Patent Publication Number: US-2021168593-A1

Title: Method for obtaining identifier of terminal device, and network element

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of International Application No. PCT/CN2018/101140, filed on Aug. 17, 2018, the disclosure of which is hereby incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The embodiments relate to the communications field, and more specifically, to a method for obtaining an identifier of a terminal device, and a network element. 
     BACKGROUND 
     With development of science and technology, a communications device being used by a suspect is usually used to obtain related evidence information during case investigation. For example, after positioning a suspect, police usually listen to a call on the suspect&#39;s mobile phone to obtain key clues to assist in case investigation. However, a cunning suspect frequently changes a mobile phone to avoid being tracked. As a result, although police can visually position the suspect remotely, it is difficult to quickly and accurately obtain a mobile phone number used by the suspect and listen to a call on the suspect&#39;s mobile phone, thereby missing key clues and delaying case investigation. Therefore, how to obtain an identifier of a terminal device used by a user becomes a problem that urgently needs to be resolved. 
     SUMMARY 
     The embodiments provide a method for obtaining an identifier of a terminal device, and a network element, to accurately obtain an identifier of a terminal device used by a user. 
     According to a first aspect, a method for obtaining an identifier of a terminal device is provided, including: a first network element obtains first information, where the first information carries location information of a first terminal device. The first network element determines an identifier set based on the first information, where the identifier set includes identifiers of N terminal devices, the N terminal devices include at least the first terminal device, and N is a positive integer. The first network element sends N first request messages to a second network element, where the N first request messages carry the identifiers of the N terminal devices, and are used to request the second network element to determine location information of the N terminal devices. The first network element receives N first response messages sent by the second network element, where the N first response messages carry the location information of the N terminal devices. The first network element compares the location information of the first terminal device with the location information of the N terminal devices, and determines an identifier of the first terminal device in the identifier set, where the identifier of the first terminal device is an identifier used by the first terminal device for communication, and communication information of the first terminal device may be obtained based on the identifier of the first terminal device. 
     According to the method for obtaining an identifier of a terminal device in this embodiment, the first network element determines the identifier set based on the first information, and separately performs positioning by using the N identifiers in the identifier set to obtain the location information of the N terminal devices. Further, the obtained location information of the N terminal devices is compared with the location information of the first terminal device that is carried in the first information, to determine the identifier of the first terminal device. An identifier of a terminal device can be further determined based on location information of the terminal device. 
     For example, in the embodiments, the identifier of the terminal device is an identifier used by the terminal device for communication, and communication information of the terminal device can be obtained based on the identifier of the terminal device. 
     For example, when the terminal device is a mobile phone, the identifier of the terminal device may be a mobile phone number, an identifier of a SIM card of the mobile phone, or the like. 
     Alternatively, when the terminal device is a wearable intelligent device, the identifier of the terminal device may be a communication channel identifier of the wearable intelligent device, or the like. 
     It should be understood that a quantity of times of obtaining first information by the first network element is not limited in this embodiment. First information may be obtained for a plurality of times, and first information obtained each time carries the location information of the first terminal device. The following provides descriptions with reference to embodiments, and details are not described herein. 
     With reference to the first aspect, in some implementations of the first aspect, the first information further carries status information of the first terminal device, the status information of the first terminal device is used to indicate a status of the first terminal device, and the determining, by the first network element, an identifier set based on the first information includes: the first network element determines, based on the location information of the first terminal device, at least one network device in at least one second location that meets a preset condition with a first location indicated by the location information of the first terminal device. The first network element determines M terminal devices that camp on the at least one network device, determines, in the M terminal devices, N terminal devices whose statuses are consistent with the status indicated by the status information of the first terminal device, and obtains the identifiers of the N terminal devices to form the identifier set, where M is a positive integer larger than or equal to N. 
     According to the method for obtaining an identifier of a terminal device in this embodiment, the status information of the first terminal device is carried in the first information, so that the first network element has more reference information in a process of determining the identifier set, can determine the identifier set that includes the identifier of the first terminal device and that has a small quantity of identifiers, and further can quickly obtain the identifier of the first terminal device. 
     For example, when the first network element obtains first information for a plurality of times, some first information may include the status information of the first terminal device, or first information obtained each time may include the status information of the first terminal device. 
     It should be understood that the location information of the first terminal device and the status information of the first terminal device that are carried in the first information may be obtained simultaneously or may be obtained separately. 
     With reference to the first aspect and the foregoing implementations of the first aspect, in another implementation of the first aspect, the obtaining, by a first network element, first information includes: the first network element receives a second request message sent by a third network element, where the second request message is used to request the first network element to obtain the identifier of the first terminal device, and the second request message includes the first information. The first network element sends a second response message to the third network element, where the second response message carries the identifier of the first terminal device. 
     According to the method for obtaining an identifier of a terminal device in this embodiment, a manner of obtaining the first information by the first network element may be receiving the first information from the third network element, thereby providing flexible selectivity for the first network element to obtain the first information. 
     For example, when the first information is sent by the third network element to the first network element, after determining the identifier of the first terminal device, the first network element needs to send the identifier of the first terminal device to the third network element. For example, the second response message is sent to the third network element, and the identifier of the first terminal device is carried in the second response message. 
     With reference to the first aspect and the foregoing implementations of the first aspect, in another implementation of the first aspect, location information of each terminal device in the location information of the N terminal devices includes positioning precision information. 
     According to the method for obtaining an identifier of a terminal device in this embodiment, the positioning precision information is carried in location information of a terminal device that is received by the first network element, so that the first network element can learn of precision of determining, by the second network element, a location of the terminal device each time, thereby providing additional reference information for the first network element to determine the identifier of the first terminal device. 
     With reference to the first aspect and the foregoing implementations of the first aspect, in another implementation of the first aspect, the determining, by the first network element, an identifier set based on the first information includes: the first network element determines a first identifier set based on first first-information, where the first identifier set includes identifiers of X terminal devices, the X terminal devices include at least the first terminal device, X is a positive integer greater than or equal to N, the first first-information is first information obtained by the first network element at a first moment, and the first first-information carries location information of the first terminal device at the first moment. The first network element determines a second identifier set based on second first-information, where the second identifier set includes identifiers of Y terminal devices, the Y terminal devices include at least the first terminal device, Y is a positive integer greater than or equal to N, the second first-information is first information obtained by the first network element at a second moment, and the second first-information carries location information of the first terminal device at the second moment. The first network element determines an intersection set of the first identifier set and the second identifier set as the identifier set. 
     According to the method for obtaining an identifier of a terminal device in this embodiment, when the first network element obtains first information for a plurality of times, first information obtained each time includes location information of the first terminal device at a different moment. The first network element can determine a plurality of identifier sets based on the first information obtained for the plurality of times, but the plurality of identifier sets all include the identifier of the first terminal device. Therefore, when an intersection set of the plurality of identifier sets is obtained, the identifier is obtained, so that the identifier of the first terminal device can be quickly determined. 
     For example, the first information obtained for the plurality of times may further include the status information of the first terminal device. 
     According to a second aspect, a method for obtaining an identifier of a terminal device is provided, including: a second network element receives N first request messages sent by a first network element, where the N first request messages carry identifiers of N terminal devices, and are used to request the second network element to determine location information of the N terminal devices. The second network element separately obtains, through calculation, the location information of the N terminal devices based on the N first request messages by using a preset positioning algorithm. The second network element sends N first response messages to the first network element, where the N first response messages carry the location information of the N terminal devices. The identifier of the terminal device is an identifier used by the terminal device for communication, and communication information of the terminal device can be obtained based on the identifier of the terminal device. 
     According to the method for obtaining an identifier of a terminal device in this embodiment, the second network element performs positioning calculation based on an identifier of a terminal device that is carried in a received first request message, to obtain location information of the terminal device. It can be understood that the performing, by the second network element, of a positioning calculation based on an identifier of a terminal device may be a positioning calculation procedure for a cellular network in the prior art. The second network element can obtain the location information of the N terminal devices based on the received N first request messages. 
     With reference to the second aspect, in some implementations of the second aspect, location information of each terminal device in the location information of the N terminal devices includes positioning precision information. 
     According to the method for obtaining an identifier of a terminal device in this embodiment, the positioning precision information is carried in location information of a terminal device that is sent by the second network element, so that when receiving the location information of the terminal device, the first network element can learn of precision of determining, by the second network element, a location of the terminal device each time, thereby providing additional reference information for the first network element to determine an identifier of a first terminal device. 
     According to a third aspect, a method for obtaining an identifier of a terminal device is provided, including: a third network element sends a second request message to a first network element, where the second request message is used to request the first network element to obtain an identifier of a first terminal device, the second request message includes first information, and the first information carries location information of the first terminal device. The third network element receives a second response message sent by the first network element, where the second response message carries the identifier of the first terminal device, the identifier of the first terminal device is an identifier used by the first terminal device for communication, and communication information of the first terminal device can be obtained based on the identifier of the first terminal device. 
     According to the method for obtaining an identifier of a terminal device in this embodiment, the third network element can request the first network element to obtain the identifier of the first terminal device, and the second request message includes the first information, thereby providing flexible selectivity for the first network element to obtain the first information. In addition, the first network element sends, to the third network element, the second response message that carries the identifier of the first terminal device, so that the third network element can obtain the identifier of the first terminal device. 
     With reference to the third aspect, in some implementations of the third aspect, the first information further carries status information of the first terminal device, and the status information of the first terminal device is used to indicate a status of the first terminal device. 
     According to the method for obtaining an identifier of a terminal device in this embodiment, the status information of the first terminal device is carried in the first information, so that the first network element has more reference information in a process of determining the identifier of the first terminal device, and further can quickly obtain the identifier of the first terminal device. 
     With reference to the third aspect and the foregoing implementations of the third aspect, in another implementation of the third aspect, before the sending, by a third network element, a second request message to a first network element, the method further includes: the third network element receives a third request message from a server, where the third request message is used to request the third network element to obtain the identifier of the first terminal device, and the third request message includes the first information. 
     According to the method for obtaining an identifier of a terminal device in this embodiment, the third network element can obtain the first information from the server, thereby providing flexible selectivity for the third network element to obtain the first information. 
     For example, the server may be a server outside a core network, and sends, to a positioning network element in the core network by using the third network element, a request message for requesting to obtain the identifier of the first terminal device. 
     With reference to the third aspect and the foregoing implementations of the third aspect, in another implementation of the third aspect, the third network element sends a third response message to the server, where the third response message carries the identifier of the first terminal device. 
     According to the method for obtaining an identifier of a terminal device in this embodiment, after receiving the third request message from the server, and obtaining the identifier of the first terminal device, the third network element needs to send the identifier of the first terminal device to the server, so that the server can obtain the identifier of the first terminal device. 
     According to a fourth aspect, a first network element is provided. The first network element is configured to perform the method for obtaining an identifier of a terminal device in any one of the first aspect or the possible implementations of the first aspect. 
     For example, the first network element may include units configured to perform the method for obtaining an identifier of a terminal device in any one of the first aspect or the possible implementations of the first aspect. 
     According to a fifth aspect, a first network element is provided. The first network element includes a processor and a transceiver. The processor and the transceiver communicate with each other through an internal connection path. 
     Optionally, the first network element further includes a memory. The memory is configured to store an instruction. The processor is configured to execute the instruction stored in the memory. 
     In an optional implementation, the processor performs the method in any one of the first aspect or the possible implementations of the first aspect. 
     According to a sixth aspect, a computer-readable storage medium is provided. The computer-readable storage medium stores a computer program. When the program is executed by a processor, the method in any one of the first aspect or the possible implementations of the first aspect is implemented. 
     According to a seventh aspect, a computer program product is provided. The computer program product includes computer program code. When the computer program code is run by a communications unit and a processing unit of a first network element or by a transceiver and a processor of a first network element, the first network element performs the method in the first aspect. 
     According to an eighth aspect, a chip system is provided, including a processor, configured to support a first network element in implementing the method in the first aspect. 
     According to a ninth aspect, a second network element is provided. The second network element is configured to perform the method for obtaining an identifier of a terminal device in any one of the second aspect or the possible implementations of the second aspect. 
     For example, the second network element may include units configured to perform the method for obtaining an identifier of a terminal device in any one of the second aspect or the possible implementations of the second aspect. 
     According to a tenth aspect, a second network element is provided. The second network element includes a processor and a transceiver. The processor and the transceiver communicate with each other through an internal connection path. 
     Optionally, the second network element further includes a memory. The memory is configured to store an instruction. The processor is configured to execute the instruction stored in the memory. 
     In an optional implementation, the processor performs the method in any one of the second aspect or the possible implementations of the second aspect. 
     According to an eleventh aspect, a computer-readable storage medium is provided. The computer-readable storage medium stores a computer program. When the program is executed by a processor, the method in any one of the second aspect or the possible implementations of the second aspect is implemented. 
     According to a twelfth aspect, a computer program product is provided. The computer program product includes computer program code. When the computer program code is run by a communications unit and a processing unit of a first network element or by a transceiver and a processor of a first network element, the second network element performs the method in the second aspect. 
     According to a thirteenth aspect, a chip system is provided, including a processor, configured to support a second network element in implementing the method in the second aspect. 
     According to a fourteenth aspect, a third network element is provided. The third network element is configured to perform the method for obtaining an identifier of a terminal device in any one of the third aspect or the possible implementations of the third aspect. 
     For example, the third network element may include units configured to perform the method for obtaining an identifier of a terminal device in any one of the third aspect or the possible implementations of the third aspect. 
     According to a fifteenth aspect, a third network element is provided. The third network element includes a processor and a transceiver. The processor and the transceiver communicate with each other through an internal connection path. 
     Optionally, the third network element further includes a memory. The memory is configured to store an instruction. The processor is configured to execute the instruction stored in the memory. 
     In an optional implementation, the processor performs the method in any one of the third aspect or the possible implementations of the third aspect. 
     According to a sixteenth aspect, a computer-readable storage medium is provided. The computer-readable storage medium stores a computer program. When the program is executed by a processor, the method in any one of the third aspect or the possible implementations of the third aspect is implemented. 
     According to a seventeenth aspect, a computer program product is provided. The computer program product includes computer program code. When the computer program code is run by a communications unit and a processing unit of a third network element or by a transceiver and a processor of a third network element, the third network element performs the method in the third aspect. 
     According to an eighteenth aspect, a chip system is provided, including a processor, configured to support a third network element in implementing the method in the second aspect. 
     According to a nineteenth aspect, a system for obtaining an identifier of a terminal device is provided, including one or more of the foregoing first network element, second network element, and third network element. 
     In a possible design, the system for obtaining an identifier of a terminal device may further include another device that interacts with the first network element, the second network element, or the third network element in the solutions provided in the embodiments, or the like. 
     According to the method for obtaining an identifier of a terminal device and the network element in the embodiments, the first network element determines the identifier set based on the obtained first information, and determines the identifier of the first terminal device in the identifier set, so that an identifier of a terminal device used by a user can be obtained. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic diagram of a system to which a method for obtaining an identifier of a terminal device according to an embodiment is applicable; 
         FIG. 2  is a positioning flowchart; 
         FIG. 3  is a schematic diagram of a method for obtaining an identifier of a terminal device; 
         FIG. 4  is a flowchart of determining an identifier set by a first network element; 
         FIG. 5  is another flowchart of determining an identifier set by a first network element; 
         FIG. 6  is a schematic diagram of an embodiment of a method for obtaining an identifier of a terminal device according to an embodiment; 
         FIG. 7  is a schematic block diagram of a first network element according to an embodiment; 
         FIG. 8  is a schematic block diagram of a second network element according to an embodiment; 
         FIG. 9  is a schematic block diagram of a third network element according to an embodiment; 
         FIG. 10  is another schematic block diagram of a first network element according to an embodiment; 
         FIG. 11  is another schematic block diagram of a second network element according to an embodiment; and 
         FIG. 12  is another schematic block diagram of a third network element according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     The following describes embodiments with reference to accompanying drawings. 
     Terminologies such as “component”, “module”, and “system” are used to indicate computer-related entities, hardware, firmware, combinations of hardware and software, software, or software being executed. For example, a component may be, but is not limited to, a process that runs on a processor, a processor, an object, an executable file, a thread of execution, a program, and/or a computer. As shown in figures, both a computing device and an application that runs on a computing device may be components. One or more components may camp within a process and/or a thread of execution, and a component may be located on one computer and/or distributed between two or more computers. In addition, these components may be executed from various computer-readable media that store various data structures. For example, the components may communicate by using a local and/or remote process and according to, for example, a signal having one or more data packets (for example, data from two components interacting with another component in a local system, a distributed system, and/or across a network such as the Internet interacting with other systems by using the signal). 
     It should be understood that the embodiments may be used in various communications systems, for example, a global system for mobile communications (GSM) system, a code division multiple access (CDMA) system, a wideband code division multiple access (WCDMA) system, a general packet radio service (GPRS), a long term evolution (LTE) system, an advanced long term evolution (LTE-A) system, a universal mobile telecommunications system (UMTS), a wireless local area network (WLAN), wireless fidelity (Wi-Fi), or a next-generation communications system. Herein, the next-generation communications system may include, for example, a fifth-generation (5G) communications system. 
     Usually, a conventional communications system supports a limited quantity of connections, and is easy to implement. However, with development of communications technologies, a mobile communications system not only supports conventional communication, but also supports, for example, device-to-device (D2D) communication, machine-to-machine (M2M) communication, machine type communication (MTC), and vehicle-to-vehicle (V2V) communication. 
     The embodiments describe the embodiments with reference to a terminal device. 
     The terminal device may also be referred to as user equipment (UE), an access terminal, a subscriber unit, a subscriber station, a mobile station, a mobile console, a remote station, a remote terminal, a mobile device, a user terminal, a terminal, a wireless communication device, a user agent, a user apparatus, or the like. The terminal device may be a station (ST) in WLAN, and may be a cellular phone, a cordless phone, a session initiation protocol (SIP) phone, a wireless local loop (WLL) station, a personal digital assistant (PDA), a handheld device having a wireless communication function, a computing device, another processing device connected to a wireless modem, a vehicle-mounted device, a wearable device, and a next-generation communications system, for example, a terminal device in a 5G network, or a terminal device in a future evolved public land mobile network (PLMN). 
     As an example, rather than a limitation, in the embodiments, the terminal device may be alternatively a wearable device. The wearable device may also be referred to as a wearable intelligent device. The wearable intelligent device is a collective name of wearable devices, such as glasses, a glove, a watch, clothing, and shoes, obtained by performing intelligent design and development on daily wearables by using a wearable technology. The wearable device is a portable device that is directly put on human body or is integrated with clothing or an accessory of a user. The wearable device is not merely a hardware device, but further implements a powerful function through software support, data exchange, and cloud-based interaction. In a broad sense, wearable intelligent devices include a device that provides a complete function, has a large size, and can implement all or some functions without relying on a smartphone, for example, a smartwatch or smart glasses; and include a device that focuses only on a specific type of application function and needs to be used in combination with another device such as a smartphone, for example, various smart bands and smart jewelry used for vital sign monitoring. 
     In addition, in the embodiments, the terminal device may be alternatively a terminal device in an internet of things (IoT) system. IoT is an important component of future information technology development. A main technical feature of the IoT is to connect an object to a network by using a communications technology, to implement an intelligent network of human-computer interconnection and inter-thing interconnection. 
     As an example, rather than a limitation, in the embodiments, the network device may be a base station (BS), and the base station may be in a plurality of forms, for example, a macro base station, a micro base station, a relay station, and an access point. 
     For example, the base station in the embodiments may be a base station in new radio (NR), where the base station in NR may also be referred to as a transmission and reception point (TRP) or a next-generation NodeB (gNB); or may be a base transceiver station (BTS) in GSM or CDMA; or may be a NodeB (NB) in a WCDMA system; or may be an evolved NodeB (eNB or eNodeB) in an LTE system. 
     The network device in the embodiments may alternatively include a device that is deployed in a radio access network and that can wirelessly communicate with a terminal. 
     For example, the network device may be a radio controller in a cloud radio access network (CRAN) scenario; or the network device may be a relay station, an access point, a network device in a future 5G network, a network device in a future evolved public land mobile network (PLMN), or the like, for example, an eNB, a radio network controller (RNC), an NB, a base station controller (BSC), a base transceiver station (BTS), a home network device (for example, a home evolved NodeB, or a Home NodeB, HNB), or a baseband unit (BBU). In the embodiments, an apparatus that implements a function of a network device may be a network device; or may be an apparatus that supports a network device in implementing the function, for example, a chip, a circuit, or another apparatus. In the embodiments, the solutions provided in the embodiments are described by using an example in which the apparatus that implements a function of a network device is a network device. 
     In addition, in the embodiments, the network device provides a service for a cell, and the terminal device communicates with the network device by using a transmission resource (for example, a frequency domain resource, in other words, a spectrum resource) used by the cell. The cell may be a cell corresponding to the network device (for example, a base station). The cell may belong to a macro base station or may belong to a base station corresponding to a small cell. The small cell herein may include a metro cell, a micro cell, a pico cell, a femto cell, and the like. These small cells have features of a small coverage range and a low transmit power and are suitable for providing high-rate data transmission services. 
     In addition, a plurality of cells may simultaneously work on a carrier at a same frequency in an LTE system or a 5G system. In some scenarios, it may also be considered that a concept of the carrier is the same as that of a cell. For example, in a carrier aggregation scenario, when a secondary carrier is configured for UE, both a carrier index of the secondary carrier and a cell identifier (Cell ID) of a secondary cell working on the secondary carrier are carried. In this case, it may be considered that a concept of a carrier is the same as that of a cell. For example, UE accessing a carrier is equivalent to UE accessing a cell. 
     In the embodiments, the terminal device or the network device includes a hardware layer, an operating system layer running above the hardware layer, and an application layer running above the operating system layer. The hardware layer includes hardware such as a central processing unit (CPU), a memory management unit (MMU), and a memory (also referred to as a main memory). The operating system may be any one or more computer operating systems that implement service processing by using a process, for example, a Linux operating system, a Unix operating system, an Android operating system, an iOS operating system, or a Windows operating system. The application layer includes applications such as a browser, an address book, word processing software, and instant messaging software. In addition, a specific structure of an entity for performing a method provided in the embodiments is not particularly limited in the embodiments, provided that the entity can run a program that records code of the method provided in the embodiments to perform communication according to the method provided in the embodiments. For example, the entity for performing the method provided in the embodiments may be a terminal device, a network device, or a functional module that is in a terminal device or a network device and that can invoke and execute the program. 
     In addition, aspects or features in the embodiments may be implemented as a method, an apparatus or a product that uses standard programming and/or engineering technologies. The term “product” covers a computer program that can be accessed from any computer readable component, carrier or medium. For example, the computer-readable medium may include, but is not limited to: a magnetic storage component (for example, a hard disk, a floppy disk or a magnetic tape), an optical disc (for example, a compact disc (CD), a digital versatile disc (DVD), a smart card and a flash memory component (for example, erasable programmable read-only memory (EPROM), a card, a stick, or a key drive). In addition, various storage media described may indicate one or more devices and/or other machine-readable media that are configured to store information. The term “machine-readable media” may include, but is not limited to, a radio channel, and various other media that can store, contain, and/or carry an instruction and/or data. 
       FIG. 1  is a schematic diagram of a system  100  to which a method for obtaining an identifier of a terminal device according to an embodiment is applicable. 
     As shown in  FIG. 1 , the wireless communications system  100  may include one or more network devices, for example, a network device #1  111 , a network device #2  112 , and a network device #3  113  shown in  FIG. 1 . The wireless communications system  100  may further include one or more terminal devices, for example, a terminal device  121  shown in  FIG. 1 . 
     The wireless communications system  100  may also support coordinated multipoint transmission/reception (CoMP). For example, a plurality of cells or a plurality of network devices may collaboratively participate in data transmission with one terminal device or jointly receive data sent by one terminal device, or a plurality of cells or a plurality of network devices perform coordinated scheduling or coordinated beamforming. The plurality of cells may belong to a same network device or different network devices and may be selected based on a channel gain or a path loss, received signal strength, a received signal instruction, and the like. 
     Optionally, in the communications system  100  shown in  FIG. 1 , one of the network device #1 to the network device #3 (for example, the network device #1) may be a serving network device. The serving network device may be a network device that provides at least one of the following services for a terminal device by using a radio air interface protocol: a radio resource control (RRC) connection, non-access stratum (NAS) mobility management, and security input. Optionally, the network device #2 and the network device #3 each may be a coordinating network device. The serving network device may send control signaling to the terminal device, and the coordinating network device may send data to the terminal device. Alternatively, the serving network device may send control signaling to the terminal device, and the serving network device and the coordinating network device may send data to the terminal device. Alternatively, both the serving network device and the coordinating network device may send control signaling to the terminal device, and both the serving network device and the coordinating network device may send data to the terminal device. Alternatively, the coordinating network device may send control signaling to the terminal device, and at least one of the serving network devices and the coordinating network device may send data to the terminal device. Alternatively, the coordinating network device may send control signaling and data to the terminal device. This is not limited in the embodiments. 
     It should be understood that, only for ease of understanding,  FIG. 1  schematically shows the network device #1 to the network device #3 and the terminal device, but this does not constitute any limitation. The wireless communications system may alternatively include more or fewer network devices or may include more terminal devices. Network devices that communicate with different terminal devices may be a same network device or different network devices, and quantities of network devices that communicate with different terminal devices may be the same or different. This is not limited. 
     The following briefly describes communication between a network device and a terminal device by using the network device #1  111  and the terminal device  121  as examples. 
     The network device #1  111  may include one or more antennas. In addition, the network device #1  111  may additionally include a transmitter chain and a receiver chain. A person of ordinary skill in the art can understand that the transmitter chain and the receiver chain each may include a plurality of components (for example, a processor, a modulator, a multiplexer, a demodulator, a demultiplexer, or an antenna) related to signal sending and receiving. 
     The network device #1  111  may communicate with a plurality of terminal devices. For example, the terminal device  121  may be a cellular phone, a smartphone, a portable computer, a handheld communications device, a handheld computing device, a satellite radio apparatus, a global positioning system, a PDA, and/or any other suitable device configured to perform communication in the wireless communications system  100 . 
     As shown in  FIG. 1 , the terminal device  121  communicates with the network device #1  111 . The network device #1  111  sends information to the terminal device  121  through a forward link (also referred to as a downlink), and the network device #1  111  receives information from the terminal device  121  through a reverse link (also referred to as an uplink). 
     For example, in a frequency division duplex (FDD) system, different frequency bands are used for a forward link and a reverse link. 
     For another example, in a time division duplex (TDD) system and a full duplex system, a same frequency band may be used for a forward link and a reverse link. 
     Each antenna (or an antenna group including a plurality of antennas) and/or area designed for communication are/is referred to as a sector of the network device #1  111 . 
     For example, the antenna group may be designed to communicate with a terminal device in a sector in a coverage area of the network device #1  111 . The network device #1  111  may send, by using a single antenna or multi-antenna transmit diversity, a signal to all terminal devices in a sector corresponding to the network device #1  111 . In a process in which the network device #1  111  communicates with the terminal device  121  through the forward link, a transmit antenna of the network device #1  111  may also increase a signal-to-noise ratio of the forward link through beamforming. 
     In addition, compared with the manner in which the network device #1  111  sends a signal to all terminal devices of the network device #1  111  by using a single antenna or multi-antenna transmit diversity, when the network device #1  111  sends, through beamforming, a signal to terminal devices  121  randomly dispersed in a related coverage area, a mobile device in a neighboring cell encounters less interference. 
     In a given time, the network device #1  111  and the terminal device  121  may be a wireless communications sending apparatus and/or a wireless communications receiving apparatus. When sending data, the wireless communications sending apparatus may encode the data for transmission. For example, the wireless communications sending apparatus may obtain (for example, generate, receive from another communications apparatus, or store in a memory) a specific quantity of data bits that need to be sent to the wireless communications receiving apparatus through a channel. The data bits may be included in a transport block (or a plurality of transport blocks) of the data, and the transport block may be segmented to generate a plurality of code blocks. 
     In addition, the communications system  100  may be a PLMN network, a D2D network, an M2M network, an IoT network, or another network. 
     It should be understood that  FIG. 1  is only a simplified schematic diagram as an example, and the communications system may further include another network device or terminal device not shown in  FIG. 1 . 
     For example,  FIG. 1  may further include another network element or another unit required for positioning the terminal device  121 . The following briefly describes network elements, other than the foregoing network devices, that are required for positioning the terminal device  121  and that are not shown in  FIG. 1 . 
     An example is a mobility management network element, or referred to as a mobility management entity (MME). Functions of the MME mainly include the following aspects: 
     1. Access control for a terminal device, including security and permission control. 
     2. Mobility management: 
     A mobile network needs to clearly know current location information of a terminal device. This is no exception to an evolved packet core (EPC) network. 
     A location area in the EPC network is referred to as a tracking area (TA). The TA is similar to a location area (LA) in capacity memory control system (MSCS) management and a routing area (RA) in service GPRS supporting node (SGSN) management and is used for mobility management for a terminal device in the EPC network. 
     Based on different scenarios, mobility management may be classified into a location update between different network devices within one MME, a location update between different MMEs, a periodic location update, and the like. A result of success of all the location updates is that a terminal device notifies a network device of a current location area TA in which the terminal device is located, and the TA is recorded on an MME and a home subscriber server (HSS) network element. 
     3. Attachment and detachment: 
     Before performing an actual service, a terminal device needs to perform a process of registering with a network device. This process is referred to as attachment. A terminal successfully attached obtains an Internet protocol (IP) address allocated by the network device, and the IP address provides an “always online” IP connection. Different from a conventional 2/3G network, in an EPS network, a default bearer is directly established for a terminal device through initial attach. However, in the 2/3G network, a terminal device needs to perform a process of activating a programmed data processor (PDP) context after attachment, so that an IP address is allocated to the terminal device. 
     When a terminal device does not need to or can no longer be attached to a network, a detachment procedure is initiated. Based on different initiators, detachment may be initiated by the terminal device, an MME, or an HSS. The MME may initiate the detachment because the terminal device has not interacted with a network device for a long time. The HSS initiates the detachment because the network device actively disconnects from the terminal device due to subscription or charging information of the terminal device, or the like. Based on whether the terminal device is successfully notified, explicit detachment and implicit detachment are further distinguished. Explicit detachment means that the network device and the terminal device notify each other by using signaling. Implicit detachment is a case in which the detachment is actively initiated by the network device but the terminal device cannot be notified due to a limitation of a radio condition. 
     4. Session management function: 
     The session management function includes: establishing, modifying, and releasing an EPC bearer; during interaction with a 2G/3G network, performing effective mapping between an EPC bearer and a PDP context; establishing and releasing an access-network-side bearer; and selecting an appropriate route based on an access point name (APN) and user subscription data. 
     5. Selection of a signaling gateway (SGW) and a PDN gateway (PGW): 
     When a terminal device has a data service request, an MME needs to select an SGW or a PGW to forward a data packet of the terminal device. 
     Generally, the MME is similar to a control plane function of an SGSN network element. Separation of the control plane function and a user plane function of the network element facilitates flattened network deployment. In addition to the foregoing functions such as mobility management, the MME is further responsible for managing lawful interception, subscriber roaming control, security authentication, and other aspects. 
     A gateway mobile location center (GMLC) network element is a first node accessed by an external unknown program when the external unknown program accesses a GSM PLMN and is configured to perform registration authorization check and request routing information from a home location register (HLR). One PLMN may have a plurality of GMLCs. 
     An evolved serving mobile location center (E-SMLC) network element is configured to convert a location requirement of a request of a terminal device into a corresponding universal terrestrial radio access network (UTRAN) measurement parameter, select a positioning method, and calculate a final result and precision based on a returned location estimation. 
     A location measurement unit (LMU) is an important measurement unit for measuring a radio signal and is configured to perform positioning measurement. The LMU may measure UL and DL signals in a UTRAN and may obtain positioning information of a terminal device or parameters related to positioning calculation from the signals. LMUs are classified into the following two types. 
     Stand-alone LMU: similar to a mobile terminal. This type of LMU is wirelessly connected to a base station. An air interface between the LMU and a terminal device and an air interface between the LMU and the base station are known and are both uu interfaces. However, the LMU is incapable of communicating with another terminal device but can exchange data only with a specific base station. Apparently, a placement location of the stand-alone LMU is comparatively flexible, and the stand-alone LMU may be at any location in a service area of the base station. In addition, there may be a plurality of stand-alone LMUs in one service area. 
     Associated LMU: similar to a base station. In physical implementation, this type of LMU may be integrated in a base station or may be disposed separately. An interface between the associated LMU and an RNC and an interface between the base station and the RNC are known and are both Iub interfaces. 
     For ease of understanding the solutions described in the embodiments, several methods for obtaining an identifier of a terminal device in the prior art are briefly described first. 
     A method for determining a suspect&#39;s mobile phone number is as follows: mounting a rogue base station to a camera, and establishing a connection to a mobile phone by using the rogue base station, to obtain information about a suspect&#39;s mobile phone; and determining the suspect&#39;s mobile phone number based on a coverage range of the camera and the rogue base station. 
     However, in the foregoing method, rogue base stations cannot be deployed on a large scale. If rogue base stations are deployed on all camera poles, great interference is caused to public network devices of operators, thereby affecting normal use of mobile phones by users. In addition, a deployment range of cameras is also limited, and this method cannot be performed in locations in which no camera is deployed. 
     Further, positioning accuracy in the foregoing method is not high. A reason is that matching is performed between a mobile phone number and the suspect by overlapping an estimation of a coverage range of the rogue base station with a coverage range of the camera. 
     However, most rogue base stations do not have a positioning function of a base station and have very low positioning accuracy. In addition, usually, the coverage range of the rogue base station can hardly perfectly overlap the coverage range of the surveillance camera, thereby causing great difficulty in performing matching between the suspect and a mobile phone number. 
     In addition, a current cellular network has a positioning function, and can position a terminal device. 
     The following briefly describes a positioning procedure in a cellular network with reference to  FIG. 2 .  FIG. 2  is a positioning flowchart. 
     Optionally, in S 211 , a terminal device initiates a positioning request to an MME. 
     Optionally, in S 212 , a GMLC initiates a positioning request to an MME. 
     Optionally, in S 213 , an MME initiates a positioning request. 
     It should be understood that S 210 , S 211 , and S 213  are several possibilities in which a positioning request can be initiated in a cellular network. For example, when there is a positioning requirement, a terminal device may initiate a positioning request, or some network elements (for example, the GMLC or the MME shown in  FIG. 2 ) in an EPC may initiate a positioning request. 
     S 220 . The MME initiates a positioning request to an E-SMLC. 
     It should be understood that, when the MME receives a positioning request from another entity (for example, the UE or the GMLC), or a positioning requirement unit in the MME initiates a positioning request, the MME needs to forward the positioning request to an E-SMLC network element in a core network. The E-SMLC network element can provide a positioning method and calculate a final result and precision. 
     S 230 . The E-SMLC selects a positioning method. 
     For example, after receiving the positioning request, the E-SMLC network element selects a positioning method to perform positioning calculation. 
     For example, positioning methods include:
         1. network-based positioning technology: a method based on a cell ID and a timing advance, an uplink time of arrival method, an uplink signal time difference of arrival method, and an uplink angle of arrival method;   2. mobile station-based positioning methods: a downlink enhanced observed time difference (E-OTD) positioning method for GSM, a method by observing a difference of arrival times in a downlink idle period for WCDMA, and the like; and   3. satellite positioning systems represented by a global positioning system (GPS), a global navigation satellite system (GLONASS), a Galileo spacecraft (GALILEO), a BeiDou navigation satellite system (BEIDOU), a quasi-zenith satellite system (QZSS), and the like, where auxiliary devices for satellite positioning are integrated on a mobile station side and a network device side.       

     It should be understood that selection of a positioning method is not limited in this embodiment, and any positioning method in the prior art may be used. 
     S 240 . The E-SMLC sends a sixth request message to the MME. 
     For example, the sixth request message carries information for requesting configuration information required for the positioning method selected by the E-SMLC. 
     For example, the positioning method selected by the E-SMLC in S 230  is the uplink signal time difference of arrival (UTDOA) method. 
     In this case, the E-SMLC sends connection oriented transfer information to the MME by using an LTE positioning protocol annex (LPPa). The connection oriented transfer information carries uplink signal time difference of arrival request information (UTDOA information request). 
     It should be understood that the foregoing UTDOA positioning method may also be referred to as a UTOA positioning method, and a network device measures a time at which a signal of a mobile terminal device arrives. 
     In the method, at least three network devices are required to participate in measurement, a location measurement unit LMU is added to each network device, and the LMU measures an arrival moment of an access burst or a normal burst sent by a terminal device. 
     For example, a time difference of arrival (TDOA) measures a difference between transmission times at which a signal transmitted by a mobile terminal device arrives at different BTSs, but not merely a transmission time. 
     It should be understood that the LPPa is a peer-layer positioning protocol between a base station and a positioning server, and is used to exchange positioning-related information, for example, multi-cell information and measurement information provided by the base station. 
     S 250 . The MME sends a seventh request message to the network device. 
     For example, after receiving the sixth request message, the MME parses the sixth request message, and sends the seventh request message to the network device based on the sixth request message. The seventh request message carries the information for requesting the configuration information required for the positioning method selected by the E-SMLC. 
     For example, the positioning method selected by the E-SMLC in S 230  is the UTDOA. 
     In this case, the MME sends downlink terminal device associated LPPa transport (downlink UE associated LPPa transport) that carries a UTDOA information request to the network device. The UTDOA information request is used to obtain requested a sounding reference signal (SRS) transmission characteristics information of the positioned terminal device. 
     It should be understood that there may be a plurality of network devices in this embodiment, that is, the MME sends a second request message to the plurality of network devices. 
     S 260 . The network device obtains the configuration information. 
     For example, after receiving the seventh request message, the network device determines, based on the information carried in the seventh request message, the configuration information required for implementing the positioning method, and further obtains the related configuration information. 
     For example, the information carried in the seventh request message is the UTDOA information request. 
     In this case, the network device receives the UTDOA information request, measures and collects a type 1 TA and a type 2 TA of the terminal device, and allocates a narrowband physical random access channel (NPRACH) resource to the terminal device based on a specific bandwidth and period. 
     It should be understood that a TA may be calculated by adding a time difference between receiving and sending of the terminal device that is reported by the terminal device to a time difference between receiving and sending that is measured by the network device (a TA calculated by using this method is referred to as a TA Type 1), or may be measured by the network device by using a dedicated random access process (a TA calculated by using this method is referred to as a TA Type 2). 
     It should be understood that there may be a plurality of network devices in this embodiment, that is, all the plurality of network devices may obtain the foregoing configuration information. 
     S 270 . The network device sends a sixth response message to the MME. 
     For example, after obtaining the foregoing parameters, the network device sends the corresponding configuration information to the MME. 
     For example, the network device sends uplink associated LPPa transport (uplink UE associated LPPa transport) that carries time difference response information (UTDOA information response) to the MME. 
     S 280 . The MME sends a seventh response message to the E-SMLC. 
     For example, after receiving the foregoing parameters, the MME sends the corresponding configuration information to the E-SMLC. 
     For example, the MME sends a UTDOA information response to the E-SMLC. 
     S 290 . The E-SMLC sends an eighth request message to the LMU. 
     For example, after receiving the seventh response message, the E-SMLC obtains the corresponding configuration information, and then sends the eighth request message to the LMU, where the eighth request message includes the configuration information, to request the LMU to perform corresponding measurement. 
     For example, the E-SMLC sends a service level management (SLm) protocol measurement request message to the LMU on which SRS measurement needs to be performed. The measurement request message includes UL RTOA Measurement Configuration configuration information, and requests UL RTOA measurement. 
     For example, the LMU is a measurement unit in the network device. 
     S 291 . The LMU performs measurement. 
     For example, after receiving the eighth request message, the LMU obtains the corresponding configuration information and performs measurement. 
     For example, after receiving the measurement request, the LMU parses NPRACH configuration information of the terminal device and performs UL RTOA measurement. 
     S 292 . The LMU sends an eighth response message to the E-SMLC. 
     For example, after completing measurement, the LMU sends a measurement result to the E-SMLC by using the eighth response message. 
     For example, after completing UL RTOA measurement, the LMU sends a measurement result to the E-SMLC by using an SLm protocol MEASUREMENT RESPONSE message. 
     S 293 . The E-SMLC performs positioning calculation. 
     For example, the E-SMLC performs UTDOA positioning calculation. 
     S 294 . The E-SMLC sends a positioning result to the MME. 
     For example, the positioning result includes success, failure, error information, and the like. 
     S 201 . The MME sends the positioning result to the terminal device. 
     It should be understood that S 201  corresponds to S 211 . When the terminal device initiates the positioning request, the MME sends the positioning result to the terminal device. 
     S 202 . The MME sends the positioning result to the GMLC. 
     It should be understood that S 202  corresponds to S 212 . When the GMLC initiates the positioning request, the MME sends the positioning result to the GMLC. 
     Further, the GMLC may then return the result to a server platform. 
     For example, the GMLC may then return the result to a dedicated network server for public security. 
     S 203 . The MME sends the positioning result to the MME. 
     It should be understood that S 203  corresponds to S 213 . When the MME initiates the positioning request, the MME sends the positioning result to the MME. 
     It can be understood from the positioning procedure shown in  FIG. 2  that, during positioning in the cellular network, an identifier of a terminal device can be input to obtain a location of the corresponding terminal device, but an identifier of a terminal device cannot be obtained by inputting a location of the terminal device. 
     The following describes in detail a method for obtaining an identifier of a terminal device in the embodiments with reference to  FIG. 3  to  FIG. 5 , so that an identifier of a terminal device can be obtained based on input location information of the terminal device. 
       FIG. 3  is a schematic diagram of a method for obtaining an identifier of a terminal device according to the embodiments. A first network element and a second network element are included, a third network element may be included, and steps S 310  to S 350  are included. 
     For example, the first network element is a mobility management entity network element in a core network. 
     In a 5G communications system, the mobility management entity network element may be an MME network element. In a future communications system, the mobility management entity network element may still be the MME network element or may have another name. This is not limited. 
     For example, the second network element is a network element that performs a positioning algorithm in the core network. 
     In the 5G communications system, the network element that performs the positioning algorithm may be an E-SMLC network element. In the future communications system, the network element that performs the positioning algorithm may still be the E-SMLC network element or may have another name This is not limited. 
     For example, the third network element is a network element responsible for a positioning function in the core network. 
     In the 5G communications system, the network element responsible for the positioning function may be a GMLC network element. In the future communications system, the network element responsible for the positioning function may still be the GMLC network element or may have another name. This is not limited. 
     S 310 . The first network element obtains first information. 
     For example, the first information carries location information of a first terminal device. The location information of the first terminal device may be location information of a user holding the first terminal device and is used to indicate a location of the terminal device. 
     For example, in this embodiment, the obtaining, by the first network element, first information may be obtaining first information for a plurality of times. The first information obtained for the plurality of times includes location information of the first terminal device at different moments. 
     For example, the first network element obtains first information (referred to as first first-information) at a first moment, and the first information includes location information of the first terminal device at the first moment; the first network element obtains first information (referred to as second first-information) at a second moment, and the first information includes location information of the first terminal device at the second moment. 
     The first moment is different from the second moment, and the location information of the first terminal device at the first moment may be different from the location information of the first terminal device at the second moment. 
     Optionally, in some embodiments, the obtaining, by the first network element, first information includes: 
     The first network element receives a second request message sent by the third network element. The second request message is used to request the first network element to obtain an identifier of the first terminal device. The first request message includes the first information. 
     For example, when the first information is sent by the third network element, the first network element obtains, at the first moment, the location information of the first terminal device at the first moment that is included in the first information. It can be understood that, due to an information transmission delay, there is a time difference between the first moment at which the first network element obtains the first information and the first moment mentioned in the location information of the first terminal device at the first moment. However, this is not considered in the embodiments. The time difference may be ignored, and both the moments are referred to as the first moment. 
     It should be understood that when the first network element obtains first information from the third network element for a plurality of times, an emphasis is that location information of the first terminal device that is included in first information obtained each time is different, and a specific obtaining time is not concerned. 
     In this case,  FIG. 3  further includes S 311 : the third network element sends the second request message to the first network element. It can be understood that the third network element receives a third request message from a server, the third request message is used to request the GMLC to obtain the identifier of the first terminal device, and the third request message includes the first information. 
     Optionally, in some other embodiments, the obtaining, by the first network element, first information includes: 
     The first network element receives the first information sent by the first terminal device. 
     Optionally, in some other embodiments, the obtaining, by the first network element, first information includes: 
     The first network element stores the first information. The first network element may obtain the first information from a storage unit periodically, according to a requirement of the first terminal device, or based on triggering by another network element. 
     S 320 . The first network element determines an identifier set. 
     For example, the first network element determines the identifier set based on the first information. The identifier set includes identifiers of N terminal devices. The N terminal devices include at least the first terminal device. N is a positive integer. 
     Optionally, in some embodiments, the first information further carries status information of the first terminal device. 
     For example, the status information of the first terminal device is used to indicate a status of the first terminal device. 
     For example, the status information of the first terminal device indicates that the first terminal device is in a powered-on state. 
     For example, a system specifies that the status information of the first terminal device that is carried in the first information is one bit; and when a bit value of the bit is 1, it indicates that the first terminal device is in the powered-on state; or when the bit value is 0, it indicates that the first terminal device is in a powered-off state. 
     For another example, the status information of the first terminal device indicates a data transmission rate of the first terminal device. 
     For example, a system specifies that the status information of the first terminal device that is carried in the first information is one bit; and when a bit value of the bit is 1, it indicates that the data transmission rate of the first terminal device is greater than a preset threshold; or when the bit value is 0, it indicates that the data transmission rate of the first terminal device is less than the preset threshold. 
     For another example, the status information of the first terminal device indicates that an application program is started on the first terminal device. 
     For another example, the status information of the first terminal device indicates a traffic usage status of the first terminal device. 
     For another example, the status information of the first terminal device indicates a call status of the first terminal device, a standby status of the first terminal device, or the like. 
     For another example, the status information of the first terminal device indicates that the first terminal device is in a powered-on and traffic-on state. 
     It should be understood that, in this embodiment, a specific status of the first terminal device that is indicated by the status information of the first terminal device is not limited, and all status information that can indicate the status of the first terminal device falls within the scope of the embodiments. 
     The following describes in detail how the first network element determines the identifier set with reference to  FIG. 4  and  FIG. 5 . 
       FIG. 4  is a flowchart of determining the identifier set by the first network element. Steps S 410  to S 430  are included. 
     S 410 . The first network element determines at least one network device. 
     For example, after obtaining the first information, the first network element determines, based on the location information of the first terminal device, the at least one network device in at least one second location that meets a preset condition with a first location indicated by the location information of the first terminal device. 
     For example, the at least one second location that meets the preset condition with the first location indicated by the location information of the first terminal device may be a location near the first location. 
     For example, the preset condition is all locations with a distance in a range of 2 meters from the first location. In this case, second locations are all locations in a circle with a radius of 2 meters and with the first location as a center of the circle (a center of a sphere when coordinates of the first location are three-dimensional). 
     Further, the first network element determines, based on the at least one second location, the at least one network device in the at least one second location. 
     S 420 . The first network element determines a first set. 
     For example, the first network element determines, based on the at least one network device, the first set of terminal devices camping on the at least one network device. 
     It should be understood that, after determining the at least one network device based on the location information of the first terminal device, the first network element can obtain the first set of terminal devices camping on the at least one network device. The first set of terminal devices includes at least the first terminal device. 
     S 430 . The first network element determines an identifier set. 
     Optionally, when the first information includes only the location information of the first terminal device, the first network element obtains an identifier of a terminal device in the first set determined in S 420 , to form the identifier set. This may be understood as that the first network element determines N terminal devices that camp on the at least one network device and obtains identifiers of the N terminal devices to form the identifier set. 
     Optionally, when the first information further includes the status information of the first terminal device, the first network element determines, in the terminal devices included in the first set determined in S 420 , a terminal device whose status is consistent with the status indicated by the status information of the first terminal device, and obtains an identifier of the terminal device that is in the first set and whose status is consistent, to form the identifier set. In this case, a quantity of terminal devices in the first set is greater than or equal to a quantity of terminals corresponding to all identifiers in the identifier set. 
     This may be understood as that the first network element determines M terminal devices that camp on the at least one network device, determines, in the M terminal devices, N terminal devices whose statuses are consistent with the status indicated by the status information of the first terminal device, and obtains identifiers of the N terminal devices to form the identifier set. M is a positive integer larger than or equal to N. 
       FIG. 5  is another flowchart of determining the identifier set by the first network element. Steps S 510  to S 530  are included. 
     S 510 . The first network element determines at least one network device for a plurality of times. 
     For example, after obtaining first information (first first-information) for the first time, the first network element determines, based on location information of the first terminal device at a first moment that is included in the first first-information, at least one network device in at least one second location that meets a preset condition with a first location indicated by the location information of the first terminal device at the first moment. 
     For example, the at least one second location that meets the preset condition with the first location indicated by the location information of the first terminal device at the first moment may be a location near the first location. 
     For example, the preset condition is all locations with a distance in a range of 2 meters from the first location. In this case, second locations are all locations in a circle with a radius of 2 meters and with the first location as a center of the circle (a center of a sphere when coordinates of the first location are three-dimensional). 
     Further, the first network element determines, based on the at least one second location, the at least one network device (a first network device) in the at least one second location. 
     For example, after obtaining first information (second first-information) for the second time, the first network element determines, based on location information of the first terminal device at a second moment that is included in the second first-information, at least one network device in at least one fourth location that meets a preset condition with a third location indicated by the location information of the first terminal device at the second moment. 
     For example, the at least one fourth location that meets the preset condition with the third location indicated by the location information of the first terminal device at the second moment may be a location near the third location. 
     For example, the preset condition is all locations with a distance in a range of 2 meters from the third location. In this case, fourth locations are all locations in a circle with a radius of 2 meters and with the third location as a center of the circle (a center of a sphere when coordinates of the third location are three-dimensional). 
     Further, the first network element determines, based on the at least one fourth location, the at least one network device (a second network device) in the at least one fourth location. 
     S 520 . The first network element determines at least one set of terminal devices. 
     For example, the first network element determines, based on the first network device, a set (a second set) of terminal devices camping on the first network device. 
     It should be understood that, after determining the first network device based on the location information of the first terminal device at the first moment, the first network element can obtain a first set of terminal devices camping on the first network device. The first set of terminal devices includes at least the first terminal device. 
     For example, the first network element determines, based on the second network device, a set (a third set) of terminal devices camping on the second network device. 
     It should be understood that, after determining the second network device based on the location information of the first terminal device at the second moment, the first network element can obtain a first set of terminal devices camping on the second network device. The first set of terminal devices includes at least the first terminal device. 
     S 530 . The first network element determines an identifier set. 
     Case 1: The first first-information includes only the location information of the first terminal device at the first moment, and the second first-information includes only the location information of the first terminal device at the second moment. 
     The first network element obtains an identifier of a terminal device in the second set determined in S 520 , to form a first identifier set. 
     This may be understood as that the first network element determines X terminal devices that camp on the first network device, and obtains identifiers of the X terminal devices, where X is a positive integer greater than or equal to N, to form the first identifier set. 
     The first network element obtains an identifier of a terminal device in the third set determined in S 520 , to form a second identifier set. 
     This may be understood as that the first network element determines Y terminal devices that camp on the second network device, and obtains identifiers of the Y terminal devices, where Y is a positive integer greater than or equal to N, to form the second identifier set. 
     The first network element determines an intersection set of the first identifier set and the second identifier set as the identifier set. 
     Case 2: The first first-information includes the location information of the first terminal device at the first moment and status information of the first terminal device at the first moment, and the second first-information includes the location information of the first terminal device at the second moment and status information of the first terminal device at the second moment. 
     The first network element determines, in the terminal devices included in the second set determined in S 520 , a terminal device whose status is consistent with a status indicated by the status information of the first terminal device at the first moment, and obtains an identifier of the terminal device that is in the second set and whose status is consistent, to form a third identifier set. 
     In this case, a quantity of terminal devices in the second set is greater than or equal to a quantity of terminals corresponding to all identifiers in the third identifier set. 
     This may be understood as that the first network element determines X1 terminal devices that camp on the first network device, determines, in the X1 terminal devices, X terminal devices whose statuses are consistent with the status indicated by the status information of the first terminal device at the first moment, and obtains identifiers of the X terminal devices to form the third identifier set. X1 is a positive integer greater than or equal to X. 
     The first network element determines, in the terminal devices included in the third set determined in S 520 , a terminal device whose status is consistent with a status indicated by the status information of the first terminal device at the second moment, and obtains an identifier of the terminal device that is in the third set and whose status is consistent, to form a fourth identifier set. 
     In this case, a quantity of terminal devices in the third set is greater than or equal to a quantity of terminals corresponding to all identifiers in the fourth identifier set. 
     This may be understood as that the first network element determines Y1 terminal devices that camp on the first network device, determines, in the Y1 terminal devices, Y terminal devices whose statuses are consistent with the status indicated by the status information of the first terminal device at the first moment, and obtains identifiers of the Y terminal devices to form the third identifier set. Y1 is a positive integer greater than or equal to Y. 
     The first network element determines an intersection set of the third identifier set and the fourth identifier set as the identifier set. 
     Case 3: The first first-information includes the location information of the first terminal device at the first moment and status information of the first terminal device at the first moment, and the second first-information includes only the location information of the first terminal device at the second moment. 
     The first network element determines, in the terminal devices included in the second set determined in S 520 , a terminal device whose status is consistent with a status indicated by the status information of the first terminal device at the first moment, and obtains an identifier of the terminal device that is in the second set and whose status is consistent, to form a third identifier set. 
     In this case, a quantity of terminal devices in the second set is greater than or equal to a quantity of terminals corresponding to all identifiers in the third identifier set. 
     This may be understood as that the first network element determines X 1  terminal devices that camp on the first network device, determines, in the X1 terminal devices, X terminal devices whose statuses are consistent with the status indicated by the status information of the first terminal device at the first moment, and obtains identifiers of the X terminal devices to form the third identifier set. X1 is a positive integer greater than or equal to X. 
     The first network element determines an intersection set of the third identifier set and the second identifier set as the identifier set. 
     Case 4: The first first-information includes only the location information of the first terminal device at the first moment, and the second first-information includes the location information of the first terminal device at the second moment and status information of the first terminal device at the second moment. This case is similar to the case 3. The first network element determines an intersection set of the fourth identifier set and the second identifier set as the identifier set. 
     It should be understood that, in  FIG. 5 , obtaining the first first-information and the second first-information by the first network element is merely used an example to describe how the first network element determines the identifier set when the first network element obtains first information for a plurality of times and the first information includes different information. This should not be considered as limiting. In the embodiments, the first network element may obtain first information more than twice. It should be understood that, because the first network element has a communication relationship with the at least one network device, the first network element includes identifiers of all terminal devices that camp on the at least one network device. 
     This may be understood as that a terminal device registers related information with the first network element when camping on the at least one network device; or
         the first network element obtains, from the at least one network device, the identifiers of all the terminal devices that camp on the at least one network device.       

     S 330 . The first network element sends N first request messages to the second network element. 
     For example, the N first request messages carry the identifiers of the N terminal devices, and are used to request the second network element to determine location information of the N terminal devices. 
     For example, the identifier set includes three identifiers: A, B, and C. The three identifiers are identifiers of a second terminal device, a third terminal device, and a fourth terminal device. 
     The first network element sends a first first-request-message to the second network element. The first first-request-message carries the identifier A, and is used to request the second network element to determine location information of the second terminal device. 
     The first network element sends a second first-request-message to the second network element. The second first-request-message carries the identifier B and is used to request the second network element to determine location information of the third terminal device. 
     The first network element sends a third first-request-message to the second network element. The second first-request-message carries the identifier C and is used to request the second network element to determine location information of the fourth terminal device. 
     S 331 . The second network element calculates the location information of the N terminal devices. 
     The second network element separately obtains, through calculation, the location information of the N terminal devices based on the N first request messages by using a preset positioning algorithm. 
     For the preset positioning algorithm, any prior-art positioning method for determining location information of a terminal device based on an identifier of the terminal device may be used. 
     For example, the second network element separately determines the location information of the second terminal device, the third terminal device, and the fourth terminal device based on the identifiers of the second terminal device, the third terminal device, and the fourth terminal device. Any one of prior-art positioning methods for determining location information of a terminal device based on an identifier of the terminal device may be used. This is not limited. 
     S 340 . The first network element receives N first response messages sent by the second network element. 
     The N first response messages carry the location information of the N terminal devices. 
     For example, the second network element determines, based on the identifier of the second terminal device, that the location information of the second terminal device is (A X x, A y ), and the second network element sends a first first-response-message to the first network element. The first first-response-message carries the location information of the second terminal device. 
     The second network element determines, based on the identifier of the third terminal device, that the location information of the third terminal device is (B X , B y ), and the second network element sends a second first-response-message to the first network element. The second first-response-message carries the location information of the third terminal device. 
     The second network element determines, based on the identifier of the fourth terminal device, that the location information of the fourth terminal device is (C X , C y ), and the second network element sends a third first-response-message to the first network element. The third first-response-message carries the location information of the fourth terminal device. 
     S 350 . The first network element determines the identifier of the first terminal device. 
     For example, the first network element compares the location information of the first terminal device with the location information of the N terminal devices and determines the identifier of the first terminal device in the identifier set. 
     It should be understood that the first network element includes the identifier set and the location information of the first terminal device. When receiving location information of terminal devices corresponding to N identifiers in the identifier set, the first network element determines, based on the received location information of the N terminal devices, which third location in at least one third location indicated by the location information of the N terminal devices is closest to the first location indicated by the location information of the first terminal device, and uses an identifier of a terminal device corresponding to the third location information as the identifier of the first terminal device. 
     For example, the identifier set determined by the first network element includes the three identifiers: A, B, and C, which are the identifiers of the second terminal device, the third terminal device, and the fourth terminal device. The location information of the first terminal device is (x, y). 
     The first network element receives the first first-response-message sent by the second network element. The first first-response-message carries the location information of the second terminal device: (A X , A y ). 
     The first network element receives the second first-response-message sent by the second network element. The second first-response-message carries the location information of the third terminal device: (B X , B y ). 
     The first network element receives the third first-response-message sent by the second network element. The third first-response-message carries the location information of the fourth terminal device: (C X , C y ). 
     The first network element determines, through comparison, which one of the three locations (A X , A y ), (B X , B y ), and (C X , C y ) is closest to (x, y). 
     For example, assuming that (x, y)=(10, 10), (A X , A y )=(9, 9), (B X , B y )=(8, 8), and (C X , C y )=(7, 7), (x, y) is closest to (A X , A y ). 
     Further, the first network element determines A as the identifier of the first terminal device. 
     Optionally, in some embodiments, location information of each terminal device in the location information of the N terminal devices includes positioning precision information. 
     For example, the first network element receives the first first-response-message sent by the second network element, and the first first-response-message carries the location information of the second terminal device: (A X ±1, A y ±1). It should be understood that “±1” is positioning precision. 
     The first network element receives the second first-response-message sent by the second network element, and the second first-response-message carries the location information of the third terminal device: (B X ±1, B y ±1). It should be understood that “±1” is positioning precision. 
     The first network element receives the third first-response-message sent by the second network element, and the third first-response-message carries the location information of the fourth terminal device: (C X ±1, C y ±1). It should be understood that “±1” is positioning precision. 
     The first network element determines, through comparison, which one of the three locations (A X ±1, A y ±1), (B X ±1, B y ±1), and (C X ±1, C y ±1) is closest to (x, y). 
     For example, assuming that (x, y)=(10, 10), (A X ±1, A y ±1)=(8-10, 8-10), (B X ±1, B y ±1)=(7-9, 7-9), and (C X ±1, C y ±1)=(6-8, 6-8), (x, y) is closest to (A X ±1, A y ±1). 
     Further, the first network element determines A as the identifier of the first terminal device. 
     Optionally, when  FIG. 3  includes S 311 ,  FIG. 3  further includes S 351 : The first network element sends a second response message to the third network element. 
     For example, the second response message carries the identifier of the first terminal device. 
     When receiving the third request message from the server, the third network element sends a third response message to the server. The third response message carries the identifier of the first terminal device. 
     Optionally, the identifier of the first terminal device is an identifier used by the first terminal device for communication, and communication information of the first terminal device can be obtained based on the identifier of the first terminal device. 
     For example, the identifier of the first terminal device is a mobile phone number of the first terminal device, the identifier of the first terminal device is an identifier of a subscriber identity module (SIM) card of the first terminal device, or the identifier of the first terminal device may be other identification information that can be used to determine the first terminal device. 
     It should be understood that the steps shown in  FIG. 3  may be repeatedly performed to obtain the identifier of the first terminal device more accurately. For example, the first network element re-determines the identifier set and the identifier of the first terminal device based on location information of the first terminal device that is updated in real time. 
     To further understand the method for obtaining an identifier of a terminal device in  FIG. 3 , the method for obtaining an identifier of a terminal device in the embodiments may be used in the determining a suspect&#39;s mobile phone number. 
     The following describes, with reference to an embodiment, the method for obtaining an identifier of a terminal device. 
       FIG. 6  is a schematic diagram of a embodiment of a method for obtaining an identifier of a terminal device. A first terminal device, an information collection device, a server, a first network element, a second network element, a third network element, a network device, and a measurement unit are included. 
     The parts shown in  FIG. 6  can form a system for determining a suspect&#39;s mobile phone number, and the system includes a core network part and a part outside the core network. The core network part includes the first network element, the second network element, the third network element, the network device, and the measurement unit shown in  FIG. 6 . The part outside the core network includes the first terminal device, the information collection device, and the server shown in  FIG. 6 . 
     For example, the first terminal device may be any one of the foregoing terminal devices. 
     S 610 . The information collection device collects first information, where the first information includes location information of the first terminal device. 
     Optionally, the first information may further include status information of the first terminal device. 
     For example, the information collection device may be a camera, an event data recorder, a device for inputting information to a human eye, or the like. It should be understood that, in this embodiment, a specific form of the information collection device is not limited, and the information collection device may be any device that can collect the first information. 
     It should be understood that the location information of the terminal device may be coordinates of a user holding the first terminal device. 
     For example, in this embodiment, the first terminal device may be a mobile phone, the user holding the first terminal device is a suspect, and the status information of the first terminal device may be information indicating whether the mobile phone is in a call state. 
     In this embodiment, descriptions are provided by using an example in which the first terminal device is the mobile phone, the location information of the first terminal device that is carried in the first information is (x, y), and the status information of the first terminal device that is carried in the first information may be information indicating that the mobile phone is in the call state. 
     S 620 . The server obtains the first information from the information collection device. 
     The server authorized to obtain the first information may obtain the first information from the information collection device when the first information needs to be known. 
     It should be understood that the obtaining, by the server, the first information from the information collection device may be as follows: the server accesses the information collection device to obtain the first information; or
         a trusted connection exists between the server and the information collection device, and when the first information is collected, the information collection device sends the first information to the server.       

     Optionally, when the first information includes a plurality of types of information (for example, the location information of the first terminal device and the status information of the first terminal device), the server may first obtain the location information of the first terminal device and then obtain the status information of the first terminal device, and combine the information to obtain the first information. 
     For example, when the method for identifying the identifier of the first terminal device in this embodiment is used to determine a suspect&#39;s mobile phone number, the server may be a dedicated network server for public security. 
     This may be understood as that the dedicated network server for public security obtains, from the camera, the location information (x, y) of the mobile phone and information indicating that the mobile phone is in a call. 
     S 630 . The server sends a third request message to the third network element. 
     For example, the third request message is used to request the third network element to obtain the identifier of the first terminal device, the third request message carries the first information, and the third network element is the third network element in  FIG. 3 . 
     S 640 . The third network element sends a second request message to the first network element. 
     For example, the second request message is used to request the first network element to obtain the identifier of the first terminal device, the second request message carries the first information, and the first network element is the first network element in  FIG. 3 . 
     It should be understood that the third request message and the second request message may be a same message or may be information in a same message body. 
     For example, both the second request message and the third request message carry the first information, the third request message is sent by the server outside the core network to the third network element in the core network, and the second request message is sent by the third network element in the core network to the first network element in the core network. 
     Therefore, message protocols of the third request message and the second request message may be different. 
     S 650 . The first network element determines an identifier set. 
     The identifier set includes at least the identifier of the first terminal device. It should be understood that the identifier set may further include identifiers of a plurality of second terminal devices. The second terminal devices are different from the first terminal device. 
     For example, the first network element determines two nearby network devices based on the location information (x, y) of the mobile phone, 20 mobile phones camp on the two network devices, and five mobile phones are in a call state. In this case, the identifier set includes identifiers of the five mobile phones. 
     S 660 . The first network element sends at least one first request message to the second network element. 
     For example, the first network element sends a first request message to the third network element for each identifier in the identifier set. For example, the first network element sends at least one first request message to the second network element, and the at least one first request message is in a one-to-one correspondence with at least one identifier in the identifier set. 
     For example, the identifier set in S 650  includes identifiers of five terminal devices. The first network element sends five first request messages to the second network element for the identifiers of the five terminal devices, and each first request message carries an identifier of one terminal device in the identifiers of the five terminal devices. 
     S 670 . The second network element sends at least one fourth request message to the network device. 
     For example, the second network element obtains at least one identifier for the received at least one first request message, and sends a fourth request message to the network device based on each identifier. For example, the second network element sends at least one fourth request message to the network device, and the at least one fourth request message is in a one-to-one correspondence with at least one identifier in the identifier set. 
     The second network element sends a first fourth-request-message to the network device for a first identifier in the at least one identifier, the first fourth-request-message includes the first identifier, and the first fourth-request-message is used to obtain calculation information required for determining a location of a terminal device corresponding to the first identifier. 
     For example, the first identifier is any identifier in the identifier set, and the first fourth-request-message is a fourth request message that carries the first identifier in the at least one fourth request message. 
     It should be understood that, in this embodiment, information exchange between the second network element and the network device may be obtaining, by using the LMU in the method shown in  FIG. 2 , the calculation information required for determining the location of the terminal device corresponding to the first identifier. 
     In this case, the schematic diagram of the method for obtaining an identifier of a terminal device in  FIG. 6  further includes the measurement unit and S 690 : The second network element sends at least one fifth request message to the measurement unit. 
     For example, after receiving a fourth response message sent by the network device, the second network element obtains, from the fourth response message, configuration information required for measuring a location of a terminal device. 
     The second network element sends the configuration information to the measurement unit by using the fifth request message. The measurement unit performs measurement based on the configuration information and sends a measurement result to the second network element by using a fifth response message. In this case,  FIG. 6  further includes S 600 : The measurement unit sends at least one fifth response message to the second network element. 
     It should be understood that the second network element sends, to the measurement unit for each identifier in the identifier set, obtained configuration information required for measuring a location of a terminal device corresponding to each identifier, and the measurement unit also feeds back a measurement result for each identifier. Therefore, there is at least one fifth request message and at least one fifth response message. 
     Alternatively, in this embodiment, information exchange between the second network element and the network device may be information exchange between a second network element and a network device in a procedure of another positioning method in a cellular network in the prior art. 
     Examples are a cell ID positioning technology in which no LMU is required and an assisted global positioning system (AGPS) positioning technology. Examples are not listed one by one herein. 
     This may be understood as that the information exchange between the second network element and the network device in S 670  may be information exchange between a second network element and a network device in any one of prior-art positioning methods for obtaining location information of a terminal device based on an identifier of the terminal device. 
     Optionally,  FIG. 6  may further include S 671 : the second network element selects a positioning method. 
     The network device is a device that provides calculation information required for a positioning algorithm. 
     For example, the network device is a base station or the foregoing another network device entity. 
     S 680 . The network device sends at least one fourth response message to the second network element. 
     After obtaining an identifier of each terminal device, the network device determines calculation information required for calculating location information of the terminal device, adds the calculation information to a fourth response message, and sends the fourth response message to the second network element. 
     For example, the network device sends five fourth response messages to the second network element. 
     S 601 . The second network element performs positioning calculation. 
     The second network element receives, for each identifier in the identifier set, calculation information required for calculating location information of a terminal device corresponding to the identifier. In this case, the second network element performs positioning calculation based on the calculation information, to obtain the location information and positioning precision of the terminal device. 
     In this embodiment, determining of positioning precision is not limited, and the positioning precision may be a value determined based on an empirical value, or may be a precision value specified by a system. 
     It should be understood that the second network element performs positioning calculation for each received identifier in the identifier set. 
     For example, the second network element receives the foregoing five first request messages or performs positioning calculation for an identifier of a terminal device that is carried in each of the five first request messages, to obtain location information of the five terminal devices. 
     S 602 . The second network element sends at least one first response message to the first network element. 
     For example, the second network element sends the location information and the positioning precision of the terminal device corresponding to each identifier in the identifier set to the first network element. 
     For example, the second network element sends five first response messages to the first network element, and each of the five first response messages carries location information of one terminal device. 
     S 603 . The first network element determines the identifier of the first terminal device. 
     For example, the first network element compares (x, y) with the location information of the foregoing five terminal devices, determines location information of a terminal device closest to (x, y) in the location information of the five terminal devices, and determines an identifier of a terminal device corresponding to the location information of the terminal device as the identifier of the first terminal device. 
     S 604 . The first network element sends a second response message to the third network element. 
     For example, the first network element adds identification information of the first terminal device to the second response message, and sends the second response message to the third network element. 
     S 605 . The third network element sends a third response message to the server. 
     For example, the third network element adds the identification information of the first terminal device to the third response message, and sends the third response message to the server. 
     It should be understood that, to accurately determine the identifier of the first terminal device, the server obtains the first information in real time, and the steps shown in  FIG. 6  are repeated, so that the identifier of the first terminal device can be accurately determined. For example, the identifier of the first terminal device is determined for a plurality of times, so that the obtained identifier of the first terminal device is more accurate. 
     The foregoing describes in detail the method for obtaining an identifier of a terminal device in the embodiments with reference to  FIG. 3  to  FIG. 6 . The following describes in detail network elements provided in the embodiments with reference to  FIG. 7  to  FIG. 12 . 
       FIG. 7  is a schematic block diagram of a first network element  500  according to an embodiment. The first network element includes a sending unit  501 , an obtaining unit  502 , and a processing unit  503 . 
     The obtaining unit  502  is configured to obtain first information. The first information carries location information of a first terminal device. 
     The processing unit  503  is configured to determine an identifier set based on the first information. The identifier set includes identifiers of N terminal devices. The N terminal devices include at least the first terminal device. N is a positive integer. 
     The sending unit  501  is configured to send N first request messages to a second network element. The N first request messages carry the identifiers of the N terminal devices and are used to request the second network element to determine location information of the N terminal devices. 
     The obtaining unit  502  is further configured to receive N first response messages sent by the second network element. The N first response messages carry the location information of the N terminal devices. 
     The processing unit  503  is further configured to compare the location information of the first terminal device with the location information of the N terminal devices and determine an identifier of the first terminal device in the identifier set. 
     The identifier of the first terminal device is an identifier used by the first terminal device for communication, and communication information of the first terminal device can be obtained based on the identifier of the first terminal device. 
     Optionally, the first information further carries status information of the first terminal device, and the status information of the first terminal device is used to indicate a status of the first terminal device. 
     For example, the determining, by the processing unit  503 , an identifier set based on the first information includes: 
     The processing unit  503  determines, based on the location information of the first terminal device, at least one network device in at least one second location that meets a preset condition with a first location indicated by the location information of the first terminal device. 
     The processing unit  503  determines M terminal devices that camp on the at least one network device, determines, in the M terminal devices, N terminal devices whose statuses are consistent with the status indicated by the status information of the first terminal device, and obtains the identifiers of the N terminal devices to form the identifier set. M is a positive integer larger than or equal to N. 
     Optionally, the obtaining, by the obtaining unit  502 , first information includes: 
     The obtaining unit  502  receives a second request message sent by a third network element. The second request message is used to request the first network element to obtain the identifier of the first terminal device. The second request message includes the first information. 
     Optionally, location information of each terminal device in the location information of the N terminal devices includes positioning precision information. 
     For example, the determining, by the processing unit  503 , an identifier set based on the first information includes: 
     The processing unit  503  determines a first identifier set based on first first-information. The first identifier set includes identifiers of X terminal devices. The X terminal devices include at least the first terminal device. X is a positive integer greater than or equal to N. 
     The first first-information is first information obtained by the obtaining unit  502  at a first moment. The first first-information carries location information of the first terminal device at the first moment. 
     The processing unit  503  determines a second identifier set based on second first-information. The second identifier set includes identifiers of Y terminal devices. The Y terminal devices include at least the first terminal device. Y is a positive integer greater than or equal to N. 
     The second first-information is first information obtained by the obtaining unit  502  at a second moment. The second first-information carries location information of the first terminal device at the second moment. 
     The processing unit  503  determines an intersection set of the first identifier set and the second identifier set as the identifier set.  FIG. 8  is a schematic block diagram of a second network element  600  according to an embodiment. The second network element includes a receiving unit  601 , a sending unit  602 , and a processing unit  603 . 
     The receiving unit  601  is configured to receive N first request messages sent by a first network element. The N first request messages carry identifiers of N terminal devices and are used to request the second network element to determine location information of the N terminal devices. 
     The processing unit  603  is configured to: separately obtain, through calculation, the location information of the N terminal devices based on the N first request messages by using a preset positioning algorithm. 
     The sending unit  602  is configured to send N first response messages to the first network element, and the N first response messages carry the location information of the N terminal devices, where
         the identifiers of the terminal devices are identifiers used by the terminal devices for communication, and communication information of the terminal devices can be obtained based on the identifiers of the terminal devices.       

     Optionally, location information of each terminal device in the location information of the N terminal devices includes positioning precision information. 
       FIG. 9  is a schematic block diagram of a third network element  700  according to an embodiment. The third network element includes a sending unit  702  and a receiving unit  703 . 
     The sending unit  702  is configured to send a second request message to a first network element. The second request message is used to request the first network element to obtain an identifier of a first terminal device. The second request message includes first information, and the first information carries location information of the first terminal device. 
     The receiving unit  703  is configured to receive a second response message sent by the first network element. The second response message carries the identifier of the first terminal device, and the identifier of the first terminal device is an identifier used by the first terminal device for communication. Communication information of the first terminal device can be obtained based on the identifier of the first terminal device. 
     Optionally, the first information further carries status information of the first terminal device, and the status information of the first terminal device is used to indicate a status of the first terminal device. 
     Before the third network element sends the second request message to the first network element, the receiving unit  703  is further configured to receive a third request message from a server, where the third request message is used to request the third network element to obtain the identifier of the first terminal device, and the third request message includes the first information. 
     The sending unit  702  is further configured to send a third response message to the server, where the third response message carries the identifier of the first terminal device. 
     As shown in  FIG. 10 , an embodiment further provides a first network element  800 . The first network element  800  includes a processor  801 , a memory  802 , and a transceiver  803 . The memory  802  stores an instruction or a program, and the processor  801  is configured to execute the instruction or the program stored in the memory  802 . When the instruction or program stored in the memory  802  is executed, the processor  801  is configured to perform the operations performed by the processing unit  503  in the embodiment shown in  FIG. 7 , and the transceiver  803  is configured to perform the operations performed by the obtaining unit  502  and the sending unit  501  in the embodiment shown in  FIG. 7 . 
     As shown in  FIG. 11 , an embodiment further provides a second network element  900 . The second network element  900  includes a processor  901 , a memory  902 , and a transceiver  903 . The memory  902  stores an instruction or a program, and the processor  901  is configured to execute the instruction or the program stored in the memory  902 . When the instruction or program stored in the memory  902  is executed, the processor  901  is configured to perform the operations performed by the processing unit  603  in the embodiment shown in  FIG. 8 , and the transceiver  903  is configured to perform the operations performed by the receiving unit  601  and the sending unit  602  in the embodiment shown in  FIG. 7 . 
     As shown in  FIG. 12 , an embodiment further provides a third network element  1000 . The third network element  1000  includes a processor  1001 , a memory  1002 , and a transceiver  1003 . The memory  1002  stores an instruction or a program, and the processor  1001  is configured to execute the instruction or the program stored in the memory  1002 . When the instruction or program stored in the memory  1002  is executed, the transceiver  1003  is configured to perform the operations performed by the receiving unit  703  and the sending unit  702  in the embodiment shown in  FIG. 9 . 
     It should be understood that, the processor mentioned in the embodiments may be a central processing unit (CPU), the processor may further be another general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), or another programmable logical device, discrete gate or transistor logical device, discrete hardware component, or the like. The general purpose processor may be a microprocessor, or the processor may be any conventional processor or the like. 
     It may be understood that the memory mentioned in the embodiments may be a volatile memory or a nonvolatile memory, or may include a volatile memory and a nonvolatile memory. The nonvolatile memory may be a read-only memory (ROM), a programmable read-only memory (programmable ROM, PROM), an erasable programmable read-only memory (erasable PROM, EPROM), an electrically erasable programmable read-only memory (electrically EPROM, EEPROM), or a flash memory. The volatile memory may be a random access memory (RAM), used as an external cache. Through example but not limitative description, many forms of RAMs may be used, for example, a static random access memory (static RAM, SRAM), a dynamic random access memory (dynamic RAM, DRAM), a synchronous dynamic random access memory (synchronous DRAM, SDRAM), a double data rate synchronous dynamic random access memory (double data rate SDRAM, DDR SDRAM), an enhanced synchronous dynamic random access memory (enhanced SDRAM, ESDRAM), a synchronous link dynamic random access memory (synch link DRAM, SLDRAM), and a direct rambus dynamic random access memory (direct rambus RAM, DR RAM). 
     It should be noted that when the processor is a general-purpose processor, a DSP, an ASIC, an FPGA or another programmable logic device, a discrete gate or a transistor logic device, or a discrete hardware component, the memory (a storage module) is integrated into the processor. 
     It should be noted that the memory described includes, but is not limited to, these and any memory of another proper type. 
     A person of ordinary skill in the art may be aware that, in combination with the examples described in the embodiments, units and algorithm steps may be implemented by electronic hardware or a combination of computer software and electronic hardware. Whether the functions are performed by hardware or software depends on particular applications and design constraint conditions of the technical solutions. A person of ordinary skill in the art may use different methods to implement the described functions for each particular application, but it should not be considered that the implementation goes beyond the scope of the embodiments. 
     It may be understood by a person of ordinary skill in the art that, for the purpose of convenient and brief description, for a detailed working process of the foregoing system, network element, and unit, reference may be made to a corresponding process in the foregoing method embodiments, and details are not described herein again. 
     In the several embodiments provided, it should be understood that the system, apparatus, and method may be implemented in other manners. For example, the described apparatus embodiment is merely an example. For example, the unit division is merely logical function division and may be other division in actual implementation. For example, a plurality of units or components may be combined or integrated into another system, or some features may be ignored or not performed. In addition, the displayed or discussed mutual couplings or direct couplings or communication connections may be implemented by using some interfaces. The indirect couplings or communication connections between the apparatuses or units may be implemented in electronic, mechanical, or other forms. 
     The units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one position, or may be distributed on a plurality of network units. Some or all of the units may be selected based on actual requirements to achieve the objectives of the solutions of the embodiments. 
     In addition, functional units in the embodiments may be integrated into one processing unit, or each of the units may exist alone physically, or two or more units are integrated into one unit. 
     When the functions are implemented in the form of a software functional unit and sold or used as an independent product, the functions may be stored in a computer-readable storage medium. Based on such an understanding, the solutions essentially, or the part contributing to the prior art, or some of the solutions may be implemented in a form of a software product. The software product is stored in a storage medium, and includes several instructions for instructing a computer device (which may be a personal computer, a server, or a network device) to perform all or some of the steps of the methods described in the embodiments. The foregoing storage medium includes: any medium that can store program code, such as a USB flash drive, a removable hard disk, a ROM, a RAM, a magnetic disk, or an optical disc. 
     The foregoing descriptions are merely implementations of the embodiments, but are not limiting. Any variation or replacement readily figured out by a person ordinary skill in the art within the scope of the embodiments shall fall within the protection scope.