Terminal device, network device, communication method, and communication system

Abstract

[Problem] To perform an efficient initial procedure. [Solution] A terminal device according to the present disclosure is for communicating with a network device including one or more communication points, the terminal device comprising: a reception unit that receives a first signal containing information necessary to receive first report information transmitted from at least one first communication point, receives the first report information containing information pertaining to a second signal, which is a known signal, transmitted from at least one second communication point on the basis of the information necessary to receive the first report information contained in the first signal, and receives the second signal transmitted from at least one third communication point on the basis of the information pertaining to the second signal contained in the first report information; and a control unit that carries out initial access control for connecting to the network device via at least one fourth communication point on the basis of the communication quality of the second signal.

Description

Terminal device, network device, communication method, and communication system

[0001] The present disclosure relates to a terminal device, a network device, a communication method, and a communication system.

[0002] In the fifth-generation mobile communication system, known as 5G, communications are controlled in spatial units based on the communication coverage area of ​​a single base station, called a cell. In the sixth-generation mobile communication system, known as 6G, for which standardization is expected to begin in the future, operation in high-frequency bands such as terahertz waves will be possible in addition to the millimeter waves currently used. Because communications in such high-frequency bands have shorter propagation distances than lower-frequency bands, the communication area will be smaller than that envisioned for 5G and previous generations of mobile communication systems.

[0003] To date, 5G has assumed the use of extended antennas called transmission and reception points (TRPs) in addition to base stations (eNodeBs, gNodeBs, etc.) to supplement communication coverage. Furthermore, the use of communication nodes such as integrated access and backhaul (IAB) nodes (i.e., base station relays) and non-terrestrial networks (NTNs) including satellite communications has also been assumed.

[0004] In the next generation, 6G, the diversification of communication nodes is expected to progress further in order to support higher frequency bands and reduce CAPEX (Capital Expenditure) / OPEX (Operating Expense). For example, smart repeaters known as RIS (Reconfigurable Intelligent Surface) and terminal-to-terminal relays are expected to be used.

[0005] These communication nodes expected to be used in the future include a variety of communication nodes, such as fully controllable communication nodes such as base stations and IAB nodes, uncontrollable communication nodes such as RF (Radio frequency) repeaters, and communication nodes where only some of the control items can be controlled.

[0006] When communication coverage is narrowed by operating in high frequency bands, the number of communication nodes required to expand the communication area becomes large, making conventional cell design extremely difficult. The diversification of communication nodes mentioned above also makes cell design more difficult.

[0007] In Patent Document 1 listed below, a plurality of communication nodes are clustered, and a terminal device connects to the clustered communication nodes to transmit and receive data. In particular, from the perspective of the clustering method, the clustering subject, and the clustering group, the clustering is adaptively controlled depending on the state of the terminal device, the type of data, the control processing content, etc. However, although Patent Document 1 describes a method for data communication after the terminal device has made an initial connection, it does not describe a method for making the initial connection.

[0008] International Publication No. 2023-112702

[0009] In order to solve the above-mentioned problems, the present disclosure provides a terminal device, a network device, a communication method, and a communication system that enable efficient initial connection.

[0010] The terminal device of the present disclosure is a terminal device that communicates with a network device that includes one or more communication points, and includes a receiving unit that receives a first signal that includes information necessary to receive first notification information transmitted from at least one first communication point among the one or more communication points, receives the first notification information that includes information regarding a second signal that is a known signal that is transmitted from at least one second communication point among the one or more communication points based on the information necessary to receive the first notification information contained in the first signal, and receives the second signal that is transmitted from at least one third communication point among the one or more communication points based on the information regarding the second signal contained in the first notification information, and a control unit that performs initial access control for connecting to the network device via at least one fourth communication point among the one or more communication points based on the communication quality of the second signal.

[0011] 1 is a diagram showing an example of a communication system of the present disclosure; FIG. 2 is a diagram showing initial access control as a comparative example of the present disclosure; FIG. 3 is a block diagram showing an example of a network device according to the present embodiment; FIG. 4 is a block diagram showing an example of a terminal device that is a communication device according to the present embodiment; FIG. 5 is a sequence diagram of a first method related to initial access; FIG. 5A is a diagram showing the sequence of FIG. 5A from a perspective based on a communication point; FIG. 6A is a sequence diagram of a second method related to initial access; FIG. 6A is a diagram showing the sequence of FIG. 6A from a perspective based on a communication point; FIG. 7A is a diagram showing the sequence of FIG. 7A from a perspective based on a communication point; FIG. 8A is a sequence diagram of a fourth method related to initial access; FIG. 8A is a diagram showing the sequence of FIG. 8A from a perspective based on a communication point.

[0012] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The following description will focus on the main components of the present disclosure, but components and functions that are not shown or described may exist. The following description does not exclude components and functions that are not shown or described.

[0013] <Explanation of Terms Related to the Present Disclosure> The terms used in the description of the present embodiment will be described. [Antenna Port] In the present disclosure, the term "antenna port" is used to recognize whether propagation path characteristics are the same or not. For example, at the same antenna port, it can be recognized that the propagation path characteristics at a certain symbol are the same as the propagation path characteristics at another symbol (or can be inferred from the propagation path characteristics at another symbol). Furthermore, different antenna ports are recognized as having different propagation path characteristics unless they are in a quasi-co-location (QCL) as described below.

[0014] Furthermore, an antenna port can associate a predetermined reference signal with a predetermined channel. The associated predetermined reference signal and the predetermined channel can be considered to have the same propagation path characteristics. Therefore, the receiving side can estimate the propagation path characteristics using the predetermined reference signal and perform reception processing on the predetermined channel associated with the predetermined reference signal based on the estimated propagation path characteristics.

[0015] Quasi-colocation (QCL) Two antenna ports can be described as quasi-colocated (QCL) if they satisfy a certain condition: the global characteristics of the propagation channel carrying symbols at one antenna port can be inferred from the propagation channel carrying symbols at another antenna port. The global characteristics include at least one of delay spread, Doppler spread, Doppler shift, mean gain, and mean delay. In other words, if antenna port A and antenna port B are QCLs, the global characteristics of the propagation channel carrying symbols at antenna port A can be inferred from the propagation channel carrying symbols at antenna port B.

[0016] The QCL between antenna ports is specified by the following TCI (Transmission Configuration Indicator) state. The TCI state is defined by the following types (1) to (4): (1) QCL-TypeA: {Doppler shift, Doppler spread, mean delay, delay spread} (2) QCL-TypeB: {Doppler shift, Doppler spread} (3) QCL-TypeC: {Doppler spread, mean delay} (4) QCL-TypeD: {Spatial Rx (Receiver, Reception) parameters} The TCI state includes parameters that set the following QCL relationships. QCL relationship between the downlink reference signal (DMRS: Demodulation Reference Signal) and the DMRS port (antenna port) of the PDSCH QCL relationship between the downlink reference signal (DMRS) and the DMRS port (antenna port) of the PDCCH QCL relationship between the downlink reference signal (DMRS) and the CSI-RS port (antenna port) of the NZP (Non-Zero-Power) CSI-RS (Channel State Information Reference Signal) resource

[0017] A terminal device (hereinafter also referred to as a terminal) is specified the TCI state (a state indicating the QCL relationship between multiple antenna ports, i.e., information about multiple antenna ports that can be considered to be in quasi-coincident positions) by Downlink Control Information (DCI), Medium Access Control Element (MAC CE), or Radio Resource Control (RRC) signaling (RRC message). Specifically, the terminal receives information about the activation / deactivation of the TCI state of a terminal-specific PDSCH by MAC CE (L2 signaling). The terminal receives a TCI state indication for a terminal-specific PDCCH by MAC CE. The terminal receives a TCI state indication for a PDSCH by DCI (L1 signaling). Reception by MAC CE and reception by DCI are examples, and MAC CE may be replaced with RRC or DCI, and DCI may be replaced with MAC CE or RRC. In addition, DCI and MAC CE are capable of high-speed operation because they exist lower in the protocol stack than RRC (higher layer).

[0018] A downlink transmit beam is defined by the index and Quasi-Co-Location (QCL) of a given signal. For example, if given signals with the same index are in a QCL relationship, they may be treated as the same downlink transmit beam. If given signals with the same index are not in a QCL relationship, they may be treated as different downlink transmit beams. Changing (switching) the beam of a certain signal / channel is equivalent to changing the TCI state (QCL) of that signal / channel.

[0019] An example of the predetermined signal is a synchronization signal (SS) / physical broadcast channel (PBCH) block (SSB). For example, multiple SS / PBCH blocks having the same information but with different indexes can be transmitted. SS / PBCH blocks with different indexes may be transmitted by different transmission beams. The relationship between the beams of other reference signals and physical channels is determined by the TCI state between the SS / PBCH block with a predetermined index and the DMRS of other reference signals or physical channels. Note that the predetermined signal is not limited to an SSB in 5G. It may also be a combination of one or more synchronization signals or other signals (the above-mentioned reference signals) and channels (physical channels) in 6G.

[0020] Another example of a predetermined signal is an NZP CSI-RS. Multiple NZP CSI-RS resources are configured. Different transmission beams may be transmitted at CSI-RS ports (antenna ports) of different CSI-RS resources. The relationship between the beams of other reference signals and physical channels is determined by the TCI state between the CSI-RS port of the CSI-RS resource and the DMRS of other reference signals or physical channels.

[0021] [Overview of Cell-Free Communication System of the Present Disclosure] In conventional communication systems, initial access control and mobility control are performed on a cell-by-cell basis. That is, a conventional cell can be defined as a unit of a transmission / reception point (communication node) that performs initial access control and mobility control.

[0022] However, in 6G systems, as described above, in addition to the complex communication topology, a higher density of communication points (communication antennas) is required (specifically, an increase in the number of communication points per unit area) through the use of high frequencies such as millimeter waves and terahertz waves. Therefore, the communication method must be designed with such communication points in mind. In other words, in 6G systems, the conventional definition of a cell may be changed, added, replaced, or the like. In this disclosure, such a system in which the definition of a cell is changed from the conventional one is also referred to as a cell-free communication system. However, the application of this disclosure does not necessarily have to be limited to cell-free communication systems, and this disclosure can also be applied to systems in which the conventional definition of a cell remains the same. In other words, one system to which this disclosure can be applied is a cell-free communication system.

[0023] In addition to cell-free communication systems, the present disclosure can also be applied to systems known as distributed MIMO systems, distributed antenna systems, and multi-TRP (Transmission and reception point) systems.

[0024] FIG. 1 illustrates an example of a communication system according to the present disclosure. Base station 1 (first base station) and base station 2 (second base station) are each connected to and control one or more communication points via wired or wireless connections. In this example, base station 1 is connected to and controls communication points 11 to 14 via wired or wireless connections. Base station 2 is connected to and controls communication points 21 to 24 via wired or wireless connections. Terminal device 31 (hereinafter also referred to as terminal 31) is connected wirelessly to one or more of communication points 11 to 14 and 21 to 24. Base station 1 and base station 2 may communicate with each other wirelessly or via wired connections. The connection between base station 1 and base station 2 may be direct, via another base station or relay device, or via another system (e.g., a core network of a 4G / 5G / 6G / NG (Next Generation) system).

[0025] [Communication Point] The definition of a communication point in this disclosure will be described. A communication point is also called a communication node or a node. Communication points 11 to 14 and 21 to 24 in Figure 1 correspond to the communication points defined below.

[0026] A communication point in the present disclosure is a cell, a gNB (base station), a TRP (Transmission and reception point), an antenna port, a set of antenna ports, an IAB node, a relay UE, or a beam.

[0027] A communication point may also be defined as a node that transmits a synchronization signal and / or broadcast control information. For example, a communication point may be a unit of a node that a terminal can recognize as transmitting a first signal and / or first broadcast information described below. For example, a communication point may be a unit of a node that a terminal can recognize as transmitting a second signal and / or second broadcast information described below. A terminal may recognize that a communication point that transmits the first signal and / or the first broadcast information and a communication point that transmits the second signal and / or the second broadcast information are different communication points.

[0028] Communication points may also be defined based on Quasi-co-location (QCL). For example, a set of antenna ports with the same QCL is recognized as a cluster.

[0029] Furthermore, the communication points do not need to be fixed, but may be mobile nodes.

[0030] Furthermore, the communication points do not have to be terrestrial nodes, but may be non-terrestrial nodes (satellites, drones, UAVs).

[0031] Furthermore, a communication point may be a set (cluster) of one or more communication nodes that are clustered by clustering. The definitions of clustering and cluster are as follows.

[0032] [Clustering] Clustering refers to setting one or more communication nodes (communication points) or communication node candidates that are connected simultaneously.

[0033] Information about QCL (Quasi-co-location) can be set for each of the clustered communication nodes. For example, when a communication node is an antenna port and multiple communication nodes (i.e., antenna ports) are set in one cluster, communication nodes with the same TRP in the cluster indicate the same QCL, and communication nodes with different TRPs indicate different QCL. In other words, communication nodes with the same QCL and different QCLs can be set together in one cluster.

[0034] [Cluster] A cluster is a set (list) of clustered communication nodes (communication points). For example, in clustering method 1 described below, a cluster is a set of communication nodes set by RRC signaling. For example, in clustering methods 2 and 3 described below, a cluster is a set of communication nodes set by RRC signaling, and is a candidate for a communication node that actually communicates.

[0035] Note that the communication nodes with which the terminal actually communicates can be defined as a sub-cluster.

[0036] Each cluster can be assigned a unique identifier (cluster ID).

[0037] Multiple clusters can be set. The multiple clusters can also be called a cluster set (cluster list). A node included in one cluster can also be included in another cluster. In other words, one node can be included in multiple clusters.

[0038] The cluster with which a terminal communicates can be switched dynamically or semi-statically.

[0039] [Other names or definitions of cluster] A cluster may be defined by the following other names: Node set Zone (area): A spatial region that may be defined according to a physical location or a virtual location. A predetermined zone may include multiple communication nodes. Cell set (cell): Particularly when the communication nodes are cells, a cluster in the present disclosure is referred to as a cell set. A cell set may also be simply referred to as a cell. Antenna port set: Particularly when the communication nodes are antenna ports, a cluster in the present disclosure is referred to as an antenna port set. Beam set: Particularly when the communication nodes are beams, a cluster in the present disclosure is referred to as a beam set.

[0040] [Base Station] The definition of a base station in the present disclosure will be described. Base stations 1 and 2 in FIG. 1 correspond to base stations or nodes defined below. A base station in the present disclosure (the function of a base station in the present disclosure) can be defined as a communication node that can control a communication point connected to that base station. For example, a base station in the present disclosure can be a node closer to the core network than a communication point.

[0041] The base station of the present disclosure may be realized in various forms from the viewpoint of an apparatus. For example, the base station of the present disclosure may be included in one or more communication points and control the other communication points. Also, for example, the base station of the present disclosure may be an independent communication node between a core network and a communication point, or may be included in the core network.

[0042] [Initial Access Control in a Cell-Free Communication System] The following first describes initial access control (initial connection procedure) as a comparative example of the present disclosure. FIG. 2 is a diagram illustrating initial access control as a comparative example of the present disclosure. A terminal receives an SSB (SS (Synchronization Signal) / PBCH (Physical Broadcast Channel) block) and a PBCH transmitted from a base station (S11), performs downlink synchronization with the base station (S12), and further receives an SIB1 (SIB1: System Information Block 1) broadcast from the base station (S13). The SSB is a block (signal, information, channel) including a PBCH, a PSS (Primary Synchronization Signal), and an SSS (Secondary Synchronization Signal). The PSS and SSS are synchronization signals used by the terminal for cell search and RSRP (Reference Signal Received Power) measurement. The PBCH contains information about the base station called MIB (Master Information Block), and the MIB contains parameters for obtaining the above-mentioned SIB1, which is more detailed information for a terminal to connect to a base station (e.g., information for performing initial access).

[0043] The terminal starts the initial access process based on the control information obtained from the base station, which is more specifically as follows.

[0044] The terminal transmits msg1 (PRACH: Physical random access channel) to the base station (S15). The PRACH includes a RACH preamble. msg1 corresponds to an initial access request.

[0045] The base station transmits msg2 (RAR: Random access response) to the terminal based on msg1 (S16). The RAR is transmitted over the PDSCH.

[0046] The terminal transmits msg3 (Physical Uplink Shared Channel (PUSCH)) based on msg2. Msg3 may include control information for the terminal to connect to the base station.

[0047] The base station can transmit msg4 (Contention resolution) based on msg3. msg4 can be transmitted via a PDSCH (Physical Downlink Shared Channel). mg4 can be transmitted for contention resolution during initial access and can be omitted. If mg4 is omitted, steps S15 to S17 are performed to complete connection between the terminal and the base station, and uplink scheduling in the terminal is also determined.

[0048] Next, a problem that occurs when the initial access control of the comparative example shown in FIG. 2 is used in the cell-free communication system of the present disclosure will be described.

[0049] In the initial access control of the comparative example, it is assumed that initial access is performed between one base station and one terminal. In addition, even if the base station has multiple antennas (antenna ports), it is assumed that the antennas are set to the same QCL (i.e., the predetermined radio characteristics are the same).

[0050] In contrast, in the cell-free communication system of the present disclosure, at least some of the multiple antennas may be configured with different QCLs. That is, it is possible that multiple antennas with different radio characteristics exist. In such an environment, it is difficult to use the initial access control of the comparative example, which is based on the premise that a base station is equipped with multiple antennas with the same QCL.

[0051] Furthermore, for example, in a cell-free communication system, it is expected that base stations will have more antennas (communication points, antenna ports) (higher density per unit area) than in conventional communication systems. Therefore, if initial access control is performed for each antenna (or antenna group) configured with the same QCL, the amount of control and control information required for initial access (frequency per unit area) will be large. As a result, there is a concern that the overhead of the entire system (in terms of processing volume, load, radio resources, etc.) will increase.

[0052] Furthermore, for example, in a cell-free communication system, if initial access control is performed using only some antennas (communication points, antenna ports) of a base station, the installation (layout, cell design) of the base station antennas becomes very complicated, and it takes a long time for a terminal to be able to communicate with the optimal antenna (communication point, antenna port).

[0053] For the above reasons, it is difficult to use the initial access control of the comparative example in a cell-free communication system, and an initial access control that can also be applied to a cell-free communication system is required.

[0054] The following describes initial access control (initial access procedure or initial access method) in the cell-free communication system of the present disclosure.

[0055] [Initial Access Control (Initial Connection Procedure) of the Present Disclosure] A terminal receives at least a first signal, first broadcast information, and a second signal from a base station and / or a communication point. The terminal performs initial access based on the signals and information. Therefore, the following first describes the definitions of the first signal, the first broadcast information, and the second signal.

[0056] [First Signal] The first signal is a predetermined signal that the terminal detects before receiving the first broadcast information. The first signal is used by the terminal to perform at least one of time synchronization, frequency synchronization, cell ID recognition, recognition of resources in which the first broadcast information is stored, and reception processing of the first broadcast information. For example, the first signal is a synchronization signal with the same or similar function, purpose, and configuration as PSS (Primary synchronization signals) / SSS (Secondary synchronization signals) in 5G. The first signal includes information necessary to receive the first broadcast information.

[0057] The terminal may recognize that the first signal is transmitted from a predetermined base station and / or communication point. If the first signal is transmitted from a communication point, the first signal may be transmitted from each of one or more predetermined communication points, or may be transmitted from each of any one or more communication points (including all communication points connected to the base station).

[0058] [First broadcast information] The first broadcast information includes information for the terminal to perform at least one of executing initial access and receiving a second signal. Information for executing initial access is called information related to initial access, and information for receiving the second signal is called information related to the second signal. Information for executing initial access is also called information necessary for performing initial access control (initial connection procedure).

[0059] The first broadcast information does not have to be information transmitted in one transmission unit, resource, or channel, and can be transmitted divided into multiple transmission units, resources, or channels. For example, the first broadcast information is information (channel) having the same or similar function, purpose, and configuration as a PBCH (Physical Broadcast Channel), MIB (Master Information block), or SIB (System Information block) in 5G.

[0060] The transmission cycle (transmission frequency) of the first signal and / or the first broadcast information can be changed depending on the presence or absence of a terminal within the cell of the communication point (i.e., within the coverage (communication area) of the communication point transmitting the first signal and / or the first broadcast information) or the number of terminals. For example, when there is no terminal within the cell (in other words, when the communication point does not recognize the presence of a terminal within the cell), the first signal and / or the first broadcast information is transmitted at a long cycle (first cycle), and when there is a terminal within the cell (in other words, when the communication point recognizes the presence of a terminal within the cell), the first signal and / or the first broadcast information is transmitted at a short cycle (second cycle). For example, the communication point can recognize the presence or absence of a terminal within its cell based on the reception of a predetermined signal or channel (such as a random access channel or a wake-up signal) from the terminal, the reception of control information from a core network or a surrounding communication point, etc.

[0061] Information about the second signal and information about the initial access will be described below.

[0062] [Information Regarding Second Signals] The information regarding second signals is information necessary for a terminal to receive the second signal. The information regarding second signals may be a list of one or more second signals that the terminal may receive (should receive). In this case, the second signals included in the list may be all of the second signals transmitted (managed or controlled) by the communication node that transmits the first signal and / or the first broadcast information, or a portion determined depending on the location of the terminal, etc.

[0063] The information about the second signal includes, for example, the following information: - The number of second signals that the terminal may receive (should receive); - Information about the time / frequency resources on which the second signals are transmitted; - Information about the code (code index) if the second signal can be code division multiplexed; - Information about the scrambling code if a scrambling code is superimposed on the second signal (generated based on the scrambling code).

[0064] The information about the second signal may be a list of communication points that can be combined (clustered).

[0065] [Information related to initial access] Information related to initial access (information necessary for performing initial access control) is information necessary for a terminal to perform initial access to at least one of a predetermined base station, a predetermined communication point connected to the predetermined base station, a core network controlling the predetermined base station, and a communication node associated with (determined based on) the predetermined base station, communication point, or core network.

[0066] The information regarding the initial access may be transmitted from each communication point as second broadcast information in addition to the second signal.

[0067] The information related to initial access includes, for example, the following information: - Information required for transmitting (selecting, determining) the random access channel (msg1) transmitted by the terminal. Specifically, there is information indicating the selectable range of random access preambles transmitted on the random access channel. There is also information related to time and frequency resources for transmitting the random access channel. - Information required for receiving (recognizing, detecting) the random access response (msg2). - Information related to the PUSCH (msg3). Specifically, this is information related to information that needs to be transmitted on the PUSCH (msg3). Details will be described later, but the information includes, for example, information related to the selected communication point and information related to the communication quality for one or more communication points.

[0068] The terminal can recognize that the first broadcast information (information about the second signal, information about initial access) is transmitted from a predetermined base station and / or communication point.

[0069] When it is recognized that the first notification information is transmitted from a communication point, the first notification information may be transmitted from each of one or more specified communication points, or may be transmitted from each of any one or more communication points (including all communication points connected to the base station).

[0070] The terminal may recognize that the first broadcast information is transmitted from the same predetermined base station and / or communication point as the first signal. That is, the terminal may recognize that the QCL of the first broadcast information is the same as the QCL of the first signal. That is, the communication point transmitting the first broadcast information and the communication point transmitting the first signal have the same QCL. For example, the terminal may demodulate and / or decode the first broadcast information using at least a portion of the propagation path characteristics of the first signal.

[0071] The terminal can recognize that the first broadcast information is transmitted from a predetermined base station and / or communication point other than the communication point from which the first signal is transmitted.

[0072] [Second Signal] The second signal is a reference signal transmitted from a communication point. In other words, the second signal is a known reference signal that a terminal can recognize as being transmitted from a predetermined communication point. For example, the QCL of the second signal can be recognized as being different from the QCL of the first broadcast information and / or the QCL of the first signal.

[0073] The second signal is, for example, a signal having the same or similar function, purpose, and configuration as CSI-RS (Channel state information-reference signals) and SSS (Secondary synchronization signals) in 5G.

[0074] The second signal is used to measure (detect, recognize, or actually measure) the communication quality for the communication point. For example, the second signal is a known signal used in initial access control to select a communication point, report communication quality, etc.

[0075] For example, communication quality includes RSRP, RSRQ, RSSI, SINR, SNR, SIR, CSI, CQI, PMI, and RI for a given communication point. The following explains the definitions of each of these indicators. RSRP (Reference Signal Received Power): Indicates the power level of the reference signal received from a specific communication point (cell). This value indicates how strongly the receiver receives the reference signal and is used to evaluate communication quality. RSRQ (Reference Signal Received Quality): An indicator of the noise level relative to RSRP. In other words, it represents the ratio of signal strength to noise level and is used to evaluate signal quality. RSSI (Received Signal Strength Indicator): A value that indicates the strength of the received signal and is usually used to measure signal strength in wireless communications. However, unlike other indicators, it does not include information about the quality of a specific signal. SINR (Signal-to-Interference-plus-Noise Ratio): Indicates the ratio between the signal and surrounding interference and noise. SNR (Signal-to-Noise Ratio): Indicates the ratio between the signal and surrounding noise.・SIR (Signal-to-Interference Ratio): Indicates the ratio of signal to interference and evaluates communication quality. ・CSI (Channel State Information): Information indicating the state of the wireless propagation path, used to understand the characteristics and quality of the communication path. ・CQI (Channel Quality Indicator): An index indicating the quality of the wireless propagation path, indicating the usable quality of the communication path. CQI corresponds to a specified modulation method and number of MIMO layers, and corresponds to the frequency utilization efficiency according to the specified modulation method and number of MIMO layers. ・PMI (Precoding Matrix Indicator): Indicates a matrix for effectively transmitting signals between transmitting antennas in MIMO (Multiple-Input Multiple-Output) communication.・RI (Rank Indicator): In MIMO communication, it indicates the number of MIMO layers (number of ranks, number of transmit antennas, available spatial multiplexing).

[0076] The second signal can be used to measure (detect, recognize, measure, report) relative characteristics (quality, features) between communication points. The communication quality of each communication point may be measured using the second signal, and the relative characteristics between the communication points (information on the difference in communication quality between the communication points) may be reported in the initial access control.

[0077] The relative characteristics (quality, features) between communication points include differences (differences, changes) in propagation characteristics between communication points. For example, differences in propagation characteristics between communication points include the following: Differences in received power (RSRP, path loss, SNR) between communication points Differences in delay time (arrival time, delay spread) between communication points Differences in Doppler frequency between communication points Differences in phase between communication points Differences in the above-mentioned communication quality between communication points.

[0078] In the difference in propagation characteristics between communication points, the reference communication point may be set or specified in advance, or may be determined according to a predetermined criterion. For example, the reference communication point may be the following: - A communication point with the smallest or largest value associated with the communication point (e.g., a communication point ID (index)). - A communication point with the largest or smallest received power. - A communication point with the earliest or latest arrival time. - A communication point with the best or worst communication quality with respect to the communication point. - The reference communication point may be determined based on a second signal transmitted by the communication point (transmission resource of the second signal, ID indicating the second signal). - The reference communication point may be set in the first broadcast information or the second broadcast information.

[0079] [Supporting Both the Initial Access Control Method of the Present Disclosure and the Initial Access Control Method of the Comparative Example] A base station and / or a terminal can support both the initial access control method of the present disclosure and the initial access control method of the comparative example. The initial access control of the comparative example corresponds to an initial access control method different from the initial access control method of the present disclosure.

[0080] If a base station supports both methods, the base station can select which method to use and can notify the terminal of instruction information instructing which method to use (whether the method can be used). When the base station notifies such information, the information can be transmitted by being included in the first broadcast information. In this case, the terminal selects and executes either the initial access control of the present disclosure or the initial access control of the comparative example based on the instruction information.

[0081] The terminal at least supports the initial access control method of the comparative example. That is, the initial access control method of the comparative example may be defined as a mandatory function. If the terminal supports the initial access control method of the present disclosure, it can notify the base station of UE (User Equipment) capability information indicating that it supports the initial access control method of the present disclosure. The UE capability information can be transmitted by including it in msg1 or msg3.

[0082] If a base station supports and uses both (i.e., if both methods are used simultaneously), the initial access control method of the present disclosure and the initial access control method of the comparative example can be switched between depending on whether the terminal supports the initial access control method of the present disclosure.

[0083] In this case, the initial access control method of the present disclosure and the initial access control method of the comparative example may differ in some or all of the following: The first signal, the first broadcast information, the second signal, and / or the second broadcast information The msg1 that can be selected by the terminal and / or the time-frequency resource that can transmit the msg1

[0084] When a terminal supports the initial access control method of the present disclosure and performs initial access using the initial access control method of the present disclosure, the terminal may perform initial access using the initial access control method of the comparative example when a predetermined condition is met. That is, when a predetermined switching condition is met during execution of the initial access control of the present disclosure, the terminal may switch to an initial access control method other than the initial access control of the present disclosure. For example, if the terminal tries the initial access control method of the present disclosure but cannot connect to a base station, the terminal falls back to the initial access control method of the comparative example.

[0085] For example, the predetermined condition (predetermined switching condition) is when the number of attempts (number of failures, number of errors) of initial access control (transmission of msg1) exceeds a predetermined number. The predetermined number may be specified in advance, or may be notified by being included in the first broadcast information or the second broadcast information.

[0086] <Configuration of Network Device> Fig. 3 is a block diagram showing an example of a network device 100 according to this embodiment. The network device 100 is a network-side device, for example, a communication device such as one or more base stations, communication nodes, or a core network. The network device 100 may be one of these communication devices, or may be a device including multiple of these communication devices. For example, the network device 100 may include base station 1, communication points 11 to 14, base station 2, and communication points 21 to 24 in Fig. 1, or may further include a core network in addition to these. The communication device that is the communication target of the network device 100 is terminal device 31.

[0087] The network device 100 includes one or more communication points 110, a wireless communication unit 120 (transceiver), a network communication unit 130, a storage unit 140, and a control unit 150. The wireless communication unit 120, the network communication unit 130, and the control unit 150 are each implemented by a processor or integrated circuit, such as a processor (hardware processor) such as a central processing unit (CPU) or a micro-processing unit (MPU), an application specific integrated circuit (ASIC), or a field-programmable gate array (FPGA). The storage unit 140 is implemented by any recording medium, such as a memory, a hard disk drive, an optical disk, or a magnetic recording device. The memory may be a volatile memory or a non-volatile memory.

[0088] The multiple communication points 110 correspond to, for example, communication points 11 to 14, or communication points 21 to 24, or communication points 11 to 14, 21 to 24. As an example, the communication points 110 are antennas (antenna ports) or clustered antennas (antenna ports). As described above, the communication points 110 can have various configurations. As an example, the multiple communication points 110 may be in different QCLs, i.e., may not be considered as quasi-co-located.

[0089] The wireless communication unit 120 transmits and receives signals via each communication point 110. The signals include data or information. The wireless communication unit 120 includes a signal transmission unit 121 that transmits signals and a signal reception unit 122 that receives signals. For example, the signal transmission unit 121 transmits a downlink signal to the terminal device 31, and the signal reception unit 122 receives an uplink signal from the terminal device 31. The wireless communication unit 120 may form multiple beams using multiple communication points 110 to communicate with the terminal device 31.

[0090] The network communication unit 130 transmits and receives information to and from other communication nodes. For example, the network communication unit 130 transmits information to and receives information from other communication nodes. The other communication nodes include, for example, at least one of the terminal device 31, a base station, a core network, and a node on the Internet.

[0091] The storage unit 140 temporarily or permanently stores programs and data for the operation of the network device 100. The storage unit 140 also temporarily or permanently stores information about the terminal device 31 and other communication nodes that are the target of communication.

[0092] The control unit 150 includes a receiving unit 152 and a transmitting unit 151. The receiving unit 152 of the control unit 150 receives data or information from the terminal device 31 via the wireless communication unit 120. The transmitting unit 151 of the control unit 150 transmits data or information addressed to the terminal device 31 via the wireless communication unit 120.

[0093] The control unit 150 controls the overall operation of the network device 100 and provides various functions of the network device 100. For example, the control unit 150 corresponds to a first control unit that controls the entire network device 100. If the network device 100 includes multiple base stations (e.g., base station 1 and base station 2), the control unit 150 includes the functions of the control units of these multiple base stations.

[0094] The control unit 150 acquires information about the terminal device 31 and one or more other communication nodes. Examples of other communication nodes include other base stations. Examples of information acquired by the control unit 150 include, but are not limited to, information about the communication quality of the propagation path between the terminal device 31 and each communication point 11, and information about the specifications and capabilities of the terminal device 31. The control unit 150 acquires the communication quality information directly from the terminal device 31 or via one or more other communication nodes (e.g., a base station, a core network).

[0095] The control unit 150 controls the generation and transmission of the first signal, the first broadcast information, the second signal, and the second broadcast information. The control unit 150 also receives an initial access request from the terminal 31 to connect to the network device 100, and performs initial access control for the terminal 31. The detailed operation of the control unit 150 will be described later in sequence examples of the first to fourth methods.

[0096] <Configuration of Terminal Device> Fig. 4 is a block diagram showing an example of a terminal device 31, which is a communication device according to this embodiment. The terminal device 31 includes one or more antennas 310, a wireless communication unit 320 (transceiver), a storage unit 340, and a control unit 350. The wireless communication unit 320 and the control unit 350 are each implemented by a processor or integrated circuit, such as a central processing unit (CPU), a micro-processing unit (MPU), an application specific integrated circuit (ASIC), or a field-programmable gate array (FPGA). The storage unit 340 is implemented by any recording medium, such as a memory, a hard disk drive, an optical disk, or a magnetic recording device. The memory may be a volatile memory or a non-volatile memory.

[0097] The antenna 310 radiates the signal output by the wireless communication unit 320 into space as radio waves. The antenna 310 converts the radio waves in space into a signal and outputs the signal to the wireless communication unit 320. The antenna 310 may be an array antenna having a plurality of antenna elements.

[0098] The wireless communication unit 320 transmits and receives signals. The signals include data or information. The wireless communication unit 320 includes a signal transmission unit 321 that transmits signals and a signal reception unit 322 that receives signals. For example, the signal reception unit 322 receives downlink signals from one or more communication points 110. The signal transmission unit 321 transmits uplink signals to one or more communication points 110.

[0099] The storage unit 340 temporarily or permanently stores programs and various data for the operation of the terminal device 31. The storage unit 340 may also store information related to the network device 100.

[0100] The control unit 350 includes a transmitting unit 351 and a receiving unit 352. The receiving unit 352 receives data or information from the network device 100 or one or more communication points 110 via the wireless communication unit 320. The transmitting unit 351 transmits data or information addressed to the network device 100 or one or more communication points 110 via the wireless communication unit 120.

[0101] The control unit 350 of the terminal device 31 controls the overall operation of the terminal device 31 and provides various functions of the terminal device 31. The control unit 350 corresponds to a second control unit that controls the entire terminal device 31, for example.

[0102] The control unit 350 also controls reception of a first signal, first broadcast information, second signal, and second broadcast signal from the network device 100 or one or more communication points 110. The control unit 350 also measures the communication quality with the source communication point 110 based on the second signal. The control unit 350 also performs initial access control, which involves transmitting an initial access request for connecting to the network device 100, based on the communication quality of each received second signal. Detailed operations of the control unit 350 will be described in sequence examples of the first to fourth methods, which will be described later.

[0103] [First Method for Initial Access] Fig. 5A is an example of a sequence diagram of the first method for initial access. Fig. 5B is a sequence in which the sequence of Fig. 5A based on the base station is rewritten as a sequence based on the communication point. The sequences of Fig. 5A and Fig. 5B are controlled by the control unit 150 of base station 1 and base station 2, respectively, and the control unit 350 of terminal 31.

[0104] It is assumed that communication points 11 to 14 of base station 1 each have a different QCL. In other words, communication points 11 to 14 are not considered to be in the same location. It is assumed that communication points 21 to 24 of base station 2 each have a different QCL. In other words, communication points 21 to 24 are not considered to be in the same location. However, for QCL-TypeC, the same QCL may be used. It is assumed that what has been described in this paragraph also applies to the second to fourth methods described below.

[0105] In the following explanation, the explanation of the parts that overlap with the second to fourth methods described later may be omitted. In other words, the contents explained in the second to fourth methods can be applied to the first method.

[0106] The base station 1 transmits a first signal and first broadcast information, and the terminal 31 receives the first signal and first broadcast information (S101). The terminal 31 receives the first signal and receives the first broadcast information based on the information for receiving the first broadcast information contained in the first signal. The base station 1 transmits the first signal through at least one of the communication points 11 to 14 and transmits the first broadcast information through at least one of the communication points 11 to 14. As an example, the communication point transmitting the first signal corresponds to the first communication point, and the communication point transmitting the first broadcast information corresponds to the second communication point. The first communication point and the second communication point may be the same, partially the same, or entirely different. The terminal 31 does not need to recognize from which of the communication points 11 to 14 of the base station 1 it received the first signal and first broadcast information. The terminal 31 only needs to recognize that the source of the first signal and the first broadcast information is the base station 1. In addition, the base station 2 may transmit the same first signal and the same first notification information, or the base station 2 may transmit a first signal and first notification information that are unique to the base station 2.

[0107] Base station 1 transmits second signals from each of communication points 11 to 14, and terminal 31 receives these second signals (S102, S104, S106, S108). Similarly, base station 2 transmits second signals from each of communication points 21 to 24, and terminal 31 receives these second signals (S103, S105, S107, S109). The first broadcast information received from base station 1 in step S101 includes information about the second signals, and terminal 31 receives the second signals based on this information about the second signals. As an example, the communication point transmitting the second signal corresponds to a third communication point. The third communication point may be the same as the first and second communication points described above, or may be partially the same or completely different. The first broadcast information received from base station 1 in step S101 may include information about the second signal transmitted from base station 2.

[0108] Note that the second signals transmitted from the multiple communication points 11 to 14 may be transmitted using different time / frequency resources, or may be code division multiplexed using the same time / frequency resources. At least from the perspective of the terminal 31, it is preferable that each second signal can be received as an individual signal. Similarly, the second signals transmitted from the multiple communication points 21 to 24 may be transmitted using different time / frequency resources, or may be code division multiplexed using the same time / frequency resources. At least from the perspective of the terminal 31, it is preferable that each second signal can be received as an individual signal.

[0109] The terminal 31 performs initial access based on random access control, based on the first signal, the first broadcast information, and / or the second signal (S110). The terminal 31 performs initial access based on at least the communication quality of the second signal. In the example shown in the figure, the terminal 31 recognizes that it will perform initial access to the base station 1 based on the communication quality of the second signal, and performs initial access to the base station 1. More specifically, the terminal 31 transmits msg1 (random access channel) to the base station 1 (S110A). The base station 1 transmits msg2 (random access response) to the terminal 31 based on msg1 (S110B). The terminal 31 transmits msg3 (PUSCH) based on msg2 (S110C). The base station 1 transmits msg4 as a random access response (S110D). Transmission of msg4 may be omitted. Transmission and reception between the base station 1 and the terminal 31 during random access (S110A to S110D) is performed via all or some of the communication points 11 to 14. The terminal 31 does not need to be aware of which communication point it is transmitting to or receiving from, at least while performing initial access control. The base station 1 performs initial access control with the terminal 31 via any one or more communication points (fourth communication point) among the communication points 11 to 14. The fourth communication point may be the same as or different from the first, second, or third communication point described above, or may be partially the same.

[0110] The terminal 31 may recognize that it will perform initial access to a communication node associated with (based on) the first signal and / or the first broadcast information. In this case, the terminal 31 does not need to recognize whether the first signal and / or the first broadcast information is transmitted from the base station 1.

[0111] In step S110C, the terminal 31 transmits information about the communication quality for one or more communication points by including it in the PUSCH (msg3). As described above, the communication quality can be determined based on the second signal.

[0112] The information regarding communication quality transmitted in msg3 may be the communication quality for all communication points at which the second signal is received (in other words, the communication quality determined based on the second signal associated with all communication points notified in the first notification information), or it may be the communication quality for some of the communication points at which the second signal is received.

[0113] When transmitting communication quality for some of the communication points from which the second signal was received, the terminal 31 can select one or more communication points with good communication quality (e.g., an RSRP value greater than or equal to a predetermined threshold or the maximum value) and transmit the information in msg3. For example, a predetermined number of communication points with good communication quality can be selected. The value of the predetermined number can be included in the first broadcast information. Note that the predetermined number may be specified in advance. For example, the predetermined number is 1. For example, communication points with communication quality greater than or equal to a predetermined threshold can be selected. The predetermined threshold can be included in the first broadcast information. For example, if reception of msg4 is omitted, the terminal 31 may decide to communicate using the communication point selected in msg3 from now on. Alternatively, when msg4 is transmitted, the base station 1 may select a communication point to be used by the terminal 31 based on the quality information, and include information on the selected communication point in msg4.

[0114] Furthermore, the terminal 31 transmits information (relative information) relating to relative characteristics between communication points by including it in the PUSCH (msg3). As described above, the relative characteristics can be determined based on the second signal. The information relating to relative characteristics between communication points may be transmitted in addition to information relating to the communication quality for the communication points, or may be transmitted independently.

[0115] In the relative information, the reference communication point may be set or specified in advance, or may be determined according to a predetermined standard.

[0116] The relative information transmitted in msg3 may be information for all communication points at which the second signal was received, or may be information for some of the communication points at which the second signal was received, similar to the information on communication quality. When transmitting relative information and information on communication quality, information on the communication quality of all communication points corresponding to the relative information may be transmitted, or information on the communication quality of only some communication points (for example, a reference communication point or another communication point compared to the reference communication point) among all communication points corresponding to the relative information may be transmitted.

[0117] The base station may determine a communication point to be used with terminal 31 based on the communication quality of each communication point or the difference in communication quality between communication points acquired from terminal 31. In this case, the determined communication point may be notified by msg4 in step S110D. Alternatively, the notification may be made after step S110D. The base station may communicate with terminal 31 after initial access control at all communication points to which it has transmitted the second signal, and may communicate with terminal 31 using the communication quality of each communication point or the difference in communication quality between communication points.

[0118] [Effects of the First Method] By using the first method, the base station (and / or core network) can select a suitable antenna (communication point) for cell-free communication for the terminal 31 during initial access control.

[0119] In the first method, even if the base station has multiple antennas (communication points), the terminal 31 does not need to recognize which antenna (communication point) is being subjected to initial access control, at least at the time of performing initial access control, and therefore the processing load can be reduced.

[0120] Furthermore, on the network side including the base station and the core network, the communication nodes that perform the initial access control from the terminal 31 can be limited to the communication nodes that transmit the first signal and the first broadcast information, so that centralized processing can be performed for at least the initial access control. For example, communication nodes other than the communication node that performs the initial access control can have lower processing capabilities, which can reduce costs.

[0121] [Second Method for Initial Access] Fig. 6A is an example of a sequence diagram of a second method for initial access. Fig. 6B is a sequence in which the sequence of Fig. 6A based on the base station is rewritten as a sequence based on the communication point. The sequences of Fig. 6A and Fig. 6B are controlled by the control unit 150 of each of base station 1 and base station 2 and the control unit 350 of terminal 31.

[0122] In the following description, explanations of parts that overlap with other methods may be omitted. That is, the contents explained in the first, third, or fourth methods can be applied to the second method.

[0123] Steps S101 to S109 are the same as those in FIGS. 5A and 5B, and therefore the description thereof will be omitted.

[0124] In the sequence of the second method, the terminal 31 selects one communication point from the communication points 11 to 14 and 21 to 24 based on the second signal received in steps S101 to S109. Communication quality may be used as a criterion for the selection. The illustrated example shows a case where communication point 22 is selected. The terminal 31 performs random access control for the selected communication point 22 (S220). More specifically, the terminal 31 transmits msg1 (random access channel) to the communication point 22 (S220A). That is, by transmitting msg1 to the communication point 22, the base station 2 transmits information indicating that the communication point 22 has been selected to the terminal 31 via the communication point 22 based on msg1. (S220B) The terminal 31 then transmits msg3 (PUSCH) to the communication point 22 based on msg2 (S220C). At this point, unless msg4 is received, the terminal 31 may recognize this communication point 22 as a communication point with which to communicate after the initial access control. Based on msg3, the base station 2 transmits msg4 as a random access response via the communication point 22 as necessary (S220D). Transmission of msg4 may be omitted.

[0125] As described above, in step S210A, the terminal 31 performs initial access to the selected communication point (communication point 22 in this example). In other words, the terminal 31 performs initial access based on parameters associated with the selected communication point. In other words, the communication point (fourth point) used when performing initial access includes the communication point selected by the terminal 31. However,

[0126] The terminal 31 may perform initial access based on the second signal of the selected communication point. For example, the msg1 to be transmitted by the terminal 31 is determined based on the selected communication point. For example, the selection of the preamble for msg1 and the transmission resource for msg1 are determined.

[0127] Information relating to initial access that is specific to the communication point can be included in the first broadcast information.

[0128] The PUSCH (msg3) includes at least information on the communication quality of the selected communication point. When the msg1 to be transmitted is determined based on the selected communication point, information indicating the selected communication point may be included in the msg1, or information indicating the selected communication point may be notified again. The PUSCH (msg3) may further include information on the communication quality for communication points other than the selected communication point. The terminal 31 can select which communication point using a selection method described in another method (third method or fourth method).

[0129] The PUSCH (msg3) may include information (relative information) about relative characteristics including at least a selected communication point, which may be a communication point that is the basis of the relative information.

[0130] [Effects of the Second Method] By using the second method, the base station (and / or core network) can select a suitable antenna (communication point) for cell-free communication for the terminal 31 during initial access control.

[0131] In the second method, initial access control from terminal 31 is performed on a suitable antenna (communication point), so the time required for initial access control (i.e., delay time) can be reduced compared to the method of the comparative example.

[0132] In addition, in the second method, from the perspective of the network side including the base station and the core network, the communication node that performs initial access control from terminal 31 can be different for each terminal 31, so that distributed processing can be performed at least with respect to initial access control.

[0133] Furthermore, in the second method, even if there are multiple suitable communication points, the terminal 31 performs initial access control for one communication point, so from the network perspective, cooperative control among multiple communication points is not required, thereby reducing the processing load on the network side.

[0134] [Third Method for Initial Access] Fig. 7A is an example of a sequence diagram of a third method for initial access. Fig. 7B is a sequence in which the sequence of Fig. 7A based on the base station is rewritten as a sequence based on the communication point. The sequences of Fig. 7A and Fig. 7B are controlled by the control unit 150 of base station 1 and base station 2, respectively, and the control unit 350 of terminal 31.

[0135] In the following description, explanations of parts that overlap with other methods may be omitted. That is, the contents explained in the first, second, or fourth methods can be applied to the third method.

[0136] Steps S101 to S109 are the same as those in FIGS. 5A and 5B or 6A and 6B, and therefore will not be described here.

[0137] In the sequence of the third method, the terminal 31 selects one or more communication points from among the communication points 11-14 and 21-24 based on the second signal received in steps S101 to S109. For example, multiple communication points are selected. Communication quality may be used as a selection criterion. The example shown in the figure illustrates a case in which communication points 12, 21, and 24 are selected. The terminal 31 performs random access control for the selected communication point 22 (S300). More specifically, the terminal 31 transmits msg1 (random access channel) to the communication points 12, 21, and 24 (S310A, S320A). Note that the transmission of msg1 itself only needs to be done once, and the transmitted msg1 can be received by each of the communication points 12, 21, and 24. However, it is not excluded to transmit msg1 separately for each communication point.

[0138] Based on msg1, base station 1 and base station 2 transmit msg2 (random access response) to terminal 31 via communication points 12, 21, and 24 (S310B, S320B). Based on msg2, terminal 31 transmits msg3 (PUSCH) to communication points 12, 21, and 24 (S310C, S320C). At this point, unless terminal 31 receives msg4, it may recognize these three communication points as a group (cluster) of communication points with which it will communicate in the future. In this case, base station 1 and base station 2 may decide to use communication points 12, 21, and 24 from which terminal 31 transmitted msg3 for communication after initial access control. However, base station 1 and base station 2 may narrow down the communication points to actually be used from communication points 12, 21, and 24. Note that msg2 may be transmitted only once, and the transmitted msg2 may be received by each of communication points 12, 21, and 24. However, it is not excluded to transmit msg2 separately for each communication point.Base station 1 and base station 2 transmit msg4 as a random access response via communication points 12 and 21, 24 based on msg3, as necessary (S310D, S320D).Transmission of msg4 may be omitted.

[0139] The combinations of selectable communication points or the number (maximum number, minimum number) of selectable communication points may be specified or set in advance. Information on the combinations may be included in the first notification information.

[0140] In the third method, the terminal 31 makes initial access to selected communication points, in this example, communication points 12, 21, and 24. In other words, the terminal 31 makes initial access based on a combination of selected communication points or parameters associated with one of the selected communication points.

[0141] Furthermore, the terminal 31 may perform initial access based on a combination of second signals of the selected communication points or a second signal for one of the selected communication points. For example, msg1 to be transmitted by the terminal 31 is determined based on the combination of selected communication points or one of the selected communication points. For example, the selection of a preamble for msg1 and the transmission resource for msg1 are determined.

[0142] For one of the selected communication points, the RACH resource is selected by that communication point, and the notification of the other selected communication points is done by the selection of the preamble.

[0143] Information regarding initial access specific to a communication point or a combination of communication points may be included in the first broadcast information.

[0144] The PUSCH (msg3) includes information on the communication quality of at least the selected communication point. When multiple communication points are selected, information on the communication quality for each communication point may be transmitted as individual information, or information on one communication quality corresponding to the multiple communication points may be transmitted. Examples of information on one communication quality corresponding to multiple communication points are as follows: Communication quality after combining second signals associated with multiple communication points. For example, communication quality determined based on the sum of RSRP values ​​at multiple communication points. Communication quality determined based on the maximum, minimum, average, and median of the communication qualities for each of the multiple communication points. For example, communication quality determined based on the maximum RSRP value at multiple communication points.

[0145] When the msg1 to be transmitted is determined based on a combination of selected communication points, information indicating the selected communication points may be included in the msg1 or may be notified separately.

[0146] The PUSCH (msg3) may further include information on the communication quality for communication points other than the selected communication point. The communication point to be selected can be determined using the selection method described in the other methods (the second method and the fourth method).

[0147] The PUSCH (msg3) includes information (relative information) on relative characteristics including at least the selected communication point. If multiple communication points are selected, any of the selected communication points can be the communication point that serves as the reference for the relative information.

[0148] [Effects of the Third Method] By using the third method, the base station (and / or core network) can select a suitable antenna (communication point) for cell-free communication for the terminal 31 during initial access control.

[0149] In the third method, initial access control from terminal 31 is performed for a suitable antenna (communication point), so the time required for initial access control (i.e., delay time) can be reduced compared to conventional methods.

[0150] Furthermore, in the third method, from the perspective of the network side including the base station and the core network, the communication node that performs initial access control from terminal 31 can be different for each terminal 31, so that distributed processing can be performed at least with respect to initial access control.

[0151] Furthermore, when there are multiple suitable communication points, initial access control is performed from terminal 31 to each of the communication points, so from the network perspective, there is no need to send and receive information about the suitable communication points between the communication points. As a result, on the network side, not only is the overhead of exchanging control information reduced, but delays related to that control can also be reduced.

[0152] [Fourth Method for Initial Access] Fig. 8A is an example of a sequence diagram of a fourth method for initial access. Fig. 8B is a rewrite of Fig. 8A, which is a sequence based on a base station, into a sequence based on a communication point. The sequences of Fig. 8A and Fig. 8B are controlled by the control units 150 of base station 1 and base station 2, respectively, and the control unit 350 of terminal 31.

[0153] In the following explanation, the explanation of the parts that overlap with other methods may be omitted. That is, the contents explained in the first to third methods can be applied to the fourth method.

[0154] In the fourth method, a two-stage random access procedure is used. A base station (base station 1 in this example) periodically transmits a first signal and / or first broadcast information (S101).

[0155] The second signal and / or the second broadcast information may be transmitted periodically or non-periodically (on-demand) when needed. When transmitted periodically, information regarding the second signal and / or the second broadcast information may be transmitted by being included in the first broadcast information, or by being included in msg1-2 as described below. When transmitted non-periodically (on-demand) when needed, information regarding the second signal and / or the second broadcast information may be transmitted by being included in msg1-2. That is, the terminal 31 cannot recognize the second signal and / or the second broadcast information by simply receiving the first broadcast information. That is, the terminal transmits msg1-1 including transmission request information requesting transmission of the second signal or acquisition request information requesting acquisition of information regarding the second signal. A base station that receives msg1-1 may start transmitting the second signal in response to the transmission request information included in msg1-1. The base station may also transmit second broadcast information including information regarding the second signal in response to the acquisition request information. The terminal receives the second signal transmitted from the base station based on information regarding the second signal included in the second broadcast information. When the base station transmits the second broadcast information, the first broadcast information may not include information regarding the second signal, but may include information regarding initial access, and the terminal may transmit the above-mentioned msg1-1 based on this information. Note that msg1-1 may also be referred to as a wake-up signal. Note that periodic transmission or on-demand transmission can be selected by the base station. For example, information indicating periodic transmission or on-demand transmission may be included in the first broadcast information.

[0156] The terminal 31 performs first random access control (first random access) for the first signal received in step S101 (e.g., to the base station 1) (S410). Specifically, the terminal 31 transmits msg1-1 to the base station 1 (S410A). msg1-1 is the same as the msg1 described above in the first to third methods. However, in this example, msg1-1 may include transmission request information requesting transmission of a second signal or acquisition request information requesting acquisition of information related to the second signal. Upon receiving msg1-1, the base station 1 transmits msg1-2 to the terminal 31 (S410B). msg1-2 includes information specific to the terminal 31 that transmitted msg1-1. Specifically, msg1-2 includes the following information: - Information related to the second random access control (information used for the second random access control, information related to msg2-1). This information corresponds to information related to the initial access to the base station 2. Information about the second signal and / or second broadcast information (time frequency resources, IDs of the second signal and / or second broadcast information, etc.) Information about communication points (information about the locations of communication points).

[0157] Note that msg1-2 in step S410B can be omitted. In this case, the terminal can transmit msg1-1 and receive a second signal from the communication point based on the first signal and / or the first broadcast information (S101). For example, the communication point starts transmitting the second signal on a predetermined resource based on msg1-1 from the terminal. After transmitting msg1-1, the terminal monitors the predetermined resource (a candidate for the predetermined resource) and detects the second signal. The predetermined resource or the candidate for the predetermined resource may be determined based on information included in the first broadcast information.

[0158] Terminal 31 receives second signals from communication points 11 to 14 and 21 to 24 (S102 to S109), and performs second random access control (second random access) to communication point 22 (in this example, communication point 22) selected based on the received second signal (S420).

[0159] The terminal 31 transmits a random access channel (msg2-1) to the communication point 22 (S420A). The msg2-1 is transmitted based on at least the information of the msg1-2. The base station 2 transmits a random access response (msg2-2) to the terminal 31 via the communication point 22 (S420B).

[0160] The terminal 31 transmits and receives msg3 and / or msg4 (i.e., notifies the terminal 31 of RRC control information and / or controls contention resolution). The transmission and reception of msg3 and / or msg4 may be performed using the first random access control or the second random access control. The figure shows the case where the second random access control is used, in which msg1-3 and / or msg1-4 are transmitted and received between the terminal 31 and the base station 2 (communication point 22) (S420C, S420D). At this point, unless the terminal 31 receives msg4, the terminal 31 may recognize this communication point 22 as a communication point with which to communicate in the future. When the first random access control is used, msg1-3 and / or msg1-4 are transmitted and received, and the transmission and reception of msg2-3 and msg2-4 may be omitted.

[0161] [Non-periodic (on-demand) transmission of second signal and / or second broadcast information] A base station (base station 1 in this example) or a core network recognizes terminal 31 by receiving msg1-1 from terminal 31 and transmits the second signal and / or the second broadcast information (S102, S104, S106, S108). That is, reception of msg1-1 from terminal 31 can trigger base station 1 to start transmitting the second signal and / or the second broadcast information. msg1-1 from terminal 31 can be on-demand (wake-up signal) information for the second signal and / or the second broadcast information. Base station 2 communicates with base station 1 directly or via a core network or the like, recognizes terminal 31, and transmits the second signal and / or the second broadcast information (S103, S105, S107, S109). By triggering the start of transmission of the second signal and / or second notification information upon receiving msg1-1, power consumption can be reduced compared to when the second signal, etc., is continuously transmitted periodically.

[0162] The second signal and / or the second broadcast information may be explicitly determined based on the information contained in msg1-2 as described above, or may be indirectly (implicitly) determined based on the first signal and / or the first broadcast information and / or msg1-1.

[0163] When the resource is determined indirectly (implicitly), for example, the resource on which the second signal and / or the second broadcast information is (can be) transmitted is implicitly determined based on the time resource for transmitting msg1-1.

[0164] After the trigger, the transmission of the second signal and / or the second broadcast information may be periodically transmitted until a predetermined condition is satisfied. That is, after the predetermined condition (predetermined termination condition) is satisfied, the transmission of the second signal and / or the second broadcast information may be stopped. By stopping the transmission of the second signal and / or the second broadcast information, the power consumption of the base station can be reduced.

[0165] For example, the specified condition can be a predetermined or set time, number of slots, number of frames, number of transmissions, or when all terminals 31 are no longer connected to the base station (communication point), and various other methods can be used.

[0166] Furthermore, for example, the resource in which the second signal and / or the second broadcast information is transmitted (can be transmitted) may be a predetermined time domain (predetermined time-frequency domain). That is, a time window (time-frequency window) for the second signal and / or the second broadcast information is notified, and the second signal and / or the second broadcast information is transmitted within the window.

[0167] The terminal 31 attempts to receive (detect) the second signal and / or the second broadcast information within the window. The window may be defined as a timer. That is, the terminal 31 receives the second signal and / or the second broadcast information based on the timer. The timer may be started, for example, before or after transmitting msg1-1, or upon receiving msg1-2.

[0168] When the timer expires (times out) (if reception is not possible within the window), the terminal 31 performs error processing (failure processing) regarding the second signal and / or the second broadcast information. For example, the terminal 31 performs the first random access control (transmission of msg1-1) again. Alternatively, the terminal 31 may not perform the two-stage random access control, but may perform a different random access control (for example, the random access control of the comparative example). In other words, the terminal 31 falls back to the random access control of the comparative example.

[0169] [Effects of the Fourth Method] By using the fourth method, the base station (and / or core network) can select a suitable antenna (communication point) for cell-free communication for the terminal 31 during initial access control.

[0170] In the fourth method, initial access control is performed in two stages, so the effects of the other methods (methods 1 to 3) can be enjoyed. In addition, the processing to be performed in the first and second stages can be set separately, which improves the flexibility of network design.

[0171] The above-described embodiment shows an example for realizing the present disclosure, and the present disclosure can be implemented in various other forms. For example, various modifications, substitutions, omissions, or combinations thereof are possible without departing from the spirit of the present disclosure. Such modifications, substitutions, omissions, etc. are also included within the scope of the present disclosure, as well as within the scope of the inventions described in the claims and their equivalents.

[0172] Furthermore, the effects of the present disclosure described in this specification are merely examples, and other effects may also be present.

[0173] The present disclosure may also be configured as follows: [Item 1] A terminal device communicating with a network device including one or more communication points, the terminal device comprising: a receiver that receives a first signal including information necessary for receiving first broadcast information transmitted from at least one first communication point among the one or more communication points; receives the first broadcast information including information on a second signal, which is a known signal, transmitted from at least one second communication point among the one or more communication points based on the information necessary for receiving the first broadcast information included in the first signal; and receives the second signal transmitted from at least one third communication point among the one or more communication points based on information on the second signal included in the first broadcast information; and a controller that performs initial access control for connecting to the network device via at least one fourth communication point among the one or more communication points based on communication quality of the second signal. [Item 2] The terminal device according to Item 1, wherein the information on the second signal includes a list of one or more second signals that the terminal device may receive. [Item 3] The terminal device according to item 1 or 2, wherein a QCL of the first broadcast information is the same as a QCL of the first signal. [Item 4] The terminal device according to item 3, wherein a QCL of at least one of the second signals is different from a QCL of the first broadcast information or a QCL of the first signal. [Item 5] The terminal device according to any one of items 1 to 4, wherein the at least one third communication point includes a plurality of the third communication points, and the control unit controls to transmit, in the initial access control, information relating to a difference in communication quality between any two third communication points among the plurality of third communication points. [Item 6] The terminal device according to any one of items 1 to 5, wherein the first broadcast information includes instruction information instructing whether to execute the initial access control or initial access control of a method different from the initial access control, and the control unit selects and executes either the initial access control or the initial access control of the method different from the initial access control based on the instruction information.[Item 7] The terminal device according to any one of items 1 to 6, wherein the control unit switches to an initial access control method different from the initial access control when a predetermined switching condition is satisfied during execution of the initial access control. [Item 8] The terminal device according to any one of items 1 to 7, wherein the at least one third communication point includes a plurality of the third communication points, and the control unit selects at least one third communication point based on communication qualities of the second signals received from the plurality of third communication points, and performs control to transmit information on the communication quality related to the selected third communication point to the network device. [Item 9] The terminal device according to item 8, wherein the control unit controls to transmit information on the communication qualities for all of the third communication points to the network device during the initial access control. [Item 10] The terminal device according to any one of items 1 to 9, wherein the control unit selects one third communication point based on communication quality of the second signals received from the at least one third communication point, and the control unit performs the initial access control via the selected third communication point. [Item 11] The terminal device according to any one of items 1 to 10, wherein the at least one third communication point includes a plurality of the third communication points, and the control unit selects a plurality of third communication points based on communication quality of the second signal received from the plurality of third communication points, and performs the initial access control via each of the selected plurality of third communication points. [Item 12] The terminal device according to any one of items 1 to 11, wherein the control unit controls transmission of transmission request information requesting transmission of the second signal to the network device, and the receiving unit receives the second signal transmitted from the network device in response to the transmission request information.[Item 13] The terminal device according to any one of items 1 to 12, wherein the first broadcast information includes information regarding initial access to the network device, the control unit controls transmission of acquisition request information requesting acquisition of information regarding the second signal based on the information regarding the initial access included in the first broadcast information, the receiving unit receives second broadcast information including information regarding the second signal that is transmitted from the network device in response to the acquisition request information, and the receiving unit receives the second signal based on the information regarding the second signal included in the second broadcast information. [Item 14] The terminal device according to item 13, wherein the network device includes a first base station and a second base station, the information regarding the initial access included in the first broadcast information is information regarding initial access to the first base station, the second broadcast information includes information regarding initial access to the second base station, and the control unit performs initial access control for the second base station based on the information regarding the initial access included in the second broadcast information and communication quality of the second signal. [Item 15] The terminal device according to Item 13 or 14, wherein the control unit activates a timer before or after transmitting the acquisition request information, and if the timer times out before the second signal is successfully received, performs control to retransmit the acquisition request information.[Item 16] A network apparatus that communicates with a terminal device, comprising: one or more communication points; a transmitter that transmits a first signal including information necessary for the terminal device to receive first broadcast information via at least one first communication point of the one or more communication points; transmits the first broadcast information including information on a second signal that is a known signal via at least one second communication point of the one or more communication points; and transmits the second signal via at least one third communication point of the one or more communication points; and a controller that receives an initial access request based on reception quality of the second signal from the terminal device that has received the second signal via at least one fourth communication point of the one or more communication points, and performs initial access control for connecting with the terminal device. [Item 17] The terminal device according to item 1, wherein the second communication point is the same communication point as the first communication point, the third communication point includes the first communication point or the second communication point, and the third communication point includes the fourth communication point. [Item 18] The network device according to Item 17, wherein the control unit determines a communication point to be used by the terminal device based on reception quality of the second signal in the initial access control. [Item 19] The network device according to Item 17 or 18, further comprising a receiving unit that receives transmission request information requesting transmission of the second signal from the terminal device, wherein the control unit controls to periodically transmit the second signal based on the transmission request information, and stops transmission of the second signal when a predetermined termination condition is met.[Item 20] The network device according to any one of Items 17 to 19, wherein the first notification information includes information related to an initial access to the network device, and the network device is equipped with a receiving unit that receives acquisition request information requesting acquisition of information related to the second signal, the acquisition request information being transmitted from the terminal device based on the information related to the initial access included in the first notification information, and the transmitting unit transmits second notification information including the information related to the second signal in response to the acquisition request information, and the transmitting unit stops transmitting the second notification information in response to a predetermined termination condition being met. [Item 21] A communication method for communicating with a network device including one or more communication points, comprising: receiving a first signal including information necessary to receive first broadcast information, transmitted from at least one first communication point of the one or more communication points; receiving the first broadcast information including information regarding a second signal, which is a known signal, transmitted from at least one second communication point of the one or more communication points based on the information necessary to receive the first broadcast information included in the first signal; receiving the second signal transmitted from at least one third communication point of the one or more communication points based on the information regarding the second signal included in the first broadcast information; and performing initial access control for connecting to the network device via at least one fourth communication point of the one or more communication points based on communication quality of the second signal.[Item 22] A communication method for communicating with a terminal device using one or more communication points, comprising: transmitting a first signal including information necessary for the terminal device to receive first broadcast information via at least one first communication point of the one or more communication points; transmitting the first broadcast information including information on a second signal, which is a known signal, via at least one second communication point of the one or more communication points; transmitting the second signal via at least one third communication point of the one or more communication points; and receiving an initial access request based on reception quality of the second signal from the terminal device that has received the second signal via at least one fourth communication point of the one or more communication points, and performing initial access control for connecting with the terminal device.[Item 23] A communication system including a network device and a terminal device communicating with the network device, wherein the network device comprises: one or more communication points; a transmitter that transmits a first signal including information necessary for the terminal device to receive first broadcast information via at least one first communication point of the one or more communication points; transmits the first broadcast information including information on a second signal, which is a known signal, via at least one second communication point of the one or more communication points; and transmits the second signal via at least one third communication point of the one or more communication points; and a first controller that receives an initial access request based on a reception quality of the second signal from the terminal device that has received the second signal via at least one fourth communication point of the one or more communication points, and performs initial access control for establishing a connection with the terminal device; wherein the terminal device receives the first signal transmitted from the at least one first communication point; and receives the first broadcast information transmitted from the at least one second communication point based on the information necessary for receiving the first broadcast information included in the first signal. a receiving unit that receives the second signal transmitted from the at least one third communication point based on information regarding the second signal included in the first broadcast information; and a second control unit that makes the initial access request for connecting to the network device via the at least one fourth communication point based on communication quality of the second signal.

[0174] REFERENCE SIGNS LIST 1 Base station 2 Base station 11 Communication point 12 Communication point 13 Communication point 14 Communication point 21 Communication point 22 Communication point 23 Communication point 24 Communication point 31 Terminal device (terminal) 100 Network device 110 Communication point 120 Wireless communication unit 121 Signal transmission unit 122 Signal reception unit 130 Network communication unit 140 Storage unit 150 Control unit 151 Transmission unit 152 Reception unit 310 Antenna 320 Wireless communication unit 321 Signal transmission unit 322 Signal reception unit 340 Storage unit 350 Control unit 351 Transmission unit 352 Reception unit

Claims

1. A terminal device that communicates with a network device that includes one or more communication points, comprising: a receiving unit that receives a first signal that includes information necessary to receive first broadcast information, transmitted from at least one first communication point among the one or more communication points; receives the first broadcast information that includes information about a second signal that is a known signal, transmitted from at least one second communication point among the one or more communication points, based on the information necessary to receive the first broadcast information included in the first signal; and receives the second signal that is transmitted from at least one third communication point among the one or more communication points, based on the information about the second signal included in the first broadcast information; and a control unit that performs initial access control for connecting to the network device via at least one fourth communication point among the one or more communication points, based on the communication quality of the second signal.

2. The terminal device according to claim 1, wherein the information regarding the second signal includes a list of one or more second signals that the terminal device may receive.

3. The terminal device according to claim 1, wherein the QCL of the first broadcast information is the same as the QCL of the first signal.

4. The terminal device according to claim 3, wherein a QCL of at least one of the second signals is different from a QCL of the first broadcast information or a QCL of the first signal.

5. The terminal device according to claim 1, wherein the at least one third communication point includes a plurality of third communication points, and the control unit controls the transmission of information regarding a difference in communication quality between any two third communication points among the plurality of third communication points during the initial access control.

6. The terminal device described in claim 1, wherein the first notification information includes instruction information instructing whether to execute the initial access control or a different type of initial access control from the initial access control, and the control unit selects and executes either the initial access control or the different type of initial access control based on the instruction information.

7. The terminal device according to claim 1, wherein the control unit switches to an initial access control method different from the initial access control method when a predetermined switching condition is satisfied during execution of the initial access control.

8. The terminal device according to claim 1, wherein the at least one third communication point includes a plurality of the third communication points, and the control unit selects at least one third communication point based on the communication quality of the second signal received from the plurality of the third communication points, and controls the transmission of information regarding the communication quality of the selected third communication point to the network device.

9. The terminal device according to claim 8, wherein the control unit performs control in the initial access control to transmit information about the communication quality for all of the third communication points to the network device.

10. The terminal device according to claim 1, wherein the control unit selects one third communication point based on the communication quality of the second signal received from the at least one third communication point, and the control unit performs the initial access control via the selected third communication point.

11. The terminal device according to claim 1, wherein the at least one third communication point includes a plurality of the third communication points, and the control unit selects a plurality of third communication points based on the communication quality of the second signal received from the plurality of third communication points, and performs the initial access control via each of the selected plurality of third communication points.

12. The terminal device according to claim 1, wherein the control unit controls the transmission of transmission request information requesting the transmission of the second signal to the network device, and the receiving unit receives the second signal transmitted from the network device in response to the transmission request information.

13. The terminal device described in claim 1, wherein the first notification information includes information regarding initial access to the network device, the control unit controls the transmission of acquisition request information requesting the acquisition of information regarding the second signal based on the information regarding the initial access included in the first notification information, the receiving unit receives second notification information including information regarding the second signal that is transmitted from the network device in response to the acquisition request information, and the receiving unit receives the second signal based on the information regarding the second signal included in the second notification information.

14. The terminal device of claim 13, wherein the network device includes a first base station and a second base station, the information relating to initial access included in the first notification information is information relating to initial access to the first base station, the second notification information includes information relating to initial access to the second base station, and the control unit performs initial access control for the second base station based on the information relating to initial access included in the second notification information and the communication quality of the second signal.

15. The terminal device according to claim 13, wherein the control unit activates a timer before or after transmitting the acquisition request information, and if the timer times out before the second signal is successfully received, controls to retransmit the acquisition request information.

16. The terminal device according to claim 1, wherein the second communication point is the same communication point as the first communication point, the third communication point includes the first communication point or the second communication point, and the third communication point includes the fourth communication point.

17. A network device that communicates with a terminal device, comprising: one or more communication points; a transmitter that transmits a first signal including information necessary for the terminal device to receive first broadcast information via at least one first communication point among the one or more communication points; transmits the first broadcast information including information on a second signal, which is a known signal, via at least one second communication point among the one or more communication points; and transmits the second signal via at least one third communication point among the one or more communication points; and a controller that receives an initial access request from the terminal device that has received the second signal based on the reception quality of the second signal via at least one fourth communication point among the one or more communication points, and performs initial access control for connecting to the terminal device.

18. The network device according to claim 17, wherein the control unit determines a communication point to be used by the terminal device based on the reception quality of the second signal during the initial access control.

19. A network device as described in claim 17, comprising a receiving unit that receives transmission request information requesting transmission of the second signal from the terminal device, and the control unit controls the periodic transmission of the second signal based on the transmission request information, and stops the transmission of the second signal when a predetermined termination condition is met.

20. A network device as described in claim 17, wherein the first notification information includes information regarding initial access to the network device, and the network device is provided with a receiving unit that receives acquisition request information requesting acquisition of information regarding the second signal, the acquisition request information being sent from the terminal device based on the information regarding the initial access included in the first notification information, the transmitting unit transmitting second notification information including information regarding the second signal in response to the acquisition request information, and the transmitting unit stopping transmission of the second notification information in response to a predetermined termination condition being met.

21. A communications method for communicating with a network device including one or more communication points, comprising: receiving a first signal including information necessary for receiving first broadcast information, transmitted from at least one first communication point among the one or more communication points; receiving the first broadcast information including information regarding a second signal, which is a known signal, transmitted from at least one second communication point among the one or more communication points based on the information necessary for receiving the first broadcast information included in the first signal; receiving the second signal transmitted from at least one third communication point among the one or more communication points based on the information regarding the second signal included in the first broadcast information; and performing initial access control for connecting to the network device via at least one fourth communication point among the one or more communication points based on the communication quality of the second signal.

22. A communications method for communicating with a terminal device using one or more communication points, comprising: transmitting a first signal including information necessary for the terminal device to receive first broadcast information via at least one first communication point among the one or more communication points; transmitting the first broadcast information including information on a second signal, which is a known signal, via at least one second communication point among the one or more communication points; transmitting the second signal via at least one third communication point among the one or more communication points; and receiving an initial access request based on the reception quality of the second signal from the terminal device that has received the second signal via at least one fourth communication point among the one or more communication points, and performing initial access control for connecting with the terminal device.

23. A communication system comprising a network device and a terminal device communicating with the network device, wherein the network device comprises: one or more communication points; a transmitter that transmits a first signal including information necessary for the terminal device to receive first broadcast information via at least one first communication point of the one or more communication points; transmits the first broadcast information including information on a second signal, which is a known signal, via at least one second communication point of the one or more communication points; and transmits the second signal via at least one third communication point of the one or more communication points; and a first controller that receives an initial access request from the terminal device that has received the second signal based on reception quality of the second signal via at least one fourth communication point of the one or more communication points, and performs initial access control to establish a connection with the terminal device; wherein the terminal device receives the first signal transmitted from the at least one first communication point; and receives the first broadcast information transmitted from the at least one second communication point based on the information necessary for receiving the first broadcast information included in the first signal; a receiving unit that receives the second signal transmitted from the at least one third communication point based on information regarding the second signal included in the first broadcast information; and a second control unit that makes the initial access request for connecting to the network device via the at least one fourth communication point based on communication quality of the second signal.

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