JP2004201003A - Device and method for deciding cause of reception disturbance in ofdm transmission system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To automatically and reliably discriminate the cause of occurrence of a reception disturbance in comparatively short time. <P>SOLUTION: An FFT processing circuit 13 demodulates a reception signal to obtain a frequency region signal. A pattern extraction circuit 18 discriminates a region where the disturbance occurs in the frequency region signal and extracts a feature pattern. Feature patterns obtained by performing the same processing as the pattern extraction of the pattern extraction circuit 18 are stored in a database 20 by correlating them to a plurality of the reception disturbance causes which are previously predicted. A pattern comparison circuit 19 compares the feature patterns obtained in the pattern extraction circuit 18 with the pattern stored in the database 20, and the cause of the reception disturbance is discriminated by extracting a similar feature pattern. A disturbance decision display device 21 displays the cause. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention is used in a transmission system employing an orthogonal frequency division multiplexing (OFDM) system such as terrestrial digital broadcasting, and determines the cause of a reception failure occurring in a received signal on the receiving side of an OFDM transmission wave. The present invention relates to a reception failure cause determination device and method.
[0002]
[Prior art]
In recent years, for terrestrial digital broadcasting scheduled to start operation, the adoption of the OFDM method has been decided. Since this broadcasting system is introduced simultaneously with analog broadcasting, the installation situation of each channel is complicated, and it is anticipated that reception troubles will occur in various places, such as a problem of SFN (Single Frequency Network) impairment. . For this reason, it is essential to accurately grasp the reception quality at the reception location.
[0003]
In the case of conventional analog broadcasting, the degree of deterioration of the reception quality (transmission path deterioration) can be determined by visually and audibly confirming the degree of deterioration of the video signal and the audio signal. However, in the case of digital broadcasting, it is not possible to visually judge the reception stability, and it is difficult to find the cause when a reception failure occurs. Therefore, it is expected that a lot of time will be required in order to take measures against reception failures by taking trial and error measures.
[0004]
In addition, digitization by the OFDM method is being promoted in inter-station transmission and FPU (Field Pickup Unit) transmission, but in these transmission systems, it is urgently necessary to solve the problem of reception failure.
[0005]
[Problems to be solved by the invention]
As described above, in the OFDM transmission system, it is conventionally difficult to find the cause when a reception failure occurs, and there is a concern that it takes a lot of time to take measures against the reception failure.
[0006]
The present invention has been made in consideration of the above circumstances, and has as its object to provide an apparatus and method for determining a cause of a reception failure in an OFDM transmission system capable of determining the cause of a reception failure in a relatively short time and reliably. .
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the present invention is used in a terrestrial digital broadcasting system, and a reception failure cause determination device that determines a reception failure cause that occurs in a reception signal on a reception side. Demodulation means for demodulating the frequency domain signal demodulated by the demodulation means, and a pattern extraction means for determining the area affected by the failure and extracting the characteristic pattern thereof, for each of a plurality of reception failure causes expected in advance, Compare the feature pattern obtained by performing the same processing as the pattern extraction of the pattern extraction means with the cause of the reception failure and store the feature pattern, and compare the feature pattern obtained by the pattern extraction means with the feature pattern in the database. And a determination means for determining the cause of a reception failure by extracting an approximate feature pattern. To.
[0008]
The pattern extracting means patterns the broadcast wave of the terrestrial digital broadcast by modulation method and coding method.
[0009]
Further, the determination means uses the required input power of the received signal and a required C / N margin amount as determination materials.
[0010]
The determination means may include frequency selective interference as the determination of the cause of the reception failure. Examples of the frequency-selective interference include co-channel interference and adjacent channel interference of analog broadcast waves, co-channel interference of digital broadcast waves, and adjacent channel interference.
[0011]
Further, an impulsive noise discriminating means for discriminating the occurrence of impulsive noise by confirming a temporal variation of the received signal is provided.
[0012]
Further, there is provided a delay profile creating unit for creating delay profile information of the received signal, wherein the determining unit refers to the delay profile information to use as an index for specifying a cause.
[0013]
The pattern extracting means is characterized in that the demodulated signal of each subcarrier is binarized to discriminate a disturbed frequency region.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0015]
In the terrestrial digital broadcasting system described below, an OFDM (Orthogonal Frequency Division Multiplex) scheme is adopted, and transmission parameter values such as a modulation scheme and a coding rate are arranged in a TMCC (Transmission and Multiplexing Configuration Control) area. Is added as mode information.
[0016]
FIG. 1 is a block diagram showing a configuration of an embodiment of a reception failure determination device according to the present invention. In FIG. 1, a received signal of a receiving antenna 11 receiving a digital broadcast wave is frequency-converted into a baseband OFDM signal by a tuner 12 in accordance with a selected channel, and then A / D (analog / digital) / FFT (high-speed). A Fourier transform) processing circuit 13 converts the signal in the time domain into a signal in the frequency domain by digital processing and demodulates and outputs the signal. The demodulated signal is subjected to the phase / amplitude equalization processing of the equalization circuit 14, the error correction processing and the decoding processing of the error correction / decoding circuit 15, and is returned to the original broadcast signal. The audio signal is decoded and reproduced by the monitor device 17.
[0017]
On the other hand, the pattern extraction circuit 18 includes a frequency domain signal (subcarrier data) demodulated by the A / D / FFT processing circuit 13, an equalization output of the equalization circuit 14, and a correction obtained by the error correction / decoding circuit 15. The received frequency information is supplied. The pattern extraction circuit 18 performs multi-level conversion of the input signal, detects the degree of dispersion, creates a distribution of error-corrected frequencies, etc., and distinguishes a faulty area in the pattern to identify a characteristic pattern. Extract. At this time, the mode information is reproduced from the TMCC in the demodulated signal, the modulation method and the coding rate are determined from the transmission parameter value included in the mode information, and the determination result is sent to the pattern comparison circuit 19 together with the characteristic pattern.
[0018]
On the other hand, in the pattern database 20, a characteristic pattern obtained by performing the same processing as the pattern extraction of the pattern extraction circuit 18 for each of a plurality of expected reception failure causes is associated with the reception failure cause, and the Separately, it is stored for each coding rate. The pattern comparison circuit 19 selects a pattern group stored in the database 20 from the modulation scheme and coding rate determined by the pattern extraction circuit 18, and detects a pattern that is the same as or similar to the input feature pattern from the group (so-called pattern comparison circuit 19). Pattern matching), and determine the cause of the reception failure of the pattern. This determination result is appropriately displayed on the failure determination display device 21.
[0019]
The characteristic pattern obtained by the pattern extraction circuit 18 is supplied to an impulse noise determination circuit 22. The impulse noise determination circuit 22 delays the input feature pattern by one or a plurality of OFDM symbols by a delay circuit 221 and compares the patterns before and after the delay by a comparison circuit 222. Is determined to be the cause, and if they match, it is determined that it is not the influence of the impulse noise. This determination result is sent to the failure determination display device 21 and displayed as appropriate.
[0020]
The input level of each subcarrier obtained by the A / D / FFT processing circuit 13 is sent to the fault determination display device 21. The fault determination display device 21 determines the required input power and the required C / N margin from the input level of each subcarrier, and displays them appropriately.
[0021]
The demodulated signal obtained by the A / D / FFT processing circuit 13 is sent to a delay profile creation device 23, where a delay profile is created. The delay profile is obtained by evaluating transmission path characteristics such as multipath, and the result is sent to the failure determination display device 21 and displayed as an index for determining various failure causes.
[0022]
In the above configuration, the processing operation for each cause of the failure will be described below with reference to FIGS.
[0023]
FIG. 2A shows a case in which an analog TV broadcast channel overlaps a digital TV broadcast reception channel and co-channel interference occurs. That is, the analog broadcast wave has strong peaks in the video carrier, the color subcarrier, and the audio carrier. For this reason, when the demodulated signal (frequency domain signal) obtained on the receiving channel of the digital broadcast wave is multi-valued by the pattern extraction circuit 18 and the failure occurrence area is determined, for example, the characteristic shown in FIG. A pattern is obtained (here, a QPSK binarization pattern is shown). This feature pattern is stored in the database 20 in advance. When the characteristic pattern shown in FIG. 2B is extracted by the pattern matching, the pattern comparison circuit 19 determines that it is an analog co-channel interference. This determination result is displayed on the failure determination display device 21.
[0024]
FIG. 3 shows an example of adjacent channel interference. FIG. 3A shows a case where analog broadcasting is performed on the (N−1) th channel and the (N + 1) th channel with respect to the Nth channel digital broadcasting. b) shows a case where digital broadcasting of the N-th channel is performed on the (N-1) th channel and the (N + 1) th channel.
[0025]
As shown in FIG. 3A, when analog broadcasting is performed on the adjacent channel, the side carrier components of the audio carrier of the lower adjacent channel (N-1) and the video carrier of the upper adjacent channel (N + 1) are received. Leak into channel (N). In addition, as shown in FIG. 3B, when digital broadcasting is performed on the adjacent channel, the upper side wave component of the lower adjacent channel (N-1) and the lower side wave component of the upper adjacent channel (N + 1). The component leaks into the receiving channel (N). Looking at the characteristic pattern of the frequency domain signal that has suffered such adjacent channel interference, the lower adjacent channel interference is as shown in FIG. 3C (a failure occurs in the lower frequency domain), and the upper adjacent channel interference In this case, the pattern is as shown in FIG. 3D (failure occurs in the upper frequency domain), and when adjacent channels are disturbed in both upper and lower directions, the pattern is a combination of FIGS. 3C and 3D (lower and upper patterns). The upper frequency domain has a fault).
[0026]
These feature patterns are stored in the database 20 in advance. In the pattern comparison circuit 19, when the characteristic pattern shown in FIG. 3C is extracted by the pattern matching, it is determined that the lower adjacent channel is disturbed, and when the characteristic pattern shown in FIG. If it is determined that adjacent channel interference occurs, and if the combination patterns of FIGS. 3C and 3D are extracted, it is determined that upper and lower adjacent channel interference will occur. These determination results are displayed on the failure determination display device 21. At this time, since it is known whether the broadcast of the adjacent channel is analog or digital, it is desirable to display the broadcast together with the determination result.
[0027]
By the way, in terrestrial digital broadcasting scheduled to start operation, adoption of the SFN (Single Frequency Network) method has been decided, and there are regions where a plurality of digital broadcast waves are simultaneously received on the same channel. In OFDM, the guard interval has a high resistance to a certain amount of delayed waves, but a delayed wave exceeding the guard interval causes an obstacle. In addition, even if the delay wave is within the guard interval, a reception failure occurs if the reception intensity is high. Also, if a plurality of digital broadcast waves overlap and the electric field intensity exceeds a required input level, reception will also be an obstacle.
[0028]
As shown in FIG. 4A, when a plurality of OFDM signals are overlapped on the same channel and each delay amount exceeds a certain amount and interference occurs, a characteristic pattern of the frequency domain signal subjected to the FFT processing is extracted. Referring to FIG. 4B, a pattern having an obstacle region in the upper and lower amplitude regions is obtained over the entire OFDM band as shown in FIG. The electric field strength at this time exceeds the required input level.
[0029]
Therefore, the characteristic pattern shown in FIG. 4B is registered in the database 20, and when this characteristic pattern is extracted by pattern matching, the failure determination display device 21 uses the electric field intensity level from the input level obtained at the time of the FFT processing. Is judged to exceed the required input level, and if so, it is judged and displayed as the same-channel interference of digital broadcasting. If the electric field strength level does not exceed the required input level, the C / N margin is determined from the input level at the time of FFT processing, and based on the result of the determination, it is simply indicated that the reception gain is low.
[0030]
Here, when judging the same channel interference due to digital broadcast wave interference, it is important to grasp the transmission state of a plurality of digital broadcast waves. Therefore, in the present embodiment, a delay profile is created by the delay profile creation device 23 and is used as an index for the same channel interference determination by digital broadcast interference by the failure determination display device 21. Thereby, the determination accuracy can be dramatically improved.
[0031]
By the way, when the spectrum of the frequency domain signal subjected to the FFT processing is viewed, it is difficult to detect the difference if the degree of waveform deterioration is small even if it is disturbed. Therefore, it is also effective to extract a pattern of the degree of dispersion of the constellation. As an example of the interference analysis, a case where the same channel interference is caused by an analog TV signal at the time of receiving a 16QAM digital broadcasting signal will be described with reference to FIG.
[0032]
FIG. 5A shows a constellation of 16QAM. When this constellation is viewed on the frequency axis, it is as shown in FIG. 5B (in the case of 16 QAM, since I and Q are each 2 bits, a distribution of 4 bits (4 lines) appears). Disturbing waveforms are seen. When the degree of dispersion of the amplitude of this frequency distribution is displayed as a histogram, as shown in FIG. 5C, the degree of dispersion of the disturbed portion rapidly increases. Looking at the waveform sequence, it substantially matches the frequency distribution of the analog TV signal. The same applies to modulation methods other than co-channel interference caused by analog TV signals with respect to the 16QAM modulation method and types of interference. Therefore, a change pattern of the amplitude variance of the constellation is extracted as a characteristic pattern, and matching is performed with a pattern that has been processed and registered in advance in the same manner. According to this method as well, the type of interference can be automatically and accurately specified by the feature pattern matching process.
[0033]
By the way, in the determination method based on the pattern matching as described above, a pattern similar to the feature pattern registered in the database is obtained due to impulsive noise, and an erroneous determination may be made. Therefore, in the present embodiment, in the impulse noise determination circuit 22, the input characteristic pattern is delayed by one or a plurality of OFDM symbols by the delay circuit 221, and the comparison circuit 222 compares the patterns before and after the delay to obtain the impulse noise. The presence or absence of the influence of noise is determined, and the result is sent to the failure determination display device 21. The failure determination display device 21 stops displaying the pattern determination result when the influence of the impulse noise is present, and performs the pattern determination again. Thereby, erroneous determination due to impulsive noise can be prevented.
[0034]
Therefore, according to the reception failure cause determination apparatus having the above configuration, various failure causes can be relatively easily and quickly determined by performing matching processing with a failure cause-specific feature extraction pattern prepared in advance. In addition, since a required input level, a required C / N margin, the presence / absence of influence of impulsive noise, and a delay profile are added to each determination as determination materials, extremely accurate determination can be performed.
[0035]
In the above embodiment, the case where the characteristic pattern is extracted from the equalization processing output has been described. However, as shown in FIG. 1, the signal before the equalization processing may be taken in to extract the characteristic pattern. In this case, since the measurement is performed before the slight waveform deterioration is rescued by the equalization processing, a finer feature pattern can be extracted, and the determination accuracy can be improved accordingly.
[0036]
Further, when the frequency selectivity is disturbed, a change is observed in the distribution of the carrier frequencies subjected to the error correction at the time of the error correction. Therefore, a pattern may be extracted for error correction / decoding.
[0037]
Although the terrestrial digital broadcasting system has been described as an example in the above embodiment, the present invention is not limited to this, and can be applied to, for example, inter-station transmission employing the OFDM method, FPU transmission, and the like. .
[0038]
【The invention's effect】
As described above, according to the present invention, it is possible to provide an apparatus and method for determining a cause of a reception failure in an OFDM transmission system capable of determining a cause of a reception failure in a relatively short time and reliably.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of an embodiment of a reception failure determination device according to the present invention.
FIG. 2 is a diagram showing an example of determining a reception failure due to analog broadcast co-channel interference in the embodiment.
FIG. 3 is a diagram showing an example of determining a reception failure due to adjacent channel interference in the embodiment.
FIG. 4 is a diagram showing an example of determining a reception failure due to digital broadcast co-channel interference in the embodiment.
FIG. 5 is a diagram showing an example in which a reception failure is determined by matching a feature pattern of an amplitude dispersion degree in the embodiment.
[Explanation of symbols]
Reference Signs List 11 receiving antenna 12 tuner 13 A / D / FFT processing circuit 14 equalizing circuit 15 error correction / decoding circuit 16 decoder 17 monitor device 18 pattern extraction circuit 19 pattern comparison circuit 20 pattern database 21 ... Failure determination display device 22 ... Impulsive noise determination circuit 221 ... Delay circuit 222 ... Comparison circuit 23 ... Delay profile creation device

Claims (20)

A reception failure cause determination device that is used in an OFDM (Orthogonal Frequency Division Multiplex) transmission system and determines a reception failure cause that occurs in a reception signal on a reception side of an OFDM transmission wave,
Demodulation means for demodulating a frequency domain signal from the received signal,
Pattern extracting means for judging an area affected by the frequency domain signal demodulated by the demodulating means and extracting a characteristic pattern thereof;
For each of a plurality of reception failure causes expected in advance, a database that stores a feature pattern obtained by performing the same processing as the pattern extraction of the pattern extraction unit in association with the reception failure cause,
Comparing the feature pattern obtained by the pattern extraction means with the feature pattern in the database, and determining the cause of the reception failure by extracting an approximate feature pattern;
An apparatus for determining the cause of a reception failure in an OFDM transmission system, comprising: In the case where the apparatus further comprises equalization processing means for performing equalization processing on the demodulated frequency domain signal, the pattern extraction means performs pattern extraction on at least one of an input signal and an output signal of the equalization processing means. 2. The reception failure cause determination device for an OFDM transmission system according to claim 1, wherein: 2. The apparatus according to claim 1, further comprising an error correction unit configured to perform an error correction process on the demodulated frequency domain signal, wherein the pattern extraction unit extracts a pattern of a frequency carrier distribution corrected by the error correction unit. Device for determining the cause of a reception failure in an OFDM transmission system. 2. The apparatus according to claim 1, wherein said pattern extracting means performs processing for each of a modulation method and an encoding method of the OFDM transmission wave. 2. The apparatus according to claim 1, wherein said determining means uses a required input power of the received signal and a required C / N margin amount as a determination material. 2. The apparatus according to claim 1, wherein said determination means includes frequency selective interference as the determination of the cause of the reception failure. The reception failure of the OFDM transmission system according to claim 4, wherein the frequency-selective interference includes any of co-channel interference, adjacent channel interference of analog transmission waves, co-channel interference of digital transmission waves, and adjacent channel interference. Cause determination device. 2. The apparatus according to claim 1, further comprising an impulse noise discriminating means for confirming a temporal variation of the received signal and discriminating occurrence of impulsive noise. Further, a delay profile creating means for creating delay profile information of the received signal,
2. The apparatus according to claim 1, wherein the determination unit refers to the delay profile information as an index for specifying a cause. 2. The apparatus according to claim 1, wherein said pattern extracting means converts the demodulated signal of each subcarrier into a multi-level signal and distinguishes a frequency region in which interference occurs. With respect to the demodulation result of the received signal of the OFDM transmission wave, a region to be damaged is determined for each of a plurality of causes of the reception failure predicted in advance, and the characteristic pattern is extracted and stored in a database. And extracting a characteristic pattern of the demodulated signal, comparing the extracted characteristic pattern with each characteristic pattern stored in the database, and determining a cause of a reception failure from a coincident or approximate characteristic pattern. Failure cause determination method. 12. The OFDM transmission system according to claim 11, wherein when equalization processing is performed on the demodulated frequency domain signal, pattern extraction is performed on at least one of an input signal and an output signal of the equalization processing. Reception failure cause determination method. 12. The OFDM transmission system according to claim 11, wherein when an error correction process is performed on the demodulated frequency domain signal, the pattern extraction extracts a pattern of a frequency carrier distribution corrected by the error correction. Reception failure cause determination method. The method according to claim 11, wherein the pattern extraction is performed for each modulation method and each encoding method of the OFDM transmission wave. 12. The method according to claim 11, wherein the cause of the failure is determined based on a required input power of the received signal and a required C / N margin. The method according to claim 11, wherein the cause of the reception failure includes frequency selective interference. 17. The reception failure of the OFDM transmission system according to claim 16, wherein the frequency selective interference includes one of co-channel interference, adjacent channel interference of an analog transmission wave, co-channel interference of a digital transmission wave, and adjacent channel interference. Cause determination method. 12. The method according to claim 11, further comprising: determining a time-dependent change in the received signal to determine whether or not impulsive noise has occurred. 12. The method according to claim 11, further comprising using the delay profile information of the received signal as an index for specifying a cause. 12. The method according to claim 11, wherein the pattern extraction includes multi-level demodulation of each subcarrier signal to distinguish a frequency region in which interference occurs.

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