JP2004241814A - Modulation error ratio measurement apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To measure a modulation error ratio of a signal to be measured by omitting troublesome setting operations. <P>SOLUTION: When receiving the signal to be measured a with a frequency f1 or f2, a frequency conversion section 2 converts the frequency of the signal into an intermediate frequency and outputs the result as an intermediate frequency signal b. An analog/digital conversion section 3 converts the intermediate frequency signal b into a digital intermediate frequency signal c. A signal detection section 5 detects a level of the digital intermediate frequency signal c outputted from the analog/digital conversion section by each frequency. A control section 6, to which the frequencies f1, f2 and a setting level of the signal to be measured a are preset, compares the level detected by the signal detection section 5 with the setting level and decides a measurement object on the basis of a result of comparison. The control section 6 controls a frequency conversion section 2 in matching with the decided measurement object and calculates and outputs a modulation error ratio on the basis of the digital intermediate frequency signal c outputted from the analog/digital conversion section 3. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a modulation error ratio measurement device (MER) for measuring a modulation error ratio (MER) of a signal under measurement having a plurality of different frequencies, and more particularly to an integrated services digital broadcasting-terrestrial integrated digital broadcasting system (ISDB-T) used for television broadcasting. Suitable for monitoring a digital broadcast signal modulated by a BST-OFDM (Band Segmented Transmission-Orthogonal Frequency Division Multiplexing) modulation scheme adopted in a terrestrial broadcast system as a signal to be measured. And a modulation error ratio measuring device.
[0002]
[Prior art]
In recent years, television signals of terrestrial broadcasting, satellite broadcasting, and cable broadcasting in television broadcasting have been digitized, and not only images and sounds but also a large number of additional information have been incorporated into one channel and transmitted. Experiments and some practical applications have been made to select additional information.
Prior art document information related to the invention of this application includes the following.
[0003]
[Patent Document 1]
JP-A-2002-124931
[0004]
It is important to evaluate the signal quality of a digital broadcast signal used in such an ISDB-T system in order to always provide a good image to a viewer.
[0005]
As a technique for quantitatively expressing the signal quality of a broadcast signal, CN (digital) is generally adopted. In the frequency distribution of each channel of the analog broadcast signal, as shown in FIG. 8A, the spectrum A of the image signal and the spectrum B of the audio signal are separated from each other. In this case, the noise level (N) in the frequency band of this channel can be easily measured. Also, the signal level (C) of the spectrum A of the image signal can be easily measured. Therefore, the CN of the analog broadcast signal can be easily obtained.
[0006]
However, in the digital broadcast signal modulated by the BST-OFDM modulation scheme adopted in the ISDB-T system in Japan, as shown in FIG. 8B, video, audio, Since a large number of spectra such as additional information are dispersed on average, the trapezoidal spectrum C becomes full within the frequency band. As a result, since the noise in this frequency band is buried in the trapezoidal spectrum C, the noise level (N) cannot be directly measured.
[0007]
In order to solve such inconvenience, as shown in FIG. 9A, a digital broadcast signal received from an antenna 51 is subjected to a known level of noise (white noise) output from a noise generator (AWGN) 52. ) Is applied by the signal adder 53, the digital broadcast signal to which the noise is applied is received by the receiver 54 and demodulated into the original digital data, and the error rate (bit error error) of the demodulated digital data is obtained. A technique of measuring the rate BER by the error rate measuring device 55 has been put to practical use.
[0008]
In general, the relationship between CN, which is represented by the ratio of carrier wave to noise (noise), and the error rate (BER) in a digital signal is represented by an error rate-CN characteristic, as shown in FIG. 9B. It is. Therefore, if the error rate (BER) can be measured, the CN of this digital signal should be uniquely determined.
[0009]
However, in a region where the error rate in the error rate-CN characteristic is small, an accurate CN cannot be obtained, and the measured value of the error rate measuring device is, for example, 2 × 10 ^-4 The noise of a known level output from the noise generator (AWGN) is increased until it matches (CN corresponding to CN1 from the error rate-CN characteristic), and CN2 corresponding to the noise applied at that time is obtained. . Therefore, the CN of the digital broadcast signal to be obtained is (CN1-CN2).
[0010]
The above-described digital broadcast signal is generated and output by a signal generator 31 as shown in FIG. 5, for example. The signal generator 31 is provided in, for example, a TV station, and modulates an MPEG-2 (original data) including an image and a sound by a BST-OFDM modulation scheme adopted in the ISTB-T system; (UPCONV) 33 that converts a digital broadcast signal modulated by the modulator 32 from an IF signal to an RF signal and outputs the converted signal, and a manual switcher 34 that is connected to the input and output of the upconverter 33. Have.
[0011]
When the signal generator 31 shown in FIG. 5 is monitored, for example, a modulation error ratio measuring device 61 disclosed in Japanese Patent Application Laid-Open No. 2002-124931 is connected to the switch 34 and the up converter 33 The modulation error ratio of the signal to be measured input via 34 is measured.
[0012]
However, the conventional modulation error ratio measurement device 61 can measure only at one set frequency (for example, the frequency of the IF signal output from the modulator 32). Therefore, when measuring another frequency (for example, the frequency of the RF signal output from the up-converter 33), it is necessary to set again so that the measurement of the frequency can be performed, which is troublesome. . In addition, since it takes several seconds (for example, 3 or 4 seconds) to calculate the modulation error ratio, if the switch 34 is operated during the measurement, an accurate modulation error ratio measurement cannot be performed, and There is a possibility of outputting the measurement result, which lacks reliability.
[0013]
Therefore, the present invention has been made in view of the above-described problem, and eliminates a troublesome setting operation, determines whether or not there is a signal for a plurality of signals to be measured having different frequencies, and based on the determination result, It is an object of the present invention to provide a modulation error ratio measurement device capable of measuring a modulation error ratio of an input signal under measurement.
[0014]
[Means for Solving the Problems]
Next, means for solving the above problems will be described with reference to the drawings corresponding to the embodiments.
2. The modulation error ratio measuring device according to claim 1, wherein signals under test a of a plurality of different frequencies are selectively switched and input, and the frequency of the selected signal under test is converted into an intermediate frequency to produce an intermediate frequency signal. a frequency conversion unit 2 that outputs the signal as b;
An A / D converter 3 for A / D converting the intermediate frequency signal output from the frequency converter into a digital intermediate frequency signal c;
A signal detector 5 for detecting the level of the digital intermediate frequency signal output from the A / D converter for each of the frequencies;
The plurality of different frequencies are set and input in advance, determine the measurement target based on the level detected by the signal detection unit, and control the frequency conversion unit in accordance with the determined measurement target. A control unit for calculating and outputting a modulation error ratio based on a digital intermediate frequency signal output by the / D conversion unit.
[0015]
3. The modulation error ratio measuring apparatus according to claim 2, wherein signals under test a of a plurality of different frequencies are selectively switched and input, and the frequency of the selected signal under test is converted to an intermediate frequency to output an intermediate frequency signal. a frequency conversion unit 2 that outputs the signal as b;
An A / D converter 3 for A / D converting the intermediate frequency signal output from the frequency converter into a digital intermediate frequency signal c;
A signal detector 5 for detecting the level of the digital intermediate frequency signal output from the A / D converter for each of the frequencies;
The plurality of different frequencies are set and input in advance, determine the measurement target based on the level detected by the signal detection unit, and control the frequency conversion unit in accordance with the determined measurement target. The validity of the digital intermediate frequency signal output by the / D converter is determined, and when it is determined that the digital intermediate frequency signal is valid, the modulation error ratio is calculated and output based on the digital intermediate frequency signal determined to be valid. And a control unit 6 that performs the control.
[0016]
A modulation error ratio measuring apparatus according to claim 5, wherein the signal under test a is a hierarchy of a plurality of digital information having different modulation schemes in a frequency band of one channel in the modulation error ratio measuring apparatus according to claim 1 or 2. And a digital broadcast signal obtained by BST-OFDM-modulating these layers.
[0017]
The modulation error ratio measurement device according to claim 3 is the modulation error ratio measurement device according to any one of claims 1 to 3, wherein the control unit 6 controls the plurality of different error signals output from the signal detection unit 5. The level of each frequency is compared, and a frequency having a higher level is determined as a measurement target.
[0018]
According to a fourth aspect of the present invention, there is provided a modulation error ratio measuring apparatus according to any one of the first to third aspects, wherein the control unit sets a preset level for each of the plurality of different frequencies in advance. The frequency output by the signal detection unit 5 is determined to be a frequency that exceeds the set level as a measurement target.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of a modulation error ratio measuring apparatus according to the present invention will be described in detail with reference to the drawings.
[0020]
FIG. 1 is a block diagram showing a schematic configuration of a modulation error ratio measuring device according to the present invention. FIG. 2 is a diagram showing an example of frequency characteristics of a digital broadcast signal to be measured by the modulation error ratio measuring device according to the present invention. FIG. 4 is a waveform diagram for explaining a method of determining validity by the modulation error ratio measuring device according to the present invention, and FIG. 4 is a flowchart at the time of measurement by the modulation error ratio measuring device according to the present invention.
[0021]
As shown in FIG. 1, a modulation error ratio measurement device 1 according to the present embodiment is schematically configured to include a frequency conversion unit 2, an A / D conversion unit 3, a waveform memory 4, a signal detection unit 5, and a control unit 6. You.
[0022]
Signals a to be measured a having different frequencies are selectively input to the frequency converter 2. In this example, one of an IF signal having a different frequency f1 and an RF signal having a different frequency f1, which is a BST-OFDM-modulated digital broadcast signal, is selectively switched from the outside to the frequency converter 2. The signal to be measured a by the IF signal f1 or the RF signal f2 has, for example, the frequency characteristics shown in FIG.
[0023]
In the example of FIG. 2, only a frequency band of, for example, 6 MHz of one channel in a digital broadcast signal for TV is shown. As shown in FIG. 2, the A-, B-, and C-layers having different modulation schemes are arranged in the 6 MHz frequency band. Further, as shown in FIG. 2, special subcarriers are evenly arranged in the frequency bands of the A, B, and C layers. Each layer includes a plurality of subcarriers modulated with digital information to be transmitted. The modulation method and the used frequency band of the special subcarrier in the 6 MHz frequency band of this one channel are fixed, but the number of other layers to be installed, each used frequency band, and the adopted modulation method (DQPSK, QPSK, 64QAM, etc.) ) Can be arbitrarily changed according to information to be transmitted in each layer.
[0024]
The frequency converter 2 converts the frequency of the digital broadcast signal input as the signal under test a into a local oscillation (local) signal applied from the drive controller 18 in accordance with a control command of a measurement controller 17 described later in the controller 6. To the A / D converter 3 as an intermediate frequency signal b.
[0025]
The A / D converter 3 converts the intermediate frequency signal b input from the frequency converter 2 into a digital intermediate frequency signal c and sends it to the waveform memory 4.
[0026]
The waveform memory 4 takes in the digital intermediate frequency signal c converted by the A / D converter 3 for a predetermined time and temporarily stores it.
[0027]
The signal detection unit 5 includes a switching unit 11, a level detection unit 12, and a signal validity detection unit 13. The switching unit 11 selects a contact so that either the level detection unit 12 or the signal validity detection unit 13 is connected to the waveform memory by a switching signal input from a measurement control unit 17 described later in the control unit 6. Can be switched.
[0028]
When connected to the waveform memory 4 via the switching unit 11, the level detection unit 12 detects the level of the digital intermediate frequency signal c captured and stored by the waveform memory 4 for each of the frequencies f1 and f2. . Then, the level detecting section 12 outputs the level of the digital intermediate frequency signal c of the frequency f1 and the level of the digital intermediate frequency signal c of the frequency f2 stored in the waveform memory 4.
[0029]
The signal validity detection unit 13 detects the validity of the digital intermediate frequency signal c stored in the waveform memory 4 when connected to the waveform memory 4 via the switching unit 11. In addition, the signal validity detecting unit 13 causes an instantaneous interruption or stop while the waveform memory 4 is taking in the digital intermediate frequency signal c, as shown by a broken line in FIG. When there is a portion not shown or a non-input portion (0 level), the waveform is detected as an invalid signal having no validity.
[0030]
When measuring the modulation error ratio of the signal under test a, the control unit 6 controls the entire apparatus, and as shown in FIG. 1, the level magnitude judgment unit 15, the re-measurement judgment unit 16, the measurement control unit 17 , A drive control unit 18 and an external input / output interface 19.
[0031]
The level magnitude determining section 15 determines the magnitude of the level value of the digital intermediate frequency signal c detected by the level detecting section 12. More specifically, the level magnitude determination unit 15 compares the level of the digital intermediate frequency signal c of the frequency f1 input from the level detection unit 12 with the level of the digital intermediate frequency signal c of the frequency f2, The judgment signal is sent to the measurement control unit 17. In this case, it is determined that the higher level is the input frequency. The level magnitude judging section 15 can also judge the magnitude of the level value based on whether the level of the digital intermediate frequency signal c from the level detecting section 12 is larger or smaller than a preset level (for example, +10 dBm). When the level determination unit 15 determines that the level of the intermediate frequency signal c is higher than the set level, the level determination unit 15 sends a determination signal indicating that the level is high to the measurement control unit 17. On the other hand, when it is determined that the level of the intermediate frequency signal c is smaller than the set level, the signal for determining the level is transmitted to the measurement controller 17. In this case, the one that sends the high level determination signal to the measurement control unit 17 determines the input frequency. Thus, for example, when neither the frequency f1 (RF) nor the frequency f2 (IF) is output, an abnormality (no signal state) can be output.
[0032]
The re-measurement determination unit 16 sends a validity determination signal to the measurement control unit 17 when a signal having validity is input from the signal validity detection unit 13. On the other hand, when an invalid signal is input from the signal validity detection unit 13, a determination signal indicating no validity is sent to the measurement control unit 17.
[0033]
The measurement control unit 17 performs the measurement process shown in FIG. 4 based on setting information (for example, setting information such as a frequency, a level, and a spectrum direction of a measurement target) which is set and input before measurement via the external input / output interface 19. Running.
[0034]
When the modulation error ratio measuring apparatus 1 of this example is employed as a monitor of the signal generator 31 of FIG. 5, the spectrum of the IF signal input from the demodulator 32 to the up converter 33 and the output of the up converter 33 are output. Since the spectrum of the RF signal is inverted by the circuit configuration of the up-converter 33, the direction of the spectrum can be set.
[0035]
The main operation of the measurement control unit 17 will be described. At the time of measurement, a switching signal is output to the switching unit 11 so that either the level detection unit 12 or the signal validity detection unit 13 is connected to the waveform memory 4. . In an actual measurement, a switching signal is output to the switching unit 11 so that the level detection unit 12 and the waveform memory 4 are first connected, and after the measurement target is determined, the signal validity detection unit 13 and the waveform memory 4 are connected. I have. At the time of measurement, a control command is output to the drive control unit 18 so that conversion tuned to one of the frequencies f1 and f2 is performed by the frequency conversion unit 2. In addition, the measurement target (frequency of the signal under measurement a) is determined based on the judgment signal from the level judgment unit 15. Here, of the IF signal or the RF signal, the one having the higher input level is determined as the measurement target using the detection result of the level. Further, the frequency converter 2 is controlled via the drive controller 18 in accordance with the determined measurement target. Further, the modulation error ratio of the signal under test a determined to be measured is measured based on the digital intermediate frequency signal c stored in the waveform memory 4. Then, the measurement result (measurement frequency, modulation error ratio) is output to the outside via the external input / output interface 19.
[0036]
Here, the modulation error ratio is measured by, for example, a method disclosed in Japanese Patent Application Laid-Open No. 2002-124931 filed by the present applicant. The measuring method will be briefly described. First, a digital intermediate frequency signal stored in the waveform memory 4 is orthogonally demodulated into a baseband signal. Subsequently, the symbol timing of the OFDM modulation is extracted from the orthogonally demodulated baseband signal. Thereafter, the baseband signal is subjected to fast Fourier transform processing using the extracted symbol timing, thereby extracting all the subcarriers constituting one channel of the digital broadcast signal. Then, the extracted subcarriers are divided into the respective layers, and the subcarriers for each of the divided layers are demodulated by a demodulation method corresponding to the phase modulation method of the layer to obtain a measurement constellation. Subsequently, a theoretical constellation is estimated from the demodulated measurement constellation, and an error between the measurement constellation and the theoretical constellation is calculated. Then, a power ratio between the calculated error of each layer and the ideal constellation of the layer is calculated as a modulation error ratio.
[0037]
The drive control unit 18 sends a local oscillation (local) signal to the frequency conversion unit 2 according to a control command from the measurement control unit 17 so that the frequency conversion unit 2 performs conversion in synchronization with the frequency to be measured.
[0038]
For example, a setting input unit and a display unit are connected to the external input / output interface 19. In the external input / output interface 19, setting information (for example, setting information such as a frequency, a level, and a spectrum direction of a measurement target) from a setting input unit is input to the measurement control unit 17, and a measurement result from the measurement control unit 17 is displayed. Output to the unit.
[0039]
Next, the operation at the time of measurement of the modulation error ratio measurement device 1 having the above configuration will be described with reference to the flowchart of FIG.
[0040]
First, in measurement, parameters are input (ST1). In this parameter input, for example, when the signal a to be measured is an IF signal and an RF signal, the frequency f1 of the IF signal (37.15 MHz), the frequency f2 of the RF signal (UHF 15ch: 485.142857 MHz), and the input of the signal to be measured a A setting level (for example, +10 dBm for both the IF signal and the RF signal) for identifying the presence or absence of the signal, a spectrum direction (normal (RF signal), reverse (IF signal)), and the like are input as setting items. When the parameters are input, hardware setting is performed by the RF signal (ST2). In the hardware setting using the RF signal, the measurement control unit 17 outputs a local oscillation signal to the frequency conversion unit 2 via the drive control unit 18 so that the frequency conversion unit 2 performs conversion synchronized with the RF signal of the frequency f2. . As a result, the signal under test a input to the frequency converter 2 is converted to an intermediate frequency by the frequency converter 2 and sent to the A / D converter 3 as an intermediate frequency signal b. The A / D converter 3 converts the intermediate frequency signal b converted by the frequency converter 2 into a digital intermediate frequency signal c and sends it to the waveform memory 4. The waveform memory 4 stores the digital intermediate frequency signal c converted by the A / D converter 3. After that, the input level of the RF signal is measured by the level detector 12 (ST3).
[0041]
Next, hardware setting is performed by an IF signal (ST4). The hardware setting by the IF signal is performed by the measurement control unit 17 via the drive control unit 18 so that the frequency conversion unit 2 performs conversion in synchronization with the IF signal of the frequency f1 in the same manner as the hardware setting by the RF signal. A local oscillation signal is output to the converter 2. As a result, the signal under test a input to the frequency converter 2 is converted to an intermediate frequency by the frequency converter 2 and sent to the A / D converter 3 as an intermediate frequency signal b. The A / D converter 3 converts the intermediate frequency signal b converted by the frequency converter 2 into a digital intermediate frequency signal c and sends it to the waveform memory 4. The waveform memory 4 stores the digital intermediate frequency signal c converted by the A / D converter 3. After that, the input level of the IF signal is measured by the level detection unit 12 (ST5).
[0042]
The above-described measurement of the input levels of the RF signal and the IF signal may be performed in the order of the IF signal and the RF signal. Here, each input level measurement is performed in about 10 msec.
[0043]
When the input level measurement of the RF signal and the input level measurement of the IF signal are performed as described above, a measurement signal is determined based on the measurement result (ST6). Normally, either the RF signal or the IF signal is input, and as a result of the input level measurement, the higher input level of the RF signal or the IF signal is selected as the measurement signal. For example, if the input level of the RF signal is higher, the RF signal is determined as the measurement signal. When the measurement signal is determined, hardware setting based on the frequency of the measurement signal is performed (ST7). In the hardware setting based on the frequency of the measurement signal, the measurement control unit 17 controls the frequency conversion unit 2 via the drive control unit 18 so that the frequency conversion unit 2 performs conversion synchronized with the f1 IF signal or the frequency f2 RF signal. And outputs a local oscillation signal to the terminal. As a result, the signal under test a input to the frequency converter 2 is converted to an intermediate frequency by the frequency converter 2 and sent to the A / D converter 3 as an intermediate frequency signal b. The A / D converter 3 converts the intermediate frequency signal b converted by the frequency converter 2 into a digital intermediate frequency signal c and sends it to the waveform memory 4. The waveform memory 4 stores the digital intermediate frequency signal c converted by the A / D converter 3 for about 100 msec (ST8).
[0044]
Next, the validity of the signal stored in the waveform memory 4 is detected by the signal validity detector 13 (ST9). Then, the validity of the signal is determined based on the detection result (ST10). Here, if it is determined that the signal is not valid (ST10-No), the process returns to ST2 and re-measurement is performed. As a method other than the re-measurement, the modulation error ratio measurement may be performed by searching the signals of the frequencies f1 and f2, or a status such as “not measured” may be output. On the other hand, if it is determined that the signal is valid (ST10-Yes), the modulation error ratio is calculated based on the digital intermediate frequency signal c stored in the waveform memory 4 (ST11), and the measurement ends. (ST12). The result of the measurement is output and displayed on, for example, a display unit via the external input / output interface 19. When one measurement is completed (ST12), the process returns to the hardware setting (RF) in ST2, and the subsequent operations are repeated.
[0045]
In the measurement processing of FIG. 4 described above, it is also possible to measure the modulation error ratio without judging the validity of the signal by the digital intermediate frequency signal c loaded into the waveform memory 4 after the hardware setting by the measurement signal. .
[0046]
The modulation error ratio measurement device 1 configured as described above can be used as, for example, a monitor of the signal generation device 31 shown in FIG.
[0047]
A signal generator 31 shown in FIG. 5 is provided in, for example, a TV station or the like, and modulates MPEG-2 (original data) including video and audio by a BST-OFDM modulation scheme adopted in an ISDB-T system. And an up-converter (UPCONV) 33 that converts a digital broadcast signal modulated by the modulator 32 from an IF signal to an RF signal and outputs the converted signal, and a switcher 34 that is connected to the input and output of the up-converter 33. Have.
[0048]
Then, the modulation error ratio measuring apparatus 1 of the present example is connected to the switch 34, and the IF signal or the RF signal from the up-converter 33 is input as the signal under test a through the switch 34, and the signal under test a And monitors whether or not the signal generator 31 is outputting a normal signal.
[0049]
As described above, in the modulation error ratio measuring apparatus 1 of the present embodiment, as shown in FIG. 5, for example, it is not necessary to instruct the apparatus which signal of f1 or f2 is input when the signal of the switch 34 is switched. By performing the setting in advance, it is possible to perform measurement by recognizing which signal of f1 or f2 is input.
[0050]
When the measurement processing of FIG. 4 is executed, the signal to be measured is used by monitoring the signal generator 31 shown in FIG. 5 and switching the signal of the switch 34 while the waveform memory 4 is capturing the waveform. A countermeasure is taken when the frequency of a changes. Specifically, after determining the measurement target, the waveform is fetched into the waveform memory 4 via the A / D converter 3 and the level of the waveform stored in the waveform memory 4 is checked to determine the measurement target. The validity of the acquired waveform (the signal is not interrupted or stopped due to switching between f1 and f2 during the acquisition of the waveform or the like) is detected by the signal validity detection unit 13 and is determined by the re-measurement determination unit 16. I have. This makes it possible to evaluate whether the modulation error ratio measurement value is true or false. Therefore, after the measurement signal is selected for the first time, it is necessary to acquire the waveform again for measuring the modulation error ratio. At that time, even if the switching has already occurred, the validity of the signal of the acquired waveform is required. Since the modulation error ratio is measured only when the characteristic is recognized, erroneous modulation error ratio measurement can be prevented. At this time, when it is determined that the validity of the signal is not recognized, for example, a waveform can be taken again to perform re-measurement, or a status such as “not measured” can be output to the outside.
[0051]
A plurality of digital information layers having different modulation schemes are arranged in the frequency band of one channel, and these layers are used as BUT-OFDM-modulated digital broadcast signals as signals to be measured. Is adopted in the signal generator 31 shown in FIG. 5, the output state of the digital broadcast signal can be constantly monitored and monitored, and good information (image and sound) can be always provided.
[0052]
By the way, in the above-described embodiment, a case has been described where two types of signals of frequencies f1 and f2 are selectively input as signals to be measured, but the same applies to a case where three or more types of signals are selectively input. Has the effect of
[0053]
FIG. 6 shows a schematic configuration in a case where three types of signals having frequencies f1, f2, and f3 are selectively input as signals to be measured. In this case, the switching means 21 is connected to the preceding stage of the modulation error ratio measuring apparatus 1 of the present example, and signals f1, f2 and f3 of three kinds of frequencies are input to the switching means 21. Then, the switching means 21 selectively switches the contacts so that any one of the three types of input signals f1, f2, and f3 is input to the modulation error ratio measuring apparatus 1 as a signal to be measured. Can be When a signal to be measured is input to the modulation error ratio measurement device 1, a process equivalent to the measurement process shown in FIG. 4 is executed. That is, in the measurement processing of FIG. 4, the processing of hardware setting and input level measurement related to the frequency f3 is added, and the modulation error ratio of the signal under measurement is measured.
[0054]
Further, the modulation error ratio measuring apparatus 1 of the present embodiment measures the modulation error ratio of the digital broadcast signal subjected to the BST-OFDM modulation. For example, the modulation error ratio (MER) -CN characteristic shown in FIG. 7 is used. It is also possible to convert the modulation error ratio to CN, measure CN, and output it.
[0055]
Further, in the above-described embodiment, the digital intermediate frequency signal A / D converted by the A / D converter 3 is taken in and stored in the waveform memory 4, but the waveform memory 4 is indispensable. Instead of the configuration, it is also possible to adopt a configuration in which the waveform memory 4 is omitted. In this case, in the switching unit 11, the A / D conversion unit 3 is selectively connected to either the level detection unit 12 or the signal validity detection unit 13 by a switching signal from the measurement control unit 17.
[0056]
【The invention's effect】
As described above, according to the modulation error ratio measurement device of the present invention, it is not necessary to instruct the device which signal of a plurality of different frequencies has been input at the time of switching of the signal of the switch, and the setting is performed in advance. By doing so, the measurement can be performed by recognizing the frequency of the input signal.
[0057]
According to the modulation error ratio measuring device of the second aspect, after determining the measurement target, the level of the waveform output from the A / D converter is confirmed, and the validity of the captured waveform (frequency Signal is not interrupted or stopped due to switching or the like), and the validity of the signal is determined. This makes it possible to evaluate whether the modulation error ratio measurement value is true or false. Therefore, after the measurement signal is selected for the first time, it is necessary to acquire the waveform again for measuring the modulation error ratio. At this time, even if the switching has already occurred, the validity of the signal of the acquired waveform is required. Since the modulation error ratio is measured only when the characteristic is recognized, erroneous modulation error ratio measurement can be prevented.
[0058]
Then, the modulation error ratio measuring apparatus of the present invention is used by arranging a plurality of digital information hierarchies having different modulation methods in the frequency band of one channel, and using a digital broadcast signal obtained by BST-OFDM-modulating these hierarchies as a signal to be measured. For example, the output state of the digital broadcast signal can be constantly monitored and monitored, and good information (image and sound) can be always provided.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a schematic configuration of a modulation error ratio measuring device according to the present invention.
FIG. 2 is a waveform chart for explaining a method of determining validity by the modulation error ratio measurement device according to the present invention.
FIG. 3 is a flowchart at the time of measurement by the modulation error ratio measurement device according to the present invention.
FIG. 4 is a diagram illustrating a schematic configuration in a case where three types of signals having frequencies f1, f2, and f3 are selectively input as signals to be measured.
FIG. 5 is a diagram showing a schematic configuration of a signal generator in which the modulation error ratio measuring device according to the present invention is adopted as a monitor.
FIG. 6 is a diagram showing another connection example of the modulation error ratio measuring device according to the present invention.
FIG. 7 is a diagram showing a relationship between a modulation error ratio (MER) and CN.
FIG. 8A is a frequency characteristic diagram of a general analog broadcast signal.
FIG. 3B is a frequency characteristic diagram of the digital broadcast signal.
FIG. 9A is a diagram showing a conventional CN measuring device.
(B) is a diagram showing an error rate-CN characteristic.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Modulation error ratio measuring device, 2 ... Frequency converter, 3 ... A / D converter, 5 ... Signal detector, 6 ... Controller, a ... Measured signal, b ... Intermediate frequency signal, c ... Digital middle Frequency signal.

Claims (5)

A signal to be measured (a) having a plurality of different frequencies is selectively switched and input, and a frequency conversion unit () that converts the frequency of the selected signal to be measured into an intermediate frequency and outputs it as an intermediate frequency signal (b) 2) and
An A / D converter (3) for A / D converting the intermediate frequency signal output from the frequency converter into a digital intermediate frequency signal (c);
A signal detector (5) for detecting the level of a digital intermediate frequency signal output from the A / D converter for each of the frequencies;
When the plurality of different frequencies are set and input in advance, a measurement target is determined based on the level detected by the signal detection unit, and the A is controlled when the frequency conversion unit is controlled in accordance with the determined measurement target. A control unit (6) for calculating and outputting a modulation error ratio based on a digital intermediate frequency signal output by the / D conversion unit. A signal to be measured (a) having a plurality of different frequencies is selectively switched and input, and a frequency conversion unit () that converts the frequency of the selected signal to be measured into an intermediate frequency and outputs it as an intermediate frequency signal (b) 2) and
An A / D converter (3) for A / D converting the intermediate frequency signal output from the frequency converter into a digital intermediate frequency signal (c);
A signal detector (5) for detecting the level of a digital intermediate frequency signal output from the A / D converter for each of the frequencies;
When the plurality of different frequencies are set and input in advance, a measurement target is determined based on the level detected by the signal detection unit, and the A is controlled when the frequency conversion unit is controlled in accordance with the determined measurement target. The validity of the digital intermediate frequency signal output by the / D conversion unit is determined, and when it is determined that the digital intermediate frequency signal is valid, the modulation error ratio is calculated and output based on the digital intermediate frequency signal determined to be valid. A modulation error ratio measuring device, comprising: The signal under test (a) is a digital broadcast signal in which a plurality of digital information layers having different modulation schemes are arranged in a frequency band of one channel, and these layers are subjected to BST-OFDM modulation. Item 3. The modulation error ratio measurement device according to Item 1 or 2. The said control part (6) compares the level of every said several different frequency which the said signal detection part (5) outputs, and determines the frequency with a large level as a measurement object. The modulation error ratio measurement device according to any one of the above. The control unit (6) sets a preset level for each of the plurality of different frequencies in advance, and determines a frequency whose level output by the signal detection unit (5) exceeds the set level as a measurement target. The modulation error ratio measuring device according to any one of claims 1 to 3, wherein the modulation error ratio is determined as:

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