Patent Publication Number: US-9906246-B2

Title: Apparatus and method for detecting a generation point of passive intermodulation

Description:
CLAIM FOR PRIORITY 
     This application claims priority to Korean Patent Application No. 10-2015-0162934 filed on November 20, 2015 in the Korean Intellectual Property Office (KIPO), the entire contents of which are hereby incorporated by reference. 
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to methods and apparatuses for finding out a generation point of a passive intermodulation (PIM), and more particularly, to methods and apparatuses for rapidly and correctly finding out a generation point of PIM. 
     2. Related Art 
     According to the current increase of demands for mobile networks and wireless data services, foreign or domestic mobile communication operators make efforts to secure more frequency bands and construct efficient mobile networks enabling multi-band services. Due to the high construction cost and maintenance cost, it&#39;s not practically easy to install and operate respective in-building feeders for multiple frequency bands. Thus, cases using a common in-building feeder to provide services through various frequency bands are increasing currently. 
     However, in the case that a common feeder is used to provide multi-band services in a building, a passive intermodulation (PIM) may occur, thereby causing interferences between upward channel and downward channel, and thus reducing a service range and deteriorating telephone connection efficiencies. Since the PIM may occur due to contact inferiority caused by deterioration of passive elements such as cable connectors, multiplexers, and circulators, the disfunctional elements should be replaced or repaired in order to solve the problem of PIM. Also, since the in-building feeders are laid in the ceiling or wall, a PIM generation point should be correctly estimated in order to promptly replace or repair the disfunctional elements. 
     For this, conventional PIM generation point detection apparatuses estimate a PIM generation point approximately by determining, through a digital signal processing, a beat frequency according to a time delay between a reference signal generated utilizing a Frequency Modulation Continuous Wave (FMCW) signal and a Continuous Wave (CW) signal, and a PIM signal returned after being inputted to an input end of the in-building feeder. However, since the conventional PIM generation point detection apparatuses have accuracy of several meters, several candidate PIM generation points may be estimated, whereby the replacement or repair of the disfunctional elements take too much time. 
     SUMMARY 
     Accordingly, example embodiments of the present disclosure are provided to substantially obviate one or more problems due to limitations and disadvantages of the related art. 
     Example embodiments of the present disclosure provide apparatuses or methods for detecting a PIM generation point, which can enhance the accuracy of the PIM generation point detection up to a level of 10 centimeters, and thus enable rapid replacement or maintenance of a disfunctional element causing the PIM by installing and controlling a time delay module in an output end of a reference signal (or, a PIM signal) for detection of the PIM generation point. 
     Technical objects of the present disclosure are not limited to the aforementioned technical objects and other technical objects which are not mentioned will be apparently appreciated by those skilled in the art from the following description. 
     In order to achieve the above-described objective, an aspect of the present disclosure provides an apparatus for detecting a passive intermodulation (PIM) generation point, comprising a time delay module configured to delay, according to a time delay amount control value, a reference signal based on a frequency modulation continuous wave (FMCW) signal and a continuous wave (CW) signal, or a PIM signal output from an in-building feeder; a time delay control module configured to generate the time delay amount control value according to a control command; and a control part configured to generate the control command, and calculate a PIM generation point based on the time delay amount control value and a signal processing result obtained by performing a Fast Fourier Transform (FFT) on a beat frequency signal based on a signal which is delayed by the time delay module among the PIM signal and the reference signal and the other signal which is not delayed signal among the PIM signal and the reference signal. 
     The control part may be configured to check a beat frequency difference according to the signal processing result and calculate a fine scanning power value in an unit frequency band of the beat frequency having a power value not less than a first threshold based on power values according to the signal processing result, in order to use a principle that a PIM signal level to the PIM generation point varies according to the signal processing result, and a distance to the PIM generation point varies according to an amount of the time delay of the PIM signal from the PIM generation point. 
     Here, a frequency of the reference signal is 2*f 1 -f 2 , f 1  is a frequency of the FMCW signal, and f 2  is a frequency of the CW signal. Also, the beat frequency signal comprises an in-phase (I) signal and a quadrature-phase (Q) signal. 
     Also, the apparatus may further comprise an I/Q demodulator generating the I signal and the Q signal, and a low pass filter (LPF), a signal level adjustor, an analog-to-digital converter (ADC), and a signal processor for the FFT which are sequentially coupled to the I/Q demodulator. 
     The control part may be configured to calculate power values of respective unit frequency bands for the signal processing result; control the time delay module to generate the signal which is delayed by a predetermined amount (Δ) according to the control command in an unit frequency band k having a power value not less than a first threshold belonging to a total frequency band; and calculate the PIM generation point based on k and i satisfying an equation 
               (         max   ⁡     [       P     B   ⁡     (     k   -     Δ   *   i       )           min   ⁡     (       P     B   ⁡     (   j   )         ,     j   =   1     ,   2   ,     …   ⁢           ⁢   K       )         ]       ≥     Th   ⁢           ⁢   2       ,     (       i   =   0     ,   1   ,   …   ⁢           ,     M   -   1       )       )     ,         
wherein P B(k−Δ*i)  is a power value at i-th sub-unit (i=1,2, . . . , M−1, M is a natural number) in the unit frequency band k, Th 2  is a second threshold, P B(j)  is a power value of an unit frequency band j (j=1, 2, . . . , K, K is a natural number, and a total frequency band is divided into K unit frequency bands).
 
     The control part may be configured to calculate the PIM generation point by checking whether the equation is satisfied by other unit frequency bands after finding the k and i and updating the k and i. 
     In order to achieve the above-described objective, another aspect of the present disclosure provides a method for detecting a passive intermodulation (PIM) generation point, comprising generating a time delay amount control value according to a control command; delaying, according to the time delay amount control value, a reference signal based on a frequency modulation continuous wave (FMCW) signal and a continuous wave (CW) signal, or a PIM signal output from an in-building feeder; and calculating a PIM generation point based on the time delay amount control value and a signal processing result obtained by performing a Fast Fourier Transform (FFT) on a beat frequency signal based on a signal which is delayed by the time delay module among the PIM signal and the reference signal and the other signal which is not delayed signal among the PIM signal and the reference signal. 
     In the calculating the PIM generation point, the PIM generation point may be calculated by checking a beat frequency difference according to the signal processing result and calculating a fine scanning power value in an unit frequency band of the beat frequency having a power value not less than a first threshold based on power values according to the signal processing result, in order to use a principle that a PIM signal level to the PIM generation point varies according to the signal processing result, and a distance to the PIM generation point varies according to an amount of the time delay of the PIM signal from the PIM generation point. 
     Here, a frequency of the reference signal is 2*f 1 -f 2 , f 1  is a frequency of the FMCW signal, and f 2  is a frequency of the CW signal. Also, the beat frequency signal comprises an in-phase (I) signal and a quadrature-phase (Q) signal. 
     In the calculating the PIM generation point, the signal processing result may be output by an FQ demodulator generating the I signal and the Q signal, and a low pass filter (LPF), a signal level adjustor, an analog-to-digital converter (ADC), and a signal processor for the FFT which are sequentially coupled to the I/Q demodulator. 
     The calculating the PIM generation point may further comprise calculating power values of respective unit frequency bands for the signal processing result; controlling the time delay module to generate the signal which is delayed by a predetermined amount (Δ) according to the control command in an unit frequency band k having a power value not less than a first threshold belonging to a total frequency band; and calculating the PIM generation point based on k and i satisfying an equation 
               (         max   ⁡     [       P     B   ⁡     (     k   -     Δ   *   i       )           min   ⁡     (       P     B   ⁡     (   j   )         ,     j   =   1     ,   2   ,     …   ⁢           ⁢   K       )         ]       ≥     Th   ⁢           ⁢   2       ,     (       i   =   0     ,   1   ,   …   ⁢           ,     M   -   1       )       )     ,         
wherein P B(k−Δ*i)  is a power value at i-th sub-unit (i=1,2, . . . , M−1, M is a natural number) in the unit frequency band k, Th 2  is a second threshold, P B(j)  is a power value of an unit frequency band j (j=1, 2, . . . , K, K is a natural number, and a total frequency band is divided into K unit frequency bands).
 
     The PIM generation point may be calculated by checking whether the equation is satisfied by other unit frequency bands after finding the k and i and updating the k and i. 
     Using a PIM generation point detection apparatus and method according to the present disclosure, the time delay module is introduced in the output end of the reference signal (or, the PIM signal), and thus the reference signal can be controlled so that the detection accuracy of the PIM generation point can be enhanced up to a level of 10 centimeters. Also, since the detection accuracy of the PIM generation point is remarkably enhanced, the time required to replace or repair the disfunctional element causing the PIM signal can be reduced and thus maintenance cost for the in-building feeder network can be decreased. Also, the mobile service range or the efficiency of telephone connection can be enhanced by rapidly resolving the problem caused by the PIM. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       Example embodiments of the present disclosure will become more apparent by describing in detail example embodiments of the present disclosure with reference to the accompanying drawings, in which: 
         FIG. 1  is a block diagram of a PIM generation point detection apparatus according to an exemplary embodiment of the present disclosure; 
         FIG. 2  is an exemplary view of a reference signal according to an exemplary embodiment of the present disclosure;  FIG. 3  is an exemplary view of a PIM signal generated in a feeder according to an exemplary embodiment of the present disclosure; 
         FIG. 4  is a concept diagram to explain a time delay between the reference signal  159  and the PIM signal  176  generated at the feeder according to an exemplary embodiment of the present disclosure; 
         FIG. 5  is an exemplary view to explain a relation between a time delay between a reference signal and a PIM signal generated at a feeder, and a beat frequency of a beat frequency signal, according to an exemplary embodiment of the present disclosure; 
         FIG. 6  is an exemplary view to explain distances between a PIM generation point detection apparatus and a PIM generation point, which are estimated based on frequencies of a beat frequency signal; 
         FIG. 7  is an exemplary view to illustrate a beat frequency difference according to the time delay between a reference signal of  FIG. 2  and a PIM signal of  FIG. 3 ; 
         FIG. 8  is an exemplary view to illustrate a wave form obtained by delaying the reference signal by 5 ns through a time delay module according to an exemplary embodiment of the present disclosure; 
         FIG. 9  is an exemplary view of beat frequency differences according to a time delay between a delayed reference signal of  FIG. 8  and a PIM signal generated at a feeder of  FIG. 3 ; 
         FIG. 10  is a flow chart to explain an operation of a PIM generation point detection apparatus according to an exemplary embodiment of the present disclosure; and 
         FIG. 11  is an exemplary view to explain unit frequency bands according to an exemplary embodiment of the present disclosure. 
     
    
    
     DESCRIPTION OF EXAMPLE EMBODIMENTS 
     Hereinafter, some exemplary embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. When reference numerals refer to elements of each drawing, it is noted that although the same elements are illustrated in different drawings, the same elements are referred to by the same reference numerals as possible. Further, in describing the exemplary embodiments of the present disclosure, when it is determined that the detailed description of known configurations or functions related to the present disclosure may obscure the understanding of the exemplary embodiment of the present disclosure, the detailed description thereof will be omitted. 
     In describing constituent elements of the exemplary embodiment of the present disclosure, terms such as first, second, A, B, (a), (b), and the like may be used. Such a term is only for discriminating the constituent element from another constituent element, and does not limit the essential feature, order, or sequence of the constituent element, or the like. Further, if it is not contrarily defined, all terms used herein including technological or scientific terms have the same meaning as those generally understood by those skilled in the art. Terms which are defined in a generally used dictionary should be interpreted to have the same meaning as the meaning in the context of the related art but are not interpreted as ideal or excessively formal meaning if it is not clearly defined in the present disclosure. 
       FIG. 1  is a block diagram of a PIM generation point detection apparatus according to an exemplary embodiment of the present disclosure. 
     Referring to  FIG. 1 , an PIM generation point detection apparatus  200  according to an exemplary embodiment of the present disclosure may comprise a control part  190 , a frequency modulation continuous wave (FMCW) signal (f 1 ) generator  100 , a signal level adjustor  102 , a high power amplifier (HPA)  106 , a frequency multiplier  153 , a continuous wave (CW) signal (f 2 ) generator  110 , a signal level adjustor  112 , a splitter  114 , a HPA  116 , a mixer  151 , a multiplexer  130 , an in-building feeder  140 , a radio frequency (RF) switch  118 , a band pass filter (BPF)  120 , a time delay module  160 , a time delay control module  165 , a low noise amplifier (LNA)  171 , a signal level adjustor  173 , a BPF  175 , an I/Q demodulator  180 , a low pass filter (LPF)  182 , a signal level adjustor  184 , an analog-to-digital converter (ADC)  186 , and a signal processor  188 . 
     The control part  190  may be implemented with a semiconductor processor such as a micro controller unit (MCU), and responsible for overall control on the above-described respective components of the PIM generation point detection apparatus  200 . Also, the control part  190  may be implemented as including at least one of the above-described components. 
     The FMCW signal (f 1 ) generator  100  may generate a FMCW signal by using a direct digital synthesizer (DDS), etc., and generate a signal having a frequency f 1  (i.e., a FMCW (f 1 ) signal  101 ) through a frequency multiplier. 
     The FMCW (f 1 ) signal  101  generated at the FMCW signal generator  100  may be amplified or attenuated by the signal level adjustor  102 , and transferred to the splitter  104 . Then, signals  105  and  152  output from the splitter  104  may be transferred respectively to the 
     HPA  106  and the multiplier  153 . 
     The CW (f 2 ) signal generator  110  may generate a signal having a frequency f 2  (i.e., a CW (f 2 ) signal  111 ) which is phase-locked to a reference clock of an oscillator such as an oven controlled crystal oscillator by using a frequency synthesizer. 
     The CW (f 2 ) signal  111  generated at the CW (f 2 ) signal generator  110  may be amplified or attenuated by the signal level adjustor  112 , and divided by the splitter  114 . Signals  115  and  151  output from the splitter  114  may be transferred respectively to the HPA  116  and the mixer  151 . 
     A first signal  107  having a frequency f 1  amplified by the HPA  106  may be output to the in-building feeder  140  through the multiplexer  130  and an input terminal  131 . 
     The RF switch  118  may selectively use one or two output ports. In the case that the RF switch  118  uses a signal output port, the RF switch  118  may transmit a second signal  117  having a frequency f 2  amplified by the HPA  116  to the multiplexer  130  under control of the control part  190 , and the multiplexer  130  may input the second signal  117  to the in-building feeder  140  through the input terminal  131 . In the case that the RF switch  118  uses two output ports, the RF switch  118  may transmit the second signal  117  to the BPF  120  under control of the control part  190 , and the BPF  120  may output the processed signal to the in-building feeder  140  through an input terminal  121 . 
     In order to detect a PIM signal, a reference signal for detecting the PIM signal, which has a frequency (2*f 1 -f 2 ), is needed. For this, a signal  154  having a frequency (2*f 1 ) that the multiplier  153  generates by frequency multiplication and a signal  151  having a frequency f 2  output by the splitter  114  may pass through the mixer  150 , the BFP  156 , and the signal level adjustor (signal level amplification or attenuation)  158 , whereby a reference signal  159  for detecting a PIM generation point is generated. The generated reference signal  159  may have a frequency of 2*f 1 -f 2 . For example, when an operation frequency band of the first signal based on the FMCW (f 1 ) signal generator  100  has a range of 2145 MHz to 2170 MHz, and a frequency of the second signal based on the CM (f 2 ) signal generator  110  is 2.34 GHz, the reference signal  159  may be a FMCW signal operating in a frequency band of 1950 MHz to 2000 MHz. For ease of understanding, hereinafter, the FMCW signal is assumed to be a signal operating in a frequency band of 1950 MHz to 2000 MHz. 
     Also, in the present disclosure, the time delay module  160  and the time delay control module  165  may be additionally used at the output ends of the reference signal  159  so that a time delay of the reference signal  159  can be controlled by unit of a nanosecond and thus a detection accuracy of the PIM generation point can be enhanced up to a level of 10 centimeter. 
     After the signals  107  and  117  are inputted to the in-building feeder  140  through the input terminal  131 , a PIM signal  133  returning through a downward channel of the feeder  140  may be inputted to the LNA  171  in a receive path through the multiplexer  130 . Then, after the PIM signal  133  passes through the signal level adjustor  173  (signal level amplification or attenuation of signal) and the BPF  175 , only a PIM signal  176  having a frequency (2*f 1 -f 2 ) in a frequency band 1950 MHz to 2000 MHz remains. For reference, if necessary, the time delay module  160  proposed in the present disclosure may also be installed behind the BPF  175  located in a PIM signal path, that is, between the IQ demodulator  180  and the BPF  175 . 
     A signal  161  which is obtained at the time delay module  160  by delaying the above-described reference signal  159  according to a time delay amount control value  166  of the time delay control module  165 , and the PIM signal  176  are inputted to the I/Q demodulator  180 , and the FQ demodulator  180  may generate corresponding beat frequency signal  181  comprising corresponding in-phase (I) signals and quadrature-phase (Q) signals. 
     Then, the beat frequency signal  181  may sequentially pass through the LPF  182  and the signal level adjustor  184  (signal level amplification or attenuation), and be inputted to the signal processor  188  through the ADC  186 . Since the beat frequency signal  187  having passed through the ADC  186  has information on a distance to the PIM generation point and a PIM signal level, the information may be converted into information on a PIM signal level by a distance to the PIM generation point through a Fast Fourier Transform signal processing (refer to  FIG. 6 ). 
     Using this, the control part  190  may finally determine the PIM generation point (e.g. a position of an element which is an origin of the PIM signal, such as a cable connector, a multiplexer, and a circulator) based on the FFT signal processing result  189  and the control value  167  of the time delay control module  165 . 
       FIG. 2  is an exemplary view of a reference signal according to an exemplary embodiment of the present disclosure. 
     The signal  154  having a frequency (2*f 1 ) which has been generated by the FMCW signal generator  100 , divided by the splitter  104 , and outputted from the multiplier  153 , and the signal  151  having a frequency of f 2  which has been generated by the CW signal generator  110 , and outputted from the splitter  114  respectively pass through the mixer  150 , the BPF  156 , and the signal level adjustor  158 , whereby the reference signal  159  for detection of a PMI signal generation point can be generated as illustrated in  FIG. 2 . 
     For example, the reference signal  159  may have a frequency in a range of f R   _   start  to f R   _   end  Hz. That is, the operating frequency of the reference signal  159  may start from f R   _   start  and increase by a predetermined value (e.g. 100 Hz) every 20 ns (nanoseconds). For example, when it is assumed that the operating frequency range of the first signal  152  is 2145˜2170 MHz and the frequency of the second signal is 2.34 GHz, the reference signal  159  may become a FMCW signal operating in a frequency range of 1950˜2000 MHz. 
       FIG. 3  is an exemplary view of a PIM signal generated in a feeder according to an exemplary embodiment of the present disclosure. 
     For example, after the PIM signal generated at the in-building feeder  140 , as a signal delayed by 425 ns as compared with the reference signal  159 , is transmitted to the multiplexer  130  through the downward channel  133 , and passes through the LNA  171 , the signal level adjustor  173 , and the BPF  175 , the PIM signal observed at a point of  176  may be represented as shown in  FIG. 3 . 
       FIG. 4  is a concept diagram to explain a time delay between the reference signal  159  and the PIM signal  176  generated at the feeder according to an exemplary embodiment of the present disclosure. 
     As illustrated in  FIG. 4 , in the case that a time delay exists between the reference signal  159  and the PIM signal  176  generated at the feeder, differences may vary between frequencies of the two signals by lapse of time. That is,  FIG. 5  illustrates a relation between a frequency of a beat frequency signal  187  and the time delay between the reference signal  159  and the PIM signal  176 . 
     Meanwhile,  FIG. 6  is an exemplary view to explain distances between the PIM generation point detection apparatus and the PIM generation point, which are estimated based on the frequency of the beat frequency signal  187 . In  FIG. 6 , a dielectric constant of the in-building feeder  140  is assumed to be 1.5. Since the distance to the PIM generation point calculated based on the beat frequency may vary according to the dielectric constant of the feeder  140 , the dielectric constant of the feeder should be accurately measured and used for estimating the distance of the PIM generation point. Like this, based on a principle that the PIM signal level to the PIM generation point may vary according to a result of FFT on the beat frequency signal, and the distance to the PIM generation point may also vary to the amount of the time delay of the PIM signal  176  from the PIM generation point, the PIM generation point can be estimated. 
       FIG. 7  is an exemplary view to illustrate a beat frequency difference according to the time delay between the reference signal  159  of  FIG. 2  and the PIM signal  176  of  FIG. 3 . 
     A signal illustrated in  FIG. 7  may correspond to an analog signal output obtained by inputting the reference signal  159  and the PIM signal  176  to the I/Q demodulator  180 , generating the beat frequency signal  181 , and making the beat frequency signal  181  pass through the LPF  182  and the signal level adjustor  184 . As shown in  FIG. 7 , since the time delay between the reference signal  159  and the PIM signal  176  (e.g. 25 ns) is not an integer multiple of 20 ns, the beat frequency difference may not be constant. That is, a signal according to a beat frequency difference of 2200 Hz may be repeatedly output during 5 ns periods, and a signal according to a beat frequency difference of 2100 Hz may be repeatedly output during 15 ns periods. In the case that the signal having such the beat frequency difference passes through the ADC  186 , and the FFT is performed on the signal in the signal processor  188 , an error may exist in the detected PIM signal generation point. For example, a beat frequency error up to 100 Hz (corresponding to a distance error of about 2 meters when the dielectric constant of the in-building feeder is assumed to be 1.5) may be generated. 
     In order to resolve the above-described problem, according to an exemplary embodiment of the present disclosure, the time delay module  160  may be located at the output end of the reference signal  159  (or, the output end of the PIM signal  176 ), and the time delay control module  165  may be configured to control the time delay of the reference signal  159  (or, the PIM signal  176 ) in unit of 1 ns. 
       FIG. 8  is an exemplary view to illustrate a wave form obtained by delaying the reference signal by 5 ns through the time delay module  160  according to an exemplary embodiment of the present disclosure. Also,  FIG. 9  is an exemplary view of beat frequency differences according to the time delay between the delayed reference signal of  FIG. 8  and the PIM signal generated at the feeder of  FIG. 3 . 
     As illustrated in  FIG. 8 , since the time delay between the reference signal  159  delayed by 5 ns and the PIM signal  176  (e.g. 20 ns) is an integer multiple of 20 ns, the beat frequency difference may be maintained constantly as 2100 Hz. Also, since the time delay of the reference signal may be controlled by the time delay control module  160  in unit of 1 ns, when FFT is performed on the output signal of the ADC  186  corresponding to the beat frequency difference, the detection accuracy of the PIM generation point may be remarkably enhanced to a level of 10 centimeter. As described above, if necessary, the time delay control module  160  may also be located between the I/Q demodulator  180  and the BPF  175 . The time delay control module  165  may generate a time delay control value for delaying the PIM signal  176  or the reference signal  159 . 
     Hereinafter, referring to a flow chart of  FIG. 10 , a PIM generation point detection procedure performed by a PIM generation point detection apparatus  200  according to an exemplary embodiment of the present disclosure will be explained in detail. 
       FIG. 10  is a flow chart to explain an operation of a PIM generation point detection apparatus according to an exemplary embodiment of the present disclosure. 
     First, the signal processor  188  of the PIM generation point detection apparatus  200  may perform a FFT signal processing on an output of the ADC  186  (S 1010 ). Here, the control part  190  may calculate K power values for K (K is a natural number) respective unit frequency bands, and store them in a storage means such as a memory (S 1020 ). For reference, in the case illustrated in  FIG. 9 , a width of each unit frequency band may be 100 Hz, the number of unit frequency bands may be 50, and a time delay for each unit frequency band may be 20 ns. The unit frequency bands can be illustrated in  FIG. 11 , and the power value for respective unit frequency bands P B(k)  may be represented as the following equation 1.
 
P B(k) , k=1,2, . . . , K  [Equation 1]
 
     Then, the control part  190  may check whether the respective P B(k)  is not less than a first threshold Th 1  sequentially from k=1 (S 1030 , S 1040 ). If the P B(k)  is less than Th 1 , the k is increased (S 1035 ) and the step S 1040  is repeated. IF the P B(k)  is not less than Th 1 , the next step S 1045  may be performed. 
     The control part  190  may generate a control command instructing the time delay control module  167  to generate a time delay amount control value  166 . Accordingly, the time delay module  165  may perform scanning to delay the reference signal  159  (or, the PIM signal  176 ) by Δ (e.g. 1 ns) for i=1, 2, . . . , M−1 (here, Δ=1/M, and M is a natural number) by controlling delay elements at the corresponding k, and the control part  190  may calculate respective power values (P B(k−Δ*i)  (i=1,2, . . . , M−1) at i-th sub-unit which is sequentially scanned at the corresponding k-th unit frequency band for the FFT result of the signal processor  188 , and temporarily store the result values in the storage means such as memory. Then, the control part  190  may check whether the following equation 2 is satisfied or not based on a second threshold Th 2  (S 1050 ). 
     
       
         
           
             
               
                 
                   
                     
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     If the above equation is satisfied, the control part  190  may store the corresponding k and i in the storage means (S 1055 ). On the contrary, the control part  190  may directly perform the step S 1060  without storing the values. 
     Then, the control part  190  may check whether k is K (S 1060 ). If k is not K, the control part  190  may increase k by 1 (S 1035 ), and repeat the steps S 1040  to S 1060 . If k is K, the control part  190  may detect a PIM generation point from the k and i stored in the storage means (S 1070 ), and finalize the PIM generation point detection procedure. That is, even after k and is are found out, k and i may be updated while it is checked whether the equation 2 is satisfied for the rest of unit frequency bands up to K-th unit frequency band belonging to the total frequency band. Then, the PIM generation point may be calculated based on the final k and i. The case that the k and i are updated may be understood as a case that the time delay of the reference signal  159  and the PIM signal  176  exists and a beat frequency difference exists as illustrated in  FIG. 7 . 
     The control part  190  may use a predetermined function or a lookup table, which may be a basis for calculation of a PIM generation point based on a beat frequency of the beat frequency signal  187  as shown in  FIG. 6 , to calculate a PIM generation distance corresponding to i at the stored k, and output information on a PIM generation point. Such the calculation of the PIM generation point is using the principle that the PIM signal level to the PIM generation point may vary according to a result of FFT on the beat frequency signal, and the distance to the PIM generation point may also vary according to the amount of the time delay of the PIM signal  176  from the PIM generation point. For this, the beat frequency difference according to the FFT result may be checked, and a fine scanning power value (a power value at i) for a unit frequency band k of the beat frequency having a power not less than Th 1  may be calculated based on the power value of FFT result as represented in the equation 2, and thus the detection accuracy of the PIM generation point can be enhanced. 
     Through utilization of the suggested time delay module, the PIM reference signal  159  (or, the PIM signal  176 ) can be controlled so that the detection performance of the PIM generation point in the in-building feeder  140  can be remarkably enhanced. 
     As described above, in the PIM generation point detection apparatus  200  according to the present disclosure, the time delay module  160  is introduced in the output end of the reference signal  159  (or, the PIM signal), and thus the reference signal can be controlled so that the detection accuracy of the PIM generation point can be enhanced up to a level of 10 centimeters. Also, since the detection accuracy of the PIM generation point is remarkably enhanced, the time required to replace or repair the disfunctional element causing the PIM signal can be reduced and thus maintenance cost for the in-building feeder network can be decreased. Also, the mobile service range or the efficiency of telephone connection can be enhanced by rapidly resolving the problem caused by the PIM. 
     While the present disclosure has been shown and described with reference to various embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present disclosure as defined by the appended claims and their equivalents. 
     Accordingly, the exemplary embodiments disclosed herein are not intended to limit the technical spirit but describe the technical spirit of the present disclosure, and the scope of the technical spirit of the present disclosure is not limited by the exemplary embodiment. The scope of the present disclosure should be construed based on the following appended claims and it should be appreciated that the technical spirit included within the scope equivalent to the claims belongs to the scope of the present disclosure.