JP2005136549A - Digital transmission device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a digital transmission device that sends and receives a transmit signal modulated by a multi-carrier digital modulation system, and grasps a deterioration state showing an abnormal state. <P>SOLUTION: This digital transmission device is equipped with, on the side of a receiving device, an output device for two-dimensional display (8A, 11, 12, and 13), which is connected to a demodulation part modulating a received transmit signal, and outputs a frequency component in an X-axial direction, and an error level component based upon a decision threshold value of the demodulated signal in a Y-axial direction. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a digital transmission device that visualizes a transmission state in a digital transmission device.

  In recent years, QAM (Quadrature Amplitude Modulation) and OFDM (Orthogonal Frequency Division Multiplexing) have begun to be used as modulation schemes for digital transmission.

  The data is a transport stream (hereinafter referred to as TS) in which video and audio signals are compressed by MPEG processing.

  Several years ago, video and audio were transmitted by analog FM. In analog FM, the SN of video and audio changes depending on the received electric field level. In mobile transmissions such as marathons, where the electric field level changes drastically, the relayed video tends to be a low-quality signal with a lot of noise and disturbance.

  In digital transmission, information is digitized and error correction processing is used together. Therefore, even when the received electric field level changes, the same quality video can be relayed and transmitted as long as error correction is possible. If the electric field level falls below the limit value, error correction becomes impossible and image transmission becomes impossible. This limit can be grasped to some extent by the signal state after demodulation.

  For example, in the 64QAM mode with a large transmission amount of 60 Mbps, the limit CN is about 27 dB, and the limit of the reception electric field needs to be about -70 dBm or more. In the 16QAM2 mode with a small transmission amount of 35 Mbps, the limit CN is about 18 dB, and the limit of the reception electric field is about −80 dBm or more so that video can be transmitted.

  FIG. 15 is an overall configuration diagram of a conventional digital transmission apparatus. In the transmission apparatus of FIG. 15, the video signal is input to the MPEG encoder 1 and becomes compressed data TS. The compressed data TS becomes two-dimensional data Dm by the mapping circuit 2 that determines the modulation mode.

  The data Dm is modulated by the modulation unit (MOD) 3 and becomes, for example, Dmod, which is an intermediate frequency signal in the 130 MHz band, and is sent to the transmission high frequency unit (Th) 4-1.

  The transmission high frequency unit (Th) 4-1 converts the frequency of the intermediate frequency signal Dmod into a signal in the microwave band, amplifies the power, and transmits the signal from the antenna 4-2.

  The radio wave that reaches the receiving antenna 6-1 of the receiving device via the transmission path 5 is input to the receiving high-frequency unit (Rh) 6-2. The reception high-frequency unit (Rh) 6-2 amplifies a weak signal and converts it to an intermediate frequency signal Ddem in the 130 MHz band.

  This Ddem signal is subjected to time timing reproduction and frequency reproduction by a demodulator (DEM) 7 and becomes two-dimensional data Dd. The data Dd is sent to the discrimination / determination unit 8 and returned to the reproduction compressed data TSr. The reproduction compressed data TSr is input to the MPEG decoder 9 and expanded into a video signal.

  Here, in order to grasp the quality of the transmission state and the synchronous reproduction state, the output I and Q data of the demodulator (DEM) 7 is normally connected to the XY input of the oscilloscope 10 and observed. If the transmission state is good, each mapping point (signal point) of the received signal is gathered small as shown in FIG. However, if the transmission state is poor, each mapping point becomes large and scattered as shown in FIG.

  For example, Patent Document 1 discloses that each data is observed by receiving and demodulating a modulated (transmission) signal modulated by the OFDM method and displaying the modulated signal on an oscilloscope.

JP 2002-340937 A (page 2-3)

  However, since the frequency response of the oscilloscope 10 on the X axis is usually less than 1 MHz and cannot follow high-speed signal point changes, it is usually necessary to prepare a dedicated thinned signal for observation.

  Further, the state of the transmission line 5 is not always constant, and changes every moment depending on the level of a river, sea, or paddy field in the middle of the transmission line. Therefore, it is difficult for an oscilloscope to record and save changes in the line conditions of digital transmission that change from time to time.

  Furthermore, recently, transmission in which the primary modulation is 64QAM is also frequently used. Therefore, each of the I and Q data has 8 levels, and the interval between the mapping points is small. In the primary modulation of 64QAM, even if the dispersion is small, the influence on the transmission characteristics is large. Therefore, even if the two-dimensional display is performed, the deterioration state that shows an abnormal state with a small interval is difficult to see.

  An object of the present invention is to provide a digital transmission device capable of grasping a deterioration state indicating an abnormal state in a digital transmission device that transmits and receives transmission signals modulated by a digital modulation method of majority carriers.

  The present invention relates to a digital transmission apparatus that receives a transmission signal modulated by a multi-carrier digital modulation scheme and mapped in two dimensions, and reproduces the transmission signal by identifying the received two-dimensional data. 2D display output device connected to a demodulator for demodulating the received transmission signal on the side and outputting an error level component with a frequency component in the X-axis direction and a discrimination threshold of the signal demodulated in the Y-axis direction It is provided with.

  According to another aspect of the present invention, there is provided a digital transmission apparatus that receives a transmission signal that is modulated by a multi-carrier digital modulation method and that is two-dimensionally mapped, and that reproduces the transmission signal by identifying the received two-dimensional data. An identification determination unit that is connected to a demodulation unit that demodulates the received transmission signal on the apparatus side, and that outputs an identification error signal at the time of identification of the signal obtained by demodulating the transmission signal by the demodulation unit; An output unit that outputs a level increase signal that increases in level according to processing timing, and an error level at the time of identifying a frequency component in the X-axis direction and a signal demodulated in the Y-axis direction from the identification error signal and the level increase signal A video processor for outputting the components is provided.

  According to another aspect of the present invention, there is provided a digital transmission apparatus that receives a transmission signal that is modulated by a multi-carrier digital modulation method and that is two-dimensionally mapped, and that reproduces the transmission signal by identifying the received two-dimensional data. On the apparatus side, connected to a demodulator that demodulates the received transmission signal, an identification determination unit that outputs an identification error signal at the time of identification of the signal demodulated by the demodulator, and the identification error signal, The demodulator generates a level increase signal that increases in level according to the timing of the demodulation process for demodulating the transmission signal, and demodulates the frequency component in the X-axis direction and the Y-axis direction from the identification error signal and the level increase signal. And a video processor for outputting an error level component at the time of identification of the received signal.

  According to the present invention, in a digital transmission device that transmits and receives a transmission signal modulated by a digital modulation method, it is possible to obtain a digital transmission device capable of grasping a deterioration state indicating an abnormal state.

  FIG. 1 is a block diagram showing the overall configuration of the first embodiment of the present invention. FIG. 1 is a diagram showing the overall configuration of the conventional digital transmission apparatus of FIG. 15. In FIG. ) 12 and a video processor 13 were added.

  As a result, an image 9a is displayed on the monitor screen (not shown) connected to the output of the MPEG decoder 9 in FIG. 1, for example, as shown in FIG. For example, as shown in FIG. 2 (b), a monitor screen (not shown) connected to the output of the image 9a has a frequency component in the X-axis direction and a signal demodulated in the Y-axis direction. A superimposed image is displayed by superimposing the two-dimensional display image 13a composed of error level components.

  In FIG. 1, an FST (frame start pulse) signal from the demodulator (DEM) 7 is input to the CNT 11.

  The CNT 11 outputs an sp signal (sampling pulse) to the SH 12 and also outputs a Ys signal (Y component sawtooth wave), and the Ys signal is input to the video processing unit 13.

  The SH 12 receives the output De signal (identification error signal) of the identification determiner 8A. The output Xh signal of SH 12 (X component sample hold of the De signal) is input to the other terminal of the video processor 13.

  FIG. 3 is a timing chart showing operations of the timing controller CNT11 and the sampling and holding device SH12 in FIG.

  In response to the FST (frame start pulse) signal from the demodulator (DEM) 7, the CNT 11 outputs an sp signal whose phase is shifted by FFT processing period × N for each symbol period (cycle). As a result, the SH 12 outputs a De signal obtained by sequentially sampling the level of each carrier arranged every 1 FFT period of the I signal from the data of the low frequency component every symbol period.

  In addition, the CNT 11 creates and outputs a Ys signal whose level is constantly increased every symbol period. The number of increases N of the Ys signal may be the same value as the number of carriers. Alternatively, the maximum number of FFT processes (for example, 1024) may be used.

  FIG. 4 is a configuration diagram of the discrimination / determination unit 8A in FIG. The output I data and Q data of the demodulator (DEM) 7 are input to the data mapper 8-1 and the identification error demapping unit 8-2, respectively. The data mapper 8-1 outputs identification data obtained by performing identification from the I data and Q data. The identification data is input to the data terminal of the error soft decision corrector 8-3.

  The identification error demapping unit 8-2 outputs a De signal (identification error signal) from a normal identification point from the I data and the Q data. The De signal (identification error signal) is output from the identification determiner 8A and also input to the soft decision terminal of the error soft decision corrector 8-3. The error soft decision corrector 8-3 performs error correction in consideration of the probability of the signal from the value of the soft decision terminal to the data terminal, and outputs a TSr signal.

  FIG. 5 is a block diagram of the video processing unit 13 in FIG. The video processing unit 13 has the Xh signal, which is the output of the SH 12 in FIG. 1, and the Ys signal, which is the output of the CNT 11, as input signals.

  Input signals Xh and Ys are input to A / D converters 14i and 14q, respectively. The outputs of the A / D converters 14i and 14q are input to the change point detectors 15i and 15q, respectively, and also input to the writing unit 16. The outputs of the change point detectors 15 i and 15 q are input to the writing unit 16.

  The address output, data output, and write enable (WE) output of the writing unit 16 are input to the control unit 19. The address output, data output, and WE output of the initialization unit 17 are input to the control unit 19. The address output and read enable (RE) output of the read display unit 18 are input to the control unit 19.

  The control unit 19 outputs an enable (EN) signal for permitting operation to the writing unit 16, the initialization unit 17, and the reading display unit 18 based on the video signal output from the MPEG decoder 9 of FIG. In addition, the address output, data output, and control signals WE and RE of the writing unit 16, the initialization unit 17, and the reading display unit 18 are switched and selected between the memory 20a and the memory 20b and output. Further, the data read from the memories 20 a and 20 b is output to the adder 21.

  The adder 21 superimposes the data read from the memories 20a and 20b on the video signal which is the output of the MPEG decoder 9 in FIG.

  FIG. 6 is a configuration diagram of the change point detectors 15i and 15q in FIG. 5 (change point detectors 15i and 15q have the same configuration). FIG. 7 is a diagram for explaining the operation of the change point detection and the writing process described below.

  It is assumed that the I and Q data that are the output of the demodulator (DEM) 7 in FIG. In this case, the Xh signal and Ys signal, which are input signals of the video processor 13, are input to the latch 15-1 and sampled at 14.3 MHz ((1) in FIG. 7). The output signal of the latch 15-1 is input to the latch 15-2 and the subtracter 15-3. The output signal of the latch 15-2 is input to the other side of the subtractor 15-3.

  The output signal of the subtractor 15-3, that is, the input differential signal is input to the absolute value converter 15-4, and the positive and negative components are converted into absolute values. The output signal of the absolute value generator 15-4 is input to the determiner 15-5 and is compared with the reference value Th by the determiner 15-5 to indicate “henka” in which a component equal to or higher than the reference value Th is regarded as a change. A change point pulse ((2) in FIG. 7) is output.

  FIG. 8 is a configuration diagram of the writing unit 16 in FIG. The Xh signal and the Ys signal are converted into a two-dimensional address in the display space by the synthesizer 16-1. The conversion result is held by the S1 pulse from the WE generator 16-2 (which operates or stops according to the EN input), and outputs an address.

  The gate 16-3 outputs a pulse h1 obtained by ORing the change point pulses ((2) in FIG. 7) indicating “henka” of the Xh signal and the Ys signal. This pulse h1 is input to the gates 16-4 and 16-5.

  Gate 16-4 is the source of the WE pulse. The gate 16-4 receives the W1 pulse from the WE generator 16-2 (a sampling pulse W1 ((3) in FIG. 7) created by dividing 14.3 MHz by 10) and generates the sampling pulse W1. Is coincident with the pulse h1 obtained by ORing the change point pulses ((2) in FIG. 7).

  If they do not match ((4) in FIG. 7), they are sampled as they are (write “1” to the SRAM address), and a WE pulse is output. If they match ((5) in FIG. 7), the sample is canceled. , WE is turned off. In this case, since the probability that the next sample will also be a change point is high, the sample phase is shifted ((6) in FIG. 7). The writing unit 16 always outputs data H. As a result, data of level “H” is written in the memory space corresponding to the values of the I and Q data.

  Here, the operation of the writing unit 16 will be described again with reference to FIG. It is assumed that the I and Q data that are the output of the demodulator (DEM) 7 in FIG. In this case, the Xh signal and Ys signal which are the input signals of the video processing unit 13 and the values of the I and Q data are the 4, 10, 16,..., (6n + 4) th sample pulse, that is, 6 samples. It is assumed that the writing unit 16 takes in at a cycle timing.

  In such a case, at the 16th sample pulse timing, "henka" and the sample pulse timing coincide ((5) in FIG. 7). Therefore, when the I and Q values are taken in at the 16th sample point, the locus that is moving transiently from the normal signal point A in FIG. 16A to another normal signal point B. The midpoint value of is taken in. If a large number of such intermediate points of the locus are taken in, the signal points appear to be scattered as shown in FIG.

  Therefore, in the embodiment of the present invention, the capturing of the Xh signal and Ys signal values at the sample point where the timing of the sample pulse coincides with “henka”. Further, since there is a high probability that the next sample timing will also be a change point, the sample pulse generation timing is changed ((6) in FIG. 7). Then, the Xh signal and Ys signal values at the sample points whose timings do not match are taken into the writing unit 16 as they are.

  FIG. 9 is a block diagram of the initialization unit 17 in FIG. The address generator 17-1 and the WE generator 17-2 operate or stop according to the EN input. The address generator 17-1 outputs an address corresponding to the EN input. The WE generator 17-2 outputs WE corresponding to the EN input. Also, “L” is output as data.

  As an overall operation, data “L” is written in the memory address space corresponding to the address generator 17-1 in accordance with the EN input. Specifically, initialization is performed so that the display space in which the constellations are accumulated is black.

  FIG. 10 is a diagram for explaining the operation of the control unit 19 in FIG. First, an F pulse is generated internally as the timing of the frame period from the input video signal. Then, display (reading), erasing (initialization), and constellation writing (writing) are performed on the two memories 20a and 20b in accordance with the F pulse.

  Specifically, when the memory 20a is displaying (reading) and erasing (initializing), the memory 20b performs constellation writing (writing). Further, when the memory 20a is (1) constellation writing (writing), the memory 20b has (1) display (reading) in field 1, (3) erasing (initialization), and (4) display (reading) in field 2. (5) Erase (initialize).

  Here, in (1) constellation writing, “1” is written to the SRAM address corresponding to the sampled Xh (I) and Ys values (performed for one frame period (cycle)). In the (2) display (field 1), the data of the SRAM address corresponding to the scanning line is read out for each pixel. If the corresponding Xh (I), Ys value exists, the read value becomes “1”, and one pixel of the NTSC screen is displayed in white.

  In (3) erasure (field 1), “0” is written to the address read in (2) (the memory is initialized and the memory contents of the displayed pixel area are returned to black). In (4) display (field 2), the same operation as in (2) display (field 1) is performed. In (5) Erase (Field 2), the same operation as in (3) Erase (Field 1) is performed.

When the memory 20a displays (reads) and erases (initializes) and the memory 20b performs constellation writing (writing), the following is repeated.
First half of field 1 of frame 1: Reading of an even address in the memory 20a.
Second half of field 1 of frame 1: erasure of even address in memory 20a.
First half of field 2 of frame 1: Reading of odd address of memory 20a
Second half of field 2 of frame 1: Erasing odd addresses in memory 20a.
Frame 1 field 1: Write to Xh (I), Ys signal corresponding address in memory 20a.
Frame 2 field 2: Write to the memory 20a at the address corresponding to the Xh (I) and Ys signals.
First half of field 1 of frame 3: read even address of memory 20a
Second half of field 1 of frame 3: Erasing even addresses in memory 20a.
Thereafter, the above operation is repeated.

On the other hand, when the memory 20b displays (reads) and erases (initializes) and the memory 20b performs the constant write (write), the following is repeated.
Frame 1 field 1: Write to Xh (I), Ys signal corresponding address to memory 20b.
Frame 1 field 2: Write to the memory 20b at the address corresponding to the Xh (I) and Ys signals.
First half of field 1 of frame 2: Reading of even address of memory 20b
Second half of field 1 of frame 2: erasure of even address in memory 20b.
First half of field 2 of frame 2: Reading of odd address of memory 20b.
Second half of field 2 of frame 2: Erasing odd addresses in memory 20b.
Thereafter, the above operation is repeated.

  As a result, the value of the I data from the demodulator (DEM) 7 is converted into the corresponding memory address space, and the level “H” is written into the memory 20a or 20b. In each of the memories 20a and 20b, the level “H” is read from the corresponding memory address in the reading period. The contents of the non-corresponding memory address remain “L”. In the erasure (initialization) performed after the reading is completed, the accumulated contents of the mapping points are initialized by writing “L” in the address space corresponding to the reading.

  FIG. 11 is a configuration diagram of the readout display unit 18 in FIG. The operations of the address generator 18-1 and the RE generator 18-2 operate or stop according to the EN input. The address generator 18-1 outputs an address corresponding to the display screen. The RE generator 18-2 outputs an RE.

  As an overall operation, the memory address space data corresponding to the display address generator 18-1 is read in accordance with the EN input. That is, the display space in which the constellation is accumulated is output according to the scanning line timing for display.

  The read constellation space is superimposed on the video signal which is the output of the MPEG decoder 9 of FIG. 1 by the adder 21 and output as a video XY signal.

  A monitor screen (not shown) connected to the output of the video processor 13 is displayed on a monitor screen (not shown) connected to the output of the MPEG decoder 9, for example, as shown in FIG. A superimposed image is displayed by superimposing a two-dimensional display image 13a composed of a frequency component in the X-axis direction and an error level component at the time of identifying the demodulated signal in the Y-axis direction on the image 9a.

  In this embodiment, since there is no band limitation for writing, there is no problem such as distorted display that occurs in a conventional oscilloscope or the like.

  In addition, according to the present embodiment, in the two-dimensional display signal 13a on the display screen of FIG. 2, the noise component of the carrier in the deteriorated band increases. It is displayed thick. Also, the thickness changes according to the degree of the deterioration. For this reason, it is possible to easily determine whether frequency selective fading has occurred in the used band and partially deteriorated, or whether the entire band has deteriorated and improvement is difficult.

  Further, according to the present embodiment, since the Y-axis direction is an error level component at the time of identifying the demodulated signal component, it is possible to grasp the deterioration state indicating an abnormal state even if the transmission signal is 64QAM modulation. .

  In the case of frequency selective fading, there is a possibility that the level of the multipath wave that causes an adverse effect is reduced by changing the direction of the receiving antenna, and as a result, frequency selective fading can be avoided.

  FIG. 12 is a block diagram showing the overall configuration of the second embodiment of the digital transmission apparatus according to the present invention. FIG. 13 is a block diagram of the video processing unit 13A in FIG.

  FIG. 11 is a diagram showing the overall configuration of the conventional digital transmission apparatus of FIG. 14, in which the oscilloscope 10 is removed, the identification / determination unit 8 is replaced with the identification / determination unit 8A of FIG. 1, and a video processing unit 13A is added. The video processing unit 13A receives the output De signal (identification error signal) of the discrimination determination unit 8A. A video processor 13A shown in FIG. 13 removes the A / D converter 14q and the change point detector 15q in the video processor 13 shown in FIG. 5, and a no-change period detector 22 and a SAW (sawtooth wave) generator 23. Was added. FIG. 14 is a timing chart showing an operation in the video processing unit 13A of FIG.

  The output De signal (identification error signal) from the identification determination unit 8A is input to the AD converter 14i. The output of the AD converter 14 i is input to the change point detector 15 i and the writing unit 16. The output henka of the change point detector 15 i is input to the writing unit 16 and the no-change detector 22. The output nasi signal of the no-change detector 22 is input to the SAW generator 23. The output Ys signal of the SAW generator 23 is input to the writing unit 16.

  The change point detector 15i outputs, as henka, the timing at which the level of the I data has changed.

  The no-change period detector 22 detects a state where there is no henka for a certain period, and outputs a nasi signal whose level is at level H.

  The SAW generator 23 generates a SAW wave whose level increases constantly every symbol period from the timing when the nasi signal falls, and outputs a Ys signal that outputs the SAW wave again from the initial level when nasi falls again. .

  The address output, data output, and WE output of the writing unit 16 are input to the control unit 19.

  The address output, data output, and WE output of the initialization unit 17 are input to the control unit 19.

  The address output and RE output of the readout display unit 18 are input to the control unit 19.

  Based on the video signal output from the MPEG decoder 9 in FIG. 12, the control unit 19 outputs two EN signals that permit the operation to the writing unit 16, the initialization unit 17, and the reading display unit 18. Further, the address output, data output, and control signals WE and RE of the writing unit 16, the initialization unit 17, and the reading display unit 18 are switched and selected between the memory 20a and the memory 20b and output. Further, the data read from the memories 20 a and 20 b is output to the adder 21.

  The adder 21 superimposes the data read from the memories 20a and 20b on the video signal which is the output of the MPEG decoder 9 in FIG.

  As a result, the values of the I and Q data from the demodulator (DEM) 7 are converted into the corresponding memory address space, and the level H is written into the memory 20a or 20b. In each of the memories 20a and 20b, the level “H” is read from the corresponding memory address in the reading period. The contents of the non-corresponding memory address remain “L”. Erasing (initialization) performed after completion of reading initializes the accumulated contents of mapping points by writing “L” in an address space corresponding to reading.

  The read constellation space is superimposed by the adder 21 on the video signal that is the output of the MPEG decoder 9 in FIG. 12, and is output as a video XY signal.

  A monitor screen (not shown) connected to the output of the video processor 13A is displayed on a monitor screen (not shown) connected to the output of the MPEG decoder 9, for example, as shown in FIG. A superimposed image is displayed by superimposing a two-dimensional display image 13a composed of a frequency component in the X-axis direction and an error level component at the time of identifying the demodulated signal in the Y-axis direction on the image 9a.

  Even in this embodiment mode, there is no problem such as distorted display that occurs in an oscilloscope because there is no band limitation for writing.

  Also in this embodiment, in the two-dimensional display signal 13a on the display screen of FIG. 2, the noise component of the carrier in the degraded band increases, so that when displayed in two dimensions, the horizontal line is vertical compared to the band in good condition. It appears thick in the direction. Also, the thickness changes according to the degree of the deterioration. For this reason, it is possible to easily determine whether frequency selective fading has occurred in the band being used and partially deteriorated, or whether the entire band has deteriorated and improvement is difficult.

  Also in the present embodiment, since the Y-axis direction is an error level component at the time of identifying the demodulated signal component, it is possible to grasp a deterioration state indicating an abnormal state even if the transmission signal is 64QAM modulation.

  In the above-described embodiment of the present invention, only the display of two-dimensional I and Q data has been described. However, the superimposed video signal includes information related to a delay profile, bit error, and input electric field, The video signal including the synchronization state of the transmission apparatus and the decompression state of the MPEG codec may be included.

1 is an overall configuration diagram showing a first embodiment of a digital transmission apparatus according to the present invention. (A) is an example of the image displayed on a monitor screen, (b) is a figure which shows the example of the image displayed on a monitor screen, and a two-dimensional display image. FIG. 2 is a timing diagram showing operations of a timing controller CNT and a sampling and holding device in FIG. 1. It is a block diagram of the identification determination device in FIG. It is a block diagram of the video processing apparatus in FIG. It is a block diagram of the change point detector in FIG. It is a figure explaining the operation | movement of a change point detection and a write-in process. It is a block diagram of the writing part in FIG. It is a block diagram of the initialization part in FIG. It is a figure explaining the operation | movement of the control in FIG. It is a block diagram of the read-out display part in FIG. It is a block diagram which shows the whole structure of 2nd Embodiment of the digital transmission apparatus by this invention. It is a block diagram of the video-ized processor in FIG. It is a timing diagram which shows the operation | movement in the video processor of FIG. It is a whole block diagram of the conventional digital transmission apparatus. It is a figure which shows each mapping point (signal point) of a received signal observed with the oscilloscope of FIG. 15, (a) is a figure when a transmission state is good, (b) is a figure when a transmission state is bad.

Explanation of symbols

1: MPEG encoder, 2: Mapping circuit, 3: Modulation unit (MOD, 4-1: Transmission high-frequency unit (Th), 4-2: Antenna, 5: Transmission path, 6-1: Antenna, 6-2: Reception High-frequency unit (Rh), 7: Demodulation unit (DEM), 8, 8A: Discriminator / determiner, 9: MPEG decoder, 9a: Image displayed on monitor screen (not shown) connected to the output of MPEG decoder, 10 : Oscilloscope, 11: timing controller (CNT), 12: sampling hold unit (SH), 13, 13A: video processing unit, 13a: two-dimensional display image, 14i, 14q: A / D converter, 15i, 15q: Change point detector, 16: writing unit, 17: initialization unit, 18: readout display unit, 19: control unit, 20a, 20b: memory, 21: adder, 22: no change period Can, 23: SAW generator.

Claims (3)

  In a digital transmission device that receives a transmission signal that is modulated by a multi-carrier digital modulation method and that is two-dimensionally mapped, and that reproduces the transmission signal by identifying the received two-dimensional data, the reception device receives the transmission signal. And a two-dimensional display output device that is connected to a demodulator that demodulates the transmission signal and that outputs a frequency component in the X-axis direction and an error level component from the discrimination threshold value of the demodulated signal in the Y-axis direction. A digital transmission device characterized by the above.   In a digital transmission device that receives a transmission signal that is modulated by a multi-carrier digital modulation method and that is two-dimensionally mapped, and that reproduces the transmission signal by identifying the received two-dimensional data, the reception device receives the transmission signal. An identification determination unit that is connected to a demodulation unit that demodulates the transmission signal and outputs an identification error signal at the time of identification of the signal demodulated by the demodulation unit, and according to a demodulation processing timing in the demodulation unit An output unit that outputs a level increase signal that increases the level, and a video that outputs a frequency component in the X-axis direction and an error level component at the time of identifying the demodulated signal in the Y-axis direction from the identification error signal and the level increase signal A digital transmission device comprising a processing processor. In a digital transmission apparatus that receives a transmission signal that is modulated by a multi-carrier digital modulation method and is mapped in two dimensions, and that reproduces the transmission signal by identifying the received two-dimensional data, the reception apparatus receives the transmission signal. An identification determination unit that is connected to a demodulation unit that demodulates the transmission signal, outputs an identification error signal at the time of identification of the signal demodulated by the demodulation unit, and from the identification error signal, the demodulation unit When generating a level increase signal that increases in level according to the timing of demodulation processing for demodulating a transmission signal, and identifying a signal demodulated in the X-axis direction and the Y-axis direction from the identification error signal and the level increase signal A digital transmission apparatus comprising a video processing unit that outputs the error level component of.

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