Patent Publication Number: US-2011050245-A1

Title: Radio device and fault position specifying method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2009-204074 filed on Sep. 3, 2009, the entire contents of which are incorporated herein by reference. 
     FIELD 
     The embodiments discussed herein relate to a radio device and a fault position specifying method. 
     BACKGROUND 
     Recently, the radio device such as a base transceiver station detects whether or not an antenna of the radio device or a cable as a transmission path has a fault. The above-described radio device detects a reflected wave of a transmission signal, which is reflected by the antenna of the radio device, and determines that the antenna or the cable has a fault if a power value of the reflected wave is larger than a prescribed value. 
     The above-described radio device performs distortion compensation on a transmission signal. For example, a signal transmitted by the radio device is distorted by being modulated or amplified. Therefore, the radio device compensates a distortion occurring in the transmission signal by feeding back the transmission signal after being modulated or amplified to a distortion compensation circuit. 
     In recent years, there is a radio device that updates a distortion compensation coefficient used for distortion compensation processing and further stops distortion compensation coefficient updating processing if a power value of an unwanted wave as a signal transmitted from another system is or larger than a prescribed value (see, for example, Japanese Laid-Open Patent Publication No. 2005-142881, No. 2006-197545). According to the technique, it is possible to prevent the distortion compensation coefficient from being updated to a wrong value because the unwanted wave is mixed into a feedback signal. 
     However, the above-described technique may not specify the fault position of the radio device. For example, the technique for determining occurrence of a fault based on the power value of the reflected wave may determine whether or not a fault occurs on a cable or an antenna but may not specify which position on a path from the cable to the antenna the fault occurs. Since a cable of tens of meters may be used for the radio device, maintenance work may be complex if the fault position may not be specified. 
     Even though the technique for stopping the distortion compensation coefficient updating processing when the power value of an unwanted wave is larger than the prescribed power value, the fault position may not be specified. 
     SUMMARY 
     According to an aspect of the invention, a radio device includes a radio unit to perform modulation processing on a signal, an antenna to transmit and receive signals to and from an external unit, a cable to connect the radio unit to the antenna, a reflection time calculation unit to calculate a reflection time taken from after the transmission signal is input into a prescribed part of the radio unit until a transmission signal which is output from the radio unit is reflected on a path from the cable to the antenna is fed back to the prescribed part of the radio device, and a fault position specifying unit to specify a position candidate at which a fault occurs on the cable based on the calculated reflection time when the calculated reflection time is less than a reflection time threshold value. 
     The object and advantages of the invention will be realized and attained by at least the features, elements, and combinations particularly pointed out in the claims. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram a configuration example of a radio device according to a first embodiment, 
         FIG. 2  is a diagram a configuration example of a radio device according to a second embodiment, 
         FIG. 3  is an explanation diagram of an example of a fault position specifying processing by the radio device according to the second embodiment, 
         FIG. 4  is a flowchart illustrating the fault position specifying processing performed by the radio device according to the second embodiment, and 
         FIG. 5  is a diagram illustrating a configuration example of a radio device that includes a plurality of antennas. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Based on the figures, description will be made below of embodiments of a radio device and a fault position specifying method. 
     In the figures, dimensions and/or proportions may be exaggerated for clarity of illustration. It will also be understood that when an element is referred to as being “connected to” another element, it may be directly connected or indirectly connected, i.e., intervening elements may also be present. Further, it will be understood that when an element is referred to as being “between” two elements, it may be the only element layer between the two elements, or one or more intervening elements may also be present. 
     As illustrated in  FIG. 1 , the radio device  1  according to the first embodiment includes a radio unit  11 , a cable  12 , an antenna  13 , a reflection time calculation unit  14 , and a fault position specifying unit  15 . 
     The radio unit  11  performs modulation processing and amplification processing on a transmission signal. The cable  12  connects the radio unit  11  to the antenna  13 . The antenna  13  transmits and receives signals to and from one or more external units. 
     For example, transmission signals that are output from the radio unit  11  to the cable  12  are transmitted to the external unit via the antenna  13 ; however, all or some of the transmission signals are reflected on a path from the cable  12  to the antenna  13  and fed back into the radio unit  11 . Hereinafter, a transmission signal that is reflected on the path from the cable  12  to the antenna  13  is referred to as a “reflected wave.” 
     The reflection time calculation unit  14  calculates a reflection time taken from after the transmission signal is input into a prescribed part of the radio unit  11  until the reflected wave of the transmission signal is fed back to the prescribed part of the radio unit  11 . 
     If the reflection time calculated by the reflection time calculation unit  14  is less than a reflection time threshold value as a prescribed threshold value, the fault position specifying unit  15  specifies a fault position candidate on the cable  12  based on the calculated reflection time. 
     For example, in the radio device  1 , the reflection time, which is measured in a state in which the radio device  1  has no fault, is set as the reflection time threshold value. In this case, based on a difference between the reflection time threshold value and the reflection time calculated by the reflection time calculation unit  14 , the fault position specifying unit  15  specifies the fault position candidate on the cable  12 . For example, as the difference between the reflection time threshold value and the reflection time becomes larger, then the fault position specifying unit  15  determines that the transmission signal is reflected in a position closer to the radio unit  11  on the cable  12  and specifies such a reflection position as the fault position candidate. As the difference between the reflection time threshold value and the reflection time becomes smaller, the fault position specifying unit  15  determines that the transmission signal is reflected in the position closer to the antenna  13  on the cable  12  and specifies such a reflection position as the fault position candidate. 
     As described above, the radio device  1  according to the first embodiment specifies the fault position candidate on the cable  12  if the reflection time is less than the reflection time threshold value. Accordingly, for example, based on the fault position candidate specified by the fault position specifying unit  15 , an administrator or the like of the radio device  1  may check the position where a fault may occur on the cable  12  and specify the fault position. 
     In a second embodiment, description will be made of an example where the radio device described in the first embodiment is used as a radio device that performs distortion compensation on a transmission signal. 
       FIG. 2  is a diagram illustrating a configuration example of a radio device  100  according to the second embodiment. The configuration of the radio device  100  illustrated in  FIG. 2  illustrates a configuration of a transmission system. 
     The radio device  100  illustrated in  FIG. 2  is, for example, a base transceiver station, a relay station or the like that relays a signal transmitted and received between the base transceiver station and a mobile station. As illustrated in  FIG. 2 , the radio device  100  includes an interface (hereinafter referred to as “I/F”)  101 , a distortion compensation unit  110 , a modulation unit  121 , a Digital to Analog Converter (DAC)  122 , a frequency conversion up-converter  123 , an amplifier (AMP)  124 , an coupler  125 , a circulator  126 , a coaxial cable  127 , an antenna  128 , a distributor  129 , a Radio Frequency (RF) switch  130 , a frequency conversion down-converter  131 , an Analog to Digital Converter (ADC)  132 , a demodulation unit  133 , a wave detector  134 , and a switch control unit  135 . 
     The distortion compensation unit  110  and each of the units  121  to  126  and  129  to  133  are, for example, included in the radio unit  11  illustrated in  FIG. 1 . The coaxial cable  127  is an example of the cable  12  illustrated in  FIG. 1 . The antenna  128  is an example of the antenna  13  illustrated in  FIG. 1 . 
     The I/F  101  transmits and receives a signal to and from another device such as an upper device. For example, the I/F  101  connects the radio device  100  to another device and outputs the signal received from the other device to the distortion compensation unit  110 . In  FIG. 2 , the radio device  100  transmits the signal, which is input to the I/F  101  from the other device, to the external unit through the antenna  128 . The signal includes, for example, user data or control data. 
     The distortion compensation unit  110 , which is, for example, an integrated circuit, compensates for a distortion occurring in the transmission signal input from the I/F  101 . The distortion compensation unit  110  performs distortion compensation coefficient updating processing and fault position specifying processing. Description will be made of the distortion compensation processing, the distortion compensation coefficient updating processing, and the fault position specifying processing performed by the distortion compensation unit  110 . 
     The modulation unit  121  is, for example, an integrated circuit and demodulates the transmission signal that is input from the distortion compensation unit  110 . The DAC  122  converts the transmission signal demodulated by the modulation unit  121  into an analog signal. The frequency conversion up-converter  123  up-converts a frequency band of the transmission signal into a radio frequency band by mixing the transmission signal and a local oscillation signal. The AMP  124  amplifies the transmission signal that is up-converted by the frequency conversion up-converter  123 . 
     The coupler  125  divides the transmission signals input from the AMP  124  and outputs the transmission signals to the circulator  126  and to the RF switch  130 . The circulator  126  outputs the signal input from the coupler  125  to the coaxial cable  127  and outputs the signal that is input from the coaxial cable  127  to the distributor  129 . The coaxial cable  127  connects the circulator  126  to the antenna  128 . 
     The distributor  129  divides the signals input from the circulator  126  and outputs the signals to the RF switch  130  and to the wave detector  134 . The RF switch  130  switches a connection so that the signal that is to be input to the frequency conversion down-converter  131  becomes either the signal that is output from the coupler  125  or the signal that is output from the distributor  129 . 
     The frequency conversion down-converter  131  down-converts the signal input from the RF switch  130  into a baseband signal. The ADC  132  converts the signal that is down-converted by the frequency conversion down-converter  131  into a digital signal. The demodulation unit  133 , which is, for example, an integrated circuit, demodulates the signal that is input from the ADC  132  and feeds back the demodulated signal to the distortion compensation unit  110 . 
     Description will be made of an example of a signal that is transmitted in the radio device illustrated in  FIG. 2 . Description will be made of a case where the connection of the RF switch  130  is switched so that the coupler  125  is connected to the frequency conversion down-converter  131 . In this case, the transmission signal output from the distortion compensation unit  110  to the modulation unit  121  is input to the demodulation unit  133  through the coupler  125 , the RF switch  130 , the frequency conversion down-converter  131 , and the ADC  132 . The demodulation unit  133  feeds back the transmission signal input from the ADC  132  to the distortion compensation unit  110  as a feedback signal. 
     If the RF switch  130  is in the connection state of the above-described example, the transmission signal is output to the coaxial cable  127  through the coupler  125  and the circulator  126 . All or some of the transmission signals input to the coaxial cable  127  are transmitted to the external unit through the antenna  128  or reflected on the path from the coaxial cable  127  to the antenna  128 . At this time, the reflected wave of the transmission signal is output to the wave detector  134  through the coaxial cable  127  and the distributor  129 . 
     Description will be made of a case where the connection of the RF switch  130  is switched so that the distributor  129  is connected to the frequency conversion down-converter  131 . In this case, the transmission signal output from the distortion compensation unit  110  to the modulation unit  121  is output to the coaxial cable  127  through the coupler  125  and the circulator  126  in substantially the same manner as in the above-described example. All or some of the transmission signals input from the coaxial cable  127  are transmitted to the external unit through the antenna  128  or reflected on the path from the coaxial cable  127  to the antenna  128 . At this time, the reflected wave of the transmission signal is output to the wave detector  134  through the coaxial cable  127 , the circulator  126 , and the distributor  129 . Furthermore, the reflected wave is input to the demodulation unit  133  through the coaxial cable  127 , the circulator  126 , and the distributor  129 , the RF switch  130 , the frequency conversion down-converter  131 , and the ADC  132 . The demodulation unit  133  feeds back the reflected wave input from the ADC  132  to the distortion compensation unit  110 . 
     Even when the radio device  100  is performing transmitting processing, the antenna  128  may receive an unwanted wave as in the signal transmitted from another carrier or system. Accordingly, the feedback signal and the reflected wave described above may include the unwanted wave. 
     The wave detector  134  detects a signal that includes the reflected wave and the unwanted wave from among the signals input from the distributor  129  and then calculates a power value of the detected signal. The wave detector  134  outputs the calculated power value to the switch control unit  135 . 
     The switch control unit  135 , which is a part formed by an integrated circuit or software, for example, controls so that the signal to be input to the distortion compensation unit  110  becomes the feedback signal or the reflected wave by switching the connection of the RF switch  130 . For example, if the power value calculated by the wave detector  134  is larger than a wave detection level threshold value as a prescribed threshold value, the switch control unit  135  switches the connection of the RF switch  130  so that the distributor  129  is connected to the frequency conversion down-converter  131 . Every time a fixed time elapses, the switch control unit  135  switches the connection of the RF switch  130  so that the distributor  129  is connected to the frequency conversion down-converter  131 . 
     A description will be made of the RF switch  130  that is switched in the above-described manner. When the feedback signal is fed back from the demodulation unit  133 , the distortion compensation unit  110  according to the second embodiment performs the distortion compensation processing and the distortion compensation coefficient updating processing. If the reflected wave is fed back from the demodulation unit  133 , the distortion compensation unit  110  performs the distortion compensation processing and fault position specifying processing. 
     If the power value calculated by the wave detector  134  is larger than the detection wave level threshold value, the power value of the reflected wave may be abnormal. If the power value of the reflected wave is abnormal, the coaxial cable  127  or the antenna  128  may have a fault. Therefore, the switch control unit  135  makes the distortion compensation unit  110  perform the fault position specifying processing by switching the connection of the RF switch  130  so that the reflected wave is input to the distortion compensation unit  110 . 
     Even if the power value calculated by the wave detector  134  is smaller than the detection wave level threshold value, a reflection time may be abnormal. If the reflection time is abnormal, the coaxial cable  127  may have a fault. Therefore, each time the prescribed time elapses, the switch control unit  135  makes the distortion compensation unit  110  perform the fault position specifying processing by switching the connection of the RF switch  130  so that the reflected wave is input to the distortion compensation unit  110 . 
     A detailed description will be made of the above-described distortion compensation unit  110 . As for each of the units included in the distortion compensation unit  110 , description will be made of a case where the distortion compensation coefficient updating processing is performed and a case where the fault position specifying processing is performed, respectively. First, the description is made of the case where the distortion compensation coefficient updating processing is performed by the distortion compensation unit  110 . 
     As illustrated in  FIG. 2 , the distortion compensation unit  110  includes a distortion compensation coefficient table  111 , a power calculation unit  112 , a predistortion unit  113 , a delay circuit  114 , a distortion compensation coefficient updating unit  115 , a Fast Fourier Transform (FFT)  116 , a monitor control unit  117 , a threshold value storage unit  118 , and a fault determination unit  119 . 
     As for each power of the transmission signals, the distortion compensation coefficient table  111  stores the distortion compensation coefficient that is used when the distorting compensation processing is performed. The distortion compensation coefficient table  111  is, for example, a Random Access Memory (RAM), a Read Only Memory (ROM), or a semiconductor memory element such as a Flash Memory, or a storage apparatus such as a hard disk or an optical disk. 
     The power calculation unit  112  measures the power value of the transmission signal input from the I/F  101 , reads out the distortion compensation coefficient corresponding to the measured electric value from the distortion compensation coefficient table  111 , and outputs the read distortion compensation coefficient to the predistortion unit  113 . The predistortion unit  113  uses the distortion compensation coefficient read out by the power calculation unit  112  to compensate for the distortion occurred in the transmission signal. 
     The delay circuit  114  sets a time (hereinafter referred to as “delay time”) taken until the feedback signal is fed back from the demodulation unit  133  to the distortion compensation unit  110  after the transmission signal is input from the I/F  101  to the distortion compensation unit  110 . The delay circuit  114  delays the transmission signal by the delay time and inputs the transmission signal to the distortion compensation coefficient updating unit  115 . That is, the delay circuit  114  inputs the transmission signal and the feedback signal whose timings are deviated to the distortion compensation coefficient updating unit  115  at substantially the same timing. 
     The distortion compensation coefficient updating unit  115  compares the transmission signal input from the delay circuit  114  with the feedback signal fed back from the demodulation unit  133  and calculates a distortion compensation coefficient based on a comparison result. For example, the distortion compensation coefficient updating unit  115  obtains a difference between the power value of the transmission signal and the power value of the feedback signal calculated by the monitor control unit  117  described below, and calculates the distortion compensation coefficient so that the obtained difference is reduced. The distortion compensation coefficient updating unit  115  updates the distortion compensation coefficient stored in the distortion compensation coefficient table  111  to the calculated distortion compensation coefficient. 
     The FFT  116  detects each frequency signal component of the feedback signal fed back from the demodulation unit  133  and outputs the detection result to the monitor control unit  117 . Based on each of the frequency signal components of the feedback signal input from the FFT  116 , the monitor control unit  117  calculates the power value of the feedback signal and inputs the calculated power value to the distortion compensation coefficient updating unit  115 . As illustrated in  FIG. 2 , the monitor control unit  117  includes a delay time control unit  117   a  and a coefficient update stopping unit  117   b.    
     Based on each of the frequency signal components input from the FFT  116 , the delay time control unit  117   a  calculates the delay time taken until the feedback signal is fed back from the demodulation unit  133  to the distortion compensation unit  110  after the transmission signal is input from the I/F  101  to the distortion compensation unit  110 . The delay time control unit  117   a  controls the delay circuit  114  by using the calculated delay time. 
     The coefficient update stopping unit  117   b  stops or restarts the distortion compensation coefficient updating processing performed by the distortion compensation coefficient updating unit  115 . For example, if the power value calculated by the wave detector  134  is or larger than the prescribed threshold value, the coefficient update stopping unit  117   b  determines that the feedback signal includes the unwanted wave and makes the distortion compensation coefficient updating unit  115  stop the distortion compensation coefficient updating processing. This prevents the coefficient update stopping unit  117   b  from updating the distortion compensation coefficient to a wrong value. 
     After making the distortion compensation coefficient updating unit  115  stop the distortion compensation coefficient updating processing, the coefficient update stopping unit  117   b  makes the distortion compensation coefficient updating unit  115  restart the distortion compensation coefficient updating processing if the power value calculated by the wave detector  134  is smaller than the prescribed threshold value. This enables the coefficient update stopping unit  117   b  to make the distortion compensation coefficient updating unit  115  perform the distortion compensation coefficient updating processing when there is a low possibility that the feedback signal includes the unwanted wave. 
     The threshold value storage unit  118  and the fault determination unit  119  are parts that are related to the fault position specifying processing. Description will be made below of the threshold value storage unit  118  and the fault determination unit  119 . 
     Description will be made of a case where the distortion compensation unit  110  performs the fault position specifying processing. In this case, the connection of the RF switch  130  is in a state where the distributor  129  is connected to the frequency conversion down-convertor  131 . That is, the demodulation unit  133  feeds back the reflected wave to the distortion compensation coefficient updating unit  115  and the FFT  116 . 
     The FFT  116  to which the reflected wave is input detects each of the frequency signal components of the reflected wave and outputs the detection result to the monitor control unit  117 . Based on each of the frequency signal components of the reflected wave, the monitor control unit  117  calculates the power value of the reflected wave and outputs the calculated power value to the fault determination unit  119 . Hereinafter, the power value of the reflected wave, which is input from the monitor control unit  117  to the fault determination unit  119 , is referred to as “reflection power.” 
     Based on each of the frequency signal components input from the FFT  116 , the delay time control unit  117   a  calculates the reflection time taken until the reflected wave is fed back from the demodulation unit  133  to the distortion compensation unit  110  after the transmission signal is input from the I/F  101  to the distortion compensation unit  110 . The delay time control unit  117   a  outputs the calculated reflection time to the fault determination unit  119 . 
     In this manner, the monitor control unit  117  calculates the reflection power when the distortion compensation unit  110  performs the fault position specifying processing. Furthermore, the delay time control unit  117   a  calculates the reflection time taken until the reflected wave is input to the distortion compensation unit  110  after the transmission signal is input to the distortion compensation unit  110 . That is, the monitor control unit  117  calculates the power value of the feedback signal and the delay time when the distortion compensation coefficient updating processing is performed, and calculates the reflection power and the reflection time when the fault position specifying processing is performed. Accordingly, the radio device  100  performs the fault position specifying processing by diverting the monitor control unit  117  that is used when the distortion compensation coefficient updating processing is performed. Therefore, the radio device  100  may perform the distortion compensation coefficient updating processing without increasing the circuit scale. 
     The threshold value storage unit  118  is, for example, a semiconductor memory element such as a RAM, a ROM, or a storage device such as a hard disk or an optical disk, and stores a reflection time threshold value and a reflection power threshold value as a threshold value of the reflection power. For example, the threshold value storage unit  118  stores the reflection time and the reflection power, which are measured in a state where the coaxial cable  127  and the antenna  128  have no fault, as the reflection time threshold value and the reflection power threshold value, respectively. The threshold value storage unit  118  stores the time taken until the reflected wave of the transmission signal reflected in the antenna  128  is input to the distortion compensation unit  110  after the transmission signal as the reflection time threshold value is input from the I/F  101  to the distortion compensation unit  110 . 
     The fault determination unit  119  specifies a fault position candidate based on the reflection power that is input from the monitor control unit  117 , the reflection time that is input from the delay time control unit  117   a , and the reflection power threshold value and the reflection time threshold value that are stored in the threshold value storage unit  118 . The fault determination unit  119  stores a combination of the reflection power and the reflection time as a log in a prescribed storage unit. 
     For example, the fault determination unit  119  specifies the coaxial cable  127  as a fault position candidate if the reflection time is less than the reflection time threshold value stored in the threshold value storage unit  118 . This is because the transmission signal is reflected on the coaxial cable  127  without reaching the antenna  128  if the reflection time is less than the reflection time threshold value. In the above-described state, there is a possibility that the coaxial cable  127  has a fault. Thus, the fault determination unit  119  specifies the coaxial cable  127  as a fault position candidate. 
     If the coaxial cable  127  is specified as the fault position candidate, the fault determination unit  119  specifies the fault position of the coaxial cable  127  based on the reflection time. For example, the fault determination unit  119  determines a possibility that there is a fault in a position near a radio unit  140  on the coaxial cable  127  as the difference between the reflection time threshold value and the reflection time is larger. The fault determination unit  119  determines the possibility that there is a fault in the position near the antenna  128  on the coaxial cable  127  as the difference between the reflection time threshold value and the reflection time is smaller. 
     The fault determination unit  119  specifies the antenna  128  as a fault position candidate if the reflection time is greater than or equal to the reflection time threshold value stored in the threshold value storage unit  118  and if the reflection power is greater than the reflection power threshold value stored in the threshold value storage unit  118 . When the reflection time is greater than or equal to the reflection time threshold value, the transmission signal is reflected in the antenna  128 . If the reflection power is greater than the reflection power threshold value, a large of numbers of the transmission signals are reflected in the antenna  128 . In the above-described state, the antenna  128  may have a fault. Thus, the fault determination unit  119  specifies the antenna  128  as a fault position candidate. 
     The fault determination unit  119  determines that no fault position candidate exists if the reflection time is greater than or equal to the reflection time threshold value stored in the threshold value storage unit  118  and if the reflection power is less than or equal to the reflection power threshold value stored in the threshold value storage unit  118 . In this case, the switch control unit  135  switches the connection of the RF switch  130  so that the distributor  129  is connected to the frequency conversion down-converter  131 . Accordingly, the radio device  100  goes back to the state in which the distortion compensation coefficient updating processing is performed. 
       FIG. 3  is a diagram illustrating an example of the fault position specifying processing performed by the fault determination unit  119 . The I/F  101 , the distortion compensation unit  110 , and the units  121  to  126  and  129  to  133  are given as an example of the radio unit  140  illustrated in  FIG. 3 . 
     State A illustrated in  FIG. 3  indicates an example of a case where the coaxial cable  127  and the antenna  128  have no fault. In State A illustrated in  FIG. 3 , the transmission signal is reflected in the antenna  128 . The reflection power of a reflected wave R 10  of the transmission signal is “P 11 ,” and the reflection time is “ΔT 11 .” In the example illustrated in  FIG. 3 , the threshold value storage unit  118  stores “P 11 ” as the reflection power threshold value and stores “ΔT 11 ” as the reflection time threshold value. 
     State B illustrated in  FIG. 3  indicates an example of a case where the reflection power of a reflected wave R 20  is “P 12 ” and the reflection time is “ΔT 11 .” In this case, the reflection power “P 12 ”&gt;the reflection power “P 11 ” is assumed. In this case, the fault determination unit  119  specifies the antenna  128  as the fault position candidate when the reflection power “P 12 ” is larger than the reflection power threshold value “P 11 ,” and the reflection time “ΔT 11 ” is equal to the reflection time threshold value “ΔT 11 .” 
     State C illustrated in  FIG. 3  indicates an example of a case where the reflection power of a reflected wave R 30  is “P 12 ,” and the reflection time is “ΔT 12 .” In this case, the reflection time “ΔT 11 ”&gt;the reflection time “ΔT 12 ” is assumed. In this case, the fault determination unit  119  determines that the coaxial cable  127  is the fault position candidate because the reflection time is “ΔT 12 ” is smaller than the reflection time “ΔT 11 .” 
     The fault determination unit  119  determines the fault position on the coaxial cable  127  based on the reflection time “ΔT 12 .” For example, the coaxial cable  127  is long enough compared to the length of the path from the I/F  101  to the coaxial cable  127 , so that the time taken until the transmission signal is input to the coaxial cable  127  after the transmission signal is output from the I/F  101  may be ignored. Due to the substantially same reason, the time taken until the reflected wave is input to the distortion compensation unit  110  after the reflected wave is output from the coaxial cable  127  may be ignored. In this case, the fault determination unit  119  specified the position near the middle of the coaxial cable  127  as the fault position if, for example, the reflection time “ΔT 12 ” is half as large as the reflection time threshold value “ΔT 11 .” 
     State D illustrated in  FIG. 3  is an example of existence of two reflected waves: a reflected wave R 41  and a reflected wave R 42 . In this case, the reflection power of the reflected wave R 41  is “P 11 ,” and the reflection time is “ΔT 12 .” The reflection power of the reflected wave R 42  is “P 12 ,” and the reflection time is “ΔT 11 .” In this case, the fault determination unit  119  specifies both the coaxial cable  127  and the antenna  128  as a fault position candidate. 
     For example, the example illustrated in State D illustrates that some of the transmission signals are reflected on the coaxial cable  127  and a large number of the transmission signals that reach the antenna  128  are reflected in the antenna  128 . Accordingly, the fault determination unit  119  determines that both the coaxial cable  127  and the antenna  128  may have a fault. 
     The above-described State C illustrates the example of processing for specifying the fault position of the coaxial cable  127  on the assumption that the coaxial cable  127  is long enough compared to the length of the path from the I/F  101  to the coaxial cable  127 . The above-described example illustrates that the time taken until the transmission signal is input to the coaxial cable  127  after the transmission signal is output from the I/F  101  and the time taken until the reflected wave is input to the distortion compensation unit  110  after the reflected wave is output from the coaxial cable  127  may be ignored. However, even if the above-described assumption is not made, the fault determination unit  119  is able to specify the fault position of the coaxial cable  127 . 
     For example, the fault determination unit  119  may specify the fault position of the coaxial cable  127  based on a rate of the reflection time and the reflection time threshold value. In this case, the radio device  100  holds information indicating the fault position of the coaxial cable  127  in association with the rate of the reflection time and the reflection time threshold value. If the rate of the reflection time and the reflection time threshold value is “6:10,” the fault determination unit  119  determines, for example, that the position near the middle of the coaxial cable  127  as the fault position. 
     For example, the distortion compensation unit  110  may hold a time T 1  taken until the transmission signal is input to the coaxial cable  127  after the transmission signal is output from the I/F  101  and a time T 2  taken until the reflected wave is input to the distortion compensation unit  110  after the reflected wave is output from the coaxial cable  127 . In this case, by subtracting the time T 1  and the time T 2  from the reflection time, the fault determination unit  119  calculates a time T 3  during which the signal travels and returns on the path from the coaxial cable  127  to the antenna  128 . The fault determination unit  119  calculates a time T 4  by subtracting the time T 1  and the time T 2  from the reflection time threshold value. The fault determination unit  119  specifies the fault position on the coaxial cable  127  by comparing the calculated time T 3  to the calculated time T 4 . For example, if the value of the time T 3  is half as large as the time T 4 , the fault determination unit  119  determines that there is a fault near the middle of the coaxial cable  127 . 
       FIG. 4  is a flowchart illustrating the fault position specifying processing procedure by the radio device  100  according to the second embodiment. 
     As illustrated in  FIG. 4 , the switch control unit  135  of the radio device  100  determines whether the power value of the signal, which includes the reflected wave and the unwanted wave calculated by the wave detector  134 , is greater than the detection wave threshold value (Operation S 101 ). If the power value calculated by the wave detector  134  is greater than the detection wave level threshold value (YES in Operation S 101 ), the switch control unit  135  switches the connection of the RF switch  130  so that the reflected wave is input to the distortion compensation unit  110  (Operation S 102 ). 
     The reflected wave that is output from the coaxial cable  127  is input to the demodulation unit  133  through the circulator  126 , the distributor  129 , the RF switch  130 , the frequency conversion down-convertor  131 , and the ADC  132 . The demodulation unit  133  to which the reflected wave is input outputs the demodulated reflected wave to the FFT  116 . The FFT  116  to which the reflected wave is input detects each of the frequency signal components of the reflected wave and outputs the detection result to the monitor control unit  117 . 
     The monitor control unit  117  calculates the reflection power based on each of the frequency signal components of the reflected wave that is input from the FFT  116  (Operation S 103 ). The delay time control unit  117   a  calculates a reflection time based on each of the frequency signal components of the reflected wave that is input from the FFT  116  (Operation S 103 ). 
     The fault determination unit  119  stores, in a log, the reflection power that is calculated by the monitor control unit  117  and the reflection time that is calculated by the delay time control unit  117   a  (Operation S 104 ). The fault determination unit  119  compares the reflection power threshold value to the reflection power stored in the threshold value storage unit  118  and compares the reflection time threshold value to the reflection time stored in the threshold value storage unit  118  (Operation S 105 ). 
     If the reflection time is less than the reflection time threshold value (YES in Operation  105 ), the fault determination unit  119  specifies the coaxial cable  127  as a fault position candidate (Operation S 106 ). Based on the reflection time, the fault determination unit  119  specifies the fault position of the coaxial cable  127 , stores the specified fault position in the log, and reports the specified fault position to the administrator (Operation S 107 ). The fault determination unit  119  starts an alarm to stop the radio device  100  (Operation S 108 ). 
     If the reflection time greater than or equal to the reflection time threshold value (NO in Operation S 105 ) and if the reflection power is greater than the reflection power threshold value (YES in Operation S 109 ), the fault determination unit  119  specifies the antenna  128  as the fault position candidate (Operation S 110 ). The fault determination unit  119  stores the fact that the antenna has a fault and reports the fact to the administrator (Operation S 111 ). The fault determination unit  119  starts the alarm to stop the radio device  100  (Operation S 108 ). 
     If the reflection time is greater than or equal to the reflection time threshold value (NO in Operation S 105 ) and if the reflection power is or smaller than the reflection power threshold value (NO in Operation S 109 ), the fault determination unit  119  determines that no fault position candidate exists (Operation S 112 ). In this case, the switch control unit  135  switches the connection of the RF switch  130  so that the feedback signal is input to the distortion compensation unit  110  (Operation S 113 ). 
     On the other hand, if the power value calculated by the wave detector  134  is less than or equal to the detection wave level threshold (NO in Operation S 101 ), the switch control unit  135  determines whether the prescribed time elapses (Operation S 114 ). When the prescribed time elapses (YES in Operation S 114 ), the switch control unit  135  switches the connection of the RF switch  130  so that the reflected wave is input to the distortion compensation unit  110  (Operation S 115 ). 
     The monitor control unit  117  calculates the reflection power, and the delay time control unit  117   a  calculates the reflection time (Operation S 116 ). The fault determination unit  119  stores, in the log, the reflection power calculated by the monitor control unit  117  and the reflection time calculated by the delay time control unit  117   a  (Operation S 117 ). 
     If the reflection time is less than the reflection time threshold value (YES in Operation S 118 ), the fault determination unit  119  specifies the coaxial cable  127  as the fault position candidate (Operation S 119 ). Based on the reflection time, the fault determination unit  119  specifies the fault position of the coaxial cable  127 , stores the specified fault position in the log, and reports the specified fault position to the administrator (Operation S 120 ). The fault determination unit  119  starts the alarm to stop the radio device  100  (Operation S 121 ). 
     If the reflection time greater than or equal to the reflection time threshold value (NO in Operation S 118 ), the fault determination unit  119  determines that no fault position candidate exists (Operation S 122 ). In this case, the fault determination unit  119  updates the reflection power threshold value stored in the threshold value storage unit  118  to the reflection power calculated by the monitor control unit  117  (Operation S 123 ). The fault determination unit  119  updates the reflection time threshold value stored in the threshold value storage unit  118  to the reflection time calculated by the delay time control unit  117   a  (Operation S 123 ). In this manner, if no fault position candidate exists, the fault determination unit  119  updates the reflection power threshold value and the reflection time threshold value that may be changed according to an operating environment or the like. Accordingly, even when the reflection power or the reflection time is changed according to a change of the operating environment, the radio device  100  may properly perform the fault position specifying processing. 
     The switch control unit  135  switches the connection of the RF switch  130  so that the feedback signal is input to the distortion compensation unit  110  (Operation S 124 ). 
     In the example illustrated in  FIG. 4 , if the power value calculated by the wave detector  134  less than or equal to the detection wave level threshold value (NO in Operation S 101 ) and if the prescribed time elapses (YES in Operation S 114 ), the fault determination unit  119  does not compare the reflection power to the reflection power threshold value. This is because, as for the radio device  100  according to the second embodiment, it is assumed that the reflection power is not greater than the reflection power threshold value if the power value calculated by the wave detector  134  less than or equal to the detection wave level threshold value. Even if the power value calculated by the wave detector  134  is less than or equal to the detection wave level threshold value, the fault determination unit  119  may determine whether the antenna  128  has a fault by performing processing for comparing the reflection power to the reflection power threshold value. 
     As described above, if the reflection time is less than the radio device  100  according to the second embodiment specifies the fault position candidate on the coaxial cable  127  based on the reflection time. This enables the administrator or the like who manages the radio device  100  may easily determine whether the coaxial cable  127  has a fault based on the fault position candidate specified by the radio device  100 . 
     The radio device  100  according to the second embodiment calculates the reflection power by using the delay time control unit  117   a  that calculates the delay time when the distortion compensation coefficient updating processing is performed. This enables the radio device  100  to perform the fault position specifying processing without increasing the circuit scale. 
     If the reflection power is greater than the reflection power threshold value, the radio device  100  according to the second embodiment specifies the antenna  128  as the fault position candidate. This enables the administrator or the like to check if the antenna  128  has a fault. 
     The radio device  100  according to the second embodiment performs the fault position specifying processing by using the reflected wave of the transmission signal that includes the user data or the control data. Accordingly, the radio device  100  may specify the fault position candidate without using a test signal such as a pilot signal. That is, the radio device  100  may specify the fault position candidate during operation. 
     The radio device  100  according to the second embodiment stores the reflection power and the reflection time in the log every time the reflection power and the reflection time are calculated. Consequently, when a fault occurs, the administrator or the like may determine whether the fault occurs gradually or the fault occurs suddenly by checking the log. For example, the radio device  100  specifies the antenna  128  as the fault position candidate. In this case, the administrator or the like checks the above-described log to determine the fault of the antenna  128  occurs gradually if the reflection power is increasing gradually. On the other hand, if the reflection power increases suddenly, the administrator or the like may determine that the fault of the antenna  128  occurs suddenly. 
     The radio device  100  according to the second embodiment calculates the power value of the signal, which includes the reflected wave and the unwanted wave, by using the wave detector  134  and switches the RF switch  130  so that the signal to be fed back to the distortion compensation unit  110  becomes the reflected wave. This enables the radio device  100  to perform the fault position specifying processing if the reflection power is greater than the reflection power threshold value. 
     The radio device  100  according to the second embodiment determines that no fault position exists if the reflection power less than or equal to the reflection power threshold value and if the reflection time is greater than or equal to the reflection time threshold value. This enables the radio device  100  to accurately determine whether a fault position exists even when receiving the unwanted wave. 
     Every time the prescribed time elapses, the radio device  100  switches the RF switch  130  so that the signal to be input to the distortion compensation unit  110  becomes the reflected wave. This enables the radio device  100  to determine whether the coaxial cable  127  has a fault by regularly performing the fault position specifying processing even if the power value calculated by the wave detector  134  is less than the detection wave level threshold value. 
     The above-described radio device or the like may be used in various configurations other than the above-described embodiments. In a third embodiment, description is made of other embodiments. 
     In the above-described first and second embodiments, description was made of a case where, for example, the radio device includes a single antenna. However, a radio device that includes a plurality of antennas may be used.  FIG. 5  is a diagram illustrating a configuration example of a radio device that includes a plurality of antennas. A radio device  2  illustrated in  FIG. 5  includes a distributor/combiner  150 . The distributor/combiner  150  is connected to antennas  128   a  to  128   c.    
     In the radio device  2  illustrated in  FIG. 5 , there are various patterns in which the transmission signal, which is input from the radio unit  140  to the coaxial cable  127 , is reflected on the path from the coaxial cable  127  to antennas  128   a  to  128   c . For example, the transmission signal may be input to the radio unit  140  after being reflected in the antenna  128   a , may be input to the radio unit  140  after being reflected in the antenna  128   b , or may be input to the radio unit  140  after being reflected in the antenna  128   c . The transmission signal may be reflected in the antenna  128   b  after being reflected in the antenna  128   a  and then input to the radio unit  140 . 
     The radio device  2  holds the reflection time threshold value for each pattern in which the transmission signal is reflected. For example, the radio device  2  holds the reflection time threshold value in the case where the transmission signal is reflected in the antenna  128   a , the reflection time threshold value in the case where the transmission signal is reflected in the antenna  128   b , or the reflection time threshold value in the case where the transmission signal is reflected in the antenna  128   c . The radio device  2  holds the reflection time threshold value in the case where the transmission signal is reflected in the antenna  128   b  or the antenna  128   c  after the transmission signal is reflected in the antenna  128   a.    
     If the reflection time calculated by the delay time control unit  117   a  is less than any of the reflection time threshold values, the fault determination unit  119  of the radio device  2  specifies the coaxial cable  127  as the fault position candidate. In this manner, the radio device  2  may specify the fault position by holding the reflection time threshold value for each pattern even if the radio device  2  includes the plurality of antennas. 
     The configuration elements of each device illustrated in the figures are functionally conceptual and may be physically configured differently than shown in the figures. That is, specific configurations of distribution and integration of the devices are not limited to the figures. All or some of the devices may be configured to be distributed or integrated by an arbitrary unit functionally or physically according to each load or use condition.  FIG. 2  illustrates the example of a case where the reflection power and the reflection time used for the fault position specifying processing by diverting the monitor control unit  117  that is used when the distortion compensation coefficient updating processing is performed. The radio device  100  may be provided with a circuit, which calculates the reflection power and the reflection time, separately from the monitor control unit  117  that is used to when the distortion compensation coefficient updating processing is performed. 
     From among the processing described in the above-described embodiments, all or some of the processing that were described to be automatically performed may be performed manually. Alternatively, all or some of the processing that are to be manually performed may be performed automatically by a known method. For example, in the example illustrated in  FIG. 1 , reflection time calculating processing by the reflection time calculation unit  14  may be performed manually. In the example illustrated in  FIG. 1 , the fault position specifying processing by the fault position specifying unit  15  may be performed manually. For example, the reflection time is checked manually by the reflection time calculation unit  14  to specify the fault position candidate. 
     All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the principles of the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. Although the embodiment(s) of the present invention(s) have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.