JP3767348B2 - Regenerative relay type relay device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a regenerative repeater type relay apparatus, and more particularly to improvement of transmission frequency accuracy of a regenerative repeater type repeater apparatus in digital broadcasting (sound, image, digital data, etc.).
[0002]
[Prior art]
FIG. 2 is a conceptual diagram of a regenerative relay system in conventional digital broadcasting, and FIG.
In FIG. 2, the digitally modulated broadcast signal transmitted from the broadcast main station 1 is transmitted to the relay station 3 via the communication satellite 2, for example.
[0003]
As the relay station 3, a regenerative relay type or a frequency conversion type is used. In the case of the regenerative repeater type, the received digital modulated wave is demodulated, then multiplexed and digitally modulated again, and sent to each receiver 4. Compared with the frequency conversion type relay station, the S / N ratio of the digital modulated wave deteriorates during the relay, whereas the regenerative repeater repeats the digital demodulation and reproduces the signal. There is an advantage that it does not occur.
[0004]
By the way, the carrier frequency deviation of the digital modulation wave transmitted from the relay station (both regenerative relay type and frequency conversion type) is required to have a high stability of about 0.01 ppm.
One of the reasons is that since the capture range of frequency tuning of each receiver is narrow, if the frequency deviation is bad, the receiver cannot accurately demodulate the digital modulation wave. In addition to this, when a receiver is installed in a moving body such as a car, it receives broadcasts while switching from a plurality of relay stations in sequence, so the receiver must be able to tune to the carrier frequency of each relay station instantaneously. Don't be.
[0005]
FIG. 3 is a block diagram showing a configuration example of a conventional regenerative repeater relay station.
A digital modulated wave transmitted from the communication satellite 2 or the like is demodulated by the reception / demodulation unit 5. The reception / demodulation unit 5 includes an antenna, a down converter, an IQ demodulator, a transmission path decoder, and the like.
[0006]
The output data of the receiving / demodulating unit 5 is input to the multiplexer 6, and multi-channel data multiplexing is performed.
[0007]
The digital data multiplexed by the multiplexer 6 is input to the transmission / modulation unit 7, converted into a digital modulated wave, and sent to each receiver 4. The transmission / modulation unit 7 includes a modulator, an up converter, a high frequency amplifier, an antenna, and the like.
[0008]
The TCXO 8 is a highly stable crystal oscillator, and outputs a highly accurate reference clock with a very small frequency error to the frequency synthesizer 9.
[0009]
The frequency synthesizer 9 outputs a highly accurate carrier wave having a very small frequency deviation to the transmission / modulation unit 7.
[0010]
[Problems to be solved by the invention]
Thus, in the conventional regenerative repeater-type repeater, the highly stable crystal oscillator 8 is used as a frequency reference. However, since the highly stable crystal oscillator is very expensive, it becomes a problem when the cost of the repeater is reduced. It was.
[0011]
Further, since each relay station uses an independent reference frequency, periodic maintenance work such as frequency calibration and inspection is required to maintain the accuracy of the reference frequency of each relay station.
[0012]
Furthermore, even when a relay station is newly opened, or when the repeater is resumed from a state where it has been suspended due to a power failure or equipment inspection, the reference frequency of the relay station is checked and the frequency is stabilized. Setup time is required.
[0013]
The present invention solves such a conventional problem, and without using a highly stable crystal oscillator, does not require periodic maintenance and inspection, and provides high stability of the carrier frequency deviation of the digital modulation wave. A regenerative relay type relay device is realized.
[0014]
[Means for Solving the Problems]
The invention of claim 1 which achieves such an object,
In the regenerative repeater type relay device that demodulates the received digital modulation wave to reproduce the digital data, digitally modulates the regenerated digital data again, and transmits it.
A clock extraction circuit for extracting a clock from the received signal;
A PLL circuit including a voltage-controlled crystal oscillator in a loop and based on a clock extracted from a received signal;
A frequency synthesizer that outputs a carrier wave signal using the output of the PLL circuit as a reference clock,
A modulation unit that performs digital modulation based on the output of this frequency synthesizer,
It is characterized by including.
[0015]
Thus, the frequency accuracy of the digital modulation unit for regenerative relay is based on the clock extracted from the received signal, and a relatively inexpensive crystal oscillator can be used.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a block diagram showing an example of an embodiment of the present invention, and the same reference numerals are given to the parts common to FIG.
The difference between FIG. 1 and FIG. 3 is that the output of the PLL circuit based on the clock extracted from the received signal is used in FIG. 1 instead of the highly stable crystal oscillator TCXO 8 of FIG.
[0017]
The clock extraction circuit 10 extracts a clock synchronized with broadcast data from the received signal, and inputs the extracted clock as a synchronization clock to one input terminal of the phase comparator 11.
[0018]
The output signal of the voltage controlled crystal oscillator (VCXO) 13 is input to the other input terminal of the phase comparator 11 via the prescaler 14. The phase comparator 11 compares the phase of the reference clock extracted by the clock extraction circuit 10 and the output signal of the crystal oscillator 13.
[0019]
The loop filter 12 filters the output of the phase comparator 11.
[0020]
The prescaler 14 divides the output of the crystal oscillator 13 to a desired division ratio.
[0021]
The phase comparator 11, loop filter 12, crystal oscillator 13 and prescaler 14 constitute a PLL circuit centered on the crystal oscillator 13, and its output frequency is a clock extracted from the received signal by the clock extraction circuit 10. It is controlled with high accuracy so as to synchronize with. In generating such a high-accuracy reference clock, it is not necessary to use an expensive TCXO 8 as in the prior art, and a significant cost reduction is possible.
[0022]
The output of the PLL circuit is input to the synthesizer 9 as a reference clock. As a result, the synthesizer 9 can generate a high-accuracy carrier signal having a very small frequency error synchronized with the clock transmitted from the broadcast main station 1 and supply it to the transmission / modulation unit 7.
[0023]
By configuring each relay station 3 in FIG. 2 as shown in FIG. 1, the output of the PLL circuit of each relay station 3 can establish high-precision synchronization, and complete compatibility of each relay station 3 can be achieved.
[0024]
【The invention's effect】
As described above, according to the present invention, a regenerative repeater type relay device that does not use a highly stable crystal oscillator, does not require periodic maintenance inspection, and provides high stability of the carrier frequency deviation of the digital modulation wave. And is suitable as a regenerative relay type relay device for digital broadcasting and the like.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an example of an embodiment of the present invention.
FIG. 2 is a conceptual diagram of a regenerative relay system in conventional digital broadcasting.
FIG. 3 is a configuration example of a conventional regenerative relay type relay device.
[Explanation of symbols]
1 Broadcast Main Station 2 Communication / Broadcast Satellite 3 Relay Station 4 Receiver 5 Receiver / Demodulator 6 Multiplexer 7 Transmitter / Modulator 9 Synthesizer 10 Clock Extraction Circuit 11 Phase Comparator 12 Loop Filter 13 Crystal Oscillator (VCXO)
14 Prescaler

Claims (1)

In the regenerative repeater type relay device that demodulates the received digital modulation wave to reproduce the digital data, digitally modulates the regenerated digital data again, and transmits it.
A clock extraction circuit for extracting a clock from the received signal;
A PLL circuit including a voltage-controlled crystal oscillator in a loop and based on a clock extracted from a received signal;
A frequency synthesizer that outputs a carrier wave signal using the output of the PLL circuit as a reference clock,
A modulation unit that performs digital modulation based on the output of this frequency synthesizer,
A regenerative repeater type relay apparatus comprising:

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