Abstract:
A communication device includes a receiving circuit and a start-up time adjustment circuit configured to transmit, to the receiving circuit, a start signal that instructs a change from a sleep state to an active state, wherein the start-up time adjustment circuit is configured to transmit, to the receiving circuit, a first start signal that instructs a change from the sleep state to the active state at a first time earlier than a second time when a first signal reaches the communication device, measure a first time difference between the second time and the first time, determine, based on the first time difference, a third time when the receiving circuit is changed from the active state to the sleep state, and transmit a second start signal that instructs a change from the sleep state to the active state to the receiving circuit at the third time.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2014-251248, filed on Dec. 11, 2014, the entire contents of which are incorporated herein by reference. 
     FIELD 
     The embodiments discussed herein are related to a communication device, a method, and a communication system. 
     BACKGROUND 
     In recent years, a wireless network in which a terminal (a receiving device, a communication device) switches between an active state and a sleep state, based on a transmission wave (a beacon) transmitted from a base station (a transmitting device), and an operation is intermittently performed has been proposed. Such a wireless network in which an intermittent operation is performed is used for, for example, a wireless network for a sensor, power consumption of which is desired to be reduced, and the like. 
     In wireless communication, transmission and reception of data are wirelessly performed between a transmitting device and a receiving device and, in many cases, when such transmission and reception of data are performed, the receiving device is driven by a battery. When the receiving device is driven by a battery, it is desired to reduce power consumption to thereby increase the lifetime of the battery and reduce the frequency of replacement or charge of the battery. 
     Therefore, the receiving device is configured to perform an intermittent operation in which a related circuit (a transmitting and receiving circuit) is put in an active state only when reception or transmission of a signal is performed, and other than that, the circuit is put in a sleep state that is a low-power consumption state. 
     That is, in wireless communication, a period of an active state in which reception or transmission of data is performed is far shorter than a period of a sleep state in many cases. Therefore, it is enabled to reduce average power consumption in the receiving device by controlling an active state and a sleep state, based on a beacon transmitted from the transmitting device. 
     Incidentally, up until now, various methods for performing control of a receiving device that receives a transmission wave, based on a transmission wave intermittently transmitted from a transmitting device, have been proposed. Japanese Laid-open Patent Publication No. 08-307342, Japanese Laid-open Patent Publication No. 2004-328501, Japanese Laid-open Patent Publication No. 09-093185, Japanese Laid-open Patent Publication No. 2010-114671, and Japanese Laid-open Patent Publication No. 2001-069107 discuss related art. 
     SUMMARY 
     According to an aspect of the invention, a communication device which receives a plurality of signals transmitted at time intervals, the communication device includes a receiving circuit configured to receive the plurality of signals, and a start-up time adjustment circuit configured to transmit, to the receiving circuit, a start signal that instructs a change from a sleep state to an active state, wherein the start-up time adjustment circuit is configured to transmit, to the receiving circuit, a first start signal that instructs a change from the sleep state to the active state at a first time earlier than a second time when a first signal among the plurality of signals reaches the communication device, measure a first time difference between the second time and the first time, determine, based on the first time difference, a third time that is a time after a time when the receiving circuit is changed from the active state to the sleep state, and transmit a second start signal that instructs a change from the sleep state to the active state to the receiving circuit at the third time. 
     The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram illustrating an example of a reception control method in a transmitting and receiving system; 
         FIG. 2  is a chart illustrating a problem in the reception control method illustrated in  FIG. 1 ; 
         FIG. 3  is a chart illustrating a reception control method according to an embodiment; 
         FIG. 4  is a block diagram illustrating a start-up adjustment circuit of a receiving device in a first embodiment; 
         FIG. 5  is a chart illustrating an operation of the start-up time adjustment circuit illustrated in  FIG. 4 ; 
         FIG. 6  is a block diagram illustrating a start-up adjustment circuit of a receiving device in a second embodiment; 
         FIG. 7  is a chart illustrating an operation of the start-up time adjustment circuit illustrated in  FIG. 6 ; 
         FIG. 8  is a chart illustrating an example of a beacon reception signal; 
         FIG. 9  is a block diagram illustrating a start-up time adjustment circuit of a receiving device in a third embodiment; 
         FIG. 10  is a chart illustrating an operation of the start-up time adjustment circuit illustrated in  FIG. 9 ; 
         FIG. 11  is a block diagram illustrating a timer unit in the start-up time adjustment circuit illustrated in  FIG. 9 ; 
         FIG. 12  is a chart illustrating an operation of the timer unit illustrated in  FIG. 11 ; 
         FIG. 13  is a block diagram illustrating a start-up time adjustment circuit of a receiving device in a fourth embodiment; 
         FIG. 14  is a chart illustrating an operation of the start-up time adjustment circuit illustrated in  FIG. 13 ; 
         FIG. 15  is a chart illustrating an intermittent temporal scaling factor used in the start-up time adjustment circuit illustrated in  FIG. 13 ; 
         FIG. 16  is a diagram schematically illustrating an example of a transmitting and receiving system to which the receiving device of the fourth embodiment is applied; 
         FIG. 17  is a block diagram illustrating a start-up time adjustment circuit of a receiving device in a fifth embodiment; and 
         FIG. 18  is a block diagram illustrating an entire configuration of a receiving device according to an embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Conventionally, for example, average power consumption in a receiving device is reduced by controlling an active state and a sleep state of the receiving device, for example, based on a beacon transmitted from a transmitting device. 
     For example, when a receiving device is applied to a wireless network for a sensor, or the like, normally, reduction in price is desired to be achieved for the receiving device, and therefore, as a timer that determines a timing at which a beacon is transmitted, for example, an inexpensive timer that does not use a crystal resonator but uses an LC resonance is preferably used. Furthermore, when a receiving device is applied to a wireless network for a sensor, or the like, as the receiving device, a receiving device with a reduced size is desired, and therefore, use of a simple timer is preferably used in view of such downsizing as well. 
     However, for example, since an inexpensive timer using an LC resonance has lower time measurement accuracy than that of a timer using a crystal resonator, a receiving device is started up such that, even when a large measurement error occurs, the receiving device may receive a beacon, and a margin is allowed for a timing at which the receiving device is put in an active state. 
     However, when the margin is increased to advance a start-up timing of the receiving device, an active state is increased. Power consumption of the receiving device in the active state is greater than that in a sleep state, and therefore, margin setting for a timing of a start up of the receiving device is difficult under the existing conditions. 
     That is, increasing a sleep state and thus delaying a start-up of the receiving device to a time immediately before reception of a beacon for the purpose of reducing power consumption, and increasing a margin of a start-up of the receiving device for the purpose of allowing plenty of time to receive a beacon are in a trade-off relationship. Therefore, it is difficult to increase a sleep state of the receiving device and thus reduce power consumption, while using a timer with low time measurement accuracy for the receiving device. 
     First, before describing a communication device, a transmitting and receiving system, and a method for controlling a communication device according to an embodiment, an example of a reception control method in a transmitting and receiving system and a problem thereof will be described with reference to  FIG. 1  and  FIG. 2 . 
       FIG. 1  is a diagram illustrating an example of a reception control method in a transmitting and receiving system, and  FIG. 2  is a chart illustrating a problem in the reception control method illustrated in  FIG. 1 .  FIG. 1  and  FIG. 2  illustrate an example where transmission waves (beacons) BN 1 , BN 2 , . . . are intermittently output from a transmitting device  2  to a receiving device  1  in a cycle of 0.5 seconds. 
     Note that the transmitting device  2  herein is a transmitting device in terms of transmitting a beacon and, for example, corresponds to a base station (Hub) in a wireless network for a sensor. Also, the receiving device  1  herein is a receiving device in terms of receiving a beacon and, for example, corresponds to a terminal (Node) in a wireless network for a sensor. 
     Therefore, the base station (a transmitting device)  2  not only transmits a beacon to a plurality of terminals (a receiving device, a communication device)  1  but also performs mutual communication including reception of data acquired by a sensor in each of the terminals  1 , and transmission and reception of a control signal. Also, the terminal  1  not only receives a beacon transmitted from the base station  2  but also performs mutual communication including transmission of data to another terminal  1  and transmission and reception of a control signal. 
     Furthermore, in  FIG. 1 , for example, a beacon interval from an end of transmission of a first beacon BN 1  to a start of transmission of a second beacon BN 2  is illustrated as a cycle, and this does not cause any problem because a time during which a beacon is transmitted is relatively short, as compared to the beacon cycle. Also, the cycle of the beacons BN 1 , BN 2 , . . . that are intermittently transmitted is not limited to 0.5 seconds and, for example, may be various cycles of several seconds to several days, depending on a use application of the system. 
     As illustrated in  FIG. 1 , in the receiving device  1 , for example, using a timer, the receiving device (a receiving circuit or the like)  1  is started up from a sleep state to an active state at a time Tps so as to be able to receive the beacon BN 2  that is transmitted from the transmitting device  2  at intervals of 0.5 seconds (in an intermittent cycle). 
     In this case, the receiving device  1  is applied to a wireless network for a sensor, or the like, power consumption of which is desired to be reduced but, normally, there are cases where an inexpensive timer (a clock generation circuit) using an LC resonance, or a simple timer that realizes downsizing is used. Note that, in the following description, a case where an error caused by a timer is 0.5% at maximum is assumed. 
     That is, assuming that an error caused by a timer is 0.5% at maximum, for example, when an intermittent cycle of 0.5 seconds is measured, an error of 0.5 seconds×0.005=0.0025 seconds (2.5 milliseconds) at maximum occurs. 
     Therefore, for example, there is a possibility that, unless, assuming that the timer is delayed by 0.5% (2.5 milliseconds), as a setting value (a standard value), the receiving device  1  is started up so as to be in an active state at a timing only 2.5 milliseconds earlier than a beacon reception timing Tpr assumed by the timer, reception of the beacons BN 2 , BN 3 , . . . is disabled. 
     As a result, as illustrated in  FIG. 2 , the receiving device  1  is in a sleep state for 99.5%, that is, 0.4975 seconds, of 0.5 seconds of an interval (one beacon cycle) in which a beacon is output, and is in an active state for 2.5 milliseconds. 
     Accordingly, in  FIG. 2 , during a time from the timing Tps at which the receiving device  1  is started up to be in an active state to the timing Tpr at which the beacon BN 2  is received, power PWo consumed by the receiving device  1  is wasted. 
     As described above, state control of a receiving device (a terminal, the communication device) is performed, for example, with reference to a timer mounted in the terminal but, when time accuracy of the timer is poor, the terminal is put in an active state with a large margin, so that power is consumed to waste. 
     Examples of a communication device, a transmitting and receiving system, and a method for controlling a communication device will be described below with reference to the accompanying drawings.  FIG. 3  is a chart illustrating a reception control method (a method for controlling a communication device) according to this embodiment, and illustrates an example in which transmission waves (beacons) BN 1 , BN 2 , . . . are intermittently output from the transmitting device (Hub)  2  of a base station or the like to the receiving device (Node)  1  of a terminal, a communication device, or the like, in a cycle of 0.5 seconds. 
     As illustrated in  FIG. 3 , first, for example, assuming that, when a first beacon BN 1  of a target period is received, an intermittent cycle of the beacons is Trx, a maximum error of a timer is ΔTtm, and a timer setting value is Vst, the reception control method according to this embodiment may be represented by an expression below. 
     Note that, when the first beacon BN 1  is received, the timer setting value Vst is the same as, for example, a timer setting initial value Vs that is given as an initial value. 
     
       
         
           
             
               
                 
                   Vst 
                   = 
                     
                   ⁢ 
                   Vs 
                 
               
             
             
               
                 
                   = 
                     
                   ⁢ 
                   
                     Trx 
                     - 
                     
                       Δ 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       Ttm 
                     
                   
                 
               
             
             
               
                 
                   = 
                     
                   ⁢ 
                   
                     
                       0.5 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       seconds 
                     
                     - 
                     
                       0.5 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       seconds 
                       × 
                       0.005 
                     
                   
                 
               
             
             
               
                 
                   = 
                     
                   ⁢ 
                   
                     0.4975 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     seconds 
                   
                 
               
             
           
         
       
     
     As described above, the timer setting value (a sleep time) when the first beacon BN 1  is received is, for example, 0.4975 seconds. Accordingly, the timing (a start-up time) Tps at which the receiving device  1  is put in an active state is 0.0025 seconds, that is, 2.5 milliseconds earlier, which is the same as that described with reference to  FIG. 1  and  FIG. 2 , than the timing (a beacon reception time) Tpr at which the beacon BN 1  is received. Therefore, the power consumption of the receiving device  1  when the first beacon BN 1  is received is the same as that described with reference to  FIG. 1  and  FIG. 2 . 
     In this case, when the first beacon BN 1  is received, a time from a timing at which the receiving device  1  is put in an active state to a timing at which the beacon BN 1  is actually received is measured. That is, when the first beacon BN 1  is received, a time Td from the start-up time Tps of the receiving device  1  to the beacon reception time Tpr is counted. Assume that this counter value (an offset value) is α. 
     Next, when a second beacon BN 2  is received, a sleep time of the receiving device  1  is corrected based on the time Td (α) from the start-up time Tps of the receiving device  1  to the beacon reception time Tpr, when the first beacon BN 1  is received. 
     That is, when the second beacon BN 2  is received, the timer setting value Vst is corrected by the offset value α from the start-up time Tps of the receiving device  1  to the beacon reception time Tpr, when the first beacon BN 1  is received. This may be represented by an expression below.
 
 Vst=Vs+α 
 
     In this case, for example, assuming that a margin until plenty of time is allowed for the receiving device  1  to receive a beacon (BN 2 ) after a reception start signal Srs was output to the receiving device  1  is β, the timer setting value Vst when the second beacon BN 2  is received may be represented by an expression below.
 
 Vst=Vs+α−β 
 
     Note that, for the timer setting value Vst when third and subsequent beacons BN 3 , BN 4 , . . . are received, the timer setting value at a second beacon reception time may be used as it is, but also, may be corrected each time using the offset value α and the margin β at an immediately previous reception time. Note that, as will be described later, this embodiment is applicable in a case where a beacon interval is changed, and the like. 
     As described above, according to a reception control method of this embodiment, at the second and subsequent beacon reception times, for example, similar to a case where a highly accurate timer using a crystal resonator is used, highly accurate start-up control of the receiving device  1  is enabled, so that reduction in power consumption is enabled. Note that, even when a highly accurate timer using a crystal resonator is used, further increase in sleep time and further reduction in power consumption may be enabled by applying this embodiment. 
       FIG. 4  is a block diagram illustrating a start-up adjustment circuit of a receiving device in a first embodiment. Note that, as will be illustrated in  FIG. 18  later, the receiving device (the terminal)  1  includes an internal circuit  100 , such as, for example, a transmitting circuit, a receiving circuit, a signal processing circuit, and the like, and a start-up time adjustment circuit  10  that controls an operation (sleep and active) of the internal circuit  100 . 
     In this case, the start-up time adjustment circuit  10  realizes the above-described expression “Vst=Vs+α” and starts up the internal circuit  100  (the receiving device  1 ) from a sleep sate a predetermined time earlier than a reach time of each of the transmission waves BN 1 , BN 2 , . . . that are intermittently transmitted. 
     As illustrated in  FIG. 4 , the start-up time adjustment circuit  10  includes a timer unit (a timer)  11 , two flip-flops (FF)  121  and  122 , a subtractor  13 , an integrator  14 , and an adder  15 . 
     The timer unit  11  receives a reference clock CKr, a timer start signal Sts, and a timer setting value Vst, counts the reference clock CKr, and outputs a reception start signal (a timer output) Srs that starts up the receiving device  1  (the internal circuit  100 ). 
     One of the two FFs, that is, the FF (a first latch)  121 , takes in a counter value Vc output from the timer unit  11  with the reception start signal Srs and holds the counter value Vc. The other one of the two FFs, that is, the FF (a second latch)  122 , takes in the counter value Vc output from the timer unit  11  with a beacon reception signal (a transmission wave reception signal) Sbr and holds the counter value Vc. 
     The subtractor  13  subtracts an output Vf 1  of the first latch  121  from an output Vf 2  of the second latch  122 , and outputs a result of the subtraction to the integrator  14 . The integrator  14  integrates an output of the subtractor  13  to generate an offset value (a counter value) α, and outputs the generated offset value α to the adder  15 . That is, the offset value α is averaged by the integrator  14 , and the averaged offset value α is input to the adder  15 . 
     The adder  15  receives a timer setting initial value Vs, adds the offset value α to the timer setting initial value Vs, and outputs a result of the addition as the timer setting value Vst that is used at a next beacon reception time to the timer unit  11 . In this case, the timer setting initial value Vs is used as the timer setting value Vst in an initial state (when a first beacon BN 1  is received), and corresponds to a sleep time in receiving the first beacon BN 1 . 
       FIG. 5  is a chart illustrating an operation of the start-up time adjustment circuit illustrated in  FIG. 4 , and illustrates a case where Vs=14 and α=4. As illustrated in  FIG. 5 , when the first beacon BN 1  is received, the timer unit  11  in the start-up time adjustment circuit  10  of the receiving device  1  counts the timer setting value Vst (=14), which is output from the adder  15  and is the same as the timer setting initial value Vs. Then, when the timer unit  11  counts the same value as the timer setting value Vst, the timer unit  11  outputs the reception start signal Srs. That is, the reception start signal Srs is caused to rise from a low level “L” to a high level “H”. 
     In this case, the first latch  121  takes in the counter value Vc output from the timer unit  11  at output (at a rising timing) of the reception start signal Srs, and inputs an output Vf 1  (=14) thereof to the subtractor  13 . The second latch  122  takes in the counter value Vc output from the timer unit  11  at a rising timing of a beacon reception signal Sbr, and inputs an output Vf 2  (=18) thereof to the subtractor  13 . 
     The subtractor  13  subtracts the output Vf 1  of the first latch  121  from the output Vf 2  of the second latch  122 , and outputs a result (18−14=4) of the subtraction to the integrator  14 . The integrator  14  integrates an output of the subtractor  13  to generate an offset value α (=4), and outputs the generated offset value α to the adder  15 . 
     The adder  15  adds the offset value α (=4) to the timer setting value Vst (=14) of the timer setting initial value Vs (when the first beacon BN 1  is received), and outputs the timer setting value Vst (=18) that is used when the next second beacon BN 2  is received to the timer unit  11 . 
     Thus, a sleep time until the second beacon BN 2  is received is increased to a time based on the timer setting value Vst (=18), which is longer than the timer setting initial value Vs (=14), and thereby, reduction in power consumption is enabled. 
       FIG. 6  is a block diagram illustrating a start-up adjustment circuit of a receiving device in a second embodiment, and  FIG. 7  is a chart illustrating an operation of the start-up time adjustment circuit illustrated in  FIG. 6 . As clearly indicated by a comparison of  FIG. 6  with  FIG. 4  described above, in the second embodiment, instead of the counter value Vc output from the timer unit  11 , an output (a timer setting value Vst) of the adder  15  is input to the first latch  121 . 
     Note that  FIG. 7  is similar to  FIG. 5  described above and, also in the start-up time adjustment circuit of the second embodiment illustrated in  FIG. 6 , similar to the first embodiment, a sleep time until the second beacon BN 2  is received is increased to the timer setting value Vst=18, and thereby, reduction in power consumption is enabled. 
       FIG. 8  is a chart illustrating an example of a beacon reception signal. As illustrated in  FIG. 8 , as a beacon reception signal Sbr (reception signal strength), for example, an output signal of a received signal strength indicator (RSSI) or an energy detector (ED), or a frame synchronization signal may be used. 
     That is, the receiving device  1  normally has a function of detecting the strength of a reception radio wave, and is capable of generating a beacon reception signal Sbr in response to an output of an RSSI exceeding a certain level, an output of an ED, or a frame synchronization detection signal obtained by modulating a reception signal. 
     Furthermore, for example, in order not to output the beacon reception signal Sbr due to noise disturbance by mistake, a logical product of an output of the RSSI and a frame synchronization detection signal of the ED is obtained, and thus, a beacon reception signal Sbr is generated, so that reliability may be increased. 
       FIG. 9  is a block diagram illustrating a start-up time adjustment circuit of a receiving device in a third embodiment, and  FIG. 10  is a chart illustrating an operation of the start-up time adjustment circuit illustrated in  FIG. 9 . As clearly indicated by a comparison of  FIG. 9  with  FIG. 4  described above, in the third embodiment, two signals Srs 1  and Srs 2  are output from the timer unit  11 . In this case, the timer output signal Srs 1  corresponds to, for example, the reception start signal Srs in  FIG. 4 . 
     That is, as illustrated in  FIG. 7 , the signal (a reception start signal of the third embodiment) Srs 2 , for example, rises two clocks of the reference clock CKr earlier than the signal Srs 1 , and the two clocks correspond to a margin β. 
     This is because, for example, in a case where a sleep time until the second beacon BN 2  is received is merely obtained as the timer setting value Vst=Vs+α, if a beacon BN is received earlier due to various changes, it is not possible to receive the beacon, and therefore, a predetermine margin β is provided. 
     That is, for example, a sleep time until the second beacon BN 2  is received is obtained based on Vst=Vs+α−β, and thus, although power consumption is comparatively increased, plenty of time may be allowed to receive the beacon BN 2 . 
       FIG. 11  is a block diagram illustrating a timer unit in the start-up time adjustment circuit illustrated in  FIG. 9 , and  FIG. 12  is a chart illustrating an operation of the timer unit illustrated in  FIG. 11 . As illustrated in  FIG. 11 , the timer unit  11  includes a counter  111 , a subtractor  112 , and comparators  113  and  114 . 
     In this case, a timer start signal Sts is input to a reset terminal (an inverting input terminal) XRST of the counter  111  and, when the timer start signal Sts falls from “H” to “L”, a counter value is reset. Then, when the timer start signal Sts rises from “L” to “H” next, a count based on the reference clock CKr is started. 
     Note that an example of the timer unit  11  in each of the first and second embodiments that have been described with reference to  FIG. 4  and FIG.  6  above corresponds to a timer unit which is obtained by removing the subtractor  112  and the comparator  114  from the timer unit of the third embodiment illustrated in  FIG. 11  and in which the output Srs 1  of the comparator  113  is set as the reception start signal Srs. 
     In the third embodiment, as the reception start signal Srs, the output Srs 2  of the comparator  114  is used, and the output Srs 1  of the comparator  113  is used as a clock input of the first latch  121  and a signal of another circuit in the receiving device  1 . 
     In the third embodiment, the margin β is subtracted from the timer setting value Vst by the subtractor  112  and an output of the subtractor  112  is input to the comparator  114 , and thereby, the reception start signal Srs 2  with which a sleep time corresponding to Vst=Vs+α−β may be ensured is generated. 
     That is, as illustrated in  FIG. 12 , the reception start signal Srs 2  in the third embodiment is output (changed from “L” to “H”), for example, the margin β (two clocks) earlier than the reception start signal Srs in the first embodiment. 
     Specifically, for example, a signal D that rises at an 18th clock based on the timer setting value Vs and the counter value Vc output from the counter  111  are input to the comparator  113 , and the output Srs 1  of the comparator  113  rises from “L” to “H” at the 18th clock. 
     For example, the signal D that is obtained by subtracting the margin β corresponding to two clocks from the timer setting initial value Vst by the subtractor  112  and rises at a 16th clock and the counter value Vc output from the counter  111  are input to the comparator  114 . Accordingly, the output Srs 2  of the comparator  114  rises from “L” to “H” at the 16th clock. Note that it is needless to say that the subtractor  112  may be replaced with an adder. 
     As described above, a value (a clock number) of the margin β may be changed, for example, by a higher-level processor in accordance with a surrounding noise environment and the like. Also, the output Srs 1  of the comparator  113  and the output Srs 2  of the comparator  114  may be switched around, and for example, one of the output Srs 1  and the output Srs 2  may be selected and used as a reception start signal (Srs) in accordance with a noise environment and the like. 
     Furthermore, for example, a plurality of pairs of the subtractor  112  and the comparator  114  may be provided, different margins β 1 , β 2 , . . . may be set to the plurality of pairs, and thus, a margin in a reception start signal (Srs) may be controlled, as appropriate. As described above, the timer unit  11  illustrated in  FIG. 11  is merely an example, and it is needless to say that various modifications and changes may be made. 
       FIG. 13  is a block diagram illustrating a start-up time adjustment circuit of a receiving device in a fourth embodiment, and illustrates an example in which the interval of the beacon BN is irregular (are not regular). Also,  FIG. 14  is a chart illustrating an operation of the start-up time adjustment circuit illustrated in  FIG. 13 , and  FIG. 15  is a chart illustrating an intermittent temporal scaling factor used in the start-up time adjustment circuit illustrated in  FIG. 13 . 
     The fourth embodiment illustrates an example in which, as illustrated in  FIG. 14 , the interval of the beacon BN changes in accordance with an intermittent temporal scaling factor Γ. Also, as illustrated in  FIG. 15 , the time interval of a beacon (BN 2 ) is included in a reception frame of a beacon (BN 1 ) received (transmitted) immediately previously. 
     That is, for example, the intermittent temporal scaling factor Γ is included in a beacon frame (a reception frame) immediately before the timer unit  11  is started up by the timer start signal Sts, is thus transmitted from the transmitting device (the base station)  2  to the receiving device (the terminal)  1 , and Γ (Γ 1 , Γ 2 , . . . ) is set. Note that an initial value (Γ 0 ) of the intermittent temporal scaling factor Γ is set in advance. 
     As clearly indicated by a comparison of  FIG. 13  with  FIG. 4  described above, in the fourth embodiment, a multiplier  16  is inserted between the adder  15  and the timer unit  11 . The multiplier  16  receives the output (the timer setting value) Vst of the adder  15 , multiplies the output Vst by the intermittent temporal scaling factor Γ, and outputs a timer setting value Vst′ to the timer unit  11 . Note that it is needless to say that the above-described second embodiment and third embodiment may be applied to the fourth embodiment. 
       FIG. 16  is a diagram schematically illustrating an example of a transmitting and receiving system to which the receiving device of the fourth embodiment is applied, and illustrates an example of a wireless transmitting and receiving system that variably controls the intermittent temporal scaling factor Γ. As illustrated in  FIG. 16 , a transmitting and receiving unit  20 , a differentiator  21 , and a Γ calculation table (a Γ calculation unit)  22  are provided in the transmitting device (a base station)  2 . Note that it is needless to say that the F calculation table  22  is not limited to a table. 
     The transmitting and receiving unit  20  transmits the transmission waves BN 1 , BN 2 , . . . to the receiving device (the terminal)  1 , receives data output from the terminal  1 , and then processes the data, and the differentiator  21  differentiates the data received from the terminal  1  via the transmitting and receiving unit  20 . 
     The Γ calculation table  22  controls, based on an output of the differentiator  21 , the intermittent temporal scaling factor Γ, and transmits the intermittent temporal scaling factor Γ to the terminal  1  via the transmitting and receiving unit  20 . The intermittent temporal scaling factor Γ is calculated with the Γ calculation table  22  such that, when an absolute value of an output (a differential value) of the differentiator  21  is large, the intermittent temporal scaling factor Γ is small. 
     That is, for example, if a change of data is rapid, an intermittent time of a beacon is reduced and control is performed such that an execution data rate is increased, and if a change of data is moderate, an intermittent time of a beacon is increased and control is performed such that an execution data rate is reduced. 
     Thus, an optimal data rate based on a data change may be set, power consumption may be reduced, so that the lifetime of a battery may be further increased. 
       FIG. 17  is a block diagram illustrating a start-up time adjustment circuit of a receiving device in a fifth embodiment. As clearly indicated by a comparison of  FIG. 17  with  FIG. 4  described above, in the fifth embodiment, a comparator  17  that receives the counter value Vc output from the timer unit  11  and a time out setting value Vto and compares the counter value Vc and the time out setting value Vto with each other is added. 
     That is, the comparator  17  is configured to output, when the counter value Vc output from the timer unit  11  is the time out setting value Vto, a reset signal rst to the integrator  14  to reset an integral value. 
     In this case, the timer setting initial value Vs given to the adder  15  is set, for example, based on a shortest sleep time, and there is a probability that, when correction is performed with the offset value α and thus the sleep time is extended, the receiving device  1  may possibly fail to receive the beacon BN. 
     Considering the above-described situation, the time out setting value Vto is set in advance and, if the beacon reception signal Sbr is not output even when the counter value Vc is the time out setting value Vto, the integrator  14  is reset by the reset signal rst output from the comparator  17 . 
     Thus, similar to when the first beacon BN 1  is received, the timer setting initial value Vs is output as the timer setting value Vst from the adder  15 , and a start-up is performed earlier, based on the shortest sleep time. 
       FIG. 18  is a block diagram illustrating an entire configuration of a receiving device according to this embodiment. As illustrated in  FIG. 18 , the receiving device  1  includes the start-up time adjustment circuit  10  and the internal circuit  100 . In this case, the internal circuit  100  includes a transmitting circuit, a receiving circuit, a signal processing circuit, and the like, and on (an active state) and off (a sleep state) thereof are controlled based on the reception start signal Srs output from the start-up time adjustment circuit  10 . 
       FIG. 18  is a block diagram illustrating an entire configuration of a receiving device according to this embodiment. As illustrated in  FIG. 18 , the receiving device  1  includes the start-up time adjustment circuit  10  and the internal circuit  100 . As described above, the beacon reception signal Sbr, the reference clock CKr, and the timer start signal Sts are input to the start-up time adjustment circuit  10 , and the reception start signal Srs is output to the internal circuit  100 . 
     In this case, the internal circuit  100  includes a transmitting circuit, a receiving circuit, a signal processing circuit, and the like, and on (an active state) and off (a sleep state) thereof are controlled based on the reception start signal Srs output from the start-up time adjustment circuit  10 . Also, as the beacon reception signal Sb, a signal output from the internal circuit  100  that has been started up is used. 
     Note that, although not illustrated in  FIG. 18 , for example, when the receiving device  1  is used as a terminal of a wireless network for a sensor, the internal circuit  100  includes various devices and circuits, such as a sensor and a memory, which are used. 
     All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although the embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.