JP3655565B2 - Ghost detection method and ghost detection device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a ghost detection method and a ghost detection device having a ghost detection function for detecting a reflected wave (ghost) in evaluation of digital signal transmission path characteristics in the fields of digital television broadcasting and digital communication.
[0002]
[Prior art]
Conventionally, measurement of a delay profile is indispensable for measuring a radio wave propagation state. Regarding the measurement of the delay profile, for example, the delay profile measurement device disclosed in Japanese Patent Application Laid-Open No. 2000-115087, and the delay profile for digital terrestrial broadcasting are described on pages 33-34 of the 1999 Video Information Media Society Annual Conference. Measuring devices are known. In these delay profile measurement apparatuses, the delay profile measurement results (delay profile data) are displayed on the monitor of the measurement apparatus or stored in the storage means, and are confirmed by visual inspection by the user.
[0003]
In particular, the terrestrial digital broadcasting system in Japan employs the OFDM (Orthogonal Frequency Division Multiplex) system, and this terrestrial digital broadcasting demodulator requires measurement of the delay profile. It has become indispensable. For example, Japanese Patent Laid-Open No. 10-224319 discloses an OFDM synchronous demodulator for digital broadcasting using the OFDM method.
[0004]
FIG. 9 is a block diagram showing an example of a conventional OFDM synchronous demodulator disclosed in JP-A-10-224319. A conventional OFDM synchronous demodulator includes an input terminal 11, a clock oscillation circuit 12, an A / D conversion circuit 13, a symbol extraction circuit 14, a DFT circuit 16, a symbol window control circuit 17, a delay circuit 18, a correlation circuit 19, and a window signal generation. The circuit 20 includes a clock circuit 21, a clock control circuit 22, an LPF circuit 23, and a D / A conversion circuit 24.
[0005]
In the conventional OFDM synchronous demodulator shown in FIG. 9, the A / D conversion circuit 13 discretely samples the baseband OFDM signal according to the clock signal from the clock oscillation circuit 12, and the symbol extraction circuit 14 outputs the signal from the window signal generation circuit 20. The signal data of the effective symbol period is extracted from the sampled data according to the symbol window signal, and the DFT (Discrete Fourier Transform) circuit 16 performs discrete Fourier transform on the signal data from the symbol extraction circuit 14 to obtain demodulated data. When demodulating an OFDM signal for terrestrial digital broadcasting, a delay profile detection unit that receives the demodulated data is provided, and the delay profile data is displayed on the monitor of the measuring instrument to measure the ghost. Has been done.
[0006]
Also, according to the terrestrial digital broadcasting system, the delay profile data uses FFT (Fast Fourier Transform) sampling frequency and bandwidth,
P = {sin (5.575 / 8.1269) T ・ π} / {(5.575 / 8.1269) T ・ π}… (2)
Can be expressed as However, since the delay profile data is actually converted into power and output in the common logarithm, taking the log of equation (2),
L = 20logP = 20log [{sin (5.575 / 8.1269) T · π} / {(5.575 / 8.1269) T · π}]… (3)
(Where T is a point (integer)).
[0007]
FIG. 5 is a graph showing an example of general delay profile data represented by the above equation (3). The vertical axis represents level (dB), and the horizontal axis represents delay time T. When ghost (noise) exists, a local maximum point other than the local maximum point at the main wave position f ₀ appears on the graph shown in FIG. The maximum point due to the ghost is confirmed by visual observation of a graph displayed on the monitor, for example, and the ghost is detected.
[0008]
[Problems to be solved by the invention]
However, in the conventional digital signal processing apparatus, the ghost detection is finally performed by visually observing the graph displayed on the monitor, and there is a problem that the accuracy of the ghost detection is poor. The output delay profile data includes a component with a constant period (a waveform with a short period appearing on the main waveform, hereinafter referred to as internal processing variation) generated by the power conversion equation (3). Since it is difficult to distinguish between a local maximum point and a local maximum point due to internal processing variation, there is a problem in that a ghost cannot be automatically detected accurately.
[0009]
In order to solve the above problem, the present invention can automatically detect a ghost delay amount, a ghost level, and the like accurately, and is generated by a power conversion formula as shown in the above formula (3) in the delay profile data. An object of the present invention is to provide a ghost detection method and a ghost detection device that eliminates internal processing fluctuations and improves the accuracy of ghost detection.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, a ghost detection method of the present invention is a ghost detection method for detecting the ghost from delay profile data including characteristics of a main wave and a ghost of a received radio wave,
An approximation step of approximating the signal waveform of the delay profile data with an envelope to generate envelope data;
A comparison step of comparing the signal waveform of the delay profile data with the envelope data;
A determination step of determining that a section where the signal waveform of the delay profile data is larger than the envelope data is a ghost presence data section where the ghost exists.
With this configuration, it is possible to detect the presence of a ghost by deleting internal processing fluctuations in the waveform generated during power conversion and detecting data above the envelope.
[0011]
The ghost detection method of the present invention is a ghost detection method for detecting a ghost from a received radio wave,
Demodulating a digital signal in the received radio wave and generating a demodulated signal;
A detection step of converting the generated demodulated signal into a frequency domain and converting it into demodulated data;
A delay profile data detecting step for detecting delay profile data describing characteristics of a main wave and a ghost of the radio wave using pilot synchronization extracted in the detection step;
An approximation step of approximating the signal waveform of the delay profile data with an envelope to generate envelope data;
A comparison step of comparing the signal waveform of the delay profile data with the envelope data;
A determination step of determining that a section where the signal waveform of the delay profile data is larger than the envelope data is a ghost presence data section where the ghost exists.
With this configuration, it is possible to detect the presence of a ghost by deleting internal processing fluctuations in the waveform generated during power conversion and detecting data above the envelope.
[0012]
In addition, the ghost detection method of the present invention is a ghost detection method according to claim 1 or 2, further comprising a data correction step of correcting the levels of the delay profile data and the envelope data.
With this configuration, it is possible to easily and accurately detect the presence of a ghost by performing a comparison process between the level-corrected envelope data and the delay profile data.
[0013]
Further, the ghost detection method of the present invention is the ghost detection method according to any one of claims 1 to 3, wherein the delay profile data is further removed in order to remove a local maximum value due to an internal processing variation of the delay profile data. A representative data replacement step of replacing predetermined data existing in the ghost presence data section with predetermined representative data;
And a second determination step of determining that the maximum value existing in the ghost presence data section is the ghost.
With this configuration, it is possible to detect only the ghost by subsequent peak detection processing by approximating the local maximum due to internal processing fluctuation remaining on the data above the envelope and erasing the local maximum other than the local maximum due to the ghost. It becomes possible.
[0014]
The ghost detection apparatus according to the present invention is the ghost detection method according to claim 4, wherein the predetermined representative data is the number of periodic data of fluctuations in internal processing of the delay profile data searched in the ghost presence data section. The configuration is the maximum value of minutes.
With this configuration, it is possible to detect only the ghost by subsequent peak detection processing by approximating the local maximum due to internal processing fluctuation remaining on the data above the envelope and erasing the local maximum other than the local maximum due to the ghost. It becomes possible.
[0015]
The ghost detection device of the present invention is a ghost detection device that detects the ghost from delay profile data including the main wave and ghost characteristics of the received radio wave,
Approximating means for generating envelope data by approximating the signal waveform of the delay profile data with an envelope;
Comparison means for comparing the signal waveform of the delay profile data and the envelope data;
The delay profile data includes a determination unit that determines that the signal waveform of the delay profile data is larger than the envelope data as a ghost presence data interval in which the ghost exists.
With this configuration, it is possible to detect the presence of a ghost by deleting internal processing fluctuations in the waveform generated during power conversion and detecting data above the envelope.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a ghost detection method and a ghost detection device of the present invention will be described with reference to the drawings. First, a ghost detection apparatus and a digital signal processing apparatus that outputs delay profile data for ghost detection will be described with reference to FIG. FIG. 1 is a block diagram showing an embodiment of a ghost detection apparatus and a digital signal processing apparatus that outputs delay profile data for ghost detection according to the present invention.
[0017]
The ghost detection device 340 according to the present invention includes a digital input board 341 for acquiring delay profile data, and data analysis means 342 for analyzing the delay profile data acquired by the digital input board 341. The delay profile data 331 acquired in the above is analyzed by the data analysis means 342, and the ghost delay amount, level, etc. automatically detected by this analysis are displayed by the connected display means 350.
[0018]
On the other hand, the delay profile data 331 is generated and output by the digital signal processing device 320. The digital signal processor 320 includes an orthogonal demodulator 321 that orthogonally demodulates an RF signal (OFDM RF signal) received by the antenna 301 and the tuner 310, an FFT unit 322 that converts the signal into a frequency domain, and a detector that converts the signal into demodulated data. 323, deinterleaving means 324 for detecting a channel superimposed by interleaving, error correcting means 325 for performing a Viterbi decoding, Reed-Solomon correction, etc., and outputting a demodulated data signal (OFDM demodulated signal) 330, and a detecting means 323 The output data is used to extract a pilot signal to be used in the synchronization detection process and to be configured by delay profile detection means 326 for obtaining transmission path characteristics.
[0019]
The delay profile data 331 output from the delay profile detection means 326 of the digital signal processing device 320 is supplied to the digital input board 341 of the ghost detection device 340 and is analyzed by the data analysis means 342, thereby detecting the ghost. Done. In the data analysis in the data analysis means 342, as will be described later, the envelope data 361 and the delay profile data 331 shown in FIG. 6 are compared, and the level of the delay profile data 331 is the reference envelope data. It is determined that a ghost exists in a section larger than the level of 361. Note that the data analysis means 342 can be realized by a computer on which a data analysis program or the like is mounted. In the present invention, the ghost detection device 340 and the digital signal processing device 320 may be collectively referred to as a ghost detection device.
[0020]
<First embodiment>
Next, a first embodiment according to the ghost detection method of the present invention executed by the ghost detection device 340 will be described. FIG. 2 is a flowchart for explaining the first embodiment according to the ghost detection method of the present invention. In step S <b> 1, the digital input board 341 of the ghost detection device 340 acquires the delay profile data 331 output from the delay profile detection means 326 of the digital signal reception device 320. The delay profile data 331 acquired at this time is data as shown in FIG. FIG. 5 is a graph showing an example of delay profile data. The horizontal axis of the graph represents the delay time, and the vertical axis of the graph represents the level. The delay profile data is preferably converted into digital data that is converted by the power conversion formula of the above-described formula (2).
[0021]
On the other hand, FIG. 6 is a graph showing an example of envelope data serving as a reference according to the present invention. As in FIG. 5, the horizontal axis of the graph represents the delay time, and the vertical axis of the graph represents the level. Next, in step S2, the envelope data 361 is compared with the delay profile data 331, and it is detected whether or not there is a section larger than the envelope data 361 in the signal waveform of the delay profile data 331. If there is a section in which the delay profile data 331 is larger than the envelope data 361, it is determined in step S3 that a ghost has been detected. On the other hand, if there is no section in which the delay profile data 331 is larger than the envelope data 361, it is determined in step S4 that no ghost has been detected.
[0022]
As described above, it is possible to detect the presence or absence of a ghost by determining whether or not there is a section (ghost existence data section) in which the signal waveform of the delay profile data 331 is larger than the envelope data 361. Become.
[0023]
<Second Embodiment>
Next, a second embodiment according to the ghost detection method of the present invention will be described. In the second embodiment, the level of the envelope data 361 and the delay profile data 331 is further corrected so that ghost detection can be performed reliably and accurately.
[0024]
FIG. 3 is a flowchart for explaining a second embodiment according to the ghost detection method of the present invention. First, in step S <b> 10, the digital input board 341 of the ghost detection device 340 acquires the delay profile data 331 output from the delay profile detection means 326 of the digital signal reception device 320. In step S11, the maximum value is searched from the delay profile data 331 to detect the main wave. The delay profile data 331 includes a main wave and a reflected wave due to a ghost.
[0025]
In step S12, in order to obtain a ghost level difference with respect to the main wave, the level is corrected by adding the difference to the delay profile data 331 so that the main wave level is 0 dB from the number of bits of the delay profile data 331. . When the delay profile data 331 level-corrected in step S12 is displayed by the display means 350 such as a monitor, the delay profile data 331 matches the level display value on the display means 350, and is not a process in the computer, but a visual check. The level value can also be determined by.
[0026]
FIG. 7 is a partially enlarged view of delay profile data for explaining ghost detection according to the present invention. In the signal waveform of the delay profile data 331, the ghost appears as a maximum value. However, when the maximum value is searched due to the influence of the internal processing fluctuation of a certain period generated by the power conversion formula (formula (3)) shown in FIG. 7 is difficult to discriminate between the ghost data (circled area A) shown in FIG. 7 and the local maximum point (circled area B) due to internal processing variation. On the other hand, the signal waveform obtained by tracing the maximum value of the internal processing variation in the delay profile data 331 shown in FIG. 5 matches the envelope data 361. Therefore, when a ghost exists, as a result of comparing the delay profile data 331 and the envelope data 361, it appears as data (data in the sections C and D) higher than the envelope data 361 as shown in FIG.
[0027]
In order to compare the level of the envelope data 361 with the level of the delay profile data 331, level correction is performed on the envelope data 361 in step S13. For example,
L = 20log [{1 / (fw / fs) × T · π}]… (1)
Level correction is performed using the envelope data 361 determined by. In equation (1), fw is a bandwidth, fs is a sampling frequency, and T is a point (integer). First, the level of the envelope data 361 is corrected from the next data of the main wave data to the point T = a = 1 in the equation (1), and the ghost detection of the previous data is performed to detect the ghost of the previous data. For the data, the same level correction is performed by replacing the point T = a with the difference c−b between the actual data point T = b and the main wave point T = c.
[0028]
In step S14, the envelope data 361 after the level correction in step S13 is compared with the delay profile data 331 after the level correction in step S12, and the level of the delay profile data 331 is compared with the level of the envelope data 361. A section with a larger value (ghost existence data section) is detected. And it is judged that a ghost exists in this ghost presence data area.
[0029]
Thus, by performing the comparison process between the envelope data 361 whose level is corrected and the delay profile data 331 whose level is also corrected, the presence of a ghost can be easily detected.
[0030]
<Third Embodiment>
Next, a third embodiment according to the ghost detection method of the present invention will be described. In the delay profile data 331 in which the ghost is detected as in the first or second embodiment, when the ghost appears as a local maximum point, the delay profile data 331 in the vicinity thereof is also ghosted as in the region B shown in FIG. Centering on the local maximum point, the curve rises in the same curve as the envelope data 361 (the level increases), and thus appears above the main wave envelope data 361 while leaving the period of the internal processing fluctuation. That is, the delay profile data 331 in the vicinity where the ghost appears as a maximum point becomes larger than the level of the envelope data 361 while drawing a waveform due to internal processing fluctuations.
[0031]
In the signal waveform of the delay profile data 331, the ghost appears as a maximum point, but the waveform of the internal processing fluctuation that occurs during power conversion also has a maximum point. Therefore, the waveform of the internal processing fluctuation is approximated by the envelope data 361 so that only the local maximum point due to the ghost is easily detected.
[0032]
FIG. 4 is a flowchart for explaining the third embodiment according to the ghost detection method of the present invention. In step S <b> 20, the digital input board 341 of the ghost detection device 340 acquires the delay profile data 331 output from the delay profile detection means 326 of the digital signal reception device 320. In step S21, the delay profile data 331 and the envelope data 361 are compared, and a section (ghost existence data section) in which the delay profile data 331 is larger than the envelope data 361 is detected. For example, in FIG. 7, sections C and D are sections in which the delay profile data 331 is larger than the envelope data 361 and are ghost presence data sections. This detection is performed, for example, by the processing described in the first or second embodiment.
[0033]
Then, with respect to the delay profile data 331 in the ghost presence data section detected in step S21, in step S22, the number of periodic data of internal processing fluctuations that occur at the time of power conversion (or the number of local maximum appearance data, for example, 3 data) Min)), and in step S23, the maximum value searched in step S22 is used as representative data, and the delay profile data 331 is replaced with the representative data.
[0034]
In order to perform this process for a plurality of ghost presence data sections, it is determined in step S24 whether or not it is final data. If it is not final data, the process moves to the next data in step S25, and step S22. The subsequent processing is repeated. On the other hand, when it is determined in step S24 that the data is the final data, the process is terminated, and in step S26, the ghost is detected by detecting the local maximum point of the delay profile data 331 in which the local maximum point is replaced. .
[0035]
FIG. 8 is a graph showing the delay profile data finally corrected by the present invention and the level of ghosts present. By the above processing, it becomes possible to remove the local maximum point due to the internal processing variation as in the region E shown in FIG. 8, and by detecting the local maximum point of the corrected delay profile data 331, the local maximum point due to the ghost is detected. Only the ghost delay amount, the ghost level, etc. can be automatically detected. Note that data such as the detected ghost delay amount and ghost level is preferably displayed on the display means 350 as shown in FIG.
[0036]
Further, as described above, in addition to performing processing for replacing the period data of internal processing variation (for example, 3 data) with the maximum value, it is replaced with arbitrary representative data (representative value), and internal processing variation It is also possible to automatically detect a ghost by removing the maximum point due to.
[0037]
【The invention's effect】
As described above, according to the first, second, and sixth aspects of the present invention, the internal processing fluctuation of the waveform generated at the time of power conversion is deleted, and the ghost is detected by detecting the data above the envelope. It is possible to detect the presence of.
[0038]
According to the third aspect of the invention, it is possible to easily and accurately detect the presence of a ghost by performing a comparison process between the level-corrected envelope data and the delay profile data.
[0039]
Further, according to the inventions according to claims 4 and 5, by approximating the maximum point due to the internal processing fluctuation remaining on the data above the envelope, and eliminating the maximum point other than the maximum point due to the ghost, Only the ghost can be detected by the peak detection process.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of a ghost detection device of the present invention and a digital signal processing device that outputs delay profile data for ghost detection. FIG. 2 shows a first embodiment of the ghost detection method of the present invention. FIG. 3 is a flowchart for explaining a second embodiment of the ghost detection method of the present invention. FIG. 4 is a flowchart of a third embodiment of the ghost detection method of the present invention. FIG. 5 is a graph showing an example of general delay profile data. FIG. 6 is a graph showing an example of envelope data serving as a reference according to the present invention. FIG. 7 is a ghost detection according to the present invention. FIG. 8 is a partially enlarged view of the delay profile data for explaining the delay profile data. FIG. Diagram illustrating an example of a table 9 conventional OFDM synchronization demodulation apparatus disclosed in JP-A-10-224319 indicating the level of paste [Description of symbols]
11 Input terminal 12 Clock oscillation circuit 13 A / D conversion circuit 14 Symbol extraction circuit 16 DFT circuit 17 Symbol window control circuit 18 Delay circuit 19 Correlation circuit 20 Window signal generation circuit 21 Clock circuit 22 Clock control circuit 23 LPF circuit 24 D / A Conversion circuit 301 Antenna 310 Tuner 320 Digital signal processor 321 Orthogonal demodulation means 322 FFT means 323 Detection means 324 Deinterleave means 325 Error correction means 326 Delay profile detection means 330 Demodulated data signal (OFDM demodulated signal)
331 Delay profile data 340 Ghost detection device 341 Digital input board 342 Data analysis means (approximation means, comparison means, determination means, data correction means, representative data replacement means, second determination means)
350 Display means 361 Envelope data

Claims (6)

A ghost detection method for detecting the ghost from delay profile data including characteristics of a main wave and a ghost of a received radio wave,
An approximation step of approximating the signal waveform of the delay profile data with an envelope to generate envelope data;
A comparison step of comparing the signal waveform of the delay profile data with the envelope data;
A determination step of determining a section where the signal waveform of the delay profile data is larger than the envelope data as a ghost presence data section where the ghost exists;
A ghost detection method. A ghost detection method for detecting a ghost from a received radio wave,
Demodulating a digital signal in the received radio wave and generating a demodulated signal;
A detection step of converting the generated demodulated signal into a frequency domain and converting it into demodulated data;
A delay profile data detecting step for detecting delay profile data describing characteristics of a main wave and a ghost of the radio wave using pilot synchronization extracted in the detection step;
An approximation step of approximating the signal waveform of the delay profile data with an envelope to generate envelope data;
A comparison step of comparing the signal waveform of the delay profile data with the envelope data;
A determination step of determining a section where the signal waveform of the delay profile data is larger than the envelope data as a ghost presence data section where the ghost exists;
A ghost detection method. The ghost detection method according to claim 1, further comprising a data correction step of correcting respective levels of the delay profile data and the envelope data. Further, a representative data replacement step of replacing predetermined data existing in the ghost presence data section in the delay profile data with predetermined representative data in order to remove a local maximum value due to fluctuations in internal processing of the delay profile data,
A second determination step of determining that the maximum value existing in the ghost presence data section is the ghost;
The ghost detection method according to any one of claims 1 to 3. The ghost detection method according to claim 4, wherein the predetermined representative data is a maximum value corresponding to the number of period data of the internal processing variation of the delay profile data searched in the ghost presence data section. A ghost detection device that detects the ghost from delay profile data including characteristics of a main wave and a ghost of a received radio wave,
Approximating means for generating envelope data by approximating the signal waveform of the delay profile data with an envelope;
Comparison means for comparing the signal waveform of the delay profile data and the envelope data;
Determining means for determining that the signal waveform of the delay profile data is larger than the envelope data as a ghost presence data section in which the ghost exists;
Ghost detection device having.

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