JP4414272B2 - Terrestrial digital broadcast retransmitter - Google Patents

Description

    The present invention relates to a terrestrial digital broadcast retransmission apparatus that retransmits a terrestrial digital broadcast in CATV, joint reception, or the like.

  The terrestrial digital broadcast re-transmission device consists of a terrestrial digital signal processor, terrestrial digital channel proper amplifier (reference Japan CATV Technology Association JCTEA STD-011), etc. It is a device to do. Digital terrestrial broadcast waves have different signal qualities such as the signal level that can be received depending on the position of the reception point, and change depending on time and season. For this reason, the terrestrial digital broadcast retransmitting device includes circuits having various functions such as an auto gain control circuit (AGC), an output level adjustment circuit, and a frequency conversion circuit. Also, the signal processing of the terrestrial digital broadcast retransmitting device is generally performed by converting the signal to an intermediate frequency using a local oscillation signal from a local oscillator, and after the signal processing, the same channel as the input channel is used. When outputting, up-conversion is performed using the same local signal. Further, when output is performed on a channel different from the input channel, it is up-converted using a local signal from another local oscillator and is output as a terrestrial digital broadcast signal of a different channel.

  Digital terrestrial broadcasting employs OFDM (Orthogonal Frequency Division Multiplexing) for modulation. In general, an OFDM signal is composed of a large number of carriers having a narrow bandwidth, and has a rectangular spectrum. As the time waveform, in order to make it less susceptible to multipath, the rear part of the effective symbol is copied and pasted in front of the effective symbol as a guard interval. Thereby, it becomes difficult to receive the influence of the interference by the multipath of the delay time below the guard interval. OFDM has a longer symbol length and longer guard interval compared to single carrier modulation, so it is more resistant to multipath interference. However, because it uses a large number of carriers, intermodulation distortion occurs between carriers due to nonlinearities in the transmission path. It is characterized by being easily affected by non-linear distortion.

  As shown in FIG. 6, the frequency spectrum of the terrestrial digital broadcast signal has a channel bandwidth of 6 MHz as in analog broadcasting, and is composed of 13 OFDM segments (about 5.6 MHz) with a bandwidth of 6/14 MHz. Yes. A continuous carrier is arranged at the upper end of the band. The center frequency of the terrestrial digital broadcast signal is offset by 1/7 MHz from the center of the 6 MHz band channel in order to reduce interference from digital broadcast to analog broadcast. One of the OFDM segments having a bandwidth of 6/14 MHz is shown in an enlarged manner, and it can be seen that one segment is composed of many carriers. The terrestrial digital broadcasting signal has three modes depending on the carrier interval. In mode 1, the number of carriers per channel is 1405, in mode 2, the number of carriers per channel is 2809, and in mode 3, the number of carriers is The number of carriers per carrier is 5617.

FIG. 4 shows the configuration of a conventional terrestrial digital signal processor as an example of such a terrestrial digital broadcast retransmission apparatus that retransmits terrestrial digital broadcasts.
The terrestrial digital signal processor 100 shown in FIG. 4 is supplied with a terrestrial digital broadcast signal of a certain channel as an RF input. The RF input is applied to the RF amplification unit 110 and amplified at a high frequency, and then applied to the first mixer (MIX1). A local oscillation signal from the first local oscillator (OSC1) 111 is supplied to MIX1, and the RF input is frequency-converted by this local oscillation signal, and an intermediate frequency signal is output from MIX1. The intermediate frequency signal is subjected to signal processing in the IF signal processing unit 112 and controlled so that the output level of the output intermediate frequency signal becomes a level defined by the AGC circuit 114. The AGC circuit 114 detects the level of the intermediate frequency signal output from the IF signal processing unit 112 and controls the amplification degree of the RF amplification unit 110 and the amplification degree of the IF signal processing unit 112 according to the detected level. is doing.

  The intermediate frequency signal output from the IF signal processing unit 112 is up-converted by a local oscillation signal applied and supplied to the second mixer (MIX2), and is converted into a terrestrial digital broadcast signal of a predetermined channel to adjust the RF level. Supplied to the unit 116. The MIX2 is supplied with a local oscillation signal via the switch SW, and when the output is performed on the same channel as the input channel, the contact a of the switch SW is switched to the contact b on the first local oscillator 111 side. When output is performed on a channel different from the selected channel, the contact a of the switch SW is switched to the contact c to the second local oscillator (OSC2) 117 side. The RF level adjustment unit 116 adjusts the level of the terrestrial digital broadcast signal, which is the RF output, to a predetermined output level, and outputs the terrestrial digital broadcast signal retransmitted from the terrestrial digital signal processor 100.

The output level of the RF output in the terrestrial digital signal processor 100 needs to be a predetermined level. When the terrestrial digital signal processor 100 is installed, the RF output level is adjusted by adjusting the RF level adjusting unit 116. The For this level adjustment, for example, a spectrum analyzer is connected to the output terminal of the RF output, and the level adjustment is performed while observing the measured value in the spectrum analyzer.
By the way, the method of measuring the broadcast wave level differs between analog television broadcasting and digital television broadcasting. FIG. 5 shows an example of the spectrum of a certain channel of analog television broadcast. In analog television broadcast, the broadcast wave level is defined by the synchronization peak value of the video carrier shown in the figure. For this reason, for example, the broadcast wave level can be easily measured by reading the measurement value of the synchronous peak value displayed on the tube surface of the spectrum analyzer.

  However, in the Cable Television Broadcasting Law Enforcement Regulation, the average power of the OFDM signal is defined as the carrier level. This is because it is difficult to measure the peak level with a digital modulated wave, and it is practical to measure the average level instead. In a multi-carrier OFDM signal, the state where each carrier is at the maximum amplitude and in phase is the theoretical maximum value, but the frequency of the amplitude is very low, and the amplitude is not taken due to hardware limitations. There are many cases. Therefore, in the OFDM signal, it is difficult to specify with the peak value, and it is specified with the average level. In this way, in the terrestrial digital broadcast wave, energy is spread over the frequency bandwidth of the channel, and the average power is defined as the level of the carrier wave. Therefore, a measuring instrument such as a spectrum analyzer with a power measurement function can be used. If there is, the broadcast wave level can be easily measured by reading the displayed measurement value. However, in the case of a measuring instrument such as a spectrum analyzer that does not have a power measurement function, the broadcast wave level cannot be measured by simply reading the displayed measurement value, and the broadcast wave level must be obtained by performing band conversion from the measurement value. I must. Further, when interference such as multipath is added to the terrestrial digital broadcast wave, undulation occurs in the band, and it is difficult to measure accurately.

Here, a power measurement method using three types of spectrum analyzers for measuring the broadcast wave level in digital terrestrial broadcasting will be described.
The first measurement method is a method for band conversion from a level value obtained by reading the average power level with a marker, and the second measurement method is a method for band conversion from a dBm / Hz or dBμV / √Hz measurement value, The third measurement method is a method of measuring by integrating the entire measurement band with the power measurement function of the spectrum analyzer. In the first measurement method and the second measurement method, a level measurement is performed at a specific point, and the entire measurement band is regarded as the same level and band conversion is performed. Therefore, when the in-band deviation is large, the error also increases. In the third measurement method, since the measurement bandwidth is set and the power of the entire band is measured, the displayed measurement value is a desired value.

More specifically, in the first measurement method in which the band is converted from the average power measurement, after the spectrum waveform is averaged, a marker is set at a point considered to be an average level within the measurement band, and the level L is read. Calculate with the formula. For a signal with in-band deviation, the result of averaging the levels of a plurality of points is calculated as L.
Power = L + 10 Log {measurement bandwidth / (1.2 × RBW)} + 2.5
Here, RBW is the resolution bandwidth, and 1.2 × RBW is the corrected noise bandwidth. This is because the spectrum analyzer is designed on the basis that CW waves, that is, line spectra, can be measured correctly. When measuring signals with bands such as digital modulation waves and noise, the level read by the marker is corrected. Necessary. That is, in the case of a signal having a bandwidth such as noise power, the power level extracted by the RBW filter is higher than the true noise power extracted by an ideal rectangular filter having the same band as the RBW, and the RBW filter This is because the bandwidth of the rectangular filter equivalent to the extracted power is about 1.2 times the RBW. +2.5 dB is LogAmp, Detector, VBW (video bandwidth), and a correction value for averaging.

In the second measurement method for converting the band from the measured value of dBm / Hz or dBμV / √Hz, using the measurement function of the spectrum analyzer of dBm / Hz or dBμV / √Hz, the noise power bandwidth correction described above, LogAmp, Detector, and VBW averaging corrections are automatically processed inside the instrument. In addition, for example, a total of 33 points including 16 points before and 16 points including the marker point are averaged and the result is displayed.
When the measured value of dBm / Hz or dBμV / √Hz is L, power measurement is obtained by the following calculation formula.
Power = L + 10 Log (measurement bandwidth)

As described above, conventionally, in order to measure the terrestrial digital broadcast wave level with a measuring instrument that does not have a power measurement function, the measured value must be converted into a band by putting it in an arithmetic expression, which is likely to cause errors and troublesome measurement. There was a problem that it took.
Accordingly, an object of the present invention is to provide a terrestrial digital broadcast retransmission apparatus that can easily measure the terrestrial digital broadcast wave level even with a measuring instrument without a power measurement function.

  In order to achieve the above object, the digital terrestrial broadcast retransmission apparatus according to the present invention includes a pseudo carrier generation unit and is characterized in that a pseudo carrier is output when the output level is adjusted.

  According to the present invention, since the pseudo carrier is output when the output level is adjusted by the pseudo carrier generation unit, the measured value measured by the measuring instrument without the power measuring function is obtained without converting the band. Thus, a terrestrial digital broadcast wave level can be easily measured even with a measuring instrument having no power measuring function.

  The purpose of providing a terrestrial digital broadcast retransmission apparatus that can easily measure the terrestrial digital broadcast wave level even with a measuring instrument without a power measurement function is provided with a pseudo carrier generation unit when the output level is adjusted. Realized by outputting a carrier.

FIG. 1 shows a circuit block diagram of a first embodiment of a terrestrial digital signal processor which is a terrestrial digital broadcast retransmission apparatus according to the present invention.
As shown in FIG. 1, the terrestrial digital signal processor 1 according to the first embodiment of the present invention is supplied with a terrestrial digital broadcast signal of a certain channel as an RF input. This RF input is applied to the RF amplification unit 10 to be amplified at a high frequency and applied to the first mixer (MIX1). A local oscillation signal from the first local oscillator (OSC1) 11 is supplied to MIX1, and the RF input is frequency-converted into an intermediate frequency signal by this local oscillation signal and output from MIX1. The intermediate frequency signal is subjected to signal processing in the IF signal processing unit 12 and controlled so that the output level of the output intermediate frequency signal becomes a level defined by the AGC circuit 14. The AGC circuit 14 detects the level of the intermediate frequency signal output from the IF signal processing unit 12, and the amplification level of the RF amplification unit 10 and the amplification level of the IF signal processing unit 12 according to the detected level. Is controlled so that the output level of the intermediate frequency signal becomes a prescribed level.

  The intermediate frequency signal output from the IF signal processing unit 12 is input to the automatic switching unit 13. The automatic switching unit 13 receives the pseudo carrier generated by the pseudo carrier generating unit 15, and either the intermediate frequency signal or the pseudo carrier is output from the automatic switching unit 13. The output from the automatic switching unit 13 is applied to the second mixer (MIX2), is up-converted by the local signal supplied to the MIX2, and is converted into a terrestrial digital broadcast signal of a predetermined channel, so that the RF level adjusting unit 16 To be supplied. A local oscillation signal is supplied to the MIX 2 via the switch SW, and when the output is performed in the same channel as the input channel, the contact a of the switch SW is switched to the contact b on the first local oscillator 11 side. When the output is performed on a channel different from the selected channel, the contact a of the switch SW is switched to the contact c to the second local oscillator (OSC2) 17 side. The RF level adjustment unit 16 adjusts the level of the RF output, which is a terrestrial digital broadcast signal, to a predetermined output level, and outputs a terrestrial digital broadcast signal of a predetermined channel.

The pseudo carrier output from the pseudo carrier generation unit 15 has a frequency that is offset by 1/7 MHz from the center of a 6 MHz band channel that is an intermediate frequency signal in order to reduce interference from digital broadcasting to analog broadcasting. Yes. The output level of the pseudo carrier is the same as the defined level of the intermediate frequency signal output from the IF signal processing unit 12.
The automatic switching unit 13 outputs a pseudo carrier output from the pseudo carrier generation unit 15 when the RF input is not input to the RF amplification unit 10, and IF when the RF input is input to the RF amplification unit 10. Automatic switching is performed to output an intermediate frequency signal from the signal processing unit 12. This automatic switching is automatically switched by the AGC signal output from the AGC circuit 14 which is a signal corresponding to the RF input. That is, the AGC signal output from the AGC circuit 14 is supplied to the automatic switching unit 13, and the automatic switching unit 13 outputs a pseudo carrier or an intermediate frequency signal according to the level of the AGC signal. When the AGC signal is at a significant level, the automatic switching unit 13 is switched to output an intermediate frequency signal, and when the AGC signal is not at a significant level, the automatic switching unit 13 outputs a pseudo carrier. To be switched.

  Therefore, a measuring instrument such as a spectrum analyzer is connected to the output terminal of the terrestrial digital signal processor 1 so that the terrestrial digital broadcast signal is not input to the input terminal of the terrestrial digital signal processor 1. Thereby, the pseudo carrier is outputted from the terrestrial digital signal processor 1, and the level of the outputted pseudo carrier can be measured by the measuring device. In this case, since the output level of the pseudo carrier is the same as the specified level of the intermediate frequency signal output from the IF signal processing unit 12, the terrestrial digital broadcast signal is input to the input terminal of the terrestrial digital signal processor 1. When this is done, the measuring device measures the broadcast wave level of the terrestrial digital broadcast signal output from the output terminal in a pseudo manner. Since the pseudo carrier is a CW wave, that is, a line spectrum, even if a measuring instrument such as a spectrum analyzer does not have a power measuring function, the measured value can be obtained as it is as the broadcast wave level without performing band conversion. become.

  As described above, in the terrestrial digital signal processor 1 according to the first embodiment of the present invention, the RF level adjustment unit 16 cuts off the RF input when adjusting the RF output to a predetermined broadcast wave level. Thus, the pseudo carrier generated in the pseudo carrier generation unit 15 is output from the automatic switching unit 13. Then, by adjusting the RF level adjustment unit 16 so that the RF output becomes a predetermined broadcast wave level while observing the value displayed on a measuring instrument such as a spectrum analyzer connected to the output terminal of the terrestrial digital signal processor 1, It becomes possible to easily adjust the broadcast wave level to a predetermined level without converting the measured value into a band. In this case, a measuring instrument such as a spectrum analyzer does not need to have a power measuring function.

Next, FIG. 2 shows a circuit block diagram of a second embodiment of the terrestrial digital signal processor which is the terrestrial digital broadcast retransmission apparatus of the present invention.
In the terrestrial digital signal processor 2 according to the second embodiment of the present invention shown in FIG. 2, the configuration in which a changeover switch 23 is provided instead of the automatic switching unit 13 is different, and the other configuration is the first configuration. Since it is the same as that of an Example, only a different structure is demonstrated.
The pseudo carrier output from the pseudo carrier generation unit 15 has a frequency that is offset by 1/7 MHz from the center of a 6 MHz band channel that is an intermediate frequency signal in order to reduce interference from digital broadcasting to analog broadcasting. Yes. The output level of the pseudo carrier is the same as the defined level of the intermediate frequency signal output from the IF signal processing unit 12. The changeover switch 23 switches the changeover switch 23 to output the intermediate frequency signal from the IF signal processing unit 12 when the RF input input to the RF amplification unit 10 is retransmitted. Then, when the RF level adjustment unit 16 adjusts the RF output to a predetermined broadcast wave level, the selector switch 23 is switched to output the pseudo carrier output from the pseudo carrier generation unit 15.

  When the changeover switch 23 is switched to output a pseudo carrier, a measuring instrument such as a spectrum analyzer is connected to the output terminal of the terrestrial digital signal processor 2. In this case, since the output level of the pseudo carrier is the same as the specified level of the intermediate frequency signal output from the IF signal processing unit 12, the terrestrial digital broadcast signal is input to the input terminal of the terrestrial digital signal processor 2. When this is done, the measuring device measures the broadcast wave level of the terrestrial digital broadcast signal output from the output terminal in a pseudo manner. Even if a measuring instrument such as a spectrum analyzer does not have a power measuring function, the pseudo carrier is a CW wave, that is, a line spectrum, so that the broadcast wave level can be obtained without converting the band. .

  As described above, in the terrestrial digital signal processor 2 according to the second embodiment of the present invention, when the RF level adjusting unit 16 adjusts the RF output so as to become the predetermined broadcast wave level, the changeover switch 23 is switched. Thus, the pseudo carrier generated in the pseudo carrier generation unit 15 is output from the automatic switching unit 13. Then, by adjusting the RF level adjustment unit 16 so that the RF output becomes a predetermined broadcast wave level while observing the value displayed on a measuring instrument such as a spectrum analyzer connected to the output terminal of the terrestrial digital signal processor 2, It becomes possible to easily adjust the broadcast wave level to a predetermined level without converting the measured value into a band. In this case, a measuring instrument such as a spectrum analyzer does not need to have a power measuring function.

Next, FIG. 3 shows a circuit block diagram of a third embodiment of the terrestrial digital signal processor which is the terrestrial digital broadcast retransmission apparatus of the present invention.
The terrestrial digital signal processor 3 according to the third embodiment of the present invention shown in FIG. 3 is different in the configuration in which a detection circuit for outputting a switching signal for switching the automatic switching unit 13 is provided. Since this is the same as that of the first embodiment, only different configurations will be described.
The pseudo carrier output from the pseudo carrier generating unit 15 is offset by +1/7 MHz from the center of the 6 MHz band channel as an intermediate frequency signal in order to reduce interference from digital broadcasting to analog broadcasting. The output level of the pseudo carrier is the same as the defined level of the intermediate frequency signal output from the IF signal processing unit 12.

  The automatic switching unit 13 outputs a pseudo carrier output from the pseudo carrier generation unit 15 when the RF input is not input to the RF amplification unit 10, and IF when the RF input is input to the RF amplification unit 10. Automatic switching is performed to output an intermediate frequency signal from the signal processing unit 12. This automatic switching is automatically switched by a switching signal obtained by detecting the intermediate frequency signal, which is a signal corresponding to the RF input, by the detection circuit 18. That is, the switching signal output from the detection circuit 18 is supplied to the automatic switching unit 13, and the automatic switching unit 13 outputs a pseudo carrier or an intermediate frequency signal according to the switching signal. When the intermediate frequency signal output from the IF signal processing unit 12 is at a significant level, the detection circuit 18 outputs a switching signal for switching to output the intermediate frequency signal, and the intermediate frequency signal is at a significant level. If not, the detection circuit 18 outputs a switching signal for switching to output a pseudo carrier, and supplies the switching signal to the automatic switching unit 13.

  Therefore, a measuring instrument such as a spectrum analyzer is connected to the output terminal of the terrestrial digital signal processor 3 so that the terrestrial digital broadcast signal is not input to the input terminal of the terrestrial digital signal processor 3. Thereby, the pseudo carrier is outputted from the terrestrial digital signal processor 3, and the level of the outputted pseudo carrier can be measured by the measuring device. In this case, since the output level of the pseudo carrier is the same as the specified level of the intermediate frequency signal output from the IF signal processing unit 12, the terrestrial digital broadcast signal is input to the input terminal of the terrestrial digital signal processor 3. When this is done, the measuring device measures the broadcast wave level of the terrestrial digital broadcast signal output from the output terminal in a pseudo manner. Since the pseudo carrier is a CW wave, that is, a line spectrum, even if a measuring instrument such as a spectrum analyzer does not have a power measuring function, the measured value can be obtained as it is as the broadcast wave level without performing band conversion. become.

Thus, in the terrestrial digital signal processor 3 according to the third embodiment of the present invention, the RF input is cut off when the RF level adjustment unit 16 adjusts the RF output to a predetermined broadcast wave level. Thus, the pseudo carrier generated in the pseudo carrier generation unit 15 is output from the automatic switching unit 13. Then, by adjusting the RF level adjustment unit 16 so that the RF output becomes a predetermined broadcast wave level while observing the value displayed on a measuring instrument such as a spectrum analyzer connected to the output terminal of the terrestrial digital signal processor 3, It becomes possible to easily adjust the broadcast wave level to a predetermined level without converting the measured value into a band. In this case, a measuring instrument such as a spectrum analyzer does not need to have a power measuring function.
In the above description, the frequency of the pseudo carrier is a frequency offset by +1/7 MHz from the center of the 6 MHz band channel as an intermediate frequency signal, but the present invention is not limited to this, and the frequency offset by −1/7 MHz. It can be. Furthermore, the frequency of the pseudo carrier does not need to be the center frequency of the 6 MHz band, which is an intermediate frequency signal, and can be any frequency within the band.

  In the above description, the terrestrial digital broadcast retransmission apparatus is described. However, the present invention is not limited to this, and can be applied to an apparatus that outputs an RF signal in which energy is spread over the frequency bandwidth of the channel. .

1 is a circuit block diagram of a first embodiment of a terrestrial digital signal processor which is a terrestrial digital broadcast retransmission apparatus according to the present invention. FIG. It is a circuit block diagram of the 2nd Example of the terrestrial digital signal processor which is a terrestrial digital broadcast re-transmission apparatus of this invention. It is a circuit block diagram of the 3rd Example of the terrestrial digital signal processor which is a terrestrial digital broadcast re-transmission apparatus of this invention. It is a figure which shows the structure of the conventional terrestrial digital signal processor. It is a figure which shows an example of the spectrum of a certain channel of analog television broadcasting. It is a figure which shows the outline | summary of the frequency spectrum of a channel with a terrestrial digital broadcast signal.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Terrestrial digital signal processor, 2 Terrestrial digital signal processor, 3 Terrestrial digital signal processor, 10 RF amplification part, 11 1st local oscillator, 12 IF signal processing part, 13 Automatic switching part, 14 AGC circuit, 15 Pseudo carrier generation part, 16 RF level adjustment unit, 17 2nd local oscillator, 18 detection circuit, 23 selector switch, 100 terrestrial digital signal processor, 110 RF amplification unit, 111 1st local oscillator, 112 IF signal processing unit, 114 AGC circuit, 116 RF level Adjustment unit, 117 Second local oscillator

Claims (3)

A first mixer for converting an input digital terrestrial broadcast signal into an intermediate frequency signal;
An intermediate frequency signal processing unit for outputting the level of the intermediate frequency signal output from the first mixer unit as a prescribed intermediate frequency level;
A switching unit that outputs either the intermediate frequency signal output from the intermediate frequency signal processing unit or the pseudo carrier output from the pseudo carrier generation unit;
A second mixer section for converting a signal output from the switching section into a predetermined digital terrestrial broadcast signal channel;
An output level adjustment unit that adjusts and outputs the channel level output from the second mixer unit to a predetermined level;
The level of the pseudo carrier output from the pseudo carrier generation unit is substantially equal to a specified level of the intermediate frequency signal output from the intermediate frequency signal processing unit, and when adjusting the output level adjustment unit In addition, the digital terrestrial broadcast retransmission apparatus is switched so that the pseudo carrier is output from the switching unit.   In the intermediate frequency signal processing unit, the output level of the intermediate frequency signal is controlled to be a prescribed intermediate frequency level by the auto gain control circuit, and no significant gain control signal is output from the auto gain control circuit. The terrestrial digital broadcast retransmission apparatus according to claim 1, wherein the switching unit is switched so that the pseudo carrier is output from the switching unit. Detection means for detecting the level of the intermediate frequency signal is provided, and the switching unit is configured to output the pseudo carrier from the switching unit when the detection unit detects that there is no significant intermediate frequency signal. 2. The terrestrial digital broadcast retransmission apparatus according to claim 1, wherein the terrestrial digital broadcast retransmission apparatus is switched.

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