Communication terminal, base station, terminal program, base station program, communication system, and communication method

Abstract

This communication terminal comprises: a terminal communication unit for performing wireless communication with a power-saving-compatible base station that switches to either a power-saving mode in which transmission of a signal is not performed and only reception of the signal is performed, or a normal mode in which both transmission and reception of the signal are performed; and a terminal control unit for controlling the terminal communication unit. When a prescribed condition is satisfied in a standby state for the signal, the terminal control unit causes the terminal communication unit to transmit a preamble signal that is for the power-saving-compatible base station and that is for changing the mode of the power-saving-compatible base station in the power-saving mode to the normal mode.

Description

Communication terminal, base station, terminal program, base station program, communication system, and communication method

[0001] The present disclosure relates to a communication terminal, a base station, a terminal program, a base station program, a communication system, and a communication method. This application claims priority based on Japanese Patent Application No. 2024-166835 filed in Japan on September 26, 2024, the content of which is incorporated herein by reference.

[0002] Currently, in 3GPP (Third Generation Partnership Project), methods for achieving power reduction in base stations (NES: Network Energy Savings) are being studied. As an example of a method for achieving such power reduction, putting a power-saving base station into a power-saving mode can be mentioned. In this case, as an example of the power-saving mode, Deep sleep (long-term transmission and reception stop), Lite sleep (short-term transmission and reception stop), or Micro sleep (instantaneous transmission and reception stop) can be considered. Also, as another example of the power-saving mode, Active DL <Downlink> (reception stop) or Active UL <Uplink> (transmission stop) can be considered.

[0003] Japanese Unexamined Patent Application Publication No. 2015-122767

[0004] The power-saving base station in the above-described power-saving mode only performs reception or discontinuous reception (DRX: Discontinuous Reception). That is, the power-saving base station does not transmit any signal even if it receives a signal from a communication terminal. Therefore, the communication terminal cannot grasp the existence of the power-saving base station in the power-saving mode. As a result, the communication terminal cannot start communication with the power-saving base station in the power-saving mode.

[0005] Furthermore, Patent Document 1, mentioned above, discloses that power-saving base stations have two states: a transmit standby mode (inactive state) and an active mode (active state), and discloses a method for transitioning from the inactive state to the active state. However, Patent Document 1 does not disclose a method for a communication terminal to initiate communication with a power-saving base station that is in power-saving mode and has stopped all transmissions, only receiving.

[0006] This disclosure has been made in view of the above-mentioned issues. The purpose of this disclosure is to provide a communication terminal capable of initiating communication with a power-saving base station in power-saving mode, as well as a base station, terminal program, base station program, communication system, and communication method corresponding to the communication terminal.

[0007] The communication terminal of this disclosure comprises a terminal communication unit that wirelessly communicates with a power-saving base station that switches between a power-saving mode in which it receives only a signal and does not transmit a signal, and a normal mode in which it transmits and receives a signal, and a terminal control unit that controls the terminal communication unit, wherein, in a signal standby state, if predetermined conditions are met, the terminal control unit causes the power-saving base station to transmit a preamble signal to the power-saving base station that changes the power-saving base station from the power-saving mode to the normal mode.

[0008] A first aspect of the base station of the present disclosure is a base station comprising a base station communication unit that performs wireless communication with a communication terminal, and a base station control unit that controls the base station communication unit, wherein the base station is a power-saving base station that switches between a power-saving mode in which it does not transmit signals but only receives signals, and a normal mode in which it does both transmit and receive signals, and the base station control unit switches from the power-saving mode to the normal mode when it receives a preamble signal for the power-saving base station that changes the power-saving base station from the power-saving mode to the normal mode.

[0009] A second aspect of the base station of the present disclosure is a base station comprising a base station communication unit that performs wireless communication with a communication terminal, and a base station control unit that controls the base station communication unit, wherein the base station is a normal base station that performs both transmission and reception of signals, and the base station control unit causes the base station communication unit to transmit power-saving base station presence information that can identify the presence of a power-saving base station at a location within range of the radio waves of the normal base station.

[0010] The terminal program of this disclosure causes a computer installed in a communication terminal to operate as a terminal control unit that controls a terminal communication unit that communicates wirelessly with a power-saving base station, which switches between a power-saving mode that only receives signals and does not transmit signals, and a normal mode that both transmits and receives signals. The terminal control unit, while in a signal standby state, causes the terminal control unit to transmit a preamble signal to the power-saving base station to change the power-saving base station from the power-saving mode to the normal mode if predetermined conditions are met.

[0011] A first aspect of the base station program of this disclosure is a base station control unit that controls a computer mounted on a base station, which controls a base station communication unit that performs wireless communication with a communication terminal, wherein the base station is a power-saving base station that switches between a power-saving mode in which it receives only signals and does not transmit signals, and a normal mode in which it transmits and receives signals, and the base station control unit is a base station program for switching from the power-saving mode to the normal mode when it receives a preamble signal for the power-saving base station that changes the power-saving base station from the power-saving mode to the normal mode.

[0012] A second aspect of the base station program of this disclosure is a base station program that causes a computer mounted on a base station to operate as a base station control unit that controls a base station communication unit that performs wireless communication with a communication terminal, wherein the base station is a normal base station that performs both transmission and reception of signals, and the base station control unit is a base station program that causes the base station control unit to transmit to the base station communication unit the presence of a power-saving base station that can identify the presence of a power-saving base station at a location where the radio waves of the normal base station can reach.

[0013] The communication system of this disclosure is a communication system comprising a communication terminal and a base station that performs wireless communication with the communication terminal, wherein the base station is a power-saving base station that switches between a power-saving mode in which it does not transmit signals but only receives signals and a normal mode in which it does both transmit and receive signals, and the communication terminal, while in a signal-waiting state, transmits a preamble signal to the power-saving base station that changes the power-saving base station from the power-saving mode to the normal mode if predetermined conditions are met, and the power-saving base station switches from the power-saving mode to the normal mode when it receives the preamble signal to the power-saving base station.

[0014] The communication method of this disclosure is a communication method between a communication terminal and a base station that performs wireless communication with the communication terminal, wherein the base station is a power-saving base station that switches between a power-saving mode in which it does not transmit signals and only receives signals, and a normal mode in which it does both transmit and receive signals, and the communication terminal, while in a signal-waiting state, transmits a preamble signal to the power-saving base station that changes the power-saving base station from the power-saving mode to the normal mode if predetermined conditions are met, and the power-saving base station switches from the power-saving mode to the normal mode when it receives the preamble signal to the power-saving base station.

[0015] This is a schematic diagram of the communication system of Embodiment 1. This is a functional block diagram of the power-saving base station of Embodiment 1. This is a functional block diagram of the communication terminal of Embodiment 1. This is a sequence diagram of the communication system of Embodiment 1. This is a flowchart showing the processes executed by the base station control unit of the power-saving base station of Embodiment 1. This is a flowchart showing the processes executed by the terminal control unit of the communication terminal of Embodiment 1. This is a schematic diagram of the communication system of Embodiment 2. This is a sequence diagram of the communication system of Embodiment 2. This is a flowchart showing the processes executed by the base station control unit of the power-saving base station of Embodiment 2. This is a flowchart showing the processes executed by the terminal control unit of the communication terminal of Embodiment 2. This is a schematic diagram of the communication system of Embodiment 3. This is a functional block diagram of the normal base station of Embodiment 3. This is a sequence diagram of the communication system of Embodiment 3. This is a flowchart showing the processes executed by the base station control unit of the power-saving base station of Embodiment 3. This is a flowchart showing the processes executed by the terminal control unit of the communication terminal of Embodiment 3.

[0016] Hereinafter, the communication terminal, base station, terminal program, base station program, communication system, and communication method of the embodiments of this disclosure will be described with reference to the drawings. In the drawings, the same or equivalent elements are denoted by the same reference numerals, and redundant descriptions will not be repeated.

[0017] (Embodiment 1) The communication terminal, base station, terminal program, base station program, communication system, and communication method of Embodiment 1 will be described with reference to Figures 1 to 6.

[0018] Figure 1 is a schematic diagram of the communication system 1 of this embodiment. As shown in Figure 1, the communication system 1 includes a power-saving base station BS and a communication terminal CT.

[0019] The communication terminal CT is located within or around the cell CA of the low-power base station BS, that is, within range of the low-power base station BS's radio waves. Therefore, the communication terminal CT can communicate wirelessly with the low-power base station BS. In reality, there are many communication terminal CTs within range of the low-power base station BS's radio waves, but in Figure 1, only one communication terminal CT is depicted, and the others are not shown.

[0020] A communication terminal (CT) is, for example, a portable mobile device called a smartphone. However, a communication terminal (CT) may also be a tablet device or a personal computer, as long as it is a mobile device capable of communicating with a base station (BS). A communication terminal (CT) is a communication terminal that supports power saving technologies such as LTE (Long Term Evolution), NR (New Radio), and NES (Network Energy Savings).

[0021] When the communication terminal CT is in a signal-waiting state (idle state) and certain conditions are met, it transmits a preamble signal for a power-saving base station that changes the power-saving base station from power-saving mode to normal mode. As a result, the communication terminal CT can start communication with the power-saving base station BS that is in power-saving mode. Details of the preamble signal for power-saving base stations will be described later.

[0022] The power-saving base station BS can communicate with multiple other power-saving base stations BS (not shown) via the core network NW. The power-saving base station BS is an NES cell. An NES cell is a base station that can switch between a power-saving mode, which only receives signals and does not transmit signals, and a normal mode, which both transmits and receives signals. When the power-saving base station BS receives a preamble signal for power-saving base stations from a communication terminal CT, it switches from power-saving mode to normal mode. The power-saving base station BS is a base station (including local 5G base stations) that supports power saving in communication standards such as LTE (Long Term Evolution) or NR (New Radio).

[0023] The core network (NW) enables the construction of high-capacity communication lines connecting concentrators, locations, operators, or even countries within a large-scale communication network. For example, the core network (NW) corresponds to the EPC (Evolved Packet Core) in a 4G (Fourth Generation) network and to the 5GC (5G Core Network) in a 5G (Fifth Generation) network.

[0024] Figure 2 is a functional block diagram of the power-saving base station BS of this embodiment. As shown in Figure 2, the power-saving base station BS comprises a base station communication unit BS1, a base station control unit BS2, and a base station storage unit BS3.

[0025] The base station communication unit BS1 performs wireless communication with the communication terminal CT. The base station communication unit BS1 includes antennas and other equipment for wireless communication.

[0026] The base station control unit BS2 reads the base station program stored in the base station memory unit BS3 from a computer and controls the base station communication unit BS1 based on the base station program. Specifically, based on the base station program, the base station control unit BS2 switches from power-saving mode to normal mode when it receives a preamble signal for a power-saving base station from the communication terminal CT that changes the power-saving compatible base station BS from power-saving mode to normal mode. The base station control unit BS2 consists of hardware called a processor, controller, or computer.

[0027] The base station memory unit BS3 stores the aforementioned base station program. The base station memory unit BS3 consists of a non-temporary, tangible recording medium called memory, such as RAM (Random Access Memory) or ROM (Read Only Memory).

[0028] The base station control unit BS2 includes a base station signal processing unit BS21, a mode switching unit BS22, and a base station preamble reception processing unit BS23.

[0029] When the base station preamble reception processing unit BS23 receives a preamble signal for a power-saving base station from the communication terminal CT, it notifies the mode switching unit BS22 to switch from power-saving mode to normal mode. When the mode switching unit BS22 receives the notification from the base station preamble reception processing unit BS23, it switches the power-saving base station BS from power-saving mode to normal mode.

[0030] However, the mode switching unit BS22 may have a function to switch the power-saving base station BS from power-saving mode to normal mode based on instructions from the core network NW or the judgment of the power-saving base station BS itself. Even if such a function is present, the base station control unit BS2 will switch from power-saving mode to normal mode when it receives a preamble signal for the power-saving base station from the communication terminal CT that changes the power-saving base station BS from power-saving mode to normal mode.

[0031] In power-saving mode, the base station signal processing unit BS21 is inactive and therefore only receives signals. In normal mode, the base station signal processing unit BS21 is active and performs processing for transmitting synchronization signals and broadcast signals, as well as processing for sending and receiving control signals and data signals with the communication terminal CT.

[0032] Figure 3 is a functional block diagram of the communication terminal CT of this embodiment. As shown in Figure 3, the communication terminal CT includes a terminal communication unit CT1, a terminal control unit CT2, and a terminal storage unit CT3.

[0033] The terminal communication unit CT1 performs wireless communication with the power-saving base station BS. The terminal communication unit CT1 includes an antenna and other components for wireless communication.

[0034] The terminal control unit CT2 reads the terminal program stored in the terminal memory unit CT3 and controls the terminal communication unit CT1 based on the terminal program. When the terminal control unit CT2 is in a signal standby state and meets predetermined conditions, it causes the terminal communication unit CT1 to transmit a preamble signal for a power-saving base station that changes the power-saving base station BS from power-saving mode to normal mode. The terminal control unit CT2 consists of hardware called a processor, controller, or computer.

[0035] The terminal storage unit CT3 stores the aforementioned terminal program. The terminal storage unit CT3 consists of a non-temporary, tangible recording medium called memory, such as RAM or ROM.

[0036] The terminal control unit CT2 includes a terminal signal processing unit CT21 and a terminal preamble transmission processing unit CT23. The terminal preamble transmission processing unit CT23 generates a preamble signal for a low-power base station and causes the terminal communication unit CT1 to transmit the generated preamble signal for the low-power base station to the low-power base station BS. The terminal signal processing unit CT21 performs processing for receiving synchronization signals and broadcast signals transmitted by the low-power base station BS, as well as processing for sending and receiving control signals and data signals with the low-power base station BS.

[0037] Figure 4 is a sequence diagram of the communication system 1 according to this embodiment 1.

[0038] As shown in Figure 4, in step S1, the power-saving base station BS is always in a state of waiting for a preamble signal for the power-saving base station in power-saving mode. In step S2, while the power-saving base station BS is in this waiting state, the communication terminal CT transmits a preamble signal for the power-saving base station to the power-saving base station BS. As a result, in step S3, after the power-saving base station BS receives the preamble signal for the power-saving base station from the communication terminal CT, if predetermined conditions are met, it transitions from power-saving mode to normal mode. Subsequently, in step S4, the power-saving base station BS transmits a synchronization signal and a broadcast signal.

[0039] In step S5, after receiving the synchronization signal and broadcast signal from the power-saving base station BS, the communication terminal CT performs camp-on to the power-saving base station BS, that is, it selects a cell of the power-saving base station BS and enters a waiting state in that cell. However, if the communication terminal CT needs to communicate with the power-saving base station BS, it connects to the power-saving base station BS using the normal procedure and starts communication with the power-saving base station BS.

[0040] Figure 5 is a flowchart showing the processes executed by the base station control unit BS2 of the power-saving base station BS in this embodiment.

[0041] In step S11, the base station control unit BS2 operates the power-saving compatible base station BS in power-saving mode. As a result, in step S12, the base station control unit BS2 is constantly in a state of waiting for the preamble signal for the power-saving compatible base station transmitted by the communication terminal CT.

[0042] When in standby mode, the base station control unit BS2 uses a frequency predetermined for power-saving base stations as the frequency of the preamble signal for power-saving base stations. For example, in the case of sub6-compatible local 5G, the base station control unit BS2 uses a frequency such as 4.85 GHz from the n79 band. Alternatively, the base station control unit BS2 may simultaneously standby using multiple predetermined frequencies.

[0043] Next, in step S13, the base station control unit BS2 determines whether or not it has received a preamble signal for a power-saving base station. If the base station control unit BS2 does not determine in step S13 that it has received a preamble signal for a power-saving base station, it continues the waiting state for a preamble signal for a power-saving base station as in step S12. On the other hand, if the base station control unit BS2 determines in step S13 that it has received a preamble signal for a power-saving base station, it operates the power-saving base station BS in normal mode in step S14. That is, the power-saving base station BS switches from a state where it cannot communicate with the communication terminal CT to a state where it can communicate with the communication terminal CT.

[0044] As the preamble signal for the power-saving base station, any one of the following three patterns (1) to (3) is used. Of course, when the power-saving base station BS operates in the normal mode, the same preamble signal as that of the normal base station is used.

[0045] (1) A preamble signal with a signal sequence different from the signal sequences of some preamble signals used by the normal base station is used as the preamble signal for the power-saving base station (for the transition from the inactive state to the active state of the power-saving base station). For example, when the normal base station uses a Zadoff-Chu sequence preamble signal, a pseudo-random sequence preamble signal other than the Zadoff-Chu sequence is used.

[0046] (2) One or more preamble signals among some preamble signals used by the normal base station are used as the preamble signal for the power-saving base station. For example, the signal sequence of the preamble signal used by the normal base station may be divided into group A and group B. In this case, the signal sequence of the preamble signal in group A is assigned to the normal base station or the power-saving non-corresponding base station BS in the normal mode, and the signal sequence of the preamble signal in group B is assigned for the power-saving base station.

[0047] (3) The preamble signal used by the normal base station is used as the preamble signal for the power-saving base station. This preamble signal for the power-saving base station is used only in an environment where there is no normal base station in the vicinity.

[0048] In the normal mode, the power-saving base station BS communicates with the communication terminal CT by transmitting synchronization signals, notification signals, etc.

[0049] Subsequently, in step S15, the base station control unit BS2 determines whether the conditions for transitioning to power-saving mode have been met. If, in step S15, the base station control unit BS2 determines that the conditions for transitioning to power-saving mode have not been met, it continues the control to operate the power-saving compatible base station BS in normal mode in step S14. On the other hand, if, in step S15, the base station control unit BS2 determines that the conditions for transitioning to power-saving mode have been met, it executes the control to operate the power-saving compatible base station BS in power-saving mode in step S11.

[0050] For a power-saving base station BS to transition from normal mode to power-saving mode, at least one of the following (A) to (F) is used as a power-saving mode transition condition.

[0051] (A) The condition for transitioning to power saving mode is that a predetermined amount of time has elapsed since there were no longer any communication terminals CT connected to a power saving compatible base station BS.

[0052] (B) The condition for transitioning to power saving mode is receiving a command signal from another power-saving compatible base station BS requesting to transition to power saving mode.

[0053] (C) The condition for transitioning to power saving mode is that the power saving-compatible base station BS receives a command signal from the core network NW requesting it to transition to power saving mode.

[0054] (D) The condition for transitioning to power saving mode is that the power saving-compatible base station BS receives a command signal from a network server (not shown) requesting it to transition to power saving mode.

[0055] (E) The condition for transitioning to power saving mode is that the timer inside the power saving compatible base station BS has reached a predetermined time.

[0056] (F) The conditions for transitioning to power saving mode are that an operation requesting a transition to power saving mode is manually performed on the power saving-compatible base station BS.

[0057] Figure 6 is a flowchart showing the process executed by the terminal control unit CT2 of the communication terminal CT in this embodiment.

[0058] In step S21, the communication terminal CT is out of range, meaning it cannot communicate with the power-saving base station BS. For example, assuming local 5G communication, the communication terminal CT is operating with a local 5G SIM (Subscriber Identity Module). Therefore, the communication terminal CT is out of range for local 5G, meaning it cannot communicate with the power-saving base station BS for local 5G. If the communication terminal CT is equipped with dual SIMs, that is, both a local 5G SIM and a public 5G SIM, it will be in standby mode for public 5G.

[0059] In step S22, the terminal control unit CT2 determines whether predetermined conditions for transmitting a preamble signal for a power-saving base station are met.

[0060] For example, one of the following (a) to (c) is used as a predetermined condition for transmitting a preamble signal for a low-power base station.

[0061] (a) The predetermined condition is that a timer in the communication terminal CT has measured a predetermined amount of time since it previously transmitted a preamble signal for a power-saving base station. In this case, the preamble signal for the power-saving base station may be transmitted periodically. The predetermined time may also change depending on the speed of movement of the communication terminal CT. For example, the faster the speed of movement, the shorter the predetermined time may be.

[0062] (b) The predetermined condition is that the communication terminal CT has moved a predetermined distance from the location where it previously transmitted the preamble signal to the low-power base station. In this case, the location information is determined within the communication terminal CT using GPS positioning or the like.

[0063] (c) The specified condition is that the communication terminal CT has moved into a predetermined range (cell CA of the low-power base station BS). In this case, the terminal memory unit CT3 of the communication terminal CT has previously stored the location information of the low-power base station BS.

[0064] Next, in step S22, if it is determined that the predetermined conditions for transmitting a preamble signal for a power-saving base station are not met, the terminal control unit CT2 repeats the process in step S21. On the other hand, if it is determined that the predetermined conditions for transmitting a preamble signal for a power-saving base station are met, the terminal control unit CT2 causes the terminal communication unit CT1 to transmit a preamble signal for a power-saving base station in step S23. One of the following three patterns (1) to (3) is used as the preamble signal for a power-saving base station. The terminal control unit CT2 causes the terminal communication unit CT1 to transmit the preamble signal for a power-saving base station at a predetermined power level and for a predetermined number of times.

[0065] Next, in step S24, the terminal control unit CT2 performs a cell search for the power-saving base station BS at the frequency of the transmitted preamble signal for the power-saving base station for a predetermined time. Then, in step S25, the terminal control unit CT2 determines whether or not the cell CA of the power-saving base station BS (NES) has been detected, that is, whether or not the synchronization signal and broadcast signal transmitted by the power-saving base station BS have been received by the terminal communication unit CT1. If the terminal control unit CT2 determines that the cell CA of the power-saving base station BS has not been detected, it repeats the processing in steps S21 to S24. On the other hand, if the terminal control unit CT2 determines in step S25 that the cell CA of the power-saving base station BS has been detected, in step S26, the terminal control unit CT2 enters a state of waiting for signals from the power-saving base station BS. These signals from the power-saving base station BS are signals transmitted from the power-saving base station BS to the communication terminal CT, excluding broadcast signals and synchronization signals.

[0066] The features of the communication terminal CT, base station BS, terminal program, base station program, communication system 1, and communication method of this embodiment, and the effects obtained therefrom, are summarized as follows.

[0067] In this embodiment, the terminal control unit CT1 of the communication terminal CT, while in a signal standby state, causes the terminal communication unit CT1 to transmit a preamble signal for a power-saving base station BS that changes the power-saving base station BS from power-saving mode to normal mode if predetermined conditions are met. Also, in this embodiment, the base station control unit BS2 of the power-saving base station BS switches from power-saving mode to normal mode when it receives a preamble signal for a power-saving base station that changes the power-saving base station BS from power-saving mode to normal mode.

[0068] According to the embodiment described above, the communication terminal CT transmits a preamble signal for a power-saving base station. This allows the power-saving base station BS, which is in power-saving mode, to change to normal mode. In other words, it is possible to activate an inactive NES cell. As a result, the communication terminal CT can start communication with the power-saving equipment BS, which is in power-saving mode.

[0069] (Embodiment 2) The communication terminal, base station, terminal program, base station program, communication system, and communication method of Embodiment 2 will be described using Figures 7 to 10. Note that the explanation of points that are the same as those of Embodiment 1 will not be repeated below. The communication terminal, base station, terminal program, base station program, communication system, and communication method of this embodiment differ from the communication terminal, base station, terminal program, base station program, communication system, and communication method of Embodiment 1 in the following points.

[0070] Figure 7 is a schematic diagram of the communication system 1 of this embodiment.

[0071] As shown in Figure 7, the communication system 1 includes a communication terminal CT and a power-saving base station BS, as well as a standard base station NBS. The cell CA of the power-saving base station BS is contained within the standard cell NCA of the standard base station NBS. The communication terminal CT is contained within the cell NCA of the standard base station NBS and the cell CA of the power-saving base station BS. The power-saving base station BS and the standard base station NBS are connected by a wire via the core network NW, or they are directly connected by a wire (Xn interface) (not shown). Furthermore, since the radio waves from the standard base station NBS reach the communication terminal CT located within or around the cell CA of the power-saving base station BS, communication is possible between the standard base station NBS and the communication terminal CT.

[0072] The functional block diagrams of the communication terminal CT and the power-saving base station BS in this embodiment are identical to the functional block diagrams of the power-saving base station BS (see Figure 2) and the communication terminal CT (see Figure 3) in Embodiment 1.

[0073] In this embodiment, the power-saving base station BS performs the following operation. Specifically, the power-saving base station BS obtains parameters related to the preamble signal used by the normal base station NBS via the core network NW in advance. The parameters used by the normal base station NBS include information such as timing, radio resource block, frequency, and sequence. The parameters related to the preamble signal for the normal base station include information such as timing, radio resource block, frequency, and sequence.

[0074] As a result, the base station preamble reception processing unit BS23 determines the timing of intermittent reception, the radio resource block to be received, the frequency to be received, and the sequence to be used for reception, based on the parameters of the preamble signal intended for the base station. The base station preamble reception processing unit BS23 causes the base station communication unit BS1 to intermittently receive the preamble signal intended for the power-saving base station from the communication terminal CT. When the base station preamble reception processing unit BS23 receives the preamble signal intended for the power-saving base station from the communication terminal CT via the base station communication unit BS1, it notifies the mode switching unit BS22 to switch from power-saving mode to normal mode.

[0075] The power-saving base station BS may obtain parameters related to the preamble signal used by the normal base station NBS directly from the normal base station NBS (e.g., via the Xn interface). Alternatively, the power-saving base station BS may store the aforementioned parameters related to the preamble signal for the normal base station in the base station memory unit BS23 beforehand.

[0076] The terminal preamble transmission processing unit CT23 generates a preamble signal for a power-saving base station based on the parameters of the preamble signal for a normal base station included in the broadcast signal transmitted from the normal base station NBS, as indicated by the dashed arrow A. Subsequently, the terminal preamble transmission processing unit CT23 causes the terminal communication unit CT1 to transmit the preamble signal for the power-saving base station to the power-saving base station BS at a timing based on the parameters of the preamble signal for a normal base station.

[0077] As a result, the power-saving base station BS switches from power-saving mode to normal mode. Consequently, the terminal signal processing unit CT21 performs processing to receive synchronization signals and broadcast signals transmitted by the power-saving base station BS, and then camps on to the power-saving base station BS. That is, the terminal signal processing unit CT21 selects cell CA of the power-saving base station BS and enters a waiting state in that cell CA. However, if the communication terminal CT needs to communicate with the power-saving base station BS, it connects to the power-saving base station BS using the normal procedure and starts communication with the power-saving base station BS.

[0078] Figure 8 is a sequence diagram of the communication system 1 according to this embodiment.

[0079] As shown in Figure 8, in step SA, the power-saving base station BS obtains parameters related to the preamble signal used by the normal base station NBS via the core network NW from the normal base station NBS in advance. Subsequently, the power-saving base station BS stores the obtained parameters related to the preamble signal for the normal base station in the base station memory unit BS3. As a result, in step S1, the power-saving base station BS enters an intermittent standby state for the preamble signal for the power-saving base station based on the aforementioned preamble signal information for the normal base station (timing, radio resource block, frequency, sequence, etc.).

[0080] Furthermore, in step SB, the normal base station NBS transmits a synchronization signal and a broadcast signal to the power-saving base station BS and then to the communication terminal CT. This broadcast signal includes parameters related to the preamble signal for the normal base station (timing, radio resource block, frequency, sequence, etc.). As a result, the communication terminal CT receives the parameters related to the preamble signal for the normal base station and stores the received parameters in the terminal storage unit CT3.

[0081] As a result, in step SC, the communication terminal CT sets preamble transmission parameters for the low-power base station based on parameters (timing, radio resource block, frequency, sequence, etc.) related to the preamble signal normally used by the base station NBS. That is, it sets the timing for preamble transmission, the radio resource block to transmit, the frequency to transmit, the sequence to use for transmission, etc. Then, in step S2, the communication terminal CT generates the set preamble signal for the low-power base station and transmits the generated preamble signal for the low-power base station to the low-power base station BS.

[0082] In step S3, the power-saving base station BS switches from power-saving mode to normal mode upon receiving a preamble signal for the power-saving base station from the communication terminal CT. Subsequently, in step S4, the power-saving base station BS transmits a synchronization signal and a broadcast signal, etc.

[0083] In step S5, when the communication terminal CT receives the synchronization signal and broadcast signal etc. transmitted by the power-saving base station BS, it camps on to the power-saving base station BS, that is, it selects cell CA of the power-saving base station BS and enters a standby state in that cell CA. However, if communication with the communication terminal CT is necessary, the power-saving base station BS connects to the communication terminal CT using the normal communication connection procedure and starts communication with the communication terminal CT.

[0084] Figure 9 is a flowchart showing the processes executed by the base station control unit BS2 of the power-saving base station BS in this embodiment.

[0085] As shown in Figure 9, in step S11, the base station control unit BS2 operates in power-saving mode. Then, in step S12A, the base station control unit BS2 enters an intermittent standby state for power-saving base station compatible preamble signals based on parameters (timing, radio resource block, frequency, sequence, etc.) related to the preamble signal for normal base stations. Note that the power-saving compatible base station BS has previously acquired parameters related to the preamble signal for normal base stations that are transmitted to the communication terminal CT by the normal base station NBS in the vicinity of the power-saving compatible base station BS as part of the broadcast signal.

[0086] In this case, the base station control unit BS2 receives a preamble signal for the low-power base station at a frequency predetermined for the low-power base station BS. For example, it receives it at a frequency among the preamble transmission parameters acquired in advance. However, if multiple frequency information exists, the base station control unit BS2 may simultaneously receive the preamble signal for the low-power base station at all frequencies of the normal base stations NBS located in a position where radio waves can reach the low-power base station BS. Furthermore, the base station control unit BS2 may select one (for example, the lowest frequency) from all frequencies of the normal base stations NBS located in a position where radio waves can reach the low-power base station BS. In this case, the base station control unit BS2 may use the selected frequency to receive the preamble signal for the low-power base station. If there are multiple normal base stations NBS in the vicinity, preamble transmission parameters are obtained from multiple normal base stations NSB. In that case, since multiple normal base stations NSB may each use different frequencies, the signals for all these frequencies may be received simultaneously as described above, or only the signal for one frequency may be selected and received.

[0087] In this embodiment, the power-saving base station BS enters an intermittent standby state for a preamble signal intended for the power-saving base station in step S12A. Therefore, the power-saving base station BS of this embodiment can reduce power consumption compared to the power-saving base station BS of Embodiment 1, which is always in a standby state for a preamble signal intended for the power-saving base station.

[0088] The processing of the base station control unit BS2 in this embodiment differs from that of the base station control unit BS2 in embodiment 1 only in step S12A. Steps S11 and S13 to S15 in this embodiment are the same as steps S11 and S13 to S15 in embodiment 1.

[0089] Figure 10 is a flowchart showing the process executed by the terminal control unit CT2 of the communication terminal CT in this embodiment.

[0090] As shown in Figure 10, the terminal control unit CT2 of this embodiment differs from the terminal control unit CT2 of Embodiment 1 in that in step S21A, it enters a state of waiting for a signal from a normal base station NBS. Furthermore, the terminal control unit CT2 of this embodiment differs from the terminal control unit CT2 of Embodiment 1 in that in step S22A, it sets preamble transmission parameters for a power-saving base station. In step S22A, the terminal control unit CT2 sets preamble transmission parameters for a power-saving base station based on the parameters related to preamble transmission for a normal base station included in the broadcast signal received from the normal base station NBS.

[0091] In step S23, the terminal control unit CT2 causes the terminal communication unit CT1 to transmit a preamble signal for a power-saving base station at the aforementioned frequency. However, if the terminal control unit CT2 is to transmit a preamble signal for a power-saving base station to the terminal communication unit CT1 at all frequencies, it may transmit all preamble signals for power-saving base stations to the terminal communication unit CT1 simultaneously. Alternatively, the terminal control unit CT2 may transmit each preamble signal separately to the terminal communication unit CT1 a number of times equal to the number of frequencies.

[0092] The processing of the base station control unit BS2 in this embodiment differs from that of the base station control unit BS2 in Embodiment 1 only in steps S21A and S22A. Steps S22, S24 to S26 in this embodiment are the same as steps S22, S24 to S65 in this embodiment.

[0093] As described above, when the terminal control unit CT2 receives parameters related to a preamble signal intended for a base station, and if the predetermined conditions mentioned above are met, it causes the terminal communication unit CT1 to transmit a preamble signal for a power-saving base station, which is generated based on those parameters.

[0094] This embodiment also provides the same effects as those obtained in Embodiment 1. Specifically, the communication terminal CT can change the power-saving base station BS from power-saving mode to normal mode by transmitting a preamble signal for the power-saving base station. As a result, the communication terminal CT can start communication with the power-saving device BS in power-saving mode.

[0095] (Embodiment 3) The communication terminal, base station, terminal program, base station program, communication system, and communication method of Embodiment 3 will be described using Figures 11 to 15. Note that the explanation of points that are the same as those of the communication terminal, base station, terminal program, base station program, communication system, and communication method of Embodiment 1 or 2 will not be repeated below. The communication terminal, base station, terminal program, base station program, communication system, and communication method of this embodiment differ from the communication terminal, base station, terminal program, base station program, communication system, and communication method of Embodiment 1 or 2 in the following points.

[0096] Figure 11 is a schematic diagram of the communication system 1 of this embodiment.

[0097] As shown in Figure 11, the configuration of the communication system 1 in this embodiment is the same as the configuration of the communication system 1 in embodiment 2. However, the normal base station NBS in this embodiment differs from the normal base station NBS in embodiment 2 in that it transmits power-saving base station presence information to the power-saving base station BS, as indicated by the solid arrow A. The power-saving base station presence information indicated by the solid arrow A is information that can identify that a power-saving base station BS in power-saving mode is located at a position where the radio waves of the normal base station NBS can reach.

[0098] A normal base station NBS transmits a broadcast signal containing information about the presence of a power-saving base station, which allows it to identify the presence of a power-saving base station BS within or around the cell NCA of the normal base station NBS (within the range of radio waves transmitted by the normal base station NBS). After receiving the broadcast signal, the communication terminal CT transmits a preamble signal for the power-saving base station if the predetermined conditions for transmitting the preamble signal for the power-saving base station are met. As a result, the power-saving base station BS switches from power-saving mode to normal mode upon receiving the preamble signal for the power-saving base station.

[0099] Figure 12 is a functional block diagram of a typical base station NBS in the configuration of this embodiment.

[0100] As shown in Figure 12, a typical base station NBS includes a base station communication unit NBS1, a base station control unit NBS2, and a base station storage unit NBS3.

[0101] The base station control unit NBS2 includes a base station signal processing unit NBS21. The base station signal processing unit NBS21 has a power-saving base station presence information generation unit NBS211. The power-saving base station presence information generation unit NBS211 generates power-saving base station presence information that can identify that a power-saving base station BS is located in a position where the radio waves of a normal base station NBS can reach, and transmits the generated power-saving base station presence information to the base station communication unit NBS1.

[0102] Specifically, a power-saving base station BS may exist within or around the cell NCA of a regular base station NBS. In this case, the power-saving base station presence information generation unit NBS211 includes the power-saving base station presence information in the broadcast signal and transmits it to the base station communication unit NBS1. However, the power-saving base station presence information generation unit NBS211 may also include the power-saving base station presence information in a control signal other than the broadcast signal and transmit it to the base station communication unit NBS1. The power-saving base station presence information is information that can identify the presence of a power-saving base station BS within or around the cell NCA of a regular base station NBS.

[0103] The following three types of power-saving base station presence information are used to identify the presence of a power-saving base station BS within or around the cell NCA of a standard base station NBS.

[0104] (1) The first type of power-saving base station presence information includes only information that can identify whether a power-saving base station BS exists within or around the cell NCA of a normal base station NBS. In this case, when the communication terminal CT receives the power-saving base station presence information, it transmits a preamble signal for the power-saving base station based on the frequency of the cell NCA of the normal base station NBS and parameters relating to the preamble signal for the normal base station (see Embodiment 2).

[0105] (2) The second type of power-saving base station presence information includes, in addition to the information in (1), the frequency information of the power-saving base station BS. In this case, when the communication terminal CT receives the power-saving base station presence information, it uses the frequency specified by the frequency information of the power-saving base station BS to transmit a preamble signal for the power-saving base station based on the parameters for the preamble signal for a normal base station. The parameters for the preamble signal for a normal base station in this case are the same as the parameters for the preamble signal for a normal base station in Embodiment 2.

[0106] (3) The third type of power-saving base station presence information includes, in addition to the information in (1), the frequency of the power-saving base station BS and the preamble setting parameters of the power-saving base station BS. In this case, when the communication terminal CT receives the power-saving base station presence information, it uses the frequency identified by the frequency information of the power-saving base station BS to transmit a preamble signal for the power-saving base station based on the preamble setting parameters of the power-saving base station BS.

[0107] The preamble reception processing unit BS23 (see Figure 2) attempts intermittently to receive the preamble signal for the power-saving base station transmitted by the communication terminal CT, based on the power-saving base station presence information normally transmitted by the base station NBS. When the preamble reception processing unit BS23 receives the preamble signal for the power-saving base station transmitted from the communication terminal CT via the base station communication unit BS21, it notifies the mode switching unit BS22 to switch from power-saving mode to normal mode.

[0108] In this embodiment, the power-saving base station BS directly receives information about the existence of the power-saving base station from the core network NW or from a normal base station NBS adjacent to the power-saving base station BS. However, the power-saving base station BS may also receive information about the existence of the power-saving base station in advance from the core network NW or from a normal base station NBS adjacent to the power-saving base station BS, and store the received information in the base station storage unit BS3.

[0109] The low-power base station BS receives the preamble signal for the low-power base station at different reception timings and frequencies depending on the patterns (1) to (3) described above.

[0110] In the case of (1) above, the low-power base station BS receives a preamble signal for the low-power base station at the timing and frequency based on the normal base station NBS.

[0111] In the case of (2) above, the power-saving base station BS receives the preamble signal for the power-saving base station at a timing based on the normal base station NBS and at a frequency included in the power-saving base station presence information.

[0112] In the case of (3) above, the power-saving base station BS receives the preamble signal for the power-saving base station at the timing and frequency included in the power-saving base station presence information.

[0113] Figure 13 is a sequence diagram of the communication system 1 of this embodiment.

[0114] As shown in Figure 13, in step SA1, the power-saving base station BS obtains power-saving base station existence information from a normal base station NBS via the core network NW. Subsequently, the power-saving base station BS stores the obtained power-saving base station existence information in the base station memory unit BS3. As a result, in step S1, the power-saving base station BS enters an intermittent waiting state for the preamble signal to be transmitted by the communication terminal CT to the power-saving base station, based on the power-saving base station existence information. In step SB1, the communication terminal CT receives a broadcast signal containing a synchronization signal and power-saving base station existence information. Subsequently, in step SC, the communication terminal CT sets the preamble transmission parameters for the power-saving base station, and in step S2, transmits the set preamble signal for the power-saving base station.

[0115] In step SD, if the power-saving base station BS receives a preamble signal for the power-saving base station from the communication terminal CT, it transmits response information to the communication terminal CT that identifies the receipt of the preamble signal for the power-saving base station. If the communication terminal CT does not receive response information from the power-saving base station BS, it does not perform a cell search to detect the power-saving base station BS. Therefore, the communication terminal CT can avoid performing unnecessary cell searches. Accordingly, according to this embodiment, the power consumption of the communication terminal CT can be reduced compared to Embodiment 2, in which the communication terminal CT confirms the existence of the power-saving base station BS by performing a cell search. However, the communication terminal CT does not have to transmit response information, as in Embodiment 2.

[0116] Steps S3 to S5 in this embodiment are the same as steps S3 to S5 in Embodiment 2, so their explanation will not be repeated.

[0117] Figure 14 is a flowchart showing the processes executed by the base station control unit BS2 of the power-saving base station BS in this embodiment.

[0118] As shown in Figure 14, in step S11, the base station control unit BS2 operates in power-saving mode. In this case, in step S12B, the base station control unit BS2 enters an intermittent standby state for preamble signals for power-saving base stations in cooperation with the normal base station NBS. Specifically, the base station control unit BS2 intermittently receives preamble signals for power-saving base stations based on the power-saving base station existence information received from the normal base station NBS. Steps S13, S14, and S15 of this embodiment are the same as steps S13, S14, and S15 of Embodiment 2, so their explanation will not be repeated. However, in step S13, if the power-saving base station BS of this embodiment receives a preamble signal from the communication terminal CA, it transmits response information to the communication terminal CT in step S13A before step S14. As will be described later, if the communication terminal CT does not receive response information, it does not perform a search for cell CA of the power-saving base station BS, thus saving power consumption for cell search.

[0119] The power-saving base station BS of this embodiment, similar to that of embodiment 2, enters an intermittent standby state for the preamble signal for the power-saving base station in step S12B, thereby reducing power consumption compared to the power-saving base station BS of embodiment 1.

[0120] Figure 15 is a flowchart showing the process executed by the terminal control unit CT2 of the communication terminal CT in this embodiment.

[0121] If the power-saving base station BS as an NES cell is not active, as shown in Figure 15, in step S21A, the terminal control unit CT2 enters a state of waiting for signals normally transmitted by the base station NBS. As a result, the terminal control unit CT2 enters a state of receiving power-saving base station presence information contained in the broadcast signal normally transmitted by the base station NBS.

[0122] For example, if LTE is used as a normal cell in a standard base station NBS and NR is used as an NES cell in a power-saving base station BS, the terminal control unit CT2 will be in standby mode for LTE. Also, if NR is used as a normal cell in a standard base station NBS and NR is used as an NES cell in a power-saving base station BS, the terminal control unit CT2 will be in standby mode for NR in the standard base station NBS.

[0123] Next, in step S21B, the terminal control unit CT2, while in a state of waiting for signals normally transmitted by the base station NBS, determines whether or not it has received information about the existence of a power-saving base station included in the broadcast signal normally transmitted by the base station NBS. If it is not determined in step S21B that information about the existence of a power-saving base station has been received, the terminal control unit CT2 repeats the process in step S21A. On the other hand, if it is determined in step S21B that information about the existence of a power-saving base station has been received, in step S22, the terminal control unit CT2 determines whether or not it has met the predetermined conditions for transmitting a preamble signal for a power-saving base station.

[0124] The first predetermined condition is that a predetermined amount of time has elapsed since the communication terminal CT previously transmitted a preamble signal for a low-power base station. In this case, the communication terminal CT periodically transmits a preamble signal for a low-power base station. The terminal control unit CT2 may change the transmission period of the preamble signal for the low-power base station according to the movement speed of the communication terminal CT. For example, the greater the movement speed of the communication terminal CT, the shorter the transmission period of the preamble signal for the low-power base station may be.

[0125] The second predetermined condition is that the communication terminal CT has moved a predetermined distance from the location where it last transmitted a signal. In this case, the location information is determined within the communication terminal CT using GPS (Global Positioning System) positioning or similar methods.

[0126] The third predetermined condition is that the communication terminal CT has moved within a predetermined range (for example, within a predetermined cell CA). In this case, the terminal memory unit CT3 of the communication terminal CT has previously stored the location information of the power-saving base station BS.

[0127] In step S22, if the predetermined conditions for transmitting a preamble signal for a power-saving base station are not met, the terminal control unit CT2 repeats the process in step S21A. On the other hand, if the predetermined conditions are met in step S22, in step S22A, the terminal control unit CT2 sets the preamble transmission parameters for the power-saving base station based on the power-saving base station existence information. The power-saving base station existence information is included in the broadcast signal. The predetermined conditions in step S22 are the conditions for transmitting the preamble signal described in (a) to (c) of Embodiment 1. In step S23, the terminal control unit CT2 causes the terminal transmission unit CT1 to transmit a preamble signal for the power-saving base station at a timing based on the power-saving base station existence information.

[0128] In step S23A, the terminal control unit CT2 determines whether or not it has received response information from the power-saving base station BS via the terminal communication unit CT1. In step S23A, if the terminal control unit CT2 determines that no response information has been received, it repeats the process in step S21A. On the other hand, if in step S23A it determines that information indicating the existence of a power-saving base station has been received, in step S24, the terminal control unit CT2 starts a cell search for the power-saving base station BS because the power-saving base station BS will switch from power-saving mode to normal mode.

[0129] Next, in step S25, the terminal control unit CT2 determines whether or not a cell of the power-saving base station BS has been detected. If it is determined in step S25 that no cell of the power-saving base station BS has been detected, the terminal control unit CT2 repeats the process in step S21A. On the other hand, if it is determined in step S25 that cell CA of the power-saving base station BS has been detected, the terminal control unit CT2 enters a state of waiting for a signal to be transmitted by the power-saving base station BS.

[0130] As described above, when the terminal communication unit CT2 receives information indicating the presence of a power-saving base station BS that can identify that the power-saving base station BS is located within range of the radio waves of the normal base station NBS, it causes the terminal communication unit CT1 to transmit a preamble signal for the power-saving base station. In addition, the base station control unit BS2 causes the base station communication unit NBS1 to transmit information indicating the presence of a power-saving base station BS in power-saving mode that can identify that the power-saving base station BS is located within range of the radio waves of the normal base station NBS.

[0131] This embodiment also provides the same effects as those obtained in Embodiment 1 or 2. Specifically, the communication terminal CT can transmit a preamble signal for the power-saving base station, thereby changing the power-saving base station BS from power-saving mode to normal mode. As a result, the communication terminal CT can start communication with the power-saving equipment BS in power-saving mode.

[0132] Furthermore, if the terminal control unit CT2 does not receive response information that identifies the power-saving base station BS as having received a preamble signal intended for the power-saving base station, it will not perform a cell search on the power-saving base station BS. Also, if the base station control unit BS2 receives a preamble signal intended for the power-saving base station, it will cause the base station communication unit BS1 to transmit response information that identifies the receipt of the preamble signal intended for the power-saving base station.

[0133] According to this, the communication terminal CT can reduce power consumption compared to when it checks whether there is an actual low-power base station BS that can communicate using cell search.

Claims

1. A communication terminal comprising: a terminal communication unit that performs wireless communication with a power-saving base station that switches between a power-saving mode in which it receives only the signal and does not transmit the signal, and a normal mode in which it transmits and receives the signal; and a terminal control unit that controls the terminal communication unit, wherein, when in a signal standby state, if predetermined conditions are met, the terminal control unit causes the terminal communication unit to transmit a preamble signal for the power-saving base station that changes the power-saving base station from power-saving mode to normal mode.

2. The communication terminal according to claim 1, wherein the terminal communication unit performs wireless communication with a normal base station that both transmits and receives the signal, and the terminal control unit, upon receiving parameters relating to a preamble signal for the normal base station, causes the terminal communication unit to transmit a preamble signal for the power-saving base station generated based on the parameters if certain conditions are met.

3. The communication terminal according to claim 1, wherein the terminal communication unit performs wireless communication with a normal base station that both transmits and receives the signal, and when the terminal control unit receives information indicating the presence of a power-saving base station that allows it to identify that the power-saving base station is located within range of the radio waves of the normal base station, it causes the terminal communication unit to transmit a preamble signal for the power-saving base station.

4. The communication terminal according to claim 3, wherein the terminal control unit does not perform a search for the power-saving base station if it does not receive response information that allows it to identify that the power-saving base station has received a preamble signal for the power-saving base station.

5. A base station comprising: a base station communication unit that performs wireless communication with a communication terminal; and a base station control unit that controls the base station communication unit, wherein the base station is a power-saving base station that switches between a power-saving mode in which it does not transmit signals but only receives signals, and a normal mode in which it does both transmit and receive signals, and the base station control unit switches from the power-saving mode to the normal mode when it receives a preamble signal for the power-saving base station that changes the power-saving base station from the power-saving mode to the normal mode.

6. The base station according to claim 5, wherein when the base station control unit receives a preamble signal for the power-saving base station, it causes the base station communication unit to transmit response information that can identify that a preamble signal for the power-saving base station has been received.

7. A base station comprising: a base station communication unit that performs wireless communication with a communication terminal; and a base station control unit that controls the base station communication unit, wherein the base station is a normal base station that performs both transmission and reception of signals; and the base station control unit causes the base station communication unit to transmit information indicating the presence of a power-saving base station that can identify the presence of a power-saving base station within the range of the radio waves of the normal base station.

8. A terminal program that causes a computer mounted on a communication terminal to operate as a terminal control unit that controls a terminal communication unit that communicates wirelessly with a power-saving base station, which switches between a power-saving mode that only receives signals and does not transmit signals, and a normal mode that both transmits and receives signals, and the terminal control unit, when in a signal standby state and certain conditions are met, causes the terminal control unit to transmit a preamble signal to the power-saving base station that changes the power-saving base station from power-saving mode to normal mode.

9. A computer mounted on a base station operates as a base station control unit that controls a base station communication unit that performs wireless communication with a communication terminal, the base station is a power-saving base station that can switch between a power-saving mode in which it does not transmit signals but only receives them, and a normal mode in which it does both transmit and receive them, and the base station control unit is a base station program for switching from the power-saving mode to the normal mode when it receives a preamble signal for the power-saving base station that changes the power-saving base station from the power-saving mode to the normal mode.

10. A computer mounted on a base station operates as a base station control unit that controls a base station communication unit that performs wireless communication with a communication terminal, the base station is a normal base station that performs both transmission and reception of signals, and the base station control unit is a base station program that causes the base station control unit to transmit to the base station communication unit the presence of a power-saving base station capable of identifying that a power-saving base station is located within range of the radio waves of the normal base station.

11. A communication system comprising a communication terminal and a base station that performs wireless communication with the communication terminal, wherein the base station is a power-saving base station that can switch between a power-saving mode in which it does not transmit signals but only receives signals and a normal mode in which it does both transmit and receive signals, the communication terminal, while in a signal-waiting state, transmits a preamble signal for the power-saving base station that changes the power-saving base station from power-saving mode to normal mode if predetermined conditions are met, and the power-saving base station switches from power-saving mode to normal mode when it receives the preamble signal for the power-saving base station.

12. A communication method between a communication terminal and a base station that performs wireless communication with the communication terminal, wherein the base station is a power-saving base station that can switch between a power-saving mode in which it does not transmit signals but only receives signals, and a normal mode in which it does both transmit and receive signals, and the communication terminal, while in a signal-waiting state, transmits a preamble signal to the power-saving base station that changes the power-saving base station from power-saving mode to normal mode if predetermined conditions are met, and the power-saving base station switches from power-saving mode to normal mode when it receives the preamble signal to the power-saving base station.

Images