JP2019087831A - Wireless communication system, base station, mobile terminal, and power control method - Google Patents

Abstract

To provide a wireless communication system capable of shortening a time to when a mobile terminal makes a transition to a power-saving mode.SOLUTION: Each of a plurality of base stations comprises: a transmission timing decision unit that decides transmission timing information prescribing a data transmission timing to a mobile terminal at random; and a transmission unit that includes the transmission timing information in the data and transmits the data as transmission data. The mobile terminal has: a reception unit that receives the transmission data from the plurality of base stations; a transmission timing extraction unit that extracts the transmission timing information from the transmission data received at the reception unit; and a power-saving mode decision unit that, in a case where the existence of a time zone in which there is no data transmission from either of the plurality of base stations is detected on the basis of the extracted transmission timing information, decides transition to a power-saving mode of operating with less power in the time zone.SELECTED DRAWING: Figure 7

Description

  The present invention relates to power saving technology in a wireless communication system.

  Conventionally, in a wireless communication system provided with a mobile terminal having a power saving mode that operates in power saving mode, as disclosed in, for example, Patent Document 1, a delay period until the mobile terminal itself receives control data from a base station Is notified to the base station in advance, the base station waits for transmission of control data until the delay period ends, and a technique is disclosed for transmitting control data to the mobile terminal after the delay period ends. According to the technology of Patent Document 1, the mobile terminal can operate in the power saving mode until the delay period notified to the base station ends.

Japanese Patent Application Publication No. 2016-524360

  In the conventional wireless communication system, the base station receives the delay period transmitted by the mobile terminal, transmits an acknowledgment from the base station to the mobile terminal, and the mobile terminal receives it, thereby saving the mobile terminal. Enter power mode. As described above, in the conventional wireless communication system, a sequence for notifying the response from the base station and receiving it by the mobile terminal is required, and it takes time to shift to the power saving mode, and the power saving mode is not completed. There was a problem that it could not work with

  The present invention has been made to solve the above problems, and it is an object of the present invention to provide a wireless communication system in which the time taken for the mobile terminal to shift to the power saving mode is shortened.

  A wireless communication system according to the present invention is a wireless communication system for performing wireless communication between a plurality of base stations and a mobile terminal, wherein each of the plurality of base stations transmits data to the mobile terminal. The mobile terminal comprises: a transmission timing determination unit that randomly determines transmission timing information to be defined; and a transmission unit that transmits the transmission data including the transmission timing information in the data as the transmission data; Any of the plurality of base stations based on the reception unit for receiving the transmission data, the transmission timing extraction unit for extracting the transmission timing information from the transmission data received by the reception unit, and the transmission timing information extracted. If it detects that there is a time zone where there is no data transmission either, it shifts to the power saving mode that operates in the power saving mode during that time zone And a, a power saving mode determination unit for determining and.

  According to the above wireless communication system, each of the plurality of base stations randomly determines transmission timing information defining the transmission timing of data to the mobile terminal, includes it in the data and transmits it as transmission data, and the mobile terminal Since the transition to the power saving mode is performed based on the transmission timing information extracted from the transmission data, there is no need to perform complicated communication between the base station and the mobile terminal, and the mobile terminal transitions to the power saving mode. Time can be shortened.

It is a block diagram showing composition of a radio communications system concerning the present invention. It is a functional block diagram which shows the structure of the base station of Embodiment 1 which concerns on this invention. It is a block diagram which shows the hardware constitutions of the base station of Embodiment 1 which concerns on this invention. It is a timing chart which shows the example of determination of the transmission timing of the base station of Embodiment 1 which concerns on this invention. It is a figure which shows typically an example of the transmission timing mapping of transmission data. It is a figure which shows typically the other example of the transmission timing mapping of transmission data. It is a functional block diagram which shows the structure of the mobile terminal of Embodiment 1 which concerns on this invention. It is a block diagram which shows the hardware constitutions of the mobile terminal of Embodiment 1 which concerns on this invention. It is a timing chart which shows an example of reception timing of a mobile terminal of Embodiment 1 concerning the present invention, and transition timing to power saving mode. It is a flowchart which shows the data transmission operation of the base station of Embodiment 1 which concerns on this invention. It is a flowchart which shows operation | movement from data reception of the mobile terminal of Embodiment 1 which concerns on this invention to transfer to a power saving mode. It is a functional block diagram which shows the structure of the mobile terminal of Embodiment 2 which concerns on this invention. It is a flowchart which shows operation | movement from data reception of the mobile terminal of Embodiment 1 which concerns on this invention to transfer to a power saving mode. It is a functional block diagram which shows the structure of the mobile terminal of Embodiment 3 which concerns on this invention. It is a timing chart which shows an example of a receiving timing of a mobile terminal of Embodiment 3 concerning the present invention, and a transition timing to power saving mode. It is a flowchart which shows operation | movement from data reception of the mobile terminal of Embodiment 3 which concerns on this invention to transfer to a power saving mode. It is a figure which shows typically an example of the transmission timing mapping of transmission data. It is a timing chart which shows an example of a receiving timing of a mobile terminal of Embodiment 4 concerning the present invention, and a transition timing to power saving mode. It is a timing chart which shows an example of a receiving timing of a mobile terminal of Embodiment 4 concerning the present invention, and a transition timing to power saving mode.

Embodiment 1
<Configuration of Wireless Communication System>
FIG. 1 is a block diagram showing the configuration of a wireless communication system to which the present embodiment is applied. As shown in FIG. 1, base station 1 (referred to as base station A) and base station 2 (referred to as base station B) are within the communication area of mobile terminal 3, and mobile terminal 3 includes base station A and base station B. It is possible to communicate with each other. Although FIG. 1 exemplifies a wireless communication system having a base station A, a base station B, and the mobile terminal 3, application of the present embodiment is not limited to this.

  The base station A can transmit transmission data at any timing, and similarly, the base station B can transmit transmission data having the same time length and frequency as the base station A at any transmission timing. . The mobile terminal 3 receives transmission data transmitted from the base station A and the base station B, respectively. The base station A and the base station B do not have to be synchronized, and each transmits data at random timing based on random numbers. Therefore, there is a possibility that the base station A and the base station B simultaneously transmit data, in which case the transmission data may collide with each other and the mobile terminal 3 may not receive the data.

<Configuration of Base Station>
FIG. 2 is a functional block diagram showing a configuration of a base station in Embodiment 1, and since base station A and base station B have the same configuration, it will be described as base station 100.

  The base station 100 includes a transmission timing determination unit 102, a payload generation unit 104, a transmission timing mapping unit 105, and a transmission unit 106. The transmission timing determination unit 102 includes a random timing generation unit 103. The transmission timing determination unit 102 inputs the random transmission timing information determined by the random timing generation unit 103 to the transmission timing mapping unit 105. The transmission timing mapping unit 105 adds the plurality of transmission timing information input from the transmission timing determination unit 102 to the payload generated by the payload generation unit 104 to create transmission data. The transmission data is input from the transmission timing mapping unit 105 to the transmission unit 106, transmission timing information of the transmission data is input from the transmission timing determination unit 102, and the transmission data is wirelessly transmitted at a designated transmission timing. After the transmission is completed, the transmission timing determination unit 102 generates new transmission timing information.

  The transmission timing information includes the number of frames up to the next transmission timing, the transmission timing time set to 100 ms, 3 seconds, 5 minutes, etc. In the following, the number of frames up to the transmission timing is the transmission timing Described as information.

  FIG. 3 is a block diagram showing a hardware configuration of base station 100 in the first embodiment. As shown in FIG. 3, the base station 100 includes a central processing unit (CPU) 111, a memory 112, a transmitter 113, a power supply unit 114, and an antenna 115. The power supply unit 114 is connected to the external power supply 119 and externally supplied with power. The transmitting device 113 converts the transmission data set by the CPU 111 into a wireless signal, and transmits it as a spatial wave through the antenna 115.

  When the hardware configuration illustrated in FIG. 3 is adopted, for example, the transmitting unit 106 illustrated in FIG. The transmission timing determination unit 102, the payload generation unit 104, and the transmission timing mapping unit 105 illustrated in FIG. 2 are realized as functions of the CPU 111 by the CPU 111 executing a program stored in the memory 112. However, the correspondence between the hardware configuration of the base station 100 and the functional blocks is not limited to the above, and, for example, the transmission timing determination unit 102, the payload generation unit 104, and the transmission timing mapping unit 105 shown in FIG. At least a part may be realized by dedicated hardware.

  FIG. 4 is a timing chart showing an example of determination of the transmission timing of the base station 100 in the first embodiment. The transmission timing determined by each of the base station A and the base station B is shown with the horizontal axis as a time axis. In addition, the arrow shown between data in FIG. 4 represents a flame | frame period, for example, when two arrows exist between data, time after receiving the data before receiving the next data is shown. Indicates that there are two frames. Further, in FIG. 4, transmission timing information included in each data is shown above each data.

  After power-on, the base station A and the base station B transmit timing information for initial transmission and transmission timings of data transmission for a plurality of times after the initial transmission included in the initial transmission data before executing the initial data transmission. Determine the information. In the example of FIG. 4, the transmission timing information for the first transmission and the transmission timing information for five times after the first transmission are determined. Transmission timing information is determined by the random timing generation unit 103 shown in FIG. 2 based on the random numbers generated by the random number generator (not shown), and the transmission timing determination unit 102 holds it.

  In FIG. 4, the base station A determines 1, 2, 4, 3, 1 as transmission timing information for five times, and transmits it by including it in the initial transmission data. In this case, the transmission timing of the base station A is as follows: after the first data transmission, the second data transmission is performed with an interval of one frame period, and thereafter, the second data transmission is performed with an interval of two frame periods. The fourth data transmission is performed after the frame period, the fifth data transmission is performed after the three frame period, and the sixth data transmission is performed after the one frame period. In FIG. 4, the fifth and sixth data transmissions are not shown.

  Also, the base station determines the final fifth transmission timing information each time data is transmitted. For example, after the first transmission of data by the base station A, the transmission timing information held by the base station A is four times of 2, 4, 3, and 1. In that case, based on the random numbers. The generated 5 is set as the final fifth transmission timing information, and the transmission timing information held by the base station A is set to 2, 4, 3, 1, 5.

  Similarly to the base station A, the base station B randomly determines transmission timing information and transmits transmission data. The base station B transmits initial transmission data later than the base station A, and the initial transmission data includes 1, 1, 3, 5, and 4 as transmission timing information for five times. After transmitting the first transmission data, the base station B determines that the final fifth transmission timing information to be included in the next transmission data is 2, and the transmission timing information held by the base station B is 1, 3, and 5. , 4, 2.

  When the transmission timing information of base station A and base station B is determined as described above, in the third data transmission from base station A and base station B, as shown in FIG. The station B transmits data in the same time zone.

  FIG. 5 schematically shows an example of transmission timing mapping of transmission data created by the transmission timing mapping unit 105 of the base station 100 shown in FIG. In the example of FIG. 5, the plurality of transmission timing information input from the transmission timing determination unit 102 (FIG. 2) is converted to data, and the fifth transmission is performed sequentially from the first transmission timing to the end of the payload 10 as the transmission timing information 11. The transmission data is created with the addition of timing.

  In the structure of the mapping shown in FIG. 5, when the first transmission data of the base station A shown in FIG. 4 is taken as an example, the transmission timing information 11 becomes 1, 2, 4, 3, 1 in order from the first, It becomes transmission data which added "12431" to the end of ten. Similarly, at the time of the second data transmission of the base station A shown in FIG. 4, the final numerical value is determined randomly each time it is transmitted once, such as "24315" and at the third time of data transmission "43151". Instead of the new transmission timing information, it is added to the payload.

  As described above, by arranging a plurality of transmission timing information in a predetermined arrangement position of the payload in a predetermined arrangement order, the mobile terminal can easily acquire the transmission timing information.

  Also, by arranging a plurality of transmission timing information consecutively, the arrangement position and arrangement order can be simplified.

  Although FIG. 5 shows an example in which the transmission timing information 11 is added to the end of the payload 10, the place to be added is not limited to this. For example, it may be added to the beginning of the payload. May be added between

  Further, the plurality of transmission timing information may not be arranged continuously as shown in FIG. 5, and each transmission timing information may be arranged discontinuously.

  FIG. 6 shows an example in which a plurality of pieces of transmission timing information are arranged discontinuously, and one piece of transmission timing information 11 is arranged between the two payloads 10 in order from the first to the fifth. As described above, even when a plurality of transmission timing information are discontinuously arranged, the arrangement position and arrangement order are fixed, and if the mobile terminal knows the arrangement position and arrangement order, the mobile terminal transmits timing information There is no problem because you can get

  When data interleaving is not performed, by arranging a plurality of transmission timing information separately, the same effect as when data interleaving is performed, that is, all transmission timing information is erroneously received by the mobile terminal when a burst error occurs. You can reduce the possibility.

<Configuration of mobile terminal>
FIG. 7 is a functional block diagram showing a configuration of a mobile terminal in the first embodiment, and mobile terminal 3 shown in FIG. 1 will be described as mobile terminal 200.

  The mobile terminal 200 includes a receiving unit 201, a transmission timing extracting unit 202, a payload processing unit 203, a power saving mode determining unit 204, and a power saving control unit 205. The mobile terminal 200 receives transmission data from the base station 100 (FIG. 2) by the receiving unit 201, and the received data is input to the transmission timing extraction unit 202. The transmission timing extraction unit 202 divides the reception data into transmission timing information and a payload, the transmission timing information is input to the power saving mode determination unit 204, and the payload is input to the payload processing unit 203. The power saving mode determination unit 204 calculates an executable period of the power saving mode operating with the power saving based on the transmission timing information, and notifies the power saving control unit 205 of it. The power saving control unit 205 performs ON / OFF control of the power saving mode based on an executable period of the power saving mode. The payload processing unit 203 processes data contained in the payload and performs processing of converting the data into audio data, video data, and the like.

  When the power saving mode determination unit 204 detects a time zone not received from any base station from the transmission timing information of all the received base stations, it determines that transition to the power saving mode is possible, and The feasible period is calculated, and the transition to the power saving mode is determined. By determining the transition to the power saving mode using the received transmission timing information for a plurality of times, even if data reception fails once, based on the transmission timing information received before that. Since the next transmission timing is known, transition to the power saving mode is possible.

  FIG. 8 is a block diagram showing a hardware configuration of mobile terminal 200 in the first embodiment. As shown in FIG. 8, the mobile terminal 200 includes a CPU 211, a memory 212, a receiving device 213, an antenna 214, a power supply unit 215, and a battery 216 for supplying power to the power supply unit 215. The receiving device 213 converts the wireless signal from the base station received via the antenna 214 into received data and inputs the received data to the CPU 211.

  When the hardware configuration illustrated in FIG. 8 is adopted, for example, the receiving unit 201 illustrated in FIG. The transmission timing extraction unit 202, the payload processing unit 203, the power saving mode determination unit 204, and the power saving control unit 205 are realized as a function of the CPU 211 by the CPU 211 executing a program stored on the memory 212. . However, the correspondence between the hardware configuration of the mobile terminal 200 and the functional blocks is not limited to the above. For example, the transmission timing extraction unit 202, the payload processing unit 203, and the power saving mode determination unit illustrated in FIG. At least a part of the power saving control unit 204 and the power saving control unit 205 may be realized by dedicated hardware.

  FIG. 9 is a timing chart showing an example of reception timing of mobile terminal 200 and transition timing to power saving mode according to Embodiment 1, and also shows transmission timings determined by base station A and base station B, respectively. .

  As shown in FIG. 9, according to the transmission timings determined by base station A and base station B, respectively, the data transmitted in the first and second data transmissions from base station A, and from base station B The data transmitted in the first and second data transmissions of the first and second times are received by the mobile terminal 200, but the data transmitted in the third data transmission from the base station A and the base station B have the same transmission time zone. Therefore, the mobile terminal 200 collides and can not receive.

  When the power saving mode determination unit 204 (FIG. 7) detects a time zone in which data is not received from either the base station A or the base station B based on the transmission timing information, transition to the power saving mode is possible. The power saving control unit 205 determines the power saving mode executable period, and notifies the power saving control unit 205 of it.

  In FIG. 9, one frame period after the second data transmission from base station B is a time zone during which data is not received from either base station A or base station B, and power saving mode determination unit 204 It is determined that the time zone can be shifted to the power saving mode.

  The power saving control unit 205 starts (ON) the power saving mode at the start timing of the power saving mode executable period notified from the power saving mode determining unit 204, and ends the power saving mode executable period. At the timing, the power saving mode is ended (OFF). As a specific example of the power saving mode, the stop of power supply to the receiving unit 201, the transmission timing extracting unit 202, the payload processing unit 203, the power saving mode determining unit 204 and the power saving control unit 205 Power consumption can be reduced by lowering the clock frequency.

  As described above, as in the third data transmission from the base station A and the base station B, when the transmission time zone is the same, the transmission data collides and the mobile terminal 200 can not receive it, but Even in such a case, transition to the power saving mode is possible.

  That is, in the case where the mobile terminal 200 can not receive the transmission data by the third data transmission from the base station A and the base station B, the third data transmission is made this time, and the previous time from the base station A, ie, the second time. It can be known from the transmission timing information included in the data transmitted by the data transmission in the next that the next data transmission from the base station A, that is, the fourth data transmission is after four frame periods. Also, from the transmission timing information included in the data transmitted in the previous or second data transmission from base station B, the next or fourth data transmission from base station B is after three frame periods. Can be seen. Therefore, the power saving mode determination unit 204 determines that it is possible to shift to the power saving mode this time, that is, a period of three frame periods after the end of the third data transmission from the base station A and the base station B. And instructs the power saving control unit 205 to shift to the power saving mode.

  If the number of transmission timings included in the transmission data from the base station is N, it is possible to predict the timing of transition to the power saving mode even if data can not be received N-2 times. Also, if data could not be received N-2 times consecutively, then even if the transition timing to the power saving mode could be predicted, it should not shift to the power saving mode until data is received. You may

<Data transmission operation of base station>
Next, the operation of the base station 100 will be described using FIG. FIG. 10 is a flowchart showing data transmission operation of base station 100 in the first embodiment. The base station 100, which has been powered on and activated, generates a random number (random data) in the random timing generation unit 103, and converts it into transmission timing information. For example, when the maximum number of frames in the transmission interval is M, the random number value is converted into an integer value of 0 to M. Since the transmission timing determination unit 102 does not hold any transmission timing information before the first transmission, the random timing generation unit 103 performs processing of determining transmission timing information from random data a plurality of times, and for the first transmission The transmission timing information and all transmission timing information to be notified to the mobile terminal are determined and stored in the memory 112 (FIG. 2) (step S121).

  In the second and subsequent transmissions, since the transmission timing information created last time is held in the memory 112, the process of determining transmission timing information from random data in the random timing generation unit 103 is performed once and notified to the mobile terminal 200. Only the last transmission timing information is determined and stored in the memory 112.

  The transmission timing mapping unit 105 adds the transmission timing information determined in step S121 and notified to the mobile terminal 200 to the predetermined arrangement position of the payload generated by the payload generation unit 104 in a predetermined arrangement order. (Mapping) creates transmission data (step S122).

  The transmission unit 106 wirelessly transmits the transmission data created in step S122 at the timing of transmitting the data. Specifically, the transmitting unit 106 waits for a predetermined transmission timing notified to the mobile terminal 200 using the timer function of the CPU 111, and wirelessly transmits transmission data after time-out (step S123). .

  After the step S123 is completed, the process returns to the step S121. In this case, the final transmission timing information to be notified to the mobile terminal 200 by the next transmission data is determined.

  In the above description, it is described that the transmission unit 106 waits for transmission until a predetermined transmission timing after creating transmission data, but the method of waiting is not limited to this.

  For example, the transmission timing determination unit 102 waits for the transmission timing to be notified to the mobile terminal 200 until transmission timing determined in advance, determines the transmission timing to be notified to the mobile terminal 200 after time out, and the transmission timing mapping unit 105 Alternatively, transmission timing information may be mapped to create transmission data, and the transmission unit 106 may transmit the transmission data by radio (a).

  In addition, after the transmission timing to be notified to the mobile terminal 200 is determined in the transmission timing determination unit 102, the transmission timing mapping unit 105 waits until the transmission timing determined in advance when the transmission timing information is received from the transmission timing determination unit 102. After time-out, the latest payload may be acquired, transmission timing information may be mapped, transmission data may be created, and transmission data may be wirelessly transmitted from the transmission unit 106 (b).

  The method described in the flowchart shown in FIG. 10 is effective when it is possible to create a payload to be transmitted next after data transmission, and the methods (a) and (b) described above transmit timing because the payload portion always changes. It is effective when you want to transmit the latest payload at the time. In addition, method (a) facilitates software control because it continuously executes a series of processes after time-out. The method (b) is more complicated in software control than the method (a), but the processing after the time-out can be shorter than the method (a), so the error of the processing time can be reduced.

<Operation of mobile terminal>
Next, the operation of the mobile terminal 200 in the first embodiment will be described using FIG. FIG. 11 is a flowchart showing an operation from data reception at the mobile terminal 200 to transition to the power saving mode.

  The mobile terminal 200 stands by in a receivable state until it can receive transmission data from the base station 100 (step S221).

  The receiving unit 201 that has received the transmission data from the base station 100 performs reception processing on the received transmission data, and inputs the received data to the transmission timing extraction unit 202 as reception data. The transmission timing extraction unit 202 extracts the mapping information mapped to the received data, that is, the transmission timing information, inputs the transmission timing information to the power saving mode determination unit 204, and inputs the payload to the payload processing unit 203 (step S222). .

  The power saving mode determination unit 204 checks whether transmission timing information from all the base stations in the communication area of the mobile terminal 200 has been received (step S223), and there is an unreceived base station (step S223) In the case of No), the process returns to step S221, and waits until transmission data from an unreceived base station is received. On the other hand, if the transmission timing information from all the base stations has been received (in the case of Yes), the process proceeds to step S224.

  The power saving mode determination unit 204 calculates, from the transmission timing information from all the base stations in the communication area of the mobile terminal 200, the shortest number of frames until the next transmission data is received from any of the base stations, and moves. The terminal 200 detects a time zone in which no transmission data is received from any of the base stations (step S224).

  The power saving mode determination unit 204 determines whether the shortest number of frames until receiving transmission data calculated in step S224 exceeds 0 (> 0) (step S225).

  If the shortest frame number is 0 (in the case of No), the next transmission data is to be received immediately, so the transition to the power saving mode is not performed, and the process proceeds to step S228. On the other hand, if it exceeds 0 (in the case of Yes), the process proceeds to step S226, assuming that the next transmission data is not received immediately, and shifts to the power saving mode.

  In step S226, the power saving mode determination unit 204 instructs the power saving control unit 205 to shift to the power saving mode with the time for the shortest number of frames as the power saving mode executable period. Specifically, using the timer function and the like possessed by the CPU 211 of the mobile terminal 200, timers for the time corresponding to the shortest number of frames are set. When the power saving control unit 205 receives an instruction to shift to the power saving mode, the power supply control to the receiving unit 201 is stopped, the transmission timing extracting unit 202, the payload processing unit 203, the power saving mode determining unit 204, and the power saving control unit A predetermined power saving control is executed, such as lowering the clock frequency of the CPU that defines the operation speed of 205.

  When it is time to receive the next transmission data, that is, when the timer set in step S226 times out, the power saving mode determination unit 204 causes the power saving control unit 205 to cancel the power saving mode. It instructs (Step S227).

  The reception unit 201 stands by until a frame period scheduled to receive transmission data from the base station, that is, until transmission data is next received from the base station, and performs reception processing when it is received (step S228).

  The receiving unit 201 confirms whether the transmission data from the base station could be received within the frame period scheduled to receive the transmission data from the base station (step S229), and the transmission data from the base station could be received. In the case (Yes), the process proceeds to step S222, and transmission timing information is extracted from the data received for the data. On the other hand, when transmission data from the base station can not be received due to a data collision or the like (No), the process proceeds to step S230.

  In step S230, it is confirmed from the transmission timing information held in the memory 212 (FIG. 8) whether or not the next transmission timing of all the base stations can be known, and the next transmission timing of all the base stations can be known If it is (Yes), the process proceeds to step S231, and if there is a base station whose next transmission timing is unknown (No), the process proceeds to step S221, and reception is performed until transmission data from the corresponding base station can be received. Wait as possible. In step S231, based on the transmission timing information held in the memory 212 (FIG. 8), the power saving mode determination unit 204 determines the shortest number of frames until next transmission data is received from any base station. Calculate and repeat the processing of step S225 and thereafter.

  In the radio communication system having the base station 100 and the mobile terminal 200 of the first embodiment described above, transmission timing information for a plurality of times is mapped to transmission data from the base station 100 to the mobile terminal 200, It is possible to shift to the power saving mode without using a special sequence including two-way exchange such as notifying a response from the base station and receiving it by the mobile terminal, and so on until the mobile terminal shifts to the power saving mode Time can be shortened.

  Also, even if transmission data from the base station 100 can not be received by the mobile terminal 200, transition to the power saving mode can be made based on transmission timing information acquired in the past, so the power saving mode can be set more reliably. It can be done.

  Steps S224 to S231 illustrated in FIG. 11 can be said to be a power control method in the mobile terminal 200. That is, when there is a time zone in which there is no data transmission from any of a plurality of base stations, transition to a power saving mode that operates with power saving in that time zone, and transmission data is received within a scheduled period of receiving transmission data. In the case where it can not be received, if it is detected based on a plurality of transmission timing information received in the past that there is a time zone where there is no data transmission from any of a plurality of base stations, saving in that time zone By performing power control to shift to the power mode, power consumption of the mobile terminal can be reduced.

  In addition, since the base station 100 randomly determines the timing of data transmission to the mobile terminal 200 each time, it is also applicable to an asynchronous wireless system in which the base station side is not synchronized. Since the base station side can be made asynchronous, there is no need for a function and device for synchronization, such as a server for receiving from GPS (Global Positioning System) or time synchronization, and the configuration of base station 100 can be simplified. Cost reduction of the entire communication system can be achieved.

  Furthermore, since the transmission data only needs to be transmitted from the base station 100 to the mobile terminal 200 when transitioning to the power saving mode, the communication direction can be limited to the direction from the base station to the mobile terminal. Since there is no need to activate the device and there is no need to activate the transmitter in the mobile terminal 200, power consumption can be reduced in each of the base station 100 and the mobile terminal 200.

Second Embodiment
<Configuration of mobile terminal>
FIG. 12 is a functional block diagram showing a configuration of mobile terminal 200A in the second embodiment. In FIG. 12, the same components as those of mobile terminal 200 described with reference to FIG. 7 are assigned the same reference numerals and redundant description will be omitted. Further, the functional block diagram of the base station 100 and the block diagram showing the hardware configuration are the same as in FIG. 2 and FIG. 3, respectively, and the configuration of the entire wireless communication system including the base station 100 and the mobile terminal 200A is the embodiment. Since it is the same as 1, any description is abbreviate | omitted.

  As shown in FIG. 12, the mobile terminal 200A is provided with a signal quality measurement unit 206 in addition to the configuration of the mobile terminal 200 shown in FIG. When the reception unit 201 receives transmission data from the base station 100 (FIG. 2), the signal quality measurement unit 206 measures the signal quality of the received signal and acquires the ID of the base station 100. Then, the measured signal quality and the ID (identification information) of the base station are linked and notified to the power saving mode determination unit 204. The base station ID is uniquely determined for each base station in order to identify the base station.

  The signal quality measured by the signal quality measurement unit 206 is a received signal strength indicator (RSSI) indicating the strength of the received signal, or BER (Bits) using fixed data or PN (Pseudo Noise) signal from the transmitter 113 of the base station 100. It is specified by Error Rate). The signal quality is well known, and although there are some that define the signal quality other than the above, since the relationship with the embodiment is thin, further description will be omitted.

  When using BER using fixed data or PN signals from the transmitter 113, the base station 100 generates fixed data or PN signals in an arithmetic circuit such as the CPU 111, incorporates it in the payload, and transmits it as transmission data. The mobile terminal 200 obtains the BER based on the fixed data or PN signal incorporated in the received transmission data and the fixed data as a reference or the PN signal generated by an arithmetic circuit such as the CPU 111 of the mobile terminal 200.

  The power saving mode determination unit 204 selects a base station to be used based on the measured signal quality. As a selection method, there may be mentioned a method of selecting a base station with the best signal quality, a method of providing a threshold for the signal quality, and a method of selecting a base station with a signal quality equal to or higher than the threshold. The power saving mode determination unit 204 selects a base station according to the determined method, and determines transition to the power saving mode based on the transmission timing from the selected base station. The transmission timing information of base stations other than the selected base station is discarded without being used.

  The hardware configuration of the mobile terminal 200A is the same as the hardware configuration of the mobile terminal 200 according to the first embodiment shown in FIG. 8. For example, the signal quality measuring unit 206 in FIG. Is executed by the CPU 211, which is realized as a function of the CPU 211. Also, the information necessary for measuring the signal quality is obtained at the receiver 213 (FIG. 8).

  Further, the operation flow of base station 100 is the same as the flowchart showing the data transmission operation of base station 100 described in Embodiment 1 with reference to FIG.

<Operation of mobile terminal>
Next, the operation of the mobile terminal 200A in the second embodiment will be described using FIG. FIG. 13 is a flowchart showing an operation from data reception at the mobile terminal 200A to transition to the power saving mode.

  The mobile terminal 200A waits in a receivable state until it can receive transmission data from the base station 100 (step S221).

  The receiving unit 201 that has received the transmission data from the base station 100 inputs the received transmission data to the transmission timing extraction unit 202 as reception data. The transmission timing extraction unit 202 extracts the mapping information mapped to the received data, that is, the transmission timing information, the transmission timing information is input to the power saving mode determination unit 204, the payload is input to the payload processing unit 203, and reception is performed. The signal quality of the transmitted data is measured, and is linked with the ID of the base station 100 and stored in the memory 212 (FIG. 8) (step S232).

  The power saving mode determination unit 204 checks whether transmission timing information from all the base stations in the communication area of the mobile terminal 200 has been received (step S223), and there is an unreceived base station (step S223) In the case of No), the process returns to step S221, and waits until transmission data from an unreceived base station is received. On the other hand, if the transmission timing information from all the base stations has been received (in the case of Yes), the process proceeds to step S233.

  The power saving mode determination unit 204 determines a base station to be received based on the signal quality measured in step S232 (step S233). As the determination method, a method of selecting a base station with the best signal quality, a method of setting a threshold for the signal quality, and a method of selecting a base station with a signal quality equal to or higher than the threshold may be mentioned. Here, base stations not selected as reception targets are excluded from reception targets.

  The power saving mode determination unit 204 transmits next from any base station based on transmission timing information from the base station selected as a reception target in step S233 among all base stations in the communication area of the mobile terminal 200A. The shortest number of frames until data reception is calculated, and a time zone in which the mobile terminal 200A does not receive transmission data from any base station is detected (step S234). The operations of subsequent steps S225 to S231 are the same as the operation flow of steps S225 to S231 of the mobile terminal 200 described with reference to FIG.

  In the radio communication system having the base station 100 and the mobile terminal 200A of the first embodiment described above, the signal quality of the signal received from the base station 100 is measured, and the base stations are selected based on the signal quality. By selecting a base station with high signal quality, the probability that the mobile terminal 200A can receive transmission data at a scheduled timing becomes higher. Further, since it is possible to exclude a base station with a low reception probability, the time for which the power saving mode can be performed becomes longer accordingly, and a greater power saving effect can be obtained.

<Modification>
In the mobile terminal 200A according to the second embodiment described above, the signal quality of the received signal from the base station 100 is measured by the signal quality measurement unit 206, and the base stations are selected based on the signal quality. The position information of the mobile terminal itself may be acquired, and only the base station within a certain distance for which the distance from the base station to the mobile terminal has been obtained may be selected as the reception target base station.

  In this case, the configuration for acquiring the position information of the mobile terminal itself using GPS or the like is standardly installed in recent mobile terminals, and a technology for measuring the distance between the own terminal and the base station in the communication area is also provided. Well known techniques can be used. Using these, the distance between the base station and the mobile terminal may be obtained, and the information may be notified to the power saving mode determination unit 204 together with the ID of the base station. The power saving mode determination unit 204 selects only base stations within a certain distance as reception target base stations. By adopting such a configuration, the device configuration can be simplified.

Embodiment 3
<Configuration of mobile terminal>
FIG. 14 is a functional block diagram showing a configuration of mobile terminal 200B in the third embodiment. In FIG. 14, the same components as those of mobile terminal 200 described with reference to FIG. 7 will be assigned the same reference numerals and overlapping descriptions will be omitted. Further, the functional block diagram of the base station 100 and the block diagram showing the hardware configuration are the same as in FIG. 2 and FIG. 3, respectively, and the configuration of the entire wireless communication system including the base station 100 and the mobile terminal 200B is the embodiment. Since it is the same as 1, any description is abbreviate | omitted.

  In the power saving mode determination unit 2041 of the mobile terminal 200B illustrated in FIG. 14, transition to the power saving mode is possible when a time zone not received from any base station is detected from the transmission timing information of all received base stations. At the same time, it is determined that transition to the power saving mode is possible also during a time zone received simultaneously from a plurality of base stations, the feasible period of the power saving mode is calculated, and transition to the power saving mode is determined.

  FIG. 15 is a timing chart showing an example of reception timing of mobile terminal 200 B and transition timing to power saving mode according to Embodiment 3, and also shows transmission timings determined by base station A and base station B, respectively. .

  As shown in FIG. 15, according to the transmission timings determined by base station A and base station B, respectively, the data transmitted in the first and second data transmissions from base station A, and from base station B The data transmitted in the first and second data transmissions of the above are received by the mobile terminal, but the data transmitted in the third data transmission from the base station A and the base station B have the same transmission time zone. Since there is a collision, the mobile terminal 200 can not receive. In the first embodiment, as described with reference to FIG. 9, as in the third data transmission from base station A and base station B, the power saving mode of the mobile terminal is canceled at the timing when data transmission overlaps. In the mobile terminal 200B according to the third embodiment, reception is not attempted at the timing when data transmission overlaps, and power saving mode is set.

  The power saving mode determination unit 2041 not only detects a time zone in which data is not received from either the base station A or the base station B based on transmission timing information, but also from both the base station A and the base station B. Also in the case where a time zone for receiving data is detected, it is determined that transition to the power saving mode is possible, the power saving mode executable period is calculated, and the power saving control unit 205 is notified.

  In FIG. 15, one frame period after the second data transmission from base station B is a time zone in which data is not received from either base station A or base station B, and power saving mode determination unit 2041 It is determined that the time zone can be shifted to the power saving mode, and it is also determined that one frame period in which there is a third data transmission from the base station A and the base station B can also be shifted to the power saving mode. Also, the three frame period after the third data transmission from base station A and base station B is a time zone in which data is not received from either base station A or base station B, and power saving mode determination unit 2041 It is determined that the time zone can be shifted to the power saving mode. As a result, the five frame periods are continuously switched to the power saving mode, and the power consumption is further reduced.

  The hardware configuration of the mobile terminal 200B is the same as the hardware configuration of the mobile terminal 200 of the first embodiment shown in FIG. 8, and the description will be omitted.

  Further, the operation flow of base station 100 is the same as the flowchart showing the data transmission operation of base station 100 described in Embodiment 1 with reference to FIG.

<Operation of mobile terminal>
Next, the operation of the mobile terminal 200B in the third embodiment will be described using FIG. FIG. 16 is a flowchart showing an operation from data reception at the mobile terminal 200B to transition to the power saving mode.

  In FIG. 16, the operations of step S221 to step S223 are the same as the operation flow of step S221 to step S223 of the mobile terminal 200 described with reference to FIG.

  The power saving mode determination unit 2041 checks whether transmission timing information from all the base stations in the communication area of the mobile terminal 200B has been received (step S223), and there is an unreceived base station (step S223) In the case of No), the process returns to step S221, and waits until transmission data from an unreceived base station is received. On the other hand, when the transmission timing information from all the base stations has been received (in the case of Yes), it progresses to step S240.

  The power saving mode determination unit 2041 calculates the shortest number of frames until the next transmission data is received from any base station from the transmission timing information from all the base stations in the communication area of the mobile terminal 200 B, and moves The terminal 200B detects a first time zone in which transmission data is not received from any of the base stations, and detects a second time zone in which transmission data is received redundantly from a plurality of base stations, If two time zones are detected, the total number of frames corresponding to the total time zone obtained by adding those time zones is calculated (step S240). If only the first time zone in which no transmission data is received from any base station is detected, only the second time zone in which transmission data is received redundantly from a plurality of base stations is detected. In some cases. In those cases, the power saving mode determination unit 2041 stores which is detected.

  The power saving mode determination unit 2041 determines whether only the second time zone in which transmission data is received redundantly from a plurality of base stations is detected (step S241), and only the second time zone is detected. If (Yes), the process proceeds to step S226, otherwise proceeds to step S242.

  If only the second time zone is detected, transition to the power saving mode is made even if the interval until the second time zone is 0 frames, and therefore the power saving mode determination unit 204 selects the power saving control unit 205. For the time period corresponding to the number of frames in the second time zone, a transition to the power saving mode is instructed as an executable period of the power saving mode (step S226).

  The power saving mode determination unit 2041 determines that the shortest number of frames until receiving transmission data calculated in step S240 exceeds 0 (> 0), and the total number of frames calculated in step S240 exceeds 1 (> 1). ) Is determined (step S242).

  When the shortest number of frames is 0 or when the total number of frames is 1, the next transmission data is received immediately, and the transmission data is received from only one base station. To step S228, and the process proceeds to step S228. On the other hand, when the shortest number of frames exceeds 0 and the total number of frames exceeds 1 (in the case of Yes), the first time zone in which transmission data is not received from any base station is overlapped with the plurality of base stations. As the second time zone for receiving transmission data is detected, the process proceeds to step S226, and the power saving mode is entered.

  After step S 242, in step S 226, the power saving mode determination unit 204 causes the power saving control unit 205 to shift to the power saving mode by setting the time for the total number of frames as the power saving mode executable period. To direct. Specifically, using the timer function and the like possessed by the CPU 211 of the mobile terminal 200, timers for a total number of frames are set.

  In addition, since the operation | movement of step S227-step S230 is the same as the operation | movement flow of step S227-step S230 of the mobile terminal 200 demonstrated using FIG. 11, description is abbreviate | omitted.

  If it is determined in step S230 that the next transmission timing of all base stations is known (in the case of Yes), the process proceeds to step S243, and in step S243, the transmission timing information stored in the memory 212 (FIG. 8) is obtained. Based on the above, the power saving mode determination unit 2041 calculates the shortest number of frames until the next transmission data is received from any of the base stations, and the mobile terminal 200 B does not receive transmission data from any of the base stations. While detecting a second time zone in which transmission data is received redundantly from a plurality of base stations, and if the first and second time zones are detected, the second time zones are detected. The total number of frames corresponding to the time zone of the summed total is calculated, and the processing after step S242 is repeated.

  In the wireless communication system having the base station 100 and the mobile terminal 200B of the third embodiment described above, power saving mode can be performed by setting a period in which transmission data from a plurality of base stations overlap as an executable power saving mode. The time for which the mode can be executed is increased, and a greater power saving effect can be obtained.

Fourth Preferred Embodiment
In Embodiments 1 to 3 described above, transmission timing determination section 102 of base station 100 shown in FIG. 2 determines a plurality of random transmission timing information, and transmission timing mapping section 105 determines transmission timing determination section 102. In the above description, transmission data is created by adding a plurality of transmission timing information input from the above to the payload generated by the payload generation unit 104.

  On the other hand, in the fourth embodiment, transmission timing determination section 102 determines one random transmission timing information, and transmission timing mapping section 105 selects one transmission timing input from transmission timing determination section 102. As the next transmission timing, transmission data is created in addition to the payload generated by the payload generation unit 104.

  The functional block diagram of the base station 100 and the block diagram showing the hardware configuration are described using FIG. 2 and FIG. 3, respectively, and the configuration of the entire wireless communication system including the base station 100 and the mobile terminal 200 is Since the description is made with reference to FIG.

  FIG. 17 schematically shows an example of transmission timing mapping of transmission data created by the transmission timing mapping unit 105, and one transmission timing information input from the transmission timing determination unit 102 is converted to data and transmitted. As the information 11, it is added to the end of the payload 10 as the next transmission timing.

  Although FIG. 17 shows an example in which the transmission timing information 11 is added to the end of the payload 10, the place to be added is not limited to this. For example, the payload may be added to the beginning. May be added between

  The functional block diagram of the mobile terminal 200 and the block diagram showing the hardware configuration are the same as those described with reference to FIGS. 7 and 8, respectively, and the power saving mode determination unit 204 of the mobile terminal 200 If a time zone not received from any base station is detected from the transmission timing information of the base station, it is determined that the transition to the power saving mode is possible, the feasible period of the power saving mode is calculated, and the power saving mode is entered. Decide on the transition. However, since the transmission data from the base station 100 includes only the next transmission timing, if data reception fails due to a collision of transmission data or the like, the process waits until the next transmission data is received.

  FIG. 18 is a timing chart showing an example of reception timing of mobile terminal 200 and transition timing to power saving mode according to Embodiment 4, and also shows transmission timings determined by base station A and base station B, respectively. .

  In FIG. 18, the base station A determines 4 as transmission timing information for one time, and transmits it by including it in the initial transmission data. In this case, in the transmission timing of the base station A, the second data transmission is performed with a 4-frame period after the first data transmission. In the second data transmission, 3 is determined as transmission timing information, and is included in the second transmission data and transmitted.

  Also, the base station B determines 1 as transmission timing information for one time, and transmits it by including it in the initial transmission data. In this case, in the transmission timing of the base station B, the second data transmission is performed with an interval of one frame after the first data transmission. In the second data transmission, 1 is determined as transmission timing information, and is included in the second transmission data and transmitted.

  As shown in FIG. 18, according to the transmission timings determined by base station A and base station B, respectively, the data transmitted in the first and second data transmissions from base station A, and from base station B The data transmitted in the first and second data transmissions of the first and second times are received by the mobile terminal 200, but the data transmitted in the third data transmission from the base station A and the base station B have the same transmission time zone. Therefore, the mobile terminal 200 collides and can not receive.

  When the power saving mode determination unit 204 (FIG. 7) detects a time zone in which data is not received from either the base station A or the base station B based on the transmission timing information, transition to the power saving mode is possible. The power saving control unit 205 determines the power saving mode executable period, and notifies the power saving control unit 205 of it.

  In FIG. 18, one frame period after the second data transmission from base station B is a time zone during which data is not received from either base station A or base station B, and power saving mode determination unit 204 It is determined that the time zone can be shifted to the power saving mode.

  The data transmitted in the third data transmission from base station A and base station B collide with each other because the transmission time zone is the same, and can not be received by mobile terminal 200, and transmission timing information can not be acquired. Therefore, after the third data transmission from base station A and base station B, mobile terminal 200 stands by until the next data transmission. Therefore, even if there is a time zone in which no signal is received from any base station, the power saving mode is not entered.

  The operation flow of base station 100 is basically the same as the flowchart showing the data transmission operation of base station 100 described with reference to FIG. 10 in the first embodiment, but in base station 100 in the fourth embodiment. In step S121, at the time of the first transmission, the random timing generation unit 103 performs processing of determining transmission timing information from random data twice, and transmits the transmission timing information for the first transmission and the next transmission timing information to be notified to the mobile terminal. The determination is made and stored in the memory 112 (FIG. 2).

  In the second and subsequent transmissions, the process of determining transmission timing information from random data in random timing generation section 103 is performed once, and only the next transmission timing information to be notified to mobile terminal 200 is determined and stored in memory 112. deep.

<Operation of mobile terminal>
Next, the operation of the mobile terminal 200 in the fourth embodiment will be described using FIG. FIG. 19 is a flowchart showing an operation from data reception at the mobile terminal 200 to transition to the power saving mode.

  In FIG. 19, the operations in step S221 to step S228 are the same as the operation flow in step S221 to step S228 of the mobile terminal 200 described with reference to FIG.

  In step S229, if transmission data from the base station can be received within a frame period scheduled to receive transmission data from the base station (in the case of Yes), the process proceeds to step S222, and data received for the data is received. Take out transmission timing information from. On the other hand, when transmission data from the base station can not be received due to a data collision or the like (in the case of No), the process proceeds to step S221, and reception is possible until transmission data from any base station can be received. stand by.

  In the radio communication system having the base station 100 and the mobile terminal 200 of the fourth embodiment described above, the transmission data of the base station 100 includes transmission timing information for one time, and hence up to the next transmission timing. If, during that time, a time zone not received from any base station is detected, the power saving mode is entered and the power saving mode is executed. As described above, in the wireless communication system of the fourth embodiment, it is possible to more easily shift the mobile terminal 200 to the power saving mode.

  In the present invention, within the scope of the invention, each embodiment can be freely combined, or each embodiment can be appropriately modified or omitted.

  DESCRIPTION OF SYMBOLS 100 base station, 102 transmission timing determination part, 105 transmission timing mapping part, 106 transmission part, 200, 200A, 200B mobile terminal, 201 receiving part, 202 transmission timing extraction part, 204 power saving mode determination part, 206 signal quality measurement part .

Claims (10)

A wireless communication system for performing wireless communication between a plurality of base stations and a mobile terminal, comprising:
Each of the plurality of base stations is
A transmission timing determination unit that randomly determines transmission timing information that defines transmission timing of data to the mobile terminal;
A transmission unit that transmits the transmission data as transmission data including the transmission timing information in the data;
The mobile terminal is
A receiving unit that receives the transmission data from the plurality of base stations;
A transmission timing extraction unit that extracts the transmission timing information from the transmission data received by the reception unit;
When it is detected that there is a time zone in which there is no data transmission from any of the plurality of base stations based on the taken out transmission timing information, transition to a power saving mode that operates with power saving in the time zone is performed And a power saving mode determination unit that determines the wireless communication system. The transmission timing determination unit
The transmission timing information is randomly determined for each of a plurality of data transmissions,
The transmission timing extraction unit
Holding the transmission timing information of the plurality of times of data transmission taken out;
The power saving mode determination unit
In the case where the data can not be received within a period scheduled to receive the transmission data, data transmission from any of the plurality of base stations is performed based on the transmission timing information of the held plurality of data transmissions. The wireless communication system according to claim 1, wherein when it is detected that there is no time zone, it is determined to shift to the power saving mode in the time zone. The mobile terminal is
The signal processing apparatus further includes a signal quality measurement unit that measures the signal quality of the transmission data received by the reception unit.
The power saving mode determination unit
The base station using the transmission timing information is selected from the plurality of base stations based on the signal quality, and transition to the power saving mode is performed based on the transmission timing information from the selected base station The wireless communication system according to claim 1, wherein the availability is determined. The power saving mode determination unit
When it is detected based on the transmission timing information that there is a time zone in which the timings of data transmission from the plurality of base stations overlap, it is determined to shift to the power saving mode in the time zone. The wireless communication system according to Item 1. Each of the plurality of base stations is
The wireless communication system according to claim 2, further comprising: a mapping unit that arranges the transmission timing information of the plurality of times of data transmission in a predetermined arrangement position of the payload in a predetermined arrangement order as the transmission data. . The mapping unit is
The wireless communication system according to claim 5, wherein the transmission timing information of the plurality of times of data transmission is continuously arranged in a predetermined arrangement position of the payload in a predetermined arrangement order. The mapping unit is
The wireless communication system according to claim 5, wherein the transmission timing information of the plurality of times of data transmission is discontinuously arranged at a predetermined arrangement position of the payload in a predetermined arrangement order. A base station that performs wireless communication with a mobile terminal;
A transmission timing determination unit that randomly determines transmission timing information that defines transmission timing of data to the mobile terminal for each of a plurality of times of data transmission;
A transmitting unit configured to transmit the transmission data as transmission data including the transmission timing information in the data. A mobile terminal that performs wireless communication with a plurality of base stations,
Transmission data from the plurality of base stations is
Transmission timing information defining the transmission timing of data to the mobile terminal for each of a plurality of data transmissions;
The mobile terminal is
A receiving unit that receives the transmission data from the plurality of base stations;
A transmission timing extraction unit that extracts the transmission timing information from the transmission data received by the reception unit;
When it is detected that there is a time zone in which there is no data transmission from any of the plurality of base stations based on the taken out transmission timing information, transition to a power saving mode that operates with power saving in the time zone is performed A power saving mode determination unit to determine the
The transmission timing extraction unit
Holding the transmission timing information of the plurality of times of data transmission taken out;
The power saving mode determination unit
In the case where the data can not be received within a period scheduled to receive the transmission data, data transmission from any of the plurality of base stations is performed based on the transmission timing information of the held plurality of data transmissions. When it is detected that there is no time zone, the mobile terminal decides to shift to the power saving mode in the time zone. A power control method in a mobile terminal that performs wireless communication with a plurality of base stations, comprising:
Transmission data from the plurality of base stations is
Transmission timing information defining the transmission timing of data to the mobile terminal for each of a plurality of data transmissions;
The mobile terminal is
When it is detected that there is a time zone in which no data transmission exists from any of the plurality of base stations based on the transmission timing information of the received data transmission for a plurality of times, operation is performed with power saving in the time zone Transition to the power saving mode
When the data can not be received within the scheduled period for receiving the transmission data, the transmission timing information of the data transmission for the plurality of times received in the past is used from any of the plurality of base stations based on the transmission timing information. When it is detected that there is a time zone without data transmission, it is determined to shift to a power saving mode in the time zone.

Images