JP2004088324A - Transmitter, receiver, and frequency multiplex transmission system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology capable of avoiding disturbance imposed on digital broadcast reception. <P>SOLUTION: The frequency multiplex transmission system includes a receiver for generating a clock signal used to demodulate transmission data from carriers of the transmission data transmitted from a transmitter. The transmitter is provided with a means for synchronizing a symbol frequency for allowing the carriers to be subjected to digital modulation among a plurality of the carriers, and the receiver is provided with a means for using the carriers other than the carrier of selected data to generate the clock signal with the symbol frequency when reproducing the data selected among the transmission data whose symbol frequency is synchronized among a plurality of the carriers. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a frequency multiplex transmission system, and more particularly to a frequency multiplex transmission system in which a demodulator is operated by reproducing a clock of a symbol from a carrier wave that receives digital modulated wave data, such as a multi-channel digital cable television system. It is related to effective technology when applied.
[0002]
[Prior art]
In a cable television using a conventional frequency multiplexing transmission system, a multi-channel carrier wave is frequency-multiplexed. For this purpose, the receiver (receiving apparatus) employs a method of tuning a desired carrier wave and reproducing and receiving the symbol timing from the signal.
[0003]
For this reason, when the frequency of the frequency-multiplexed digital carrier symbol is not synchronized, or when the carrier wave to be received is changed, the receiving device uses the tuner output signal (demodulator input signal) each time. It was necessary to regenerate the symbol clock. Furthermore, the operation of the clock recovery circuit may not function when the transmission characteristics deteriorate significantly due to interference waves being mixed into the receiving channel.
[0004]
[Problems to be solved by the invention]
As a result of examining the prior art, the present inventor has found the following problems.
[0005]
In digital modulation on a cable television using a conventional frequency multiplex transmission system, a multi-level modulation scheme in which the number of bits transmitted per symbol is increased is used in order to increase frequency utilization efficiency.
[0006]
For this reason, the receiver is required to regenerate a clock with less jitter in order to identify the symbol with accurate timing. In particular, it is desired that the quality of the recovered clock satisfies the required characteristics even when the characteristics of the transmission line are deteriorated due to the influence of the interference wave. For this reason, development of a technique for avoiding interference with digital broadcast reception is eagerly desired. Furthermore, it is desired to improve the function of the receiver by shortening the time required from channel selection switching to data reproduction.
[0007]
An object of the present invention is to provide a technique capable of avoiding interference with digital broadcast reception.
[0008]
Another object of the present invention is to provide a technique capable of shortening the time required from channel selection switching to data reproduction.
[0009]
The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.
[0010]
[Means for Solving the Problems]
Of the inventions disclosed in this application, the outline of typical ones will be briefly described as follows.
[0011]
(1) In a transmission device of a frequency multiplex transmission system that generates a clock signal used for demodulation of transmission data from a carrier wave of transmission data, means for synchronizing a symbol frequency for digitally modulating the carrier wave among a plurality of carrier waves is provided.
[0012]
(2) Receiving data selected from transmission data in which a symbol frequency is synchronized among a plurality of carriers in a receiving device of a frequency multiplexing transmission system that generates a clock signal used for demodulation of the transmission data from a carrier wave of transmission data And means for generating a clock signal having the symbol frequency using a carrier other than the carrier of the selected data.
[0013]
(3) When receiving selection data from transmission data in which a symbol frequency is synchronized among a plurality of carrier waves in a receiving device of a frequency multiplexing transmission system that generates a clock signal used for demodulation of the transmission data from a carrier wave of transmission data And a means for holding the control signal output of the PLL for a predetermined time when the selected data is switched to a carrier other than the carrier to shorten the time required for synchronous reproduction.
[0014]
(4) In a frequency multiplex transmission system having a receiver that generates a clock signal used for demodulation of the transmission data from a carrier wave of transmission data transmitted from the transmitter, the transmitter has a plurality of symbol frequencies for digitally modulating the carrier wave. Means for synchronizing between carrier waves, and the receiver uses a carrier wave other than the carrier wave of the selected data when reproducing data selected from transmission data having a symbol frequency synchronized between a plurality of carrier waves. Means for generating a clock signal of the symbol frequency is provided.
[0015]
According to the means (1) to (4) described above, a frequency multiplexed signal obtained by multiplexing information on a carrier whose clock is synchronized is supplied from the transmission apparatus, and the reception apparatus selects the reception channel using the reception channel selection means. In addition to the carrier wave corresponding to the selected channel, the best clock is selected from the clocks of symbols obtained from the carrier waves of other different channels, and the transmission data is demodulated. Even when interference waves such as noise are mixed into the frequency multiplexed signal corresponding to the channel and the state of the transmission path is deteriorated, the influence on the quality of the recovered clock can be reduced. As a result, it is possible to perform stable reception while avoiding interference with transmission data.
[0016]
In particular, when reproducing selected data from transmission data whose symbol frequency is synchronized among a plurality of carriers, the control signal output of the PLL is held for a predetermined time when the selected data is switched to a carrier other than the carrier. The time required for synchronous reproduction can be shortened.
[0017]
Even when the data reproduction operation is continued by providing means for switching the carrier wave used for generating the clock signal during the reproduction operation of the selected data to another data carrier wave different from the selected data. Since the carrier used for reproducing the clock can be switched to another carrier, a clock having a high signal-to-noise ratio and low jitter can be selected and used.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the drawings together with embodiments (examples) of the invention.
[0019]
Note that components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiment of the invention, and the repetitive description thereof is omitted.
[0020]
FIG. 1 is a diagram for explaining a schematic configuration of a transmission apparatus constituting a frequency multiplex transmission system according to an embodiment of the present invention, and FIG. 2 is a diagram illustrating the configuration of the frequency multiplex transmission system according to an embodiment of the present invention. It is a figure for demonstrating schematic structure of the receiver which performs.
[0021]
1 and 2, 1 is a transmission device, 2 is a digital signal, 3 is a multiplexing device, 4 is a digital modulator, 5 is timing synchronization information, 6 is a clock generator, 7 is a frequency multiplexing device, and 8 is a transmission. Path, 9 is a distributor, 10 is a receiving device, 11 is a carrier wave selection unit, 12-1 is a digital demodulator, 12-2 to 12-4 are clock recovery circuits, 13 is a recovery clock selection unit, 14 is a digital signal, Reference numeral 15 denotes an MPEG decoder, 16 denotes timing synchronization information, and 17 denotes a display device.
[0022]
As shown in FIG. 1, the transmitting apparatus 1 according to the first embodiment is information indicating that the clock of a carrier symbol is synchronized with a digital signal 2 which is broadcast program data corresponding to each channel. A plurality of multiplexers 3 to which timing synchronization information 5 is added, a plurality of known digital modulators 4 that respectively modulate digital signals to which timing synchronization information 5 is added, and a clock signal to be supplied to the digital modulator 4 The clock generator 6 is composed of a frequency multiplexing device that multiplexes the modulation signal generated by each digital modulator 4 and generates a transmission signal.
[0023]
Next, based on FIG. 1, operation | movement of the transmitter 1 of this Embodiment is demonstrated. In the transmission apparatus 1, in order to transmit the digital signal 2, the digital signal 2 is input to the multiplexing apparatus 3 that conforms to the MPEG-2 Systems (ISO / IEC 13818-1) standard to convert the MPEG-2TS signal into cable television. The data is converted into data for distribution at, and then input to the digital modulator 4. At this time, the symbol rate of each digital modulator 4 is synchronized with the clock supplied from the clock generator 6 regardless of the modulation method. However, it is needless to say that the symbol rates of the digital modulators 4 do not necessarily have the same frequency, and may have an integer ratio relationship.
[0024]
In the present embodiment, the timing synchronization information 5 is transmitted to the multiplexing device 3 in order to transmit to the receiving device 10 that the clocks of the symbols of the plurality of carrier waves frequency-multiplexed by the frequency multiplexing device 7 are synchronized. Insert it. At this time, as a method of multiplexing information (timing synchronization information 5) that symbols of a plurality of carrier waves are synchronized with an MPEG-2 TS signal (transport stream packet defined by ISO / IEC 13818-1), international Recommendations of the Telecommunications Union “Program Information for Digital Broadcasting in Cable Television Systems: Service Information For Digital Broadcasting In Cable Television Systems” (ITU-TRec, J.94) and “ “Program Arrangement Information Used for Digital Broadcasting” (ARIB STD-B10) and “Design and Identification of Digital Wired Telehivision Broadcast Program Arrangement Information” stipulated by the Japan CATV Technology Association A method using a operational criteria "(JCTEA STD-003 · 2.0) descriptor specified in like. In addition, a method that does not use descriptors can be realized by inserting information into the extended information portion of the multiple frame header of the multiple TS transmission frames of cable television defined in the Enforcement Rules of the Cable Television Broadcasting Law ( Japanese Patent Application 2001-237404).
[0025]
As shown in FIG. 2, the receiving apparatus 10 according to the second embodiment includes a distributor 9 that distributes a frequency-multiplexed signal that is input via a transmission path 8 to which a plurality of receiving apparatuses 10 are connected, and a receiving device (not shown). A first to fourth carrier selection unit 11 that selects a carrier corresponding to the channel selected by the channel selection means and a carrier selected according to a preset condition, and generates a symbol clock from the carrier A digital demodulator 12-1 that includes a first clock recovery circuit (not shown) for (reproducing) and demodulates a digital signal (MPEG-2TS signal) 14 from the selected carrier wave output from the first carrier wave selection unit 11 And second to fourth clock recovery circuits 1 for generating (reproducing) a symbol clock from the carrier wave output from the second to fourth carrier wave selection units 11. −2 to 12-4, a reproduction clock selection unit 13 that selects a good clock from the clocks from the first to fourth clock reproduction circuits and supplies the selected clock to the digital demodulator 12-1, and video and audio from the digital signal 14. , MPEG decoder 15 for reproducing data, program arrangement information, and service information.
[0026]
Next, based on FIG. 2, operation | movement of the receiver 10 of this Embodiment is demonstrated. The frequency multiplexed signal is input from the distributor 9 to the first to fourth carrier wave selection units (tuners) 11 through the transmission path 8. The carrier wave selected by the tuner 11 is output as a baseband signal from the digital demodulator 12-1 and becomes an MPEG-2TS signal 14. At this time, in the digital demodulator 12-1 of the present embodiment, a demodulation operation is performed based on the symbol clock selected and output from the reproduction clock selection unit 13 depending on the presence or absence of timing synchronization information. Furthermore, the clock of this symbol is a carrier wave input to the digital demodulator 12-1, that is, a carrier wave corresponding to a channel selected and designated by a receiving channel selection means (not shown), and other three channels different from this carrier wave. The clock of the symbol having the best quality selected by the recovered clock selection unit 13 is obtained from the clocks of the four symbols generated (regenerated) from the carrier waves. As a result, even when interference waves such as noise are mixed in the frequency multiplexed signal corresponding to the channel instructed to be selected and the state of the transmission line deteriorates, the influence on the quality of the recovered clock can be reduced. As a result, it becomes possible to perform stable reception while avoiding interference with digital broadcast reception.
[0027]
The MPEG signal decoder 14 reproduces video, audio, and data, as well as program arrangement information (PSI: Program Specific Information) and service information (SI: Service Information), and is included in the MPEG-2TS signal. And information about the services and networks making up the program can be detected as a table on the receiver side. Among them, the timing synchronization information 16 in which the symbol timings of a plurality of carrier waves multiplexed on the transmission device 1 side are synchronized can be grasped on the reception device side by a descriptor inserted into a network information table (NIT) or the like.
[0028]
FIG. 3 is a diagram for explaining a schematic configuration of the clock recovery circuit according to the present embodiment, in which 18 is a symbol timing extraction unit, 19 is a phase difference detection unit, 20 is a loop filter, 21 is a sample hold unit, and 22 is A hold control unit 23 is a voltage controlled oscillator.
[0029]
In the symbol timing extraction unit 18, as illustrated in the document “Digital Communication” (Science and Technology Publishing) and the like, after the symbol timing information is extracted by a non-linear circuit, the phase difference detection unit 19, the loop filter 20, and the voltage controlled oscillator 23. A symbol clock can be recovered from a modulated wave by a PLL (Phase locked loop) configuration using (VCO: Voltage Control Oscillator).
[0030]
Since the recovered clock selection unit 13 can select a recovered clock from a plurality of carriers whose symbol timings are synchronized, the receiving device can perform clock recovery using a carrier other than the carrier for recovering data, It can be used.
[0031]
On the other hand, when there is one circuit for clock recovery, that is, when the second to fourth clock recovery circuits 12-2 to 12-4 are not used, a loop filter is used when switching a carrier wave for clock recovery. The change of the control signal level of the voltage controlled oscillator 23 is stopped by the hold control unit 22 in the sample hold unit 21 and the output of 20 can be shortened until the PLL is locked.
[0032]
Furthermore, by providing a function for comparing and evaluating clock jitter, SN, etc. in the reproduction clock selection circuit, a high quality clock can be used for data reproduction. In addition, by providing a clock synthesis unit that extracts frequency components from a plurality of regenerated clocks and combines them in place of the regenerated clock selection unit, it is possible to reduce jitter components and improve the quality of the regenerated clocks.
[0033]
As described above, in the cable television based on the frequency multiplexing transmission system of the present embodiment, the frequency multiplexing signal obtained by multiplexing the information of the carrier wave with which the clock is synchronized is supplied from the transmission apparatus 1 and the reception apparatus 10 Together with the carrier wave corresponding to the channel selected by the receiving channel selection means, the recovered clock selection unit selects the best clock from the clocks of the symbols obtained from the other three carrier waves, and the digital demodulator 12- The quality of the regenerated clock even when the state of the transmission line deteriorates due to interference waves such as noise mixed in the frequency multiplexed signal corresponding to the channel instructed to be selected. As a result, it is possible to reduce the influence on the digital broadcast, so that stable reception that avoids interference with digital broadcast reception is possible.
[0034]
The invention made by the present inventor has been specifically described based on the embodiment of the invention, but the invention is not limited to the embodiment of the invention and does not depart from the gist of the invention. Of course, various changes can be made.
[0035]
【The invention's effect】
The effects obtained by the representative ones of the inventions disclosed in the present application will be briefly described as follows.
[0036]
(1) Along with the carrier wave corresponding to the channel selected by the receiving channel selection means, the best clock is selected from among the clocks of symbols obtained from the carrier waves of other different channels, and the transmission data is demodulated. As a result, the quality of the recovered clock will be affected even if interference conditions such as noise are mixed into the frequency-multiplexed signal corresponding to the selected channel and the state of the transmission line deteriorates. Can be small.
[0037]
(2) Since the influence on the quality of the regenerated clock can be reduced, stable reception can be performed while avoiding interference with transmission data.
[0038]
(3) Even when the data reproduction operation is continued by switching the carrier wave used for generating the clock signal during the reproduction operation of the selected data to a carrier wave of other data different from the selected data, Can be switched to another carrier, so that a clock having a high signal-to-noise ratio and low jitter can be selected and used.
[0039]
(4) When reproducing selected data from transmission data in which the symbol frequency is synchronized among a plurality of carriers, the PLL control signal output is held for a predetermined time when the selected data is switched to a carrier other than the carrier, thereby synchronizing The time required for reproduction can be shortened.
[Brief description of the drawings]
[Figure 1]
It is a figure for demonstrating schematic structure of the transmitter which comprises the frequency multiplexing transmission system which is one embodiment of this invention.
[Figure 2]
It is a figure for demonstrating schematic structure of the receiver which comprises the frequency multiplexing transmission system which is one embodiment of this invention.
[Fig. 3]
It is a figure for demonstrating schematic structure of the clock reproduction circuit of this Embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Transmitter 2 ... Digital signal 3 ... Multiplexer 4 ... Digital modulator 5 ... Timing synchronization information 6 ... Clock generator 7 ... Frequency multiplexer 8 ... Transmission path 9 ... Divider 10 ... Receiver 11 ... Carrier wave selection part 12-1 ... Digital demodulator 12-2 to 12-4 ... Clock recovery circuit 13 ... Regeneration clock selection unit 14 ... Digital signal 15 ... MPEG decoder 16 ... Timing synchronization information 17 ... Display device 18 ... Symbol timing extraction unit 19 ... Phase difference detection unit 20 ... Loop filter 21 ... Sample hold unit 22 ... Hold control unit 23 ... Voltage controlled oscillator

Claims (6)

In a transmission device of a frequency multiplexing transmission system that generates a clock signal used for demodulation of the transmission data from a carrier wave of transmission data,
A transmission apparatus comprising means for synchronizing a symbol frequency for digitally modulating a carrier wave among a plurality of carrier waves. In a receiver of a frequency multiplex transmission system that generates a clock signal used for demodulation of the transmission data from a carrier wave of transmission data,
Means for generating a clock signal of the symbol frequency using a carrier other than the carrier of the selected data when reproducing the data selected from transmission data in which the symbol frequency is synchronized among a plurality of carriers; A receiving apparatus. The receiving device according to claim 2,
The receiving means includes means for switching a carrier wave used for generating the clock signal during a reproduction operation of the selected data to a carrier wave of other data different from the selected data. apparatus. The receiving device according to claim 2,
The generating means includes means for generating a clock signal corresponding to each data from the two or more data carriers, and means for synthesizing the two or more clock signals, and the generating means is the synthesized clock. A receiver which reproduces data selected using a signal and reduces jitter of a clock signal. In a receiver of a frequency multiplex transmission system that generates a clock signal used for demodulation of the transmission data from a carrier wave of transmission data,
When reproducing selection data from transmission data whose symbol frequency is synchronized among a plurality of carriers, means for holding a control signal output of the PLL for a predetermined time when switching to a carrier other than the carrier of the selection data is provided. A receiving apparatus characterized by shortening the time required for. In a frequency multiplex transmission system having a receiving device that generates a clock signal used for demodulation of the transmission data from a carrier wave of transmission data transmitted from a transmission device,
The transmitter comprises means for synchronizing a symbol frequency for digitally modulating a carrier wave between the plurality of carrier waves,
The receiver generates a clock signal of the symbol frequency using a carrier other than the carrier of the selected data when reproducing data selected from transmission data whose symbol frequency is synchronized among a plurality of carriers. A frequency multiplex transmission system comprising means.

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