JP2005167906A - Qam modulation signal transmitting method, transmitting side device and receiving side device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a QAM modulation signal transmitting method, a transmitting side device, and a receiving side device for ensuring C/N of a QAM modulation signal and carrying out long-distance transmission without requiring an external signal from different system. <P>SOLUTION: A QAM modulation signal is subjected to PCM modulation by using a reference clock synchronized with a network clock of a digital optical line network 45, and the PCM modulation signal through the PCM modulation is transmitted to two or more spots through the digital optical line network 45. At each of two or more spots, the PCM modulation signal is received from the digital optical line network 45. Then, the PCM modulation signal received by a reference clock synchronized with the network clock of the digital optical line network is subjected to PCM demodulation to obtain a QAM modulation signal. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  TECHNICAL FIELD The present invention relates to a QAM modulated signal transmission method and its transmitting side device and receiving side device, and more particularly to a QAM modulated signal transmission method for transmitting a QAM modulated signal to a plurality of broadcast stations in a single frequency network, and its transmitting side device and receiving side device. About.

  In terrestrial digital television broadcasting, a broadcast TS (Transport Stream) signal is digitally modulated by OFDM (Orthogonal Frequency Division Multiplexing) with high frequency efficiency and broadcast. OFDM is also resistant to multipath interference, and by providing a temporal guard called a guard interval in the transmission signal, signal degradation due to multipath interference with a long delay time can be suppressed. A single frequency network (SFN) that broadcasts at a frequency becomes possible, which can greatly save the frequency.

  In order to construct a single frequency network, the transmission frequency difference is required to be within 1 Hz between the broadcast waves in order to suppress inter-carrier interference occurring in the SFN service area, and inter-symbol interference is suppressed. Therefore, it is required that the frequency of the reference clock of the OFDM modulated wave in each SFN broadcaster is the same.

  Here, the STL / TTL (Studio Transmitter Link / Transmitter Transmitter Link) system of the national digital broadcasting communication equipment standard specifications defines a TS transmission system and an IF transmission system.

  The TS transmission method transmits a 64QAM modulated TS signal, has a degree of freedom in selecting an AC (Auxionary Channel) in a modulated wave, and is not easily affected by signal degradation in a transmission path (STL / TTL section). There is an advantage. The IF transmission method transmits OFDM modulation signals as they are, and there is no need to prepare an OFDM modulator at each broadcasting station.

  FIG. 3 is a block diagram showing an example of a single frequency network configured by a conventional QAM modulation signal transmission method. In the figure, a 64QAM modulator 12 disposed in the performance room 10 modulates a digital television broadcast signal by 64QAM. The obtained 64QAM modulated signal is converted into an optical signal by the optical transmitter 14 and transmitted to the analog optical line 16. The optical signal transmitted through the analog optical line 16 is received by the optical receivers 18A and 18B and converted into a 64QAM modulated signal of an electrical signal. The 64QAM modulated signal is delayed and adjusted by a certain amount of delay by delay adjusting devices 19A and 19B, respectively, and then 64QAM demodulated by 64QAM demodulators 20A and 20B. Thereafter, OFDM modulation is performed by the OFDM modulators 21A and 21B, and the OFDM modulated signal is wirelessly transmitted from the broadcasters 22A and 22B to the SFN service area 23.

  FIG. 4 shows a block diagram of another example of a single frequency network configured by a conventional QAM modulation signal transmission method. In the figure, a 64QAM modulator 12 disposed in the performance room 10 performs 64QAM modulation on a broadcast TS signal. The obtained 64QAM modulated signal is converted into a microwave by the SHF transmitter 24 and transmitted through a microwave fixed radio line. The microwaves transmitted through the wireless transmission paths 25A and 25B are received by the SHF receivers 26A and 26B and converted into 64QAM modulated signals. The 64QAM modulated signal is delayed and adjusted by a certain amount of delay by the delay adjusting devices 27A and 27B, and then 64QAM demodulated by the 64QAM demodulators 28A and 28B. Thereafter, OFDM modulation is performed by the OFDM modulators 29A and 29B, and the OFDM modulated signal is wirelessly transmitted from the broadcasters 22A and 22B to the SFN service area 23.

Moreover, although not transmitting OFDM modulation signals, what transmits a broadcast TS (Transport Stream) using an ATM line is conventionally known (see Non-Patent Document 1, for example).
The Journal of the Institute of Image Information and Television Engineers Vol. 56, no. 2, pp. 165-167 (2002)

  In the conventional method shown in FIG. 3, an analog optical line 16 is used. Although it is easy to synchronize with an analog optical line, the transmission level of the transmitter is 0 dBm, the standard light reception level is about -5 dBm, and the transmission loss of the optical fiber is 0.3 to 0.5 dB / km. Communication at an appropriate level can be performed only at a transmission distance of 10 to 15 km, and if the transmission distance becomes longer than that, the C / N (Carrier / Noise) in the optical receivers 18A and 18B deteriorates, and the broadcasters 20A and 20B There is a problem that the C / N that can be actually transmitted cannot be obtained in 20B.

  Further, in the conventional method shown in FIG. 4, since a 64QAM modulated signal is transmitted through a microwave fixed radio line, it is difficult to secure a necessary frequency, and the radio equipment of the SHF transmitter 24 and the SHF receivers 26A and 26B is used. There is a problem that the cost is increased and the C / N deteriorates due to the fading of the microwave fixed radio line.

  In addition, although it is conceivable that broadcast TS transmitted to a plurality of transmitting stations using an ATM line is OFDM-modulated at each transmitting station and wirelessly transmitted to the SFN service area, it is affected by jitter of the ATM line. In order to synchronize the OFDM modulator at each transmitting station, for example, it must be synchronized with an external signal such as GPS (Global Positioning System), and the reliability is low because it depends on another system such as GPS. There was a problem.

  The present invention has been made in view of the above points, and a QAM modulation signal transmission method capable of long-distance transmission while ensuring C / N of a QAM modulation signal without requiring an external signal from another system and its It is an object of the present invention to provide a transmitting device and a receiving device.

According to the first aspect of the present invention, PCM modulation is performed on a QAM modulated signal using a reference clock synchronized with a network clock of a digital optical network, and the PCM modulated signal obtained by the PCM modulation is transmitted to a plurality of locations by the digital optical network. And receiving a PCM modulated signal from the digital optical network at each of the plurality of locations, and PCM demodulating the received PCM modulated signal using a reference clock synchronized with the network clock of the digital optical network to perform QAM modulation By getting the signal
An external signal from another system is not required, and long distance transmission can be performed while ensuring C / N of the QAM modulated signal.

According to a second aspect of the present invention, a PCM modulation is performed on a QAM modulated signal using a reference clock synchronized with a network clock of an ATM network, and a plurality of PCM modulated signals obtained by the PCM modulation are assembled into an ATM cell by the ATM network. The PCM modulation signal is obtained by disassembling the ATM cells received from the ATM network at each of the plurality of locations to obtain a PCM modulation signal, and the PCM modulation signal is PCM demodulated using a reference clock synchronized with the network clock of the ATM network. By obtaining a QAM modulated signal,
An external signal from another system is not required, and long distance transmission can be performed while ensuring C / N of the QAM modulated signal.

According to a third aspect of the present invention, there is provided a PCM modulation means for PCM modulating a QAM modulated signal using a reference clock synchronized with a network clock of a digital optical network, and a PCM modulation signal obtained by the PCM modulation means as the digital optical signal. Having signal sending means for sending to the network,
According to a fourth aspect of the present invention, a receiving means for receiving a PCM modulated signal from a digital optical network, and a PCM modulated signal received using a reference clock synchronized with a network clock of the digital optical network is PCM demodulated. By having a PCM demodulation means for obtaining a QAM modulated signal,
The invention of claim 1 can be realized.

According to a fifth aspect of the present invention, there is provided a PCM modulation means for PCM modulating a QAM modulated signal using a reference clock synchronized with a network clock of an ATM network, and assembling the PCM modulated signal obtained by the PCM modulation into an ATM cell. An ATM cell sending means for sending to the ATM network;
According to a sixth aspect of the present invention, there is provided an ATM cell disassembling unit for decomposing an ATM cell received from an ATM network to obtain a PCM modulation signal, and a reference clock in which the PCM modulation signal is synchronized with a network clock of the ATM network. PCM demodulation means for obtaining a QAM modulated signal by PCM demodulation,
The invention of claim 2 can be realized.

  According to the first aspect of the present invention, the QAM modulated signal is PCM modulated using a reference clock synchronized with the network clock of the digital optical network, and the PCM modulated signal obtained by the PCM modulation is transmitted to a plurality of locations by the digital optical network. And receiving a PCM modulated signal from the digital optical network at each of a plurality of locations, and PCM demodulating the received PCM modulated signal using a reference clock synchronized with the network clock of the digital optical network to obtain a QAM modulated signal. This eliminates the need for an external signal from another system, allows long-distance transmission while ensuring the C / N of the QAM modulated signal, and allows easy construction of a single frequency network, leading to improved frequency utilization.

  According to a second aspect of the present invention, a PCM modulation is performed on a QAM modulated signal using a reference clock synchronized with a network clock of the ATM network, and a PCM modulated signal obtained by the PCM modulation is assembled into an ATM cell and a plurality of signals are assembled by the ATM network. The PCM modulation signal is obtained by disassembling the ATM cells received from the ATM network at each of the plurality of locations to obtain a PCM modulation signal, and the PCM modulation signal is PCM demodulated using a reference clock synchronized with the network clock of the ATM network. Therefore, it is possible to transmit long distances while ensuring C / N of QAM modulation signals without the need for external signals from other systems, and it is possible to easily construct a single frequency network, improving frequency utilization. Leads to.

  Moreover, according to the invention of Claim 3 and Claim 4, invention of Claim 1 is realizable.

  Moreover, according to the invention of Claim 5 and Claim 6, invention of Claim 2 is realizable.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a block diagram of a first embodiment of a single frequency network constructed by the QAM modulated signal transmission method of the present invention. In the figure, a 64QAM modulator 31 disposed in the performance room 30 performs 64QAM modulation on a broadcast TS signal.

  For example, a 64QAM modulated signal having a frequency output from the 64QAM modulator 31 of 130 MHz, for example, is frequency-converted by removing frequency components other than the desired frequency band by the band limiting filter 32 for quantization processing by the A / D converter at the subsequent stage. 33. The frequency converter 33 uses the reference signal supplied from the frequency oscillator 34 to convert the carrier frequency of the 64QAM modulated signal from the band limiting filter 32 into an appropriate frequency for quantization.

  The band limiting filter 35 removes unnecessary frequency components generated by frequency conversion from the 64QAM modulated signal and supplies the result to the A / D converter 36. The A / D converter 36 performs A / D conversion (PCM modulation) on the 64QAM modulated signal from the band limiting filter 35 using the quantization reference clock supplied from the frequency oscillator 37. The numerical data output from the A / D converter 36 is matched with the data rate in the digital optical line interface 39 by the numerical processing unit 38, and is converted into a digital optical line via the digital optical line interface 39 as a PCM (pulse code modulation) signal. It is sent to the network 45.

  The digital optical line interface 39 is supplied with a network clock from the connected digital optical line network 45. This network clock is supplied from the digital optical line interface 39 to the PLL circuits 40 and 41. The PLL circuit 40 controls the frequency oscillator 34 to generate a reference signal synchronized with the network clock, and the PLL circuit 41 controls the frequency oscillator 34 to generate a quantized reference clock synchronized with the network clock.

  The 64QAM modulator 31, band limiting filters 32 and 35, frequency converter 33, frequency oscillators 34 and 37, A / D converter 36, digital optical line interface 39, and PLL circuits 40 and 41 constitute a transmission side device. ing.

  The digital optical line interface 39 is supplied with a network clock from the connected digital optical line network 45. This network clock is supplied from the digital optical line interface 39 to the PLL circuits 40 and 41. The PLL circuits 40 and 41 are connected to the network clock. The frequency oscillators 34 and 37 generate a reference signal and a quantized reference clock synchronized with each other. For this reason, the PCM signal output after PCM modulation is synchronized with the network clock of the digital optical network 45, and the frequency stability of the PCM signal depends on the network clock.

  The PCM signal is transmitted from the digital optical line interface 39 to the digital optical line network 45 and received by the digital optical line interfaces 50A and 50B. Each of the digital optical line interfaces 50A and 50B supplies a PCM signal supplied from the digital optical line network 45 to each of the numerical processing units 51A and 51B, and supplies a network clock to each of the PLL circuits 52A and 53A and 52B and 53B. To do.

  The numerical processing units 51A and 51B convert the PCM signal from the digital optical network 45 into a data format that can be converted by the D / A converters 54A and 54B. The conversion data output from the numerical processing units 51A and 51B are D / A converted (PCM demodulated) by the D / A converters 54A and 54B using the quantization reference clock supplied from the frequency oscillators 55A and 55B, and analog 64QAM. The modulated signal. In the 64QAM modulated signal, frequency components other than the desired frequency band generated by the D / A conversion are removed by the band limiting filters 56A and 56B.

  Each of the frequency converters 57A and 57B converts the carrier frequency of the 64QAM modulated signal from the band limiting filters 56A and 56B into a desired carrier frequency using the reference signal supplied from the frequency oscillators 58A and 58B. The frequency-converted 64QAM modulated signal is subjected to removal of frequency components other than the desired frequency band by the band limiting filters 59A and 59B and supplied to the 64QAM demodulators 60A and 60B.

  Each of the 64QAM demodulators 60A and 60B demodulates the supplied 64QAM modulated signal, and supplies the obtained broadcast TS signal, the reference clock of the OFDM modulator, and the OFDM frame synchronization signal to the OFDM modulators 61A and 61B.

  The OFDM modulators 61A and 61B perform OFDM modulation on the broadcast TS signal using the reference clock of the OFDM modulator. This OFDM modulated signal is transmitted from the broadcasters (or repeaters) 62A and 62B to the SFN service area 63.

  Digital optical line interface 50A, numerical processing unit 51A, PLL circuit 52A, 53A, D / A converter 54A, frequency oscillator 55A, 58A, band limiting filter 56A, 59A, 64QAM demodulator 60A, OFDM modulator 61A, broadcast The receiving device is constituted by the device 62A, and the receiving device is similarly constituted by the digital optical line interface 50B to the broadcasting device 62B.

  Each of the digital optical line interfaces 50A and 50B is supplied with a network clock from the connected digital optical line network 45, and this network clock is supplied from each of the digital optical line interfaces 50A and 50B to the PLL circuits 52A and 53A and 52B and 53B. The PLL circuits 52A and 53A are respectively supplied to the frequency oscillators 55A and 58A to generate the quantization reference clock and the reference signal synchronized with the network clock, and the PLL circuits 52B and 53B are the quantization reference synchronized with the network clock. A clock and a reference signal are generated in the frequency oscillators 55B and 58B.

  Accordingly, the 64QAM modulated signal that is output after being PCM demodulated by each receiving side device is synchronized with the network clock of the digital optical network 45, and the frequency stability of the OFDM modulated signal obtained by performing 64QAM demodulation and OFDM modulation on the 64QAM modulated signal is Depends on network clock. In a normal digital optical network, communication is performed based on a network clock generated by a cesium atomic oscillator placed in a network center. Therefore, the network clock in each of the digital optical network interfaces 39, 50A, and 50B is different from the transmission delay difference. And in terms of frequency, they match. As described above, since the OFDM modulation signals transmitted from the respective broadcasters 62A and 62B to the SFN service area 63 coincide in frequency, a single frequency network (SFN) can be configured.

  In the case of a digital optical network, assuming that the C / N required for a 64QAM modulated signal is 50 dB, if the A / D converter 36 performs 10-bit quantization of the 64QAM modulated signal, about 60 dB is ensured and the distance is large. Regardless of this, transmission with a C / N of 60 dB is possible.

  FIG. 2 shows a block diagram of a second embodiment of a single frequency network constructed by the QAM modulated signal transmission method of the present invention. In the figure, a remultiplexer 70 supplies a broadcast TS signal, a reference clock for an OFDM modulator, and an OFDM frame synchronization signal to a 64QAM modulator 71.

  The 64QAM modulator 71 performs 64QAM modulation of the broadcast TS signal. The obtained QQ modulation signal having a frequency of 130 MHz, for example, is supplied to the frequency conversion unit 73 after the frequency components other than the desired frequency band are removed by the band limiting filter 72 for quantization processing by the A / D converter at the subsequent stage. The The frequency converter 73 uses the reference signal supplied from the frequency oscillator 74 to convert the carrier frequency of the 64QAM modulated signal from the band limiting filter 72 into an appropriate frequency for quantization.

  The band limiting filter 75 removes unnecessary frequency components generated by frequency conversion from the 64QAM modulated signal and supplies the result to the A / D converter 76. The A / D converter 76 performs A / D conversion (PCM modulation) on the 64QAM modulated signal from the band limiting filter 75 using the quantization reference clock supplied from the frequency oscillator 77. The numerical data output from the A / D converter 76 is matched with the data rate in the cladding (CLAD) circuit 79 by the numerical processing unit 78 and supplied to the cladding circuit 79 as a PCM signal. The clad circuit 79 assembles the PCM signal into the ATM cell format and sends it to the ATM network 85.

  The clad circuit 79 is supplied with a network clock from the connected ATM network 85. This network clock is supplied from the clad circuit 79 to the PLL circuits 80 and 81. The PLL circuit 80 controls the frequency oscillator 74 to generate a reference signal synchronized with the network clock, and the PLL circuit 81 controls the frequency oscillator 74 to generate a quantized reference clock synchronized with the network clock.

  The remultiplexer 70, 64QAM modulator 71, band limiting filters 72 and 75, frequency converter 73, frequency oscillators 74 and 77, A / D converter 76, clad circuit 79 and PLL circuits 80 and 81 are used as transmission side devices. Is configured.

  The clad circuit 79 is supplied with a network clock from the connected ATM network 85, and this network clock is supplied from the clad circuit 79 to the PLL circuits 80 and 81. The PLL circuits 80 and 81 receive a reference signal synchronized with the network clock and A quantization reference clock is generated in the frequency oscillators 74 and 77. For this reason, the PCM signal output after PCM modulation is synchronized with the network clock of the ATM network 85, and the frequency stability of the PCM signal depends on the network clock.

  The ATM cells transmitted through the ATM network 85 are received by the clad circuits 90A and 90B. Each of the clad circuits 90A and 90B disassembles the supplied ATM cell to obtain a PCM signal. Each of the clad circuits 90A and 90B supplies a PCM signal supplied from the ATM network 85 to each of the numerical processing units 91A and 91B, and supplies a network clock to each of the PLL circuits 92A and 93A and 92B and 93B.

  The numerical processing units 91A and 91B convert the PCM signal from the ATM network 85 into a data format that can be converted by the D / A converters 94A and 94B. The conversion data output from the numerical processing units 91A and 91B is D / A converted (PCM demodulated) by the D / A converters 94A and 94B using the quantization reference clock supplied from the frequency oscillators 95A and 95B, and analog 64QAM. The modulated signal. In the 64QAM modulated signal, frequency components other than the desired frequency band generated by the D / A conversion are removed by the band limiting filters 96A and 96B.

  Each of the frequency converters 97A and 97B converts the carrier frequency of the 64QAM modulated signal from the band limiting filters 96A and 96B into a desired carrier frequency using the reference signal supplied from the frequency oscillators 98A and 98B. The frequency-converted 64QAM modulated signal is subjected to frequency components other than the desired frequency band removed by the band limiting filters 99A and 99B and supplied to the 64QAM demodulators 60A and 60B.

  Each of the 64QAM demodulators 100A and 100B demodulates the supplied 64QAM modulated signal, and supplies the obtained broadcast TS signal, the OFDM modulator reference clock, and the OFDM frame synchronization signal to the OFDM modulators 101A and 101B.

  The OFDM modulators 101A and 101B perform OFDM modulation on the broadcast TS signal using the reference clock of the OFDM modulator. This OFDM modulation signal is transmitted from the broadcasters (or repeaters) 102A and 102B to the SFN service area 103.

  The clad circuit 90A, the numerical processor 91A, the PLL circuits 92A and 93A, the D / A converter 94A, the frequency oscillators 95A and 98A, the band limiting filters 96A and 99A, the 64QAM demodulator 100A, the OFDM modulator 101A, and the broadcaster 102A. The reception side apparatus is configured, and similarly, the reception side apparatus is configured by the clad circuit 90A to the broadcaster 102B.

  Each of the clad circuits 90A and 90B is supplied with a network clock from the connected ATM network 85, and this network clock is supplied from the clad circuits 90A and 90B to the PLL circuits 92A and 93A and 92B and 93B, respectively. The PLL circuits 92A and 93A cause the frequency oscillators 95A and 98A to generate a quantized reference clock and a reference signal synchronized with the network clock, and the PLL circuits 92B and 93B have the frequency of the quantized reference clock and the reference signal synchronized with the network clock. It is generated in the oscillators 95B and 98B.

  Therefore, the 64QAM modulated signal output after PCM demodulation at each receiving side device is synchronized with the network clock of the ATM network 85, and the frequency stability of the OFDM modulated signal obtained by performing 64QAM demodulation and OFDM modulation on the 64QAM modulated signal is the network clock. Depends on. Since the ATM network 85 performs communication based on a network clock generated by a cesium atomic oscillator placed in a network center, the network clock in each of the cladding circuits 79, 90A, 90B is different in frequency from the transmission delay difference. Are consistent. Thus, since the OFDM modulation signals transmitted from the respective broadcasters 102A and 102B to the SFN service area 103 coincide in frequency, a single frequency network (SFN) can be configured.

  In the case of an ATM network, assuming that the C / N required for a 64QAM modulated signal is 50 dB, if the A / D converter 76 performs 10-bit quantization of the 64QAM modulated signal, about 60 dB is ensured, and the distance becomes large. Regardless, transmission with a C / N of 60 dB is possible.

  Band limiting filters 32 and 35, frequency converter 33, frequency oscillators 34 and 37, A / D converter 36, PLL circuits 40 and 41, or band limiting filters 72 and 75, frequency converter 73, frequency oscillator 74 77, A / D converter 76 corresponds to the PCM modulation means described in the claims, the digital optical line interface 39 corresponds to the signal sending means, the digital optical line interfaces 50A, 50B correspond to the receiving means, and numerical processing Units 51A, 51B, PLL circuits 52A, 53A, 52B, 53B, D / A converters 54A, 54B, frequency oscillators 55A, 58A, 55B, 58B, band limiting filters 56A, 59A, 56B, 59B, or numerical processing units 91A, 91B, PLL circuits 92A, 93A, 92B, 93B, D / A converters 94A, 94B, frequency generator The devices 95A, 98A, 95B, 98B, the band limiting filters 96A, 99A, 96B, 99B correspond to PCM demodulation means, the clad circuit 79 corresponds to ATM cell sending means, and the clad circuits 90A, 90B serve as ATM cell disassembling means. Correspond.

1 is a block diagram of a first embodiment of a single frequency network configured by a QAM modulated signal transmission method of the present invention. FIG. It is a block diagram of 2nd Example of the single frequency network comprised with the QAM modulation signal transmission method of this invention. It is a block diagram of an example of the single frequency network comprised with the conventional QAM modulation signal transmission method. It is a block diagram of the other example of the single frequency network comprised with the conventional QAM modulation signal transmission method.

Explanation of symbols

30, 69 Performances 31, 71 64 QAM modulators 32, 35, 56A, 56B, 59A, 59B, 72, 75, 96A, 96B, 99A, 99B, band limiting filter 33 frequency converter 34, 37 frequency oscillator 36 A / D converter 39, 50A, 50B Digital optical line interface 38, 78, 51A, 51B, 91A, 91B Numerical processing unit 40, 41, 52A, 52B, 53A, 53B, 70, 71, 92A, 92B, 93A, 93B PLL Circuit 45 Digital optical network 54A, 54B D / A converter 60A, 60B, 100A, 100B 64QAM demodulator 61A, 61B, 101A, 101B OFDM modulator 62A, 62B, 102A, 102B Broadcaster 63, 103 SFN service area 70 Remultiplexer 79, 90A, 90B Rudd circuit 85 ATM network

Claims (6)

PCM modulation of the QAM modulated signal using a reference clock synchronized with the network clock of the digital optical network,
PCM modulation signal obtained by the PCM modulation is transmitted to a plurality of locations by the digital optical network,
Receiving a PCM modulated signal from the digital optical network at each of the plurality of locations;
A QAM modulated signal transmission method, comprising: PCM demodulating a PCM modulated signal received using a reference clock synchronized with a network clock of the digital optical network to obtain a QAM modulated signal. PCM modulation of the QAM modulated signal using a reference clock synchronized with the network clock of the ATM network,
The PCM modulation signal obtained by the PCM modulation is assembled into an ATM cell and transmitted to a plurality of locations by the ATM network.
Disassembling ATM cells received from the ATM network at each of the plurality of locations to obtain PCM modulated signals,
A QAM modulated signal transmission method comprising: obtaining a QAM modulated signal by PCM demodulating the PCM modulated signal using a reference clock synchronized with a network clock of the ATM network. PCM modulation means for PCM modulating a QAM modulated signal using a reference clock synchronized with the network clock of the digital optical network;
A transmission-side apparatus comprising signal transmission means for transmitting a PCM modulation signal obtained by the PCM modulation means to the digital optical network. Receiving means for receiving a PCM modulated signal from a digital optical network;
A receiving-side apparatus comprising PCM demodulating means for obtaining a QAM modulated signal by PCM demodulating a PCM modulated signal received using a reference clock synchronized with a network clock of the digital optical network. PCM modulation means for PCM modulating the QAM modulated signal using a reference clock synchronized with the network clock of the ATM network;
A transmission side device comprising ATM cell sending means for assembling a PCM modulation signal obtained by the PCM modulation into an ATM cell and sending it to the ATM network. ATM cell disassembling means for decomposing an ATM cell received from the ATM network to obtain a PCM modulated signal;
A receiving-side apparatus comprising PCM demodulation means for obtaining a QAM modulated signal by PCM demodulating the PCM modulated signal using a reference clock synchronized with a network clock of the ATM network.

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