JP2015119410A - Multipath determination device and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multipath determination device capable of appropriately determining whether a multipath is generated even under a reception environment where an electric field is varied.SOLUTION: An audio signal is acquired by detecting a received radio wave (steps S201-S203). Regarding each of a plurality of frames which are time domains in a part of the audio signal, inclination of power indicating a degree of power reduction with respect to increase of a frequency in a predetermined frequency component of a frame is calculated (steps S304 and S405). On the basis of whether the inclination of power in each frame is equal to or smaller than a predetermined threshold for determination, it is determined whether the multipath is generated in the plurality of frames (steps S406 and S307). This determination is implemented on all the frames within the audio signal (steps S308 and S310).

Description

  The present invention relates to a multipath determination device that determines the presence or absence of multipath generation during propagation of received radio waves, and a multipath determination method that is executed by the multipath determination device.

  Conventionally, multipaths that occur during propagation of R / F signals are detected using audio signals (audio signals) obtained by detecting radio wave signals (R / F signals) that have propagated through space. The technology to do 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. Patent Document 2 describes a receiver including an integration circuit that detects a multipath by integrating a control signal having a predetermined pulse width in order to ensure detection of multipath noise.

JP-A-8-79109 JP 63-164632 A

However, in the conventional technique described above, a threshold value for determining the presence / absence of multipath 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 the presence / absence of multipath in a reception environment where the electric field fluctuates.
Also, consider the case where the presence or absence of multipath generation is determined using a threshold for an audio signal having a large dynamic range. In this case, an audio signal having a large dynamic range has a small change in the audio signal due to the multipath even if the multipath occurs, and there is a possibility that the multipath is not properly determined by the threshold.

  Therefore, the present invention provides a multipath determination device capable of appropriately determining the presence or absence of multipath even in a reception environment where the electric field varies, and a multipath determination method executed by the multipath determination device. With the goal.

  In order to achieve the above object, a first aspect according to the present invention is a multipath determination device that determines the presence or absence of multipath generation when a received radio wave is propagated, and is obtained by detecting the received radio wave. For a frame that is a partial time interval of the audio signal, a calculation unit that calculates a power gradient indicating a degree of power decrease with respect to an increase in frequency in a predetermined frequency range, and a determination for which the power gradient of the frame is predetermined And a determination unit that determines whether or not a multipath has occurred in a frame based on whether or not the threshold is equal to or less than a threshold value.

  A second aspect according to the present invention is the multipath determination device according to the first aspect, wherein the determination unit obtains an average value of power gradients in at least two consecutive frames, and determines the power gradient. Based on whether or not the average value is equal to or less than a determination threshold, the presence or absence of multipath occurrence in at least two frames is determined.

  A third aspect according to the present invention is the multipath determination device according to the first and second aspects, wherein the determination unit sets a determination threshold based on the dynamic range of the audio signal.

  A fourth aspect according to the present invention is the multipath determination device according to the first to third aspects, wherein the determination unit determines whether or not multipath has occurred in each of all the frames of the audio signal. It is characterized in that a ratio of time when multipath occurs in an audio signal is obtained.

  Furthermore, a fifth aspect according to the present invention is a multipath determination method executed by an apparatus for determining the presence or absence of multipath generation when a received radio wave is propagated, wherein an audio signal is detected by detecting the received radio wave. A step of obtaining, a step of calculating a power gradient indicating a degree of power decrease with respect to an increase in frequency in a predetermined frequency range, and a power gradient of the frame are determined in advance for a frame that is a partial time interval of the audio signal. And determining whether or not a multipath has occurred in the frame based on whether or not the threshold is below the determination threshold.

According to the first aspect of the present invention, the power gradient indicating the degree of power reduction with respect to the increase in the frequency of the power spectrum is obtained for each frame of the audio signal, and is used to determine the presence or absence of multipath generation.
As a result, since the power gradient becomes 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.
In addition, since the presence / absence of multipath occurrence is sequentially determined in units of frames, it is possible to proceed with the determination processing for the presence / absence of multipath occurrence in a frame without waiting for all the audio signals to be received and detected. .

Further, according to the second aspect of the present invention, the power gradient to be compared with the determination threshold value used for determining the presence or absence of the occurrence of multipath is the average value of the power gradient in at least two consecutive frames.
As a result, it can be expected to appropriately determine a single frame that may not be properly determined whether or not multipath has occurred, such as when an extreme power change appears in the frame. Therefore, it is possible to improve the accuracy of the multipath rate obtained by the determination.

According to the third aspect of the present invention, the determination threshold is set based on the dynamic range of the audio signal.
As a result, it is possible to avoid as much as possible the situation in which the presence or absence of multipath is erroneously determined due to the size of the dynamic range of the audio signal. Thereby, the improvement of the precision of the multipath rate obtained by determination can be expected.

According to the fourth aspect of the present invention, the ratio of the time when multipath occurs in the audio signal is determined according to the presence / absence of multipath occurrence determined in each of all frames of the audio signal.
As a result, a more accurate multipath rate can be calculated.

Furthermore, according to the fifth aspect of the present invention, a power gradient indicating the degree of power reduction with respect to an increase in the frequency of the power spectrum is obtained for each frame of the audio signal, and used to determine the presence or absence of multipath occurrence. .
As a result, since the power gradient becomes 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.
In addition, since the presence / absence of multipath occurrence is sequentially determined in units of frames, it is possible to proceed with the determination processing for the presence / absence of multipath occurrence in a frame without waiting for all the audio signals to be received and detected. .

Schematic configuration diagram of a radio evaluation system using a multipath determination device related to all embodiments The flowchart which shows the process sequence of the multipath determination method which concerns on 1st Embodiment. The figure explaining an example of the idea of the multipath determination method which concerns on 1st Embodiment The figure explaining an example of the idea of the multipath determination method which concerns on 1st Embodiment The flowchart which shows the process sequence of the multipath determination method which concerns on 2nd Embodiment. The figure explaining an example of the idea of the multipath determination method which concerns on 2nd Embodiment The flowchart which shows the process sequence of the multipath determination method which concerns on 3rd Embodiment. The figure explaining an example of the idea of the multipath determination method which concerns on 3rd Embodiment The figure explaining an example of the idea of the multipath determination method which concerns on 3rd Embodiment The figure explaining an example of the idea of the multipath determination method which concerns on 3rd Embodiment

Hereinafter, a plurality of embodiments will be described in detail with reference to the drawings.
Prior to a description of a plurality of embodiments, a system configuration and an operation concept common to all the embodiments will be described.

[About radio evaluation system]
First, the radio evaluation system 10 that is a system using the multipath determination device 20 according to all the embodiments will be described.
As shown in FIG. 1, the radio evaluation system 10 includes a signal output device (R / F output device) 11, a radio 12, and a multipath determination device 20. The signal output device (R / F output device) 11 outputs an R / F signal as a test signal. The radio 12 receives the R / F signal from the signal output unit 11 and detects the audio signal. The radio 12 is, for example, an in-vehicle radio mounted on a vehicle, and includes an antenna and a tuner. The multipath determination device 20 performs multipath determination described later based on the audio signal detected by the radio 12.

The test signal is, for example, an R / F signal received in the field by a data acquisition radio (which may be the same as or different from the radio 12). That is, the test signal is an R / F signal received by the radio in the field while the vehicle equipped with the data acquisition radio is running. This test signal is a signal that has not been detected, that is, a signal before being input to the tuner. Typically, test signals are acquired in the field, for example over a predetermined period, and stored in memory. This memory is attached to the signal output unit 11, and the signal output unit 11 outputs a test signal stored in the memory. The test signal is affected by the multipath generated during propagation of the R / F signal (radio wave) received in the field by the radio for data acquisition. The audio signal obtained by detecting the test signal includes multipath noise.
Instead of inputting the R / F signal received in the field to the radio 12, the output signal from the signal output unit 11 may be input to the radio 12 via a pseudo antenna.

[About Multipath Judgment Device]
Next, the configuration of the multipath determination device 20 according to all the embodiments will be described.
The multipath determination device 20 uses the entire period of the time-series data of the audio signal input from the radio 12 as the target period, and the multipath generation period in which the multipath has occurred during propagation of the R / F signal in the field from the target period Determine. This determination is performed by dividing the audio signal into a plurality of frames (time intervals) and determining the presence / absence of multipath during radio wave propagation for each of the plurality of frames. Then, the multipath determination device 20 quantifies the ratio of the multipath generation period in the target period as the multipath ratio. The longer the total time of the multipath generation period, the greater the multipath rate.

  As shown 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 basic processing operation of these configurations is as follows. It is as follows.

  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 threshold setting unit 23 sets a determination threshold used for multipath determination based on the result of the frequency analysis performed by the frequency analysis unit 22. The determination unit 24 uses the determination threshold set by the threshold setting unit 23 to determine whether multipath has occurred in the audio signal.

In each embodiment described in this specification, in addition to the basic processing operation described above, the frequency analysis unit 22, the threshold setting unit 23, and the determination unit 24 perform further characteristic processing operations.
Hereinafter, further characteristic processing operations performed by the frequency analysis unit 22, the threshold setting unit 23, and the determination unit 24 will be described in detail for each embodiment.

<First Embodiment>
With reference to FIGS. 2 to 4 in addition to FIG. 1, the multipath determination device 20 according to the first embodiment will be described. FIG. 2 is a flowchart illustrating a processing procedure of a multipath determination method executed by the multipath determination apparatus 20 according to the first embodiment. 3 and 4 are diagrams for explaining an example of the concept of the multipath determination method according to the first embodiment.

[1-1. Issues and solution principles]
First, the problem and the principle for solving the problem will be described.
As described above, in the conventional method in which the threshold for determining the presence / absence of multipath is determined in advance, that is, in the conventional method for determining the presence / absence of multipath using the absolute threshold value, the electric field is Appropriate determination cannot be made under changing reception environments.
Therefore, in the first embodiment of the present disclosure, the presence or absence of multipath generation is determined using a threshold value that is a relative value. This threshold value, which is a relative value, is set using the maximum value and the average value of the power that fluctuates with the fluctuation of the electric field at the time of reception. Therefore, if a threshold value that is a relative value is used, it is possible to appropriately determine whether or not multipath has occurred even in a reception environment where the electric field fluctuates.
Further, in the first embodiment of the present disclosure, the magnitude of the power in the high frequency band is also based on the knowledge by the present inventor that when the multipath occurs, the power spectrum easily affects the power in the high frequency band. By paying attention and evaluating, the presence or absence of the occurrence of multipath is accurately determined.

[1-2. Configuration of multipath determination device]
The frequency analysis unit 22 of the first embodiment performs frequency analysis on the audio signal recorded in the sound collection unit 21 using FFT (Fast Fourier Transform) or the like.
Specifically, the frequency analysis unit 22 divides the audio signal recorded in the sound collection unit 21 into a plurality of frames (for example, one frame is 0.1 second) on the time axis. In the example shown in FIG. 3A, the entire period of the audio signal is divided into first to nth frames (n is an arbitrary integer). Then, the frequency analysis unit 22 performs frequency analysis on the audio signal in units of divided frames, and the power representing the frequency characteristic of the intensity of the audio signal for each of the plurality of frames (first to nth frames). A spectrum is output (see FIG. 3B). The vertical axis described in FIG. 3B represents the power magnitude of the power spectrum, and the unit is dBv.

  The power spectrum of each frame is created with a human audible range (for example, a band of 20 Hz to 14 kHz) as a target range. In the following description, the entire target range (human audible range) of the power spectrum is referred to as “all frequency band (Overall illustrated in FIG. 3B)”. Further, a high frequency band (for example, a frequency band of 10 kHz to 14 kHz) of the entire target range (human audible range) of the power spectrum is referred to as a “high frequency band (Band illustrated in FIG. 3B)”. The high frequency component of the audio signal is a frequency component belonging to the high frequency band.

The threshold setting unit 23 of the first embodiment sets a determination threshold used for multipath determination of an audio signal.
As a specific setting example 1, the threshold value setting unit 23 limits the maximum power value in a predetermined frequency range over the entire period of the audio signal (that is, all frames, the first to nth frames in the example of FIG. 3A). As a value, a threshold value for determination is set using an average value of power in a predetermined frequency range of all frames of the audio signal as a reference value. For example, the threshold setting unit 23 sets the maximum value of power in the entire frequency band (Overall) of the power spectrum of all frames of the audio signal to 100% and the average value of power in the entire frequency band (Overall) of the power spectrum of all frames. When expressed as a percentage reference value (for example, 0% or 50%), the magnitude of the power corresponding to the set value (for example, 70%) represented by the percentage is set as the determination threshold value (FIG. )). That is, the determination threshold value is set to a value obtained by dividing the maximum value of power and the average value of power in the entire frequency band (Overall) of the power spectrum of all frames at a predetermined ratio.

  As setting example 2, the threshold setting unit 23 sets the maximum power value in the high frequency range of the entire period of the audio signal (that is, all frames, the first to nth frames in the example of FIG. 3A) as the upper limit value. As described above, the determination threshold is set using the average value of power in the high frequency range of all frames of the audio signal as a reference value. For example, the threshold value setting unit 23 sets the maximum value of the power in the high frequency band (Band) of the power spectrum of all frames of the audio signal to 100% and the average value of the power in the high frequency band (Band) of the power spectrum of all frames as a percentage. When represented by a reference value (for example, 0% or 50%), the magnitude of power corresponding to a set value (for example, 90%) represented as a percentage is set as a threshold for determination (FIG. 4B). . That is, the determination threshold value is set to a value that is proportionally distributed between the maximum value of power and the average value of power in the high frequency band (Band) of the power spectrum of all frames.

  Further, as setting example 3 in which setting example 1 and setting example 2 are combined, the following method can be considered. The threshold value setting unit 23 according to the first embodiment first divides the maximum value of power and the average value of power in a predetermined ratio between all the frequency bands (Overall) of the power spectrum of all frames of the audio signal. Is determined as a first determination threshold value. A corresponding frame (candidate frame) is extracted from all frames based on the first determination threshold. Then, the threshold value setting unit 23 uses a value obtained by dividing the maximum value of the power in the high frequency band (Band) of the power spectrum and the average value of the power by a predetermined ratio with respect to the extracted candidate frame. Set as threshold.

The determination unit 24 according to the first embodiment uses the determination threshold set by the threshold setting unit 23 to determine the rate of occurrence of multipath in the audio signal.
Specifically, in the case of the determination threshold value according to the setting example 1, the determination unit 24 uses the determination threshold value for the entire frequency band (Overall) for each of all frames (first to nth frames) of the audio signal. It is determined whether there is a possibility that each frame is a frame (time interval) in which multipath occurs (determination example 1).

  In the case of the determination threshold value according to the setting example 2 described above, the determination unit 24 sets the power level of the high-frequency band (Band) using the determination threshold value for each of all frames (first to nth frames) of the audio signal. By evaluating, it is determined whether there is a possibility that each frame is a frame (time interval) in which multipath occurs (determination example 2).

  In the case of the determination threshold value according to the setting example 3 described above, the determination unit 24 uses the first determination threshold value for the entire frequency band (Overall) for each of all frames (first to nth frames) of the audio signal. By evaluating the power level, it is determined whether there is a possibility that each frame is a frame (time interval) in which multipath occurs, and first candidate frames are extracted. Then, the determination unit 24 evaluates the power level of the high frequency band (Band) using the second determination threshold for each of the extracted candidate frames, so that each candidate frame has a frame (time interval) in which multipath occurs. ) Is determined (determination example 3).

  Then, the determination unit 24 obtains the number of frames determined to have multipath, and determines that multipath has occurred for the entire period (all frames) of the audio signal as necessary. Find the percentage of frames.

  The determination methods according to the above determination examples 2 and 3 are newly discovered by the inventor of the present application, and when multipath occurs, the power is present in the high frequency band (Band) in the power spectrum. Based on. Thus, by evaluating the power level of the high frequency band (Band), it is possible to accurately determine the presence or absence of multipath.

  In any of the determination examples 1 to 3 described above, a cepstrum (Cepstrum) analysis is performed on a frame in which it is determined that multipath has occurred, and cepstrum (a feature vector representing a human voice signal) exists. Whether or not the target frame is a multipath frame in which a multipath has occurred may be determined by determining whether or not there is any. Here, as with the occurrence of multipath, there is a “human voice” as an audio signal having power up to the high frequency band (Band). The determination using the cepstrum analysis is further performed to distinguish between multipath and “human voice”.

[1-3. Multipath judgment method]
Next, with reference to the flowchart of FIG. 2, the multipath determination method executed by the multipath determination apparatus 20 according to the first embodiment using the radio evaluation system 10 is applied to the audio signal shown in FIG. A case will be described as an example.

First, in step S201, the signal output unit 11 of the multipath determination device 20 starts outputting an R / F signal modulated by an audio signal.
Next, in step S202, the radio 12 of the multipath determination device 20 receives the R / F signal output from the signal output unit 11, and detects the audio signal. The radio 12 extracts an audio signal from the R / F signal.
Next, in step S203, the sound signal output from the radio 12 is recorded by the sound collection unit 21 of the multipath determination device 20. The signal output unit 11 continues to output the R / F signal over a predetermined measurement period. 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 entire period that is the measurement period of the audio signal is divided into a plurality of frames, that is, the first to nth frames, and frequency analysis is performed on each of the divided audio signals of the first to nth frames. By this frequency analysis, a power spectrum representing the frequency characteristic of the strength of the audio signal is obtained for each of the first to nth frames.

In step S205, the threshold value for determination is calculated and set by the threshold value setting unit 23 of the multipath determination device 20.
The threshold for determination is set with the maximum power (MAX_Overall) in the entire frequency range (Overall) of the first to nth frames, which are all frames of the audio signal, as the upper limit, and the average power (Ave_Overall) as the reference value In the case of being set (the setting example 1 or 3 above), the determination threshold value T1 is obtained by the following formula [1]. The constant X is a set value (for example, 70%) of a percentage between the maximum value and the average value of power in the entire frequency range (Overall), and is set in advance in the multipath determination device 20, for example.
T1 = Ave_Overall + (X / 100) × (MAX_Overall−Ave_Overall) ... [1]

In addition, the threshold value for determination is set to the maximum value (MAX_Band_PWR) of power in all or part of the high-frequency band (Band) of the first to nth frames, which are all frames of the audio signal, and the average value of power (Ave_Band_PWR) ) Is set as a reference value (the above setting example 2 or 3), the determination threshold T2 is obtained by the following formula [2]. The constant Y is a set value (for example, 90%) of a percentage between the maximum value and the average value of power in the high frequency band (Band), and is set in advance in the multipath determination device 20, for example.
T2 = Ave_Band_PWR + (Y / 100) × (MAX_Band_PWR−Ave_Band_PWR) [2]

In step S206, the determination unit 24 of the multipath determination device 20 determines the presence or absence of multipath occurrence for a plurality of frames in the audio signal using the determination threshold.
When only the determination threshold value T1 is used, for each of the first to nth frames of the audio signal, there is a condition that the average power value of all frequency bands (Overall) of the power spectrum in the frame exceeds the determination threshold value T1. It is determined whether or not it is established. As a result of the determination, frames satisfying this condition (all or part of the first to nth frames) are selected as multipath frames. In this determination, a frame with a relatively high average value of power in all frequency bands (Overall) is selected as a multipath frame among the first to nth frames, which are all frames. A multipath frame can be appropriately selected even in an environment.

  When only the determination threshold value T2 is used, the condition that the average value of the power in the high frequency band of the power spectrum in the frame exceeds the determination threshold value T2 for each of the first to nth frames of the audio signal. Whether or not is established is determined. As a result of the determination, frames satisfying this condition (all or part of the first to nth frames) are selected as multipath frames. In this determination, a frame having a relatively high average power in the high frequency band (Band) among the first to nth frames, which are all frames, is selected as a multipath frame. A multipath frame can be appropriately selected even underneath.

  When both the determination thresholds T1 and T2 are used, first, for each of the first to nth frames of the audio signal, the average value of the power in the entire frequency band (Overall) of the power spectrum in the frame is determined. It is determined whether or not the first condition that T1 is exceeded is satisfied. As a result of the determination, a frame (all or a part of the first to nth frames) that satisfies the first condition is selected as a candidate frame. Next, for each of the candidate frames, it is determined whether or not the second condition that the average value of the power in the high frequency band (Band) of the power spectrum in the candidate frame exceeds the determination threshold value T2 is satisfied. As a result of the determination, a frame (all or a part of the candidate frames) that satisfies this second condition is selected as a multipath frame.

  In addition, when further considering the cepstrum, cepstrum analysis is performed on a frame that satisfies the second condition described above, and the presence or absence of the cepstrum is determined. Then, the frame determined as “no cepstrum” is finally selected as a multipath frame (multipath time section).

In step S207, the ratio of the multipath time interval (multipath frame) in the entire period (all frames) of the audio signal is calculated as the multipath rate. In the example of FIG. 3, the multipath frame is present in the first to nth frames in the entire period. For example, if there are m multipath frames, the multipath rate is “m / n”. .
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.

[1-4. Effects of the embodiment]
As described above, in the first embodiment, the maximum value of power in a candidate frame in the entire period (all frames) of the audio signal or a partial period of the audio signal is set as the upper limit value, and the average value of the power is used as a reference. As a value, a determination threshold value used for determining whether or not multipath has occurred 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 determination threshold value corresponds to the fluctuation of the electric field at the time of reception, the multipath determination device 20 according to the first embodiment appropriately determines whether or not multipath has occurred even in a reception environment where the electric field fluctuates. Can be determined.

<Second Embodiment>
A multipath determination device 20 according to the second embodiment used in the above-described radio evaluation system 10 will be described with reference to FIGS. 5 and 6 in addition to FIGS. FIG. 5 is a flowchart illustrating a processing procedure of a multipath determination method executed by the multipath determination apparatus 20 according to the second embodiment. FIG. 6 is a diagram for explaining an example of the concept of the multipath determination method according to the second embodiment.

[2-1. Issues and solution principles]
First, the problem and the principle for solving the problem will be described.
In the method described in the first embodiment, the determination threshold value is obtained from the maximum value and the average value of the power over the entire period (all frames) of the audio signal. For this reason, in the multipath determination process, the entire period (all frames) of the audio signal is recorded in the sound collection unit 21, and the presence / absence of the occurrence of multipath in each frame is not started until the frequency analysis of all frames is completed. Determination processing is started. Accordingly, it takes some time before the final multipath rate for the entire period of the audio signal is obtained.
Therefore, in the second embodiment of the present disclosure, the frequency analysis is sequentially performed on some frames without waiting for the entire period (all frames) of the audio signal to be recorded in the sound collection unit 21, and multipath Devise to proceed with the process of determining whether or not it has occurred.
Further, in the second embodiment of the present disclosure, attention is paid to the magnitude of the power in the high frequency band based on the knowledge by the inventor that the power spectrum easily affects the power in the high frequency band when multipath occurs. Thus, the presence or absence of multipath occurrence is accurately determined.

[2-2. Configuration of multipath determination device]
The frequency analysis unit 22 according to the second embodiment performs frequency analysis on the audio signal recorded in the sound collection unit 21 using FFT (Fast Fourier Transform) or the like.
Specifically, the frequency analysis unit 22 divides the audio signal recorded in the sound collection unit 21 into a plurality of frames (first to nth frames) on the time axis. Then, the frequency analysis unit 22 performs frequency analysis on the audio signal in units of divided frames, and the power representing the frequency characteristic of the intensity of the audio signal for each of the plurality of frames (first to nth frames). A spectrum is output (similar to FIG. 3B).

The threshold setting unit 23 of the second embodiment sets a determination threshold used for multipath determination of an audio signal in units of a plurality of frames (first to nth frames).
Specifically, for each of a plurality of frames (first to nth frames) of the audio signal, the threshold setting unit 23 sets the maximum power value in the high frequency range of the frame as an upper limit value, and sets the high frequency range of the frame. The determination thresholds are respectively set using the average value of the power at the reference value. For example, the threshold value setting unit 23 sets the maximum value of power in the high frequency band (Band) of the power spectrum of the frame to 100% and the average value of power in the high frequency band (Band) of the power spectrum of the frame as a reference value (for example, 0). % Or 50%), the magnitude of power corresponding to a set value (for example, 90%) expressed as a percentage is set as the determination threshold for this frame (see FIG. 4B). . That is, each determination threshold value is set to a value obtained by dividing the maximum value of power and the average value of power in a high frequency band (Band) of the power spectrum of the corresponding frame by a predetermined ratio.

The determination unit 24 of the second embodiment determines the presence / absence of multipath occurrence in each frame using the plurality of determination thresholds set by the threshold setting unit 23 for each of the plurality of frames. Then, the determination unit 24 obtains the ratio of occurrence of multipath in the entire period of the audio signal based on the result of presence / absence of multipath occurrence determined for each of the plurality of frames.
Specifically, for each of the first to nth frames of the audio signal, the determination unit 24 may use a determination threshold set for each frame and each frame may be a time interval in which multipath occurs. Each is determined whether or not there is. Then, the determination unit 24 obtains the number of frames determined to have multipath, and determines that multipath has occurred for the entire period (all frames) of the audio signal as necessary. Find the percentage of frames.

  Note that, as described above, the determination unit 24 performs cepstrum analysis on a frame in which it is determined that multipath has occurred, and determines whether or not a cepstrum exists, thereby generating multipath in the target frame. It may be determined whether or not it is a multipath frame.

[2-3. Multipath judgment method]
Next, a multipath determination method executed by the multipath determination apparatus 20 according to the second embodiment using the radio evaluation system 10 will be described with reference to the flowchart of FIG.
In the multipath determination method according to the second embodiment shown in FIG. 5, the same step numbers are assigned to the steps for performing the same processing as the multipath determination method according to the first embodiment. The description is omitted.

  In step S <b> 203, the sound signal received and output by the radio 12 is sequentially recorded by the sound collection unit 21 of the multipath determination device 20.

In step S304, every time an audio signal of a frame is recorded in the sound collection unit 21, the frequency analysis unit 22 of the multipath determination device 20 performs FFT (Fast Fourier Transform) or the like on the audio signal of the recorded frame. The frequency analysis of the frame is performed.
For example, when the first frame, which is the first frame of the audio signal, is recorded in the sound collection unit 21, the frequency analysis unit 22 performs frequency analysis on the audio signal of the first frame. By this frequency analysis, a power spectrum representing the frequency characteristic of the strength of the audio signal is obtained for the first frame.

In step S <b> 305, the threshold setting unit 23 of the multipath determination device 20 calculates and sets a determination threshold used for the frame for which the frequency analysis has been completed.
For example, the maximum value (MAX_Band_PWR) of power in the high frequency band (Band) of the first frame is set as an upper limit value, and the average value (Ave_Band_PWR) of power in the high frequency band (Band) of the first frame is set as a reference value. A determination threshold is set. As a specific example, the threshold value for frame determination is obtained by the above-described equation [2].

In step S306, the determination unit 24 of the multipath determination device 20 determines the presence / absence of multipath occurrence in one frame using a determination threshold set for the frame.
For example, it is determined whether or not the condition that the average value of the power in the high frequency band (Band) of the power spectrum in the first frame exceeds the determination threshold value in the first frame is satisfied. If this condition is satisfied, the first frame is determined as a multipath frame. In this determination, since a frame having a relatively high average power in the high frequency band (Band) is determined as a multipath frame, a multipath frame can be appropriately selected even in a reception environment where the electric field varies. .

  The multipath frame determination processing performed in steps S304 to S306 performed on the first frame is sequentially performed in steps S307 and S309 every time a sound signal having a time length corresponding to one frame is recorded in the sound collection unit 21. Repeatedly executed. With this process, multipath frame determination is performed in the first to nth frames corresponding to the entire period of the audio signal.

When multipath frames are determined in the first to nth frames, in step S308, the ratio of the multipath time interval (number of multipath frames) in the entire period of the audio signal (first to nth frames) Calculated as pass rate.
For example, if there are m multipath frames among the first to nth frames, the multipath rate of the entire period of the audio signal is “m / n”.
The multipath determination device 20 presents the multipath rate to the user by displaying the multipath rate of the entire period of the audio signal 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.

In the above-described embodiment, the frames are divided and set so as not to have overlapping time sections, but the frames may be set to have overlapping sections in time. For example, FIG. 6 shows a case where a plurality of frames that divide the entire period of the audio signal are set by overlapping 50% of the frames.
In this way, if the frames are set so as to overlap in time, the same time interval is used for the determination twice or more, and a more accurate multipath rate in the audio signal can be calculated.

[2-4. Effects of the embodiment]
As described above, in the second embodiment, the entire period of the audio signal is divided into a plurality of frames, and the presence / absence of multipath is generated using the maximum value and the average value of the power of the audio signal as reference values in this frame unit. The determination threshold value used for the determination is set. Therefore, since the threshold for determination changes according to the fluctuation of the electric field at the time of reception together with the maximum value and the average value of the power, the multipath determination device 20 according to the second embodiment is in a reception environment where the electric field fluctuates. In addition, it is possible to appropriately determine the presence or absence of multipath.
In the second embodiment, the entire period of the audio signal is divided into a plurality of frames, and the presence / absence of multipath generation is sequentially determined in units of frames. It is possible to proceed with the determination processing for the presence or absence of the occurrence of multipath in each frame without waiting for the data to be recorded.

<Third Embodiment>
With reference to FIGS. 7 to 10 in addition to FIGS. 1 and 3, a multipath determination device 20 according to the third embodiment used in the above-described radio evaluation system 10 will be described. FIG. 7 is a flowchart illustrating a processing procedure of a multipath determination method executed by the multipath determination apparatus 20 according to the third embodiment. 8 to 10 are diagrams for explaining the concept of the multipath determination method according to the third embodiment.

[3-1. Issues and solution principles]
First, the problem and the principle for solving the problem will be described.
In the method described in the second embodiment, a determination threshold value obtained from the maximum power value and the average power value in the high frequency band of the power spectrum of the frame is used (see FIG. 4). However, when such a determination threshold is used, an audio signal having a large dynamic range (FIG. 10A) or the like has a small change in the audio signal due to the multipath even if the multipath occurs. If a multipath has occurred, there is a risk that it will not be properly determined (FIG. 10B). Such a multipath misjudgment leads to a decrease in the accuracy of the multipath rate.
Therefore, in the third embodiment of the present disclosure, when multipath occurs, the power spectrum easily affects the power in the high frequency band, and when multipath occurs, multipath does not occur. Compared with the knowledge of the present inventor that the degree of power decrease with respect to the increase in frequency is small ((b) and (d) with respect to (b) and (c) in FIG. 10), the power with respect to the increase in frequency An embodiment will be described in which the degree of decrease is used for determination to reduce the occurrence of erroneous multipath determination and improve the accuracy of the multipath rate.

[3-2. Configuration of multipath determination device]
The frequency analysis unit 22 of the third embodiment performs frequency analysis on the audio signal recorded in the sound collection unit 21 using FFT (Fast Fourier Transform) or the like.
Specifically, the frequency analysis unit 22 divides the audio signal recorded in the sound collection unit 21 into a plurality of frames (first to nth frames) on the time axis, as in the second embodiment. Then, the frequency analysis unit 22 performs frequency analysis on the audio signal in units of divided frames, and the power representing the frequency characteristic of the intensity of the audio signal for each of the plurality of frames (first to nth frames). A spectrum is output (similar to FIG. 3B).

The threshold value setting unit 23 of the third embodiment sets a determination threshold value used for multipath determination of an audio signal in each of a plurality of frames (first to nth frames).
This threshold for determination is a value that is compared with a power gradient indicating the degree of power decrease with respect to an increase in frequency in a power spectrum, which will be described later, and is based on, for example, the characteristics (power spectrum) of an audio signal that is a test signal. It is arbitrarily set in advance. As described above, when multipath occurs, the amount of power decrease with respect to the increase in frequency is small compared to when multipath does not occur, in other words, the characteristic that the power gradient is small. However, even if multipath occurs, the power gradient varies depending on the dynamic range of the audio signal (see FIG. 10). Therefore, it is desirable that the determination threshold value is set to be larger as the dynamic range is larger in consideration of the dynamic range of the audio signal (all periods).

The determination unit 24 of the third embodiment first determines the frequency of the power spectrum in each frame based on the power spectrum of a plurality of frames (first to nth frames) obtained by frequency analysis by the frequency analysis unit 22. A power gradient indicating the degree of power decrease with respect to the increase is calculated.
Specifically, the determination unit 24 calculates the power gradient in the entire frequency band (Overall) of the power spectrum of each frame for each of the first to nth frames of the audio signal (FIG. 8). The slope of this power is calculated using, for example, a well-known linear prediction method, or is calculated from the slope of a linear line passing through the maximum value of power on the low frequency side and the maximum value of power on the high frequency side, May be.

Alternatively, the determination unit 24 may obtain an average value of the power gradient obtained from several (at least two) consecutive frames. For example, assuming that the power gradients calculated in k consecutive frames are a1, a2,..., Ak, the average value AVE of the power gradients in k frames is obtained by the following equation [3]. .
AVE = (a1 + a2 + ... + ak) / k ... [3]

  In this way, if the average value of the power gradient obtained in several consecutive frames is used, advantageous effects can be obtained in the following points. First, with the power gradient of a single frame, when an extreme power change appears in the single frame, there is a possibility that the presence or absence of multipath generation cannot be properly determined. If the average value is used, the accuracy of determination can be improved. On the other hand, if there are too many frames for obtaining the average value of the power gradient, the frame in which multipath is generated is buried and hardly appears in the average value, and there is a possibility that the presence or absence of multipath cannot be determined appropriately. The accuracy of determination can be improved by using the average value of the gradient of the optimum number of powers.

The number of consecutive frames for obtaining the average value of the power gradient may be determined by the number of seconds in each frame or the number n of all frames. FIG. 9 shows an image example of the change transition of the average value of the calculated power gradient with respect to the number of consecutive frames. In FIG. 9, if the number of consecutive frames is x to y, the average value of the power gradient of the frame falls below the determination threshold set by the threshold setting unit 23, and a frame (time interval) in which multipath occurs ) Is shown as an example.
It should be noted that instead of the average value of the power gradient of consecutive frames, it is also possible to use a change amount (total or average) of the power gradient of consecutive frames.

Next, the determination unit 24 uses the power gradient indicating the degree of power decrease with respect to the calculated frequency increase and the determination threshold set by the threshold setting unit 23 to generate multipath in a plurality of frames. Each is determined. Then, the determination unit 24 obtains the ratio of occurrence of multipath in the entire period of the audio signal based on the result of presence / absence of multipath occurrence determined for each of the plurality of frames.
Specifically, the determination unit 24 calculates the power gradient calculated for each of the first to nth frames of the audio signal, or the average value (or change) of the power gradient calculated for several consecutive frame units. It is determined whether each frame is likely to be a time interval in which multipath occurs, by evaluating whether the amount) exceeds the determination threshold. Then, the determination unit 24 obtains the number of frames determined to have multipath, and determines that multipath has occurred for the entire period (all frames) of the audio signal as necessary. Find the percentage of frames.

  Note that, as described above, the determination unit 24 performs cepstrum analysis on a frame in which it is determined that multipath has occurred, and determines whether or not a cepstrum exists, thereby generating multipath in the target frame. It may be determined whether or not it is a multipath frame.

[3-3. Multipath judgment method]
Next, a multipath determination method executed by the multipath determination apparatus 20 according to the third embodiment using the radio evaluation system 10 will be described with reference to the flowchart of FIG.
In the multipath determination method according to the third embodiment shown in FIG. 7, the same step numbers are used for the steps for performing the same processing as in the multipath determination methods according to the first and second embodiments. A description thereof will be omitted.

  In step S <b> 404, the threshold setting unit 23 of the multipath determination device 20 obtains a determination threshold used in the entire period (all frames) of the audio signal.

In step S304, every time an audio signal of one frame is recorded in the sound collection unit 21, the frequency analysis unit 22 of the multipath determination device 20 performs FFT (fast Fourier transform) on the recorded audio signal of one frame. The frequency analysis of the frame is performed using the conversion.
For example, when the first frame, which is the first frame of the audio signal, is recorded in the sound collection unit 21, the frequency analysis unit 22 performs frequency analysis on the audio signal of the first frame. By this frequency analysis, a power spectrum representing the frequency characteristic of the strength of the audio signal is obtained for the first frame.

In step S405, the determination unit 24 of the multipath determination device 20 calculates a power gradient indicating the degree of power decrease with respect to an increase in frequency in the entire frequency band (Overall) of the power spectrum for one frame.
For example, the power gradient in the entire frequency band (Overall) is calculated for the first frame of the audio signal.

In step S406, the determination unit 24 of the multipath determination device 20 determines the presence / absence of multipath occurrence in one frame using the power gradient and the determination threshold calculated for the frame.
For example, it is determined whether or not a condition that the power gradient in the first frame exceeds the determination threshold is satisfied. If this condition is satisfied, the first frame is determined as a multipath frame. In this determination, a frame having a relatively high power in the high frequency band (Band) is determined as a multipath frame, so that a multipath frame can be appropriately selected even in a reception environment where the electric field varies.

The multipath frame determination processing performed in steps S304, S405, and S406 performed on the first frame is performed every time a sound signal having a time length corresponding to one frame is recorded in the sound collection unit 21. The process is repeatedly executed sequentially by S309. With this process, multipath frame determination is performed in the first to nth frames corresponding to the entire period of the audio signal.
The method of calculating the ratio of the multipath time interval (the number of multipath frames) in the entire period of the audio signal from the determination results of the multipath frames in the first to nth frames is the same as in the second embodiment. Yes (step S308).

  In addition, there is a section that overlaps in time in the method of presenting the multipath rate that quantifies the rate of multipath occurrence in the audio signal to the user on the screen or the frame for calculating the power slope of the power spectrum. The use of a frame is the same as in the second embodiment.

[3-4. Effects of the embodiment]
As described above, in the third embodiment, the entire period of the audio signal is divided into a plurality of frames, and the power gradient indicating the degree of power decrease with respect to the increase in the frequency of the power spectrum is obtained for each frame, Used to determine whether a pass has occurred. Since the power spectrum changes according to the fluctuation of the electric field at the time of reception, the multipath determination device 20 according to the third embodiment appropriately determines the presence / absence of multipath generation even in a reception environment where the electric field fluctuates. Can do.
In the third embodiment, the entire period of the audio signal is divided into a plurality of frames, and the presence / absence of multipath generation is sequentially determined in units of frames. It is possible to proceed with the determination processing for the presence or absence of the occurrence of multipath in each frame without waiting for the data to be recorded.
Furthermore, since the power gradient in the power spectrum of the audio signal is determined, it is possible to avoid as much as possible the situation in which the presence or absence of multipath is erroneously determined due to the size of the dynamic range of the audio signal. This improves the accuracy of the multipath rate obtained by the determination.

  Each function of the multipath determination device 20 according to the first to third embodiments may be realized by interpreting and executing predetermined program data capable of executing the above-described processing procedure by the CPU. . In this case, the program data may be stored in a storage device (ROM, RAM, hard disk, etc.) via a recording medium, or may be directly executed from the recording medium. Here, the recording medium refers to a recording medium such as a semiconductor memory such as a ROM, a RAM, or a flash memory, a magnetic disk memory such as a flexible disk or a hard disk, an optical disk such as a CD-ROM, DVD, or BD, or a memory card. The recording medium is a concept including a communication medium such as a telephone line or a conveyance path.

  The present invention is applicable 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 11 Signal output device 12 Radio 20 Multipath determination apparatus 21 Sound collection part 22 Frequency analysis part 23 Threshold setting part 24 Determination part

Claims (5)

A multipath determination device that determines the presence or absence of multipath occurrence during propagation of received radio waves,
A calculation unit that calculates a power gradient indicating a degree of power decrease with respect to an increase in frequency in a predetermined frequency range for a frame that is a partial time interval of an audio signal obtained by detecting received radio waves;
A multipath determination device, comprising: a determination unit configured to determine whether or not the multipath has occurred in the frame based on whether the power gradient of the frame is equal to or less than a predetermined determination threshold. .   The determination unit obtains an average value of the power gradient in at least two consecutive frames, and determines the multi-value in the at least two frames based on whether the average value of the power gradient is equal to or less than the determination threshold. The multipath determination apparatus according to claim 1, wherein presence / absence of path generation is determined.   The multipath determination device according to claim 1, wherein the determination unit sets the determination threshold based on a dynamic range of the audio signal.   The said determination part calculates | requires the ratio of the time when the multipath generate | occur | produced in the said audio | voice signal according to the presence or absence of the multipath generation | occurrence | production determined in each of all the frames of the said audio | voice signal. The multipath determination device according to any one of the above. A multipath determination method executed by a device that determines the presence or absence of multipath occurrence during propagation of received radio waves,
Obtaining an audio signal by detecting received radio waves;
Calculating a power gradient indicating a degree of power decrease with respect to an increase in frequency in a predetermined frequency range for a frame that is a partial time interval of the audio signal;
And determining whether or not multipath has occurred in the frame based on whether or not the power gradient of the frame is equal to or less than a predetermined threshold for determination.

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