JP6217247B2 - Multipath determination device - Google Patents

Description

  The present invention relates to a multipath determination device that determines the presence or absence of multipath occurrence during propagation of received radio waves.

  2. Description of the Related Art Conventionally, a technique for determining the presence or absence of multipath when a received radio wave (for example, radio radio wave) is propagated is known. For example, Patent Document 1 describes a receiver used for an in-vehicle radio receiver or the like. In this receiver, the occurrence of multipath is detected based on at least one of an audio signal and a received signal level. Specifically, when it is detected that the intermediate frequency signal includes a pulsed noise component of a predetermined level or higher, it is determined that multipath has occurred.

JP-A-8-79109

  However, in the conventional technique, a threshold value for determining whether or not multipath occurs is determined in advance. Therefore, the predetermined threshold value does not correspond to the fluctuation of the electric field at the time of reception, and it is not possible to appropriately determine whether or not multipath occurs in a reception environment where the electric field fluctuates.

  Therefore, an object of the present invention is to provide a multipath determination device that can appropriately determine the presence or absence of multipath even in a reception environment where the electric field varies.

  In order to achieve the above object, a first aspect according to the present invention is a multipath determination device that determines whether or not a multipath has occurred during propagation of a received radio wave, and is obtained by detecting the received radio wave. The maximum value of power in a predetermined frequency range of all or part of the input signal in the predetermined frequency range is the upper limit value, and the average value of power in the predetermined frequency range of all or part of the input signal is the reference value As a threshold setting unit for setting a threshold for determination, and by evaluating the power level of the determination interval of the input signal using the threshold for determination, whether or not the determination interval is a time interval in which multipath occurs And a determination unit for determining whether or not.

  In the first aspect of the present invention, determination of the presence / absence of multipath using the maximum value of power in all or part of the time interval of the input signal as an upper limit value and the average value of the power as a reference value The threshold value for determination used for is set. The maximum value and the average value of power change according to the fluctuation of the electric field at the time of reception. Therefore, the threshold for determination also changes according to the fluctuation of the electric field at the time of reception. Therefore, since the threshold for determination is a value corresponding to the fluctuation of the electric field at the time of reception, it is possible to appropriately determine whether or not multipath has occurred even in a reception environment where the electric field fluctuates.

Schematic configuration diagram of a radio evaluation system using a multipath determination device according to an embodiment Flow chart showing multipath determination method

  Hereinafter, embodiments will be described in detail with reference to FIGS. 1 and 2.

[1. About Radio Evaluation System]
First, the radio evaluation system 10 using the multipath determination device 20 according to the present embodiment will be described. As shown in FIG. 1, the radio evaluation system 10 includes a high-frequency signal generator 11 that outputs a high-frequency signal modulated by an audio signal, and a radio that receives the high-frequency signal from the high-frequency signal generator 11 and detects the audio signal. 12 and a multipath determination device 20 that performs multipath determination to be described later based on an audio signal detected by the radio 12. The radio 12 is an in-vehicle radio mounted on a vehicle, for example. In the radio evaluation system 10, a cable connected to the output terminal of the high-frequency signal generator 11 is connected to the antenna terminal of the radio 12 via a pseudo antenna (not shown).

[2. About Multipath Judgment Device]
Next, the multipath determination device 20 will be described.

  The multipath determination device 20 divides an audio signal detected by the radio 12 into a plurality of frames (time intervals), and determines the presence or absence of multipath generation during radio wave propagation for each frame. Make a decision. As illustrated in FIG. 1, the multipath determination device 20 includes a sound collection unit 21, a frequency analysis unit 22, a threshold setting unit 23, and a determination unit 24. The sound collection unit 21 records an audio signal (time-series digital signal) output from the radio 12. The frequency analysis unit 22 performs frequency analysis on the audio signal recorded in the sound collection unit 21 using FFT (Fast Fourier Transform) or the like. The frequency analysis unit 22 divides the audio signal recorded in the sound collection unit 21 into a plurality of frames, performs frequency analysis on the audio signal of each frame, and frequency characteristics of the intensity of the audio signal for each frame. A power spectrum representing is output.

  The threshold setting unit 23 sets a first threshold and a second threshold as determination thresholds used for multipath determination. The threshold setting unit 23 sets the maximum value of power in a predetermined frequency range of the entire period (all frames) of the audio signal as an upper limit value, and averages the power in the predetermined frequency range of the entire period (all frames) of the audio signal. Is used as a reference value to set a first threshold. Specifically, the threshold setting unit 23 sets the maximum value of power in the entire frequency band of the power spectrum of all frames (all frequency bands in which the power spectrum is calculated) to 100%, and the power in all frequency bands of the power spectrum of all frames. When the average value is expressed as a percentage reference value (for example, 0% or 50%), the magnitude of power corresponding to the first set value (for example, 70%) expressed in percentage is set as the first threshold value. Set. That is, the threshold setting unit 23 expresses the maximum value and the average value of power in all frequency bands of the power spectrum of all frames as a percentage, and sets the first threshold as a percentage. The first threshold value is set to a value obtained by apportioning a predetermined ratio between the maximum value of power and the average value of power in all frequency bands of the power spectrum of all frames. The first threshold is set using the maximum value and the average value of power as reference values.

  Further, the threshold setting unit 23 sets the maximum value of power in a predetermined frequency range of all primary candidate frames (described later) as an upper limit value, and uses the average value of power in the predetermined frequency range of all primary candidate frames as a reference. A second threshold is set using the value. Specifically, the threshold value setting unit 23 sets the maximum power value in the high frequency band (for example, a band of 10 kHz to 14 kHz) of the power spectrum of all primary candidate frames to 100%, and the power spectrum of all primary candidate frames. When the average value of power in the high frequency band is expressed as a percentage reference value (for example, 0% or 50%), the magnitude of the power corresponding to the second set value (for example, 90%) expressed in percentage , Set to the second threshold. That is, the threshold value setting unit 23 expresses the maximum value and the average value of the power in the high frequency band of the power spectrum of all the primary candidate frames as a percentage, and sets the second threshold value as a percentage. The second threshold value is set to a value that is prorated by a predetermined ratio between the maximum power value and the average power value in the high frequency band of the power spectrum of all primary candidate frames. The second threshold is set using the maximum value and average value of power as reference values.

  The determination unit 24 performs, as multipath determination, a first determination that selects a primary candidate frame of a multipath frame from all frames, and a secondary of a multipath frame from the primary candidate frame selected by the first determination. A second determination for selecting a candidate frame and a third determination for finally detecting a multipath frame from the secondary candidate frames selected by the second determination are performed.

  In the first determination, each frame has a multipath occurrence time by evaluating the power levels of all frequency bands in each determination section using the first threshold value with each frame as a determination section. It is determined whether there is a possibility of a section.

  In the second determination, each of the primary candidate frames is used as a determination section, and the power level of the high frequency band of each determination section is evaluated using the second threshold value. It is determined whether or not there is a possibility that this is a time interval. In addition, this inventor discovered that when multipath generate | occur | produces, power exists even in a high frequency band in a power spectrum. The second determination is made based on this content. According to the second determination, the presence / absence of multipath can be accurately determined by evaluating the power level in the high frequency band.

  In the third determination, each secondary candidate frame is determined as a determination section, and the presence / absence of a cepstrum (a feature vector representing a human voice signal) is determined by cepstrum analysis. It is determined whether or not the path is a multipath frame. Here, as in the case of the occurrence of multipath, there is a “human voice” as an audio signal whose power exists in a high frequency band. In the third determination, cepstrum analysis is performed to distinguish between multipath and “human voice”.

[3. About multipath judgment method]
Next, a multipath determination method using the radio evaluation system 10 will be described with reference to the flowchart of FIG.

  First, in step S201, the high frequency signal generator 11 starts outputting a high frequency signal (a high frequency signal modulated by an audio signal). Next, in step S202, the radio 12 receives the high frequency signal output from the high frequency signal generator 11, and detects the audio signal. An audio signal is extracted from the high-frequency signal by the radio 12. Next, in step S <b> 203, the sound collection unit 21 of the multipath determination device 20 records the audio signal output from the radio 12. The high-frequency signal generator 11 continues to output a high-frequency signal over a predetermined measurement period while changing the output so that the reception environment in which the electric field fluctuates can be simulated. The radio 12 detects the audio signal over the measurement period. The sound collection unit 21 records the sound signal detected over the measurement period. Step S204 is performed after the end of the measurement period.

  In step S204, the frequency analysis unit 22 of the multipath determination device 20 performs frequency analysis on the audio signal recorded in the sound collection unit 21 using FFT (Fast Fourier Transform) or the like. The frequency analysis unit 22 divides the entire measurement period into a plurality of frames for the audio signal detected by the radio 12 and performs frequency analysis on the audio signal of each frame. By frequency analysis, a power spectrum representing the frequency characteristic of the strength of the audio signal is obtained for each frame.

In step S205, a primary candidate frame is selected. In the selection of the primary candidate frame, first, the threshold value setting unit 23 calculates the first threshold value T1 using Equation 1, for example.

  In Equation 1, MAX_Overall represents the maximum value of power in all frequency bands (Overall) of the power spectrum of all frames, and Ave_Overall represents the average value of power in all frequency bands of the power spectrum of all frames. X is a first setting value (for example, 70%), and is set in advance in the multipath determination device 20 or set by the user of the multipath determination device 20, for example. The first threshold value may be determined by the maximum power value in the determination section expressed as 100% and the average power value in all sections expressed as a percentage reference value (for example, 50%). This also applies to the second threshold value.

  In step S205, after the calculation of the first threshold T1, the determination unit 24 satisfies the first condition that, for each frame, the average value of the power in all frequency bands of the power spectrum in the frame exceeds the first threshold T1. It is determined whether or not to perform (first determination). By the first determination, a frame that satisfies the first condition is selected as a primary candidate frame of the multipath frame. In the first determination, a frame having a relatively high average power value in all frequency bands among all the frames is selected as a primary candidate frame. According to the first determination, since the presence of power is determined based on a relative value, a primary candidate frame can be appropriately selected even in a reception environment where the electric field varies.

In step S206, a secondary candidate frame is selected from the primary candidate frames selected by the first determination. In selecting a secondary candidate frame, first, the threshold value setting unit 23 calculates the second threshold value T2 using Equation 2, for example.

  In Equation 2, MAX_Band_PWR represents the maximum value of power in the high frequency band (for example, band of 10 kHz to 14 kHz) of the power spectrum of all primary candidate frames, and Ave_Band_PWR represents the power spectrum of all primary candidate frames. Represents the average power in the high frequency band. Y is a second setting value (for example, 90%), and is set in advance in the multipath determination device 20 or set by the user of the multipath determination device 20, for example.

  In step S206, after the calculation of the second threshold T2, the determination unit 24 says that the average value of the power in the high frequency band of the power spectrum in the primary candidate frame exceeds the second threshold T2 for each primary candidate frame. It is determined whether or not the second condition is satisfied (second determination). By the second determination, a frame that satisfies the second condition is selected as a secondary candidate frame of the multipath frame. In the second determination, a frame having a relatively high average power value in the high frequency band among all the primary candidate frames is selected as a secondary candidate frame. According to the second determination, since the presence of power is determined by a relative value, a secondary candidate frame can be appropriately selected even in a reception environment where the electric field varies.

  In step S207, cepstrum analysis is performed on each secondary candidate frame selected by the second determination, and the presence / absence of cepstrum (a feature vector representing a human voice signal) is determined (third). Judgment). The determination unit 24 determines whether or not the third condition “no cepstrum” is satisfied for each secondary candidate frame. By the third determination, a secondary candidate frame that satisfies the third condition is finally detected as a multipath frame (multipath section). That is, the determination unit 24 detects a frame that satisfies all of the first condition, the second condition, and the third condition as a multipath frame.

  In step S208, the ratio of the multipath section (multipath rate) in the entire measurement period is calculated. The multipath determination device 20 presents the multipath rate to the user by displaying the multipath rate on the screen. Thus, according to the multipath determination device 20, the degree of occurrence of multipath is quantified by a numerical value called a multipath rate.

[4. Effects of the embodiment]
In the present embodiment, the maximum value of the power in the entire time interval of the audio signal (or the time interval of a part of the primary candidate frames) is used as the upper limit value, and the average value of the power is used as the reference value. A threshold value for determination used for determining whether or not the occurrence of the occurrence of the error is set. The maximum value and the average value of the power of the audio signal change according to the fluctuation of the electric field at the time of reception. Therefore, the threshold for determination also changes according to the fluctuation of the electric field at the time of reception. Therefore, since the threshold for determination is a value corresponding to the fluctuation of the electric field at the time of reception, it is possible to appropriately determine whether or not multipath has occurred even in a reception environment where the electric field fluctuates.

  The present invention can be applied to a multipath determination device that determines the presence or absence of multipath generation during propagation of received radio waves.

DESCRIPTION OF SYMBOLS 10 Radio evaluation system 12 Radio 20 Multipath determination apparatus 23 Threshold setting part 24 Determination part

Claims (1)

A multipath determination device that determines whether or not a multipath has occurred during propagation of a received radio wave,
As the upper limit of the maximum value of the power in the entire frequency range of the total time between intervals of the input signal obtained by detecting the received electric wave, based on the average value of the power in the entire frequency range of the entire time interval of the input signal A first threshold value setting unit for setting a first threshold value corresponding to a predetermined first setting value as a value;
For each time interval of the input signal, it is determined whether or not the power average value in the entire frequency range of one time interval exceeds the first threshold, and the multipath indicates the time interval exceeding the first threshold. A first determination unit that is selected as a primary candidate time interval that may have occurred;
The maximum value of power in a predetermined high frequency range of all the primary candidate time intervals is set as an upper limit value, and the average value of power in the predetermined high frequency range of all the primary candidate time intervals is set as a reference value. A second threshold value setting unit for setting a second threshold value corresponding to the set value;
For each primary candidate time interval, it is determined whether the power average value in the high frequency range of one primary candidate time interval exceeds the second threshold, and the primary candidate that exceeds the second threshold A second determination unit that selects a time interval as a secondary candidate time interval in which multipath may have occurred;
A third determination unit that determines whether or not the secondary candidate time interval is a time interval in which a multipath has occurred by evaluating a power level of each of the secondary candidate time intervals ;
A multipath determination apparatus comprising:

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