Base station device and communication system

Abstract

Provided are a base station device and a communication system capable of smoothly switching a plurality of states, including a power saving state. This base station device comprises: a communication unit that, by switching between a normal communication state in which information communication with a terminal device can be executed and a non-normal communication state in which at least some information communication with the terminal device is restricted as compared to the normal communication state, can execute inter-base-station communication with a plurality of other base station devices that operate in either the normal communication state or the non-normal communication state; and a control unit that, when receiving selection information indicating that one other base station device among the plurality of other base station devices has been selected as a handover destination from the terminal device that is executing information communication with the host device, causes the communication unit to transmit, to the one other base station device selected as the handover destination, a first request signal requesting switching from the non-normal communication state to the normal communication state, on the basis of the selection information.

Description

Base station device and communication system

[0001] This application claims priority to Japanese Patent Application No. 2024-082985, filed May 22, 2024, the contents of which are incorporated herein by reference.

[0002] Currently, there are known techniques for reducing power consumption by putting a base station device into a power-saving state. For example, Non-Patent Document 1 discloses a technique in which a base station device transitions to a power-saving state when there are no terminals requiring communication within the communication area of ​​the base station device.

[0003] 3GPP TR 38.864 v18.1.0, “3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Study on network energy savings for NR (Release 18)”

[0004] When communication quality deteriorates, a mobile wireless communication terminal performs handover, which is an operation to switch the base station device with which it communicates. However, handover using a base station device in a power saving state has not been fully studied.

[0005] The present disclosure has been made in view of the above-mentioned problems, and an object of the present disclosure is to provide a base station apparatus and a communication system that are capable of smoothly switching between a plurality of states including a power saving state.

[0006] A base station device of one embodiment of the present disclosure comprises a communication unit capable of performing inter-base station communication with a plurality of other base station devices operating in either the normal communication state or the non-normal communication state by switching between a normal communication state in which information communication with a terminal device can be performed and a non-normal communication state in which at least a portion of information communication with the terminal device is restricted compared to the normal communication state, and a control unit that, when selection information indicating that one of the plurality of other base station devices has been selected as a handover destination is received from a terminal device currently performing information communication with the base station device, causes the communication unit to transmit a first request signal to the one other base station device selected as the handover destination, based on the selection information, requesting a switch from the non-normal communication state to the normal communication state.

[0007] A base station device of one embodiment of the present disclosure includes a control unit that, when there is no terminal device currently performing information communication with the base station device, switches the operating state of the base station device from a normal communication state in which information communication with the terminal device can be performed to a non-normal communication state in which at least a portion of information communication with the terminal device is restricted compared to the normal communication state.

[0008] A communication system according to one embodiment of the present disclosure includes a base station device that is currently performing information communication with a terminal device, and a plurality of other base station devices that are not currently performing information communication with the terminal device, and the base station device and the plurality of other base station devices are capable of performing base station-to-base station communication with each other, wherein each of the plurality of other base station devices performs operation in either the normal communication state or the non-normal communication state by switching between a normal communication state in which information communication with the terminal device can be performed, and a non-normal communication state in which at least a portion of information communication with the terminal device is restricted compared to the normal communication state, and when the base station device receives selection information from the terminal device that is currently performing information communication with the base station device, indicating that one of the plurality of other base station devices has been selected as a handover destination, the base station device transmits a first request signal to the one other base station device selected as the handover destination, requesting switching from the non-normal communication state to the normal communication state, based on the selection information.

[0009] According to the present disclosure, it is possible to provide a base station device and a communication system that are capable of smoothly switching between a plurality of states including a power saving state.

[0010] FIG. 1 is a schematic diagram showing a communication system according to a first embodiment. FIG. 2 is a diagram schematically showing a communication state when the base station device shown in FIG. 1 is in a power saving state. FIG. 3 is a functional block diagram showing an example of a schematic configuration of the base station device shown in FIG. 1. FIG. 4 is a functional block diagram showing an example of a schematic configuration of a terminal device shown in FIG. 1. FIG. 5 is a sequence diagram showing an example of a processing procedure executed by the communication system of FIG. 1. FIG. 6 is a flowchart showing an example of a processing procedure executed by a first base station device shown in FIG. 1. FIG. 7 is a sequence diagram showing an example of a processing procedure executed by a communication system according to a second embodiment. FIG. 8 is a schematic diagram showing a communication system according to a third embodiment. FIG. 9 is a sequence diagram showing an example of a processing procedure executed by the communication system of FIG. 8. FIG. 10 is a sequence diagram showing an example of a processing procedure executed by a communication system according to a fourth embodiment. FIG. 11 is a flowchart showing an example of a processing executed by a base station device of a communication system according to a fifth embodiment.

[0011] Hereinafter, several embodiments of the present disclosure will be described with reference to the drawings. In the drawings, identical or equivalent components are denoted by the same reference numerals, and redundant descriptions of identical or equivalent components will be omitted as appropriate.

[0012] [First Embodiment] Fig. 1 is a schematic diagram of a communication system 1 according to a first embodiment. As shown in Fig. 1, the communication system 1 includes a first base station device 10A, a second base station device 10B, and a terminal device 20. However, the number of base station devices included in the communication system 1 is not limited to two, and may be any number of devices. In this embodiment, when there is no need to distinguish between the first base station device 10A and the second base station device 10B, they are collectively referred to as "base station device 10." Furthermore, the number of terminal devices 20 included in the communication system 1 is not limited to one, and may be multiple.

[0013] The base station device 10 provides a communication network using a predetermined wireless communication method. The predetermined wireless communication method is, for example, a communication method using a fifth-generation mobile communication system (5G system). Specifically, the base station device 10 is a base station that applies the NR (New Radio) standard, which is a radio access technology (RAT) for 5G cellular mobile communication systems. The base station device 10 is connected to a 5G core network (not shown) so that information can be communicated.

[0014] The terminal device 20 is a mobile wireless communication terminal capable of communicating with the base station device 10. The terminal device 20 performs data communication with the base station device 10 using a communication network provided by the base station device 10. The terminal device 20 is, for example, a router terminal, a smartphone, or a tablet terminal.

[0015] In this embodiment, the base station device 10 operates in one of a plurality of states by switching between the plurality of states. In this embodiment, the base station device 10 operates in one of the normal communication state and the abnormal communication state by switching between the normal communication state and the abnormal communication state. In the first to fourth embodiments, an example will be described in which the base station device 10 switches from the abnormal communication state to the normal communication state.

[0016] The normal communication state is a state in which information communication (data communication) with the terminal device 20 can be performed. In the normal communication state, the base station device 10 constantly transmits a reference signal at regular intervals, for example. The reference signal is received by the terminal device 20 and is used by the terminal device 20 to determine whether or not to perform a handover. When the terminal device 20 performs a handover, the reference signal is also used to determine the base station device 10 to which the terminal device 20 should perform the handover.

[0017] The non-normal communication state is a state in which, compared to the normal communication state, at least a part of information communication with the terminal device 20 is restricted. The non-normal communication state may include one or more states depending on the degree of restriction on information communication.

[0018] For example, the non-normal communication state includes a power saving state in which information communication with the terminal device 20 is periodically alternately enabled and disabled. For example, when the base station device 10 is in the power saving state, as shown in FIG. 2 , the base station device 10 periodically alternates between a state in which data transmission and reception with the terminal device 20 is enabled and a state in which data transmission and reception is disabled. When data transmission and reception with the terminal device 20 is enabled, the base station device 10 performs data communication with the terminal device 20 and transmits a reference signal. On the other hand, when data transmission and reception with the terminal device 20 is disabled, the base station device 10 cannot perform data communication with the terminal device 20 or transmit a reference signal. In this way, by periodically disabling information communication in the power saving state, some of the information communication by the base station device 10 is restricted, while power consumption by the base station device 10 can be reduced. In this embodiment, a case where the non-normal communication state is the power saving state will be described.

[0019] The base station device 10 can also perform inter-base station communication, which is data communication with other base station devices 10. Therefore, in the example shown in FIG. 1, the first base station device 10A and the second base station device 10B can perform inter-base station communication with each other, for example, as indicated by the dashed arrows. Inter-base station communication can be performed regardless of whether the base station device 10 is in a normal communication state or an abnormal communication state. In other words, the normal communication state and the abnormal communication state indicate states when the base station device 10 performs communication with the terminal device 20. The base station device 10 can transmit and receive various data through inter-base station communication.

[0020] Fig. 3 is a functional block diagram showing an example of a schematic configuration of the base station device 10 shown in Fig. 1. As shown in Fig. 3, the base station device 10 includes, as functional units, a control unit 11, a storage unit 12, and a communication unit 13.

[0021] The control unit 11 controls and manages the entire base station device 10, including each functional unit of the base station device 10. The control unit 11 includes at least one processor. The control unit 11 is configured with a processor such as a CPU (Central Processing Unit) that executes a program that defines a control procedure, or a dedicated processor specialized for processing each function.

[0022] In this embodiment, the control unit 11 controls communication by the communication unit 13. For example, the control unit 11 controls communication between base stations by the communication unit 13, and controls communication with the terminal device 20. For example, the control unit 11 transmits various signals when the terminal device 20 executes handover. Specific examples of processing executed by the control unit 11 will be described later.

[0023] The storage unit 12 is a storage medium capable of storing programs and data. The storage unit 12 may be configured, for example, as a semiconductor memory or a magnetic memory. The storage unit 12 stores, for example, programs for operating the base station device 10.

[0024] The communication unit 13 transmits and receives data (radio signals) by wireless communication with the terminal device 20 via the antenna. The radio signals are used for data communication with the terminal device 20. By transmitting and receiving data, data communication between the base station device 10 and the terminal device 20 is performed. The control unit 11 performs predetermined processing on the data received by the communication unit 13. The predetermined processing is well-known processing including, for example, AD conversion and Fourier transform. Furthermore, the communication unit 13 transmits and receives data (radio signals) by inter-base station communication with other base station devices 10 via the antenna. By transmitting and receiving data, inter-base station communication is performed.

[0025] Fig. 4 is a functional block diagram showing an example of a schematic configuration of the terminal device 20 shown in Fig. 1. As shown in Fig. 4, the terminal device 20 includes, as functional units, a control unit 21, a storage unit 22, a communication unit 23, a display unit 24, and an input unit 25.

[0026] The control unit 21 controls and manages the entire terminal device 20, including each functional unit of the terminal device 20. The control unit 21 includes at least one processor. The control unit 21 is configured with a processor such as a CPU that executes a program that defines a control procedure, or a dedicated processor specialized for processing each function.

[0027] The control unit 21 determines whether to perform a handover based on the communication quality of the base station device 10. The communication quality is determined based on the strength of the signal received from the base station device 10. If the communication quality satisfies a predetermined condition, the control unit 21 determines to perform a handover and determines the base station device 10 as the handover destination. For example, if the strength of the signal received from the base station device 10 currently performing information communication (i.e., currently performing data communication) falls below a predetermined strength, the control unit 21 determines to perform a handover to another base station device 10. The control unit 21 can determine the base station device 10 as the handover destination based on the reception strength of the reference signal received from each base station device 10. Alternatively, if the base station device 10 with the highest reception strength of the reference signal among multiple base station devices 10 is different from the base station device 10 currently performing information communication, the control unit 21 determines to perform a handover to the base station device 10 with the highest reception strength of the reference signal. The control unit 21 can perform a handover and determine the base station device 10 as the handover destination using any method other than the method described here.

[0028] When the control unit 21 determines the base station device 10 as the handover destination, it generates selection information and transmits the selection information to the base station device 10 currently performing information communication. The selection information is information indicating that one of multiple base station devices 10 other than the base station device 10 currently performing information communication has been selected as the handover destination. Therefore, the selection information includes information that can identify the base station device 10 as the handover destination.

[0029] The storage unit 22 is a storage medium capable of storing programs and data. The storage unit 22 may be configured, for example, as a semiconductor memory or a magnetic memory. The storage unit 22 stores, for example, programs for operating the terminal device 20.

[0030] The communication unit 23 transmits and receives data by wireless communication via an antenna. By transmitting and receiving data, data communication is performed between the base station device 10 and the terminal device 20. The control unit 21 performs predetermined processing on the data received by the communication unit 23. The predetermined processing is well-known processing including, for example, AD conversion and Fourier transform. The communication unit 23 also transmits a wireless signal generated by the control unit 21 from the antenna. For example, the communication unit 23 transmits selection information to the base station device 10.

[0031] The display unit 24 includes a display device such as a liquid crystal display (LCD), an organic electroluminescence panel (EL panel), or an inorganic electroluminescence panel. The display unit 24 displays characters, images, symbols, figures, and the like. The display unit 24 may be configured as a touchscreen display that not only has a display function but also a touchscreen function. In this case, the touchscreen detects contact with the user's finger, a stylus pen, or the like of the terminal device 20.

[0032] The input unit 25 accepts operation input from the user of the terminal device 20. The input unit 25 is configured by, for example, operation buttons (operation keys). The input unit 25 may be configured by a touch screen, and an input area for accepting operation input from the user may be displayed on a part of the display device that is the display unit 24, thereby accepting touch operation input from the user.

[0033] Next, an example of processing executed in the communication system 1 will be described. FIG. 5 is a sequence diagram showing an example of processing procedures executed by the communication system 1 of FIG. 1. Specifically, FIG. 5 illustrates an example of processing executed in the communication system 1 when, for example, as shown in FIG. 1, a terminal device 20 moves from the range of the cell of a first base station device 10A into the range of the cell of a second base station device 10B, thereby performing a handover from the first base station device 10A to the second base station device 10B. Therefore, at the start of the sequence of FIG. 5, the terminal device 20 is performing information communication with the first base station device 10A, for example, as indicated by the arrow in FIG. 1. In this specification, the base station device 10 with which the terminal device 20 is performing information communication is referred to as a "serving cell," and the base station device 10 as the handover destination determined by the terminal device 20 is also referred to as a "target cell." Therefore, at the start of FIG. 5, the first base station device 10A is the serving cell. Also, it is assumed here that the second base station device 10B is in a power saving state (non-normal communication state) at the start of the sequence in FIG.

[0034] For example, the first base station device 10A transmits a reference signal to the terminal device 20 (step S11). The first base station device 10A transmits the reference signal, for example, at regular intervals. The terminal device 20 receives the reference signal from the first base station device 10A.

[0035] Similarly, the second base station device 10B transmits a reference signal to the terminal device 20 (step S12). Here, since the second base station device 10B is in a power saving state, it does not always transmit reference signals at regular intervals, but since it periodically becomes capable of performing information communication with the terminal device 20, it transmits the reference signal at a timing when it is capable of performing information communication with the terminal device 20. The terminal device 20 receives the reference signal transmitted at this timing.

[0036] Note that the first base station device 10A and the second base station device 10B do not necessarily transmit reference signals in the order and at the timing shown in Fig. 5, but transmit reference signals at appropriate timings controlled by the control unit 11 of each base station device 10. Therefore, the first base station device 10A and the second base station device 10B may transmit reference signals at appropriate timings in the sequence shown in Fig. 5.

[0037] The terminal device 20 performs information communication with the first base station device 10A, which is the serving cell, and determines whether a handover is necessary, i.e., whether to perform a handover (step S13). For example, the terminal device 20 determines whether a handover is necessary based on the reception strength of reference signals received from the first base station device 10A and the second base station device 10B.

[0038] Assume that the terminal device 20 determines, as a result of determining whether or not a handover is necessary, to perform a handover from the first base station device 10A to the second base station device 10B. That is, the terminal device 20 determines the second base station device 10B as the target cell. In this case, the terminal device 20 generates selection information indicating that the handover destination is the second base station device 10B, and transmits the selection information to the first base station device 10A with which information communication is being performed (step S14).

[0039] When the first base station device 10A receives the selection information from the terminal device 20 that is currently communicating with the first base station device 10A, the first base station device 10A transmits a first request signal via inter-base station communication to one other base station device (i.e., the second base station device 10B, which is the target cell in this case) that has been selected as the handover destination based on the selection information (step S15). The first request signal is a signal that requests switching from a non-normal communication state (here, a power saving state) to a normal communication state. The first base station device 10A transmits the first request signal to the handover destination base station device 10 (here, the second base station device 10B) indicated in the selection information.

[0040] Upon receiving the first request signal, the second base station device 10B transitions its operation from a non-normal communication state (power saving state) to a normal communication state (step S16). This enables the second base station device 10B to perform information communication with the terminal device 20. If the second base station device 10B is in a power saving state, there will be periodic periods during which information communication between the second base station device 10B and the terminal device 20 is not possible, potentially preventing the terminal device 20 from performing a handover to the second base station device 10B. However, by transitioning the second base station device 10B to a normal communication state as shown in the flow chart of FIG. 5 before performing a handover, this problem can be prevented. This allows the communication system 1 to perform a smooth handover. Furthermore, because the second base station device 10B is in a non-normal communication state before performing a handover, power consumption by the second base station device 10B can be reduced when not necessary.

[0041] When the second base station device 10B switches its operation to the normal communication state in step S14, it transmits a response signal to the first request signal to the first base station device 10A (step S17). The response signal may include information indicating that the operation has been switched to the normal communication state.

[0042] When the first base station device 10A receives the response signal transmitted by the second base station device 10B in step S15, it transmits an execution signal to the terminal device 20 currently performing information communication with the first base station device 10A to cause it to perform a handover (step S18).

[0043] Upon receiving the execution signal, the terminal device 20 executes handover (step S19). The handover may be executed by a known procedure. In this way, by transmitting the execution signal when the first base station device 10A receives the response signal, the terminal device 20 can be made to execute handover after the second base station device 10B, which is the handover destination, has completed preparation for handover, i.e., transition to a normal communication state. This prevents the terminal device 20 from executing handover before the second base station device 10B, which is the handover destination, is ready, and therefore allows the handover to be performed smoothly.

[0044] Note that if the second base station device 10B is in a normal communication state rather than an abnormal communication state when it receives the first request signal from the first base station device 10A (step S15), it does not need to transition its operation to the normal communication state. That is, in this case, the second base station device 10B does not need to execute step S16. Therefore, if the second base station device 10B is operating in an abnormal communication state when it receives the first request signal from the first base station device 10A, it only needs to switch its operation to the normal communication state. In this way, the first base station device 10A does not recognize whether the second base station device 10B is operating in a normal communication state or an abnormal communication state, and therefore transmits the first request signal in step S15 regardless of the operating state of the second base station device 10B. When the second base station device 10B receives the first request signal, it can execute different processes depending on whether it is operating in a normal communication state or an abnormal communication state.

[0045] If the second base station device 10B is operating in a normal communication state when it receives the first request signal from the first base station device 10A, it may transmit a response signal to the first base station device 10A in response to the first request signal without switching its operation (step S17). That is, the second base station device 10B transmits a response signal to the first base station device 10A regardless of whether it has transitioned from a non-normal communication state to a normal communication state in step S16 or whether it has been operating in a normal communication state before receiving the first request signal and has not transitioned its operation state. In this case, the response signal may include information indicating that the second base station device 10B is in a normal communication state. By transmitting an execution signal when receiving the response signal, the first base station device 10A can transmit an execution signal to the terminal device 20 in a state in which handover to the second base station device 10B is executable, regardless of the original operation state of the second base station device 10B.

[0046] Fig. 6 is a flowchart showing an example of processing executed by the first base station device 10A shown in Fig. 1. In other words, Fig. 6 is a diagram showing details of processing executed by the first base station device 10A in the sequence of Fig. 5. Note that, although not shown in Fig. 6, the first base station device 10A transmits a reference signal at regular intervals while executing the flow shown in Fig. 6.

[0047] The control unit 11 of the first base station device 10A determines whether or not the first base station device 10A has received selection information from the terminal device 20 that is currently performing information communication with the first base station device 10A (step S21).

[0048] If the control unit 11 determines that the first base station device 10A has not received the selection information (No in step S21), it repeats step S21 until it determines that the first base station device 10A has received the selection information.

[0049] If the control unit 11 determines that the first base station device 10A has received the selection information (Yes in step S21), it transmits a first request signal from the communication unit 13 to the base station device 10 to which the selection information indicates the handover destination (step S22).

[0050] Next, the control unit 11 determines whether or not a response signal to the first request signal transmitted by the first base station device 10A in step S22 has been received (step S23).

[0051] If the control unit 11 determines that the first base station device 10A has not received a response signal (No in step S23), it repeats step S23 until it determines that the first base station device 10A has received a response signal.

[0052] When the control unit 11 determines that the first base station device 10A has received the response signal (Yes in step S23), the control unit 11 transmits an execution signal to the terminal device 20 from the communication unit 13 (step S24).

[0053] In this way, the first base station device 10A transmits a first request signal to the second base station device 10B selected as the handover destination, requesting switching from a non-normal communication state to a normal communication state. As a result, when the terminal device 20 executes handover, the second base station device 10B, which is operating in either the non-normal communication state or the normal communication state, can be transitioned to a normal communication state in which information communication with the terminal device 20 can be executed. Therefore, the first base station device 10A executes handover smoothly in the communication system 1. That is, in the first embodiment, it is possible to smoothly execute switching between multiple states, including a power saving state, for the base station device 10.

[0054] [Second Embodiment] Next, a second embodiment will be described. The configuration of a communication system 1 according to the second embodiment is the same as the configuration of the communication system 1 according to the first embodiment described with reference to FIG. 1. That is, the communication system 1 according to the second embodiment includes a first base station device 10A, a second base station device 10B, and a terminal device 20, similar to the first embodiment. Hereinafter, the second embodiment will be described, focusing on the differences from the first embodiment, while omitting a description of the same aspects as the first embodiment as appropriate.

[0055] In the second embodiment, the non-normal communication state includes a dormant state in addition to the power saving state described in the first embodiment. The dormant state is a state in which the base station device 10 cannot execute information communication with the terminal device 20. When the base station device 10 is in the dormant state, it cannot execute information communication with the terminal device 20, and therefore cannot perform data communication with the terminal device 20 or transmit a reference signal. In this way, by making information communication impossible in the dormant state, information communication by the base station device 10 is restricted, while power consumption by the base station device 10 can be further reduced compared to the power saving state. In the second embodiment, when the base station device 10 is in a non-normal communication state, it operates in either the power saving state or the dormant state.

[0056] In the second embodiment, the storage unit 12 of each base station device 10 stores information relating to the installation locations of other base station devices 10 (hereinafter also referred to as "base station location information"). For example, the storage unit 12 of the base station device 10 stores identification information that uniquely identifies the other base station device 10 in association with the location of the base station device 10. In this embodiment, the storage unit 12 of the first base station device 10A stores the base station location information of the second base station device 10B. Similarly, the storage unit 12 of the second base station device 10B stores the base station location information of the first base station device 10A.

[0057] In the second embodiment, the serving cell receives, from a terminal device 20 that is performing information communication with the serving cell, terminal location information indicating the location of the terminal device 20. When the control unit 11 of the serving cell receives the terminal location information, the control unit 11 selects, from among a plurality of other base station devices 10, a candidate base station device that is a candidate for the handover destination of the terminal device 20, based on the terminal location information and the base station location information stored in the storage unit 12, and causes the communication unit 13 to transmit a second request signal to the candidate base station device, requesting that the candidate base station device switch from a dormant state to a power saving state.

[0058] 7 is a sequence diagram showing an example of a processing procedure executed by the communication system 1 according to the second embodiment. At the start of the sequence in FIG. 7, the terminal device 20 is performing information communication with the first base station device 10A, for example, as indicated by the arrow in FIG. 1. That is, the first base station device 10A is functioning as a serving cell. Also, at the start of the sequence in FIG. 7, the second base station device 10B is in a dormant state (a non-normal communication state).

[0059] For example, the first base station device 10A transmits a reference signal to the terminal device 20 (step S11). The first base station device 10A transmits the reference signal, for example, at regular intervals. The terminal device 20 receives the reference signal from the first base station device 10A.

[0060] On the other hand, the second base station device 10B is in a dormant state and is therefore unable to perform any information communication with the terminal device 20, nor does it transmit any reference signal. Therefore, in the example shown in Fig. 7, the terminal device 20 receives reference signals only from the first base station device 10A, and does not receive reference signals from the second base station device 10B.

[0061] The terminal device 20 acquires terminal location information and transmits the terminal location information to the first base station device 10A functioning as a serving cell (step S31). The terminal device 20 can acquire the terminal location information using a known method, for example, using a Global Positioning System (GPS). The terminal device 20, for example, periodically acquires the terminal location information and transmits it to the serving cell.

[0062] When the first base station device 10A, functioning as a serving cell, acquires the terminal location information, it selects a candidate base station device that is a candidate handover destination for the terminal device 20 based on the terminal location information and the base station location information (step S32). The first base station device 10A uses a predetermined algorithm, for example, based on the terminal location information, to select a base station device 10 that can be the next handover destination for the terminal device 20 as a candidate base station device. As an example, the first base station device 10A selects a base station device 10 whose location indicated by the base station location information is within a predetermined distance from the location indicated by the terminal location information as a candidate base station device. However, the first base station device 10A is not limited to this, and can select a candidate base station device that is a candidate handover destination for the terminal device 20 using any appropriate method. The number of selected candidate base station devices is not limited to one, and may be multiple. Here, it is assumed that the second base station device 10B is selected as the candidate base station device.

[0063] The first base station device 10A transmits, via inter-base station communication, a second request signal to the candidate base station device selected in step S32, requesting that the candidate base station device switch from a dormant state to a power saving state (step S33). In this case, since the second base station device 10B is selected as the candidate base station device, the first base station device 10A transmits the second request signal to the second base station device 10B. If multiple candidate base station devices are selected, the first base station device 10A transmits the second request signal to all of the selected candidate base station devices.

[0064] When the second base station device 10B receives the second request signal from the first base station device 10A, it transitions its operation from a dormant state to a power saving state based on the second request signal (step S34). After transitioning to the power saving state, the second base station device 10B periodically becomes capable of performing information communication with the terminal device 20, and therefore transmits a reference signal at a timing when the second base station device 10B is capable of performing information communication with the terminal device 20. Therefore, after step S34 is executed, the communication system 1 can execute processing similar to the sequence described with reference to FIG.

[0065] When the second base station device 10B receives the second request signal and transitions to a power saving state, the second base station device 10B may transmit a response signal to the second request signal to the first base station device 10A. In this case, the response signal may include information indicating that the operation has been switched to the power saving state.

[0066] Furthermore, if the second base station device 10B is operating in a power saving state or a normal communication state when it receives the second request signal, it does not need to transition its operation in step S34. Even in this case, the second base station device 10B may transmit a response signal to the second request signal to the first base station device 10A, and the response signal in this case may include information indicating that the second base station device 10B is in a dormant state.

[0067] As described above, in the second embodiment, a second request signal is transmitted from the serving cell to a base station device 10 that can be a candidate for the handover destination, in accordance with the location information of the terminal device 20. The base station device 10 that receives the second request signal transitions its operation from a hibernation state to a power-saving state based on the second request signal. By transitioning the base station device 10 that can be the next handover destination from a hibernation state to a power-saving state in advance in this manner, the base station device 10 that can be the handover destination can be placed in a state in which it can perform information communication with the terminal device 20 at least partially, thereby allowing the handover to be performed smoothly thereafter.

[0068] In the second embodiment, the terminal device 20 may transmit, to the serving cell, in addition to the terminal location information, movement direction information indicating the movement direction of the terminal device 20. That is, the terminal device 20 may transmit the terminal location information and the movement direction information to the first base station device 10A in step S31 of Fig. 7. The movement direction information can be acquired by the terminal device 20 using a known technology such as GPS, for example.

[0069] When the first base station device 10A receives the terminal location information and the moving direction information, it selects a candidate base station device based on the terminal location information, the moving direction information, and the base station location information. That is, the first base station device 10A selects a candidate base station device that can be a handover destination, further taking into account the direction in which the terminal device 20 is moving based on the moving direction information. This allows the first base station device 10A to select a candidate base station device that can be a handover destination with higher accuracy.

[0070] [Third Embodiment] Next, a third embodiment will be described. FIG. 8 is a schematic diagram of a communication system 2 according to the third embodiment. As shown in FIG. 8, the communication system 2 includes a first base station device 10A, a second base station device 10B, a third base station device 10C, and a terminal device 20. However, the number of base station devices included in the communication system 2 is not limited to three, and may be three or more. In this embodiment, when the first base station device 10A, the second base station device 10B, and the third base station device 10C are not to be distinguished from each other, they will be collectively referred to as the "base station device 10." Below, the third embodiment will be described, focusing on the differences from the first embodiment, while omitting explanations of the same aspects as the first embodiment as appropriate. Note that the specific configurations of the base station device 10 and the terminal device 20 are the same as those in the first embodiment.

[0071] In the third embodiment, the power saving state includes a first power saving state and a second power saving state. In the first power saving state and the second power saving state, the base station device 10 periodically alternates between a state in which information communication with the terminal device 20 is executable and a state in which information communication with the terminal device 20 is not executable. In the second power saving state, the proportion of times when information communication with the terminal device 20 is not executable is greater than in the first power saving state. For example, if the base station device 10 periodically alternates between a state in which information communication with the terminal device 20 is executable and a state in which information communication with the terminal device 20 is not executable in the first power saving state as shown in FIG. 2 , in the second power saving state, the period of time when information communication with the terminal device 20 is executable is shorter and / or the period of time when information communication with the terminal device 20 is executable is longer. As a result, the proportion of times when information communication with the terminal device 20 is executable is smaller in the second power saving state than in the first power saving state, but power consumption by the base station device 10 can be reduced accordingly. In the third embodiment, the base station device 10 operates in either the first power saving state or the second power saving state when in a non-normal communication state.

[0072] In the third embodiment, the storage unit 12 of each base station device 10 stores information about base station devices adjacent to the base station device itself (hereinafter also referred to as "adjacent base station information"). Whether a base station device is adjacent to the base station device itself is determined as appropriate, for example, by a carrier that provides the communication system 2, and the storage unit 12 stores identification information that uniquely identifies the base station device 10 adjacent to the base station device itself as the adjacent base station information.

[0073] In the example shown in Figure 8, the memory unit 12 of the first base station device 10A stores identification information of the second base station device 10B as neighboring base station information, the memory unit 12 of the second base station device 10B stores identification information of the first base station device 10A and the third base station device 10C as neighboring base station information, and the memory unit 12 of the third base station device 10C stores identification information of the second base station device 10B as neighboring base station information.

[0074] In the third embodiment, when the target cell receives the first request signal from the serving cell, the target cell transmits a request signal (herein referred to as a "third request signal") to a base station device adjacent to the target cell, requesting that the base station device switch from the second power saving state to the first power saving state, based on the adjacent base station information. Here, the base station device adjacent to the target cell is also referred to as a "neighbor cell" hereinafter.

[0075] FIG. 9 is a sequence diagram showing an example of a processing procedure executed by the communication system 2 of FIG. 8 . Specifically, FIG. 9 illustrates an example of processing executed in the communication system 2 when, for example, as shown in FIG. 8 , the terminal device 20 moves from the range of the cell of the first base station device 10A to the range of the cell of the second base station device 10B, thereby performing a handover from the first base station device 10A to the second base station device 10B. Therefore, at the start of the sequence of FIG. 9 , the terminal device 20 is performing information communication with the first base station device 10A, for example, as indicated by the arrow in FIG. 1 . That is, at the start of the flow of FIG. 9 , the first base station device 10A is the serving cell. Also, at the start of the sequence of FIG. 9 , the second base station device 10B is in the first power saving state, and the third base station device 10C is in the second power saving state.

[0076] For example, the first base station device 10A transmits a reference signal to the terminal device 20 (step S11). The first base station device 10A transmits the reference signal, for example, at regular intervals. Similarly, the second base station device 10B transmits a reference signal to the terminal device 20 (step S12). Here, since the second base station device 10B is in the first power saving state, it does not always transmit the reference signal at regular intervals. However, since it periodically becomes capable of performing information communication with the terminal device 20, it transmits the reference signal at a timing when it is capable of performing information communication with the terminal device 20. Similarly, the third base station device 10C transmits a reference signal to the terminal device 20 (step S41). Since the third base station device 10C is in the second power saving state, the interval at which the third base station device 10C transmits a reference signal to the terminal device 20 is longer than the interval at which the second base station device 10B, which is in the first power saving state, transmits a reference signal to the terminal device 20. The terminal device 20 receives the transmitted reference signal.

[0077] The terminal device 20 performs information communication with the first base station device 10A, which is the serving cell, and determines whether a handover is necessary, i.e., whether to perform a handover (step S13). For example, the terminal device 20 determines whether a handover is necessary based on the reception strength of reference signals received from the first base station device 10A, the second base station device 10B, and the third base station device 10C.

[0078] Assume that the terminal device 20 determines, as a result of determining whether or not a handover is necessary, to perform a handover from the first base station device 10A to the second base station device 10B. That is, the terminal device 20 determines the second base station device 10B as the target cell. In this case, the terminal device 20 generates selection information indicating that the handover destination is the second base station device 10B, and transmits the selection information to the first base station device 10A with which information communication is being performed (step S14).

[0079] When the first base station device 10A receives the selection information from the terminal device 20 that is performing information communication with the first base station device 10A, the first base station device 10A transmits a first request signal to the second base station device 10B that has been selected as the handover destination based on the selection information through inter-base station communication (step S15). The first request signal is a signal that requests switching from a non-normal communication state (here, the first power saving state) to a normal communication state.

[0080] When the second base station device 10B receives the first request signal, it transitions its operation from the non-normal communication state (first power saving state) to the normal communication state (step S16). As a result, the second base station device 10B becomes able to perform information communication with the terminal device 20.

[0081] Furthermore, the second base station device 10B transmits a third request signal to the neighbor cell requesting a switch from the second power saving state to the first power saving state based on the neighboring base station information stored in the storage unit 12 (step S42). In this example, the neighbor cells of the second base station device 10B are the first base station device 10A and the third base station device 10C, and therefore the second base station device 10B may transmit the third request signal to the first base station device 10A and the third base station device 10C. However, because the first base station device 10A is the serving cell, the second base station device 10B may transmit the third request signal only to neighbor cells excluding the serving cell, that is, in this case, the third base station device 10C.

[0082] Upon receiving the third request signal, the third base station device 10C transitions its operation from the second power saving state to the first power saving state (step S43), thereby increasing the proportion of times that the third base station device 10C is in a state in which it can perform information communication with the terminal device 20.

[0083] The second base station device 10B further transmits a response signal to the first base station device 10A in response to the first request signal (step S17). When the first base station device 10A receives the response signal, it transmits an execution signal to the terminal device 20 that is performing information communication with the first base station device 10A to cause the terminal device 20 to perform handover (step S18). Upon receiving the execution signal, the terminal device 20 performs handover (step S19).

[0084] As described above, in the third embodiment, the target cell transmits a third request signal to the neighbor cell requesting switching from the second power saving state to the first power saving state. The neighbor cell may become the next handover destination after the target cell becomes the serving cell through handover. Therefore, by transitioning the neighbor cell from the second power saving state to the first power saving state and increasing the proportion of the state in which information communication with the terminal device 20 can be performed, the next handover can be performed more smoothly.

[0085] [Fourth Embodiment] Next, a fourth embodiment will be described. The configuration of a communication system 2 according to the fourth embodiment is the same as the configuration of the communication system 1 according to the third embodiment described with reference to FIG. 8. That is, like the third embodiment, the communication system 2 according to the fourth embodiment includes a first base station device 10A, a second base station device 10B, a third base station device 10C, and a terminal device 20. Hereinafter, the fourth embodiment will be described, focusing on the differences from the third embodiment, while omitting a description of the same aspects as the third embodiment as appropriate.

[0086] In the fourth embodiment, the non-normal communication state includes a power saving state and a dormant state. The power saving state and the dormant state are the states described in the first and second embodiments, respectively. In the fourth embodiment, when the base station device 10 is in a non-normal communication state, the base station device 10 operates in either the power saving state or the dormant state.

[0087] In the fourth embodiment, the storage unit 12 of each base station device 10 stores neighboring base station information. In the fourth embodiment, when the target cell receives the first request signal from the serving cell, the target cell transmits a request signal (herein referred to as a "fourth request signal") to a base station device adjacent to the target cell, requesting that the base station device switch from a dormant state to a power saving state, based on the neighboring base station information.

[0088] Fig. 10 is a sequence diagram showing an example of a processing procedure executed by the communication system 2 according to the fourth embodiment. Specifically, Fig. 10 shows an example of processing executed when a handover is performed from a first base station device 10A to a second base station device 10B in the communication system 2. At the start of the flow in Fig. 10, the first base station device 10A is the serving cell. Also, at the start of the sequence in Fig. 10, it is assumed that the second base station device 10B is in a power saving state and the third base station device 10C is in a dormant state.

[0089] 10 , steps S11 to S16 are the same as those in the third embodiment. However, unlike the third embodiment, the third base station device 10C is in a dormant state and therefore does not transmit a reference signal to the terminal device 20. Therefore, in the fourth embodiment, the third base station device 10C does not transmit a reference signal, as in step S41 in the third embodiment, until it transitions to a power saving state.

[0090] When the second base station device 10B transitions to the normal communication state based on the first request signal in step S15, it transmits a fourth request signal to the neighbor cell based on the neighbor base station information stored in the storage unit 12, requesting that the neighbor cell switch from the dormant state to the power saving state (step S44). As described in the third embodiment, the second base station device 10B may transmit the fourth request signal only to the neighbor cell excluding the serving cell, that is, the third base station device 10C in this case.

[0091] Upon receiving the fourth request signal, the third base station device 10C transitions its operation from the hibernation state to the power saving state (step S45), thereby enabling the third base station device 10C to periodically perform information communication with the terminal device 20.

[0092] The second base station device 10B further transmits a response signal to the first base station device 10A in response to the first request signal (step S17). When the first base station device 10A receives the response signal, it transmits an execution signal to the terminal device 20 that is performing information communication with the first base station device 10A to cause the terminal device 20 to perform handover (step S18). Upon receiving the execution signal, the terminal device 20 performs handover (step S19).

[0093] As described above, in the fourth embodiment, the target cell transmits a fourth request signal to the neighbor cell requesting that the neighbor cell switch from the dormant state to the power saving state. The neighbor cell may become the next handover destination after the target cell becomes the serving cell through handover. Therefore, by transitioning the neighbor cell from the dormant state to the power saving state and enabling information communication with the terminal device 20, the next handover can be executed more smoothly.

[0094] [Fifth Embodiment] In the fifth embodiment, an example will be described in which a base station device 10 is switched from a normal communication state to a non-normal communication state. The fifth embodiment can be applied in combination with any of the first to fourth embodiments. In the fifth embodiment, a communication system includes at least one base station device 10. The configuration of the base station device 10 may be the same as that of the first embodiment, and therefore a detailed description thereof will be omitted here.

[0095] Fig. 11 is a flowchart showing an example of processing executed by the base station device 10 of the communication system according to the fifth embodiment. At the start of the flow in Fig. 11, it is assumed that the base station device 10 is operating in a normal communication state. That is, the operation state of the base station device 10 is the normal communication state at the start of the flow in Fig. 11.

[0096] The control unit 11 of the base station device 10 determines whether or not there are any terminal devices 20 currently communicating with the base station device 10 (step S51). For example, the storage unit 12 stores the number of terminal devices 20 currently communicating with the base station device 10, and the control unit 11 can determine whether or not there are any terminal devices 20 currently communicating with the base station device 10 by referring to the number stored in the storage unit 12. That is, if the number stored in the storage unit 12 is 0, the control unit 11 determines that there are no terminal devices 20 currently communicating with the base station device 10, and if the number stored in the storage unit 12 is 1 or more, the control unit 11 determines that there are any terminal devices 20 currently communicating with the base station device 10. The number of terminal devices 20 currently communicating with the base station device 10, which is stored in the storage unit 12, is recorded by the control unit 11, for example, when the base station device 10 starts or ends information communication with a terminal device 20.

[0097] When the control unit 11 determines that there is a terminal device 20 that is currently performing information communication with the control unit 11 (Yes in step S51), the control unit 11 repeats step S51.

[0098] On the other hand, if the control unit 11 determines that there is no terminal device 20 currently communicating with the control unit 11 (No in step S51), it determines whether a predetermined time has elapsed (step S52). The control unit 11 determines, for example, whether a predetermined time has elapsed since there was no terminal device 20 currently communicating with the control unit 11. In other words, the control unit 11 determines whether a predetermined time has elapsed since the state switched from a state in which it was determined that there was a terminal device 20 currently communicating with the control unit 11 to a state in which it was determined that there was no terminal device 20 currently communicating with the control unit 11. The predetermined time can be set as an appropriate time period that allows reliable confirmation that there is no terminal device 20 currently communicating with the control unit 11, and can be set, for example, between several seconds and several tens of seconds.

[0099] If the control unit 11 determines that the predetermined time has not elapsed (No in step S52), the control unit 11 proceeds to step S51.

[0100] On the other hand, if the control unit 11 determines that the predetermined time has elapsed (Yes in step S52), the control unit 11 causes the base station device 10 to transition from the normal communication state to the non-normal communication state (step S53).

[0101] As described above, in the fifth embodiment, when there is no terminal device 20 currently performing information communication with the base station device 10, the control unit 11 switches the operation state of the base station device 10 from a normal communication state to a non-normal communication state. This makes it possible to reduce power consumption by the base station device 10 that is not performing information communication with the terminal device 20. This makes it possible to smoothly switch between multiple states, including the power saving state.

[0102] 11, the control unit 11 may execute the switchover after a predetermined time has elapsed after determining that there is no terminal device 20 currently performing information communication with the base station device 10. In this case, the base station device 10 can transition to the non-normal communication state after more reliably confirming that there is no terminal device 20 currently performing information communication with the base station device 10.

[0103] The control unit 11 may not execute step S52. In this case, after determining that there is no terminal device 20 currently performing information communication with the base station device 10, the control unit 11 can transition the base station device 10 to the non-normal communication state without waiting for the lapse of a predetermined time.

[0104] Furthermore, the processing described in the fifth embodiment is not necessarily limited to that executed between a normal communication state and a non-normal communication state. For example, the processing described in the fifth embodiment can be similarly applied to the processing between the first power saving state and the second power saving state described in the third embodiment, or between the power saving state and the hibernation state described in the fourth embodiment.

[0105] Although the present disclosure has been described based on the drawings and embodiments, it should be noted that those skilled in the art can easily make various modifications and alterations based on the present disclosure. Therefore, it should be noted that these modifications and alterations are included in the scope of the present disclosure. For example, functions included in each functional unit or step can be rearranged so as not to be logically inconsistent, and multiple functional units or steps can be combined or divided into one.

Claims

1. A base station device comprising: a communication unit capable of performing base station-to-base station communication with a plurality of other base station devices operating in either the normal communication state or the non-normal communication state by switching between a normal communication state in which information communication with a terminal device can be performed and a non-normal communication state in which at least a portion of information communication with the terminal device is restricted compared to the normal communication state; and a control unit that, when selection information indicating that one other base station device out of the plurality of other base station devices has been selected as a handover destination is received from a terminal device performing information communication with the base station device itself, causes the communication unit to transmit a first request signal to the one other base station device selected as the handover destination, based on the selection information, requesting a switch from the non-normal communication state to the normal communication state.

2. The base station device according to claim 1, wherein the non-normal communication state includes a power saving state in which a state in which information communication with the terminal device can be performed and a state in which information communication with the terminal device cannot be performed are periodically repeated.

3. A base station device as described in claim 2, further comprising a memory unit that stores base station location information regarding the installation locations of the plurality of other base station devices, wherein the non-normal communication state further includes a dormant state in which information communication with the terminal device is not possible, and wherein the control unit, when receiving terminal location information from the terminal device that is performing information communication with the base station device, indicating the location of the terminal device that is performing information communication with the base station device, selects a candidate base station device from the plurality of other base station devices that is a candidate for a handover destination of the terminal device that is performing information communication with the base station device based on the terminal location information and the base station location information, and causes the communication unit to transmit a second request signal to the candidate base station device requesting that it switch from the dormant state to the power saving state.

4. The base station device described in claim 3, wherein when the control unit further receives, from a terminal device currently performing information communication with the device itself, movement direction information indicating the movement direction of the terminal device currently performing information communication with the device itself, the control unit selects the candidate base station device based on the terminal location information, the movement direction information, and the base station location information.

5. A base station device having a control unit that, when there is no terminal device currently performing information communication with the base station device, switches the operating state of the base station device from a normal communication state in which information communication with the terminal device can be performed to a non-normal communication state in which at least part of the information communication with the terminal device is restricted compared to the normal communication state.

6. The base station device according to claim 5, wherein the control unit executes the switching after a predetermined time has elapsed after determining that there is no terminal device currently performing information communication with the base station device.

7. A communications system including a base station device currently performing information communications with a terminal device and a plurality of other base station devices that are not currently performing information communications with the terminal device, wherein the base station device and the plurality of other base station devices are capable of performing inter-base station communications with each other, wherein each of the plurality of other base station devices performs operations in either the normal communication state or the non-normal communication state by switching between a normal communication state in which information communications with the terminal device can be performed and a non-normal communication state in which at least a portion of information communications with the terminal device is restricted compared to the normal communication state, and wherein when the base station device receives selection information from the terminal device currently performing information communications with the base station device, indicating that one of the plurality of other base station devices has been selected as a handover destination, the base station device transmits a first request signal to the one other base station device selected as the handover destination, based on the selection information, to request switching from the non-normal communication state to the normal communication state.

8. A communication system as described in claim 7, wherein said one other base station device switches said operation to said normal communication state if said operation is being performed in said non-normal communication state when said one other base station device receives said first request signal from said base station device.

9. The communication system according to claim 8, wherein said one other base station device transmits a response signal to said first request signal to said base station device when said operation is switched to said normal communication state.

10. A communication system as described in claim 7, wherein, if the one other base station device is performing the operation in the normal communication state when it receives the first request signal from the base station device, it transmits a response signal to the first request signal to the base station device without switching the operation.

11. A communication system according to claim 9 or 10, wherein, when the base station device receives the response signal, the base station device transmits an execution signal to a terminal device currently performing information communication with the base station device to cause the terminal device to perform a handover.

12. The communication system described in claim 7, wherein the non-normal communication state includes a first power saving state in which information communication with the terminal device is periodically alternately switched between a state in which information communication with the terminal device is executable and a state in which information communication with the terminal device is not executable, and a second power saving state in which information communication with the terminal device is periodically alternately switched between a state in which information communication with the terminal device is executable and a state in which information communication with the terminal device is not executable, and the proportion of the non-executable state is higher than that of the first power saving state; each of the plurality of other base station devices stores neighboring base station information regarding base station devices neighboring the own device; and when the one other base station device receives the first request signal from the base station device, the one other base station device transmits a second request signal to a base station device neighboring the one other base station device based on the neighboring base station information, requesting switching from the second power saving state to the first power saving state.

13. The communication system described in claim 7, wherein the non-normal communication state includes a power saving state in which information communication with the terminal device is executable and not executable, and a dormant state in which information communication with the terminal device is not executable, each of the plurality of other base station devices stores neighboring base station information regarding base station devices adjacent to the base station device itself, and when the one other base station device receives the first request signal from the base station device, it transmits a third request signal to a base station device adjacent to the one other base station device based on the neighboring base station information, requesting switching from the dormant state to the power saving state.

Images