JP4363828B2 - Relay broadcast wave switching device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a relay broadcast wave switching device for selectively switching and transmitting individually received digital broadcast signals of a plurality of systems according to quality degradation.
[0002]
[Prior art]
In the terrestrial broadcasting system, a relay station is installed for the purpose of expanding the broadcasting service area and eliminating difficult viewing areas. In the relay station, a signal directly receiving a broadcast wave or a broadcast signal received on a dedicated line such as TTL (broadcast program relay line) is input to the transmitter again and transmitted. There are usually a plurality of reception systems, and when the quality of the received signal of the system being used deteriorates for some reason and becomes unusable for broadcasting, the system is immediately switched to another system.
[0003]
The current analog broadcasting relay station monitors the reception signal level of the transmission system in use, and if the level drops, confirms that the reception signal level of the standby transmission system is sufficiently high, and then goes to that transmission system. The method of switching is taken. The delay and phase adjustment between the input signals of each transmission system are only roughly adjusted, and there is no problem that causes a big problem in actual broadcasting.
[0004]
By the way, in Japanese terrestrial broadcasting, the transition from the current analog broadcasting to digital broadcasting using the OFDM modulation method has been decided, and various developments are being promoted to realize it. Here, in digital broadcasting, it is desired to improve the following problems when selectively switching and transmitting relay broadcast waves of a plurality of transmission systems.
[0005]
First, since the frequency characteristics in the band of the OFDM signal are flat, even if the signal is not received, the noise component may rise due to AGC (automatic gain control) or the like of the receiving unit, and may appear as an OFDM signal. is there. For this reason, it is difficult to monitor signal quality degradation at the level of the received signal, and it is not possible to use quality monitoring technology for switching relay broadcast waves in conventional analog broadcasting.
[0006]
In particular, in the OFDM signal, when there is a no-signal period even for a moment when switching between transmission systems, discontinuity occurs in the signal of the switching output, and the quality of the transmission signal is greatly degraded. Further, if the delay and phase between the signals in each transmission system are slightly shifted, the signal is discontinuous before and after switching, and the signal quality of the switching output is deteriorated.
[0007]
[Problems to be solved by the invention]
As described above, in order to start digital terrestrial broadcasting, it is desirable that digital broadcast signal relay stations should not degrade signal quality when switching transmission systems with relay broadcast wave switching devices. Has been.
[0008]
The present invention has been made to solve the above-described problems. When switching the transmission system of a digital broadcast signal, the signal quality of each transmission system is appropriately monitored, and the signal quality of the switching output is improved. It is an object to provide a relay broadcast wave switching device that can be maintained.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a reception quality of digital broadcast signals transmitted to each of the plurality of systems in a relay broadcast wave switching apparatus for selectively switching and transmitting digital broadcast signals of a plurality of systems received individually. Monitoring means for monitoring, switching determination means for determining a switching time point of the transmission system based on a monitoring result of the monitoring means, and detection means for detecting a mutual delay difference and phase difference for the digital broadcasting signals of the plurality of systems , Based on the delay difference and the phase difference detected by this means, the adjusting means for matching the delay and phase of the digital broadcast signal of the other system with the digital broadcast signal of the system being transmitted, and each adjusted after this means Switching means for capturing a digital broadcast signal of the system and switching the transmission system based on the determination result of the quality determination means, the switching means While attenuating switching source signal when switching to increase the switching destination of the signal is characterized by using a switch for switching seamlessly.
[0010]
In the relay broadcast wave switching device having the above configuration, the reception quality of the digital broadcast signal input to each system is monitored, and the transmission system switching time point is determined based on the monitoring result. On the other hand, the mutual delay difference and phase difference are detected for the digital broadcast signals of each system, and based on the detected delay difference and phase difference, the digital broadcast signal of the other system is added to the digital broadcast signal of the other system. The delay and phase are matched. A seamless switch is used for system switching to increase the switching destination signal while attenuating the switching source signal to eliminate instantaneous interruption of output and to maintain the output level constant. In this way, there is no fear of instantaneous interruption and the output level is kept constant, so that the quality of the output signal can be maintained satisfactorily.
[0011]
In the above configuration, the monitoring unit branches the plurality of systems, superimposes a noise signal on the branch path, measures the error rate of the received signal, and outputs the measurement result as the evaluation value of the reception quality of the digital broadcast signal It is characterized by doing.
[0012]
Further, the digital broadcast signal is an OFDM (Orthogonal Frequency Division Multiplex) signal, and the detection means and adjustment means detect and adjust the delay difference and phase difference of the OFDM signal after orthogonal demodulation, and are orthogonal again. Modulated and sent to the switching means.
[0013]
In this case, the monitoring means monitors reception quality of the signal after orthogonal demodulation of the OFDM signal.
[0014]
Further, the switching determination means compares the reception quality of the system being sent out with the reception quality of the stand-by system from the monitoring result of the monitoring means, and the quality of the system being sent out is compared with the quality of the stand-by system. It is characterized in that the time point below is determined as the switching time point.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0016]
FIG. 1 is a block diagram showing a configuration of a relay broadcast wave switching device according to the present invention. In FIG. 1, a digital broadcast signal by OFDM system, which is individually received, is supplied to the system 1 input and system 2 input. The 1-system input OFDM signal is demodulated into a complex baseband signal by the orthogonal demodulator 101, subjected to delay / phase adjustment by the delay / phase adjuster 102, and then returned to the OFDM signal by the orthogonal modulator 103 again. And supplied to the seamless switch 104. Similarly, the OFDM signal of the 2-system input is demodulated into a complex baseband signal by the quadrature demodulating unit 105, subjected to delay / phase adjustment by the delay / phase adjusting unit 106, and then again subjected to OFDM by the quadrature modulating unit 107. The signal is returned to the seamless switch 104.
[0017]
On the other hand, the OFDM signals input to the first and second systems are branched from the main line system and supplied to the signal quality monitoring units 108 and 109. Each of the signal quality monitoring units 108 and 109 monitors the quality using the amount of noise that can obtain a certain error rate in the input signal as an index, and evaluates the degree of deterioration. The evaluation value output from 109 is supplied to the signal switching determination unit 110.
[0018]
The signal switching determination unit 110 determines which system is connected to the transmission system from the comparison result of the signal quality evaluation values of the 1st system and the 2nd system, and determines the time of signal switching. The control signal is supplied to the seamless switch 104 and also supplied to the delay / phase detector 111.
[0019]
In addition, the signals after quadrature demodulation of the first and second systems are branched from the main line system and supplied to the delay / phase detection unit 111. The delay / phase detection unit 111 performs cross-correlation between the orthogonally demodulated signals of the first and second systems, detects a delay difference and a phase difference between the signals, and determines the detection result based on the determination result of the signal switching determination unit 110. To the delay / phase adjustment unit 102 or 106 of the system in the standby state. As a result, the digital broadcast signal in the standby state is adjusted so that the delay and phase coincide with those of the digital broadcast signal in the transmission state.
[0020]
In the switching device having the above system configuration, a specific configuration of each main part will be described.
[0021]
FIG. 2 is a block diagram showing a specific configuration of the signal quality monitoring units 108 and 109. As shown in FIG. 2, these signal quality monitoring units 108 and 109 place the noise signal generated by the noise signal source 201 on the branch path by the mixer 202, and measure the error rate of the received signal by the measuring unit 203. The measurement result is output as an evaluation value of signal quality. That is, in the signal quality monitoring method used here, the amount of noise that can obtain a certain error rate in the OFDM signal is determined by looking at the C / N ratio with the noise signal on the OFDM signal transmission line. The degree of deterioration is detected from the ratio.
[0022]
FIG. 3 is a flowchart showing a specific processing procedure of the signal switching determination unit 110. Here, it is assumed that system 1 is selected in the initial state. First, in step S1, quality evaluation values for the first and second systems are taken from the signal quality monitoring units 108 and 109, and the two are compared. At this time, if the quality evaluation value of the first system falls below the quality evaluation value of the second system, a switching control signal is output so as to select the second system in step S2. Next, in step S3, the signal quality evaluation values of system 1 and system 2 are compared. If the quality evaluation value of system 2 falls below the quality evaluation value of system 1, the system 1 is selected in step S4. The switching control signal is output so that Thereafter, steps S1 to S4 are repeatedly executed.
[0023]
FIG. 4 is a block diagram showing a specific configuration of the seamless switch 104. As shown in FIG. 4, the seamless switching unit 104 inputs the OFDM signals from the 1-system quadrature modulation unit 103 and the 2-system quadrature modulation unit 104 to the adder 303 via the variable attenuators 301 and 302, respectively, and performs signal switching. A switching control signal from the determination unit 110 is input to the crossover controller 304.
[0024]
When the crossover controller 304 is instructed to switch from system 1 to system 2 by a switching control signal, the resistance value of system 1 variable attenuator 301 is increased from substantially 0 to infinity to attenuate system 1 output. Then, the resistance value of the second system variable attenuator 302 is decreased from substantially infinity to 0 to increase the second system output. Conversely, when the switching control signal instructs to switch from the 2nd system to the 1st system, the resistance value of the 2nd system variable attenuator 302 is increased from substantially 0 to infinity to attenuate the 2nd system output. The resistance value of the variable attenuator 301 of the system is decreased from substantially infinity to 0 to increase the output of the 1 system. The rate of increase / decrease in the resistance value may be linear or exponential.
[0025]
The adder 303 adds the OFDM signals from the 1-system and 2-system variable attenuators 301 and 302 and outputs the result. At the time of switching, since the rate of increase / decrease of the variable attenuators 301 and 302 is the same, the output level of the adder 303 is kept constant.
[0026]
In other words, in the relay broadcast wave switching device having the above-described configuration, the delay difference and the phase difference are detected in the baseband region by orthogonal demodulation for the OFDM signals input to the first and second systems, and the signal of the system in the transmission state is used as a reference. The delay and phase of the signal of the system in the standby state are adjusted and controlled so as to always have the same timing. On the other hand, when the signal quality is monitored using the amount of noise that can obtain a certain error rate in the input OFDM signal of each system as an index, and the quality evaluation value of the system in the transmission state falls below the quality evaluation value of the system in the standby state Execute system switching. For switching, the seamless switching device 104 is used to increase and decrease the transmission system and standby system at a predetermined rate and add and output while crossover, so there is no risk of instantaneous interruption and the output level is also constant. Therefore, the quality of the output signal can be maintained satisfactorily.
[0027]
The error rate is usually measured by comparing the received signal with the original signal, or by comparing the data before and after correction assuming that the data after error correction is correct and counting the number of errors. It can also be determined by the method. In terrestrial digital broadcasting, TS (transport stream) signals defined in MPEG2 are used. It defines a flag (Reed-Solomon error indicator) that is set when an error is included in the data after Reed-Solomon decoding in the process of error correction at the time of reception. By monitoring the flag, it is possible to measure the error rate of the received signal more easily than measuring the bit error rate.
[0028]
Therefore, according to the configuration of the above embodiment, when switching the transmission system of individually received OFDM signals, the signal quality of each transmission system can be properly monitored, and the timing is matched and instantaneous interruption occurs. Since the switching output is performed at a constant level without any change, the signal quality of the switching output can be maintained satisfactorily.
[0029]
In the above embodiment, the signal quality monitoring is performed by the signal before the quadrature demodulation. However, as shown in FIG. 5, the outputs of the quadrature demodulation units 101 and 105 are input to the signal quality monitoring units 108 and 109, respectively. Alternatively, monitoring may be performed using a baseband IQ signal.
[0030]
Moreover, although the said embodiment demonstrated the case of two input systems, even when it has many more systems, it can implement similarly.
[0031]
In addition, the present invention is not limited to the above embodiment, and can be implemented with various modifications.
[0032]
【The invention's effect】
As described above, according to the present invention, when switching the transmission system of a digital broadcast signal, the relay can appropriately monitor the signal quality of each transmission system and maintain the signal quality of the switching output well. A broadcast wave switching device can be provided.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a relay broadcast wave switching device according to an embodiment of the present invention.
FIG. 2 is an exemplary block diagram showing a specific configuration of a signal quality monitoring unit according to the embodiment;
FIG. 3 is an exemplary flowchart illustrating a specific processing procedure of a signal switching determination unit according to the embodiment;
FIG. 4 is an exemplary block diagram illustrating a specific configuration of the seamless switch according to the embodiment;
FIG. 5 is a block diagram showing a configuration of a relay broadcast wave switching device according to another embodiment of the present invention.
[Explanation of symbols]
101, 105 ... quadrature demodulation units 102, 106 ... delay / phase adjustment units 103, 107 ... quadrature modulation unit 104 ... seamless switchers 108, 109 ... signal quality monitoring unit 110 ... signal switch determination unit 111 ... delay / phase detection unit 201 ... Noise signal source 202 ... Mixer 203 ... Measuring instruments 301 and 302 ... Variable attenuator 303 ... Adder 304 ... Crossover controller

Claims (2)

In a relay broadcast wave switching device for selectively switching and transmitting digital broadcast signals of multiple systems of OFDM (orthogonal frequency division multiplexing) signals received individually,
Monitoring means for monitoring the reception quality of the digital broadcast signal transmitted to each of the received plurality of systems;
A switching determination means for determining a switching point of the transmission system based on the monitoring result of the monitoring means;
Orthogonal demodulation means for orthogonally demodulating and converting into a baseband signal for the received digital broadcast signals of a plurality of systems;
Detection means for detecting a mutual delay difference and phase difference for the baseband signal from the orthogonal demodulation means;
Based on the delay difference and phase difference detected by the detection means, adjustment means for matching the delay and phase of the baseband signal of the digital broadcast of the other system with the baseband signal of the digital broadcast of the system being transmitted,
Orthogonal modulation means for orthogonally modulating the digital broadcast baseband signal of each system after adjustment by this adjustment means to the digital broadcast signal of OFDM (orthogonal frequency division multiplexing) signal;
Switching means for taking in a digital broadcast signal of OFDM (orthogonal frequency division multiplexing) signal from the orthogonal modulation means , and switching the transmission system based on the determination result of the quality determination means,
The switching determination means compares the reception quality of the system being sent out with the reception quality of the stand-by system from the monitoring result of the monitoring means, and the quality of the sending system is lower than the quality of the stand-by system Determine the time as the switching time and repeat this,
The switching means includes a switching device for switching seamlessly by increasing a switching destination signal while attenuating a switching source signal at the time of switching. When the OFDM signal is a transport stream signal defined in MPEG2 (Moving Picture Experts Group phase 2) of digital terrestrial broadcasting as the reception quality of the OFDM signal before the detection unit and the adjustment unit, the monitoring unit 2. The relay broadcast wave switching device according to claim 1, wherein the bit error rate is measured by monitoring a Reed-Solomon error indicator obtained in the process of error correction at the time of reception .

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