JP4374271B2 - Digital modulation signal evaluation device - Google Patents

Description

  The present invention relates to a technique for evaluating a digital modulation signal used in terrestrial digital broadcasting or the like.

  Television terrestrial broadcasts have shifted to digital instead of conventional analog methods, and various devices for evaluating digital modulation signals used in terrestrial digital broadcasts have been proposed.

  The quality of this kind of digital modulation signal is generally evaluated by a CN ratio, a bit error rate (BER), a modulation error ratio (MER), etc., which represent the ratio of carrier wave to noise (noise). In addition to the method of calculating these numerically, the orthogonal coordinates of the vertical axis I and the horizontal axis Q are displayed on the screen of the display, and the baseband signals I and Q obtained by demodulating the digital modulation signal on the coordinates are displayed. Plotting the coordinate points is also done.

  This display is generally called a constellation display, and the approximate position of the plotted coordinate point depends on the modulation format of the digital modulation signal.

For example, if the digital modulation signal to be evaluated is a four-phase QPSK, and there is no error in the digital modulation signal, as shown in FIG. A specific coordinate point (reference point),
A = (i, q), B = (i, −q),
C = (− i, −q), D = (− i, q)
However, i = q (> 0)
Only will be plotted.

  However, the digital modulation signal to be actually evaluated contains various noise components, and the coordinate points of the baseband signals I and Q obtained by demodulating them are as shown in FIG. The reference points A to D are dispersed.

  That is, the worse the quality of the digital modulation signal, the greater the variance of the plotted points with respect to the reference points A to D.

  Therefore, it is possible to grasp the quality of the digital modulation signal by observing the plot points.

  Various devices having such a constellation display function are disclosed, and are also disclosed in the following Patent Document 1.

JP 2002-124931 A

  However, in the method of simply plotting the coordinate points of the baseband signal on the Cartesian coordinates as in the conventional constellation display described above, even if a plurality of plots are plotted at the same coordinate position, this cannot be recognized. There is a problem that the degree of concentration cannot be accurately grasped.

  In addition, in order to grasp the transition of the constellation state, it is necessary to observe the position change of each plot point. However, the transition of the constellation state is grasped from the minute changes of many points displayed on the display. That was not easy.

  An object of the present invention is to solve this problem and provide a digital modulation signal evaluation apparatus that can easily grasp the degree of constellation concentration and state transition.

In order to achieve the above object, the digital modulation signal evaluation apparatus of the present invention comprises:
A demodulator (22) that demodulates the digital modulation signal to be evaluated and sequentially outputs a baseband signal of a modulation component of the digital modulation signal;
For each baseband signal output from the demodulator, position calculation means (23) for obtaining coordinate points on orthogonal coordinates determined by the in-phase component (I) and the orthogonal component (Q) ;
And Table示器(30),
Constellation display means (27) for displaying the orthogonal coordinates on the display and displaying the constellation state of the baseband signal on the orthogonal coordinates based on the coordinate points obtained by the position calculation means. In the digital modulation signal evaluation apparatus provided ,
A frequency distribution calculating means (25) for dividing the four quadrants of the orthogonal coordinates into a plurality of regions including a plurality of different neighboring coordinate points, and calculating the frequency of the coordinate points for each region;
The constellation display means has a different color, shading or pattern depending on the frequency of the coordinate points located in each area over the entire area so that the magnitude of the frequency obtained by the frequency distribution display means can be identified. Is characterized by the uniform application .
The digital modulation signal evaluation apparatus according to claim 2 is the digital modulation signal evaluation apparatus according to claim 1,
The constellation display means displays a boundary line of each region.
The digital modulation signal evaluation apparatus according to claim 3 is the digital modulation signal evaluation apparatus according to claim 1 or 2,
The constellation display means displays a correspondence relationship between the frequency range and the color or shade or pattern difference.
Furthermore, the digital modulation signal evaluation apparatus according to claim 4 is the digital modulation signal evaluation apparatus according to any one of claims 1 to 3,
The constellation display means uniformly displays the respective areas in different colors, shades or patterns depending on the display mode in which the coordinate points obtained by the position calculation means are plotted on the orthogonal coordinates and the frequency of the coordinate points. The display mode can be arbitrarily selected .

As described above, in the digital modulation signal evaluation apparatus of the present invention, the four quadrants of orthogonal coordinates are divided into a plurality of regions, the frequency distribution of coordinate points for each baseband signal for each region is obtained, and each region is represented by its frequency. The baseband signal coordinate points are displayed in different colors, shades or patterns uniformly depending on the frequency of the coordinate points located in each region over the entire region. Can accurately grasp the variation and concentration level.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a configuration of a digital modulation signal evaluation apparatus 20 (hereinafter referred to as an evaluation apparatus 20) to which the present invention is applied.

  Similar to the modulation error ratio measuring apparatus of Patent Document 1, the evaluation apparatus 20 demodulates a digital modulation signal output from various devices including a receiver used for terrestrial digital broadcasting, and the demodulated baseband signal. Constellation display processing for is performed.

  As shown in FIG. 1, the digital modulation signal d (t) to be evaluated is converted into a digital signal sequence D (k) by the A / D converter 21 and input to the demodulator 22. Here, the digital modulation signal d (t) to be evaluated is directly sampled by the A / D converter 21, but a frequency converter is provided in the previous stage of the A / D converter 21 to provide a higher frequency. The digital modulation signal (digital broadcast wave) may be directly input.

  The demodulator 22 performs demodulation processing on the digital signal sequence D (k), and sequentially outputs the in-phase component I (k) and the quadrature component Q (k) of the baseband signal of the modulation component.

  The position calculation means 23 sequentially obtains the coordinate point P (k) on the orthogonal coordinates determined by the in-phase component I (k) and the orthogonal component Q (k) for the baseband signals sequentially output from the demodulator 22. Store in the memory 24.

  The demodulator 22 performs a demodulation process based on the modulation scheme of the input digital modulation signal d (t), but also performs a correction process such as a frequency error necessary for the demodulation.

  The frequency distribution calculating means 25 uses I = ± Im and Q = ± Qm in the orthogonal coordinate space of I and Q as a definition area, and the first to fourth quadrants in the definition area are shown in FIG. As shown, each of N regions (N, a plurality represented by an integer product a × b) E (i, j), E (-i, j), E (-i, -J) and E (i, -j), and the frequencies H (i, j), H (-i, j), H (-i, -j), H (i , -J) (where i = 1 to a, j = 1 to b).

  FIG. 2 shows an example in which each region is a square region with a = b = 8, but the method of dividing the region may be arbitrarily set according to the modulation method to be evaluated.

  The constellation display means 27 displays the above-described I and Q orthogonal coordinates on the screen of the display 30 and identifies each magnitude of the frequency obtained by the frequency distribution calculating means 25 for each area of the displayed orthogonal coordinates. Display as you can.

  This area is identified by using different colors, different darknesses, different patterns (for example, hatching intervals), or a combination thereof.

  In addition, the number of identification stages is arbitrary. For example, when the above-described QPSK is divided into three stages excluding frequency 0, the number of coordinate points to be acquired (number of samples) is set to 1000 for each quadrant. It is divided into a first range up to 199, a second range of frequencies 200 to 499, and a third range of frequencies 500 or more, and the identification display is performed according to the range including the frequencies.

  In addition to the method of dividing the range by the frequency itself, it is also possible to perform the identification display by dividing the range by the ratio of the frequency of each region to the total number of coordinate points.

  The constellation display means 27 displays not only the frequency distribution but also the frequency range information about the identification display on the display 30 together.

  FIG. 3 shows one display example by the constellation display means 27. On the left side of the screen, the modulation method (QPSK in this case), the number of samples (1000 in this case), the frequency range and the identification display are shown. A correspondence diagram (in this case, “red”, “blue”, “green” identification display and frequency range) is displayed.

  In addition, on the right side of the screen, orthogonal coordinates of I and Q are displayed, and among the regions in each quadrant, the region excluding the frequency 0 is displayed in a color corresponding to the range including the frequency (note that the color is shown in the drawing). (They are shown in letters because they cannot be represented.)

  In the coordinate screen thus identified and displayed, the area where more than half of the coordinate points of the baseband signal are concentrated can be accurately and intuitively grasped from the position displayed in “red”, and the area is described above. If the region includes the reference point or is close to the region, it can be evaluated that the quality of the digital modulation signal is high.

  Conversely, when there is no “red” area and only “blue” and “green” areas, the baseband signal coordinate points vary greatly and the quality of the digital modulation signal Can be evaluated as low.

  Thus, each area is identified and displayed according to the frequency of the coordinate points included in the area, so that the degree of constellation concentration can be accurately and intuitively grasped.

  In the above example, the degree of frequency is identified by the difference in color. However, the same color may be represented by shading or light and shade, and as shown in FIG. It is also possible to display the identification by, for example.

  The display processing by the constellation display means 27 is performed for a predetermined number of coordinate points P stored in the memory 24. The contents of the memory 24 are sequentially updated, and the above-described coordinate points P are used for the above-described display processing. By continuously performing the display process, it is possible to observe the change in the state of the constellation of the digital modulation signal almost in real time.

  Moreover, when the constellation display is performed in real time as described above, conventionally, the position change of each coordinate point has to be observed, but in the evaluation apparatus 20 of this embodiment, the identification display is performed in units of each region. Therefore, it is possible to accurately grasp the tendency of the state change without being confused by the minute change of the coordinate point itself.

  For example, when the phase or amplitude of the digital modulation signal is changed to a different state, a certain region as shown in (a) in FIG. 5 is indicated by “red”, and as shown in (b) in FIG. The color of the area becomes “red” and the color of the original area changes to the “blue” state. In this way, the state transition can be easily grasped by the color change and the color movement, but this is the movement of many coordinate points. It is difficult to do by observing.

  In addition to the real-time display as described above, as in the evaluation apparatus 20 shown in FIG. 6, the frequency information of each area calculated by the frequency distribution calculating unit 25 for a predetermined number of samples is stored in a plurality of sets of memories 26. In addition, the constellation display means 27 reads out the frequency information of the set designated by the operation of the operation unit (not shown) at an arbitrary timing and displays it on the screen of the display 30 as described above. There may be.

  In addition, the display mode for plotting the coordinate points of the baseband signals I and Q on the orthogonal coordinates as in the conventional device, and the frequency distribution for each area as in this embodiment can be represented by color, shading, pattern, etc. The display mode for identifying and displaying may be arbitrarily selected.

  In the above description, the evaluation apparatus having only the constellation display function has been described. However, as shown in Patent Document 1, the CN ratio of the digital modulation signal is calculated based on the baseband signal obtained by the demodulation unit 22. , MER (modulation error ratio) and BER (error rate) are calculated, and the present invention can also be applied to an evaluation apparatus having a function of displaying it on a display.

The figure which shows the structure of embodiment of this invention The figure for demonstrating the process of the principal part of embodiment The figure which shows an example of the processing result of embodiment The figure which shows an example of the processing result of embodiment The figure which shows the correspondence example of the change of the quality of the digital modulation signal and the change of the display The figure which shows the modification of embodiment Figure showing a display example of a conventional device

Explanation of symbols

  DESCRIPTION OF SYMBOLS 20 ... Digital modulation signal evaluation apparatus, 21 ... A / D converter, 22 ... Demodulator, 23 ... Position calculation means, 24, 26 ... Memory, 25 ... Frequency distribution calculation means, 27 ... Consta Display means, 30 ... indicator

Claims (4)

A demodulator (22) that demodulates the digital modulation signal to be evaluated and sequentially outputs a baseband signal of a modulation component of the digital modulation signal;
For each baseband signal output from the demodulator, position calculation means (23) for obtaining coordinate points on orthogonal coordinates determined by the in-phase component (I) and the orthogonal component (Q) ;
And Table示器(30),
Constellation display means (27) for displaying the orthogonal coordinates on the display and displaying the constellation state of the baseband signal on the orthogonal coordinates based on the coordinate points obtained by the position calculation means. In the digital modulation signal evaluation apparatus provided ,
A frequency distribution calculating means (25) for dividing the four quadrants of the orthogonal coordinates into a plurality of regions including a plurality of different neighboring coordinate points, and calculating the frequency of the coordinate points for each region;
The constellation display means has a different color, shading or pattern depending on the frequency of the coordinate points located in each area over the entire area so that the magnitude of the frequency obtained by the frequency distribution display means can be identified. A digital modulation signal evaluation apparatus characterized by uniformly applying 2. The digital modulation signal evaluation apparatus according to claim 1, wherein the constellation display means displays a boundary line of each region. 3. The digital modulation signal evaluation apparatus according to claim 1, wherein the constellation display means displays a correspondence relationship between a frequency range and the color or shade or pattern difference. The constellation display means uniformly displays the respective areas in different colors, shades or patterns depending on the display mode in which the coordinate points obtained by the position calculation means are plotted on the orthogonal coordinates and the frequency of the coordinate points. 4. The digital modulation signal evaluation apparatus according to claim 1, wherein the display mode can be arbitrarily selected.

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