Core network device, method for controlling core network device, and base station

Abstract

Provided are a core network device, etc., capable of suppressing wasteful power consumption by a base station. The core network device comprises: a detecting unit that detects the number of UEs within range in an area managed by one or more base stations connected to the core network device, the number of UEs including the number of UEs in an idle mode; and a base station control unit that, if the detected number of UEs becomes zero, performs processing for transitioning the base stations to a power saving mode.

Description

Core network device, method for controlling core network device, and base station

[0001] The present disclosure relates to a core network device, a method for controlling a core network device, and a base station. This application claims priority to Japanese Patent Application No. 2024-188698, filed in Japan on October 28, 2024, the content of which is incorporated herein by reference.

[0002] Regarding a communication system, Patent Document 1 discloses a technique for suppressing a decrease in interference detection accuracy and reducing power consumption during a power saving mode by setting the measurement period to be longer in a time band with lower usage frequency.

[0003] Japanese Patent Application Laid-Open No. 2018-110457

[0004] For example, there is a tracking area managed by a plurality of base stations as an area for providing a communication service to a terminal. Here, when a UE (User Equipment) that was within the tracking area moves, the UE may no longer be within the tracking area. At this time, if each base station maintains a state where it can provide a normal communication service even though the UE for which the communication service is provided is no longer within the tracking area, each base station continues to consume unnecessary power. Patent Document 1 does not solve such a problem.

[0005] As one aspect, an object of the present disclosure is to provide a core network device or the like capable of suppressing wasteful power consumption of a base station.

[0006] A core network device according to an aspect of the present invention includes a detection unit that detects the number of UEs in an area managed by one or more base stations connected to the core network device, including the number of UEs in an idle mode, and a base station control unit that performs a process of shifting the base station to a power saving mode when the detected number of UEs becomes zero.

[0007] A base station according to one aspect of the present invention includes a communication unit that receives a power saving instruction from the core network device when it is detected that the number of UEs located in the area managed by the base station connected to the core network device, including the number of UEs in idle mode, has become zero, and a control unit that performs processing to switch the base station to power saving mode when the power saving instruction is received.

[0008] This is a diagram showing an example of the system. This is a diagram showing an example where the UE in idle mode moves from the state in Figure 1. This is a diagram showing an example of a core network device. This is a diagram showing an example of a base station. This is a flowchart showing an example of the processing flow of the core network device in the first embodiment. This is a diagram showing an example of registration information. This is a flowchart showing an example of the processing flow of the base station in the first embodiment. This is a flowchart showing an example of the system processing flow in the first embodiment. This is a flowchart showing an example of the processing flow of the core network device in the second embodiment. This is a flowchart continuing from Figure 8. This is a flowchart showing an example of the processing flow of the base station in the second embodiment. This is a flowchart showing an example of the system processing flow in the second embodiment.

[0009] <First Embodiment> The first embodiment will be described below. Figure 1 is a diagram showing an example of the system 100 of each embodiment. The system 100 includes a core network device 101, base stations 102A to 102I and UEs 103A to 103C.

[0010] The core network device 101 manages base stations 102A to 102I. Hereinafter, base stations 102A to 102I may be collectively referred to as base station 102. Also, UE 103A to 103C may be collectively referred to as UE 103.

[0011] Base station 102 is managed by core network device 101 and provides communication services to UE 103 based on control from core network device 101. UE 103 is a user terminal, such as a smartphone or tablet device. The number of base stations 102 and UE 103 can be any number.

[0012] In the example shown in Figure 1, base stations 102A, 102B, and 102C constitute tracking area TA1. Base stations 102D, 102E, and 102F constitute tracking area TA2. Base stations 102G, 102H, and 102I constitute tracking area TA3. Each of the tracking areas TA1 to TA3 can be identified by a TAC (Tracking Area Code).

[0013] UE103 has two states (modes): Connected mode and Idle mode. Connected mode is a mode in which the communication functions of UE103 are not restricted. When set to Connected mode, UE103 can access the data network via the base station 102 and the core network device 101. This allows UE103 to receive communication services such as access to the internet.

[0014] Base station 102 maintains a state where it can communicate with UE 103 as long as UE 103 is in connected mode. Therefore, base station 102 can detect UE 103 located within its cell. As a result, base station 102 can detect the number of connected mode UE 103 located within its cell.

[0015] When the number of UEs 103 located within a cell of base station 102 becomes zero, base station 102 switches from normal mode (a mode that provides normal communication services to the UEs 103 located within the cell) to power-saving mode. This reduces the power consumption of base station 102. Base station 102 that can switch to power-saving mode is sometimes referred to as a Network Energy Saving (NES) compatible base station.

[0016] On the other hand, the idle mode described above is a mode that reduces the power consumption of the UE 103 by restricting some of the communication functions of the UE 103. In idle mode, some of the communication functions of the UE 103 are restricted, and the base station 102 cannot detect the UE 103 in idle mode.

[0017] For example, when the UE 103 has not been communicating with the data network via the base station 102 and the core network device 101 for a certain period of time, it switches from connected mode to idle mode. This reduces the power consumption of the UE 103. On the other hand, even if the UE 103 switches from connected mode to idle mode, the base station 102 maintains its connection with the UE 103 in idle mode.

[0018] Here, suppose that UE 103 in idle mode moves from the tracking area TA to which the base station 102, which maintains its connection state, belongs, to another tracking area TA and undergoes cell reselection. Alternatively, suppose that UE 103 in idle mode is detached due to a power-off operation or the like.

[0019] As described above, base station 102 cannot detect UE 103 in idle mode. Therefore, if UE 103 in idle mode undergoes cell reselection, base station 102 cannot detect that UE 103 has undergone cell reselection. Similarly, if UE 103 in idle mode detaches, base station 102 cannot detect that UE 103 has detached.

[0020] Here, if an idle-mode UE 103 undergoes cell reselection or detaches from the tracking area TA to which base station 102 belongs, the number of UE 103s located within the tracking area TA may become zero. At this time, as described above, base station 102 maintains its connection with the idle-mode UE 103, and therefore cannot switch to power-saving mode even though the number of UE 103s located within the tracking area TA has become zero.

[0021] Meanwhile, the core network device 101 detects and manages the UEs 103 located in each tracking area TA (including UEs 103 in idle mode). For example, if an idle UE 103 undergoes cell reselection or detaches, a cell reselection message or detach request is sent to the core network device 101. Based on the cell reselection message or detach request, the core network device 101 can detect idle UEs 103 located in each tracking area TA.

[0022] Furthermore, the UE 103 in connected mode has no restrictions on its communication functions. Therefore, the core network device 101 can detect the connected mode UE 103 located in each tracking area TA.

[0023] In each embodiment, when the core network device 101 detects a tracking area TA1 to TA3 in which the number of resident UEs 103 (including UEs 103 in idle mode) has become zero, it transmits an instruction (power saving instruction) to each base station 102 belonging to the detected tracking area TA to switch to power saving mode. Upon receiving the power saving instruction, each base station 102 switches to power saving mode. A specific example will be explained using Figure 2.

[0024] Figure 2 shows an example of a transition from the state shown in Figure 1 to idle mode for UE103A. For example, suppose UE103A in connected mode was connected to base station 102B belonging to tracking area TA1. Then, suppose UE103A transitioned from connected mode to idle mode.

[0025] Base station 102B stops detecting UE103A because the connected UE103A has entered idle mode. For example, when base station 102B stops detecting the connected UE103A, it transmits information to the core network device 101 indicating that UE103A has entered idle mode and information identifying UE103A. The information identifying UE103A is, for example, an IP address, which is managed by base station 102B. Base station 102B also maintains the connection status with UE103A.

[0026] As shown in Figure 2, assume that UE103A, in idle mode, has moved from tracking area TA1 to tracking TA2. Also, assume that UE103A, in idle mode, has moved into the cell of base station 102D, which belongs to tracking area TA2.

[0027] In idle mode, UE103A has its communication restricted in normal mode, but its cell reselection function is not restricted. Therefore, base station 102D, which belongs to tracking area TA2, receives a cell reselection message from UE103A in idle mode. Base station 102D, which belongs to tracking area TA2, receives the cell reselection message and performs processing related to cell reselection.

[0028] When a base station 102D belonging to tracking area TA2 performs cell reselection processing, it sends a notification to the core network device 101 indicating that it has performed the cell reselection processing. This notification includes information that identifies UE 103A (for example, an IP address).

[0029] As described above, the core network device 101 recognizes that UE103A, identified by its IP address, is in idle mode. Furthermore, based on the above notification, the core network device 101 recognizes that UE103A, in idle mode, has undergone cell reselection to base station 102D belonging to tracking area TA2.

[0030] The core network device 101 changes the tracking area TA where the idle UE 103A was located from TA1 to TA2, using the registration information (Figure 5) described later. The registration information is information for managing the UE 103 located in each tracking area TA. Details will be described later.

[0031] Here, let's assume that no UE103 units other than UE103A in idle mode were present within tracking area TA1. In this case, of the registration information mentioned above, only UE103A in idle mode is registered in tracking area TA1.

[0032] Then, the core network device 101 recognizes, based on the notification described above, that the idle UE 103A has undergone cell reselection from tracking area TA1 to base station 102D belonging to tracking TA2. In this case, the core network device 101 deletes the information for UE 103A from tracking area TA1 in the registration information described above. As a result, the core network device 101 recognizes that the number of UE 103A entries corresponding to tracking area TA1 in the registration information described above has become zero.

[0033] In this case, the core network device 101 issues an instruction to all base stations 102A to 102C corresponding to the tracking area TA1 to switch to power-saving mode. Based on this instruction, base stations 102A to 102C switch to power-saving mode.

[0034] As a result, when UE103A in idle mode is no longer located within tracking area TA1, and the number of UE103s located within tracking area TA1 becomes zero, base stations 102A to 102C belonging to tracking area TA1 can be switched to power-saving mode.

[0035] Furthermore, suppose a user performs a power-off operation on an idle UE103A located within the tracking area TA1. While the idle UE103A is restricted from communicating in normal mode, it can send a detach message indicating that it has been detached. The detach message includes information that identifies the UE103A (e.g., its IP address).

[0036] The base station 102 sends a detach message to the core network device 101. The core network device 101 deletes the information of the idle mode UE103A corresponding to tracking area TA1 from the above registration information. As a result, the core network device 101 recognizes that the number of UE103s corresponding to tracking area TA1 in the above registration information is zero.

[0037] In this case, the core network device 101 issues an instruction to all base stations 102A to 102C corresponding to the tracking area TA1 to switch to power-saving mode. Based on this instruction, base stations 102A to 102C switch to power-saving mode.

[0038] Next, the configuration of the core network device 101 will be described. Figure 3A shows an example of the core network device 101. The core network device 101 includes a control unit 201, a storage unit 202, and a communication unit 203.

[0039] The control unit 201 is, for example, a processor such as a CPU. The control unit 201 may also be an MCU (Micro Control Unit) or an MPU (Micro Processor Unit). The processor of the control unit 201 executes a program to control the core network device 101 of this embodiment. The control unit 201 may also be a circuit with arithmetic functions such as an FPGA (Field Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit).

[0040] The memory unit 202 stores various types of information. The communication unit 203 is a communication circuit for communicating with each base station 102. The core network device 101 is also communicably connected to the data network.

[0041] The control unit 201 includes a detection unit 211 and a base station control unit 212. The detection unit 211 detects the number of UEs 103 present in each tracking area TA. The number of such UEs 103 includes the number of UEs 103 in the idle mode.

[0042] For the number of UEs 103 in the connected mode for each tracking area TA, the detection unit 211 detects the number of UEs 103 in the connected mode based on the information of the UEs 103 that are communicably connected in the normal mode. On the other hand, for the number of UEs 103 in the idle mode for each tracking area TA, the detection unit 211 detects the number of UEs 103 in the idle mode based on the above-described cell reselection messages and detach requests.

[0043] When there is a tracking area TA in which the number of present UEs 103 has become zero, the base station control unit 212 shifts all the base stations 102 belonging to the tracking area TA from the normal mode to the power-saving mode.

[0044] The detection unit 211 stores the detected number of UEs 103 for each tracking area TA in registration information (FIG. 5) described later. The base station control unit 212 refers to the registration information to determine whether the number of UEs 103 present in the tracking area TA has become zero. The base station control unit 212 shifts all the base stations 102 belonging to the tracking area TA where the number of UEs 103 has become zero to the power-saving mode. Information on each base station 102 belonging to the tracking area TA is recognized in advance by the core network device 101.

[0045] FIG. 3B is a diagram showing an example of the base station 102. The base station 102 includes a control unit 301, a memory unit 302, a first communication unit 303, and a second communication unit 304.

[0046] The control unit 301 is a processor such as a CPU, MCU, MPU, etc. By the processor of the control unit 301 executing a program, the control of the base station 102 of the present embodiment is realized. The control unit 201 may be a circuit having an arithmetic function such as an FPGA or an ASIC.

[0047] The storage unit 302 stores various kinds of information. The first communication unit 303 is a communication circuit that performs wireless communication with the UE 103 located within its own cell. The second communication unit 304 (communication unit) is a communication circuit that performs wired or wireless communication with the core network device 101.

[0048] FIG. 4 is a flowchart showing an example of the processing flow of the core network device 101 in the first embodiment. The control unit 201 determines whether it has received a detach message from any of the base stations 102 (step S101).

[0049] If it has not received a detach message, the control unit 201 determines No in step S101 and advances the process to step S102. In this case, the control unit 201 determines whether it has detected cell reselection based on whether it has received a notification indicating that any of the base stations 102 has performed processing related to cell reselection (step S102).

[0050] If it has not detected cell reselection, the control unit 201 determines No in step S102 and returns the process to step S101. In this case, it waits until it receives a detach message or cell reselection is detected.

[0051] If it has received a detach message, the control unit 201 determines Yes in step S101 and advances the process to step S103. Also, if it has detected cell reselection, the control unit 201 determines Yes in step S102 and advances the process to step S103.

[0052] The control unit 201 updates the registration information (step S103). FIG. 5 is a diagram showing an example of the registration information. The registration information is, for example, a table stored in the storage unit 202. The registration information includes information on TA, UE, IP address, connection mode, and connection time.

[0053] TA is information indicating the tracking area. UE is information representing UE103. IP address is information indicating the IP address of UE103. Connection mode is information indicating the connection mode of UE103.

[0054] In the registration information in Figure 5, "Connected" indicates that the UE is in connected mode. "Idle" indicates that the UE is in idle mode. "RRC" indicates that the UE is in RRC (Radio Resource Control) mode.

[0055] Each base station 102 transmits information to the core network device 101 indicating which mode each connected UE 103 is in. Based on this information, the control unit 201 recognizes which mode each UE 103 is in and records it in the registration information.

[0056] Furthermore, each base station 102 transmits information regarding the connection time with the UE 103 in connected mode to the core network device 101. Based on this information, the control unit 201 updates the connection time information corresponding to the UE in connected mode.

[0057] As shown in Figure 4, the detection unit 211 detects the number of UE103 located within the updated tracking area TA based on the registration information (step S104). If the number of UE103 located within the updated tracking area TA is not zero, the detection unit 211 determines "No" in step S105 and returns to step S101.

[0058] On the other hand, if the number of UE103s located within the updated tracking area TA is zero, the detection unit 211 determines Yes in step S105 and proceeds to step S106.

[0059] The control unit 201 notifies all base stations 102 belonging to the updated tracking area TA of a power saving instruction (step S106). Each base station 102 that receives the power saving instruction switches to power saving mode based on the instruction. For example, each base station 102 that receives the power saving instruction may disable the function of the first communication unit 303. This allows each base station 102 that receives the power saving instruction to switch to power saving mode.

[0060] For example, suppose that UE1 in the registration information of Figure 5 is the aforementioned UE103A and has been detached. This UE103A is in idle mode. As mentioned above, UE103A in idle mode has its communication restricted in normal mode, but its function of sending detach messages is not restricted. This UE103A sends a detach message to the base station 102B, which is connected.

[0061] Base station 102B transmits a detach message to core network device 101. Based on the receipt of the detach message from base station 102B, detection unit 211 deletes the information of UE1 (UE103A) in the registration information. As a result, the information of UE corresponding to TA1 in the registration information becomes zero.

[0062] The detection unit 211 detects that the number of UEs 103 located in the tracking area TA1 is zero, based on the fact that the information for the UE corresponding to TA1 in the registered information has become zero. In this case, the control unit 201 transmits a power saving instruction to all base stations 102A to 102C belonging to the tracking area TA1. As a result, base stations 102A to 102C switch to power saving mode.

[0063] Figure 6 is a flowchart showing an example of the processing flow of the base station 102 in the first embodiment. The control unit 301 of the base station 102 determines whether it has received a power saving instruction from the core network device 101 (step S201).

[0064] If no power saving instruction is received, the control unit 301 determines No in step S201 and returns to step S201 to wait. If a power saving instruction is received, the control unit 301 determines Yes in step S201 and proceeds to step S202. In this case, the control unit 201 switches to a pre-set power saving mode (step S202).

[0065] Information regarding the power saving mode to be transitioned to in step S202 is, for example, stored in the memory unit 302 beforehand. For example, suppose there are multiple power saving levels in the power saving mode. The highest level power saving mode is a mode that sets the power consumption of the base station 102 to the minimum.

[0066] For example, the highest level of power saving mode may be deep sleep mode. A base station 102 that switches to the highest level of power saving mode has the greatest power consumption reduction effect, but it takes the longest time to return to normal mode. On the other hand, a base station 102 that switches to the lowest level of power saving mode has the least power consumption reduction effect, but it takes the shortest time to return to normal mode.

[0067] For example, among the base stations 102 belonging to a tracking area TA, the base station 102 closest to the edge may be initially set to the lowest level of power saving mode. This is because the base station 102 is the base station that a UE 103 is likely to attempt to connect to when a UE 103 performs cell reselection from another tracking area TA. As a result, the base station 102 that has switched to the lowest level of power saving mode can quickly return to communication capability when a UE 103 performs cell reselection from another tracking area TA.

[0068] As described above, the weakest power-saving mode may be initially set for the base station 102 closest to the edge in the tracking area TA, and the power-saving mode may be initially set for the base station 102 with increasing levels as it moves further away from the edge. This makes it possible to shorten the time it takes to return to normal mode when the UE 103 undergoes cell reselection from another tracking area TA, and to reduce power consumption at the same time.

[0069] The control unit 301 of the base station 102, which has switched to power-saving mode, determines whether it has received an attach request from the UE 103 (step S203). The attach request is, for example, a request to register an attach with the core network device 101.

[0070] If no attach request has been received, the control unit 301 determines No in step S203 and proceeds to step S204. The control unit 301 determines whether a Wakeup request has been received from the core network device 101 (step S204). A Wakeup request is, for example, a request from the core network device 101 to start up the base station 102.

[0071] For example, suppose a UE 103 in idle mode moves into a tracking area TA1 where base stations 102A to 102C have switched to power-saving mode. The core network device 101 performs control to send a Paging signal to each tracking area TA1 to TA3 at regular intervals. The Paging signal is a signal that can detect the position of the UE 103 in idle mode.

[0072] In idle mode, UE103 sends a message to the core network device 101 corresponding to the Paging signal. This allows the core network device 101 to detect which tracking area TA UE103 is located in idle mode.

[0073] For example, suppose the core network device 101 detects that UE 103, which is in idle mode, is located in tracking area TA1. In this case, the core network device 101 sends a Wakeup request to each base station 102A to 102C belonging to tracking area TA1. In step S204, the control unit 301 of base station 102 determines whether it has received the Wakeup request.

[0074] If a Wakeup signal is not received, the control unit 301 determines No in step S204 and returns to step S203. Therefore, the base station 102, which has entered power-saving mode, maintains power-saving mode until it receives an attach request or a Wakeup signal.

[0075] If an attach request is received, the control unit 301 determines "Yes" in step S203 and proceeds to step S205. If a wakeup signal is received, the control unit 301 determines "Yes" in step S204 and proceeds to step S205. In this case, the number of UEs located within the tracking area TA1 increases.

[0076] If the control unit 301 determines Yes in step S203, or if it determines Yes in step S204, it restores the base station 102, which has transitioned to power-saving mode, back to normal mode (step S205). For example, if the function of the first communication unit 303 is disabled in power-saving mode, the control unit 301 may perform the process in step S205 by enabling the function of the first communication unit 303.

[0077] Next, the processing flow of the system in the first embodiment will be described. Figure 7 is a sequence chart showing an example of the processing flow of the system 100 in the first embodiment. The sequence chart in Figure 7 is an example in which UE 103 sends a detach request.

[0078] UE103 sends a detach request to core network device 101 via base station 102 (step S301). Here, it is assumed that UE103 is set to idle mode.

[0079] The core network device 101 updates the registration information in response to receiving a detach request. Specifically, it deletes the information of the UE corresponding to the tracking area TA where the UE 103 that sent the detach request was located.

[0080] The core network device 101 refers to the registration information and detects the number of UEs 103 in the tracking area TA where the UE that sent the detach request was located (step S302). Here, it is assumed that the number of UEs 103 in the tracking area TA has become zero. The core network device 101 confirms that the number of UEs 103 in the tracking area TA has become zero (step S303).

[0081] Upon receiving a power saving instruction, each base station 102 switches to power saving mode (step S305).

[0082] As described above, the core network device 101 manages cell reselection, detachment, etc., of each UE 103, including UE 103 in idle mode. The core network device 101 detects a tracking area TA where the number of UE 103s present has become zero due to cell reselection, detachment, etc., of UE 103 in idle mode.

[0083] When the core network device 101 detects a tracking area TA where the number of UEs 103 located within the area has become zero, it switches all base stations 102 belonging to that tracking area TA to power-saving mode. This ensures that even if a base station 102 cannot switch to power-saving mode due to its inability to recognize cell reselection or detachment of UEs 103 in idle mode, all base stations 102 belonging to the tracking area TA can be switched to power-saving mode.

[0084] In this embodiment, the core network device 101 switches all base stations 102 belonging to a tracking area TA where the number of UEs 103 present in the area has become zero to power-saving mode, but it is also possible to switch some of the base stations 102 to power-saving mode.

[0085] For example, suppose that the number of UE103s in tracking area TA1 becomes zero as a UE103 in idle mode is detached. The core network device 101 may switch base stations 102A and 102B, among the base stations 102A to 102C belonging to tracking area TA1, to power-saving mode. In this case, base station 102C does not switch to power-saving mode and maintains normal mode.

[0086] Base station 102C is located within a predetermined distance from the edge of tracking area TA1. For example, base station 102 (base station 102C) located within a predetermined distance from the edge of tracking area TA1 may be pre-configured not to switch to power-saving mode even when it receives a power-saving instruction.

[0087] Base station 102C is located near the edge of tracking area TA1 and is a base station 102 from which UE 103 is likely to undergo cell reselection from the adjacent tracking area TA2. For this reason, the core network device 101 does not need to switch base station 102C to power-saving mode.

[0088] The system 100 of each embodiment may be applied to a local communication system such as local 5G. For example, if the system 100 is a local communication system operated at a disaster site, it is required to reduce the overall power consumption of each base station 102A to 102I compared to a normal carrier communication system.

[0089] As described above, the core network device 101 switches all base stations 102 belonging to a tracking area TA where the number of UEs 103, including the number of UEs 103 in idle mode, has become zero, to power-saving mode. This allows the system 100, including the core network device 101, to satisfy the above requirements when it is operated in a local communication environment, such as a disaster site.

[0090] <Second Embodiment> Next, a second embodiment will be described. In the second embodiment, the core network device 101 changes the power saving mode to which it switches depending on the time of day and the number of UEs 103 located in other tracking area TAs.

[0091] Figure 8 is a flowchart showing an example of the processing flow of the core network device 101 in the second embodiment. The processing in steps S101 to S105 is the same as in Figure 4, so its explanation is omitted.

[0092] The base station control unit 212 of the core network device 101 determines whether the current time is within the nighttime period (step S401). The nighttime period is a predetermined time period, for example, between 8 PM and 6 AM. The nighttime period may be any time period. Information about the nighttime period is stored in advance, for example, in the storage unit 202 of the core network device 101.

[0093] If the current time is nighttime, the base station control unit 212 determines Yes in step S401 and proceeds to step S402. In this case, the base station control unit 212 sends a transmit / receive stop instruction to all base stations 102A to 102I belonging to all tracking areas TA1 to TA3 to stop transmitting and receiving (step S402).

[0094] When base stations 102A to 102I receive a transmission / reception stop instruction, they switch to a power-saving mode that disables the transmission and reception functions. In this case, since the transmission and reception functions are disabled, the power consumption reduction effect of base stations 102A to 102I is significant.

[0095] If system 100 is a local communication system that does not operate during nighttime hours (for example, a system used at a disaster site), there is little need to operate base stations 102A to 102I during nighttime hours. By disabling the transmission and reception functions of base stations 102A to 102I during nighttime hours, the effect of reducing power consumption can be enhanced.

[0096] The base station control unit 212 determines whether the nighttime period has ended (step S403). For example, the base station control unit 212 may make the determination in step S403 based on whether the current time is the last time of the nighttime period.

[0097] If the nighttime period has not yet passed, the base station control unit 212 determines No in step S403 and returns to step S403. In this case, the base station control unit 212 waits until the nighttime period has passed.

[0098] If the nighttime period has passed, the base station control unit 212 determines Yes in step S403 and proceeds to step S404. In this case, the base station control unit 212 sends an instruction to all base stations 102A to 102I belonging to all tracking areas TA1 to TA3 to switch to normal mode (step S402). Each base station 102A to 102I switches to normal mode based on this instruction. Then, the base station control unit 212 proceeds from "B" to Figure 9 and terminates the process.

[0099] If the base station control unit 212 determines "No" in step S401 of the flowchart in Figure 8, it proceeds the process from "A" to step S405 in Figure 9. Figure 9 is a flowchart that continues from Figure 8.

[0100] The detection unit 211 refers to the registration information and confirms the number of UE103 located in tracking areas TA other than the updated tracking area TA (step S405).

[0101] For example, suppose a UE103A in idle mode is detached in tracking area TA1. The UE103A in idle mode sends a detach message to the core network device 101, for example, via the nearest base station 102.

[0102] The detection unit 211 refers to the registered information and obtains information on the number of UEs corresponding to the other tracking areas TA2 and TA3 besides tracking area TA1. Based on this information, the detection unit 211 detects the number of UEs corresponding to the other tracking areas TA2 and TA3.

[0103] The base station control unit 212 determines whether the number of UEs 103 located in other detected tracking areas TA is equal to or greater than a predetermined number (step S406). The predetermined number may be any number. Information on the predetermined number is stored in the storage unit 202 in advance, for example.

[0104] If the number of UEs 103 located in other tracking area TAs is greater than or equal to a predetermined number, the base station control unit 212 determines Yes in step S406 and proceeds to step S407. In this case, the base station control unit 212 sends an instruction to all base stations 102 belonging to the updated tracking area TA (tracking area TA with zero UEs) to perform intermittent operation (step S407).

[0105] Each base station 102 that receives an instruction to perform intermittent operation performs intermittent operation based on that instruction. For example, each base station 102 alternates between periods of normal operation and periods of sleep for the first communication unit 303. As a result, each base station 102 can reduce power consumption compared to when it is always in normal operation.

[0106] If the number of UEs 103 located in other tracking area TAs is less than a predetermined number, the base station control unit 212 determines "No" in step S406 and proceeds to step S408. In this case, the base station control unit 212 sends an instruction to all base stations 102 belonging to the updated tracking area TA (tracking area TA with zero UEs) to stop their transmission function (step S408).

[0107] When each base station 102 receives an instruction to stop the transmission function, it stops the transmission function based on that instruction. For example, each base station 102 controls the function of the first communication unit 303 to be in sleep mode at all times. As a result, each base station 102 can reduce power consumption compared to when it is always in normal operation.

[0108] Now, let's assume that the number of UEs in tracking area TA1 has become zero because UE103 in idle mode has been detached. And let's assume that there are many more UE103s than a predetermined number in the other tracking areas TA2 and TA3. In this case, there is a high probability that the UE103s in the other tracking areas TA2 and TA3 will undergo cell reselection to tracking area TA1.

[0109] Therefore, if the base station control unit 212 determines Yes in step S409, it causes each base station 102 belonging to tracking area TA1 to operate intermittently. As a result, each base station 102 belonging to tracking area TA1 switches to a power-saving mode, but can quickly return to normal operation when a UE 103 located in another tracking area TA2 or TA3 undergoes cell reselection to tracking area TA1.

[0110] On the other hand, assume that the number of UE103s located in the other tracking areas TA2 and TA3 is less than a predetermined number. In other words, the number of UE103s located in the other tracking areas TA2 and TA3 is small. In this case, the probability of UE103s located in the other tracking areas TA2 and TA3 undergoing cell reselection to tracking area TA1 is lower than when the result in step S406 is determined to be Yes.

[0111] Therefore, if the base station control unit 212 determines No in step S409, it stops the transmission function of each base station 102 belonging to the tracking area TA1. As a result, each base station 102 belonging to the tracking area TA1 can switch to a power-saving mode that has a greater power consumption reduction effect than the power-saving mode when performing intermittent operation.

[0112] The base station control unit 212 determines whether there has been an attach request for an updated tracking area TA (a tracking area TA with zero UEs) (step S409). For example, if UE 103 sends an attach request to any of the base stations 102A to C belonging to a tracking area TA that has transitioned to power saving mode, the attach request is sent to the core network device 101. The base station control unit 212 may perform the determination in step S409 based on whether it has received the attach request.

[0113] If there is no attach request, the base station control unit 212 proceeds to step S410. In this case, the base station control unit 212 determines whether there is a cell reselection request for the updated tracking area TA (tracking area TA with zero UEs) (step S410).

[0114] For example, if UE 103 requests cell reselection from any of the base stations 102A to C belonging to the tracking area TA that has switched to power saving mode, the cell reselection request is transmitted to the core network device 101. The base station control unit 212 may perform the determination in step S410 based on whether it has received the cell reselection request.

[0115] If there is no cell reselection request, the base station control unit 212 returns to step S409. In other words, if the base station control unit 212 has not received either an attach request or a cell reselection request, it maintains the power saving mode for each base station 102 belonging to the updated tracking area TA (a tracking area TA with zero UEs).

[0116] If the base station control unit 212 determines Yes in step S409 or Yes in step S410, it proceeds to step S411. In this case, the base station control unit 212 sends an instruction to all base stations 102 belonging to the updated tracking area TA (tracking area TA with zero UEs) to return from power-saving mode to normal mode (step S411). Based on this instruction, each base station 102 returns from power-saving mode to normal mode. This completes the processing of the flowcharts in Figures 8 and 9.

[0117] In addition, the base station control unit 212 may, in step S407, transmit an instruction to some of the base stations 102 belonging to the updated tracking area TA (tracking area TA with zero UEs) to perform intermittent operation. Alternatively, the base station control unit 212 may transmit an instruction to some of the base stations 102 belonging to the updated tracking area TA (tracking area TA with zero UEs) to stop the transmission function.

[0118] Figure 10 is a flowchart showing an example of the processing flow of the base station 102 in the second embodiment. The control unit 301 of the base station 102 determines whether it has received an instruction from the core network device 101 (step S501).

[0119] If no instruction is received from the core network device 101, the control unit 301 determines "No" in step S501 and terminates the flowchart in Figure 10. If an instruction is received from the core network device 101, the control unit 301 determines whether the instruction is an instruction to stop the transmission function (transmission / reception stop instruction) (step S502). A transmission / reception stop instruction is the instruction transmitted by the core network device 101 in step S408.

[0120] If the received instruction is a transmission / reception stop instruction, the control unit 301 determines Yes in step S502 and proceeds to step S503. In this case, the control unit 301 stops the transmission and reception functions of its base station 102 and performs control to switch to power saving mode (first power saving mode) (step S503). As a result, the base station 102 switches to the first power saving mode.

[0121] If the received instruction is not a transmission / reception stop instruction, the control unit 301 determines No in step S502 and does not execute the process in step S503. Then, the control unit 301 determines whether the received instruction is an instruction to perform intermittent operation (intermittent operation instruction) (step S504).

[0122] If the received instruction is an intermittent operation instruction, the control unit 301 determines Yes in step S504 and proceeds to step S505. In this case, the control unit 301 controls its base station 102 to operate intermittently and transition to a power saving mode (second power saving mode) (step S505). As a result, the base station 102 transitions to the second power saving mode.

[0123] If the received instruction is not an intermittent operation instruction, the control unit 301 determines No in step S504 and does not execute the process in step S505. Then, the control unit 301 determines whether the received instruction is an instruction to stop the transmission function (transmission stop instruction) (step S506).

[0124] If the received instruction is a transmission stop instruction, the control unit 301 determines Yes in step S506 and proceeds to step S507. In this case, the control unit 301 stops the transmission function of its base station 102 and performs control to switch to power saving mode (third power saving mode) (step S507). As a result, the base station 102 switches to the third power saving mode.

[0125] If the received instruction is not a transmission stop instruction, or after executing the process in step S507, the control unit 301 determines Yes in step S506 and proceeds to step S203. The processes in steps S203 to S205 are the same as in Figure 6.

[0126] Here, the first power saving mode is a power saving mode in which the base station 102 disables its transmission and reception functions, and therefore has the greatest power consumption reduction effect. The second power saving mode is a power saving mode of intermittent operation, and therefore has the lowest power consumption reduction effect. The third power saving mode is a power saving mode in which the base station 102 disables its transmission function, and therefore has a power consumption reduction effect that is lower than the first power saving mode but higher than the second power saving mode.

[0127] Figure 11 is a sequence chart showing an example of the processing flow of system 100 in the second embodiment. The sequence chart in Figure 11 is an example in which UE 103 sends a detach request. Each process from step S301 to S303 is the same as in Figure 7, so its explanation is omitted.

[0128] In step S303, the core network device 101 confirms that the number of UEs 103 in the updated tracking area TA (tracking area TA with zero UEs) has become zero. In this case, the core network device 101 determines whether to transition each base station 102 belonging to the updated tracking area TA (tracking area TA with zero UEs) to one of the first to third power saving modes, depending on the time period and the number of UEs 103 located in other tracking area TAs (step S601). Step S601 corresponds to steps S401 and S406 described above.

[0129] The core network device 101 transmits a power saving instruction to each base station 102 belonging to the updated tracking area TA (tracking area TA with zero UEs) to transition to a specified power saving mode (step S602). Each base station 102 transitions to a power saving mode in accordance with the received power saving instruction (step S603).

[0130] <Modification> In each of the above embodiments, the power saving mode transition control of multiple base stations belonging to a tracking area TA has been described. The tracking area TA described above does not have to be a tracking area TA, as long as it is an area managed by one or more base stations 102 connected to the core network device 101. For example, the above area may be a RAN (Radio Access Network) paging area.

[0131] This disclosure is not limited to the embodiments described above, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment. In addition, the processing order of the flowcharts described in the embodiments described above can be changed as much as possible.

[0132] The program that implements the functions of this embodiment is stored in a non-temporary recording medium such as a semiconductor medium, an optical recording medium, or a magneto-optical recording medium. For example, a non-volatile memory card may be used as the semiconductor medium. For example, a CD (Compact Dick) or DVD (Digital Versatile Disk) may be used as the optical recording medium or magneto-optical recording medium. Furthermore, the program may be supplied to a computer via any transmission medium capable of transmission.

Claims

1. A core network device comprising: a detection unit for detecting the number of UEs located within an area managed by a base station connected to the core network device, including the number of UEs in idle mode; and a base station control unit for performing a process to switch the base station to power-saving mode when the detected number of UEs becomes zero.

2. The core network device according to claim 1, wherein the area managed by the base station is a tracking area.

3. The core network device according to claim 1, wherein the area is composed of multiple base stations, and when it is detected that the number of UEs, including the idle UEs, located within the area has become zero, the base station control unit performs a process to switch all of the multiple base stations to power-saving mode.

4. The core network device according to claim 1, wherein the area is composed of multiple base stations, and when it is detected that the number of UEs, including the idle UE, located within the area has become zero, the base station control unit performs a process to switch one or more of the multiple base stations, excluding base stations within a predetermined distance from the edge of the area, to power-saving mode.

5. When it is detected that the number of UEs, including idle UEs, located within the area has become zero, the base station control unit controls some or all of the base stations in the area to switch to a first power-saving mode if the number of other UEs located in other areas other than the area is greater than or equal to a predetermined number, and controls some or all of the base stations in the area to switch to a second power-saving mode with lower power consumption than the first power-saving mode if the number of other UEs located in the other areas is less than a predetermined number, the core network device according to claim 1.

6. The core network device according to claim 1, wherein when it is detected that the number of UEs, including idle UEs, located within the area has become zero, and the current time is within a predetermined time period, the base station control unit performs control to switch all base stations in all areas, including the area, to a power-saving mode that stops transmitting and receiving.

7. The core network device according to claim 1, wherein the communication method of the core network device is local communication.

8. The core network device according to claim 1, wherein if the number of UEs located within the area, including UEs in idle mode, increases from zero, the base station control unit restores the base station in power-saving mode to normal mode.

9. A method for controlling a core network device, comprising: detecting the number of UEs located within an area managed by a base station connected to the core network device, including the number of UEs in idle mode; and, if the detected number of UEs becomes zero, performing a process to switch the base station to power-saving mode.

10. A base station comprising: a communication unit that receives a power saving instruction from the core network device when it is detected that the number of UEs located in the area managed by the base station connected to the core network device, including the number of UEs in idle mode, has become zero; and a control unit that performs processing to switch the base station to power saving mode when the power saving instruction is received.

11. The base station according to claim 10, wherein if the number of UEs located within the area, including UEs in idle mode, increases from zero, the control unit returns the base station from the power-saving mode to the normal mode.

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