JP7577441B2 - Apparatus and method for monitoring signal quality - Google Patents

Description

Embodiments of the present invention relate to a signal quality monitoring device and method.

In digital broadcasting systems, it is important to monitor the signal quality of the broadcast waves. Indicators that represent signal quality include C/N (Carrier to Noise Ratio), MER (Modulation Error Rate), and BER (Bit Error Rate). Even if the broadcast waves are maintained, signal quality may be degraded, and in such a state, visual impairment occurs on the receiver's side. Most of the degradation of signal quality that leads to visual impairment is caused by incorrect settings or malfunctions of the equipment.

JP 2011-109332 A JP 2007-221346 A JP 2003-111105 A

Even if it is possible to monitor BER, C/N, frequency accuracy, etc., there are some failures that cannot be detected by these indices. That is, if an error occurs in a broadcast TS (Transport Stream) signal before an error correction code is added during the process of receiving and retransmitting the TS signal, the BER, C/N, and frequency accuracy may not deteriorate. There is no known technology that can detect such abnormalities (called silent failures). Silent failures are said to be caused, for example, when semiconductor memory in a device is exposed to weak cosmic rays or radiation, causing unexpected bit errors.

The objective is to provide a signal quality monitoring device and method capable of detecting deterioration in the quality of a signal that has not been error-correction coded.

According to an embodiment, the signal quality monitoring device includes a demodulator, a comparator, and a judging unit. The demodulator takes in a digital broadcast signal before being emitted from an antenna from a transmitter having a modulator that performs forward error correction coding processing on a broadcast transport stream signal and digitally modulates the signal to generate a digital broadcast signal, and generates a reproduced transport stream signal based on the digital broadcast signal. The comparator compares the identity of a broadcast transport stream signal supplied from a microwave receiver via an STL line or a TTL line that has not been subjected to the forward error correction coding processing by the modulator with a reproduced transport stream signal that has been subjected to the forward error correction coding processing by the modulator, at a 1-bit level . The judging unit judges the quality of the digital broadcast signal based on the result of the comparison .

FIG. 1 is a diagram illustrating an example of a terrestrial digital broadcasting system according to an embodiment. FIG. 2 is a block diagram for explaining signals input to the signal quality monitor 18. As shown in FIG. FIG. 3 is a functional block diagram showing another example of the signal quality monitoring device 18 according to the embodiment. FIG. 4 is a flowchart showing an example of a processing procedure of the signal quality monitor 18.

Next, an embodiment of the present invention will be described. In terrestrial digital broadcasting, in order to transmit broadcast programs, a performance studio, a broadcast transmitting station (master station), and each relay station are connected by an STL (Studio to Transmitter Link)/TTL (Transmitter to Transmitter Link) line such as a microwave line, and multi-stage relaying is performed using these STL/TTL lines. Modulation methods such as DQPSK, QPSK, 16QAM, and 64QAM (Quadrature Amplitude Modulation) are used in terrestrial digital broadcasting. For example, the 64QAM modulation method is a method of transmitting signals by changing a carrier wave into 64 different states (symbols) with different amplitudes and phases, and can transmit 6 bits of information per symbol.

Figure 1 is a diagram showing an example of a terrestrial digital broadcasting system according to an embodiment. This system includes a transmission station 100 and a relay station 200. The transmission station 100 converts a TS signal received from a broadcast station via a microwave band STL (Studio to Transmitter Link) line into a broadcast wave (broadcast TS signal) in the terrestrial digital television broadcast band, and transmits it to an assigned area. The relay station 200 relays and transmits the transmitted broadcast wave.

At the transmitting station 100, the digital microwaves received by the antenna 10 are distributed and input via the distribution unit 11 to the operating system (e.g., system 1) and the redundant system (e.g., system 2).

In system 1, the digital microwave is received and demodulated by microwave receiver 12 to generate a transport stream (TS) signal. From this TS signal, a broadcast wave (output signal) at a transmission level is generated by transmitter 13 and input to system switching unit 16. Similarly, in system 2, the digital microwave from distribution unit 11 is received and demodulated by microwave receiver 14 to generate a TS signal. From this TS signal, a broadcast wave (output signal) at a transmission level is generated by transmitter 15 and input to system switching unit 16.

Transmitters 13 and 15 are mutually redundant, and each reproduces a broadcast signal based on a common digital microwave. System switching unit 16 connects the broadcast wave from either transmitter 13 or transmitter 15 to broadcast antenna 17, and outputs it to space (air region).

The broadcast waves output from the broadcast antenna 17 are received by the receiving antenna 20 of the relay station 200, and are distributed and input to the relay devices 22 and 23 by the distribution unit 21. Here too, the relay device 22 functions as system 1, and the relay device 23 functions as system 2, and they operate as redundant systems for each other.

The relay devices 22 and 23 each regenerate the broadcast waves, amplify them to the output level of the relay device, and output them to the system switching unit 24. The system switching unit 24 connects the broadcast waves from either the relay device 22 or the relay device 23 to the relay device antenna 25. This causes the broadcast waves to be relayed.

The transmitting station 100 is equipped with a signal quality monitoring device 18 for monitoring the quality of the transmitted broadcast waves. The signal quality monitoring device 18 takes in the transport stream (TS) signal from the microwave receiving unit 12 of system 1 and the broadcast waves output from the transmitter 13 of system 1, and compares them with each other. Then, based on the results of this comparison, it monitors the quality of the broadcast waves.

Figure 2 is a block diagram to explain the signals input to the signal quality monitoring device 18. The broadcast transport stream signal from the microwave receiving unit 12 is input to both the transmitter 13 and the signal quality monitoring device 18.

Here, the transmitter 13 comprises a modulation unit (MOD) 131, an exciter (EX) 132, and a transmission power amplifier (PA) 133. The modulation unit 131 performs forward error correction (FEC) coding processing on the broadcast transport stream signal, and further digitally modulates it to generate a digital broadcast signal. The exciter 132 frequency-converts this digital broadcast signal up to the transmission frequency band (RF). This digital broadcast signal in the RF band is input to the signal quality monitoring device 18, and is amplified to a transmission level by the transmission power amplifier 133 and radiated from the broadcast antenna 17 (Figure 1).

Figure 3 is a functional block diagram showing another example of a signal quality monitoring device 18 according to an embodiment. The signal quality monitoring device 18 includes a frequency conversion unit 31, an orthogonal demodulation unit 32, an FFT unit 33, an equalization processing unit 34, a signal comparison unit 51, a quality determination unit 60, and a delay adjustment unit 71. Of these, the frequency conversion unit 31, the orthogonal demodulation unit 32, the FFT unit 33, and the equalization processing unit 34 function as a demodulation unit that captures a digital broadcast signal from the transmitter 13 and generates a reproduced transport stream signal based on this digital broadcast signal.

In FIG. 3, the digital broadcast signal is down-converted to an intermediate frequency (IF) band signal by the frequency conversion unit 31. The orthogonal demodulation unit 32 performs orthogonal demodulation (OFDM (Orthogonal Frequency Division Multiplex) demodulation) of the IF signal to generate a demodulated signal. The FFT unit 33 performs fast Fourier transform (FFT) calculation processing on the demodulated signal to obtain a frequency axis signal. The equalization processing unit 34 performs equalization processing using, for example, a pilot signal on this frequency axis signal to generate a received constellation signal. The equalization processing unit 34 further performs FEC processing on the received constellation signal. As a result, a reproduced transport stream signal based on the digital broadcast signal is generated.

The signal quality monitoring device 18 also receives a broadcast transport stream signal (broadcast TS) supplied via the STL line from the microwave receiving unit 12. The delay of this broadcast transport stream signal is adjusted by the delay adjustment unit 71, and the signal is input to the signal comparison unit 51 in phase with the reproduced transport stream signal. The signal comparison unit 51 compares the reproduced transport stream signal with the broadcast transport stream signal.

Both the broadcast transport stream signal that has not undergone FEC processing by the modulation unit 131 and the reproduced transport stream signal that has undergone FEC processing by the modulation unit 131 are input to the signal comparison unit 51. If no failures such as bit errors (silent failures) have occurred in the modulation unit 131, the signals input to the signal comparison unit 51 should be the same. Therefore, the results of comparing the two signals will be the same, and the difference between the two signals will be zero. On the other hand, if the results of comparing the two signals are different, the difference between the signals will be a non-zero value.

The quality judgment unit 60 acquires the comparison result, judges whether or not there is an abnormality based on, for example, the magnitude relationship with a predetermined threshold value, and outputs the judgment result. That is, the quality judgment unit 60 judges the quality of the digital broadcast signal output from the modulation unit 131 based on the result of comparing the two signals. In other words, the quality judgment unit 60 compares the broadcast transport stream signal with the playback transport stream signal, and if the two are different, the quality judgment unit 60 detects the occurrence of a silent failure.

Figure 4 is a flowchart showing an example of the processing procedure of the signal quality monitoring device 18. The signal quality monitoring device 18 receives a broadcast transport stream signal from the microwave receiving unit 12 (step S1) and receives a digital broadcast signal from the transmitter 13 (step S2). Next, the signal quality monitoring device 18 frequency-converts the digital broadcast signal to an IF signal (step S3). Next, the signal quality monitoring device 18 performs orthogonal demodulation on the IF signal (step S4), and then performs FFT processing (step S5) and equalization processing (step S6) to generate a received constellation signal of the digital broadcast signal. Furthermore, the signal quality monitoring device 18 performs forward error correction coding processing on the received constellation signal (step S7) to generate a reproduced transport stream signal. The process of steps S3 to S7 corresponds to the process of generating a reproduced transport stream signal based on the digital broadcast signal.

Next, the signal quality monitoring device 18 compares the reproduced transport stream signal with the transmitted transport stream signal (step S8) and determines whether the difference is equal to or greater than a threshold value (step S9). If the difference is less than the threshold value, the process returns to the beginning. If the difference is equal to or greater than the threshold value, the signal quality monitoring device 18 outputs an alert (step S10).

As described above, in the embodiment, the broadcast transport stream signal is compared with the reproduced transport stream signal reproduced by demodulating the digital broadcast signal output from the transmitter 13, and the identity of the signals is monitored. That is, at the transmitting station, by comparing the reproduced transport stream signal obtained by demodulating the transmitter output signal before it is emitted from the antenna with the transmitted transport stream signal before it is input to the modulation unit 131, errors occurring in the modulation unit 131 can be detected.

Existing technology can only monitor the signal quality of one system using indicators such as BER, C/N, and frequency accuracy, and can only detect abnormalities that appear in these indicators. Errors that occur after error correction coding processing is performed in the modulation unit 131 can be corrected within the range of the error correction capability. However, errors that occur in the signal before the error correction code is added cannot naturally be corrected, nor can they be detected externally.

In contrast, in the embodiment, the input signal (broadcast transport stream signal) to the modulation unit 131 of the transmitter 13 is compared with the TS signal (reproduced transport stream signal) that has undergone all demodulation processing, thereby making it possible to monitor the identity of the transport stream signal at the 1-bit level.

Therefore, according to the embodiment, it is possible to provide a signal quality monitoring device and method capable of detecting deterioration in the quality of a signal that has not been error correction coded.

Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the gist of the invention. These embodiments and their modifications are included within the scope and gist of the invention, and are included in the scope of the invention and its equivalents as set forth in the claims.

10...antenna, 11...distribution section, 12...microwave receiving section, 13, 15...transmitter, 14...microwave receiving section, 16...system switching section, 17...broadcast antenna, 18...signal quality monitoring device, 20...receiving antenna, 21...distribution section, 22, 23...relay device, 24...system switching section, 25...relay device antenna, 31...frequency conversion section, 32...orthogonal demodulation section, 33...FFT section, 34...equalization processing section, 51...signal comparison section, 60...quality determination section, 71...delay adjustment section, 100...transmitting station, 131...modulation section, 132...exciter, 133...transmission power amplifier, 200...relay station.

Claims (4)

a demodulation unit which receives a digital broadcast signal before being emitted from an antenna from a transmitter having a modulation unit which performs forward error correction coding processing on the broadcast transport stream signal and digitally modulates the signal to generate a digital broadcast signal, and generates a reproduced transport stream signal based on the digital broadcast signal;
a comparison unit that compares, at a 1-bit level, the identity of a broadcast transport stream signal supplied from a microwave receiving unit via an STL line or a TTL line that has not been subjected to the forward error correction coding processing by the modulation unit and a reproduced transport stream signal that has been subjected to the forward error correction coding processing by the modulation unit;
a determination unit that determines a quality of the digital broadcast signal based on a result of the comparison. The signal quality monitoring device according to claim 1, further comprising a phase matching unit that aligns the phase of the playback transport stream signal with the phase of the broadcast transport stream signal and inputs the aligned signals to the comparison unit. The signal quality monitoring device according to claim 2, wherein the phase matching unit is a delay unit that delays the phase of the broadcast transport stream signal. A method for monitoring signal quality, which is applied to a signal quality monitoring device that captures a digital broadcast signal before it is emitted from an antenna from a transmitter having a modulation unit that performs forward error correction coding processing on a broadcast transport stream signal and digitally modulates the signal to generate a digital broadcast signal, comprising:
a step of the signal quality monitoring device generating a reproduced transport stream signal based on the digital broadcast signal;
a step of the signal quality monitoring device comparing, at a 1-bit level, the identity between a broadcast transport stream signal supplied from a microwave receiving unit via an STL line or a TTL line that has not been subjected to the forward error correction coding processing by the modulation unit and a reproduced transport stream signal that has been subjected to the forward error correction coding processing by the modulation unit;
and a step of said signal quality monitoring device determining a quality of said digital broadcast signal based on a result of said comparison.