Patent Publication Number: US-2019200397-A1

Title: Random Access Method, Apparatus, and System

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of International Application No. PCT/CN2016/097389, filed on Aug. 30, 2016, the disclosure of which is hereby incorporated by reference in its entirety 
    
    
     TECHNICAL FIELD 
     The present invention relates to the communications field, and in particular, to a random access method, apparatus, and system. 
     BACKGROUND 
     The development of communications technologies imposes more demands for frequency resources. Spectrum resources are limited, and therefore, a new network may probably operate at a high frequency in the future. The new network has high capacity and performance, and a better service can be provided for a user when a terminal accesses a high frequency network. 
     According to a channel fading principle, a fading intensity is proportional to a frequency. A high frequency signal is easy to fade, and a diffraction capability of the high frequency signal is weaker than that of a relatively low frequency signal. Therefore, a higher frequency of the high frequency network indicates a smaller coverage area. Because of concentrated signal energy, a beamforming (beamforming) technology is used to expand the coverage area of the high frequency network, so that a terminal at the edge of the high frequency network can access the high frequency network and enjoy a good service of the high frequency network. 
     Currently, a solution of expanding the coverage area of the high frequency network in a beamforming manner is as follows: The terminal gives priority to random access to the high frequency network, establishes a radio resource control (English full name: Radio Resource Control, RRC) connection to an access device of the high frequency network, and then sends a sounding reference signal (English full name: Sounding Reference Signal, SRS) to the access device of the high frequency network. The access device estimates, based on symmetry of an uplink channel and a downlink channel, a determined optimal beam between the terminal and the access device. Then data transmission is performed between the terminal and the access device in the beamforming manner. 
     When the terminal randomly accesses the high frequency network, the terminal first needs to establish a connection to the access device, and then accesses a beam (beam) after interaction. Consequently, the terminal cannot access the beam in time, and a success rate at which the terminal accesses the high frequency network is low. 
     SUMMARY 
     Embodiments of the present invention provide a random access method, apparatus, and system, so that a terminal can access a beam in time, thereby increasing a success rate at which the terminal accesses a network. 
     The following technical solutions are used in the embodiments of the present invention to achieve the foregoing objective. 
     According to a first aspect, a random access method is provided, specifically including: receiving, by a terminal, a plurality of signals generated by a first access device in a beamforming manner on a plurality of beams; determining a beam of a strongest signal in the plurality of beams; generating a preamble signal for the beam of the strongest signal based on configuration information; and sending, by the terminal, the generated preamble signal to the first access device. 
     In this way, before accessing the first access device, to be specific, in an initial access stage of the terminal, the terminal has determined that the beam of the strongest signal is used as a beam accessing the first access device, and sends the preamble signal of the determined beam of the strongest signal to the first access device. Therefore, the first access device may identify, based on the received preamble signal, the beam that is of the strongest signal and that is determined by the terminal, and establish the connection to the terminal by using the beam, so as to complete the random access for the terminal. In the process, the terminal accesses the beam of the first access device in time. This increases a success rate at which the terminal accesses the first access device. 
     Optionally, the configuration information may include a beam configuration of the beam of the strongest signal, or the configuration information may include an identifier of the beam of the strongest signal and a cell configuration, or the configuration information may include a beam configuration of the beam of the strongest signal and an identifier of the beam of the strongest signal. 
     The beam configuration of the beam of the strongest signal includes at least one preamble allocated by the first access device to the beam of the strongest signal and time-frequency resource information used to send the preamble signal. The time-frequency resource information is used to indicate a time-frequency resource occupied when the preamble signal is sent. The cell configuration includes at least one preamble allocated by a network to the network provided by the first access device and time-frequency resource information used to send the preamble signal. The identifier of the beam is used to indicate a unique beam. 
     A preamble signal of a beam may uniquely determine the beam. 
     Optionally, when a preamble signal of a beam is generated, a preamble in the beam configuration of the beam may be selected through contention as the preamble signal, and a time-frequency resource in the beam configuration of the beam may be selected through contention to send the preamble signal. In this way, a receiver can uniquely determine the beam based on the beam configuration, to be specific, by using content of the preamble signal and the time-frequency resource occupied to send the preamble signal. 
     Optionally, when a preamble signal of a beam is generated, an identifier of the beam may be added to the preamble signal of the beam, so that a receiver can uniquely determine the beam by using the beam identifier carried by the preamble signal. 
     Further, when the network provided by the first access device is a high frequency network, the terminal can access the high frequency network in time in the solution of this application, thereby increasing a success rate at which the terminal accesses the high frequency network. 
     With reference to the first aspect, in a possible implementation, to improve feasibility of the solution, the configuration information may include the beam configuration of the beam of the strongest signal, and the receiving, by a terminal, a plurality of signals on a plurality of beams from a first access device may be specifically implemented as: receiving, by the terminal, a broadcast signal on the beam of the strongest signal, where the broadcast signal is used to broadcast the beam configuration of the beam of the strongest signal. 
     In another possible implementation, when the configuration information includes the beam configuration of the beam of the strongest signal, the method may further include: receiving, by the terminal, the beam configuration of the beam of the strongest signal from a second access device. In other words, the second access device assists the first access device in broadcasting the beam configuration of the beam of the strongest signal. 
     Specifically, the terminal is within a coverage area of a network provided by the second access device. 
     Further, if the network provided by the second access device and the network provided by the first access device are co-sited, the second access device may directly obtain and broadcast a beam configuration of each beam configured by the first access device. If the network provided by the second access device and the network provided by the first access device are not co-sited, the second access device may exchange information with the first access device through an X2 interface, to obtain and broadcast a beam configuration of each configured beam. 
     With reference to the first aspect or any of the foregoing possible implementations, in another possible implementation, when the configuration information is the beam configuration of the beam of the strongest signal, the generating, by the terminal, a preamble signal for the beam of the strongest signal based on configuration information may be specifically implemented as follows: The terminal first obtains preambles in the beam configuration of the beam of the strongest signal, and time-frequency resource information used to send a random access preamble sequence; selects, through contention, one preamble as the random access preamble sequence; obtains, through contention, one time-frequency resource as a random access time-frequency resource; and sends the selected random access preamble sequence, which is used as the preamble signal, to the first access device on the random access time-frequency resource obtained through contention. In this way, when receiving the preamble signal, the first access device may search, based on content of the preamble signal and the occupied time-frequency resource, a beam configuration of each beam, so as to uniquely determine the beam of the strongest signal that is determined by the terminal, to be specific, uniquely determine a beam selected by the terminal to access the network provided by the first access device. 
     With reference to the first aspect or any of the foregoing possible implementations, in another possible implementation, the receiving, by a terminal, a plurality of signals on a plurality of beams from a first access device may be specifically implemented as: when the terminal receives the broadcast signal on the beam of the strongest signal, receiving, by the terminal, a synchronization signal on the beam of the strongest signal. 
     It should be noted that when the plurality of signals on the plurality of beams from the first access device include a broadcast signal and a synchronization signal, the terminal may determine any beam of a strongest signal in the broadcast signal or the synchronization signal as the beam of the strongest signal in the plurality of beams. 
     With reference to the first aspect or any of the foregoing possible implementations, in another possible implementation, the configuration information may include an identifier of the beam of the strongest signal and a cell configuration, or the configuration information includes a beam configuration of the beam of the strongest signal and an identifier of the beam of the strongest signal. The receiving, by a terminal, a plurality of signals on a plurality of beams from a first access device may be specifically implemented as: receiving, by the terminal, a synchronization signal or a broadcast signal on the beam of the strongest signal, where the synchronization signal or the broadcast signal on the beam of the strongest signal carries the identifier of the beam of the strongest signal. 
     With reference to the first aspect or any of the foregoing possible implementations, in another possible implementation, when the configuration information includes the identifier of the beam of the strongest signal and the cell configuration, or the configuration information includes the beam configuration of the beam of the strongest signal and the identifier of the beam of the strongest signal, the generating, by the terminal, a preamble signal for the beam of the strongest signal based on configuration information may be specifically implemented as follows: The terminal selects, through contention, one preamble as the preamble signal from the cell configuration or from the beam configuration of the beam of the strongest signal, selects, through contention, a time-frequency resource used to send the preamble signal, sends the preamble signal on the time-frequency resource selected through contention, and adds, to the preamble signal, the identifier of the beam that is of the strongest signal and that is determined by the terminal. In this way, when receiving the preamble signal, the first access device can quickly and accurately identify the beam based on the beam identifier carried by the preamble signal. This effectively ensures accuracy in which the terminal communicates with the access device in the beamforming manner. 
     With reference to the first aspect or any of the foregoing possible implementations, in another possible implementation, there may be a plurality of forms of beam identifiers. Optionally, the broadcast signal includes the beam identifier, in other words, the beam identifier is explicitly carried. Optionally, the first access device uses a beam uniquely corresponding to a downlink synchronization signal (primary synchronization signal (English full name: Primary Synchronization Signal, PSS)/secondary synchronization signal (English full name: Secondary Synchronization Signal, SSS)), in other words, the synchronization signal implicitly carries the beam identifier. 
     Specifically, if physical cell identifiers (English full name: Physical Cell Identifier, PCI) of the beam beam are different from each other, a PCI uniquely corresponding to the PSS/SSS may be used to identify different beams. If PCIs of beams are the same, similarly, an extended PSS/SSS may be used to identify different beams. 
     With reference to the first aspect or any of the foregoing possible implementations, in another possible implementation, when the configuration information includes the identifier of the beam of the strongest signal and the cell configuration, or the configuration information includes the beam configuration of the beam of the strongest signal and the identifier of the beam of the strongest signal, the receiving, by a terminal, a beam configuration of the beam of the strongest signal or a cell configuration may be specifically implemented as: receiving the beam configuration of the beam of the strongest signal or the cell configuration from a second access device; or the broadcast signal on the beam of the strongest signal is used to broadcast the beam configuration of the beam of the strongest signal or the cell configuration. 
     According to a second aspect, the present invention provides another random access method, specifically including: sending, by a first access device, a plurality of signals to a terminal on a plurality of beams generated in a beamforming manner; receiving, by the first access device, a preamble signal of a beam of a strongest signal, where the preamble signal is sent by the terminal; and identifying, by the first access device based on the received preamble signal, a beam on which the terminal accesses a network provided by the first access device, and establishing an RRC connection to the terminal. 
     In the random access method provided in the present invention, the first access device sends signals to the terminal on the plurality of beams generated in the beamforming manner, and this expands a coverage area of the network provided by the first access device. The terminal may determine the beam of the strongest signal in an access stage based on the plurality of signals on the plurality of beams, and send the preamble signal of the beam of the strongest signal to the terminal. The first access device can accurately identify, based on the received preamble signal, an optimal beam selected by the terminal to access the first access device. In the process, the terminal accesses the beam in time. This increases a success rate at which the terminal accesses the network provided by the first access device. 
     A preamble signal of a beam may uniquely determine the beam. 
     Corresponding to generating a preamble signal of a beam in the first aspect, optionally, when receiving a preamble signal of a beam, the first access device may uniquely determine the beam based on the beam configuration, to be specific, by using content of the preamble signal and a time-frequency resource occupied to send the preamble signal. Alternatively, the first access device may uniquely determine the beam by using a beam identifier carried by the preamble signal. 
     With reference to the second aspect, in a possible implementation, the sending, by a first access device, a plurality of signals to a terminal on a plurality of beams may be specifically implemented as: sending, by the first access device, a broadcast signal to the terminal on the plurality of beams, where the broadcast signal is used to broadcast a beam configuration of the first access device. Correspondingly, the identifying, by the first access device based on the preamble signal, a beam on which the terminal accesses the first access device, and establishing an RRC connection to the terminal may be implemented as: identifying, by the first access device based on the preamble signal and the beam configuration of the first access device, the beam on which the terminal accesses the network provided by the first access device, and establishing the RRC connection. 
     A beam configuration of an access device is a preamble allocated by the access device to each beam of the access device and time-frequency resource information used to send the preamble signal. 
     With reference to the second aspect or any of the foregoing possible implementations, in another possible implementation, the identifying, by the first access device based on the preamble signal and the beam configuration of the beam of the strongest signal, the beam on which the terminal accesses the network provided by the first access device may be specifically implemented as: identifying, by the first access device, that the beam on which the terminal accesses the network provided by the first access device is a beam corresponding to the preamble signal received by the first access device and the time-frequency resource occupied by the preamble signal in the beam configuration. 
     With reference to the second aspect or any of the foregoing possible implementations, in another possible implementation, to save a system resource and ensure a success rate and accuracy in which the terminal obtains the beam configuration, the first access device may send the beam configuration of the first access device to the terminal by using a second access device instead of the broadcast signal. 
     With reference to the second aspect or any of the foregoing possible implementations, in another possible implementation, the sending, by the first access device, the beam configuration of the first access device to the terminal by using a second access device may be specifically implemented as: sending, by the first access device, the beam configuration of the first access device to the second access device, and forwarding, by the second access device, the beam configuration of the first access device to the terminal. In other words, the beam configuration of the first access device is sent to the terminal with the assistance of the second access device. 
     With reference to the second aspect or any of the foregoing possible implementations, in another possible implementation, the sending, by a first access device, a plurality of signals to a terminal on a plurality of beams may be specifically implemented as: sending, by the first access device, a broadcast signal to the terminal on the plurality of beams. When the broadcast signal is used to broadcast a beam configuration of the first access device, the sending, by a first access device, a plurality of signals to a terminal on a plurality of beams further includes: sending, by the first access device, a synchronization signal to the terminal on the plurality of beams. In the implementation, the first access device sends both the synchronization signal and the broadcast signal to the terminal on the plurality of beams, and the broadcast signal is used to broadcast a beam configuration of each beam. 
     Further, when the first access device sends both the synchronization signal and the broadcast signal to the terminal on the plurality of beams, the terminal may determine the beam of the strongest signal based on any one of the synchronization signal or the broadcast signal on the plurality of beams. 
     With reference to the second aspect or any of the foregoing possible implementations, in another possible implementation, the sending, by a first access device, a plurality of signals to a terminal on a plurality of beams may be specifically implemented as: sending, by the first access device, a synchronization signal to the terminal on the plurality of beams, and broadcasting, by the first access device, the beam configuration of the first access device to the terminal by using the second access device. 
     With reference to the second aspect or any of the foregoing possible implementations, in another possible implementation, the sending, by a first access device, a plurality of signals to a terminal on a plurality of beams may be specifically implemented as: sending, by the first access device, a synchronization signal or a broadcast signal to the terminal on the plurality of beams, where the synchronization signal or the broadcast signal carries an identifier of each beam. In this way, after receiving the plurality of signals on the plurality of beams, the terminal may obtain the identifier of the determined beam of the strongest signal, and add the identifier to the preamble signal to provide the identifier for the first access device, so that the first access device identifies the beam that is of the strongest signal and that is determined by the terminal. 
     With reference to the second aspect or any of the foregoing possible implementations, in another possible implementation, the preamble signal carries the identifier of the beam that is of the strongest signal and that is determined by the terminal. 
     With reference to the second aspect or any of the foregoing possible implementations, in another possible implementation, when the preamble signal carries the identifier of the beam that is of the strongest signal and that is determined by the terminal, the first access device identifies that the beam on which the terminal accesses the network provided by the first access device is a beam indicated by the beam identifier carried by the preamble signal. 
     With reference to the second aspect or any of the foregoing possible implementations, in another possible implementation, the method further includes: sending, by the first access device, a beam configuration of the first access device or a cell configuration to the terminal by using a second access device; or the broadcast signal is used to broadcast a beam configuration of the first access device or a cell configuration. 
     The cell configuration is described in detail in the first aspect, and details are not described herein again. 
     With reference to the second aspect or any of the foregoing possible implementations, in another possible implementation, the method further includes: receiving, by the first access device, a beam configuration that is sent and allocated by a third access device, and broadcasting, by the first access device, the beam configuration allocated by the third access device. 
     According to a third aspect, an embodiment of the present invention provides a terminal, and the apparatus may implement a function performed by the terminal in the foregoing method example. The function may be implemented by hardware, or may be implemented by hardware executing corresponding software. The hardware or the software includes one or more modules corresponding to the foregoing function. 
     With reference to the third aspect, in a possible implementation, a structure of the terminal includes a processor and a transceiver, and the processor is configured to support the terminal in performing a corresponding function in the foregoing method. The transceiver is configured to support the terminal in communicating with another network element. The terminal may further include a memory. The memory is configured to couple to the processor and store necessary program instructions and data of the terminal. 
     According to a fourth aspect, an embodiment of the present invention provides a first access device, and the first access device may implement a function performed by the first access device in the foregoing method example. The function may be implemented by hardware, or may be implemented by hardware executing corresponding software. The hardware or the software includes one or more modules corresponding to the foregoing function. 
     With reference to the fourth aspect, in a possible implementation, a structure of the first access device includes a processor and a transceiver, and the processor is configured to support the first access device in performing a corresponding function in the foregoing method. The transceiver is configured to support the first access device in communicating with another network element. The first access device may further include a memory. The memory is configured to couple to the processor and store necessary program instructions and data of the apparatus. 
     According to a fifth aspect, an embodiment of the present invention provides a random access system. The system includes at least one terminal according to any one of the foregoing aspects or any one of the foregoing possible implementations and at least one first access device according to any one of the foregoing aspects or any one of the foregoing possible implementations. 
     According to a sixth aspect, an embodiment of the present invention provides a computer storage medium, configured to store a computer software instruction used by the foregoing terminal, and the computer storage medium includes a program designed to perform the foregoing aspects. 
     According to a seventh aspect, an embodiment of the present invention provides a computer storage medium, configured to store a computer software instruction used by the foregoing first access device, and the computer storage medium includes a program designed to perform the foregoing aspects. 
     The solutions provided in the third aspect to the seventh aspect are used to implement the random access method provided by the first aspect or the second aspect. Therefore, the solutions have same beneficial effects with the first aspect or the second aspect, and details are not described herein again. 
     In accordance with an example of the invention, this application further provides the following embodiments: 
     Embodiment 1: A first access device, wherein the first access device comprises at least one processor and a transceiver, wherein the at least one processor is configured to: send a plurality of signals to a terminal on a plurality of beams by using the transceiver, wherein the plurality of beams are generated in a beamforming manner; receive, by using the transceiver, a preamble signal of a beam of a strongest signal, wherein the preamble signal is sent by the terminal; and identify, based on the preamble signal, a beam on which the terminal accesses a network provided by the first access device, and establish a radio resource control (RRC) connection to the terminal. 
     Embodiment 2: According to the access device in Embodiment 1, wherein, the at least one processor is configured to: send a broadcast signal to the terminal on the plurality of beams by using the transceiver, wherein the broadcast signal is used to broadcast a beam configuration of the first access device; and identify, based on the preamble signal and the beam configuration, the beam on which the terminal accesses the network provided by the first access device, and establish the RRC connection. 
     Embodiment 3: According to the access device in Embodiment 2, wherein the at least one processor is further configured to: send a synchronization signal to the terminal on the plurality of beams by using the transceiver. 
     Embodiment 4: According to the access device in Embodiment 1, wherein the at least one processor is configured to: send a synchronization signal or a broadcast signal to the terminal on the plurality of beams by using the transceiver, wherein the synchronization signal or the broadcast signal carries an identifier of each beam. 
     Embodiment 5: According to the access device in Embodiment 4, wherein the preamble signal carries an identifier of the beam that is of the strongest signal and that is determined by the terminal. 
     Embodiment 6: According to the access device in Embodiment 4 or 5, wherein the at least one processor is further configured to send a beam configuration of the first access device or a cell configuration to the terminal by using the transceiver and a second access device; or the broadcast signal is used to broadcast the cell configuration or the beam configuration. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       To describe the technical solutions in the embodiments of the present invention more clearly, the following briefly describes the accompanying drawings required for describing the embodiments or the prior art. Apparently, the accompanying drawings in the following description show merely some embodiments of the present invention, and a person of ordinary skill in the art may still derive other drawings from these accompanying drawings without creative efforts. 
         FIG. 1  is a schematic diagram of a network architecture according to an embodiment of the present invention; 
         FIG. 2  is a schematic structural diagram of a terminal  20  according to an embodiment of the present invention; 
         FIG. 3  is schematic structural diagram of a first access device  30  according to an embodiment of the present invention; 
         FIG. 4  is a schematic diagram of a scenario of a random access method according to an embodiment of the present invention; 
         FIG. 5  is a schematic flowchart of a random access method according to an embodiment of the present invention; 
         FIG. 6  is a schematic structural diagram of another terminal  20  according to an embodiment of the present invention; 
         FIG. 7  is a schematic structural diagram of still another terminal  20  according to an embodiment of the present invention; 
         FIG. 8  is schematic structural diagram of another first access device  30  according to an embodiment of the present invention; 
         FIG. 9  is schematic structural diagram of still another first access device  30  according to an embodiment of the present invention; and 
         FIG. 10  is a schematic structural diagram of a random access system according to an embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The following clearly and completely describes the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Apparently, the described embodiments are merely some but not all of the embodiments of the present invention. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention. 
     In addition, the terms “system” and “network” may be used interchangeably in this specification. The term “and/or” in this specification describes only an association relationship for describing associated objects and represents that three relationships may exist. For example, A and/or B may represent the following three cases: Only A exists, both A and B exist, and only B exists. In addition, the character “/” in this specification generally indicates an “or” relationship between the associated objects. 
     In a current random access process, an access device sends a synchronization signal in a conventional manner, so that a terminal finds and accesses a network. The access device communicates with the terminal in a beamforming manner only when the terminal performs data transmission, so as to enlarge a system capacity. However, in a terminal access stage, because of a small coverage area of a high frequency network, the terminal cannot access a beam generated in a beamforming manner in time in the current random access process. Consequently, a success rate at which the terminal accesses the high frequency network is not high. 
     In view of this, according to a basic principle of the present invention, an access device sends a plurality of signals to a terminal on a plurality of beams generated in a beamforming manner. The terminal determines a beam of a strongest signal based on intensities of the signals, and sends a preamble signal to the access device based on the beam of the strongest signal, so that the access device can uniquely and accurately identify, based on the received preamble signal, the beam that is of the strongest signal and that is determined by the terminal. The beam of the strongest signal is determined before the access, so that the terminal can access the beam in time. This greatly increases a success rate at which the terminal randomly accesses the network. 
     A random access method provided in the embodiments of the present invention is applied to a network architecture shown in  FIG. 1 . The network architecture shown in  FIG. 1  includes at least one access device and at least one terminal. Quantities of access devices and terminals in  FIG. 1  are merely an example, and constitute no limitation on quantities of access devices and terminals in the network architecture. The at least one access device in  FIG. 1  is configured to provide at least one network, and the terminal randomly accesses the network to implement a service of the terminal. 
     Optionally, the access device in  FIG. 1  may be a base station or another network element having an access function. This is not specifically limited in this embodiment of the present invention. 
     It should be understood that in this embodiment of the present invention, the terminal may be referred to as user equipment (English full name: User Equipment, UE), a mobile station (English full name: Mobile Station, MS), a mobile terminal (English full name: Mobile Terminal), or the like. The terminal may communicate with one or more core networks through a radio access network (Radio Access Network, RAN). For example, the terminal may be a mobile phone (or referred to as a “cellular” phone) or a computer with a mobile terminal. For example, the terminal may be a portable, pocket-sized, handheld, computer built-in, or in-vehicle mobile apparatus. The terminal exchanges voice and/or data with the radio access network. 
     The random access method provided in the embodiments of the present invention may be performed by a terminal or a first access device provided in the embodiments of the present invention. 
       FIG. 2  is a schematic structural diagram of a terminal  20  in the embodiments of the present invention. The terminal  20  may be a part of or all of any terminal in  FIG. 1 . 
     As shown in  FIG. 2 , the terminal  20  may include a processor  201 , a memory  202 , and a transceiver  203 . 
     The following specifically describes each component of the terminal  20  with reference to  FIG. 2 : 
     The memory  202  may be a volatile memory (English full name: volatile memory) such as a random-access memory (English full name: random-access memory, RAM), a non-volatile memory (English full name: non-volatile memory) such as a read-only memory (English full name: read-only memory, ROM), a flash memory (English full name: flash memory), a hard disk drive (English full name: hard disk drive, HDD) or a solid-state drive (English full name: solid-state drive, SSD), or a combination of such types of memories, configured to store related application programs and configuration files that can implement the method in the present invention. 
     As a control center of the terminal  20 , the processor  201  may be a central processing unit (English full name: central processing unit, CPU) or an application-specific integrated circuit (English full name: Application Specific Integrated Circuit, ASIC), or is configured as one or more integrated circuits for implementing the embodiments of the present invention, for example, one or more microprocessors (English full name: digital signal processor, DSP) or one or more field programmable gate arrays (English full name: Field Programmable Gate Array, FPGA). The processor  201  may execute various functions of the terminal  20  by running or executing the software program and/or the module stored in the memory  202  and by invoking the data stored in the memory  202 . 
     The transceiver  203  may be a transceiver antenna of the terminal  20 . 
     Further,  FIG. 3  is a schematic structural diagram of a first access device  30  in the embodiments of the present invention. The first access device  30  may be a part of or all of any access device (a first access device) in  FIG. 1 . 
     As shown in  FIG. 3 , the first access device  30  may include a processor  301 , a memory  302 , and a transceiver  303 . 
     The following specifically describes each component of the first access device  30  with reference to  FIG. 3 . 
     The memory  302  may be a volatile memory such as a RAM, a non-volatile memory such as a ROM, a flash memory, an HDD, an SSD, or a combination of such types of memories, configured to store related application programs and configuration files that can implement the method in the present invention. 
     As a control center of the first access device  30 , the processor  301  may be a CPU or an ASIC, or is configured as one or more integrated circuits for implementing the embodiments of the present invention, for example, one or more DSPs or one or more FPGAs. The processor  301  may execute various functions of the first access device  30  by running or executing the software program and/or the module stored in the memory  302  and by invoking the data stored in the memory  302 . 
     The transceiver  303  may be a transceiver antenna of the first access device  30 . 
     The following specifically describes the embodiments of the present invention with reference to the accompanying drawings. 
     An embodiment of the present invention provides a random access method, applied to a scenario shown in  FIG. 4 . In the scenario shown in  FIG. 4 , a terminal is located at an edge of a coverage area (denoted by a solid line shown in  FIG. 4 ) of a network provided by a first access device, the terminal is located within an expanded coverage area (denoted by a dashed line shown in  FIG. 4 ) of the network provided by the first access device, and the terminal is located within a coverage area (denoted by a solid line shown in  FIG. 4 ) of a network provided by a second access device. By using the random access method provided in this embodiment of the present invention, the terminal accurately accesses a beam in time, and further accurately accesses, in time, the network provided by the first access device. 
     In this embodiment of the present invention, an interaction process between the terminal and the first access device or between the terminal and each of the first access device and the second access device is used as an example to describe in detail the random access method provided in this embodiment of the present invention. As shown in  FIG. 5 , the random access method provided in this embodiment of the present invention may include the following steps. 
     S 501 . The first access device sends a plurality of signals to the terminal on a plurality of beams. 
     The plurality of beams are generated in a beamforming manner, and are used to expand a coverage area of the network provided by the first access device. 
     Optionally, the plurality of signals sent by the first access device to the terminal on the plurality of beams may include a synchronization signal, or may include a broadcast signal, or may include a synchronization signal and a broadcast signal. 
     Further, optionally, when sending the plurality of signals to the terminal on the plurality of beams, the first access device may further send a beam configuration of the first access device to the terminal. The beam configuration of the first access device is used for the terminal to generate a preamble signal sent to the first access device. 
     The beam configuration of the first access device is preconfigured by the first access device. The beam configuration of the first access device includes at least one preamble allocated by the first access device to each beam of the first access device and time-frequency resource indication information used to send the preamble signal. 
     Optionally, the beam configuration of the first access device may be broadcast by using the broadcast signal, or the beam configuration of the first access device may be sent to the terminal by using the second access device. 
     The terminal is within the coverage area of the network provided by the second assess device. 
     Further, if the network provided by the second access device and the network provided by the first access device are co-sited, the second access device may directly obtain and broadcast a beam configuration of each beam configured by the first access device. If the network provided by the second access device and the network provided by the first access device are not co-sited, the second access device may exchange information with the first access device through an X2 interface, to obtain and broadcast a beam configuration of each configured beam. 
     For example, if the first access device generates 8 beams in the beamforming manner, specific content of the beam configuration of the first access device configured by the first access device for the eight beams includes: a beam 0 is configured with preambles (preamble) 0 to 7, a beam 1 is configured with preambles 8 to 15, . . . , and a beam 7 is configured with preambles 56 to 63. Allocated time-frequency resource information indicates: allocating time-frequency resources 0 to 2 to the beam 0, allocating time-frequency resources 3 to 5 to the beam 1, . . . , and allocating time-frequency resources 21 to 23 to the beam 7. The beam configuration of the first access device may be stored in a form of Table 1 and sent. 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Configured 
                   
               
               
                 Number of a beam 
                 preamble 
                 Allocated time-frequency resource 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 0 
                 0-7 
                 0-2 
               
               
                 1 
                  8-15 
                 3-5 
               
               
                 2 
                 16-23 
                 6-8 
               
               
                 3 
                 24-31 
                  9-11 
               
               
                 4 
                 32-39 
                 12-14 
               
               
                 5 
                 40-47 
                 15-17 
               
               
                 6 
                 48-55 
                 18-20 
               
               
                 7 
                 56-63 
                 21-23 
               
               
                   
               
            
           
         
       
     
     It should be noted that Table 1 merely uses an example to describe the beam configuration of the first access device, and constitutes no specific limitation on the form and the content of the beam configuration of the first access device. In actual application, the content and the form of the beam configuration of the first access device may be set based on an actual requirement. 
     Further, optionally, when sending the plurality of signals to the terminal on the plurality of beams, the first access device may further add a beam identifier of each beam to each beam. 
     The beam identifier may be used to uniquely indicate a beam. 
     Optionally, the beam identifier described in this embodiment of the present invention may include but is not limited to the following two forms: 
     Form 1: an explicit beam identifier. 
     The explicit beam identifier is used to explicitly indicate identification information of a beam. The explicit beam identifier may be directly added to the beam, and may be directly obtained by a receiver. 
     For example, when sending the plurality of signals on the beams generated in the beamforming manner, the first access device may add an identifier of each beam to a signal sent on each beam. This beam identifier form is provided as the explicit beam identifier described in form 1. 
     Form 2: an implicit beam identifier. 
     The implicit beam identifier is used to determine indication information of a beam identifier, and the beam identifier may be obtained after calculation by using the implicit beam identifier. 
     For example, when sending a downlink synchronization signal on the plurality of beams generated in the beamforming manner, the first access device may implicitly notify the terminal of an identifier of each beam by using a PSS/SSS. A receiver may uniquely determine a beam based on the PSS/SSS, to be specific, obtain an identifier of the beam. 
     Specifically, if PCIs of beams are different from each other, the receiver may identify different beams by using a PCI uniquely corresponding to the PSS/SSS. If PCIs of beams are the same, the receiver may similarly use an extended PSS/SSS to identify different beams. 
     The PSS is a sequence transferred on a primary synchronization channel (English full name: primary synchronous channel, P-SCH), and has 3 possible forms; and the SSS is a sequence transferred on a secondary synchronization channel 
     (English full name: Secondary synchronous channel, S-SCH), and has 168 possible forms. A beam ID may be obtained when sequence numbers of the two sequences are combined. 
     It should be noted that a process in which the beam ID is obtained based on the combination of the two sequences PSS and SSS is not described in this embodiment of the present invention. 
     Specifically, a plurality of implementations in which the first access device sends the plurality of signals to the terminal on the plurality of beams may include but is not limited to the following five solutions: 
     Solution 1: 
     The first access device sends a broadcast signal to the terminal on the plurality of beams, where the broadcast signal is used to broadcast a beam configuration of the first access device. 
     It should be noted that in this embodiment of the present invention, a form and a location of the beam configuration of the first access device in the broadcast signal may be set based on an actual requirement. This is not specifically limited in this embodiment of the present invention. 
     Solution 2: 
     The first access device sends a synchronization signal and a broadcast signal to the terminal on the plurality of beams, where the broadcast signal is used to broadcast a beam configuration of the first access device. 
     Solution 3: 
     The first access device sends a synchronization signal to the terminal on the plurality of beams, where the first access device sends a beam configuration of the first access device to the terminal by using the second access device. 
     Solution 4: 
     The first access device sends a broadcast signal to the terminal on the plurality of beams, where a broadcast signal sent on each beam carries a beam identifier of the broadcast signal, and the broadcast signal is used to broadcast a beam configuration of the first access device. 
     Solution 5: 
     The first access device sends a synchronization signal to the terminal on the plurality of beams, where a synchronization signal sent on each beam carries a beam identifier of the synchronization signal. 
     In solution 5, the first access device may further send a beam configuration of the first access device or a cell configuration to the terminal. 
     The cell configuration is at least one preamble allocated to the network provided by the first access device and time-frequency resource information used to send the preamble signal. The time-frequency resource information is used to indicate at least one time-frequency resource. 
     Optionally, in solution 5, that the first access device may further send a beam configuration of the first access device or a cell configuration to the terminal may include: directly sending, by the first access device, the beam configuration of the first access device or the cell configuration to the terminal, or sending, by the first access device, the beam configuration of the first access device or the cell configuration to the terminal by using the second access device. 
     It should be noted that a cell configuration may be pre-configured in the terminal, and therefore, the cell configuration in solution 5 cannot be sent to the terminal. 
     It should be further noted that the foregoing five solutions merely use an example to describe the implementation solution of S 501 , and constitute no specific limitation on an implementation process of S 501 . In actual application, there may be another implementation of S 501 . This is not specifically limited in this embodiment of the present invention. 
     S 502 . The terminal receives the plurality of signals on the plurality of beams from the first access device. 
     It should be noted that the signals received by the terminal in S 502  are the signals sent by the first access device in S 501 . Content of the plurality of signals on the plurality of beams is described in detail in S 501 , and details are not described herein again. 
     S 503 . The terminal determines a beam of a strongest signal in the plurality of beams. 
     S 504 . The terminal generates a preamble signal for the beam of the strongest signal based on configuration information. 
     A preamble signal of a beam may uniquely determine the beam. 
     Optionally, when a preamble signal of a beam is generated, a preamble in the beam configuration of the beam may be selected through contention as the preamble signal, and a time-frequency resource in the beam configuration of the beam may be selected through contention to send the preamble signal. In this way, a receive end may uniquely determine the beam based on the beam configuration, to be specific, by using content of the preamble signal and the time-frequency resource occupied to send the preamble signal. 
     Optionally, when a preamble signal of a beam is generated, an identifier of the beam may be added to the preamble signal of the beam, so that the receiver can uniquely determine the beam by using the beam identifier carried by the preamble signal. 
     It should be noted that when a preamble signal of a beam is generated, how to configure a preamble signal of a beam so that the preamble signal of the beam may be used to uniquely determine the beam may be determined based on an actual requirement. This is not specifically limited in this embodiment of the present invention. 
     The configuration information may include a beam configuration of the beam of the strongest signal, or the configuration information may include an identifier of the beam of the strongest signal and a cell configuration, or the configuration information includes a beam configuration of the beam of the strongest signal and an identifier of the beam of the strongest signal. 
     Specifically, specific content of the configuration information depends on content sent by the first access device to the terminal. When the first access device sends only a beam configuration of the first access device to the terminal, the configuration information includes the beam configuration of the beam of the strongest signal. When the first access device sends only a beam configuration of the first access device and an identifier of each beam to the terminal, the configuration information includes the beam configuration of the beam of the strongest signal and the identifier of the beam of the strongest signal. When the first access device sends only an identifier of each beam and a cell configuration to the terminal, the configuration information includes the identifier of the beam of the strongest signal and the cell configuration. 
     Specifically, content of the configuration information is different, and therefore, solutions in which the terminal generates the preamble signal for the beam of the strongest signal based on the configuration information in S504 include but are not limited to the following two solutions. 
     Solution 1: The configuration information includes the beam configuration of the beam of the strongest signal. 
     In solution 1, a process that the terminal performs S504 may specifically include: 
     selecting, by the terminal through contention, one preamble as the preamble signal in at least one preamble included in the beam configuration of the beam of the strongest signal. 
     For example, it is assumed that the beam configuration of the first access device is shown in Table 1. The terminal determines that the beam 3 is the beam of the strongest signal, to be specific, determines that an optimal beam accessing the first access device is the beam 3. Therefore, when performing S 504 , the terminal first obtains preambles 24 to 31 in a beam configuration of the beam 3 determined in the beam configuration of the first access device shown in Table 1, and then selects, through contention, one preamble (it is assumed that a preamble 26 is selected) in the preambles 24 to 31 as the preamble signal. 
     Solution 2: The configuration information includes the cell configuration. 
     In solution 2, a process that the terminal performs S 504  may specifically include: 
     selecting, by the terminal through contention, one preamble as the preamble signal in at least one preamble included in the cell configuration. 
     S 505 . The terminal sends the preamble signal of the beam of the strongest signal to the first access device. 
     Specifically, content of the configuration information is different, and therefore, solutions in which the terminal sends the preamble signal of the beam of the strongest signal to the first access device in S505 include but are not limited to the following two solutions. 
     Solution A: The configuration information does not include the identifier of the beam of the strongest signal. 
     In solution A, corresponding to solution  1  in S 504 , the solution that the terminal sends the preamble signal to the first access device may be implemented as follows: 
     The terminal selects, through contention, one time-frequency resource from at least one time-frequency resource indicated by time-frequency resource indication information included in the beam configuration of the beam of the strongest signal, and sends the generated preamble signal to the first access device on the selected time-frequency resource. 
     For example, corresponding to the example in solution  1  in S 504 , it is assumed that beam identification information allocated by the first access device is shown in Table 1. The terminal obtains, through contention, one time-frequency resource (it is assumed that a time-frequency resource  10  is obtained through contention) in time-frequency resources  9  to  11  indicated by time-frequency resource information included in the beam configuration of the beam 3, and sends the preamble 26 to the first access device on the time-frequency resource  10 . 
     In solution A, corresponding to solution  2  in S 504 , the solution that the terminal sends the preamble signal to the first access device may be implemented as follows: 
     The terminal selects, through contention, one time-frequency resource from at least one time-frequency resource indicated by time-frequency resource indication information included in the cell configuration, and sends the generated preamble signal to the first access device on the selected time-frequency resource. 
     Solution B: The configuration information includes the identifier of the beam of the strongest signal. 
     In solution B, corresponding to solution  1  in S 504 , the solution that the terminal sends the preamble signal to the first access device may be implemented as follows: 
     The terminal selects, through contention, one time-frequency resource from at least one time-frequency resource indicated by time-frequency resource indication information included in the beam configuration of the beam of the strongest signal, and sends the generated preamble signal to the first access device on the selected time-frequency resource, where the preamble signal carries the identifier of the beam of the strongest signal. 
     In solution B, corresponding to solution  2  in S 504 , the solution that the terminal sends the preamble signal to the first access device may be implemented as follows: 
     The terminal selects, through contention, one time-frequency resource from at least one time-frequency resource indicated by time-frequency resource indication information included in the cell configuration, and sends the generated preamble signal to the first access device on the selected time-frequency resource, where the preamble signal carries the identifier of the beam of the strongest signal. 
     For example, it is assumed that the beam configuration of the first access device is shown in Table 1. The terminal determines that the beam 3 of the strongest signal is the optimal beam for accessing the network provided by the first access device, and determines that a beam ID in the beam 3 is an ID  3 . Therefore, when performing S 504 , the terminal first selects, through contention, one preamble (it is assumed that a preamble 26 is selected) in preambles 24 to 31 in the beam configuration of the beam 3 shown in Table 1 as the preamble signal, and then obtains, through contention, one time-frequency resource (it is assumed that a time-frequency resource  10  is obtained through contention) in time-frequency resources  9  to  11  indicated by time-frequency resource information in the beam configuration of the beam  3 3 shown in Table 1. Therefore, the terminal sends the preamble 26 carrying the ID 3 to the first access device on the time-frequency resource 10. 
     S 506 . The first access device receives the preamble signal of the beam of the strongest signal, where the preamble signal is sent by the terminal. 
     It should be noted that the preamble signal received by the first access device in S 506  is the preamble signal sent by the terminal in S 505 , and details are not described herein again. 
     S 507 . The first access device identifies, based on the received preamble signal, a beam selected by the terminal to access a network provided by the first access device, and establishes an RRC connection to the terminal. 
     A preamble signal of a beam may uniquely determine the beam. 
     Corresponding to generating a preamble signal of a beam in S 504 , optionally, in S 506 , when receiving a preamble signal of a beam, the first access device may uniquely determine the beam based on the beam configuration, to be specific, by using content of the preamble signal and a time-frequency resource occupied to send the preamble signal. Alternatively, the first access device may uniquely determine the beam by using a beam identifier carried by the preamble signal. 
     Optionally, solutions that the terminal sends the preamble signal are different in S 505 , and therefore, methods that the first access device identifies, based on the preamble signal, the beam on which the terminal accesses a network provided by the first access device are different in S 507 . Specifically, there are two implementations: 
     Implementation 1: Corresponding to solution A in S 505 , the configuration information does not include the identifier of the beam of the strongest signal, the preamble signal sent by the terminal does not carry the identifier of the beam that is of the strongest signal and that is determined by the terminal, and a process in which the first access device performs S 507  may specifically include the following steps: 
     The first access device first obtains the received preamble signal sent by the terminal and the time-frequency resource occupied by the preamble signal, and then searches the beam configuration of the first access device to determine that the beam on which the terminal accesses the network provided by the first access device is a beam corresponding to the received preamble signal sent by the terminal and the time-frequency resource occupied by the preamble signal in the beam configuration of the first access device. 
     For example, it is assumed that the beam configuration of the first access device is shown in Table 1, and the preamble signal that is received by the first access device on the time-frequency resource  10  and that is sent by the terminal is the preamble 26. The first access device searches the beam configuration of the first access device shown in Table 1, and determines that the beam on which the terminal accesses the first access device is the beam 3 corresponding to the preamble signal (preamble 26) and the time-frequency resource  10  occupied by the preamble signal. 
     Implementation 2: Corresponding to solution B in S 505 , the configuration information includes the identifier of the beam of the strongest signal, and the preamble signal sent by the terminal carries the identifier of the beam that is of the strongest signal and that is determined by the terminal. 
     In implementation 2, a process in which the first access device performs S 507  may specifically include the following step: 
     The first access device identifies that the beam selected by the terminal to access the network provided by the first access device is a beam indicated by the beam identifier included in the preamble signal received by the first access device. 
     Further, when a coverage area of the network provided by the first access device is larger than a coverage area provided by a third access device, the third access device may send a beam configuration of the third access device or a cell configuration to the terminal by using the first access device. In this case, the method may further include the following steps: 
     A first receiving device receives the beam configuration of the third access device or the cell configuration sent by the third access device, and then broadcasts the beam configuration of the third access device or the cell configuration. 
     According to the random access method provided in this embodiment of the present invention, before accessing the first access device, to be specific, in an initial access stage of the terminal, the terminal has determined that the beam of the strongest signal is used as the beam accessing the first access device, and sends the preamble signal of the determined beam of the strongest signal to the first access device. Therefore, the first access device may identify, based on the received preamble signal, the beam that is of the strongest signal and that is determined by the terminal, and establish the connection to the terminal by using the beam, so as to complete the random access for the terminal. In the process, the terminal accesses the beam of the first access device in time. This increases a success rate at which the terminal accesses the first access device. 
     The foregoing mainly describes the solutions provided in the embodiments of the present invention from the perspective of interaction between network elements. It may be understood that, to implement the foregoing function, each network element, such as the terminal and the first access device, includes a corresponding hardware structure and/or software module to perform each function. A person of ordinary skill in the art should be easily aware that, the units and algorithm steps in the examples described with reference to the embodiments disclosed in this specification may be implemented by hardware or a combination of hardware and computer software in the present invention. Whether the function is performed by hardware or computer software driving hardware depends on particular applications and design constraint conditions of the technical solutions. A person skilled 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 present invention. 
     In this embodiment of the present invention, function module division may be performed on the terminal, the first access device, and the like based on the foregoing method example, for example, function modules may be divided based on functions, or two or more functions may be integrated in one processing module. The integrated module may be implemented in a form of hardware, or may be implemented in a form of a functional module of software. It should be noted that the module division in the embodiments of the present invention is an example, and is merely logical function division. There may be another division manner in an actual implementation. 
     In a case of dividing function modules based on functions,  FIG. 6  is a possible schematic structural diagram of the terminal  20  in the foregoing embodiments. The terminal  20  includes a receiving unit  601 , a determining unit  602 , a generation unit  603 , and a sending unit  604 . The receiving unit  601  is configured to support the terminal  20  in performing the process S 502  in  FIG. 5 , the determining unit  602  is configured to support the terminal  20  in performing the process S 503  in  FIG. 5 , the generation unit  603  is configured to support the terminal  20  in performing the process S 504  in  FIG. 5 , and the sending unit  604  is configured to support the terminal  20  in performing the process S 505  in  FIG. 5 . All related content of steps in the foregoing method embodiments may be cited in function description of corresponding function modules, and details are not described herein again. 
     In a case of an integrated unit,  FIG. 7  shows a possible schematic structural diagram of the terminal  20  in the foregoing embodiments. The terminal  20  may include a processing module  701  and a communications module  702 . The processing module  701  is configured to perform control management on actions of the terminal  20 . For example, the processing module 701 is configured to support the terminal  20  in performing the processes S 503  and S 504  in  FIG. 5 , and/or another process of technologies described in this specification. The processing module  701  is further configured to support the terminal  20  in performing the processes S 502  and S 505  in  FIG. 5  by using the communications module  702 . The communications module  702  is configured to support the terminal  20  in communicating with another network entity. The terminal  20  may further include a storage module  703 , configured to store program code and data of the terminal  20 . 
     The processing module  701  may be the processor  201  in an entity structure of the terminal  20  shown in  FIG. 2 , may be a processor or a controller such as a CPU, a general purpose processor, a DSP, an ASIC, an FPGA, or another programmable logic device, a transistor logic device, a hardware component, or any combination thereof. It may implement or execute various examples of logical blocks, modules, and circuits that are described with reference to the content disclosed in the present invention. The processor may be a combination of computing functions, for example, a combination of one or more microprocessors or a combination of a DSP and a microprocessor. The communications module  702  may be the transceiver in the entity structure of the terminal  20  shown in  FIG. 2 , or may be a transceiver circuit, a communications interface, or the like. The storage module  703  may be the memory in the entity structure of the terminal  20  shown in  FIG. 2 . 
     When the processing module  701  is the processor, the communications module  702  is the transceiver, and the storage module  703  is the memory, the terminal  20  in  FIG. 7  in this embodiment of the present invention may be the terminal  20  shown in  FIG. 2 . 
     In a case of dividing function modules based on functions,  FIG. 8  shows a possible schematic structural diagram of the first access device  30  in the foregoing embodiments. The first access device  30  includes a sending unit  801 , a receiving unit  802 , and an identifying unit  803 . The sending unit  801  is configured to support the first access device  30  in performing the process S 501  in  FIG. 5 , the receiving unit  802  is configured to support the first access device  30  in performing the process S 506  in  FIG. 5 , and the identifying unit  803  is configured to support the first access device  30  in performing the process S 507  in  FIG. 5 . All related content of steps in the foregoing method embodiments may be cited in function description of corresponding function modules, and details are not described herein again. 
     In a case of an integrated unit,  FIG. 9  shows a possible schematic structural diagram of the first access device  30  in the foregoing embodiments. The first access device  30  may include a processing module  901  and a communications module  902 . The processing module  901  is configured to perform control management on actions of the first access device  30 . For example, the processing module  901  is configured to support the first access device  30  in performing the process S 507  in  FIG. 5 , and/or another process of technologies described in this specification. The processing module  901  is further configured to support the first access device  30  in performing the processes S 501  and S 506  in  FIG. 5  by using the communications module  902 . The communications module  902  is configured to support the first access device  30  in communicating with another network entity. The first access device  30  may further include a storage module  903 , configured to store program code and data of the first access device  30 . 
     The processing module  901  may be the processor  301  in an entity structure of the first access device  30  shown in  FIG. 3 , may be a processor or a controller such as a CPU, a general purpose processor, a DSP, an ASIC, an FPGA, or another programmable logic device, a transistor logic device, a hardware component, or any combination thereof. It may implement or execute various examples of logical blocks, modules, and circuits that are described with reference to the content disclosed in the present invention. The processor may be a combination of computing functions, for example, a combination of one or more microprocessors or a combination of a DSP and a microprocessor. The communications module  902  may be the transceiver in the entity structure of the first access device  30  shown in  FIG. 3 , or may be a transceiver circuit, a communications interface, or the like. The storage module  903  may be the memory in the entity structure of the first access device  30  shown in  FIG. 2 . 
     When the processing module  901  is the processor, the communications module  902  is the transceiver, and the storage module  903  is the memory, the first access device  30  in  FIG. 9  in this embodiment of the present invention may be the first access device  30  shown in  FIG. 3 . 
     The methods or algorithm steps described with reference to the content disclosed in the present invention may be implemented in a hardware manner, or may be implemented in a manner of executing a software instruction by a processor. The software instruction may include a corresponding software module. The software module may be stored in a RAM, a flash memory, a ROM, an erasable programmable read-only memory (Erasable Programmable ROM, EPROM), an electrically erasable programmable read-only memory (Electrically EPROM, EEPROM), a register, a hard disk, a removable hard disk, a compact disc read-only memory (CD-ROM), or a storage medium in any other forms well-known in the art. A storage medium used as an example is coupled to the processor, so that the processor can read information from the storage medium, and can write information into the storage medium. Certainly, the storage medium may be a part of the processor. The processor and the storage medium may be located in an ASIC. In addition, the ASIC may be located in a core network interface device. Certainly, the processor and the storage medium may exist in the core network interface device as discrete components. 
     In addition, an embodiment of the present invention provides a random access system  100 . As shown in  FIG. 10 , the random access system  100  may include: 
     at least one terminal  20  described in any of the foregoing embodiments and at least one first access device  30  described in any of the foregoing embodiments. 
     It should be further noted that  FIG. 10  merely describes an example of an architecture of the random access system  100 , and constitutes no limitation on quantities of the terminals  20  and the first access devices  30  included in the random access system  100 . 
     A person of skill in the art should be aware that in one or more of the foregoing examples, the functions described in the present invention may be implemented by using hardware, software, firmware, or any combination thereof. When the present invention is implemented by software, these functions may be stored in a computer-readable medium or transmitted as one or more instructions or code in the computer-readable medium. The computer-readable medium includes a computer storage medium and a communications medium, where the communications medium includes any medium that enables a computer program to be transmitted from one place to another. The storage medium may be any available medium accessible to a general or dedicated computer. It may be clearly understood by a person skilled in the art that, for the purpose of convenient and brief description, for a detailed working process of the foregoing system, apparatus, and unit, reference may be made to a corresponding process in the foregoing method embodiments, and details are not described herein. 
     In the several embodiments provided in this application, it should be understood that the disclosed 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 through some interfaces. The indirect couplings or communication connections between the apparatuses or units may be implemented in electrical or other forms. 
     The units described as separate components may or may not be physically separate, and components 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 according to actual needs to achieve the objectives of the solutions of the embodiments. 
     In addition, functional units in the embodiments of the present invention 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. The integrated unit may be implemented in a form of hardware, or may be implemented in a form of hardware in addition to a software functional unit. 
     When the foregoing integrated unit is implemented in a form of a software functional unit, the integrated unit may be stored in a computer-readable storage medium. The software functional unit 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 some of the steps of the methods described in the embodiments of the present invention. The foregoing storage medium includes: any medium that can store program code, such as a USB flash drive, a removable hard disk, a read-only memory (Read-Only Memory, ROM for short), a random access memory (Random Access Memory, RAM for short), a magnetic disk, or an optical disc. 
     Finally, it should be noted that the foregoing embodiments are merely intended for describing the technical solutions of the present invention but not for limiting the present invention. Although the present invention is described in detail with reference to the foregoing embodiments, a person of ordinary skill in the art should understand that they may still make modifications to the technical solutions described in the foregoing embodiments or make equivalent replacements to some technical features thereof, without departing from the spirit and scope of the technical solutions of the embodiments of the present invention.