specified or logically conflicting, the terms and / or descriptions between different embodiments are consistent and can be referenced by each other. The technical features in different embodiments can be combined to form new embodiments according to their inherent logical relationships.

[0232] The above description is merely a specific implementation of the embodiments of this application, but the protection scope of the embodiments of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the embodiments of this application should be included within the protection scope of the embodiments of this application. Therefore, the protection scope of the embodiments of this application should be determined by the protection scope of the claims.

Claims

1. A communication method, characterized in that, include: Search for a public terrestrial mobile network (PLMN) that uses a first radio access technology (RAT), where the first RAT is the highest priority RAT supported by the terminal and has not been selected. If a PLMN using the first RAT exists, select the first RAT; Attempt to reside in the PLMN that uses the first RAT.

2. The method according to claim 1, characterized in that, The attempt to reside in the PLMN using the first RAT includes: Attempt to reside in the first PLMN, which is the highest priority PLMN among the candidate PLMNs that the terminal has not attempted to reside in, using the first RAT.

3. The method according to claim 2, characterized in that, The method further includes: If attempting to reside in the first PLMN fails, an attempt is made to reside in the second PLMN, which is the highest priority PLMN among the PLMNs in the candidate PLMN set that the terminal has not attempted to reside in.

4. The method according to claim 2 or 3, characterized in that, The method further includes: The candidate PLMN set is determined based on at least one of the following: the user-defined PLMN priority set, the pre-configured PLMN priority set, or the PLMN set obtained by searching the PLMN of the first RAT, and network coverage information.

5. The method according to any one of claims 1 to 4, characterized in that, The method further includes: If no PLMN using the first RAT exists, search for a PLMN using the second RAT; or... If it fails to reside in a PLMN using the first RAT, search for a PLMN using the second RAT. The second RAT is the highest priority RAT supported by the terminal and which has not been selected.

6. The method according to claim 5, characterized in that, The method further includes: If a PLMN using the second RAT exists, the terminal selects the second RAT; Try to reside in the PLMN that uses the second RAT.

7. The method according to any one of claims 1 to 6, characterized in that, The search employs the PLMN of the first RAT, including: In the absence of an available home PLMN and an equivalent PLMN of the home network, the search employs the first RAT for the PLMN.

8. The method according to any one of claims 1 to 7, characterized in that, The search employs the Public Land Mobile Network (PLMN) of the first RAT, including: When the network selection mode is set to automatic, the search uses the PLMN of the first RAT.

9. The method according to any one of claims 1 to 8, characterized in that, The search employs the PLMN of the first RAT, including: Based on the configuration parameters stored in the non-volatile NV memory, the search is performed on the PLMN using the first RAT, the configuration parameters being used to control the selection of the network with the priority of the RAT.

10. A communication device, characterized in that, The device includes a processor coupled to a memory for storing a computer program, the processor for executing the computer program stored in the memory to cause the communication device to perform the method as described in any one of claims 1 to 9.

11. A communication device, characterized in that, It includes a processor and a communication interface, wherein the processor is used to control the communication interface to implement the method as described in any one of claims 1 to 9.

12. A computer-readable storage medium, characterized in that, The device stores instructions that, when executed on the communication device, cause the communication device to perform the method as described in any one of claims 1 to 9.

13. A computer program product, characterized in that, The computer program product includes: a computer program that, when run on a communication device, causes the communication device to perform the method of any one of claims 1 to 9.

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