Patent Publication Number: US-2009237218-A1

Title: Wireless communication device

Description:
TECHNICAL FIELD 
     Embodiments relate to a wireless communication device. 
     BACKGROUND ART 
     Ubiquitous network technology means technology allowing a natural access to various networks without limitation in time and space. Examples of the ubiquitous network technology comprise RFID technology. 
     Generally, the RFID technology comprises a tag device and a reader device. The tag device is attached on an object such as goods to record detail information of the object. The reader device performs RF communication with the tag device to obtain the information of the object from the tag device. This RFID technology provides an infrastructure on which distribution/circulation management such as distribution, assembly, price change, and selling can be efficiently processed. 
     DISCLOSURE OF INVENTION 
     Technical Problem 
     Embodiments provide a wireless communication device that can analyze a change in a communication environment with a tag device using a reception state of at least one of received baseband I signal and Q signal, and change a channel frequency transmitted to the tag device. 
     Embodiments provide a wireless communication device that can control the frequency and the phase of a transmission channel in the case where the state of a signal received from a tag device is unstable. 
     Embodiments provide a wireless communication device that can minimize crosstalk between channels generated in wireless short distance communication and stably communicate according to a tag recognition distance by changing the frequency of a transmission channel. 
     Embodiments provide a wireless communication device that can improve tag energy supply and a tag recognition rate. 
     Embodiments provide a wireless communication device that can easily recover a signal of a tag device by amplifying a baseband signal received from a tag device to a predetermined level and cutting the signal to process the signal in the form of positive and negative square wave signals. 
     Embodiments provide a wireless communication device that can stably recover a reception signal even when the phase and the energy transfer position of a tag device change. 
     Embodiments provide a wireless communication device that can improve the sensitivity and signal-to-noise ratio (SNR) of a signal modulated using amplitude shift keying (ASK), and minimize influences of a DC offset and a crosstalk signal. 
     Embodiments provide a wireless communication device that can swiftly supply energy to a tag device and improve the recognition rate of the tag device by separating a tag device operation section and a reader device operation section to perform coding and then summing again. 
     Technical Solution 
     An embodiment provides a wireless communication device comprising: a reception signal processor demodulating a received signal; a first signal state detector detecting a reception state of a first signal from the received signal; a second signal state detector detecting a reception state of a second signal from the received signal; a transmission signal processor modulating a transmission signal; and a controller controlling a change of a frequency of a channel transmitted to the transmission signal processor depending on a reception state of at least one of the first signal of the first signal state detector and the second signal of the second signal state detector. 
     An embodiment provides a wireless communication device comprising: a mixer converting a received signal into a baseband first signal and a baseband second signal; a plurality of first signal processors sequentially amplifying the baseband first signal and cutting the signal to a predetermined level to output a positive square wave; a plurality of second signal processors sequentially amplifying the baseband second signal and cutting the signal to a predetermined level to output a negative square wave; a summer summing the positive and negative square wave signals output from the plurality of first signal processors and second signal processors to output corresponding digital signals; and a controller recognizing the digital signals of the summer as reception information. 
     An embodiment provides a wireless communication device comprising: a first mixer mixing a signal corresponding to an operation section of a tag device with a first local frequency signal to output an energy signal; a second mixer mixing a signal corresponding to an operation section of a reader device with a second local frequency signal to output a data signal; and a synthesizer synthesizing the energy signal of the first mixer and the data signal of the second mixer to output a reader device signal. 
     ADVANTAGEOUS EFFECTS 
     Embodiments can reduce crosstalk between channels. 
     Embodiments can improve a signal recognition distance with a tag device and a tag signal recognition rate. 
     Embodiments can improve a degree of freedom in arrangement of a reader device. 
     Embodiments can prevent a non-linear crosstalk signal by a peak-to-average power ratio (PAR). 
     Embodiments can prevent an increase in an SNR. 
     Embodiments can prevent reception sensitivity and an SNR from reducing in the case where a tag device uses an ASK modulation method, and recover a digital signal to a sufficient voltage level. 
     Embodiments can improve an amplification gain without distortion of a signal received from a tag device to perform stable RFID communication. 
     Embodiments can minimize an influence of a DC offset through sequential amplification and cutting of a received tag signal. 
     Embodiments can minimize generation of a fading phenomenon. 
     Embodiments can exclude an influence of a crosstalk signal caused by a change in the phase of a received signal. 
     Embodiments can swiftly supply energy to a tag device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a construction view of a wireless communication system according to a first embodiment. 
         FIG. 2  is a construction view of the reader device of  FIG. 1 . 
         FIG. 3  is a construction view of the reception signal power controller of  FIG. 2 . 
         FIG. 4  is a construction view of a reception signal processor of  FIG. 2 . 
         FIG. 5  is a construction view of the I signal state detector and the Q signal state detector of  FIG. 2 . 
         FIG. 6  is a construction view of the first controller of  FIG. 2 . 
         FIG. 7  is a construction view of the transmission signal processor of  FIG. 2 . 
         FIG. 8  is a graph illustrating the states of I and Q signals according to the first embodiment. 
         FIG. 9  is a view illustrating a signal state in which the states of the I and Q signals of  FIG. 8  have been compensated for. 
         FIG. 10  is a view of a wireless communication device in a wireless communication system according to a second embodiment. 
         FIG. 11  is a construction view of the I signal processor of  FIG. 10 . 
         FIG. 12  is a view of a signal waveform processed by the detector of  FIG. 11 . 
         FIG. 13  is a view of a signal waveform processed by the limiter of  FIG. 11 . 
         FIG. 14  is a view of a signal waveform output by the first summer of  FIG. 11 . 
         FIG. 15  is a view of a wireless communication device according to a third embodiment. 
         FIG. 16  is a view illustrating a timing standard of an electronic product code standard applied to the reader device of  FIG. 15 . 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Hereinafter, embodiments will be described with reference to the accompanying drawings. 
     First Embodiment 
       FIG. 1  is a construction view of a wireless communication system according to a first embodiment. 
     Referring to  FIG. 1 , the wireless communication system  500  is a system communicating with an individual object using a frequency. For example, the wireless communication system can comprise one of an RFID type, a near field communication (NFC) type, a Bluetooth type, a Zigbee type, an ultra-wide band (UWB) type, a wireless local area network (LAN), a Wibree, a Z-wave, and a dedicated short range communication (DSRC) type. The RFID type is described for example for convenience in description. 
     The wireless communication system  500  is designed for communication between wireless communication devices, and comprises a tag (or transponder) device  10  and a reader (or interrogator) device  100 , for example. 
     The reader device  100  communicates with the tag device  10  using wireless short distance communication to collect information of at least one tag device  10 . For example, the reader device  100  can collect the information of the tag device  10  by transmitting an information request signal to the tag device  10 , and receiving object detailed information from the tag device  10 . The reader device  100  transmits/receives the collected information to/from a middle ware or other nodes. 
     The tag device  10  has various shapes and sizes, and is classified into an active tag and a passive tag depending on whether power is supplied, classified into a low frequency system and a high frequency system depending on a frequency in use. The tag device  10  is attached to persons, automobiles, goods, livestock, and buildings, and contains detailed information of a corresponding object. Also, the tag device  10  can operate in cooperation with a device such as an electronic card to perform user authentication and electronic payment. The tag device  10  can be directly attached or function in cooperation with another device to provide various services. 
     The RF frequency tag of the RFID system  300  can be classified into a low frequency (LF) tag of 124-134 kHz used for access control and animal management, a high frequency (HF) tag of 13.56 MHz used for an integrated circuit (IC) card and an identification card, an ultra HF (UHF) tag of 400-915 MHz used for identification of containers in distribution and circulation, and a microwave tag of 2.45 GHz. Also, a 5.8 GHz tag can be used for telematics. These communication bands are provided for an exemplary purpose, and can change within the technical spirit and the scope of the embodiments. 
     The reader device  100  should efficiently receive the information of the tag device  10  even when a communication environment changes as the tag device  10  moves. 
       FIG. 2  is a view of the reader device of  FIG. 1 . 
     Referring to  FIG. 2 , the reader device  100  comprises a first reception circuit  100 A, a first transmission circuit  100 B, a first controller  160 , and a frequency control circuit  170 . Here, the reader device  100  is a terminology for explaining an embodiment. The function and the elements of the reader device  100  can be applied to the tag device, and is not limited to the reader device. 
     The first reception circuit  100 A demodulates a signal received from the tag device, converts the signal into a digital signal. The first transmission circuit  100 B transmits a tag information request signal, for example, as a reader signal. 
     The frequency control circuit  170  outputs a local frequency to demodulate a signal received to the first reception circuit  100 A, and outputs a local frequency to modulate a signal transmitted to the first transmission circuit  100 B. Here, the local frequencies supplied to the reception circuit  100 A and the transmission circuit  100 B can be the same or different from each other. 
     The first controller  160  transmits the tag information request signal, and collects and stores tag information from a received signal. Also, the first controller  160  can communicate with another reader device or a host computer, detects a change of a communication environment using a signal state received from the tag device, and adaptively controls the frequency of a transmission channel. 
     Specifically, the first reception circuit  100 A comprises a reception antenna  101 , a reception signal power controller  110 , a first switch unit  118 , a reception signal processor  120 , an I signal state detector  130 , a Q signal state detector  140 , and a second switch unit  150 . 
     The reception signal power controller  110  controls the power of a signal received from the reception antenna  101  in response to a control signal from the first controller  160 . The output of the reception signal power controller  110  is output through the first switch unit  118 . That is, the reception signal power controller  110  controls the power gain of a signal received to the antenna  101 , thereby prevents a received signal from being saturated due to influences of a crosstalk signal, an antenna gain, and an amplification gain of an internal circuit. 
     The first switch unit  118  divides a received signal and outputs the divided signals to the reception signal processor  120 , the I signal state detector  130 , and the Q signal state detector  140 . The first switch unit  118  can be a divider, a circulator, or a 3-way divider circuit. 
     The reception signal processor  120  demodulates a received signal, converts the signal into a digital signal, and delivers the digital signal to the first controller  160 . 
     The I signal state detector  130  detects the reception state of a signal having an I phase (In-phase) (referred to as an I signal hereinafter) from received signals to output the same to the first controller  160 . The Q signal state detector  140  detects the reception state of a signal having a Q phase (Quadrature-phase) (referred to as a Q signal hereinafter) from received signals to output the same to the first controller  160 . Here, the I signal state detector  130  and the Q signal state detector  140  control a signal level in response to a control signal from the first controller  160 . 
     The second switch unit  150  selectively delivers the output signals of the I signal state detector  130  and the Q signal state detector  140  to the first controller  160 . The second switch unit  150  can be a divider, a circulator, or a 2-way divider circuit. 
     The first controller  160  generates analysis information using the reception state of at least one of the I signal state detector  130  and the Q signal state detector  140 . That is, the first controller  160  detects a change in a communication environment with the tag device using an I signal state and/or a Q signal state, and changes a channel frequency when the communication environment changes. Here, the frequency of another channel can be changed by reassigning the frequency of a first channel, for example. 
     The frequency control circuit  170  can control a local frequency in response to a control signal from the first controller  160 . The frequency control circuit  170  comprises a phase synchronizer  172 , a third switch unit  174 , and a first phase shifter  176 . The internal elements of the frequency control circuit  170  are grouped for convenience in description, and not limited thereto but can change. 
     The phase synchronizer  172  can comprise a phase-locked-loop (PLL) unit (not shown) and a voltage oscillator (not shown). The PPL unit generates a reference signal in response to a control signal from the first controller  160 , and the voltage oscillator generates a local frequency using the reference signal. 
     The third switch unit  174  can output the local frequency in at least two paths. The third switch unit  174  receives a local frequency from the phase synchronizer  172  to selectively divide the same. For example, the local frequency is delivered to the I signal state detector  130  and the Q signal state detector  140  through the reception signal processor  120 , the transmission signal processor  180 , and the first phase shifter  176 . 
     The first phase shifter  176  outputs local frequencies as an I phase signal and a Q phase signal to the I signal state detector  130  and the Q signal state detector  140 . 
     The first transmission circuit  100 B comprises the transmission signal processor  180  and a transmission antenna  102 . The transmission signal processor  180  modulates a transmission signal output from the first controller  160  to output the same to the transmission antenna  102 . 
     Here, the reception antenna  101  and the transmission antenna  102  can be formed independently. Also, one of the antennas can be provided in a plurality of elements, and there is no limit in the characteristic or the number of the antenna. 
       FIG. 3  is a construction view of the reception signal power controller of  FIG. 2 . 
     Referring to  FIG. 3 , the reception signal power controller  110  comprise a first amplifier  112 , a first attenuator  114 , and a first filter  116 . When the power of a received signal is less than reference power, the first amplifier  112  amplifies the power of the received signal. When the power of a received signal is greater than a predetermined level, the first attenuator  114  can attenuate the received signal, or amplify the power of a low-controlled signal to output the same. 
     The first controller  160  can control the gain of the first amplifier  112  and the first attenuator  114  using the reception state of a received I signal and the reception state of a received Q signal. 
       FIG. 4  is a view of a reception signal processor of  FIG. 2 . 
     Referring to  FIG. 4 , the reception signal processor  120  comprises: a signal separator  121 , a second phase shifter  122 , a first mixer  123 , a second filter  124 , a second mixer  125 , a third filter  126 , and an analog-to-digital converter (ADC)  127 . 
     The signal separator  121  can separate a signal divided by the first switch unit  118  into an RF I signal and an RF Q signal to output the same, or separate the signal into two RF signals having the same power. 
     The first mixer  123  mixes an RF I signal from the signal separator  121  with a first local frequency shifted by the second phase shifter  122  to convert the signal into a baseband I signal. 
     The second mixer  125  mixes an RF Q signal from the signal separator  121  with a second local frequency shifted by the second phase shifter  122  to convert the signal into a baseband Q signal. Here, the second phase shifter  122  receives a local frequency from the third switch unit  174  to output a first local frequency having a phase of 0° and a second local frequency having a phase of 90°. 
     A signal output to the first mixer  123  can be output as I+ and I− signals in a baseband. A signal output to the second mixer  125  can be output as Q+ and Q− signals in the baseband. 
     The second filter  124  removes a noise comprised in a baseband I signal output from the first mixer  123 , and the third filter  126  removes a noise comprised in a baseband Q signal output from the second mixer  125 . 
     The ADC  127  converts the baseband I signal and the baseband Q signal into a digital I signal and a digital Q signal to output them to the first controller  160 . The first controller  170  can analyze a tag signal using at least one of the digital I signal and the digital Q signal. Here, at least one ADC  127  is disposed to selectively convert a baseband I signal and a baseband Q signal into a digital signal to output the same. Also, the ADC  127  can be comprised in the first controller  160  and is not limited thereto. 
       FIG. 5  is a view of the I signal state detector and the Q signal state detector of  FIG. 2 . 
     Referring to  FIG. 5 , the first I signal state detector  130  comprises a first isolator  131 , a first mixer  132 , a fourth filter  133 , a second amplifier  134 , a second attenuator  135 , a fifth filter  136 , and a second isolator  137 . The Q signal state detector  140  comprises a third isolator  141 , a fifth mixer  142 , a sixth filter  143 , a third amplifier  144 , a third attenuator  145 , a seventh filter  146 , and a fourth isolator  147 . 
     The first isolator  131  of the I signal state detector  130  and the third isolator  141  of the Q signal state detector  140  block a reflected wave signal introduced through the first switch unit  118 . 
     The third mixer  132  mixes a received signal output from the first isolator  131  with a third local frequency output from the first phase shifter  176  to output a baseband I signal. 
     The fourth mixer  142  mixes a received signal output from the third isolator  141  with a fourth local frequency output from the first phase shifter  176  to output a baseband Q signal. 
     Here, the first phase shifter  176  receives a local frequency to output a third local frequency having a phase of 0° and a fourth local frequency having a phase of 90°. That is, the first phase shifter  176  can delay the phase of one of the local frequencies and output the same. 
     The fourth filter  133  removes a noise introduced during a mixing operation of the third mixer  132  from a baseband I signal. The second amplifier  134  amplifies the baseband I signal to a predetermined level, and the second attenuator  135  attenuates the baseband I signal to a predetermined level. 
     The fifth filter  136  removes a noise mixed in a baseband I signal. That is, the fifth filter  136  removes a noise comprised in a baseband I signal during an amplification and/or attenuation operation. 
     The second isolator  137  delivers a baseband I signal that has passed through the fifth filter  136  to the second switch unit  150  and prevents a reflected wave from being introduced. Here, the first controller  160  controls the power of a baseband I signal amplified and/or attenuated by the first amplifier  134  and the second attenuator  135 . 
     Meanwhile, the sixth filter  143  removes the noise of a baseband Q signal output from the fourth mixer  142 . The baseband Q signal is amplified to a predetermined level by third amplifier  144  or attenuated to a predetermined level by the third attenuator  145 . 
     Also, the seventh filter  146  removes a noise comprised in a baseband Q signal during an amplification and/or attenuation operation. The fourth isolator  147  delivers the baseband Q signal to the first controller  160  through the second switch unit  150 , and prevents a reflected wave from being introduced. Here, the first controller  160  controls the power of a baseband Q signal amplified and/or attenuated by the third amplifier  144  and the third attenuator  145 . 
     Since the I signal state detector  130  and the Q signal state detector  140  can be described using the same elements with difference in a phase of a signal, detailed descriptions of the elements of the Q signal state detector  140  are omitted. 
     The I signal state detector  130  and the Q signal state detector  140  can control the gains of a baseband I signal and a baseband Q signal under control of the first controller  160 . 
     A baseband I signal and a baseband Q signal of the I signal state detector  130  and the Q signal state detector  140  are delivered to the second switch unit  150 . The second switch unit  150  selectively switches the baseband I signal and the baseband Q signal to deliver to the first controller  160 . 
     The first controller  160  can judge whether a communication environment changes using the reception states of the input I signal and Q signal. That is, the controller  160  judges whether to reassign a channel frequency according to a difference in the phase or the power level of a current channel using the states of the I signal and the Q signal to perform control. Also, when the phase or the power level of the channel is unstable, the first controller  160  reassigns a channel frequency. At this point, the channel is reassigned by shifting the frequency of a first channel or a start channel by a predetermined frequency. 
       FIG. 6  is a construction view of the first controller of  FIG. 2 . 
     Referring to  FIG. 6 , the first controller  160  comprises a channel multiplexing module  161 , a phase-locked loop control module  162 , a phase control module  163 , a reception state analysis module  164 , and a reception sensitivity control module  165 . 
     The first controller  160  detects a communication environment state with the tag device, for example, a recognition distance to the tag device, a phase change, a difference in the gains of I/Q signals, a difference in the power of I/Q signals according to the reception state of the I signal and/or the Q signal, and controls a frequency assigned to each channel using detected information. 
     The reception state analysis module  164  analyzes the reception state of the I signal and/or the Q signal input through the second switch unit  150  to generate analysis information by a communication environment change. Here, the analysis information comprises at least one of the voltage level, power, phase of the received signal, a recognition distance to the tag device, and a crosstalk between channel signals. 
     For example, in the case where a recognition distance to the tag device changes, first, a change is generated to a phase at a point at which a received signal arrives at the antenna, and second, in the case where there is a difference in the gain between an I signal a Q signal according to a frequency, a power difference between channels can be generated during an amplification operation. In this case, at least one of the I signal and the Q signal cannot be recovered. Also, the change in the recognition distance to the tag device is generated by a difference a phase difference and a phase difference and a difference in a synchronization time and remarkably reduces a signal recovery rate. 
     Also, the reception state analysis module  164  has a standard table according to the signal reception state, and generates the analysis information with reference to the standard table. At this point, the reception state analysis module  164  converts a signal format to analyze a signal, and processes a filtering operation to extract necessary information. 
     When the I signal state and/or the Q signal state analyzed by the reception state analysis module  164  is unstable, the reception state analysis module  164  delivers control information to the reception sensitivity control module  165 , the phase control module  163 , and the channel multiplexing module  161 . 
     The channel multiplexing module  161  codes N channels necessary for a communication frequency band. Here, the channel multiplexing module  161  changes a first channel frequency or a specific channel frequency to newly assign all channels using the control information of the reception state analysis module  164 . 
     Here, the frequency of each channel can be changed within an RFID frequency band. In the case where the RFID band is 900 MHz, the frequency of a multiplexed channel can be changed within the range of about 910-914 MHz. For example, in a channel before change, the frequency of the first channel is 910.8 MHz, and a channel interval is 200 KHz, so that sixteen channels can be assigned. The channel interval is assigned according to domestic/international standards. Also, the frequency of a changed first channel is 910.9 MHz in case of being moved by 100 KHz, for example. The frequency of a second channel can be 911.1 MHz. In this manner, sixteen channels can be reassigned. Here, the frequency of the first channel can be changed at random or by a predetermined interval. 
     Also, when the frequency of the first channel or a specific channel is changed by a random frequency within the RFID band, a set of changed channels can be changed in tens of sets to hundreds of sets. The multiplexed channel can have a transmission speed of 40 Kbps to 640 Kbps. Also, as the number of channels increases, reduction in a recognition rate is solved and a difference in a gain by a wavelength can be remarkably reduced. 
     When a channel is multiplexed by the channel multiplexing module  161 , the PLL control module  162  delivers a control signal commanding a change of a local frequency to the phase synchronizer  172 . The phase synchronizer  172  generates a local frequency corresponding to a new channel to output the same. Here, the changed local frequency is delivered to respective parts, for example, the I signal state detector  130 , the Q signal state detector  140 , the reception signal processor  120 , and the transmission signal processor  180  illustrated in  FIG. 1 . 
     The phase control module  163  generates phase control information for compensating for the states of an I signal and a Q signal using the control information of the reception state analysis module  164 , and outputs the generated phase control information to a digital-to-analog converter (DAC)  181  of the transmission signal processor  180 . Here, the DAC  181  controls the voltage level of a transmission signal to control the phase of the transmission signal. That is, the DAC  181  controls the phase of the transmission signal to synchronize the phases of an I signal and a Q signal. 
     The reception sensitivity control module  165  compares the power of the I signal and/or the Q signal with a reference level using the control information of the reception state analysis module  164 , and controls the amplification degree and/or the attenuation degree of the I signal and/or the Q signal. That is, the reception sensitivity control module  165  delivers a control signal to the I signal state detector  130  and the Q signal detector  140  to control the second amplifier  134  (of  FIG. 5 ) and the second attenuator  135  (of  FIG. 5 ) of the I signal state detector  130 , and the third amplifier  144  (of  FIG. 5 ) and the third attenuator  145  (of  FIG. 5 ) of the Q signal state detector  140 . 
     The first controller  160  reassigns a channel frequency depending on the state of a received signal to generate the state information of a new received signal through the above process when the reader signal is transmitted using a phase synchronized channel and a signal is received from the tag device. At this point, the first controller  160  generates information analyzing and interpreting the state of a new signal. 
     Also, since the first controller  160  measures and analyzes an RFID signal precisely for each channel, the first controller  160  can selectively store a channel having a high signal recovery rate from multiplexed channels, use the information of the stored channel, and swiftly supply energy to the tag device. 
       FIG. 7  is a construction view of the transmission signal processor of  FIG. 2 . 
     Referring to  FIG. 7 , the transmission signal processor  180  comprises the DAC  181 , an eighth filter  182 , a fifth mixer  183 , a third phase shifter  184 , a ninth filter  185 , a sixth mixer  186 , a signal synthesizer  187 , a tenth filter  188 , and a fourth amplifier  189 . 
     The DAC  181  converts a digital signal delivered from the first controller  160  into a baseband signal, which is an analog signal. The eighth filter  182  and the ninth filter  185  filter a signals of channel bandwidth from the baseband signals. The fifth mixer  183  converts the baseband signals into RF I signals using a fifth local frequency output from the third phase shifter  184 . The sixth mixer  186  converts the baseband signals into RF Q signals using the sixth local frequency shifted by the third phase shifter  184 . 
     Here, the first controller  160  controls the phase of a digital signal delivered to the DAC  181  using the phase control information to output the same. At this point, the phases of an I signal and a Q signal can be synchronized and output. The DAC  181  controls a voltage level using the phase control information to convert a transmission signal into a baseband signal. Therefore, the phases of the I signal and the Q signal of the baseband signal can be synchronized, and a voltage between the two signals, and a gain is not saturated to one side but uniformly processed. 
     The eighth filter  182  and the ninth filter  185  pass baseband signals delivered from the DAC  181  according to channel bandwidths, respectively. The signals that have passed through the filters  182  and  185  are delivered to the fifth mixer  183  and the sixth mixer  186 , respectively. The third phase shifter  184  outputs a fifth local frequency having a phase of 0° delivered from the third switch unit  174  to the fifth mixer  183 , and outputs a sixth local frequency having a phase of 90° to the sixth mixer  186 . 
     The fifth mixer  183  mixes the fifth local frequency with a baseband signal to generate an RF I signal. The sixth mixer  186  mixes the sixth local frequency with a baseband signal to generate an RF Q signal. 
     At this point, the modulation formats of the RF I signal and the RF Q signal can be a pulse-interval encoding (PIE) format according to an UHF RFID protocol such as ISO 18000-A, ISO 18000-B, Electronic Product Code (EPC) Generation-0, EPC Generation-1, and EPC Generation-2. As the modulation standards are applied, all of Double SideBand-Amplitude Shift Keying (DSB-ASK), Single SideBand-Amplitude Shift Keying (SSB-ASK), and Phase Reversal-Amplitude Shift Keying (PR-ASK) can be used. 
     The signal synthesizer  187  synthesizes an RF I signal and the RF Q signal into a single RF signal, and the tenth filter  188  removes a noise component generated during the synthesis operation. 
     An RF signal filtered by the tenth filter  188  is amplified to a power level that allows transmission by the fourth amplifier  189 , and transmitted through the transmission antenna  102 . Here, the fourth amplifier  189  can be realized using a power amplifier. 
     At this point, since the reader device transmits signals through a multiplexed channel using a changed frequency, crosstalk between channels with another device can be excluded, and a recognition distance to the tag device, a reception sensitivity, and a recognition rate can be improved. Also, a degree of freedom in disposing the reader device can be secured. Also, since the frequency interval of the multiplexed channel can be maintained constant, a non-linear crosstalk signal due to PAR, reduction in reception sensitivity, and increase in a signal-to-noise ratio (SNR) can be prevented. 
       FIG. 8  is a graph illustrating the states of I and Q signals according to the first embodiment, and  FIG. 9  is a view illustrating a signal state in which the states of the I and Q signals of  FIG. 8  have been compensated for. 
     Referring to  FIG. 8 , since the states of an I signal A 1  and a Q signal A 2  are synchronized with a phase difference of 90 degrees, the voltage levels G 1  and G 2  of the two signals A 1  and A 2  are balanced during a data section D 1 . Therefore, the states of the I signal and the Q signal in the data section D 1  are corrected to states that can be accurately recovered. 
       FIG. 9  illustrates states in which an I signal and a Q signal have been compensated for. A horizontal axis represents a gain level (V) in the horizontal direction around zero, and a vertical axis represents a gain level in the vertical direction around zero. The states of I signals and Q signals having phases of 0°, 270°, 180°, and 90° are displayed on a quadrant  1 , a quadrant  2 , a quadrant  3 , and a quadrant  4 , respectively. At this point, the states of I signals and Q signals displayed with different symbols have the same interval and are concentrated on four regions for each channel. A signal for each channel has the same recognition distance, a synchronized phase, and a time standard. 
     The above-described first embodiment can reassign a channel frequency to communicate with the tag device through a stable channel when the state of a signal of the tag device is unstable. Also, the first embodiment can exclude crosstalk between channels and improve a distance limitation to the tag device, reception sensitivity, and a recognition rate. 
     Second Embodiment 
       FIGS. 10 to 13  illustrate a second embodiment. 
     Referring to  FIG. 10 , a wireless communication receiver  200  comprises a receiver in a wireless communication system and can be applied to a wireless short distance communication band, for example, a reader device, a tag device, and a Zigbee node. 
     The receiver  200  comprises a second reception circuit  200 A and a second controller  260 . The second reception circuit  200 A can stably recover a received signal regardless of an environment where the phase and the energy delivery position of a signal change. 
     For this purpose, the second reception circuit  200 A comprises a reception antenna  201 , a first low noise amplifier (LNA)  211 , a first balun circuit  213 , a seventh mixer  215 , a phase synchronizer  217 , an eighth mixer  219 , an eleventh filter  221 , a twelfth filter  223 , an I signal processor  230 , a Q signal processor  240 , a first summer  251 , a second summer  253 , a thirteen filter  255 , and a fourteenth filter  257 . 
     The LNA  211  amplifies a desired signal factor and minimizes the noise of the signal received from the reception antenna  201 . The LNA  211  excludes a noise component and amplifies signals in a desired band according to an adjacent channel power ratio (ACPR) standard regulation, for example. Here, the first balun circuit  213  separates an RF signal delivered from the first LNA  211  into an I signal (ex. E sin ωt) and a Q signal (E cos ωt). For example, the first balun circuit  213  separates a signal RF signal into a signal having a phase of 0° and a signal having a phase of 90°. 
     In the first balun circuit  213 , balun is an abbreviation of balance-unbalance. The balun circuit  213  converts a balanced signal into an unbalance signal and vice versa. 
     The first balun circuit  213  outputs an RF I signal to the seventh mixer  215  and outputs an RF Q signal to the eighth mixer  219 . The seventh mixer  215  converts the RF I signal into a baseband I signal using a first local frequency. The eighth mixer  219  converts the RF Q signal into a baseband Q signal using a second local frequency. Here, the ACPR defines linearity of a power amplification operation. 
     The first local frequency and the second local frequency can have the same phase or have a different phase by 90°. 
     The phase synchronizer  217  comprises a VCO and PLL, and supplies the first and second local frequencies required for synthesis of the baseband I signal and the baseband Q signal to the seventh mixer  215  and the eighth mixer  219 . 
     The eleventh filter  221  removes a noise signal generated during the synthesis operation of the baseband I signal and the first local frequency, and the twelfth filter  223  removes a noise signal generated during the synthesis operation of the baseband Q signal and the second local frequency. 
     The I signal processor  230  processes the baseband I signal output from the eleventh filter  221  to output a positive square wave. The Q signal processor  240  processes the baseband Q signal output from the twelfth filter  223  to output a negative square wave. 
     The I signal processor  230  comprises a plurality of I signal processors  231 - 23   n . The plurality of I signal processors  231 - 23   n  are sequentially connected. Each of the I signal processors  231 - 23   n  amplifies a signal at a predetermined gain, cuts the amplified signal to a predetermined voltage, and removes the negative component of the cut signal to output a signal of a positive component. 
     The Q signal processor  240  comprises a plurality of Q signal processors  241 - 24   n . The plurality of Q signal processors  241 - 24   n  are sequentially connected. Each of the Q signal processors  241 - 24   n  amplifies a signal at a predetermined gain, cuts the amplified signal to a predetermined voltage, and removes the positive component of the cut signal to output a signal of a negative component. 
     The first summer  251  sums output signals from the plurality of I signal processors  231 - 23   n  to output the same, and the second summer  253  sums output signals from the plurality of Q signals processor  241 - 24   n  to output the same. 
     The thirteenth filter  255  removes a noise mixed in the I signal output from the first summer  251 , and the fourteenth filter  257  removes a noise mixed in the Q signal output from the second summer  253 . That is, the thirteenth filter  255  and the fourteenth filter  257  remove a noise component mixed during the signal summing operation. 
     Here, the I signal processor  230  ( 231 - 23   n ) and the first summer  251  serve as an analog-to-digital converter recovering an I signal into a digital signal. The Q signal processor  240  ( 241 - 24   n ) and the second summer  253  serve as an analog-to-digital converter recovering a baseband Q signal into a digital signal. The number of the I signal processors  231 - 23   n  and the Q signal processor  241 - 24   n  can be 5 to 10. That is, n=5-10. 
     The second controller  260  receives a digital I signal and a digital Q signal from the first summer  251  and the second summer  253 , and synchronizes the two digital signals to analyze the signals. 
     Also, the second controller  260  receives a digital I signal of a square wave and a digital Q signal of a square wave to analyze the information of the tag device. The second controller  260  has a communication protocol to control RFID communication, analyzes a code of the analyzed received signal, and generates a transmission signal as a result of the analysis result. 
     Also, since the second controller  260  receives a digital I signal and a digital Q signal processed in the form of a square wave, it can accurately recover a signal of the tag device regardless of a phase change. Also, the second controller  260  can minimize the characteristic change of a DC offset that can be generated depending on the DC level of the digital I/Q signal. 
       FIG. 11  is a view illustrating a I signal processor according to the second embodiment. Here, since the I signal processor  230  and the Q signal processor  240  are different in a signal processing object and are the same in a basic construction and operation and process a signal in the same sequence, description of the Q signal processor  240  is omitted. 
     Referring to  FIG. 11 , each of the plurality of I signal processors  231 - 23   n  comprises a voltage gain amplifier (VGA)  230 A, a limiter  230 B, and a detector  230 C. 
     The VGA  230 A amplifies a baseband I signal to a predetermined gain. The input terminal of the limiter  230 B is connected to the output terminal of the VGA  230 A, and cuts the signal amplified by the VGA  230 A using a predetermined DC level. Here, the VGA  230 A can amplify a signal using an amplification gain of about 10 dB, and the limiter  230 B can set the cut DC level to a voltage of about a positive 1 V, or set levels increased by 1 V (ex. 1 V, 2V, . . . , nV) as cutting levels, but is not limited thereto. 
     The limiter  230 B can be roughly realized in three parts. That is, the limiter  230 B comprises a circuit for maintaining the power of an analog signal having a DC component in a stable range such that it is not influenced by outside interference, a compensation circuit for controlling an analog swing voltage up/down, and a limiting circuit for determining a signal range that is not to be cut, and cutting the rest of a signal. 
     The detector  230 C is connected to the output terminal of the limiter  230 B in the form of coupling, and detects an output signal of the limiter  230 B to output the same to the first summer  251 . At this point, the detector  230 C outputs a positive component, and removes a signal of a negative component. The signal of the negative component means a DC level of a (−) component. 
     An output signal of the limiter  230 B is input to the detector  230 C and the VGA of the next I signal processor. An output signal of the detector  230 C is input to the first summer  251 . The operation of amplifying and cutting a signal is repeated in this sequence up to the n-th I signal processor  23   n.    
     The n-th I signal processor  23   n  receives an output signal of the (n−1)th limiter to amplify the signal using a predetermined gain. The amplified signal is cut by the limiter  230 B, and output to the detector  230 C. The detector  230 C outputs a positive component to the first summer  251 . Therefore, the first summer  251  receives output signals of the detector  230 C of the n I signal processors  231 - 23   n  to sum the signals and output the summed signal. 
     At this point, since the summed signal is obtained by processing baseband I signals, the signal is output in the form of a positive square wave. 
     The Q signal processor and the second summer operate in the same sequence as in the I signal processor  230  and the first summer  251 . Since the summed signal is obtained by processing baseband Q signals, the signal is output in the form of a negative square wave. 
       FIG. 12  is a view of a signal waveform processed by the detector of  FIG. 11 , and  FIG. 13  is a view of a signal waveform processed by the limiter of  FIG. 11 . 
     Referring to  FIGS. 11 and 12 ,  FIGS. 12A ,  12 B, and  12 C illustrate waveforms of an I signal amplified by the VGAs  230 A of three signal processors and cut by the limiters  230 B, the waveforms being detected by respective detectors  230 C. That is, here, the VGA  230 A amplifies a signal using a gain of 10 dB, and the limiter  230 B cuts the amplified signal at a voltage increased by positive DC 1 V, and the above operations are repeated, so that a baseband I signal detected by the detector  230 C approaches close to a digital signal waveform, i.e., a positive square wave. 
     Referring to  FIGS. 11 and 13 ,  FIGS. 13A to 13D  illustrate the output waveforms of the limiters  230 B of four I signal processors. A baseband I signal is amplified by the VGA  230 A of each I signal processor, and the upper/lower portions of the amplified signal are cut by each limiter  230 B and then output. 
     Referring to  FIGS. 11 to 13 , the first summer  251  receives detection signals from the plurality of detectors  230 C, and sums the received detection signals to recover a digital I signal suitable for an RFID signal standard. Also, A digital Q signal can be recovered using the above-described method of generating the digital I signal. 
       FIG. 14  is a view of a signal waveform output by the first summer of  FIG. 11 . 
     Referring to  FIGS. 11 and 14 , an output waveform of the first summer of  FIG. 14  is obtained by summing baseband I signals processed by the respective signal processors. For accurate analysis, the second controller performs position correction on the sections of the digital I signals output from the first summer to analyze the signals. That is, the second controller analyzes a section Tb as a section  1  of the digital I signal using a point past a section Ta as a reference from a point at which the rising section of the digital I signal ends. Accordingly, the second controller can always analyze a voltage (nV, n is the number of the signal processors) obtained by summing cut signals as 1. 
     Also, the second controller can accurately recover a digital Q signal through position correction of a digital Q signal in the same method as in the digital I signal. Since the digital I signal and the digital Q signal contain the same reader information and tag information, the second controller synchronizes the two signals to perform analysis. 
     This receiver can minimize reduction in reception sensitivity and an SNR in the case where a counterpart device uses an ASK modulation method, and recover a digital signal to a sufficient voltage level. Also, since the receiver can increase an amplification gain without signal distortion, a recognition rate is improved and RFID communication can be stably performed. Also, the receiver can minimize an influence of a DC offset through sequential amplification and cutting process, and minimize generation of fading phenomenon by processing two phase signals, respectively, and summing the same. Also, the receiver can exclude an influence of a crosstalk signal by a phase change. 
     Third Embodiment 
       FIGS. 15 and 16  illustrate the third embodiment. 
       FIG. 15  illustrates a transceiver of a wireless communication system according to the third embodiment. 
     Referring to  FIG. 15 , the reader device  300  represents a transceiver of an RFID system, for example, and comprises a third reception circuit  300 A, a third phase synchronizer  323 , a third controller  360 , and a third transmission circuit  370 . 
     The third reception circuit  300 A comprises a reception antenna  301 , a second low noise amplifier (LNA)  311 , a second balun circuit  315 , a ninth mixer  317 , a first oscillator  319 , a tenth mixer  321 , a first low pass filter (LPF)  325 , a second LPF  327 , and an ADC  329 . 
     The second LNA  311  amplifies a desired signal factor and minimizes the noise of the signal received through the reception antenna  301 , a reception filter  313  filters signals in a RFID reception band from signals amplified by the second LNA  311 , and the second balun circuit  315  separates received signals that have passed through the reception filter  313  into RF I signals and RF Q signals having a phase difference of 90° with respect to each other. 
     The ninth mixer  317  converts an RF I signal into a baseband I signal using a first local frequency input from the first oscillator  319 , and the tenth mixer  321  converts an RF Q signal into a baseband Q signal using a second local frequency input from the first oscillator  319 . 
     The first LPF  325  removes a noise generated during the mixing operation from the baseband I signal, and the second LPF  327  removes a noise generated during the mixing operation from the baseband Q signal. 
     The ADC  329  converts at least one of the baseband I signal output from the first LPF  325  and the baseband Q signal output from the second LPF  327  into a digital signal to output the same to the third controller  360 . 
     The third controller  360  comprises a signal processor  362  and a signal separator  364 , and controls the operations of the third phase synchronizer  323  and a fourth phase synchronizer  377 , and respective parts. 
     The third controller  360  controls the third transmission circuit  370 . At this point, the third controller  360  transmits a control signal for controlling the phase of an RF signal and selection timing according to a PIE format. For the PIE format, a format according to an UHF RFID protocol such as ISO 18000-A, ISO 18000-B, EPC Generation-0, EPC Generation-1, and EPC Generation-2, can be applied. In the third embodiment, an EPC Generation-2 protocol is used. As this modulation standard is applied, all of Double SideBand-Amplitude Shift Keying (DSB-ASK), Single SideBand-Amplitude Shift Keying (SSB-ASK), and Phase Reversal-Amplitude Shift Keying (PR-ASK) can be used. 
     The signal processor  362  of the third controller  360  processes a transmitted/received signal according to a linking timing standard of a reader device and a tag device defined by EPC Generation-2 UHF RFID protocol. 
     The signal separator  364  separates a signal processed by the signal processor  362  into a tag signal section and a reader signal section. A partial frequency signal of the tag signal section is delivered to the first summer  371  of the transmission circuit  370 , and the frequency signal of the reader signal section is delivered to the second summer  373 . 
     The third transmission circuit  370  comprises a first summer  371 , a second summer  373 , a second oscillator  375 , a third oscillator  379 , an eleventh mixer  381 , a twelfth mixer  383 , a synthesizer  385 , a transmission filter  387 , a power amplifier  389 , and a transmission antenna  391 . 
     The first summer  371  sums an I signal and a Q signal having a phase difference of 90° which are partial frequency signals of the tag signal section to output a single signal, and the second summer  373  sums an I signal and a Q signal having a phase difference of 90° which are partial frequency signals of the reader signal section to output a single signal. 
     Here, the second oscillator  375  generates a third local frequency using a reference signal of the third phase synchronizer  323  to output the third local frequency to the eleventh mixer  381 , and the third oscillator  379  generates a fourth local frequency using a reference signal of the fourth phase synchronizer  377  to output the fourth local frequency to the twelfth mixer  383 . 
     The eleventh mixer  381  mixes the third local frequency supplied from the second oscillator  375 , which is used as a carrier, with a signal delivered from the first summer  371  to generate an energy signal. 
     The twelfth mixer  383  mixes the fourth local frequency supplied from the third oscillator  379 , which is used as a carrier, with a signal delivered from the second summer  373  to generate a data signal. 
     Here, the third local frequency is controlled by the reference signal of the third phase synthesizer  323 . The third local frequency is a signal in Industrial, Scientific and Medical (ISM) band. The fourth local frequency is controlled by the reference signal of the fourth phase synthesizer  377 . The fourth local frequency is a signal in a UHF band. The third phase synchronizer  323  and the fourth phase synchronizer  377  generate the reference signals, respectively, in response to a control signal of the third controller  360 . The reference signals of the third phase synchronizer  323  and the fourth phase synchronizer  377  are phase synchronization signals for stably maintaining the third and fourth local frequencies, which are oscillation frequencies, without fluctuation. 
     Since an energy signal output from the eleventh mixer  381  and a data signal output from the twelfth mixer  383  belong to frequency bands different from each other, respectively, and are synchronized in different sections according to a timing standard, a crosstalk phenomenon, a data interpretation error, a DC offset, and a double modulation/demodulation can be excluded. 
     The synthesizer  385  synthesizes an energy signal output from the eleventh mixer  381  and a data signal output from the twelfth mixer  383  into one signal according to a timing standard. The synthesized signal passes through the transmission filter  387  and the power amplifier  389  and is transmitted through the transmission antenna  391 . 
     The transmission filter  387  passes a signal in a transmission band and removes a noise component generated by the synthesizer during the synthesis operation. The power amplifier  389  amplifies a transmission signal to a power level that allows transmission. 
       FIG. 16  is a view illustrating a timing standard of an EPC Generation-2 standard applied to the reader device according to the third embodiment. 
     Referring to  FIG. 16 , a timing diagram of the reader device operation is illustrated in the upper section of the drawing, and a timing diagram of the tag device operation is illustrated in the lower section of the drawing. 
     The linking timing sections of the reader device and the tag device comprise sections of a ready state, an arbitrate state, a reply state, an acknowledged state, and an open state. 
     The ready state section comprises a select command section and a continuous wave (CW) section. The arbitrate state section comprises a query command, a CW section, a QueryRep command, and a CW section. The reply state section comprises a QueryRep command and a CW section. The acknowledged state section comprises an Ack command and a CW section. The open state section comprises a Req_RN command and a CW section. 
     A signal output from the reader device operation section operates in at least one state of a select command, a Query command, a QueryRep command, an ACK command, and Req_RN command depending on a command kind. A CW section corresponding to the tag device operation exists between respective commands. 
     The CW section can be divided into four kinds of time intervals, that is, a first time interval T 1 , a second time interval T 2 , a third time interval T 3 , and a fourth time interval T 4 . The first to fourth time intervals T 1 -T 4  are frequencies output during the tag device operation section. 
     The tag device operation section is processed during a CW section, and operates in at least one CW section of the four kinds of time intervals T 1 -T 4 . Also, the CW section comprises operations such as 16-bit random or pseudo-random number (RN 16 ), Protocol Control (PC) bits, Electronic Product Code(EPC) bits, Cyclic Redundancy Check (CRC 16 ) bits, and Handle data. 
     The respective sections and commands are described are described below in detail. 
     The ready state means a state where the tag device can communicate without losing energy. When tag energy is consumed, the tag device can be restored to the ready state. A select command for the ready state is a command for selecting the tag device to be added to or deleted from a communication inventory. The fourth time interval T 4  of the ready state means a minimum interval secured between reader commands. 
     The arbitrate state is a state where the tag device and the reader device perform a connection procedure together with a tag response not made. A Query command of the arbitrate state is a command for transmitting a response request signal to the tag device selected as a communication object. The first time interval T 1  of the arbitrate state means a time at which communication authority is transferred from the reader device to the tag device, which can be judged using whether a signal has been received from the tag antenna. The first time interval T 1  can exist in each state interval. The third time interval T 3  of the arbitrate state means a standby time of the reader device in response to a response request signal. A QueryRep command of the arbitrate state is a command reducing a reader slot value when there is no reply, and retransmitting a response request signal. 
     The reply state is a state where the tag device transmits a response code to the reader device. The second time interval T 2  of the reply state means a time secured for the tag device to demodulate a signal of the reader device. 16-bit random or pseudo-random number (RN 16 ) of the replay state means a response code of the tag device. 
     The acknowledged state is a state where as a response code of the tag device is transmitted, the reader device transmits the response code and tag information is transmitted. An ACK command of the acknowledged state means a acknowledge code with respect to the tag response. The protocol control (PC) bits of the acknowledged state is information regarding a physical layer of the tag information, and the EPC bits are the tag information for identification. Also, the CRC  16  is error detection information. 
     The open state is a state where a series of commands and responses for delivery of the tag information are processed after tag recognition. A Req_RN command of the open state is a command transmitted to the tag device to request new RN 16 . The Handle command of the open state is a state where a new command/response structure is processed after a Req_RN command. The new command/response structure can comprise all structures corresponding to the above-described plurality of states. 
     Also, besides the above section states, a timing standard according to an EPC protocol can comprise more various time sections. 
     Referring to  FIGS. 15 and 16 , a signal transmitted in the first time interval T 1  to fourth time interval T 4  is a signal in a tag operation section, and represents a partial frequency signal in the tag operation section output from the signal separator  364  of the third controller  360 . Signals corresponding to the first time interval T 1  to the fourth time interval T 4  are I and Q signals having a phase difference of 90°, which are summed as a single signal at the first summer  371 . The single signal is mixed with the third local frequency by the eleventh mixer  381  and generated as an energy signal. 
     Also, the reader operation section comprises a state where a select command, a Query command, a QueryRep command, an ACK command, and Req_RN command are processed. 
     Also, signals in the reader signal section are I and Q signals having a phase difference of 90°, which are summed as a single signal at the second summer  373 . The single signal is mixed with the fourth local frequency at the twelfth mixer  383  and generated as a data signal. 
     Here, the third local frequency signal is a signal in an industrial scientific and medical (ISM) band, and the fourth local frequency signal is a signal in a UHF band. 
     Therefore, since the energy signal and the data signal have a different frequency band and synchronized in a different section according to the timing standard, phenomena such as crosstalk, a data interpretation error, a DC offset, and double modulation/demodulation can be excluded. 
     Also, since a coding operation is performed using a signal in an UHF band and a signal in an ISM band simultaneously, energy can be stably supplied to the tag device, information of the tag device can be stably received, and a characteristic influence of a DC offset that may be generated according to a DC level can be minimized. 
     Meanwhile, in an embodiment, a wireless communication device described using the reader device disclosed in the first to third embodiments can be applied to the tag device of an RFID system, and is not limited to the reader device. Also, the transmission circuit and the reception circuit disclosed in each embodiment can serve as the transmission circuit and the reception circuit of another embodiment and are not limited to the embodiment. 
     Although embodiments have been described with reference to a number of illustrative embodiments thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of the principles of this disclosure. For example, elements specifically described in the embodiments can be modified, and differences associated with these modifications and applications should be construed as being comprised in the scope of the present disclosure as defined by appended claims. 
     INDUSTRIAL APPLICABILITY 
     Embodiments can reduce crosstalk between channels. 
     Embodiments can improve a signal recognition distance with a tag device and a tag signal recognition rate. 
     Embodiments can improve a degree of freedom in arrangement of a reader device. 
     Embodiments can prevent a non-linear crosstalk signal by a peak-to-average power ratio (PAR). 
     Embodiments can prevent an increase in an SNR. 
     Embodiments can prevent reception sensitivity and an SNR from reducing in the case where a tag device uses an ASK modulation method, and recover a digital signal to a sufficient voltage level. 
     Embodiments can improve an amplification gain without distortion of a signal received from a tag device to perform stable RFID communication. 
     Embodiments can minimize an influence of a DC offset through sequential amplification and cutting of a received tag signal. 
     Embodiments can minimize generation of a fading phenomenon. 
     Embodiments can exclude an influence of a crosstalk signal caused by a change in the phase of a received signal. 
     Embodiments can swiftly supply energy to a tag device.