Patent Publication Number: US-9426761-B2

Title: Wireless communication device

Description:
TECHNICAL FIELD 
     The present disclosure relates to a wireless communication device which performs communication, for example, using frequencies of a millimeter-wave band. 
     BACKGROUND ART 
     WiGig wireless devices operate in accordance with a Wireless Gigabit (WiGig) specification that is a wireless communication standard of a frequency band of 60 GHz, that is, a millimeter-wave band. The WiGig specification is defined by the Wireless Gigabit Alliance. The communication distance of WiGig wireless devices is short, for example, about 10 m, but WiGig wireless devices can communicate a large capacity of data at high-speeds. 
     In order to design a wireless communication device (for example, the WiGig wireless device) or to test an operation of a wireless communication device, it is necessary to understand antenna radiation patterns, that is, radiation patterns of radio waves, by using an actual wireless communication device, for performance improvement. 
     In the related art, in order to measure the antenna radiation pattern of a WiGig wireless device, the WiGig wireless device is brought into an anechoic chamber and the antenna radiation pattern thereof is measured. If the antenna radiation pattern is measured in an environment other than an anechoic chamber, reflected waves are generated from objects in the vicinity of the WiGig wireless device. In particular, in short-range communication, a distinction between a direct wave and the reflected waves is difficult because a time difference between the direct wave and the reflected waves which are to be detected is small, such that it is difficult to measure a correct antenna radiation pattern. 
     For example, PTL 1 discloses a radio wave environment measuring device which can detect a radio wave condition in an environment other than an anechoic chamber, in which the direct wave and the reflected wave are mixed. In PTL 1, the direct wave and the reflected waves can be separated by a pulse compression technology. 
     In the pulse compression technology, a reception side which receives a wireless signal detects a correlation between a reception pulse and a reference pulse. A time width of a pulse to be detected can be compressed to a narrower range than the pulse width of a pulse signal that is actually transmitted, and time resolution is improved. In other words, the radio wave environment measuring device disclosed in PTL 1 can separately detect the direct wave and the reflected waves, which have a small time difference from each other. 
     CITATION LIST 
     Patent Literature 
     [PTL 1] Japanese Patent No. 3112746 
     SUMMARY OF INVENTION 
     Technical Problem 
     However, in PTL 1, since the pulse compression technology needs to be implemented in the WiGig wireless device for use, the circuit size becomes large and the development effort of the WiGig wireless device increases, leading to an increase in production cost. 
     The present disclosure has been made in view of the circumstances of the related art, and its object is to provide a wireless communication device which generates a pulse compression signal for measuring a radiation pattern from an antenna, by a simple configuration. 
     Solution to Problem 
     The present disclosure relates to a wireless communication device configured to transmit a signal frame in a time series including a data main body and a preamble, including: a signal masking section configured to intermittently perform a mask processing on a signal output in a specific position in the preamble of the signal frame; and a mask timing generation section configured to determine a control timing of the signal masking section. 
     Advantageous Effects of Invention 
     According to the present disclosure, it is possible to generate a pulse compression signal for measuring a radiation pattern from an antenna, by a simple configuration. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram illustrating an internal configuration of a WiGig wireless device as a wireless communication device of a first embodiment. 
         FIG. 2  is a block diagram illustrating an internal configuration of a sensor which measures an antenna radiation pattern of the wireless communication device illustrated in  FIG. 1 . 
         FIG. 3  is a schematic diagram illustrating a format of a preamble of a signal transmitted by the WiGig wireless device in data communication. 
         FIG. 4  is a time chart illustrating an operation of generating a pulse compression signal in the WiGig wireless device. 
         FIG. 5  is a block diagram illustrating an internal configuration of a WiGig wireless device as a wireless communication device of a second embodiment. 
         FIG. 6  is a time chart illustrating an operation in which the WiGig wireless device of  FIG. 5  generates a pulse compression signal. 
         FIG. 7  is a block diagram illustrating a specific configuration of a Golay signal generation section. 
         FIG. 8  is a graph illustrating a specific example of a reception correlation output characteristic of a sensor. 
         FIG. 9  is a schematic diagram illustrating a format of a signal frame of CONTROL-PHY. 
         FIG. 10  is a schematic diagram illustrating a format of a preamble of the signal frame of CONTROL-PHY. 
         FIG. 11  is a block diagram illustrating a system configuration of a radiation pattern measurement system and an internal configuration of a wireless communication device in a third embodiment. 
         FIG. 12  is a block diagram illustrating an internal configuration of a sensor in the radiation pattern measurement system illustrated in  FIG. 11 . 
         FIG. 13  is a graph illustrating a specific example of a reception correlation output characteristic of the sensor. 
         FIG. 14  is a table illustrating an example of a phase parameter in a phase shifter of each branch which is given to a transmission beam of each index in the third embodiment. 
         FIG. 15  is an explanatory view illustrating in time series, a transmission example of a case in which transmission beams of the same code sequence are successively transmitted, and thereafter, transmission beams of the subsequent code sequence are successively transmitted. 
         FIG. 16  is an explanatory view illustrating in time series, a transmission example of a case in which transmission beams of respective code sequences are transmitted in order one by one, and thereafter, transmission beams are sequentially transmitted in order from a transmission beam of a first code sequence. 
         FIG. 17  is an explanatory view illustrating in time series, a transmission example of a case in which transmission beams are successively transmitted at different transmission intervals for respective transmission beams. 
         FIG. 18  is a table illustrating an example of a candidate value of a phase parameter in a phase shifter of each branch which is given to a transmission beam of each index in a fourth embodiment. 
         FIG. 19  is a block diagram illustrating an internal configuration of a sensor in the fourth embodiment. 
         FIG. 20  is a sequence diagram illustrating operations of a wireless communication device and a sensor in the fourth embodiment. 
         FIG. 21  is a sequence diagram illustrating operations of the wireless communication device and the sensor in the fourth embodiment. 
         FIG. 22  is a block diagram illustrating an internal configuration of a sensor in a modification example of the fourth embodiment. 
         FIG. 23  is a table illustrating an example of a phase parameter in a phase shifter of each branch which is given to a transmission beam of each index in a modification example of the fourth embodiment. 
         FIG. 24  is a sequence diagram illustrating operations of the wireless communication device and the sensor in a modification example of the fourth embodiment. 
         FIG. 25  is a block diagram illustrating a configuration example of a wireless communication device of a fifth embodiment. 
         FIG. 26  is a block diagram illustrating a configuration example of a sensor device of the fifth embodiment. 
         FIG. 27  is a time chart illustrating a specific example (1) of transmission timings and reception timings of a distance measurement pulse signal transmitted as a wireless signal from a wireless communication device. 
         FIG. 28  is a graph illustrating a specific example (1) of a change of P value. 
         FIG. 29  is a time chart illustrating a specific example (2) of transmission timings and reception timings of a wireless signal. 
         FIGS. 30A and 30B  are graphs illustrating a specific example (2) of a change of P value, in which  FIG. 30A  illustrates a case where a state of being contacted continues for a predetermined time Tp or more, and  FIG. 30B  illustrates a case where a state of being contacted continues for less than a predetermined time Tp. 
         FIG. 31  is a sequence diagram illustrating an overview of an operation of a distance measurement system of the fifth embodiment. 
         FIG. 32  is a flowchart illustrating details of an operation of the wireless communication device of the fifth embodiment. 
         FIG. 33  is a flowchart illustrating details of an operation ( 1 ) of the sensor device of the fifth embodiment. 
         FIG. 34  is a flowchart illustrating details of an operation ( 2 ) of the sensor device of the fifth embodiment. 
         FIG. 35  is a schematic diagram conceptually illustrating an initial state of the distance measurement system. 
         FIG. 36  is a schematic diagram conceptually illustrating a sensing state of the distance measurement system. 
         FIG. 37  is a schematic diagram conceptually illustrating a measurement state of the distance measurement system. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     &lt;Details Leading to Contents of Embodiments of the Present Disclosure&gt; 
     First, before describing embodiments of a wireless communication device according to the present disclosure, the details leading to the contents of the embodiments of the wireless communication device according to the present disclosure will be described. 
     An antenna radiation pattern in an actual wireless communication device changes under the influence of the shape and the material of the case of the wireless communication device. Accordingly, even when the antenna radiation pattern is measured using a single antenna, it is difficult to understand a correct antenna radiation pattern. 
     If the antenna radiation pattern is not optimal, communication performance deteriorates. Even if a beam forming technique for controlling the directivity of the antenna is used, since each antenna radiation pattern is not optimal, high frequency characteristic varies, and communication performance deteriorates due to a change in the radiation pattern of the beam. 
     Therefore, in order to prevent deterioration of the communication performance of the actual wireless communication device, it is necessary to measure the radiation pattern of the radio wave radiated from the wireless communication device in its final shipping state. 
     However, in a case where a radio wave radiated from the wireless communication device is actually detected by the sensor, particularly in a WiGig wireless device that performs short distance communication, the separation of a direct wave and reflected waves reflected on a near object is difficult. Accordingly, in order not to be affected by the reflected waves, a WiGig wireless device must be brought into an anechoic chamber and a radiation pattern thereof must be measured. 
     In fact, when developers of a WiGig wireless device consider the design thereof, or, when the directivity is adjusted at the time of shipping from a factory, it is necessary to measure the antenna radiation pattern. In addition, for example, when the shape and the material of a case are changed, it is necessary to re-measure the antenna radiation pattern. On each measurement occasion, an anechoic chamber is prepared and the device is brought into the anechoic chamber, thereby leading to an increase in manufacturing cost and a prolonged development period. 
     Therefore, in order to measure the antenna radiation pattern while the WiGig wireless device is not brought into the anechoic chamber, adopting the pulse compression technology in PTL 1 is considered. However, in the pulse compression technology, a pulse compression signal needs to be radiated from the WiGig wireless device in order for a receiving side (sensor side) to detect the correlation of the received pulse signal. Since the pulse compression signal is not used in general wireless communication, a special circuit needs to be implemented in the WiGig wireless device. The special circuit has a relatively large size in general, such that the development effort for the WiGig wireless device increases and manufacturing cost increases. 
     Thus, in the following embodiments, a wireless communication device will be described which generates a pulse compression signal for measuring a radiation pattern from an antenna, by a simple configuration. 
     Specific embodiments relating to a wireless communication device of the present disclosure will be described below with reference to drawings. 
     &lt;First Embodiment&gt; 
     (Wireless Communication Device) 
       FIG. 1  is a block diagram illustrating an internal configuration of a WiGig wireless device  20  as a wireless communication device of a first embodiment. The WiGig wireless device  20  operates in accordance with a WiGig specification defined by the Wireless Gigabit Alliance. A frequency band used for wireless communication is a millimeter wave band, for example, 60 GHz band. A wireless communication distance is about 10 m. In addition,  FIG. 1  illustrates the main part of the transmission system of the WiGig wireless device  20 , and other circuits are omitted. 
     The WiGig wireless device  20  illustrated in  FIG. 1  has a configuration that includes an antenna  21 , an RF section  22 , a Digital-Analog Converter (DAC)  23 , a modulation section  24 , a selector section  25 , a mask circuit section  30 , and a mask timing generation section  31 . 
     The modulation section  24  generates a signal frame of the WiGig specification and outputs the generated signal frame as a modulation signal to the mask circuit section  30 . The DAC  23  converts the digital modulation signal which is input from the modulation section  24  through the mask circuit section  30  to an analog signal and outputs the analog signal to the RF section  22 . 
     The Radio Frequency (RF) section  22  converts the analog signal which is output from the DAC  23  to a high frequency signal and supplies the high frequency signal to the antenna  21 . The high frequency signal which is output from the RF section  22  is radiated as an electromagnetic wave to airspace through the antenna  21 . 
     In the present embodiment, the WiGig wireless device  20  uses a pulse compression signal in order to suppress the influence of reflected waves and to measure a correct radiation pattern of a radio wave, even in an environment in which the reflected waves occur, in measuring the radiation pattern of the radio wave radiated from the WiGig wireless device  20 . In order to use the pulse compression signal, a reception side (a sensor  10  in  FIG. 1 ) calculates a correlation value of a received pulse using a known correlator. Accordingly, in order for the reception side to detect a correlation, the WiGig wireless device  20  transmits a pulse compression signal different from that used at the time of data communication. 
     Specifically, the WiGig wireless device  20  transmits a signal in which signal pulses having a same time width repeatedly appear in a constant period as a pulse compression signal. Known codes are used in the pulse compression signal. The reception side extracts a pulse compression signal and calculates a self-correlation of a received pulse. The time width of the pulse compression signal extracted by the correlation detection of the reception side is shorter than the time width of the pulse transmitted by the WiGig wireless device  20 . Thus, separation of the direct wave and the reflected waves having a small arrival time difference becomes easy. 
     The selector section  25  selects a parameter used in modulation of a signal generated by the modulation section  24  in response to an external control signal CON 1 . Specifically, the WiGig wireless device  20  prepares as parameters two kinds of parameters including a parameter P 1  for communication and a parameter P 2  for a sensor in advance, and the selector section  25  selects any one of them. For example, a value, which is contained in the signal frame transmitted by the WiGig wireless device  20  and for which a length of data body is shorter than that used at the time of data communication, is assigned to the parameter P 2  for a sensor. Thus, the WiGig wireless device  20  can transmit a pulse compression signal which is more suitable for measurement of the antenna radiation pattern. 
     The external control signal CON 1  is a control signal for switching between a data communication mode and a measurement mode for measuring the antenna radiation pattern in the WiGig wireless device  20 . The state of the external control signal CON 1  may be switched by a user&#39;s operation (for example, a button operation), or may be switched by a control command input from outside. 
     The mask circuit section  30  partially performs a mask processing on a modulation output signal SSG 1  which is output by the modulation section  24  in response to a mask control signal SSG 2 . The mask circuit section  30  outputs a signal subjected to the mask processing as a mask circuit output signal SSG 3 . That is, the mask circuit section  30  partially performs the mask processing on the modulation output signal SSG 1  and generates the mask circuit output signal SSG 3  as a pulse compression signal. 
     The mask timing generation section  31  generates the mask control signal SSG 2  for informing a control timing at which the mask circuit section  30  performs the mask processing. The mask timing generation section  31  outputs the mask control signal SSG 2  for informing the control timing of the mask circuit section  30  in a case where the external control signal CON 1  represents the measurement mode of measuring the antenna radiation pattern. The mask timing generation section  31  prohibits the mask circuit section  30  from performing the mask processing in a case where the external control signal CON 1  represents the data communication mode. 
     (Sensor  10 ) 
       FIG. 2  is a block diagram illustrating an internal configuration of a sensor which measures an antenna radiation pattern of the wireless communication device illustrated in  FIG. 1 . 
     The sensor  10  illustrated in  FIG. 2  receives a pulse compression signal transmitted by the WiGig wireless device  20  and measures a radiation pattern of a radio wave. 
     The sensor  10  illustrated in  FIG. 2  has a configuration that includes a transmission section  11  and a reception section  12 . A signal transmitted by the transmission section  11  is radiated from an antenna  10   a . A direct wave of the radio wave radiated from the antenna  10   a  and reflected waves reflected on an any object reach the antenna  10   b  and are received in the reception section  12 . 
     In the present embodiment, in a case where the sensor  10  measures an antenna radiation pattern of the WiGig wireless device  20 , the sensor  10  receives the radio wave radiated from the WiGig wireless device  20  through an antenna  10   b  without using the transmission section  11 . 
     The transmission section  11  has a configuration that includes a pulse compression wave generating section  13 , a DAC  14 , and a transmission RF section  15 . The pulse compression wave generating section  13  generates a pulse compression wave (pulse compression signal) suitable for correlation detection of the reception section  12 . The DAC  14  converts a signal generated by the pulse compression wave generating section  13  from a digital signal to an analog signal and outputs the analog signal to the transmission RF section  15 . The transmission RF section  15  converts the analog signal which is output from the DAC  14  to a high frequency signal based on a local signal (not illustrated) in a sensor  10  and supplies the signal to the antenna  10   a.    
     The reception section  12  has a configuration that includes a reception RF section  16 , an Analog-Digital Converter (ADC)  17 , a correlator  18 , and a signal processing section  19 . 
     The reception RF section  16  receives the high frequency signal of the radio wave received by the antenna  10   b  and converts the high frequency signal to an analog reception signal of a low frequency by a predetermined signal processing on a basis of a local signal (not illustrated) in the sensor  10 . The ADC  17  converts the analog reception signal, which is output from the reception RF section  16 , to a digital reception signal. 
     The correlator  18  performs a predetermined correlation processing on the digital reception signal which is output from the ADC  17 . For example, in a case where pulse signals having a same time width, which repeatedly appear in a constant period as a pulse compression signal generated by the pulse compression wave generating section  13 , are input as a digital reception signal, a sufficient self-correlation output is achieved. 
     For example, the signal obtained at the output of the correlator  18  shows a characteristic illustrated in  FIG. 8 .  FIG. 8  is a graph illustrating a specific example of a reception correlation output characteristic of a sensor  10 . That is, the time elapsed from after the transmission section  11  transmits a radio wave until a received wave corresponding thereto appears at the output of the correlator  18  is different in a direct wave and each reflected wave due to a difference in a radio wave propagation distance. When the time difference between the direct wave and each reflected wave is small, separation of these waves becomes difficult. 
     However, since the correlator  18  performs a correlation processing, the time width of a peak waveform obtained as the output of the correlation processing is sufficiently shorter than the width of a transmitted pulse signal. Accordingly, even in a case of receiving a direct wave and a reflected wave which have a small time difference therebetween, it is possible to reliably separate the direct wave and the reflected wave in  FIG. 8 . 
     The signal processing section  19  acquires necessary information from the output signal (see  FIG. 8 ) of the correlator  18 . For example, the signal processing section  19  respectively specifies the direct wave and each reflected wave on a basis of a peak position of a signal which is input from the correlator  18  to the signal processing section  19  and detects a reception level of the direct wave and a reception level of each reflected wave. 
     (Form of a Communication Signal in a Wireless Device of WiGig Specification) 
     A packet of a high frequency signal to be transmitted has a configuration that includes the following various fields. 
     1. Short Training Field (STF) 
     2. Channel Estimation Field (CEF) 
     3. Header 
     4. Data 
     5. TRN-R/T sub-field 
     Further, a common preamble is present in the packet to be transmitted. The preamble is used for the following applications. 
     1. Detection of a packet 
     2. Automatic Gain Control (AGC) 
     3. Frequency offset estimation 
     4. Clear statement of synchronous modulation 
     5. Channel estimation 
       FIG. 3  illustrates a configuration of a preamble.  FIG. 3  is a schematic diagram illustrating a format of a preamble of a signal frame transmitted by the WiGig wireless device in data communication. The preamble illustrated in  FIG. 3  has a configuration that includes a Short Training Field (STF) and a Channel Estimation Field (CEF). 
     The STF of the preamble is configured by a sequence in which fourteen Golay codes Ga 128 (n), each of which has a length of 128 bits, are repeated and one Golay code −Ga 128 (n) is used. Accordingly, the entire length of the STF is 1920 bits (one unit is Tc). The waveform of the STF is represented by Expression (1). 
     
       
         
           
             
               
                 
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     The CEF of the preamble has a configuration in which Golay code sequences Gu 512 (n) and Gv 512 (n), a pair of two complementary codes, are connected. Gu 512 (n) and Gv 512 (n) are represented by Expression (2). 
     [Expression 2]
 
 Gu   512 ( n )=[− Gb   128   −Ga   128   Gb   128   −Ga   128 ]
 
 Gv   512 ( n )=[− Gb   128   Ga   128   −Gb   128   −Ga   128 ]  (2)
 
     (Generation of a Pulse Compression Signal) 
     A known repetition signal suitable for correlation detection can be used as the pulse compression signal. The STF of the preamble illustrated in  FIG. 3  includes a Golay code sequence in which Golay codes are repeated. In the present embodiment, the WiGig wireless device  20  can generate the pulse compression signal by extracting a part of the repeated Golay code sequence. 
     That is, the mask circuit section  30  performs a mask processing on the modulation output signal SSGI, extracts a part of the preamble, and outputs the mask circuit output signal SSG 3  as the pulse compression signal. In other words, the mask circuit section  30  performs a mask processing on a part of the preamble, thereby allowing a pulse compression signal used in measuring the antenna radiation pattern to be generated. 
     In addition, in each of the embodiments including this embodiment, the WiGig wireless device  20  and the sensor  10  process the negotiation of communication in the measurement mode in advance. Accordingly, the sensor  10  knows timings at which the WiGig wireless device  20  transmits or receives the mask circuit output signal SSG 3  as the pulse compression signal. 
       FIG. 4  is a time chart illustrating an operation in which the WiGig wireless device  20  generates a pulse compression signal. The operation illustrated in  FIG. 4  is performed in the measurement mode of measuring the antenna radiation pattern by the external control signal CON 1 . That is, the mask timing generation section  31  generates the mask control signal SSG 2  on a basis of the external control signal CON 1 . The mask circuit section  30  generates the mask circuit output signal SSG 3  as the pulse compression signal in response to the mask control signal SSG 2 . 
     In  FIG. 4 , a high level (H) of the mask control signal SSG 2  indicates a mask state, and a low level (L) of the mask control signal SSG 2  indicates a mask release state. In the example illustrated in  FIG. 4 , the mask control signal SSG 2  causes a part of the STF in the preamble of the modulation output signal SSGI to be intermittently subjected to the mask processing and parts other than the STF to be entirely subjected to the mask processing. 
     Thus, the mask circuit section  30  intermittently extracts Golay code sequences from the STF in the preamble. As a result, a plurality of same Golay codes Ga 128 (n) are repeated periodically in the mask circuit output signal SSG 3 . If the WiGig wireless device  20  transmits the signal, the sensor  10  obtains a correlation output illustrated in  FIG. 8  with respect to the repetition pattern of the same Golay codes Ga 128 (n) in the correlator  18 . That is, the WiGig wireless device  20  can transmit to the sensor  10  the pulse compression signal required for measuring the antenna radiation pattern. 
     In the example illustrated in  FIG. 4 , the mask release period and the mask period are alternately and repeatedly switched in the mask control signal SSG 2 , by regarding a period T of one cycle of Golay code Ga 128 (n) in the STF as a unit. 
     Mask release period (T)-&gt;mask period (6T)-&gt;mask release period (T)-&gt;mask period (6T)-&gt;mask release period (T)-&gt; . . . . 
     The length (6T) of the mask period may be appropriately changed so as to obtain a suitable correlation output, in accordance with a distance between the WiGig wireless device  20  and the sensor  10  under actual measurement conditions. 
     The timing of the mask control signal SSG 2  generated by the mask timing generation section  31  can be generated in synchrony with an operation timing of the control section (for example, the modulation section  24 ) that generates a signal frame for transmission of a WiGig specification. 
     (Measurement Method of an Antenna Radiation Pattern) 
     In  FIG. 1 , the sensor  10  is disposed in the vicinity of the WiGig wireless device  20 . Here, the sensor  10  causes an operation of the transmission section  11  to stop and the reception section  12  to operate. Further, the sensor  10  switches the external control signal CON 1  to be input to the WiGig wireless device  20 , thereby switching the operation mode of the WiGig wireless device  20  from a data communication mode to a measurement mode of measuring an antenna radiation pattern. 
     The selector section  25  selects the parameter P 2  for a sensor suitable for measuring an antenna radiation pattern on a basis of the external control signal CON 1  and outputs the parameter P 2  to the modulation section  24 . The mask timing generation section  31  starts generation of the mask control signal SSG 2  on a basis of the external control signal CON 1 . The mask circuit section  30  intermittently performs the mask processing on the modulation output signal SSG 1  in response to the mask control signal SSG 2  and intermittently outputs the Golay code sequence of the STF in the preamble as the mask circuit output signal SSG 3 . 
     Thus, the WiGig wireless device  20  can transmit a pulse compression signal suitable for correlation detection. Further, the sensor  10  detects a radio wave radiated from the WiGig wireless device  20 . The reception section  12  of the sensor  10  obtains a pulse compression signal which is received as a repetition pattern, that is, a large correlation value for the mask circuit output signal SSG 3  illustrated in  FIG. 4  as an output of the correlator  18 . As illustrated in  FIG. 8 , the correlation values for the direct wave and the respective reflected waves have peak values at different timings. For this reason, the sensor  10  can respectively detect the direct wave and the reflected waves independently of each other. 
     That is, even in the measurement of the antenna radiation pattern in an environment such as a general laboratory in which reflected waves are generated, the sensor  10  can detect the direct wave of the radio wave radiated from the WiGig wireless device  20  in a state of being separated from the reflected wave. Accordingly, it is possible to measure the antenna radiation pattern without the WiGig wireless device  20  being brought into an anechoic chamber. 
     Further, since the WiGig wireless device  20  itself transmits the pulse compression signal, it is possible to measure an actual antenna radiation pattern of the entire WiGig wireless device  20  including the effect of a final shape and material of a case, rather than the characteristic of the antenna alone. 
     That is, the WiGig wireless device  20  illustrated in  FIG. 1  can transmit a pulse compression signal suitable for measuring the antenna radiation pattern by adding a mask circuit section  30  and a mask timing generation section  31 . 
     &lt;Second Embodiment&gt; 
     (Wireless Communication Device) 
       FIG. 5  is a block diagram illustrating an internal configuration of the WiGig wireless device  20 BB as a wireless communication device of a second embodiment. The present embodiment is a modification example of the first embodiment. In the WiGig wireless device  20 BB illustrated in  FIG. 5 , the components corresponding to the WiGig wireless device  20  of the first embodiment are denoted by the same reference numerals, and the description thereof will be omitted. 
     The WiGig wireless device  20 BB illustrated in  FIG. 5  has a configuration that includes an antenna  21 , a RF section  22 , a DAC  23 , a modulation section  24 B, a selector section  25 , a mask circuit section  30 , and a mask timing generation section  31 . That is, the modulation section  24 B is different from the modulation section  24  illustrated in the first embodiment. 
     The modulation section  24 B has a configuration that includes a Golay signal generation section (referred to as “FGCF” in  FIG. 5 )  40  and a selector section  41 . 
     The Golay signal generation section  40  is implemented as a modulation section of the wireless device that conforms to the WiGig specification. In order to efficiently generate a Golay signal, the Golay signal generation section  40  is configured by using for example, a Fast Golay Correlator Filter (FGCF), that is, a high-speed Golay correlator filter. An example of a circuit configuration of the Golay signal generation section  40  is illustrated in  FIG. 7 .  FIG. 7  is a block diagram illustrating a specific configuration of a Golay signal generation section  40 . Since a circuit configuration of  FIG. 7  is described in detail, for example, in reference NPL 1, the description thereof will be omitted. 
     [NPL 1] “EFFICIENT PULSE COMPRESSOR FOR GOLAY COMPLEMENTARY SEQUENCES”, ELECTRONICS LETTERS 31 st , Vol. 27 No. 3 p. 219-220, January 1991 
     The Golay signal generation section  40  simultaneously generates a pair of two complementary codes (Ga and Gb) as an output of two systems. 
     The selector section  41  selects the output of two systems which is output by the Golay signal generation section  40 , that is, Golay codes Ga and Gb which are complementary codes that are in complementary relationship to each other in accordance with the timing of the mask control signal SSG 2  which is output from the mask timing generation section  31 . 
     Although the WiGig wireless device in the related art uses the Golay code Ga in the STF of the preamble, the selector section  41  of the WiGig wireless device  20 BB of the present embodiment selectively uses the Golay code Gb that is generated by the Golay signal generation section  40  at the same time. 
     (Generation of a Pulse Compression Signal) 
       FIG. 6  is a time chart illustrating an operation in which the WiGig wireless device  20 BB of  FIG. 5  generates a pulse compression signal. 
     The selector section  41  alternately selects output signals SSG 5   a  and SSG 5   b  of two systems from the Golay signal generation section  40  in response to the control signal SSG 21  from the mask timing generation section  31 . The SSG 5   a  corresponds to the output of the Golay code Ga, and the SSG 5   b  corresponds to the output of the Golay code Gb. 
     The mask timing generation section  31  determines the content (H or L) of the control signal SSG 21  on a basis of the mask control signal SSG 2 . The selector section  41  selects an output signal SSG 5   a  indicating that the control signal SSG 21  selects the Golay code Ga at a high level H (Hi) and outputs the Golay code Ga as a selector output signal SSG 4  on a basis of the output signal SSG 5   a . The selector section  41  selects an output signal SSG 5   b  indicating that the control signal SSG 21  selects the Golay code Gb at a low level L (Low) and outputs the Golay code Gb as a selector output signal SSG 4  on a basis of the output signal SSG 5   b.    
     The content (H or L) of control signal SSG 21  is switched alternately at timings when the control signal SSG 21  switches from a high level H to a low level L. That is, every time the mask timing generation section  31  releases a mask, the selector section  41  alternately switches between the Golay codes Ga and Gb for selection. 
     As a result, in  FIG. 6 , the Golay codes Ga and Gb which are in the complementary relationship to each other alternately and intermittently appear in the mask circuit output signal SSG 3 B. In the example illustrated in  FIG. 6 , the state (H or L) of the control signal SSG 21  is switched, for example, at a time interval (7T) which is seven times one period (T) of the Golay code Ga or Gb. Accordingly, the state of the mask circuit output signal SSG 3 B repeatedly changes. 
     Mask release period (code Ga: T)-&gt;mask period (6T)-&gt;mask release period (code Gb: T)-&gt;mask period (6T)-&gt;mask release period (code Ga: T)-&gt;mask period (6T)-&gt;mask release period (code Gb: T)-&gt;mask period (6T)-&gt; . . . . 
     The WiGig wireless device  20 BB can alternately transmit the Golay codes Ga and Gb which are in the relationship of complementary codes to each other as a pulse compression signal in measuring the antenna radiation pattern. 
     The sensor  10  adds the signals of complementary codes, the Golay codes Ga and Gb, which are received by the sensing processing, that is, measurement of the antenna radiation pattern of a radio wave transmitted from the WiGig wireless device  20 , thereby allowing a side lobe characteristic as a correlation characteristic to be cancelled. Therefore, in the present embodiment, a better correlation characteristic can be obtained compared with the first embodiment. In other words, in the present embodiment, the sensor  10  can detect the antenna radiation pattern of the WiGig wireless device  20 BB with high accuracy. 
     Accordingly, the above described circuit is added to the WiGig wireless device  20 BB, thereby allowing the wireless device itself to radiate the radio wave of the pulse compression signal. Accordingly, the radiation characteristic of a single antenna is not measured, but the final antenna radiation pattern of the overall WiGig wireless device can be measured. Further, the influence of the reflected waves at the time of measuring the antenna radiation pattern can be eliminated by using the pulse compression signal. That is, even in an environment other than the anechoic chamber, in which the reflected waves are generated, it is possible to measure the antenna radiation pattern. 
     In addition, the configuration of the preamble of a packet transmitted by the WiGig wireless device is not limited to the configuration of the preamble illustrated in  FIG. 3 , but the size of the preamble may be long in order to generate the pulse compression signal, and for example, the configuration of the preamble of a signal frame termed as CONTROL-PHY may be possible. CONTROL-PHY will be described with reference to  FIGS. 9 and 10 . 
       FIG. 9  is a diagram illustrating a format of a signal frame of CONTROL-PHY. The signal frame of the CONTROL-PHY illustrated in  FIG. 9  has a configuration that includes respective areas of a preamble PR, a header HD, a payload PD, and a TRN-NT. The area of the TRN-NT is optional.  FIG. 10  is a schematic diagram illustrating the format of the preamble of the signal frame of CONTROL-PHY. 
     The preamble PR illustrated in  FIG. 10  has a configuration that includes STF and CEF. The STF of the preamble PR is configured by a sequence in which thirty eight Golay codes Gb 128 (n), each of which has a length of 128 bits, are repeated, one Golay code −Gb 128 (n) and one Golay code −Ga 128 (n). Accordingly, the entire length of the STF is 5120 bits and is longer than that of the STF of the preamble illustrated in  FIG. 3 . The waveform of the STF is represented by Expression (3). Since the CEF has the same configuration as that of the preamble illustrated in  FIG. 3 , the description thereof will be omitted. 
     
       
         
           
             
               
                 
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     Although the WiGig wireless device of each embodiment described above transmits the signal frame suitable for the WiGig specification one time, the WiGig wireless device may continue to transmit the signal frame suitable for the WiGig specification having a minimum payload continuously, without limiting the number of times of transmission to one. 
     Further, the WiGig wireless device of each embodiment described above may successively transmit only preamble or header of the signal frame suitable for the WiGig specification. Thus, the WiGig wireless device can transmit the pulse compression signal having a smaller size in which the size of the payload is reduced, and thus the measurement of the radiation pattern of the sensor can be simplified. 
     In addition, in  FIG. 5 , the WiGig wireless device  20 BB may output the mask control signal SSG 2  to the mask circuit section  30  and may transmit it to sensors other than the sensor  10  illustrated in  FIG. 1  at the same time. Although the mask control signal SSG 2  is a signal by which the mask circuit section  30  partially performs a mask processing, timings when the WiGig wireless device  20 BB transmits the pulse compression signal may be also considered. In addition, other sensors and the WiGig wireless device  20 BB may communicate in a wired or wireless manner. 
     If the WiGig wireless device  20 BB knows timings of transmitting the mask control signal SSG 2  in advance, other sensors can specify distances with the WiGig wireless device  20 BB on a basis of times when the mask control signals transmitted by the WiGig wireless device  20 BB are received. 
     Next, a wireless communication device which performs communication using a beam forming function will be described. 
     A beam forming function is a multi-antenna technology in order for a transmission terminal to transmit a radio wave in a direction in which a reception terminal is present and causes a transmission radio wave to have directivity in a specific direction. For example, by using a plurality of antennas, the transmission terminal can transmit the radio wave farther or can transmit the radio wave while an interference with radio waves transmitted from an adjacent base station or a reception terminal is suppressed. The beam forming function adjusts power or a phase of a signal (radio wave) transmitted by a plurality of antennas, thereby allowing the radio wave to be transmitted in a desired direction. 
     In a design or an operation test of a wireless communication device having a beam forming function, it is necessary to understand an antenna radiation pattern, that is, a radiation pattern of a radio wave, by using an actual wireless communication device for the sake of determination and improvement of performance. 
     In the related art, in a case of measuring the antenna radiation pattern of the wireless communication device using the beam forming function, the wireless communication device is brought into a anechoic chamber and the antenna radiation pattern thereof is measured. If the antenna radiation pattern is measured in an environment other than an anechoic chamber, reflected waves are generated from objects located in the vicinity of the wireless communication device. In particular, in a short-range communication, a distinction between the direct wave and the reflected waves is difficult due to a small time difference between the direct and the reflected waves which are to be detected, and thus the measurement of the correct antenna radiation pattern is difficult. 
     On the other hand, PTL 1 discloses a radio wave environment measuring device which can detect a radio wave condition in an environment other than the anechoic chamber in which the direct wave and the reflected waves are mixed. In PTL 1, the direct wave and the reflected waves are separated by a pulse compression signal. 
     In PTL 1 below, a pulse compression signal is used, and a reception device detects a correlation between a received pulse and a reference pulse. Thus, the radio wave environment measuring device of PTL 1 can compress a time width of a detected pulse to a range narrower than a pulse width of a pulse signal to be transmitted actually. Accordingly, due to an improvement in time resolution, the radio wave environment measuring device of PTL 1 can separate and detect the direct wave and the reflected waves, which have a small time difference, from each other. 
     [PTL 1] Japanese Patent No. 3112746 
     Problems in the Related Art 
     However, the beam forming function is not taken into account in PTL 1, so that in the beam forming of controlling the directivity of the antenna, if respective antenna radiation patterns are not optimal, a characteristic of a high frequency signal (for example, phase characteristic) varies. Accordingly, the radiation pattern of a radio wave (beam) is changed, and thus a communication performance of the wireless communication device is deteriorated. 
     In a case where in a wireless communication device has a beam forming function using a plurality of antennas, a sensor detects all beams actually radiated from the wireless communication device, a communication setting for communication negotiation between the wireless communication device and the sensor becomes complicated. That is, measurement times of radiation patterns of all beams become long. 
     In order to solve the above-described problems in the related art, an object of the present disclosure is to provide a wireless communication device which measures a radiation pattern of a beam having a desired directivity in a beam forming in a short time. 
     Solution to Problem 
     The present disclosure relates to a wireless communication device including a plurality of antenna system processing sections, in which each of the antenna system processing sections includes a code sequence selection section configured to select a code sequence of a transmission signal, a pulse compression signal generation section configured to perform a pulse compression processing on the selected code sequence, a phase shifter configured to adjust the phase of the signal subjected to the pulse compression processing in accordance with the selected code sequence, and a transmission RF section configured to convert the signal, of which phase is adjusted, to a high frequency signal and transmits the high frequency signal from a transmission antenna. 
     Advantageous Effects of Invention 
     According to the present disclosure, it is possible to measure a radiation pattern of a beam having a desired directivity in a beam forming in a short time. 
     Each embodiment of a wireless communication device according to the present disclosure will be described below with reference to drawings. 
     &lt;Third Embodiment&gt; 
     (Wireless Communication Device  2000 ) 
       FIG. 11  is a block diagram illustrating a system configuration of a radiation pattern measurement system  100 PPP and an internal configuration of a wireless communication device  2000  in a third embodiment. The frequency band used for wireless communication by the wireless communication device  2000  is a millimeter-wave band, for example, 60 GHz band. A wireless communication distance is about 10 m. Further, in  FIG. 11 , the main parts of the transmission system of the wireless communication device  2000  are illustrated, and other circuits are not illustrated. 
     The wireless communication device  2000  has a beam forming function and has a configuration that includes a plurality of antenna system processing sections (branches)  20 A,  20 B,  20 C, and  20 D. Hereinafter, the antenna system processing section is termed as a “branch”. Although the wireless communication device  2000  illustrated in  FIG. 11  is configured to include for example, four branches  20 A,  20 B,  20 C, and  20 D, the number of branches of the wireless communication device  2000  is not limited to four. Further, since each branch has the same configuration, in the following description, a branch  20 A is described as an example. 
     The branch  20 A illustrated in  FIG. 11  has a configuration that includes a transmission antenna  21 A, a modulation section  2200 , a Digital Analog Converter (DAC)  2300 , a phase shifter  2400 , a transmission RF section  2500 , a control section  2600 , a code sequence selection section  2700  and a pulse compression signal generation section  2800 . In addition, the modulation section  2200  may be included in each branch, or one modulation section  2200  may be included in the wireless communication device  2000  as a configuration in which the modulation section is independent of all branches. 
     The external control signal CON 1  is a control signal which is input to each of the branches  20 A to  20 D and switches between a data communication mode and a measurement mode for measuring the radiation pattern of the transmission beam in the wireless communication device  2000 . The content of the external control signal CON 1  may be switched by a user&#39;s operation (for example, button operation) or may be switched by an input of a control command from outside. 
     Further, the external control signal CON 1  may include control information for measuring the radiation pattern of a specific transmission beam, and a radiation pattern measurement system  100 PP measures the radiation pattern of the specific transmission beam. The external control signal CON 1  is input to the modulation section  2200 , the control section  2600 , the code sequence selection section  2700 , and the pulse compression signal generation section  2800  in the branch  20 A. 
     The modulation section  2200  receives the external control signal CON 1 , operates when the content of the external control signal CON 1  is the data communication mode, and generates a modulation signal of a signal frame (for example, a signal frame suitable for the Wireless Gigabit (WiGig) specification) of a transmitted signal and outputs the modulation signal to the DAC  2300 . In addition, a modulation method between the wireless communication device  2000  and the sensor  10  is assumed to be well-known. Further, the modulation section  2200  does not operate when the content of the external control signal CON 1  is the measurement mode. 
     The DAC  2300  converts a digital modulation signal which is output from the modulation section  2200  in the data communication mode and a digital pulse compression signal which is output from the pulse compression signal generation section  2800  in the measurement mode to an analog signal and outputs the analog signal to the phase shifter  2400 . 
     The phase shifter  2400  adjusts the phase of the analog signal which is output from the DAC  2300  in accordance with a phase parameter which is given from the control section  2600 . The phase shifter  2400  outputs the analog signal of which the phase is adjusted to the transmission RF section  2500 . 
     The transmission Radio Frequency (RF) section  2500  converts the analog signal which is output from the phase shifter  2400  to a high frequency signal and supplies the high frequency signal to a transmission antenna  21 A. One transmission antenna  21 A is provided for each branch and transmits (radiates) the high frequency signal (radio wave) which is output from the transmission RF section  2500  as an electromagnetic wave to a space. 
     In the present embodiment and the fourth embodiment, the wireless communication device  2000  uses a pulse compression signal in order to suppress the influence of a reflected wave and to measure a correct radiation pattern of a radio wave in an environment in which the reflected waves are generated, in measuring the radiation pattern of a radio wave radiated from the wireless communication device  2000 . In order to use the pulse compression signal, the sensor  10  calculates a correlation value between a code sequence of a transmission beam which is held in the correlator and a received signal (received pulse) using the correlator. Accordingly, in order for the sensor  10  to detect a correlation, the wireless communication device  2000  transmits a pulse compression signal in the measurement mode. 
     Specifically, the wireless communication device  2000  transmits a signal in which pulses having a same time width repeatedly occur in a constant period as a pulse compression signal. Known codes are used in the pulse compression signal. The sensor  10  calculates a correlation value between a code sequence of a transmission beam and a received signal and determines that a beam of which code sequence was transmitted, on a basis of a maximum value (peak correlation value) of a correlation value. The time width of the pulse compression signal extracted by the correlation detection of the reception side is shorter than the time width of the pulse of the transmission beam transmitted by the wireless communication device  2000 . Thus, separation of the direct wave and the reflected wave, which have a small arrival time difference from each other, becomes easy. 
     The control section  2600  receives the external control signal CON 1  and gives a parameter for adjusting a phase of an analog signal which is output from the DAC  2300  to the phase shifter  2400 , when the content of the external control signal CON 1  is the data communication mode or the measurement mode. 
     Here, the parameter of a phase will be described with reference to  FIG. 14 .  FIG. 14  is a table illustrating an example of a phase parameter in a phase shifter of each branch which is given to a transmission beam of each index in the third embodiment. The branches B 1 , B 2 , B 3 , and B 4  illustrated in  FIG. 14  respectively correspond to the branches  20 A,  20 B,  20 C, and  20 D illustrated in  FIG. 11 . In addition, it is preferable that the content of a table illustrated in  FIG. 14  be stored in, for example, a storage area (not illustrated) of the control section  2600  in advance. 
     In the present embodiment, the code sequences used for respective transmission beams are predetermined and different from each other. For example, “code sequence F 1 ” is used in a transmission beam  1  of an index  1  for identifying a transmission beam, “100 degrees” is set in the phase shifter of the branch  20 A, “110 degrees” is set in the phase shifter of the branch  20 B, “120 degrees” is set in the phase shifter of the branch  20 C, and “130 degrees” is set in the phase shifter of the branch  20 D. 
     In a similar manner, “code sequence F 2 ”, “code sequence F 3 ”, . . . , and “code sequence FN” are respectively used in a transmission beam  2 , a transmission beam  3 , . . . , and a transmission beam N, and the parameter of a corresponding phase is set in the phase shifter of each branch (see  FIG. 14 ). N represents the number of code sequences and the number of branches of the wireless communication device. 
     In a case where the content of the external control signal CON 1  is the measurement mode, the control section  2600  outputs a selection instruction to the code sequence selection section  2700 , and specifically, causes the code sequence selection section  2700  to select the code sequence of the transmission beam in the measurement mode. 
     The code sequence selection section  2700  selects a code sequence corresponding to a transmission beam on a basis of a selection instruction from the control section  2600 . Further, although it is preferable that the code sequence corresponding to each transmission beam be stored in the storage area of the code sequence selection section  2700  in advance, the wireless communication device  2000  may include a memory (not illustrated) storing a code sequence. The code sequence selection section  2700  outputs the selected code sequence to the pulse compression signal generation section  2800 . 
     Here, examples of a selection order of a code sequence of the code sequence selection section  2700  will be described with reference to  FIGS. 15 and 16 .  FIG. 15  is an explanatory view illustrating in time series, a transmission example of a case in which transmission beams of a same code sequence are successively transmitted, and thereafter transmission beams of the subsequent code sequence are successively transmitted.  FIG. 16  is an explanatory view illustrating in time series, a transmission example of a case in which transmission beams of respective code sequences are transmitted in order one by one, and thereafter transmission beams are sequentially transmitted in order from a transmission beam of a first code sequence again. 
     In  FIG. 15 , the code sequence selection section  2700  successively selects the same code sequence (for example, code sequence F 1 ) a predetermined number of times (for example, NP), after continuous selection of NP number of times, successively transmits the subsequent code sequence (for example, code sequence F 2 ) which is different from the code sequence that was already selected a predetermined number of times (for example, NP). In a similar manner, the code sequence selection section  2700  successively transmits the code sequence of the same sequence which is different from the code sequence that was already selected and successively selects a final code sequence (for example, code sequence FN) a predetermined number of times (for example, NP). 
     Otherwise, in  FIG. 16 , the code sequence selection section  2700  selects all code sequences (for example, code sequences F 1 , F 2 , F 3 , . . . , FN) which are different from each other, in order, and after selecting the all code sequences which are different from each other, again selects the code sequences which are different from each other, in order. The code sequence selection section  2700  may repeat selections of the all code sequences which are different from each other in accordance with order, a predetermined number of times (for example, NP). In addition, in  FIGS. 15 and 16 , it is preferable that the order of selection of the code sequence be defined in the operation of the code sequence selection section  2700  in advance. 
     However, a selection method of a code sequence by the code sequence selection section  2700  is not limited to a selection method of a code sequence illustrated in  FIG. 15 or 16 . For example, the code sequence selection section  2700  may select any code sequence in any order. 
     The pulse compression signal generation section  2800  receives the external control signal CON 1 , and operates in a case where the content of the external control signal CON 1  is the measurement mode. Specifically, the pulse compression signal generation section  2800  performs a known pulse compression processing on a basis of code sequences which are output from the code sequence selection section  2700 . The pulse compression signal generation section  2800  outputs a pulse compression signal generated by the pulse compression processing to the DAC  2300 . 
     (Sensor  10 ) 
       FIG. 12  is a block diagram illustrating an internal configuration of a sensor  10  in the radiation pattern measurement system  100 PP illustrated in  FIG. 11 . The sensor  10  illustrated in  FIG. 12  receives a transmission beam as a pulse compression signal transmitted by the wireless communication device  2000  in the reception antenna  1100  and measures the radiation pattern of a radio wave. Further,  FIG. 12  illustrates main parts of the reception system of the sensor  10  and does not illustrate other circuits. 
     The sensor  10  illustrated in  FIG. 12  has a configuration that includes a reception antenna  1100 , a reception RF section  1200 , an Analog Digital Converter (ADC)  1300 , a plurality of N correlators C 1 , . . . , Ck, . . . , and CN and signal processing sections SP 1 , . . . , SPk, . . . , and SPN. Here, k is an integer among 1 to N. N represents the number of the correlators and signal processing sections and is the same as the number of code sequences of the transmission beam which are transmitted from the wireless communication device  2000  and the number of branches of the wireless communication device  2000 . 
     The reception RF section  1200  receives a high frequency signal of a radio wave that is received by the reception antenna  1100  and converts the high frequency signal to an analog reception signal of a low frequency, on a basis of a local signal (not illustrated) in the sensor  10 . The ADC  1300  converts an analog reception signal, which is output from the reception RF section  1200 , to a digital reception signal. 
     The operation of the correlators C 1 , . . . , Ck, . . . , and CN will be described by taking the correlator Ck as an example. The correlator Ck holds a code sequence of a transmission beam of an index k and calculates a correlation value of a digital reception signal which is output from the ADC  17  by a predetermined correlation processing. Specifically, the correlator Ck calculates a correlation value between a code sequence that the correlator Ck itself holds and a reception signal and obtains a sufficient correlation value, that is a peak correlation value, in a case where the transmission beam of the same code sequence as the code sequence that the correlator Ck holds is input as a reception signal (see  FIG. 13 ). 
     For example, the correlator C 1  holds the code sequence F 1  of the transmission beam BM 1  of an index  1  illustrated in  FIG. 14  and obtains a sufficient correlation value (correlation peak) in a case where the transmission beam of the same code sequence as the code sequence F 1  that the correlator Ck holds is input from the wireless communication device  2000  as a reception signal (see  FIG. 13 ). In a similar manner, the correlator CN holds the code sequence FN of the transmission beam BMN of an index N illustrated in  FIG. 14  and obtains a sufficient correlation value (correlation peak) in a case where the transmission beam of the same code sequence as the code sequence FN that the correlator Ck holds is input from the wireless communication device  2000  as a reception signal (see  FIG. 13 ). 
     In addition, the signal obtained at the output of the correlator Ck shows, for example, a characteristic illustrated in  FIG. 13 .  FIG. 13  is a graph illustrating a specific example of a reception correlation output characteristic of the sensor  10 . That is, a time elapsed from after the wireless communication device  2000  transmits a transmission beam until a corresponding reception signal occurs as an output of the correlator Ck is different in a direct wave and each reflected wave due to a difference in a radio wave propagation distance. In addition, a distinction between the direct wave and each reflected wave is difficult in a case where the time difference between the direct wave and each reflected wave is small. 
     However, in the present embodiment, a time width of a peak waveform which is obtained as an output of a correlation processing becomes sufficiently short with respect to the width of a pulse signal which is transmitted by a correlation processing of the correlator Ck. Accordingly, a reliable distinction between the direct wave and each reflected wave is possible in  FIG. 13 , even if the direct wave and the reflected wave are received with a small reception time difference. 
     The operations of the signal processing sections SP 1 , . . . , SPk, . . . , and SPN will be described by taking the signal processing section SPk as an example. The signal processing section SPk acquires necessary information on a basis of an output (correlation value) of the correlator Ck. For example, the signal processing section SPk respectively specifies a direct wave and each reflected wave on a basis of a peak position of a signal which is input from the correlator Ck to the signal processing section SPk and detects the reception level of the direct wave and the reception level of each reflected wave. 
     (Measurement Method of a Radiation Pattern) 
     Next, a measurement method of measuring a radiation pattern of a transmission beam in a radiation pattern measurement system  100 PP illustrated in  FIG. 11  will be described. In  FIG. 11 , a sensor  10  is disposed in the vicinity of the wireless communication device  2000 . Further, the content of the external control signal CON 1  to be input to the wireless communication device  2000  is switched, the operation mode of the wireless communication device  2000  being switched from the data communication mode to the measurement mode of measuring a radiation pattern, and the control information for measuring the radiation pattern of the transmission beam of an index k is input. 
     In addition, in the present embodiments and the fourth embodiment, the wireless communication device  2000  and the sensor  10  process the negotiation of communication in advance. Accordingly, the sensor  10  knows timings at which the wireless communication device  2000  transmits or receives the transmission beam as a pulse compression signal. 
     The control section  2600  causes the code sequence selection section  2700  to select a code sequence corresponding to the transmission beam in the measurement mode on a basis of the external control signal CON 1 . Further, the control section  2600  selects a phase parameter given to the transmission beam of the index k and gives the parameter to the phase shifter  2400 . 
     The code sequence selection section  2700  selects a code sequence corresponding to a transmission beam of an index k on a basis of a selection instruction from the control section  2600  and outputs the selected code sequence to the pulse compression signal generation section  2800 . 
     The pulse compression signal generation section  2800  generates a pulse compression signal on a basis of a code sequence which is output from the code sequence selection section  2700  and outputs the generated pulse compression signal to the DAC  2300 . The DAC  2300  converts a digital pulse compression signal which is output from the pulse compression signal generation section  2800  to an analog signal and outputs the analog signal to the phase shifter  2400 . The phase shifter  2400  adjusts the phase of the analog signal which is output from the DAC  2300  in accordance with the phase parameter which is given from the control section  2600 . 
     The phase shifter  2400  outputs the analog signal of which the phase was adjusted to the transmission RF section  2500 . The transmission RF section  2500  converts the analog signal which is output from the phase shifter  2400  into a high frequency signal and supplies the high frequency signal to the transmission antenna  21 A. The transmission antenna  21 A transmits (radiates) the high frequency signal (radio wave) which is output from the transmission RF section  2500  as an electromagnetic wave to a space. Thus, the wireless communication device  2000  can transmit a pulse compression signal suitable for correlation detection in the sensor  10 . 
     In  FIG. 12 , the sensor  10  receives a radio wave, that is, a transmission beam of an index k which is radiated (transmitted) from the wireless communication device  2000 , in the reception antenna  1100 . The reception RF section  1200  receives a high frequency signal of the radio wave which is received by the reception antenna  1100  and converts the high frequency signal to an analog reception signal of low frequency. The ADC  1300  converts an analog reception signal which is output from the reception RF section  1200  to a digital reception signal. The digital reception signal which is output from the ADC  1300  is input to a plurality of N correlators C 1 , . . . , Ck, . . . , and CN. 
     N correlators C 1 , . . . , Ck, . . . , and CN calculate a correlation value between a code sequence corresponding to a transmission beam of an index that each correlator holds and a reception signal which is output from the ADC  1300 . Among respective outputs of N correlators C 1 , . . . , Ck, . . . , and CN, the correlation calculation value of a correlator which does not hold the code sequence corresponding to a transmission beam of an index k becomes zero, and the correlation calculation value of the correlator Ck which holds a code sequence corresponding to a transmission beam of an index k becomes non-zero. 
     The signal processing section SPk detects the signal power (reception level) of a transmission beam of an index k on a basis of a correlation calculation value of the correlator Ck, for example, a peak value of a correlation value. Thus, the sensor  10  can measure the radiation pattern of the transmission beam of the index k. 
     Thus, the wireless communication device  2000  of the present embodiment performs a pulse compression processing on a transmission beam having a desired directivity by using a code sequence as an index and transmits the transmission beam. Thus, the sensor  10  can measure the radiation pattern of the transmission beam in a short time, on a basis of a result of the correlation calculation by a plurality of correlators. Accordingly, the wireless communication device  2000  can measure a radiation pattern of a beam having a desired directivity in a short time. 
     &lt;Modification Example of Third Embodiment&gt; 
     In the third embodiment, “code sequence” is used as an index of each transmission beam as a measurement object of a radiation pattern. In the modification example of the third embodiment, “transmission interval” is used as an index of each transmission beam as a measurement object of a radiation pattern. In addition, in the modification example of the third embodiment, since a configuration of the wireless communication device is the same as the wireless communication device  2000  of the third embodiment, the same reference numerals as the third embodiment are used in a description of the present modification example. 
     (Wireless Communication Device  2000 ) 
     In the modification example, the code sequence selection section  2700  may store one code sequence (for example, code sequence F 1 ). That is, the code sequence selection section  2700  selects one code sequence (for example, code sequence F 1 ) as the code sequence of a transmission beam. Specifically, the code sequence selection section  2700  changes a selection interval in which one code sequence (for example, code sequence F 1 ) is selected in accordance with the index of the transmission beam as a measurement object.  FIG. 17  is an explanatory view illustrating in time series, a transmission example of a case in which transmission beams are successively transmitted at different transmission intervals for respective transmission beams. 
     In  FIG. 17 , the selection interval of a code sequence corresponding to a transmission beam of an index  1  is L 1 , and the code sequence selection section  2700  selects the code sequence corresponding to the transmission beam as a measurement object, each time the interval L 1  has elapsed. The selection interval of a code sequence corresponding to a transmission beam of an index  2  is L 2 , and in a similar manner, the selection interval of a code sequence corresponding to a transmission beam of an index N is LN. Accordingly, the wireless communication device  2000  transmits the transmission beam of the index  1  at each interval L 1 , transmits the transmission beam of the index  2  at each interval L 2 , and transmits the transmission beam of the index N at each interval LN, in a similar manner. 
     However, a selection method of a code sequence by the code sequence selection section  2700  is not limited to a selection method of a code sequence illustrated in  FIG. 17 . That is, in the modification example, the wireless communication device  2000  may transmit the transmission beams of the code sequences corresponding to indexes in accordance with the orders illustrated in  FIG. 17 . 
     (Sensor  10 ) 
     In the modification example, the sensor  10  may have a configuration that includes at least one correlator and a signal processing section (for example, a correlator C 1  and a signal processing section SP 1 ). That is, the correlator C 1  holds the code sequence F 1 , and thus calculates a correlation value between a reception signal of a transmission beam transmitted from the wireless communication device  2000  and the code sequence F 1 . 
     The signal processing section SP 1  detects an interval in which a peak value of a correlation value calculated by the correlator C 1  appears, that is, the interval between the peak correlation value corresponding to the transmission beam that is received at the previous time and the peak correlation value corresponding to the transmission beam that is received at this time and determines that a transmission beam of which index is received. 
     In addition, in the present modification example, it is preferable that a transmission interval of a transmission beam which is transmitted from the wireless communication device  2000 , that is, a selection interval of a code sequence by the code sequence selection section  2700 , be a sufficiently large value in consideration of reception of a reflected wave in addition to a direct wave. 
     Thus, the wireless communication device  2000  of the present modification example can measure a radiation pattern of a beam having a desired directivity in a short time in a similar manner with the third embodiment. 
     &lt;Fourth Embodiment&gt; 
     In the third embodiment or the modification example of the third embodiment, the parameter of the phase given by the phase shifter are searched for and determined in advance. In a fourth embodiment, a wireless communication device and a sensor search for and determine an optimal value of a parameter of a phase given by a phase shifter of each branch. 
     Specifically, the wireless communication device successively transmits transmission beams while changing the parameter of the phase in a specific branch as the search object and using N code sequences and candidate values of parameters of a total of N phases in which the parameters of the phases in other branches, which are not the search object or for which searches are already ended, are fixed. 
     The sensor determines an optimal value of the parameter of the phase in the phase shifter of the branch as the search object on a basis of a coherent addition value of a correlation value between a reception signal and a code sequence of a transmission beam. In a similar manner, the wireless communication device successively transmits transmission beams using candidate values of parameters of a total of N phases of a specific branch as the subsequent search object and N code sequences. In a similar manner, the sensor determines the optimal value of the parameter of the phase in the phase shifter of the branch as the search object on a basis of the coherent addition value of the correlation value between the reception signal and the code sequence of the transmission beam. 
     In this manner, the wireless communication device and the sensor search for and determine optimal values of parameters of the phases in the phase shifters of all branches of the wireless communication device. In addition, in the present embodiment, since the configuration of the wireless communication device is the same as the configuration of the wireless communication device  2000  of the first embodiment, the same reference numerals as the third embodiment are used in the description of the present embodiment. In the present embodiment, since a radio wave for radiation pattern measurement transmitted by the wireless communication device  2000  has directivity, it is preferable that the sensor be disposed in consideration of the directivity of the radio wave. 
     (Table of Candidate Values of Parameters of Phases) 
       FIG. 18  is a table illustrating an example of a candidate value of a phase parameter in a phase shifter of each branch which is given to a transmission beam of each index in the fourth embodiment. The branches B 1 , B 2 , B 3 , and B 4  illustrated in  FIG. 18  correspond to the branches  20 A,  20 B,  20 C, and  20 D illustrated in  FIG. 11 , respectively. In addition, it is preferable that the candidate values of parameters in the table illustrated in  FIG. 18  be stored in advance, for example, in the storage area (not illustrated) of the control section  2600 . 
     In the present embodiment, the code sequences used for respective transmission beams are determined in advance and are different from each other, such that unlike the code sequences in the third embodiment or the modification example of the third embodiment, in a case where a parameter in a phase shifter of each branch is not set to an optimal value, a description is given of a method of determining an optimal value in a sensor  10 B. In the present embodiment, the sensor  10 B illustrated in  FIG. 19  can determine an optimal value of a phase parameter in a phase shifter of each branch of the wireless communication device  2000 , on a basis of a correlation value between a code sequence of a transmission beam and a reception signal. 
     In addition, in the table illustrated in  FIG. 18 , with respect to the parameters of respective phase shifters of the branches B 1 , B 2 , and B 3  (branches  20 A,  20 B, and  20 C), “100”, “110”, “120” are searched for as optimal values or are temporarily set without being searched, and the optimal value of the parameter of the phase shifter of the branch B 4  (branch  20 D) is not searched for. 
     In other words, since  FIG. 18  is a diagram illustrating a specific setting state in the middle of a search for an optimal phase parameter, it is assumed that the values capable of being taken as phase parameters are 0 to 200 in a temporal setting, and the phase parameters can be set in a unit of 10 steps. 
     The search starts when the phase parameters of all branches are set to zero, and  FIG. 18  illustrates a state in which the search is finished for the branches B 1  to B 3 , and thus 100 is allocated to the index  1  of the branch B 4 . 
     In order to determine the optimal value of the phase parameter in the phase shifter of the branch B 4 , the wireless communication device  2000  transmits a pulse compression signal of each code sequence, in which a phase parameter as a candidate value is set, by using a different code sequence for each transmission beam. That is, as the candidate value of the phase parameter and the code sequence in the phase shifter of the branch B 4 , “100” and “F 1 ” are allocated to the transmission beam BM 1  of the index  1 , “120” and “F 2 ” are allocated to the transmission beam BM 2  of the index  2 , “130” and “F 3 ” are allocated to the transmission beam BM 3  of the index  3 , . . . , in a similar manner, “180” and “FN” are allocated to the transmission beam of the index N. 
     In addition, the wireless communication device  2000  uses a different code sequence for each transmission beam such that the sensor  10 B illustrated in  FIG. 19  determines a transmission beam of which a phase parameter is an optimal value, on a basis of a coherent addition value of a plurality of N different correlation values. 
     (Sensor  10 B) 
       FIG. 19  is a block diagram illustrating an internal configuration of a sensor  10 B in the fourth embodiment. The sensor  10 B illustrated in  FIG. 19  receives a transmission beam as a pulse compression signal transmitted by the wireless communication device  2000  in the reception antenna  1100 . Further, the sensor  10 B determines that a candidate value of a parameter of which phase is an optimal value of the parameter of the phase in the phase shifter of the branch as the search object, on a basis of a coherent addition value of a correlation value of a code sequence of a transmission beam and a reception signal. In the sensor  10 B illustrated in  FIG. 19 , the same reference numerals are given to the configuring components corresponding to the sensor  10  of the third embodiment, and thus the description thereof is omitted. 
     The sensor  10 B illustrated in  FIG. 19  has a configuration that includes a reception antenna  1100 , a reception RF section  1200 , an ADC  1300 , a plurality of N correlators C 1 , . . . , Ck, . . . , and CN, signal processing sections SP 1 , . . . , SPk, . . . , and SPN, threshold value determination sections TJ 1 , . . . , TJk, . . . , and TJN, a search continuation determination section  1500 , a transmission antenna  16 , and a transmission section TX. In addition, for example, a display  50  which displays a determination result as to whether or not the determination result is an optimal value of a phase parameter may be connected to the sensor  10 B. 
     The operations of the correlators C 1 , . . . , Ck, . . . , and CN, the signal processing section SP 1 , . . . , SPk, . . . , and SPN and the threshold value determination sections TJ 1 , . . . , TJk, . . . , and TJN will be described by taking the correlator Ck, the signal processing section SPk and the threshold value determination section TJk as an example. 
     The correlator Ck holds a code sequence corresponding to the transmission beam of an index k and calculates a correlation value by performing a predetermined correlation processing on a digital reception signal which is output from the ADC  1300 . Specifically, the correlator Ck calculates a correlation value between a code sequence that the correlator Ck itself holds and a reception signal and obtains a sufficient correlation value, that is a peak correlation value, in a case where the transmission beam of the same code sequence as the code sequence that the correlator Ck holds is input as a reception signal. The correlator Ck outputs a calculated correlation value, that is, a peak correlation value or a non-peak correlation value, to the signal processing section SPk. 
     In addition, the code sequences of  FIGS. 15 and 16  may be repeatedly transmitted a plurality of times (for example, M number of times). Since the code sequences of  FIGS. 15 and 16  are repeatedly transmitted M number of times, the signal processing section SPk performs a coherent addition on a basis of M correlation values that are output from the correlator Ck. Thus, the signal processing section SPk improves a Signal to Noise Ratio (SNR) of N reception signals. The signal processing section SPk outputs the coherent addition value to the threshold value determination section TJk. 
     The threshold value determination section TJk compares the coherent addition value which is output from the signal processing section SPk with a predetermined threshold value and determines whether or not the coherent addition value exceeds a predetermined threshold value. The predetermined threshold value is determined in advance by the user who previously measures a radiation pattern, and the same is applied to each of the following embodiments. The threshold value determination section TJk outputs a comparison result of the coherent addition value and the predetermined threshold value, to the search continuation determination section  1500 . 
     If the coherent addition value exceeds the predetermined threshold value, the search continuation determination section  1500  determines a phase parameter given to a transmission beam of the code sequence Sk held by the correlator Ck corresponding to the signal processing section SPk that performs a coherent addition, as the parameter of the phase in the phase shifter of the branch as the search object. In other words, in the table of  FIG. 18 , among unsearched phases of the branch B 4 , the most suitable phase can be selected. 
     In a case where the coherent addition value does not exceed the predetermined threshold value and an appropriate value (optimal value) is not present among 100 to 180, the search continuation determination section  1500  searches for a range by setting the phase parameter  190  in the index  1  and setting the phase parameter  200  in the index  2 . 
     In addition, if all phase parameters are searched for, but the coherent addition value does not exceed the predetermined threshold value, the parameter of the phase given to the transmission beam of the code sequence Sk held by the correlator Ck corresponding to the signal processing section SPk that calculates a maximum coherent addition value is determined as the parameter of the phase in the phase shifter of the branch as the search object. 
     The transmission section TX transmits the determination result of the search continuation determination section  1500  from the transmission antenna  16  to the wireless communication device  2000 . The transmission section TX transmits, for example, a search instruction of the parameter of the phase in the phase shifter of the branch as the search object or the parameter of the phase in the phase shifter of the branch as the subsequent search object, to the wireless communication device  2000 . In addition, the above information may be informed to the wireless communication device  2000  by wired communication in addition to wireless communication. 
     (Search Method of Phase Parameter in Phase Shifter of Each Branch) 
     A search method of a phase parameter in a phase shifter of each branch of the present embodiment will be described with reference to  FIG. 20 .  FIG. 20  and  FIG. 21  are sequence diagrams illustrating operations of the wireless communication device  2000  and the sensor  10 B in the fourth embodiment. In the descriptions of  FIGS. 20 and 21 , the number of branches as the search object is assumed as N and the parameter of the phase in the phase shifter of an N-th branch is a first search object. 
     The wireless communication device  2000  sets, as a setting value of a first transmission beam BM N1 , a parameter having a fixed value of a phase in a phase shifter of each of first to (N−1)-th branches which are not the search object, a parameter (for example, 100) as a first candidate value of a phase in a phase shifter of the N-th branch as the search object, and a first code sequence F 1  (S 11 ). The wireless communication device  2000  transmits the first transmission beam BM N1  in accordance with the setting value to the sensor  10 B (S 12 ). The sensor  10 B calculates, in the correlators C 1  to CN, the correlation value between the reception signal of the first transmission beam BM N1  and the code sequence held by each of the correlators C 1  to CN (S 13 ). 
     In a similar manner, after transmission of step S 12 , the wireless communication device  2000  sets, as a setting value of a second transmission beam BM N2 , a parameter having a fixed value of a phase in a phase shifter of each of the first to (N−1)-th branches, which are not the search object, a parameter (for example, 110) as a second candidate value of a phase in a phase shifter of the N-th branch as the search object, and a second code sequence F 2  (S 14 ). The wireless communication device  2000  transmits the second transmission beam BM N2  in accordance with the setting value to the sensor  10 B (S 15 ). The sensor  10 B calculates, in the correlators C 1  to CN, the correlation value between the reception signal of the second transmission beam BM N2  and the code sequence held by each of the correlators C 1  to CN (S 16 ). 
     The wireless communication device  2000  repeats the same processing and sets, as a setting value of a N-th transmission beam BM NN , a parameter having a fixed value of a phase in a phase shifter of each of the first to (N−1)-th branches which are not the search object, a parameter (for example, 180) as a N-th candidate value of a phase in a phase shifter of the N-th branch as the search object, and the N-th code sequence FN (S 17 ). The wireless communication device  2000  transmits the N-th transmission beam BM NN  in accordance with the setting value to the sensor  10 B (S 18 ). The sensor  10 B calculates, in the correlators C 1  to CN, the correlation value between the reception signal of the N-th transmission beam BM NN  and the code sequence held by each of the correlators C 1  to CN (S 19 ). 
     Each of the signal processing sections SP 1  to SPN of the sensor  10 B coherently adds each correlation value that is calculated in the steps S 13 , S 16 , and S 19  (S 20 ), and outputs the coherent addition value to each of the threshold value determination sections TJ 1  to TJN. In  FIG. 21 , the threshold value determination sections TJ 1  to TJN compares the coherent addition value with the predetermined threshold value (S 21 ) and outputs the comparison result to the search continuation determination section  1500 . 
     In a case where the coherent addition value exceeds the predetermined threshold value (S 21 , YES), the search continuation determination section  1500  determines a phase parameter given to a transmission beam of a code sequence Sk held by the correlator Ck corresponding to the signal processing section SPk that performs the coherent addition as the parameter of the phase in the phase shifter of the branch as the search object (S 22 ). 
     In a case where the coherent addition value does not exceed the predetermined threshold value (S 21 , NO), the search continuation determination section  1500  determines whether or not an optimal value of a phase parameter is searched for by using the parameters of all phases, that is, the values obtained by setting values of 100 to 200 in a 10-step unit (S 23 - 1 ). In a case where the search is performed by using the parameters of all phases (S 23 - 1 , YES), the search continuation determination section  1500  determines a phase parameter given to a transmission beam of the code sequence Sk held by the correlator Ck corresponding to the signal processing section SPk which calculates a maximum coherent addition value as the parameter of the phase in the phase shifter of a branch as the search object (S 23 - 2 ). Thereafter, it is followed by step S 24 . 
     In a case where the search is not performed by using the parameters of all phases (S 23 - 1 , NO), the search continuation determination section  1500  transmits a transmission instructions of a transmission beam in accordance with a setting value of a parameter “190” of a phase and the first code sequence F 1 , and a transmission beam in accordance with a setting value of a parameter “200” of a phase and the second code sequence F 2 , to the transmission section TX (S 23 - 3 ). 
     The wireless communication device  2000  sets, as a setting value of the first transmission beam BM N1 , a parameter having a fixed value of a phase in a phase shifter of each of the first to (N−1)-th branches which are not the search object, a parameter (for example, 190) as a first candidate value of a phase in a phase shifter of the N-th branch as the search object, and the first code sequence F 1  (S 23 - 4 ). 
     Further, the wireless communication device  2000  sets, as a setting value of the second transmission beam BM N2 , a parameter having a fixed value of a phase in a phase shifter of each of the first to (N−1)-th branches which are not the search object, a parameter (for example, 200) as a second candidate value of a phase in a phase shifter of the N-th branch as the search object, and the second code sequence F 2  (S 23 - 4 ). 
     The wireless communication device  2000  transmits respectively a first and second transmission beams in accordance with the setting value, to the sensor  10 B, M number of times (S 23 - 5 ). The sensor  10 B calculates a correlation value between a first transmission beam and a second reception signal and the code sequences held by respective correlators C 1  to CN, in the correlators C 1  to CN, and coherently adds respective correlation values that are calculated for each transmission beam transmitted M number of times (S 23 - 6 ). Thereafter, it is followed by step S 21 . 
     In a case where it is determined that searches of parameters of the phases in the phase shifters of all branches of the wireless communication device  2000  are ended (S 24 , YES), the search continuation determination section  1500  transmits the parameter of the phase in the phase shifter of the last branch as the search object to the transmission section TX (S 25 ). Thus, the operations of the wireless communication device  2000  and the sensor  10 B of the present embodiment are ended. 
     In a case where it is determined that a search of parameter of the phase in the phase shifter of all branches of the wireless communication device  2000  is not ended (S 24 , NO), the search continuation determination section  1500  transmits a search instruction of the parameter of the phase in the phase shifter of the subsequent branch which is not searched to the transmission section TX (S 26 ). 
     The wireless communication device  2000 , on a basis of a search instruction that is transmitted from the sensor  10 B, sets, as a setting value of a first transmission beam BM k1 , a parameter having a fixed value of a phase in a phase shifter of each branch which is not the search object or for which searching is already finished, a parameter as a first candidate value of a phase in a phase shifter of a branch as the subsequent search object, and a first code sequence F 1  (S 27 ). The wireless communication device  2000  transmits the first transmission beam BMk 1  in accordance with the setting value to the sensor  10 B (S 28 ). The sensor  10 B calculates, in the correlators C 1  to CN, the correlation value between the reception signal of the first transmission beam BM k1  and the code sequence held by each of the correlators C 1  to CN (S 29 ). 
     In a similar manner, after transmission of step S 28 , the wireless communication device  2000  sets, as a setting value of a second transmission beam BM k2 , a parameter having a fixed value of a phase in a phase shifter of each branch which is not the search object or for which searching is already finished, a parameter as a second candidate value of a phase in a phase shifter of the N-th branch as the search object, and the second code sequence F 2  (S 30 ). The wireless communication device  2000  transmits the transmission beam BM k2  of the second code sequence F 2  in accordance with the setting value to the sensor  10 B (S 31 ). The sensor  10 B calculates, in the correlators C 1  to CN, the correlation value between the reception signal of the second transmission beam BM k2  and the code sequence held by each of the correlators C 1  to CN (S 32 ). 
     The wireless communication device  2000  repeats the same processing and sets, as a setting value of a N-th transmission beam BM kN , a parameter having a fixed value of a phase in a phase shifter of each branch which is not the search object or for which searching is already finished, a parameter as the N-th candidate value of a phase in a phase shifter of the N-th branch as the search object, and a N-th code sequence FN (S 33 ). The wireless communication device  2000  transmits the N-th transmission beam BM kN  in accordance with the setting value to the sensor  10 B (S 34 ). The sensor  10 B calculates, in the correlators C 1  to CN, the correlation value between the reception signal of the N-th transmission beam BM kN  and the code sequence held by each of the correlators C 1  to CN (S 35 ). Since the processing following step S 35  is the same as step S 20 , description thereof will be omitted. However, in the description of step S 27  to step S 35 , k is in the range of 1 to (n−1). 
     The wireless communication device  2000  of the present embodiment successively transmits N number of times the transmission beams based on the candidate values of parameters of N phases in a phase shifter of the branch as the search object. The sensor  10 B does not determine the optimal value of the parameter of the phase in the phase shifter of the branch as the search object each time a transmission beam transmitted by the wireless communication device  2000  is received. The sensor  10 B determines the optimal value of the parameter of the phase in the phase shifter of a branch as the search object, on a basis of the coherent addition value of the correlation values of the transmission beam that is successively transmitted N number of times. 
     Thus, the wireless communication device  2000  of the present embodiment can transmit a transmission beam for searching for an optimal value of a phase parameter given by the phase shifter of each branch. In addition, the sensor  10 B of the present embodiment can determine (search) the optimal value of the parameter of the phase given by the phase shifter of each branch of a wireless communication device, in a short time. 
     &lt;Modification Example of Fourth Embodiment&gt; 
     In the fourth embodiment, respective different “code sequences” are used as setting values of N transmission beams in the phase shifter of the branch as the search object. In the modification example of the fourth embodiment, “the transmission interval” of one code sequence (for example, code sequence F 1 ) is used as a setting value of N transmission beams in the phase shifter of the branch as the search object. Therefore, the number of correlators in the sensor is one. 
     In addition, in the modification example of the fourth embodiment, since the configuration of the wireless communication device is the same as the configuration of the wireless communication device  2000  of the fourth embodiment, the same reference numerals as the fourth embodiment are used in the description of the present modification example. 
     (Wireless Communication Device  2000 ) 
     In the modification example, the code sequence selection section  2700  may store one code sequence (for example, code sequence F 1 ). That is, the code sequence selection section  2700  does not select code sequences of a transmission beam as a radiation object, among a plurality of code sequences, as the second embodiment. The code sequence selection section  2700  selects a code sequence while changing a timing (selection interval) in which one code sequence (for example, code sequence F 1 ) is selected in accordance with the transmission beam as the radiation object. 
     (Sensor  10 C) 
       FIG. 22  is a block diagram illustrating an internal configuration of a sensor  10 C in a modification example of the fourth embodiment. In the sensor  10 C illustrated in  FIG. 14 , the same reference numerals are given to the configuring components corresponding to the sensor  10 B of the fourth embodiment, and thus the description thereof is omitted. 
     The sensor  10 C illustrated in  FIG. 22  has a configuration that includes a reception antenna  1100 , a reception RF section  1200 , an ADC  1300 , a correlator CC 1 , a signal processing section SPC 1 , a search continuation determination section  1500 C, a transmission antenna  16 , and a transmission section TX. In addition, for example, a display  50  which displays a determination result as to whether or not the determination result is an optimal value of a phase parameter may be connected to the sensor  10 C. 
     The correlator CC 1  holds a code sequence of a transmission beam of the index  1  and calculates a correlation value by performing a predetermined correlation processing on a digital reception signal which is output from the ADC  1300 . Specifically, the correlator CC 1  calculates a correlation value between a code sequence that the correlator CC 1  itself holds and a reception signal and obtains a sufficient correlation value, that is, a peak correlation value, in a case where the transmission beam of the same code sequence as the code sequence that the correlator CC 1  holds is input as a reception signal. The correlator CC 1  outputs the calculated correlation value, that is, a peak correlation value or a non-peak correlation value to the signal processing section SPC 1 . 
     The signal processing section SPC 1  detects an interval in which a peak value of a correlation value calculated by the correlator CC 1  appears, that is, the interval between the peak correlation value corresponding to the transmission beam that is received at the previous time and the peak correlation value corresponding to the transmission beam that is received at this time and determines that a transmission beam of which index is received. 
     The signal processing section SPC 1  compares the correlation value which is output from the correlator CC 1  with a predetermined threshold value and determines whether the correlation value exceeds the predetermined threshold value. The signal processing section SPC 1  processes the operations of the signal processing section (for example, signal processing section SP 1 ) and threshold value determination section (for example, threshold value determination section TJ 1 ) of the sensor  10 B illustrated in  FIG. 19 . The signal processing section SPC 1  outputs a comparison result to the search continuation determination section  15 C. 
     In a case where the correlation value exceeds a predetermined threshold value, the search continuation determination section  1500 C estimates parameter of a phase corresponding to the transmission beam determined by the signal processing section SPC 1  as the parameter of the phase in the phase shifter of a branch as the search object. 
     The transmission section TX transmits a determination result of the search continuation determination section  1500 C from the transmission antenna  16  to the wireless communication device  2000 . The transmission section TX transmits, for example, a search instruction of parameter of the phase in the phase shifter of a branch as the search object or parameter of the phase in the phase shifter of the branch as the subsequent search object to the wireless communication device  2000 . 
     (Table of Candidate Values of Parameter of a Phase) 
       FIG. 23  is a table illustrating an example of a phase parameter in a phase shifter of each branch which is given to a transmission beam of each index in a modification example of the fourth embodiment. The branches B 1 , B 2 , B 3 , and B 4  illustrated in  FIG. 23  correspond to the branches  20 A,  20 B,  20 C, and  20 D illustrated in  FIG. 11 , respectively. In addition, it is preferable that the candidate values of parameters in the table illustrated in  FIG. 23  be stored in advance, for example, in the storage area (not illustrated) of the control section  2600 . 
     In the modification example, the code sequence used for each transmission beam is determined in advance, and is for example, the code sequence F 1 , but in a similar way with the fourth embodiment, the parameter of the phase shifter of each branch is not set to an optimal value. Accordingly, in the modification example, the sensor  10 C illustrated in  FIG. 22  determines the optimal value of parameter of the phase in the phase shifter of each branch of the wireless communication device  2000  on a basis of a correlation value between a code sequence of a transmission beam and a reception signal. 
     In addition, in the table illustrated in  FIG. 23 , for the parameters of respective phase shifters of the branches B 1 , B 2 , and B 3  (branches  20 A,  20 B, and  20 C), “100”, “110”, “120” are searched as optimal values or temporarily set without being searched, and the optimal value of the parameter of the phase shifter of the branch B 4  (branch  20 D) is not searched. 
     In order to determine optimal values of parameter of the phase in the phase shifter of the branch B 4 , the wireless communication device  2000  changes a transmission interval for each transmission beam and transmits a pulse compression signal of each code sequence, in which parameter of a phase as candidate values is set. That is, as the candidate values of the parameter of a phase and the transmission interval in the phase shifter of the branch B 4 , “100” and “L 1 ” are allocated to the transmission beam BM 1  of the index  1 , “120” and “L 2 ” are allocated to the transmission beam BM 2  of the index  2 , “130” and “L 3 ” are allocated to the transmission beam BM 3  of the index  3 , . . . , in a similar manner, and “180” and “LN” are allocated to the transmission beam BMN of the index N. 
     (Search Method of Parameter of Phase in the Phase Shifter of Each Branch) 
     A search method of a phase parameter in a phase shifter of each branch of the present modification example will be described with reference to  FIG. 24 .  FIG. 24  is a sequence diagram illustrating operations of the wireless communication device  2000  and the sensors  10 C in a modification example of the fourth embodiment. In the description of  FIG. 24 , the number of branches to be the search object is assumed as N and the parameter of the phase in the phase shifter of the N-th branch is the first search object. 
     The wireless communication device  2000  sets, as a setting value of the first transmission beam BM N1 , a parameter having a fixed value of a phase in a phase shifter of each of the first to (N−1)-th branches which are not the search object, a parameter as a first candidate value of a phase in a phase shifter of the N-th branch as the search object, and a transmission interval L 1  of a first transmission beam (S 41 ). The wireless communication device  2000  transmits the first transmission beam BM N1  in accordance with the setting value to the sensor  10 C (S 42 ). The sensor  10 C calculates, in the correlators CC 1 , the correlation value between the reception signal of the first transmission beam BM N1  and the code sequence held by the correlator CC 1  (S 43 ). 
     The correlator CC 1  outputs the correlation value calculated in step S 43  to the signal processing section SPC 1 . The signal processing section SPC 1  compares the correlation value which is output from the correlator CC 1  with a predetermined threshold value and determines whether or not the correlation value exceeds the predetermined threshold value (S 44 ). The signal processing section SPC 1  outputs the comparison result to the search continuation determination section  1500 C. 
     In a case where the correlation value exceeds the predetermined threshold value (S 44 , YES), the search continuation determination section  1500 C determines the parameter of the phase corresponding to the transmission beam determined by the signal processing section SPC 1  as the parameter of the phase in the phase shifter of the branch as the search object (S 45 ). 
     In a case where the correlation value does not exceed the predetermined threshold value (S 44 , NO), the search continuation determination section  1500 C determines whether or not an optimal value of a phase parameter is searched by using the parameters of all phases, that is, by using values obtained by setting values of 100 to 200 in a 10-step unit (S 46 - 1 ). In a case where the search is performed by using the parameters of all phases (S 46 - 1 , YES), the search continuation determination section  1500 C determines a phase parameter given to the transmission beam corresponding to a maximum correlation value as the parameter of the phase in the phase shifter of the branch as the search object (S 46 - 2 ). Thereafter, it is followed by step S 49 . 
     In a case where the search is not performed by using the parameters of all phases (S 46 - 1 , NO), the search continuation determination section  1500 C transmits a transmission instruction of a transmission beam in which the parameter of the subsequent phase in the phase shifter of the branch as the search object is set (S 46 - 3 ). In addition, in a case where values of “100” to “180” are already set in a 10-step unit as the parameters of phases in step S 46 - 3 , “190” is set by further increasing the parameter of the phase by a 10-step unit, and “200” is set as a maximum value. 
     The wireless communication device  2000  sets, as a setting value of the second transmission beam BM N2 , a parameter having a fixed value of a phase in a phase shifter of each of the first to (N−1)-th branches which are not the search object, a parameter as a second candidate value of a phase in a phase shifter of the N-th branch as the search object, and a transmission interval L 2  of a second transmission beam (S 47 ). The wireless communication device  2000  transmits the second transmission beam BM N2  in accordance with the setting value to the sensor  10 C (S 48 ). The sensor  10 C calculates, in the correlators CC 1 , the correlation value between the reception signal of the second transmission beam BM N2  and the code sequence held by the correlator CC 1  (S 43 ). 
     In this manner, until it is determined that the correlation value exceeds a predetermined threshold value in step S 44 , the wireless communication device  2000  continuously transmits the transmission beam in which the parameter of the phase in the phase shifter of the N-th branch as the search object and the transmission interval are changed. 
     After the parameter of the phase in the phase shifter of the branch as the search object is determined in step S 45 , the search continuation determination section  1500 C of the sensor  10 C determines whether or not searches of parameters of phases in the phase shifters of all branches of the wireless communication device  2000  are ended (S 49 ). 
     In a case where it is determined that the searches of parameters of phases in the phase shifters of all branches of the wireless communication device  2000  are ended (S 49 , YES), the search continuation determination section  1500 C transmits the parameter of the phase in the phase shifter of the last branch as the search object to the transmission section TX (S 50 ). Thus, the operations of the wireless communication device  2000  and the sensor  10 C of the present embodiment are ended. 
     In a case where it is determined that the searches of parameters of phases in the phase shifters of all branches of the wireless communication device  2000  are not ended (S 49 , NO), the search continuation determination section  1500 C transmits a search instruction of the parameter of the phase in the phase shifter of the subsequent branch which is not searched to the transmission section TX (S 51 ). 
     The wireless communication device  2000 , on a basis of a search instruction that is transmitted from the sensor  10 C, sets, as a setting value of a first transmission beam BM k1 , a parameter having a fixed value of a phase in a phase shifter of each branch which is not the search object or for which searching is already finished, a parameter as a first candidate value of the phase in the phase shifter of the branch as the subsequent search object, and a first transmission interval L 1  of a first transmission beam (S 52 ). The wireless communication device  2000  transmits the first transmission beam BM k1  in accordance with the setting value to the sensor  10 C (S 53 ). The sensor  10 C calculates, in the correlator CC 1 , the correlation value between the reception signal of the first transmission beam BM k1  and the code sequence held by the correlator CC 1  (S 54 ). 
     The correlator CC 1  outputs the correlation value calculated in step S 53  to the signal processing section SPC 1 . The signal processing section SPC 1  compares the correlation value which is output from the correlator CC 1  with a predetermined threshold value and determines whether or not the correlation value exceeds the predetermined threshold value (S 55 ). The signal processing section SPC 1  outputs the comparison result to the search continuation determination section  1500 C. 
     In a case where the correlation value exceeds the predetermined threshold value (S 55 , YES), the search continuation determination section  1500 C determines the parameter of the phase corresponding to the transmission beam determined by the signal processing section SPC 1  as the parameter of the phase in the phase shifter of the branch as the search object (S 56 ). 
     In a case where the correlation value does not exceed the predetermined threshold value (S 55 , NO), the search continuation determination section  1500 C determines whether or not an optimal value of a phase parameter is searched by using the parameters of all phases, that is, by using values obtained by setting values of 100 to 200 in a 10-step unit (S 56 - 1 ). In a case where the search is performed by using the parameters of all phases (S 56 - 1 , YES), the search continuation determination section  1500 C determines a phase parameter given to the transmission beam corresponding to a maximum correlation value as the parameter of the phase in the phase shifter of the branch as the search object (S 56 - 2 ). Thereafter, it is followed by step S 49 . 
     In a case where the search is not performed by using the parameters of all phases (S 56 - 1 , NO), the search continuation determination section  1500 C transmits a transmission instruction of a transmission beam in which the parameter of the subsequent phase in the phase shifter of the branch as the search object is set (S 57 ). In addition, in a case where values of “100” to “180” are already set in a 10-step unit as the parameters of phases in step S 57 , “190” is set by further increasing the parameter of the phase by a 10-step unit, and “200” is set as a maximum value. 
     The wireless communication device  2000  sets, as a setting value of the second transmission beam BM N2 , a parameter having a fixed value of a phase in a phase shifter of each branch which is not the search object or for which searching is already finished, a parameter as a second candidate value of the phase in the phase shifter of the branch as the present search object and the transmission interval L 2  of the second transmission beam (S 58 ). The wireless communication device  2000  transmits the second transmission beam BM N2  in accordance with the setting value to the sensor  10 C (S 59 ). The sensor  10 C calculates, in the correlator CC 1 , the correlation value between the reception signal of the second transmission beam BM N2  and the code sequence held by the correlator CC 1  (S 54 ). 
     In this manner, until it is determined that the correlation value exceeds a predetermined threshold value in step S 55 , the wireless communication device  2000  continuously transmits the transmission beam in which the parameter of the phase in the phase shifter of the branch as the search object and the transmission interval are changed. 
     The wireless communication device  2000  of the present embodiment transmits the transmission beams based on the candidate values of parameters of N phases in a phase shifter of the branch as the search object, while changing a transmission interval for each transmission beam. The sensor  10 C determines the optimal value of the parameter of the phase in the phase shifter of the branch as the search object, on a basis of the correlation value of each transmission beam that is transmitted over the transmission interval of each transmission beam. 
     Thus, the wireless communication device  2000  of the present embodiment can transmit a transmission beam for searching for an optimal value of a phase parameter given by the phase shifter of each branch. In addition, the sensor  10 C of the present embodiment can determine (search) the optimal value of the parameter of the phase given by the phase shifter of each branch of the wireless communication device. 
     Further, the wireless communication device according to the present disclosure has the following configuration. 
     The present disclosure relates to a wireless communication device including a plurality of antenna system processing sections, 
     in which each of the antenna system processing sections including: 
     a code sequence selection section that selects a code sequence of a transmission signal, 
     a pulse compression signal generation section that performs a pulse compression processing on the selected code sequence, 
     a phase shifter that adjusts the phase of the signal subjected to the pulse compression processing in accordance with the selected code sequence, and 
     a transmission RF section that converts the signal, of which phase is adjusted, to a high frequency signal and transmits the high frequency signal from a transmission antenna. 
     Further, the present disclosure relates to the above described wireless communication device, 
     in which each of the antenna system processing sections further including: 
     a control section causes the phase shifter to adjust a parameter of the phase in accordance with the selected code sequence. 
     Further, the present disclosure relates to the above described wireless communication device, 
     in which the code sequence selection section successively selects a same code sequence a predetermined number of times and, after the aforesaid selection, successively selects a same code sequence which is different from the aforesaid code sequence a predetermined number of times. 
     Further, the present disclosure relates to the above described wireless communication device, 
     in which the code sequence selection section sequentially selects all different code sequences, and after the selection, repeatedly selects the all different code sequences. 
     Further, the present disclosure relates to the above described wireless communication device, 
     in which the code sequence selection section sets a different selection interval for each code sequence and successively selects a same code sequence a predetermined number of times. 
     Next, a description will be given of a distance measurement system, a sensor device, and a wireless communication device, which measure a distance with a wireless communication device. 
     A radar device has been known as a device capable of distance measurement. The radar device radiates a radio wave and receives a radio wave reflected by the detection target, that is, the reflected wave. The radar device receives a radio wave which travels back and forth linearly between the radar device itself and the detection target and measures a distance between the radar device and the detection target on a basis of a time difference between a time when the radio wave is received and a time when the reflected wave is received. 
     For example, PTL 2 below discloses a so-called one way distance measurement technology which measures a distance between a target and a measurement station on a basis of reception of a radio wave (direct wave) radiated in one direction without using the reflected wave. In PTL 2, a transmission device is provided in a flying object (for example, an aircraft, a rocket, and a radiosonde) of a distance measurement target, and a distance measurement device is disposed in a measurement station on the ground. For example, the transmission device periodically transmits a radio wave including the distance measurement pulse. The distance measurement device generates a reference pulse for distance measurement and calculates a distance between the transmission device and the distance measurement device, on a basis of a time difference between the distance measurement pulse from the transmission device and the reference pulse for distance measurement. 
     In the on way distance measurement method, since the transmission device and the distance measurement device operate independently of each other, it is necessary to adjust the operation timing before starting the distance measurement. In PTL 2, the distance measurement is performed at a point in which a flying distance is zero before a flying object is launched, a time difference between a distance measurement reference pulse and a received pulse received by the distance measurement device is obtained, and the time difference is stored in the distance measurement calculation section in advance. 
     [PTL 2] JP-A-7-234272 
     Problems in the Related Art 
     However, in the one way distance measurement method illustrated in above described PTL 2, it is necessary to synchronize an operation timing of transmission and reception of a signal between the transmission device (wireless communication device) and the distance measurement device (sensor device) before starting the distance measurement. 
     For example, synchronizing the operation timing between the wireless communication device and the sensor device by connecting the wireless communication device and the sensor device using a cable in a wired manner is considered as a synchronization method of an operation timing. However, a synchronization processing of the operation timing becomes complicated, and thus it is difficult to simply perform the synchronization processing. 
     Otherwise, it is considered that the wireless communication device and the sensor device perform wireless communication without being connected in a wired manner, and thus the operation timing between the wireless communication device and the sensor device is synchronized. However, since the distance between the wireless communication device and the sensor device is not constant in the wireless communication, a synchronization processing of the operation timing becomes complicated, and thus it is difficult to simply perform the synchronization processing. 
     In order to solve the above described problems in the related art, an object of the present disclosure is to provide a distance measurement system, a sensor device, and a wireless communication device, which simply measure a distance between the wireless communication device and the sensor device without informing in advance a sensor device of transmission timings of a signal from a wireless communication device. 
     Solution to Problems 
     The present disclosure relates to a distance measurement system which includes: a wireless communication device configured to transmit a wireless signal and a sensor device configured to measure a distance with the wireless communication device on a basis of the transmitted wireless signal, the wireless communication device including a terminal control section configured to switch the operation mode of the wireless communication device to a terminal normal mode of transmitting and receiving the wireless signal or to a continuous transmission mode of periodically transmitting the distance measurement pulse signal and the sensor device including a sensor control section configured to switch the operation mode of the sensor device to a sensor normal mode of transmitting and receiving a wireless signal or to a shortest distance estimation mode of estimating a time difference parameter between transmission timings and reception timings of the wireless signal on a basis of a wireless signal transmitted from the wireless communication device; a terminal-side mode control section configured to switch the operation mode of the wireless communication device from the terminal normal mode to the continuous transmission mode in a case where the wireless communication device receives a wireless signal having signal power of a first threshold value or more; and a sensor-side mode control section configured to switch the operation mode of the sensor device from the sensor normal mode to the shortest distance estimation mode in a case where the sensor device receives a wireless signal having signal power of a second threshold value or more. 
     Further, the present disclosure relates to a wireless communication device configured to transmit a wireless signal which includes a pulse compression signal generation section configured to periodically generate a pulse compression signal using a known code sequence suitable for correlation detection and a terminal control section configured to switch the operation mode of the wireless communication device to a terminal normal mode of transmitting and receiving the wireless signal or a continuous transmission mode of transmitting the pulse compression signal as a distance measurement pulse signal, the terminal control section switching the operation mode of the wireless communication device from the terminal normal mode to the continuous transmission mode in a case where the wireless communication device receives a wireless signal having signal power of a first threshold value or more. 
     Further, the present disclosure relates to a sensor device configured to measure a distance with a wireless communication device on a basis of reception timings when a wireless signal transmitted from the wireless communication device is received and which includes: a sensor reception section configured to receive the wireless signal transmitted from the wireless communication device; a sensor control section configured to switch the operation mode of the sensor device to a sensor normal mode of receiving a wireless signal or to a shortest distance estimation mode of estimating a time difference parameter between transmission timings and reception timings of the wireless signal on a basis of a wireless signal transmitted from the wireless communication device; and a sensor-side mode control section configured to switch the operation mode of the sensor device from the sensor normal mode to the shortest distance estimation mode in a case where a sensor-side reception section receives a wireless signal having signal power of a second threshold value or more. 
     Advantageous Effects of Invention 
     According to the present disclosure, it is possible to easily measure the distance between the wireless communication device and the sensor device without informing a sensor device of transmission timings of a signal from the wireless communication device in advance. 
     &lt;Fifth Embodiment&gt; 
     Hereinafter, a fifth embodiment of a distance measurement system, a sensor device, and a wireless communication device will be described with reference to drawings. The distance measurement system of the present embodiment is configured using a sensor device and a wireless communication device and can measure a distance between the wireless communication device and the sensor device in the sensor device. The distance measurement technology using the distance measurement system of the present embodiment is widely available in everyday life. 
     For example, inside a museum building, by implementing the sensor device in an entrance gate, if a visitor carrying the wireless communication device passes through the gate, it is possible to establish synchronization with the wireless communication device. Further, by implementing the sensor device at each exhibition, the sensor device can detect whether the visitor who owns the synchronized wireless communication device (for example, a mobile phone) approaches an exhibition and offer a special service (transmission of contents relevant to the exhibition) to the wireless communication device for the person who approaches the exhibition. 
     Further, for example, the sensor devices could be implemented in off-limits areas of railway station premises, detect whether a person carrying the wireless communication device (for example, mobile phone) approaches the off-limits areas, and cause the wireless communication device to output a warning sound to the person who approaches the off-limits areas. 
     Further, by implementing the sensor device in a ticket gate of a station, if a passenger who owns the wireless communication device passes through the ticket gate, the sensor device can establish synchronization. Because of this, a processing of synchronization establishment of the wireless communication device and a processing of using the wireless communication device as a ticket or a season ticket can be completed while the passenger passes through the ticket gate. 
     &lt;Configuration of Distance Measurement System&gt; 
     &lt;Outline of Entire Distance Measurement System&gt; 
     The distance measurement system  1000  of the present embodiment includes, for example, a wireless communication device (terminal)  100  and a sensor device  200 , illustrated in  FIG. 35 .  FIG. 35  is a schematic diagram conceptually illustrating an initial state of the distance measurement system. 
     The wireless communication device  100  is a portable wireless device (for example, a mobile phone) capable of transmitting and receiving a wireless signal. For example, the wireless communication device  100  is a wireless terminal capable of transmitting and receiving a wireless signal in accordance with a Wireless Gigabit (WiGig) specification. 
     The sensor device  200  measures a distance between the wireless communication device  100  and the sensor device  200  itself by using a wireless signal. That is, the sensor device  200  measures a distance between the wireless communication device  100  and the sensor device  200  on a basis of a time difference from when the wireless communication device  100  transmits a wireless signal until when the sensor device  200  receives the wireless signal. However, since the wireless communication device  100  and the sensor device  200  operate independently of each other, it is necessary to adjust operation timings of the wireless communication device  100  and the sensor device  200  before detecting a time difference until the sensor device  200  receives a wireless signal from the wireless communication device  100 . 
     &lt;Configuration of Wireless Communication Device  100 &gt; 
       FIG. 25  is a block diagram illustrating a configuration example of a wireless communication device  100 . The wireless communication device  100  illustrated in  FIG. 25  includes an antenna  110 , a high frequency section  120 , a modulation section  130 , a demodulation section  140 , a pulse compression detection section  150 , a pulse compression generation section  160 , a wireless device control section  170  as a terminal control section, a timer  180 , and a reception power calculation section  190 . 
     The wireless communication device  100  transmits and receives a wireless signal. That is, the data that is to be transmitted by the wireless communication device  100  is input from the wireless device control section  170  to the modulation section  130 , modulated in the modulation section  130 , and converted into an analog signal by a DAC (not illustrated, Digital Analog Converter) provided between the modulation section  130  and the high frequency section  120 . The data converted into the analog signal is input to the high frequency section  120 , converted into a high frequency signal, and amplified in the high frequency section  120 , and then transmitted as a radio wave from the antenna  110 . The frequency band of the high frequency signal is, for example, 60 GHz band, and the frequency band used in the sensor device  200  is the same. 
     Further, a radio wave not illustrated is transmitted from another wireless station, is received in the antenna  110 , and is input to the high frequency section  120  as a reception signal. The reception signal of a high frequency, which is input to the high frequency section  120 , is amplified and converted into a baseband signal in the high frequency section  120 , and then converted into a digital signal by an ADC (not illustrated, Analog Digital Converter) provided between the high frequency section  120  and the demodulation section  140 . The reception signal converted into a digital signal is input to and demodulated in the demodulation section  140  and input to the wireless device control section  170  as reception data. 
     The pulse compression detection section  150  and the pulse compression generation section  160  are provided in order for the sensor device  200  to measure a distance between the wireless communication device  100  and the sensor device  200 . The pulse compression detection section  150  detects a distance measurement pulse signal (pulse compression signal) transmitted from the sensor device  200 . The pulse compression generation section  160  generates the distance measurement pulse signal capable of being transmitted by the wireless communication device  100 . 
     The distance measurement pulse signal detected by the pulse compression detection section  150  and the distance measurement pulse signal generated by the pulse compression generation section  160  are the following signals. That is, the distance measurement pulse signal is a pulse-shaped signal recurring periodically in a fixed period and a signal suitable for correlation detection. The distance measurement pulse signal is a signal modulated using a predetermined and known code sequence in the wireless communication device  100  and the sensor device  200 . Although, for example, Golay code is used as a specific example of the code sequence, the code sequence is not limited to the Golay code. 
     Code sequences different from each other are used for the distance measurement pulse signal transmitted by the sensor device  200  and the distance measurement pulse signal generated by the pulse compression generation section  160  of the wireless communication device  100 . Accordingly, the wireless communication device  100  or the sensor device  200  determines the code sequence of the distance measurement pulse signal, thereby distinguishing a plurality of kinds of distance measurement pulse signals. The pulse compression detection section  150  includes a correlator for detecting the code sequence of the distance measurement pulse signal. 
     The wireless device control section  170  generally controls the operation of the wireless communication device  100 . For example, the wireless device control section  170  switches a plurality of predetermined operation modes in accordance with a communication state with the sensor device  200 . The switching of the operation modes will be described in detail. 
     The timer  180  is used for time measurement. The reception power calculation section  190  monitors the output signal of the high frequency section  120  and calculates the size of signal power of radio waves received by the antenna  110  from another station (for example, sensor device  200 ). 
     &lt;Configuration of Sensor Device  200 &gt; 
       FIG. 26  is a block diagram illustrating a configuration example of a sensor device  200 . The sensor device illustrated in  FIG. 26  includes an antenna  210  as a sensor reception section, a high frequency section  220 , a pulse compression generation section  230 , a correlation signal processing section  240  as a correlation detection section, a shortest distance estimation section  250 , a reception power calculation section  260 , a sensor control section  270 , and a timer  280 . 
     The pulse compression generation section  230  generates the above described distance measurement pulse signal (pulse compression signal). The distance measurement pulse signal generated by the pulse compression generation section  230  is converted into an analog signal by a DAC (not illustrated) provided between the pulse compression generation section  230  and the high frequency section  220 . Data converted into the analog signal is input to the high frequency section  220 , converted into a high frequency signal and amplified in the high frequency section  220 , and then transmitted as a radio wave from the antenna  210 . 
     On the other hand, a radio wave transmitted from another station (for example, wireless communication device  100 ) is received in the antenna  210  and is input to the high frequency section  220  as a reception signal. The reception signal of a high frequency, which is input to the high frequency section  220 , is amplified and converted into a baseband signal in the high frequency section  220 . 
     The correlation signal processing section  240  includes a correlator and obtains a peak correlation value as an output from the correlator at a timing in which a signal including a code sequence that matches the predetermined code sequence is received. Accordingly, in a case where a distance measurement pulse signal generated on a basis of the predetermined code sequence is received, the sensor device  200  can detect the reception timing of the distance measurement pulse signal on a basis of an output (peak correlation value) from the correlation signal processing section  240 . Further, the correlation signal processing section  240  can detect a signal having a pulse width compressed compared to the pulse width of the distance measurement pulse signal transmitted from the wireless communication device  100  by the detection of the peak correlation value. That is, the correlation signal processing section  240  uses a pulse compression technology, thereby detecting timings in which each distance measurement pulse signal is received with high accuracy. 
     The shortest distance estimation section  250  estimates a shortest state of a distance between the wireless communication device  100  and the sensor device  200  and adjusts distance measurement timings on a basis of the estimation result. For measuring the distance, the shortest distance estimation section  250  measures a time difference between a timing in which the wireless communication device  100  transmits the distance measurement pulse signal and a timing in which the sensor device  200  receives the distance measurement pulse signal from the wireless communication device  100 . 
     However, since the operation timing of the sensor device  200  is not synchronous with the operation timing of the wireless communication device  100 , it is difficult for the sensor device  200  to understand the time difference between the operation timing of the wireless communication device  100  and the operation timing of the sensor device  200  in an initial state (see  FIG. 35 ). The shortest distance estimation section  250  performs an estimation processing in order to understand the time difference between the operation timing of the wireless communication device  100  and the operation timing of the sensor device  200 . Specific operations will be described below. 
     The reception power calculation section  260  monitors the output signal of the high frequency section  220  and calculates the size of signal power of a radio wave received by the antenna  210  from another station (for example, wireless communication device  100 ). 
     The sensor control section  270  generally controls the operation of the sensor device  200 . For example, the sensor control section  270  switches a plurality of predetermined operation modes in accordance with a communication state with the wireless communication device  100 . The switching of the operation modes will be described below. The timer  280  is used for time measurement. 
     &lt;Distance Measurement Method&gt; 
     &lt;Transmission and Reception Timing of a Distance Measurement Pulse Signal&gt; 
       FIG. 27  is a time chart illustrating a specific example (1) of transmission timings and reception timings of a distance measurement pulse signal transmitted as a wireless signal from a wireless communication device  100 . 
     The distance measurement pulse signal SG 1  illustrated in  FIG. 27  denotes a wireless signal transmitted by the wireless communication device  100 . The distance measurement pulse signal SG 2  illustrated in  FIG. 27  denotes the distance measurement pulse signal SG 1  that the sensor device  200  actually receives. That is, since a time delay occurs in accordance with the distance between the wireless communication device  100  and the sensor device  200  until the distance measurement pulse signal SG 1  reaches the sensor device  200  after the wireless communication device  100  transmits the distance measurement pulse signal SG 1 , a time difference occurs between the distance measurement pulse signals SG 1  and SG 2 . Further, in an initial state of communication between the wireless communication device  100  and the sensor device  200 , the operation timing of the wireless communication device  100  and the operation timing of the sensor device  200  are not synchronous with each other. 
     In  FIG. 27 , the distance measurement pulse signal SG 1  is a signal in which distance measurement pulse signals SG 1 ( 1 ), SG 1 ( 2 ), SG 1 ( 3 ), . . . are repeatedly transmitted from the wireless communication device  100  at a constant time period Ta. The distance measurement pulse signal SG 2 ( 1 ) corresponds to the distance measurement pulse signal SG 1 ( 1 ), that is, a signal obtained when the sensor device  200  receives the distance measurement pulse signal SG 1 . In a similar manner, distance measurement pulse signals SG 2 ( 2 ), SG 2 ( 3 ), SG 2 ( 4 ), . . . respectively correspond to the distance measurement pulse signals SG 1 ( 2 ), SG 1 ( 3 ), SG 1 ( 4 ), . . . , in other words, the distance measurement pulse signals SG 2 ( 1 ), SG 2 ( 2 ), SG 2 ( 3 ), SG 2 ( 4 ), . . . are signals received in the sensor device  200 . 
     Accordingly, the first distance measurement pulse signal SG 1 ( 1 ) transmitted from the wireless communication device  100  at time t 11  is received as the distance measurement pulse signal SG 2 ( 1 ) by the sensor device  200  at time t 12 . In a similar manner, the second distance measurement pulse signal SG 1 ( 2 ) transmitted from the wireless communication device  100  at time t 21  is received as the distance measurement pulse signal SG 2 ( 2 ) by the sensor device  200  at time t 22 . The third distance measurement pulse signal SG 1 ( 3 ) transmitted from the wireless communication device  100  at time t 31  is received as the distance measurement pulse signal SG 2 ( 3 ) by the sensor device  200  at time t 32 . 
     In  FIG. 27 , a time difference between a second transmitted distance measurement pulse signal SG 1 ( 2 ) and a second received distance measurement pulse signal SG 2 ( 2 ) is denoted as X( 1 ). A time difference between a third transmitted distance measurement pulse signal SG 1 ( 3 ) and a third received distance measurement pulse signal SG 2 ( 3 ) is denoted as X( 2 ). A time difference between a fourth transmitted distance measurement pulse signal SG 1 ( 4 ) and a fourth received distance measurement pulse signal SG 2 ( 4 ) is denoted as X( 3 ). 
     The time interval between a distance measurement pulse signal SG 2 ( 1 ) that the sensor device  200  first receives and a distance measurement pulse signal SG 2 ( 2 ) that the sensor device  200  second receives is denoted as Tb( 1 ). The time interval between a distance measurement pulse signal SG 2 ( 2 ) that the sensor device  200  second receives and a distance measurement pulse signal SG 2 ( 3 ) that the sensor device  200  third receives is denoted as Tb( 2 ). The time interval between a distance measurement pulse signal SG 2 ( 3 ) that the sensor device  200  third receives and a distance measurement pulse signal SG 2 ( 4 ) that the sensor device  200  fourth receives is denoted as Tb( 3 ). 
     In a case where a distance between the wireless communication device  100  and the sensor device  200  changes, time differences X( 1 ), X( 2 ), X( 3 ), . . . illustrated in  FIG. 27  change. Further, the time intervals Tb( 1 ), Tb( 2 ), Tb( 3 ), . . . of the distance measurement pulse signals received by the sensor device  200  change. 
     Further, in  FIG. 27 , based on a certain time K, the first distance measurement pulse signal SG 1 ( 1 ) is transmitted from the wireless communication device  100  after time Y 0  has elapsed from the time K, and the first distance measurement pulse signal SG 2 ( 1 ) is received in the sensor device  200  after the time Z 0  has elapsed from the time K. 
     &lt;Operation of Sensor Device  200 : Measurement of Time Interval Tb(n)&gt; 
     The sensor control section  270  monitors the output of the correlation signal processing section  240  so as to understand the reception timing of the distance measurement pulse signal SG 2  at each distance measurement pulse signal and measures time intervals Tb( 1 ), Tb( 2 ), Tb( 3 ), . . . of the distance measurement pulse signal received after the reference time K to store all of them in a memory, not illustrated. 
     Accordingly, for example, after the reference time K, in a case where first to n-th distance measurement pulse signals transmitted from the wireless communication device  100  are received, the sensor device  200  obtains a total of (n−1) data of time intervals Tb( 1 ) to Tb(n−1). The sensor device  200  causes the operation timing of the sensor device  200  to be synchronous with the operation timing of the wireless communication device  100  by using a total of (n−1) data. 
     &lt;Description of P Value&gt; 
     In  FIG. 27 , after the reference time K, the time tn 1  in which the wireless communication device  100  transmits the n-th distance measurement pulse signal SG 1 (n) is represented by Expression (4). The time tn 2  in which the sensor device  200  receives the n-th distance measurement pulse signal SG 2 (n) is represented by Expression (5). In Expression (5), Tb( 0 )=0. 
     [Expression 4]
 
 tn 1= Yo +( n− 1)× Ta   (4)
 
     
       
         
           
             
               
                 
                   [ 
                   
                     Expression 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     5 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     tn 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     2 
                   
                   = 
                   
                     Zo 
                     + 
                     
                       
                         ∑ 
                         
                           k 
                           = 
                           1 
                         
                         n 
                       
                       ⁢ 
                       
                         Tb 
                         ⁡ 
                         
                           ( 
                           
                             k 
                             - 
                             1 
                           
                           ) 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   5 
                   ) 
                 
               
             
           
         
       
     
     Accordingly, the time difference X(n−1) between the time tn 2  in which the sensor device  200  receives the n-th distance measurement pulse signal SG 2 (n) and the time tn 1  is represented by Expression (6). 
     
       
         
           
             
               
                 
                   [ 
                   
                     Expression 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     6 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     X 
                     ⁡ 
                     
                       ( 
                       
                         n 
                         - 
                         1 
                       
                       ) 
                     
                   
                   = 
                   
                     
                       [ 
                       
                         Zo 
                         + 
                         
                           
                             ∑ 
                             
                               k 
                               = 
                               1 
                             
                             
                               n 
                               - 
                               1 
                             
                           
                           ⁢ 
                           
                             Tb 
                             ⁡ 
                             
                               ( 
                               
                                 k 
                                 - 
                                 1 
                               
                               ) 
                             
                           
                         
                       
                       ] 
                     
                     - 
                     
                       [ 
                       
                         Yo 
                         + 
                         
                           
                             ( 
                             
                               n 
                               - 
                               1 
                             
                             ) 
                           
                           × 
                           Ta 
                         
                       
                       ] 
                     
                   
                 
               
               
                 
                   ( 
                   6 
                   ) 
                 
               
             
           
         
       
     
     In Expression (6), the period Ta is constant and information known to the sensor device  200 . Further, the sensor device  200  counts the number of distance measurement pulse signals which are received, thereby understanding the number n of the distance measurement pulse signal which is received last. Further, the sensor device  200  can understand a value of (k−1)-th time interval Tb(k) for the first to (n−1)-th distance measurement pulse signals. 
     In Expression (6), times Z 0  and Y 0  are unknown numbers. However, the sensor device  200  may understand the relative value of the time difference X(n−1) and may not understand times Z 0  and Y 0  separately. Here, for convenience, in a state where the wireless communication device  100  and the sensor device  200  are most adjacent to each other, that is, in a case where Z 0 −Y 0 =0, the sensor device  200  obtains a P value corresponding to the time difference X (n−1). The P value in a case where the sensor device  200  receives the (n−1)-th distance measurement pulse signal, that is, P(n−1) is represented by Expression (7). 
     
       
         
           
             
               
                 
                   [ 
                   
                     Expression 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     7 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     P 
                     ⁡ 
                     
                       ( 
                       
                         n 
                         - 
                         1 
                       
                       ) 
                     
                   
                   = 
                   
                     
                       
                         ∑ 
                         
                           k 
                           = 
                           1 
                         
                         
                           n 
                           - 
                           1 
                         
                       
                       ⁢ 
                       
                         Tb 
                         ⁡ 
                         
                           ( 
                           
                             k 
                             - 
                             1 
                           
                           ) 
                         
                       
                     
                     - 
                     
                       
                         ( 
                         
                           n 
                           - 
                           1 
                         
                         ) 
                       
                       × 
                       Ta 
                     
                   
                 
               
               
                 
                   ( 
                   7 
                   ) 
                 
               
             
           
         
       
     
     In a case where the distance between the wireless communication device  100  and the sensor device  200  does not change, the P value represented by Expression (7) is a constant value. Further, in a case where the wireless communication device  100  is approaching the sensor device  200 , the P value is reduced, whereas in a case where the wireless communication device  100  is moving away from the sensor device  200 , the P value is increased. 
       FIG. 28  is a graph illustrating a specific example (1) of a change of P value. That is, in a case where the wireless communication device  100  approaches and moves away from the sensor device  200 , the change characteristic curve of P value illustrated in  FIG. 28  is observed. The minimum value of the P value as an extreme value of the change characteristic curve illustrated in  FIG. 28  means a state where the wireless communication device  100  is closest to the sensor device  200 , that is, the distance between the wireless communication device  100  and the sensor device  200  is shortest. 
     The shortest distance estimation section  250  calculates the P value represented by Expression (7) and understands the extreme value of the change characteristic curve illustrated in  FIG. 28 , and thus estimates the shortest distance between the wireless communication device  100  and the sensor device  200 . However, in a case where the change characteristic curve of the P value is not the change characteristic curve having one extreme value illustrated in  FIG. 28  but a change characteristic curve having a plurality of extreme values, there is also a possibility of erroneously determining any one of extreme value in the characteristic curve as a shortest distance state. 
     The shortest distance estimation section  250  considers as a condition, whether or not the signal power of a distance measurement pulse signal received by the sensor device  200  exceeds a predetermined threshold value in the estimation of the shortest distance, thereby avoiding an erroneous determination of the extreme value in the characteristic curve. 
     &lt;Understanding of Time Difference&gt; 
     The time that the sensor device  200  can detect using the above method is the time in a case of where the distance between the wireless communication device  100  and the sensor device  200  are adjacent to each other in a shortest distance. As a real situation, in the present embodiment, when the wireless communication device  100  is close to or in contact with the sensor device  200 , the sensor device  200  observes the change characteristic curve of the P values illustrated in  FIG. 28 . 
     A distance L (for example, 10 cm) is treated as a known value in a position state in which the wireless communication device  100  and the sensor device  200  are expected to be in contact with each other in a case where the wireless communication device  100  is in contact with the sensor device  200 . That is, in a case where a m-th P value P(m) is a shortest distance, Expression (8) is established. In Expression (8), C is a light speed. 
     
       
         
           
             
               
                 
                   [ 
                   
                     Expression 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     8 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     
                       
                         P 
                         ⁡ 
                         
                           ( 
                           m 
                           ) 
                         
                       
                       + 
                       Zo 
                       - 
                       Yo 
                     
                     = 
                     
                       L 
                       C 
                     
                   
                   ⁢ 
                   
                     
 
                   
                   ⁢ 
                   
                     
                       ( 
                       
                         Zo 
                         - 
                         Yo 
                       
                       ) 
                     
                     = 
                     
                       
                         L 
                         C 
                       
                       - 
                       
                         P 
                         ⁡ 
                         
                           ( 
                           m 
                           ) 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   8 
                   ) 
                 
               
             
           
         
       
     
     Z 0  and Y 0  which were unknown numbers are not still known, but the value (Z 0 −Y 0 ) of the difference as a relative value is found by Expression (8). Accordingly, a time difference X(j) can be specified by Expression (9) with respect to a distance measurement pulse signal which is received in the j-th time among the first to (n−1)-th distance measurement pulse signals based on Expression (6). In Expression (9), Tb(k) can be acquired as data of a observed value, (Z 0 −Y 0 ) is calculated from Expression (8), and period Ta is known. 
     
       
         
           
             
               
                 
                   [ 
                   
                     Expression 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     9 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     X 
                     ⁡ 
                     
                       ( 
                       j 
                       ) 
                     
                   
                   = 
                   
                     
                       
                         ∑ 
                         
                           k 
                           = 
                           1 
                         
                         
                           j 
                           - 
                           1 
                         
                       
                       ⁢ 
                       
                         Tb 
                         ⁡ 
                         
                           ( 
                           
                             k 
                             - 
                             1 
                           
                           ) 
                         
                       
                     
                     - 
                     
                       
                         ( 
                         
                           j 
                           - 
                           1 
                         
                         ) 
                       
                       × 
                       Ta 
                     
                     + 
                     
                       ( 
                       
                         Zo 
                         - 
                         Yo 
                       
                       ) 
                     
                   
                 
               
               
                 
                   ( 
                   9 
                   ) 
                 
               
             
           
         
       
     
     The sensor device  200  can calculate a distance between the wireless communication device  100  and the sensor device  200  by using a time difference X(j) and a light speed C. Further, since the time difference X(j) is known, the sensor device  200  knows the transmission times t 21 , t 31 , t 41 , . . . of the wireless communication device  100 , thereby establishing synchronization with the wireless communication device  100 . 
     &lt;(Modification Example): Measurement of Time Difference Tc(n)&gt; 
     Next, a modification example regarding a time measurement operation will be described.  FIG. 29  is a time chart illustrating a specific example (2) of transmission timings and reception timings of a wireless signal. 
     Similar to  FIG. 27 , the distance measurement pulse signal SG 1  illustrated in  FIG. 29  indicates a wireless signal transmitted by the wireless communication device  100 . The distance measurement pulse signal SG 2  illustrated in  FIG. 29  indicates the distance measurement pulse signal SG 1  that the sensor device  200  actually receives. 
     In  FIG. 29 , the distance measurement pulse signal SG 1  is a signal in which distance measurement pulse signals SG 1 ( 1 ), SG 1 ( 2 ), SG 1 ( 3 ), . . . are repeatedly transmitted from the wireless communication device  100  at a constant time period Ta. The distance measurement pulse signal SG 2 ( 1 ) corresponds to the distance measurement pulse signal SG 1 ( 1 ), that is, a signal obtained when the sensor device  200  receives the distance measurement pulse signal SG 1 . In a similar manner, distance measurement pulse signals SG 2 ( 2 ), SG 2 ( 3 ), SG 2 ( 4 ), . . . respectively correspond to the distance measurement pulse signals SG 1 ( 2 ), SG 1 ( 3 ), SG 1 ( 4 ), . . . , that is, the distance measurement pulse signals SG 2 ( 1 ), SG 2 ( 2 ), SG 2 ( 3 ), SG 2 ( 4 ), . . . are signals that are received in the sensor device  200 . 
     In  FIG. 29 , a time difference between the first distance measurement pulse signal SG 1 ( 1 ) transmitted by the wireless communication device  100  and the distance measurement pulse signal SG 2 ( 1 ) received by the sensor device  200  is denoted as X( 1 ). A time difference between the second distance measurement pulse signal SG 1 ( 2 ) transmitted by the wireless communication device  100  and the distance measurement pulse signal SG 2 ( 2 ) received by the sensor device  200  is denoted as X( 2 ). A time difference between the third distance measurement pulse signal SG 1 ( 3 ) transmitted by the wireless communication device  100  and the distance measurement pulse signal SG 2 ( 3 ) received by the sensor device  200  is denoted as X( 3 ). 
     Further, a time difference between the reception time of the first distance measurement pulse signal SG 2 ( 1 ) received by the sensor device  200  and the first reference time K( 1 ) is denoted as Tc( 1 ). A time difference between the reception time of the second distance measurement pulse signal SG 2 ( 2 ) received by the sensor device  200  and the second reference time K( 2 ) is denoted as Tc( 2 ). A time difference between the reception time of the third distance measurement pulse signal SG 2 ( 3 ) received by the sensor device  200  and the third reference time K( 3 ) is denoted as Tc( 3 ). 
     In  FIG. 29 , based on a certain time K, the wireless communication device  100  transmits the first distance measurement pulse signal SG 1 ( 1 ) after time Y 0  has elapsed from the time K, and the sensor device  200  receives the first distance measurement pulse signal SG 2 ( 1 ) after the time Z 0  has elapsed from the time K and the time difference Tc( 1 ) has elapsed. 
     In addition, since the time Z 0  and time Y 0  are unknown, the sensor device  200  sets a time when time Z 0  has elapsed from the reference time K as a first reference time K( 1 ). 
     Further, since the transmission period Ta of the distance measurement pulse signal transmitted from the wireless communication device  100  is known and is constant, the sensor device  200  sets a time when the same time as the period Ta has elapsed from the first reference time K( 1 ) as a second reference time K( 2 ). 
     In a similar manner, the sensor device  200  sets a time when the same time as the period Ta has elapsed from the second reference time K( 2 ) as a third reference time K( 3 ) and sets a time when the same time as the period Ta has elapsed from the third reference time K( 3 ) as a fourth reference time K( 4 ). 
     In a modification example 1, the sensor device  200  sets each of reference times K( 1 ), K( 2 ), K( 3 ), . . . , sequentially measures and stores the reception timing of the n-th distance measurement pulse signal SG 2 (n) as a time difference Tc(n) from the n-th reference time K(n) to when the n-th distance measurement pulse signal SG 2 (n) is received. In addition, the time difference Tc(n) may have a negative value. 
     Accordingly, the n-th time difference X(n) illustrated in  FIG. 29  is represented by Expression (10). 
     
       
         
           
             
               
                 
                   [ 
                   
                     Expression 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     10 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     
                       
                         
                           X 
                           ⁡ 
                           
                             ( 
                             n 
                             ) 
                           
                         
                         = 
                           
                         ⁢ 
                         
                           
                             [ 
                             
                               Zo 
                               + 
                               
                                 Ta 
                                 × 
                                 
                                   ( 
                                   
                                     n 
                                     - 
                                     1 
                                   
                                   ) 
                                 
                               
                               + 
                               
                                 
                                   ∑ 
                                   
                                     k 
                                     = 
                                     1 
                                   
                                   n 
                                 
                                 ⁢ 
                                 
                                   Tc 
                                   ⁡ 
                                   
                                     ( 
                                     k 
                                     ) 
                                   
                                 
                               
                             
                             ] 
                           
                           - 
                           
                             [ 
                             
                               Yo 
                               + 
                               
                                 Ta 
                                 × 
                                 
                                   ( 
                                   
                                     n 
                                     - 
                                     1 
                                   
                                   ) 
                                 
                               
                             
                             ] 
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                           
                         ⁢ 
                         
                           
                             ( 
                             
                               Zo 
                               - 
                               Yo 
                             
                             ) 
                           
                           + 
                           
                             
                               ∑ 
                               
                                 k 
                                 = 
                                 1 
                               
                               n 
                             
                             ⁢ 
                             
                               Tc 
                               ⁡ 
                               
                                 ( 
                                 k 
                                 ) 
                               
                             
                           
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   10 
                   ) 
                 
               
             
           
         
       
     
     Accordingly, in the modification example, the sensor device  200  measures a time difference Tc(n) illustrated in  FIG. 29 , thereby understanding the n-th time difference X(n), in a similar manner with a case of measuring a time interval Tb(n) illustrated in  FIG. 27 . 
     In a case of measuring a time interval Tb(n) illustrated in  FIG. 27 , since the number value is calculated for summing times from the reference time K, if a reception time of the distance measurement pulse signal is longer than the reference time, it is necessary to handle the large number value in the calculation process, and thus the circuit scale of the sensor device  200  is increased. However, in a case of measuring a time difference Tc (n) in the present modification example, since difference information from the n-th reference time K(n) may be added, it is possible to suppress increase in the number value to be handled and to reduce the circuit scale of the sensor device  200 . 
     &lt;Operation of System&gt; 
     The wireless communication device  100  illustrated in  FIG. 25  performs communication with other reception devices (not illustrated) in general, in addition to transmitting the distance measurement pulse signal for measuring a distance in the distance measurement system  1000 . Further, the operation timing of the sensor device  200  illustrated in  FIG. 26  is not synchronous with the operation timing of the wireless communication device  100  illustrated in  FIG. 25 , in an initial state of the distance measurement system  1000 . 
     &lt;Operation Sequence of Distance Measurement System  1000 &gt; 
       FIG. 31  is a sequence diagram illustrating an overview of an operation of a distance measurement system  1000  of the fifth embodiment.  FIG. 35  is a schematic diagram conceptually illustrating an initial state of a distance measurement system  1000 .  FIG. 36  is a schematic diagram conceptually illustrating a sensing state of the distance measurement system  1000 .  FIG. 37  is a schematic diagram conceptually illustrating a measurement state of the distance measurement system  1000 . 
     In a case where a normal communication state (normal mode) is transited to a distance measurement state (distance measurement mode), the wireless communication device  100  and the sensor device  200  of the distance measurement system  1000  sequentially switch respective operation modes. That is, in  FIG. 31 , respective states of the wireless communication device  100  and the sensor device  200  are changed from “state  1 ” to “state  4 ”. 
     The “state  1 ” is, for example, in  FIG. 35 , an initial state in which the distance between the wireless communication device  100  and the sensor device  200  is substantially far from each other. In the “state  1 ”, the wireless communication device  100  and the sensor device  200  respectively operate as the normal mode. 
     That is, the wireless communication device  100  transmits and receives packets suitable for a predetermined wireless specification as a wireless signal. The sensor device  200  transmits a predetermined distance measurement pulse signal SGO and monitors the presence or absence of the reception of a predetermined distance measurement pulse signal SG 1 . 
     As the wireless communication device  100  approaches the sensor device  200 , a transition to the sensing state illustrated in  FIG. 36  is started, so that the wireless communication device  100  and the sensor device  200  detect the wireless signals of each other. In fact, after the wireless communication device  100  approaches and is in contact temporarily with the sensor device  200 , the wireless communication device  100  moves away from the sensor device  200 . 
     The wireless communication device  100  determines whether or not the received wireless signal is a predetermined distance measurement pulse signal SG 0  and whether or not the reception power of the received signal exceeds a specific threshold value. The wireless communication device  100  switches the operation mode of the wireless communication device  100  from the normal mode to the continuous transmission mode on a basis of the determination result. Thus, the “state  1 ” corresponding to the initial state illustrated in  FIG. 35  is transited to the “state  2 ” corresponding to the sensing state illustrated in  FIG. 36 . 
     If the transition to the “state  2 ” occurs, the wireless communication device  100  operates as the continuous transmission mode. That is, the wireless communication device  100  temporarily stops the normal communication state and successively transmits the distance measurement pulse signal (SG 1 ). That is, the wireless communication device  100  in  FIG. 27  or  FIG. 29  repeatedly transmits the distance measurement pulse signal (SG 1 ) at a constant period Ta. 
     In the “state  2 ”, the sensor device  200  keeps the normal mode and receives the distance measurement pulse signal SG 1  transmitted by the wireless communication device  100  as the distance measurement pulse signal SG 2 . That is, in the sensing state illustrated in  FIG. 36 , the wireless communication device  100  detects the distance measurement pulse signal SG 0  transmitted by the sensor device  200 , and the sensor device  200  detects the distance measurement pulse signal SG 1  transmitted by the wireless communication device  100 . 
     In “state  2 ”, the sensor device  200  determines whether or not the signal power of the received distance measurement pulse signal SG 2  is sufficiently large and exceeds a predetermined threshold value. In a case where the signal power exceeds the threshold value, the sensor device  200  switches the operation mode of the sensor device  200  from the normal mode to the shortest distance estimation mode. Thus, the “state  2 ” corresponding to the sensing state illustrated in  FIG. 36  is transited to the “state  3 ” corresponding to the measurement state illustrated in  FIG. 37 . 
     In addition, in the “state  2 ”, the sensor device  200  receives the distance measurement pulse signal SG 0  transmitted by the sensor device  200  itself and the distance measurement pulse signal SG 1  transmitted by the wireless communication device  100 . In a case of receiving the distance measurement pulse signals SG 0  and SG 1 , the sensor device  200  receives the distance measurement pulse signal SG 1  having greater signal power than the distance measurement pulse signal SG 0 . 
     Accordingly, the sensor device  200  can distinguish two distance measurement pulse signals SG 0  and SG 1  on a basis of a difference of a size of signal power. Further, the sensor device  200  identifies the code sequence in a case where the code sequence corresponding to the distance measurement pulse signal SGI and the code sequence corresponding to the distance measurement pulse signal SG 0  are different, thereby distinguishing two distance measurement pulse signals SG 0  and SG 1 . 
     In the “state  3 ”, the wireless communication device  100  continues the operation of the continuous transmission mode, and the sensor device  200  operates as the shortest distance estimation mode. In the shortest distance estimation mode, in the measurement state illustrated in  FIG. 37 , the sensor device  200  stops transmission of the distance measurement pulse signal SG 0  from the sensor device  200  itself and continues reception of the distance measurement pulse signal SG 1  from the wireless communication device  100 . The shortest distance estimation section  250  of the sensor device  200  estimates a shortest distance between the wireless communication device  100  and the sensor device  200  in accordance with the above described shortest distance measurement method, and the sensor control section  270  of the sensor device  200  compares the size of the signal power of the received distance measurement pulse signal with a predetermined threshold value. If it is determined that the signal power of the received distance measurement pulse signal exceeds the threshold value and the shortest distance measurement is successful after the determination, the sensor device  200  is transited to the “state  4 ” corresponding to the measurement state illustrated in  FIG. 37 . 
     In the “state  4 ”, the wireless communication device  100  continues the operation of the continuous transmission mode, and the sensor device  200  operates as the distance measurement mode. In the distance measurement mode, the sensor device  200  in the measurement state illustrated in  FIG. 37  continues reception of the distance measurement pulse signal SG 1  from the wireless communication device  100 . The sensor device  200  succeeds in the shortest distance measurement in the “state  3 ” and already understands the transmission timing of the wireless communication device  100 , so that the sensor device  200  detects the time difference X(n−1) between the distance measurement pulse signals SG 1  and SG 2  and calculates a distance between the wireless communication device  100  and the sensor device  200  on a basis of the detected time difference X(n−1). 
     Further, after a certain predetermined time has elapsed from the starting time of the continuous transmission mode in which the “state  1 ” is transited to “state  2 ”, the wireless communication device  100  is transited to the normal mode, that is, the operation mode corresponding to the “state  1 ”. In the similar manner, after a certain predetermined time has elapsed from the starting time of the distance measurement mode in which the “state  3 ” is transited to “state  4 ”, the sensor device  200  is transited to the normal mode, that is, the operation mode corresponding to the “state  1 ”. 
     &lt;Operation of Wireless Communication Device  100 &gt; 
       FIG. 32  is a flowchart illustrating details of an operation of a wireless communication device  100  of the fifth embodiment. 
     If the power of the wireless communication device  100  is turned on, the wireless device control section  170  initializes the operation of the wireless communication device  100  (S 11 ) and selects the normal mode as the operation mode. In the normal mode, the wireless communication device  100  transmits and receives a wireless signal (S 12 ). 
     Further, in a case where a wireless signal is received in the normal mode (S 13 ), the wireless device control section  170  determines whether or not the wireless signal is the distance measurement pulse signal SG 0  transmitted from the sensor device  200  (S 14 ). For example, since the pulse compression detection section  150  determines whether or not the code sequence contained in the received wireless signal is consistent with the predetermined code sequence, the wireless device control section  170  can distinguish between the distance measurement pulse signal SG 0  and the other wireless signals. 
     In a case where the wireless communication device  100  receives the distance measurement pulse signal SG 0  (S 14 , YES), the reception power calculation section  190  calculates the size PX of the signal power of the distance measurement pulse signal SG 0  (S 15 ) and compares the size PX of the signal power with a predetermined threshold value Pth 1  (S 16 ). In addition, the wireless device control section  170  may perform the comparison of step S 16 . 
     If the condition of “Px&gt;Pth 1 ” is satisfied (S 16 , YES), that is, in a case where the wireless communication device  100  is close to the sensor device  200  to some extent, the wireless device control section  170  of the wireless communication device  100  switches the operation mode from the normal mode to the continuous transmission mode (S 17 ). Accordingly, it is transited to the sensing state illustrated in  FIG. 36 . 
     If the operation mode is transited to the continuous transmission mode, the wireless device control section  170  starts the timer  180  that measures the continuous transmission time T 10  (S 18 ). The wireless device control section  170  controls the pulse compression generation section  160  to start transmission of the distance measurement pulse signal SG 1  (S 19 ). 
     Further, if the continuous transmission time T 10  in accordance with the output of the timer  180  exceeds a predetermined time (S 20 , YES), time is over (S 20 ), and the operation mode of the wireless communication device  100  is transited to the normal mode (S 21 ). 
     &lt;Operation ( 1 ) of Sensor Device&gt; 
       FIG. 33  is a flowchart illustrating details of an operation (1) of a sensor device  200  of the fifth embodiment. 
     If the power of the sensor device  200  is turned on, the sensor control section  270  initializes the operation of the sensor device  200  (S 31 ) and selects the normal mode as the operation mode. In the normal mode, the sensor device  200  successively transmits the distance measurement pulse signal SG 0  that the pulse compression generation section  230  generates at a constant period (S 32 ). 
     Further, the sensor device  200  receives a wireless signal transmitted from another station in the normal mode (S 33 ). In a case where the wireless signal from another station is received (S 33 , YES), the sensor control section  270  determines whether or not the wireless signal is the predetermined distance measurement pulse signal SG 1  (S 34 ). For example, the sensor control section  270  determines whether or not the code sequence contained in the received wireless signal is consistent with the predetermined code sequence, and thus the sensor control section  270  can distinguish between the distance measurement pulse signal SG 1  and the other wireless signals. 
     In a case where the sensor device  200  receives the distance measurement pulse signal SG 1  (S 34 , YES), the reception power calculation section  260  calculates the size Py of the signal power of the distance measurement pulse signal SG 1  (S 35 ) and compares the size Py of the signal power of the calculated distance measurement pulse signal SGI with a predetermined threshold value Pth 2  (S 36 ). In addition, the sensor control section  270  may perform the comparison of step S 36 . 
     In a case where the wireless communication device  100  is located in a position close to the sensor device  200  to some extent (for example, the distance is within 50 cm), the size Py of the signal power of the distance measurement pulse signal is increased, so that the condition of “Py&gt;Pth 2 ” is established, and the sensor control section  270  switches the operation mode from the normal mode to the shortest distance estimation mode (S 37 ). In the shortest distance estimation mode, the shortest distance estimation section  250  of the sensor device  200  estimates the shortest distance between the wireless communication device  100  and the sensor device  200  in accordance with the above described shortest distance measurement method. 
     After the transition to the shortest distance estimation mode, the sensor control section  270  compares the size Py of the signal power of the distance measurement pulse signal SGI with a predetermined threshold value Pth 3  (S 38 ). However, the threshold value Pth 2  in step S 36  is smaller than the threshold value Pth 3  in step S 38 . In other words, in step S 38 , the sensor control section  270  determines whether or not the wireless communication device  100  is located in a position closer to the sensor device  200  compared to step S 36  (for example, the distance is within 20 cm). 
     In a case where a condition of “Py&gt;Pth 3 ” is established (S 38 , YES), the wireless communication device  100  is in a state of being close enough to the sensor device  200 , so that the sensor device  200  can obtain the data of P value of the change characteristic curve illustrated in  FIG. 33  for the change in the distance. 
     Accordingly, the shortest distance estimation section  250  regards the extreme value (minimum value) of the P value as the shortest distance and outputs the estimation result (S 39 ). That is, the shortest distance estimation section  250  determines the time difference parameter (Z 0 −Y 0 ) between the transmission timing and the reception timing of the distance measurement pulse signal SG 1  (S 39 ). 
     If the time difference parameter (Z 0 −Y 0 ) between the transmission timing and the reception timing of the distance measurement pulse signal SG 1  is determined, it is possible to measure the distance between the wireless communication device  100  and the sensor device  200 , and thus the sensor control section  270  of the sensor device  200  switches the operation mode from the shortest distance estimation mode to the distance measurement mode (S 40 ). 
     After the transition to the distance measurement mode, the sensor control section  270  starts the timer of the continuous transmission time T 20  (S 41 ). The sensor control section  270  continues the measurement of the distance until the timer of the continuous transmission time T 20  is time-over. That is, the sensor control section  270  calculates the time difference X(j) between the transmission timing and the reception timing of the distance measurement pulse signal SG 1  for each received distance measurement pulse signal (see Expression (9) or Expression (10)) and calculates the distance between the wireless communication device  100  and the sensor device  200  on a basis of the calculated time difference. 
     If the continuous transmission time T 20  exceeds the predetermined time (S 42 , YES), time is over (S 42 ), and the operation mode of the sensor device  200  is transited to the normal mode (S 43 ). 
     &lt;Operation ( 2 ) of Sensor Device  200 &gt; 
       FIG. 34  is a flowchart illustrating an operation ( 2 ) of the sensor device  200 . In  FIG. 34 , since the operation content of each step other than step S 39 B is the same as the content of the  FIG. 9 , the description thereof is omitted. 
     In the operation ( 2 ) illustrated in  FIG. 34 , the wireless communication device  100  is in contact with the sensor device  200 , in order to adjust the respective operation timings of the wireless communication device  100  and the sensor device  200 . 
     The P value changes as the change characteristic curve illustrated in  FIG. 30A . In other words, as the wireless communication device  100  gradually approaches the sensor device  200 , the wireless communication device  100  comes into contact with the sensor device  200 . The wireless communication device  100  keeps the state of being contacted for a predetermined time Tp or more, and then the wireless communication device  100  gradually moves away from the sensor device  200  after the contact continues for a predetermined time Tp or more.  FIG. 30A  is a graph illustrating a change of P value when a state in which the wireless communication device  100  is in contact with the sensor device  200  continues for a predetermined time Tp or more. 
     In  FIG. 30A , in the change characteristic curve of the P value, a state in which the P value hardly changes in the minimum value P 0 , that is, a state appears in which the contact state continues over a certain time. Thus, it is possible to estimate that the wireless communication device  100  is in contact with the sensor device  200 . 
     However, in  FIG. 30B , in a case where the wireless communication device  100  may gradually move away from the sensor device  200  after a time less than a predetermined time Tp has elapsed, it may be estimated that the wireless communication device  100  is separated from the sensor device  200  before the wireless communication device  100  comes into contact with the sensor device  200 . Therefore, P 1  that is not expected originally is detected as the minimum distance.  FIG. 30B  is a graph illustrating a change of P value when the wireless communication device  100  is in contact with the sensor device  200  for less than a predetermined time Tp. 
     In contrast, in step S 39 B of  FIG. 34 , the sensor control section  270  regards the state of minimum value as the state of the shortest distance among P values satisfying the conditions of the contact state to determine the timing. For example, in the change characteristic curve of the detected P value, a case where a state in which the P value remains unchanged with a minimum value continues for a predetermined time Tp or more, but the P value is a predetermined threshold value (for example, 10 cm) or less is defined as a condition of a contact state in advance. 
     The predetermined time Tp corresponds to a time period when the wireless communication device  100  is kept in a contact state with the sensor device  200 . The greater the predetermined time Tp is, the smaller the occurrence of the erroneous detection of the condition of the contact state is. However, since the wireless communication device  100  and the sensor device  200  should be kept in the contact state during a certain time, the detection easiness decreases. 
     The erroneous detection of the shortest distance can be reduced by estimating the state of the shortest distance on a basis of the P value satisfying the condition of the contact state as illustrated in  FIGS. 30A and 30B . 
     Thus, in the distance measurement system  1000  of the present embodiment, the wireless communication device  100  performs normal wireless communication in the normal communication state (normal mode) in which the distance measurement is not necessary and can switch the operation mode in a case where the distance measurement is necessary. 
     Further, the wireless communication device  100  periodically generates a signal modulated using a known code sequence suitable for a correlation detection as the distance measurement pulse signal SG 1  in the pulse compression generation section  160 . Further, the sensor device  200  performs the correlation detection on the received distance measurement pulse signal SG 1  in the correlation signal processing section  240 . 
     Accordingly, the sensor device  200  can detect the reception timing of a distance measurement pulse signal from the wireless communication device  100  with high accuracy using a pulse compression technology. Further, the sensor device  200  determines a code sequence, thereby distinguishing a plurality of distance measurement pulse signals transmitted from a plurality of wireless communication devices. 
     Further, in a case of being switched to the shortest distance estimation mode, the sensor device  200  repeatedly detects the reception timing of the received distance measurement pulse signal in the shortest distance estimation section  250  and calculates the time difference parameter (Z 0 −Y 0 ) of the transmission timing and the reception timing of a distance measurement pulse signal from the wireless communication device  100  in a case where the wireless communication device  100  is close to the sensor device  200 . In addition, the sensor device  200  estimates the time difference parameter based on a minimum value of the P value in response to the change in the time difference parameter. 
     Accordingly, the wireless communication device  100  is close to the sensor device  200 , so that the sensor device  200  can simply calculate the time difference parameter necessary for the distance measurement and simply calculate a distance between the wireless communication device  100  and the sensor device  200 . 
     Further, the sensor device  200  can estimate the time difference parameter based on a state in which the minimum value of the P value in response to the change in the time difference parameter is a constant value over a predetermined certain period of time. 
     Accordingly, since the wireless communication device  100  is in contact with the sensor device  200 , the sensor device  200  can suppress an erroneous determination of the time difference parameter necessary for the distance measurement and can simply calculate the distance between the wireless communication device  100  and the sensor device  200 . 
     Further, after the shortest distance estimation section  250  completes the estimation of the time difference parameter, the sensor control section  270  switches the operation mode of the sensor device  200  from the shortest distance estimation mode to the distance measurement mode and calculates the distance between the wireless communication device  100  and the sensor device  200  on a basis of the reception timing and the time difference parameter of the distance measurement pulse signal SG 1 . 
     Accordingly, after the sensor device  200  obtains the time difference parameter necessary for the distance measurement, the distance measurement between the wireless communication device  100  and the sensor device  200  can be reliably started. 
     In addition, a meaning that the distance between the wireless communication device  100  and the sensor device  200  is close is considered as an operation, for example, in which the user who owns the wireless communication device  100  approaches the sensor device  200 , the user-owned wireless communication device  100  is directly brought into contact with the sensor device  200 , or the user-owned wireless communication device  100  is brought into a certain part of the sensor device  200 . 
     Further, a plurality of sensor devices  200  are disposed and connected to a network, so that a synchronization established by other sensor devices can be shared in the plurality of sensor devices. 
     Further, the distance measurement system, the wireless communication device and the sensor device according to the present disclosure have the following configurations. 
     The present disclosure relates to a distance measurement system including a wireless communication device that transmits a wireless signal and a sensor device that measures a distance with the wireless communication device on a basis of the transmitted wireless signal, 
     in which the wireless communication device includes: 
     a terminal control section that switches the operation mode of the wireless communication device to a terminal normal mode of transmitting and receiving the wireless signal or to a continuous transmission mode of periodically transmitting the distance measurement pulse signal and 
     in which the sensor device includes: 
     a sensor control section that switches the operation mode of the sensor device to a sensor normal mode of transmitting and receiving a wireless signal or to a shortest distance estimation mode of estimating a time difference parameter between transmission timings and reception timings of the wireless signal on a basis of a wireless signal transmitted from the wireless communication device, 
     in which a terminal-side mode control section switches the operation mode of the wireless communication device from the terminal normal mode to the continuous transmission mode in a case where the wireless communication device receives a wireless signal having signal power of a first threshold value or more and 
     in which a sensor-side mode control section switches the operation mode of the sensor device from the sensor normal mode to the shortest distance estimation mode in a case where the sensor device receives a wireless signal having signal power of a second threshold value or more. 
     Further, the present disclosure relates to the above described distance measurement system, 
     in which the wireless communication device further includes: 
     a pulse compression generation section that periodically generates a pulse compression signal using a known code sequence suitable for correlation detection as the distance measurement pulse signal and 
     in which the sensor device further includes: 
     a correlation detection section that detects a correlation of the distance measurement pulse signal transmitted from the wireless communication device. 
     Further, the present disclosure relates to the above scribed distance measurement system, 
     in which the sensor device further includes: 
     a shortest distance estimation section that repeatedly detects the reception timing of the distance measurement pulse signal in the shortest distance estimation mode, in a case where the wireless communication device is close to the sensor device, and estimates the time difference parameter between the transmission timing and the reception timing of the wireless signal. 
     Further, the present disclosure relates to the above described distance measurement system, 
     in which the shortest distance estimation section repeatedly detects the reception timing of the distance measurement pulse signal in the shortest distance estimation mode, in a case where the wireless communication device is in contact with the sensor device, calculates the distance parameter between the wireless communication device and the sensor device on a basis of the reception timing, and in a case where the distance parameter is a predetermined value over a constant period of time, estimates the time difference parameter between the transmission timing and the reception timing of the wireless signal. 
     Further, the present disclosure relates to the above described distance measurement system, 
     in which after the shortest distance estimation section estimates the time difference parameter between the transmission timing and the reception timing of the wireless signal, the sensor control section switches the operation mode of the sensor device from the shortest distance estimation mode to the measurement mode and calculates the distance between the wireless communication device and the sensor device on a basis of the reception timing of the distance measurement pulse signal and the time difference parameter. 
     Further, the present disclosure relates to a wireless communication device which transmits the above described wireless signal, including: 
     a pulse compression generation section that periodically generates a pulse compression signal using a known code sequence suitable for correlation detection and 
     a terminal control section that switches the operation mode of the wireless communication device to a terminal normal mode of transmitting and receiving the wireless signal or a continuous transmission mode of transmitting the pulse compression signal as a distance measurement pulse signal, 
     in which the terminal control section switches the operation mode of the wireless communication device from the terminal normal mode to the continuous transmission mode in a case where the wireless communication device receives a wireless signal having signal power of a first threshold value or more. 
     Further, the present disclosure relates to a sensor device which measures a distance with a wireless communication device on a basis of reception timings when a wireless signal transmitted from the above wireless communication device is received, including: 
     a sensor reception section that receives the wireless signal transmitted from the wireless communication device and 
     a sensor control section that switches the operation mode of the sensor device to a sensor normal mode of transmitting and receiving a wireless signal or to a shortest distance estimation mode of estimating a time difference parameter between transmission timings and reception timings of the wireless signal on a basis of a wireless signal transmitted from the wireless communication device, 
     in which a sensor-side mode control section switches the operation mode of the sensor device from the sensor normal mode to the shortest distance estimation mode in a case where a sensor-side reception section receives a wireless signal having signal power of a second threshold value or more. 
     Although the foregoing has described various embodiments with reference to the drawings, the present disclosure is not limited to these embodiments. It may be conceived that various variations and modifications will be apparent to those skilled in the art within the scope described in the claims and these belong to the technical scope of the present disclosure. 
     In addition, the present application is based on Japanese patent application filed on Feb. 8, 2012 (Japanese patent application No. 2012-025492), Japanese patent application filed on Feb. 27, 2012 (Japanese patent application No. 2012-040451), and Japanese patent application filed on Mar. 29, 2012 (Japanese patent application No. 2012-078307), and the contents thereof are incorporated as reference herein. 
     INDUSTRIAL APPLICABILITY 
     The present disclosure is useful as a wireless communication device that generates a pulse compression signal for measuring the radiation pattern from the antenna by a simple configuration. 
     The present disclosure is useful as a wireless communication device that measures the radiation pattern of a beam having a desired directivity in a beam forming in a short time. 
     The present disclosure is useful as a distance measurement system, a sensor device, and a wireless communication device which simply measure a distance between the wireless communication device and the sensor device, without informing in advance a sensor device of transmission timings of a signal from a wireless communication device. 
     REFERENCE SIGNS LIST 
       10 ,  10 B,  10 C sensor 
       10   a ,  10   b ,  21  antenna 
       11  transmission section 
       12  reception section 
       13  pulse compression wave generating section 
       14 ,  23  DAC 
       15  transmission RF section 
       16  reception RF section 
       17  ADC 
       18  correlator 
       19  signal processing section 
       20 ,  20 BB WiGig wireless device 
       20 A,  20 B,  20 C,  20 D antenna system processing section (branch) 
       21 A,  21 B,  21 C,  21 D transmission antenna 
       22  RF section 
       24  modulation section 
       25  selector section 
       30  mask circuit section 
       31  mask timing generation section 
       40  Golay signal generation section 
       41  selector section 
       100  radiation pattern measurement system 
       120 ,  220  high frequency section 
       130  modulation section 
       140  demodulation section 
       150  pulse compression detection section 
       160  pulse compression generation section 
       170  wireless device control section 
       180 ,  280  timer 
       190 ,  260  reception power calculation section 
       200  sensor device 
       230  pulse compression generation section 
       240  correlation signal processing section 
       250  shortest distance estimation section 
       270  sensor control section 
       1000  wireless communication device 
       1200  reception RF section 
       1300  ADC 
       1500 ,  1500 C search continuation determination section 
       2000  wireless communication device 
       2200  modulation section 
       2300  DAC 
       2400  phase shifter 
       2500  transmission RF section 
       2600  control section 
       2700  code sequence selection section 
       2800  pulse compression signal generation section 
     C 1 , CC 1 , Ck, CN correlator 
     SP 1 , SPC 1 , SPk, SPN signal processing section 
     TJ 1 , TJk, TJN threshold value determination section 
     TX transmission section