JP4142425B2 - Reception failure cause determination apparatus and reception failure cause determination method for OFDM transmission system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention is used in a transmission system employing an OFDM (orthogonal frequency division multiplex) system such as terrestrial digital broadcasting, and determines the cause of a reception failure that occurs in a received signal on the receiving side of an OFDM transmission wave. The present invention relates to a reception failure cause determination apparatus and method.
[0002]
[Prior art]
Recently, it has been decided to adopt the OFDM method in terrestrial digital broadcasting scheduled to start operation. Since this broadcasting system is introduced simultaneously with analog broadcasting, the installation situation of each channel is complicated, and reception failures such as SFN (Single Frequency Network) difficulty are expected to occur in various places. . 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 degradation of reception quality (transmission path degradation) can be performed by visually and audibly confirming the degree of degradation of video signals and audio signals. However, in the case of digital broadcasting, the reception stability cannot be visually determined, and it is difficult to investigate the cause when a reception failure occurs. Therefore, even when taking countermeasures against reception failures, it is expected that a lot of time is required without taking trial and error measures.
[0004]
Also, digitization based on OFDM is being promoted in inter-station transmission and FPU (Field Pickup Unit) transmission. However, in these transmission systems, there is an urgent need to solve a problem with respect to reception failure.
[0005]
[Problems to be solved by the invention]
As described above, in the conventional OFDM transmission system, it is difficult to investigate 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]
In view of the above circumstances, an object of the present invention is to provide an OFDM transmission system reception failure cause determination apparatus and method capable of reliably determining the cause of reception failure in a relatively short time. .
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the present invention is a reception failure cause determination device that is used in a digital terrestrial broadcasting system and determines a cause of reception failure that occurs in a reception signal on the reception side. A demodulating means for demodulating, a pattern extracting means for extracting a characteristic pattern by determining a region that has been damaged for the frequency domain signal demodulated by the demodulating means, and a plurality of reception failure causes that are 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 a cause of reception failure, and a feature pattern obtained by the pattern extraction unit is compared with a feature pattern in the database. And a discriminating means for discriminating the cause of reception failure by extracting approximate feature patterns. To.
[0008]
The pattern extracting means performs patterning for each broadcasting wave modulation method and coding method of the terrestrial digital broadcasting.
[0009]
Further, the determination means uses a required input power of the received signal and a margin amount of a required C / N as a determination material.
[0010]
The determination means includes frequency selective interference as the determination of the cause of the reception failure. As the frequency selective interference, analog broadcast wave co-channel interference, adjacent channel interference, digital broadcast wave co-channel interference, adjacent channel interference can be considered.
[0011]
Further, the present invention is characterized by comprising impulsive noise discriminating means for discriminating the occurrence of impulsive noise by checking the variation in the time direction of the received signal.
[0012]
The information processing apparatus further includes delay profile creation means for creating delay profile information of the received signal, and the determination means refers to the delay profile information and serves as a cause identification index.
[0013]
The pattern extraction means binarizes the demodulated signal of each subcarrier, and distinguishes the frequency region receiving the interference.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0015]
The terrestrial digital broadcasting system described below employs an OFDM (Orthogonal Frequency Division Multiplex) method, and transmission parameters such as a modulation method and a coding rate in a TMCC (Transmission and Multiplexing Configuration Control) region. A value is added as mode information.
[0016]
FIG. 1 is a block diagram showing a configuration of an embodiment of a reception failure determination apparatus according to the present invention. In FIG. 1, a received signal of a receiving antenna 11 that has received a digital broadcast wave is frequency-converted to a baseband OFDM signal by a tuner 12 in accordance with a selected channel, and then A / D (analog / digital) / FFT (high speed). (Fourier transform) processing circuit 13 converts the signal in the time domain into a signal in the frequency domain by digital processing, and outputs the demodulated signal. This demodulated signal is subjected to phase / amplitude equalization processing by the equalization circuit 14, error correction processing and decoding processing by the error correction / decoding circuit 15, and 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 the frequency domain signal (subcarrier data) demodulated by the A / D / FFT processing circuit 13, the equalization output of the equalization circuit 14, and the correction obtained by the error correction / decoding circuit 15. The received frequency information is supplied. This pattern extraction circuit 18 performs multi-valued input signal detection, detection of the degree of dispersion, creation of frequency distribution subjected to error correction, etc. Extract. At this time, the mode information is reproduced from the TMCC in the demodulated signal, the modulation method and the coding rate are discriminated from the transmission parameter value included in the mode information, and the discrimination result is sent to the pattern comparison circuit 19 together with the feature 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 reception failure causes that are predicted in advance is associated with the cause of the reception failure, and the modulation method. 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 pattern group (so-called pattern pattern). Pattern matching), the cause of reception failure of the pattern is determined. This determination result is appropriately displayed on the failure determination display device 21.
[0019]
The feature pattern obtained by the pattern extraction circuit 18 is supplied to the impulsive noise determination circuit 22. The impulsive noise determination circuit 22 delays the input feature pattern by one or a plurality of OFDM symbols by the delay circuit 221, and compares the pattern before and after the delay by the comparison circuit 222. It is determined that the noise is the cause, and if they are the same, it is determined that the noise is not the influence of the impulse noise. The 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 failure determination display device 21. The failure 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 the delay profile creating device 23, where a delay profile is created. This delay profile is an evaluation of 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 failure will be described below with reference to FIGS.
[0023]
FIG. 2A shows a case where an analog TV broadcast channel overlaps a digital TV broadcast reception channel, resulting in interference with the same channel. That is, the analog broadcast wave has strong peaks in the video carrier, the color subcarrier, and the audio carrier. For this reason, demodulated signals (frequency domain signals) obtained in the digital broadcast wave reception channel are multi-valued by the pattern extraction circuit 18 to determine the fault occurrence area. 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 feature pattern shown in FIG. 2B is extracted by pattern matching, the pattern comparison circuit 19 determines that analog co-channel interference has occurred. 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 for the Nth channel digital broadcasting. b) shows a case where digital broadcasting is performed on the (N−1) th channel and the (N + 1) th channel with respect to the Nth channel digital broadcasting.
[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). Further, 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 of the upper adjacent channel (N + 1). Components leak into the receiving channel (N). Looking at the characteristic pattern of the frequency domain signal subjected to such adjacent channel interference, the lower adjacent channel interference is as shown in FIG. 3C (failure occurs in the lower frequency domain). In this case, the pattern is as shown in FIG. 3 (d) (failure occurs in the upper frequency region), and when both the upper and lower sides are affected by adjacent channel interference, the pattern is a combination of FIGS. 3 (c) and 3 (d) (lower and Failure in the upper frequency range).
[0026]
These feature patterns are stored in the database 20 in advance. When the feature pattern shown in FIG. 3C is extracted by pattern matching, the pattern comparison circuit 19 determines that the channel is adjacent to the lower adjacent channel, and when the feature pattern shown in FIG. When it is determined that the adjacent channel is disturbed and the combination patterns of FIGS. 3C and 3D are extracted, it is determined that the channel is adjacent to the upper and lower adjacent channels. 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 it together with the determination result.
[0027]
By the way, in the terrestrial digital broadcasting scheduled to start operation, the adoption of the SFN (Single Frequency Network) system has been decided, and there are areas where a plurality of digital broadcasting waves are received simultaneously on the same channel. OFDM has a strong tolerance to a certain amount of delayed waves due to the guard interval, but if there is a delayed wave exceeding the guard interval, it becomes an obstacle. Even for a delayed wave within the guard interval, a reception failure occurs when the reception strength is high. In addition, if a plurality of digital broadcast waves overlap and the electric field strength exceeds the required input level, it also becomes a reception 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, the feature pattern of the frequency domain signal subjected to FFT processing is extracted. As shown in FIG. 4B, a pattern having a failure region in the upper and lower amplitude regions can be obtained over the entire OFDM band. Further, the electric field strength at this time exceeds the required input level.
[0029]
Therefore, when the feature pattern shown in FIG. 4B is registered in the database 20 and this feature pattern is extracted by pattern matching, the failure determination display device 21 determines the electric field strength level from the input level obtained during the FFT processing. Is judged to exceed the required input level, and if it exceeds, it is judged that the same channel of digital broadcasting is disturbed and displayed. 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 the FFT processing, and based on this determination result, it is simply displayed that the reception gain is low.
[0030]
Here, when determining co-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 determining the same channel interference by digital broadcast interference by the failure determination display device 21. Thereby, the determination accuracy can be greatly improved.
[0031]
By the way, when looking at the spectrum of the frequency domain signal that has been subjected to the FFT processing, 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 constellation dispersion pattern. As an example of interference analysis, a case where the same channel interference is received by an analog TV signal when receiving a 16QAM modulation type digital broadcast signal will be described with reference to FIG.
[0032]
FIG. 5A shows a 16QAM constellation. When this constellation is viewed on the frequency axis, it becomes as shown in FIG. 5B (in the case of 16QAM, since each of I and Q is 2 bits, a distribution of 4 bits (4 lines) appears). Interference waveform can be seen. When the amplitude dispersion degree is displayed as a histogram for this frequency distribution, as shown in FIG. 5C, the dispersion degree of the part that has been disturbed increases rapidly. Looking at the waveform train, it almost matches the frequency distribution of the analog TV signal. The same applies to the modulation method other than the co-channel interference by the analog TV signal for the 16QAM modulation method and the type of interference. Therefore, a change pattern of the constellation amplitude dispersion degree is extracted as a feature pattern, and matched with a pattern that has been processed in advance and registered. Also with this method, the type of disturbance can be specified automatically and accurately by the feature pattern matching process.
[0033]
By the way, in the determination method using pattern matching as described above, a pattern approximated to the feature pattern registered in the database may be obtained due to impulsive noise, which may be erroneously determined. Therefore, in the present embodiment, the impulsive noise determination circuit 22 delays the input feature pattern by one or a plurality of OFDM symbols by the delay circuit 221, and the comparison circuit 222 performs pattern comparison before and after the delay to impulsive characteristics. The presence or absence of the influence of noise is determined, and the result is sent to the failure determination display device 21. When the failure determination display device 21 is affected by the impulsive noise, the display of the pattern determination result is stopped and the pattern determination is performed again. Thereby, erroneous determination due to impulsive noise can be prevented in advance.
[0034]
Therefore, according to the reception failure cause determination apparatus having the above-described configuration, various failure causes can be determined relatively easily and quickly by matching processing with a failure cause-specific feature extraction pattern prepared in advance. Further, for each determination, a required input level, a required C / N margin, the presence / absence of an impulsive noise, and a delay profile are added as determination materials, so that determination with extremely high accuracy can be performed.
[0035]
In the above embodiment, the case where the feature pattern is extracted from the equalization processing output has been described. However, as shown in FIG. 1, the feature pattern may be extracted by taking in the signal before the equalization processing. In this case, since the measurement is performed in a state before a slight waveform deterioration is rescued by the equalization processing, a finer feature pattern can be extracted, and accordingly, the determination accuracy can be improved.
[0036]
Further, when the frequency selectivity is disturbed, a change is seen in the carrier frequency distribution subjected to error correction at the time of error correction. Therefore, pattern extraction may be performed for error correction / decoding.
[0037]
In the above-described embodiment, the terrestrial digital broadcasting system has been described as an example. However, the present invention is not limited to this, and can be applied to inter-station transmission, FPU transmission, and the like employing the OFDM method, for example. .
[0038]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a reception failure cause determination apparatus and method for an OFDM transmission system that can determine the cause of occurrence of a reception failure in a relatively short time and with certainty.
[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 view 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 of determining a reception failure by matching feature patterns of amplitude dispersion in the embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 ... Reception antenna 12 ... Tuner 13 ... A / D / FFT processing circuit 14 ... Equalization 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)

An OFDM (Orthogonal Frequency Division Multiplex) transmission system is a reception failure cause determination device for determining a reception failure cause that occurs in a received signal on the receiving side of an OFDM transmission wave,
Demodulation means for demodulating a frequency domain signal from the received signal;
Error correction means for performing error correction on the demodulated frequency domain signal; and
Pattern extraction means for extracting the distribution pattern of the frequency domain signal corrected by the error correction means as a feature pattern ;
For each of a plurality of reception failure causes that are predicted in advance, a database that stores a characteristic pattern obtained by performing the same processing as the pattern extraction of the pattern extraction unit in association with a reception failure cause,
A determination unit that compares the feature pattern obtained by the pattern extraction unit with the feature pattern in the database and determines a cause of reception failure by extracting an approximate feature pattern;
An apparatus for determining a cause of reception failure in an OFDM transmission system, comprising:   When equipped with an equalization processing means for equalizing the demodulated frequency domain signal, the pattern extraction means performs pattern extraction on at least one of the input and output signals of the equalization processing means. The reception failure cause determination device for an OFDM transmission system according to claim 1. 2. The reception failure of the OFDM transmission system according to claim 1 , wherein the pattern extraction unit further determines a region in which a failure has occurred in the frequency domain signal demodulated by the demodulation unit and extracts a feature pattern thereof. Cause determination device.   2. The reception failure cause determination apparatus for an OFDM transmission system according to claim 1, wherein the pattern extraction means performs processing for each modulation method and coding method of the OFDM transmission wave.   2. The apparatus according to claim 1, wherein the determining means uses a required input power of the received signal and a margin amount of required C / N as determination materials.   The apparatus according to claim 1, wherein the determination unit includes frequency selective interference as the determination of the cause of the reception failure. 7. The reception failure of the OFDM transmission system according to claim 6, wherein the frequency selective interference includes any one of an analog transmission wave co-channel interference, an adjacent channel interference, a digital transmission wave co-channel interference, and an adjacent channel interference. Cause determination device.   2. The apparatus according to claim 1, further comprising an impulsive noise discriminating means for discriminating the occurrence of impulsive noise by confirming fluctuations in the time direction of the received signal. Furthermore, a delay profile creating means for creating delay profile information of the received signal is provided,
2. The reception failure cause determination apparatus for an OFDM transmission system according to claim 1, wherein the determination means uses the delay profile information as a cause identification index. The pattern extracting means binarizes the signal of each subcarrier is demodulated, received failure origin discrimination system OFDM transmission system according to claim 1, wherein the distinguishing frequency domain receiving the reception failure . The distribution pattern of the frequency domain signal obtained by performing error correction processing on the demodulation result of the received signal of the OFDM ( Orthogonal Frequency Division Multiplex ) transmission wave is extracted as a feature pattern, The feature pattern is extracted for each cause of reception failure and stored in a database, and the feature pattern of the signal actually received and demodulated by the OFDM transmission wave is extracted and compared with each feature pattern stored in the database. Then, a cause of reception failure is determined from a feature pattern that matches or approximates.   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 the input and output signals of the equalization processing. Reception failure cause determination method. Further, the demodulated frequency domain signal is discriminated in the region where the fault has been detected and the feature pattern is extracted, and the feature pattern of the faulted region is extracted for each of a plurality of possible reception fault causes. 12. The reception failure cause determination method for an OFDM transmission system according to claim 11, wherein the reception failure cause determination method is stored in the database .   12. The method according to claim 11, wherein the pattern extraction is performed for each modulation method and coding method of the OFDM transmission wave.   12. The reception failure cause determination method for an OFDM transmission system according to claim 11, wherein the determination of the cause of the failure is based on a required input power of the received signal and a margin amount of required C / N.   12. The reception failure cause determination method of the OFDM transmission system according to claim 11, wherein the cause of 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 any one of an analog transmission wave co-channel interference, an adjacent channel interference, a digital transmission wave co-channel interference, and an adjacent channel interference. Cause determination method.   12. The reception failure cause determination method for an OFDM transmission system according to claim 11, further comprising: determining occurrence of impulsive noise by confirming a variation in a time direction of the reception signal.   12. The method of determining a cause of reception failure in an OFDM transmission system according to claim 11, further comprising using the delay profile information of the received signal as an indicator for specifying the cause. The pattern extraction binarizes the signal of each subcarrier is demodulated, received failure cause determination method of OFDM transmission system according to claim 11, wherein the distinguishing frequency domain receiving the reception failure.

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