JPH0457415A - Frequency detection system - Google Patents

Abstract

PURPOSE:To reduce the detection error and to decrease the circuit scale by obtaining how much frequency difference exists in a reception frequency selected by a 2nd frequency conversion means based on a reception frequency selected by a 1st frequency conversion means. CONSTITUTION:First and 2nd frequency conversion means 11, 13 convert respectively 1st and 2nd digital modulation waves into 1st and 2nd digital modulation waves in a frequency f0 by using 1st and 2nd reception local oscillation signals. The 1st and 2nd demodulators 12, 14 recover 1st and 2nd reference carriers from outputs of the 1st and 2nd frequency conversion means and demodulate the 1st and 2nd digital modulation waves. A frequency discriminator 2 compares the frequencies of the 1st and 2nd reference carriers to output an output relating to the frequency difference. Then frequency difference information of the 1st and 2nd carriers to generate the 1st and 2nd digital modulation waves is obtained from the output of the frequency discriminator 2.

Description

[Detailed Description of the Invention] [Summary] For example, regarding a frequency detection method used when communicating between earth stations using a communication satellite as a repeater, the present invention aims to reduce detection errors when detecting frequencies. In addition, in a receiving apparatus that receives digitally modulated waves generated by digitally modulating a plurality of carrier waves having different frequencies, the first. Second
The digital modulated wave of 1. frequency f using the second receiving station oscillation signal.

1st. The first and second waves are converted into a second digital modulated wave.
frequency converting means; and the first frequency converting means. From the output of the second frequency converting means to the first one. While regenerating the second reference carrier wave, the first. The first demodulates the second digitally modulated wave. A second demodulator is provided, and a frequency discriminator that compares the frequencies of the reproduced first and second reference carrier waves and sends out an output corresponding to the frequency difference. ．． The first one that generated the second digital modulated wave. The configuration is configured to obtain frequency difference information of the second carrier wave.

[Industrial application field]

The present invention relates to a frequency detection method used, for example, when communicating between earth stations using a communication satellite as a repeater.

Satellite communication, which uses communication satellites in geostationary orbit as repeaters, has been put into practical use, and in recent years, this communication satellite has been used. The so-called VSAT (Very Small Aper
(Ture Terminal) communication system has been researched and is reaching the stage of practical application.

This νSAT communication method is based on a hub (HU) that has an exchange function.
B) A large number of earth stations (OPT stations: On Prem.
data is transmitted between a small station and a large station, or between small stations via a communication satellite.

It establishes a communication line for transmitting voice and other information.

Here, in the case of satellite communication, the causes of frequency fluctuation are ■ Frequency fluctuation of the local oscillator of the repeater mounted on the satellite ■ Frequency fluctuation of the transmitting local oscillator of the transmitting station ■ Frequency fluctuation of the receiving local oscillator of the receiving station .

Now, when receiving signals from multiple transmitting stations,
term gives the same amount of frequency fluctuation for all received signals, but
In item (2), the amount of frequency fluctuation varies depending on the transmitting station. here,
The terms ■ and ■ are called common frequency fluctuation components.

Therefore, for example, it is possible to receive a pilot signal sent from a specific transmitting station at a receiving station and compress the frequency fluctuations in terms ■ and ■ from the amount of frequency fluctuation in the received Byront, but the fluctuation in the transmission frequency in cannot be compressed.

On the other hand, in addition to the VSAT communication method, SCPC (Singing
In the channel per carrier) method, data transmission is performed at a relatively low speed of, for example, 56 Kb/s, but the above transmission frequency fluctuation (for example, ±2
5 KHz), correct demodulation may not be possible in some cases.

Therefore, based on the transmission frequency from a specific transmitting station,
It detects how much the transmission frequency of other transmitting stations differs by one frequency, and uses the detection result to shift the transmission frequency and compress the frequency difference. At the same time, it is necessary to reduce the circuit scale.

[Prior Art] FIG. 11 shows a block diagram of a conventional example. Below, 5Cpc
The operation shown in the figure will be explained assuming that satellite communication is performed using this method.

First, the 5cpc signal consists of multiple modulated waves (
For example, 4-phase PSK modulated waves) are arranged at predetermined positions on the frequency axis, but if the transmitting station is different, the position will be shifted from the original position on the frequency axis by the amount of variation in the transmission frequency.

Now, these signals are received by the antenna, and are sent to the low noise amplifier 81. Frequency converter 83 via down converter 82
Add to a, 83b. Frequency converters 83a, 83b
Since the receiving station oscillation signals from the corresponding synthesizers 84a and 84b are also added, the signals S, , S, among the 5 cpc signals in FIG. 85b.

The quadruple multipliers 85a and 85b output signals 5R5S1. l to 4
After multiplying to obtain carrier waves, these carrier waves are applied to frequency discriminators 86a and 86b, frequency discrimination outputs are taken out, and a subtracter 82 calculates the difference between the two frequency discrimination outputs. Thereby, the frequency difference between the carrier frequencies fRtfM of the two 5cpc signals can be determined.

Note that the selected 5cpc signal changes by changing the frequency of the receiving station oscillation signal. Further, in the case of a two-phase PSK wave, the multiplication number is 2.

[Problems to be Solved by the Invention] In order to obtain the difference in carrier frequencies as described above, the amount of variation in each received frequency is determined by a frequency discriminator, and then the difference in frequency discrimination output is calculated.

Therefore, an error occurs in detection depending on the stability of the frequency discriminator, and if there is a difference in the discrimination characteristics, the error increases. Furthermore, since a discriminator is required in addition to signal demodulation, there are two problems: the circuit scale increases.

The present invention aims to reduce detection errors and reduce the circuit scale when detecting frequencies.

(Means for solving problems) FIG. 1 shows a block diagram of the principle of the first invention.

In the figure, ratio 13 is the first. The second digitally modulated wave is transmitted to the first.
Using the second receiving station oscillation signal, the first . These are first and second frequency conversion means for converting into a second digital modulated wave.

Also, 12.14 is the 1st. From the output of the second frequency converting means to the first one. While regenerating the second reference carrier wave,
．． The first demodulates the second digitally modulated wave. 2 in the second demodulator, the regenerated first . It is a frequency discriminator that compares the frequencies of the second reference carrier wave and sends out an output corresponding to the frequency difference.

Then, from the output of the frequency discriminator, the first and second digital modulated waves are generated. Obtain frequency difference information of the second carrier wave.

FIG. 2 shows a block diagram of the principle of the second invention.

In the figure, reference numeral 21 denotes branching/product calculation means for performing in-phase branching of the reproduced first reference carrier wave and orthogonal branching of the second reference carrier wave, and then performing a product operation of the in-phase branch component and the orthogonal branch component;
23 is a differentiator that differentiates one of the product outputs from the branch/product calculation means, and 23 is a product calculation unit that multiplies the other output of the branch/product calculation means and the output of the differentiator. It is.

The frequency converter described above is composed of a branch/product calculation means, a differentiator, and a product calculation unit.

FIG. 3 shows a block diagram of the principle of the third invention.

In the figure, 24 is a low-pass filter, and 25 is a high-pass filter having the same cutoff frequency as the low-pass filter.

The above-mentioned frequency discriminator is composed of a branch/product calculation means, a low-pass filter, a high-pass filter, and a product calculation unit.

FIG. 4 shows a block diagram of the principle of the fourth invention.

In the figure, 3 is orthogonal detection means for orthogonally detecting a digitally modulated wave generated by digitally modulating a specific carrier wave using a reproduced reference carrier wave and outputting demodulated data, and 4 is a quadrature detection means for outputting demodulated data using the demodulated data. This is a carrier wave reproducing means that generates a carrier wave.

Further, 5 is a quasi-synchronous orthogonal detection means for orthogonally detecting and demodulating a digital modulated wave generated using a carrier other than the specific carrier using the recovered reference carrier from the carrier reproducing means, and 6 is the quasi-synchronous This phase tracking means cancels the phase rotation of the demodulated output of the orthogonal detection means and outputs demodulated data.

Then, frequency difference information between the specific carrier wave and a carrier wave other than the specific carrier wave is extracted from the phase tracking means.

[Effect] The first invention was arranged in 5 cpc. Among the different digital modulated waves of the transmitting station, the digital modulated wave whose frequency difference is to be detected is selected as the first one. The second receiving station oscillation signal and the first . The selection is made using the second frequency conversion means.

For example, with respect to the receiving frequency (corresponding to the transmitting frequency) selected by the first frequency converting means as a reference, how much one frequency difference does the receiving frequency selected by the second frequency converting means have from the reference? In order to find the corresponding first.
Add to the second demodulator. In addition, 1st. The input frequency of the second demodulator is 1, for example, 70 MHz.

1st. The second demodulator reproduces a reference carrier wave necessary for demodulation from the input digital modulated wave, and uses known inverse modulation or Costas loop as a reproduction means.

Also, 1st. from the second demodulator to the first demodulator. The second reproduction reference carrier wave is applied to a two-frequency comparison type frequency discriminator, which outputs a frequency difference indicating how much the second reproduction reference carrier wave deviates from the first reproduction reference carrier wave. However, this becomes the transmission frequency difference between the transmitting stations.

Here, the above-mentioned two-frequency comparison type frequency discriminator has a configuration as shown in FIG.

That is, 1st. The second reproduction reference carrier wave is branched into two by the branching/product calculation means, one in phase and the other in orthogonal, and then multiple accumulation is taken. Then, by calculating the product of the differentiated product output and the other product output using a product calculator, a DC voltage proportional to the frequency difference is obtained.

Incidentally, although components of the sum frequency and the difference frequency of the reproduced reference carrier wave are outputted as the output of the multi-accumulator, a low-pass filter is required to pass only the difference frequency component.

FIG. 3 shows another configuration of a two-frequency comparison type frequency discriminator. The difference with Fig. 2 is that a differentiator is required in Fig. 2, whereas a low-pass filter and a high-pass filter are inserted in the complex product outputs (each filter's cut-off frequencies are chosen equally).

FIG. 4 is a diagram showing the principle of detecting a frequency difference by combining a synchronous detection demodulator and a quasi-synchronous detection demodulator.

In the fourth invention, 5 cpc were sequenced. In order to obtain a frequency difference signal between different reception carrier frequencies of transmitting stations, the reproduction reference carrier wave for demodulation of one reception 5cpc signal is used for the demodulation of the reception 5cpc signal of the other reception 5c.
It is used as a carrier wave for quasi-coherent detection for PC signal demodulation, and frequency difference information is obtained by processing the baseband signal of the quasi-coherent detection output.

A demodulator that demodulates a specific wave of the 5 cpc signal carried on a plurality of carrier waves performs orthogonal detection and demodulation using a reference carrier wave reproduced by a normal carrier wave reproducing means. Further, this reference carrier wave is used as a quasi-synchronization carrier wave for demodulating signals of other frequencies.

That is, since the reference carrier wave has a frequency difference with respect to the other carrier wave, a phase rotation corresponding to the frequency difference occurs in the baseband signal obtained as the quasi-synchronous quadrature detection output. Therefore, by providing a phase tracking means that removes the complex phase rotation occurring in this baseband signal, a normal demodulated signal (baseband signal) can be obtained as the output of this phase tracking means.

The control information for this phase tracking means is nothing but the frequency difference from the quasi-synchronization reference carrier wave described above. Therefore, by extracting the control information of this phase tracking means, it is possible to obtain the target frequency difference information between the two carrier waves.

In the present invention shown in FIG. 5, the frequency difference information of the phase tracking means is taken out from the output side of the phase tracking loop filter in the phase tracking means.

That is, since the reproduced reference carrier wave is used to detect the difference between two frequency waves, errors due to imperfections in hardware do not occur. Furthermore, since the demodulator that constitutes the frequency discriminator can be used as is, the one originally prepared for signal demodulation can be used as is, so the circuit scale can be significantly reduced.

〔Example〕

FIG. 5 is a block diagram of the first embodiment of the present invention, FIG. 6 is an example of a frequency arrangement of a 5cpc signal, FIG. 7 is a block diagram of the second embodiment of the present invention, and FIG. 8 is a block diagram of the third embodiment of the present invention. A block diagram of an embodiment of the present invention, FIG. 9 is an explanatory diagram of the operation of FIG. 8, and FIG.
The figure is 4th. A block diagram of an embodiment of the fifth invention is shown.

Here, the frequency converter 1111 frequency synthesizer 11
2 is a component of the first frequency conversion means 11, a frequency converter 1321, a frequency synthesizer 131 is a component of the second frequency conversion means 13, an in-phase branching portion 211. 2 orthogonal branch sections 2. The product calculators 213 and 214 are components of the branch/product calculator 21.

Further, the detectors 33a, 33b and the 90 degree hybrid 48 in FIG. 10 are the main components of the quadrature detection means 3 in FIG. 4, the polarity determiners 41a, 41b, the coefficient unit 42a,
42b, 43, loop filter 45, and VCO 47 are main components of carrier wave regeneration means 4, and detectors 53a and 53b.
, 90 degree high print 56 are the main components of the quasi-synchronous quadrature detection means 5.

Furthermore, coefficient units 61a, 62a, 65a, 61b,
62b, 65b.

72, subtractor 63a, adder 63b, 66, 73.7
4, polarity determiner 54a, 64b, delay circuit 7L 7
5. A sin table 76 and a cos table 77 show the main components of the phase tracking means 6.

Here, the same reference numerals indicate the same objects throughout the figures. Hereinafter, FIG. 5 will be described with reference to FIGS. 6 and 9.

The operation will be explained starting from FIGS. 7 and 8.

First, as shown in Fig. 6, a 5cpc signal in which multiple PSK modulated waves are arranged on the frequency axis is sent to the frequency converter LLL.
132.

Since receiving station oscillation signals from the corresponding synthesizers 112 and 131 (both generated using the output of the reference oscillator 133) are also added to the frequency converter LLL 132, among the 5 cpc signals, the signals S, , S, 4 is converted into an intermediate frequency band signal (the frequency is the same as 1, for example 70 MHz) and is applied to a demodulator 12.14.

The demodulators 12 and 14 use known inverse modulation or Costas loops to reproduce reference carrier waves necessary for demodulation from the input digital modulated waves, but these reproduced reference carrier waves (hereinafter referred to as 1st and 1st 2) is applied to a frequency discriminator 2 of the two-frequency comparison type.

The frequency discriminator outputs a frequency difference indicating how much the reproduced reference carrier wave from the demodulator 14 deviates from the reproduced reference carrier wave from the demodulator 12, and this is the difference between the transmission frequency of the corresponding transmitting station. Become.

Now, the two-frequency comparison type frequency discriminator has a configuration as shown in FIG.
Assume that ω,1 is input to the in-phase branch part 211, and cosω2t is input to the orthogonal branch part 212 as a second reproduction reference carrier wave.

In these branching parts, as shown in FIG.
Therefore, the product operator 213 calculates the double accumulation of the two carrier waves, and then the (ω1 +ωz) cos (ωI +ωz)t −Δωc obtained via the differentiator 22
os ΔωL (1) is added to the product operator 23.

Here, Δω·(ω1−ω2).

On the other hand, the product calculator 214 calculates the double accumulation of the two carrier waves and calculates cos(ω + + ωz)t +C03(ω
I −ωz)t ・ ・ ・ (2) is also added to the product operator 23.

Therefore, after calculating the product of equations (1) and (2) using the product calculator 23, if only the difference frequency Δω is extracted from the product output, a DC voltage proportional to the frequency difference Δω can be obtained.

Moreover, FIG. 8 shows a configuration in which a low-pass filter 24 and a high-pass filter 25 having the same cutoff frequency fc as the low-pass filter are operated in the same way as the differentiator in FIG. It is.

That is, the input/output phase characteristics of the differentiator 22 shown in FIG. 7 have a phase difference of 90 degrees regardless of the frequency. On the other hand, the low pass filter 24. The phase characteristic of the output wave of the high-pass filter 25 has a phase difference of 90 degrees regardless of the frequency, as shown in FIG. 9(a), and corresponds to the differential operation described above.

The amplitude characteristics of the output waves of these filters are shown in Figure 9 (b
), but when the product of this output wave is calculated by the product operator 23, the amplitude reaches its maximum at the cut-off frequency and the frequency is 0, as shown in the bottom of Figure 9(b). output 0
When the frequency difference becomes negative, a frequency discrimination curve that changes as shown by the dotted line is obtained.

As a result, a DC voltage proportional to the frequency difference Δω is obtained, and it can be seen that it has the same function as in FIG. 7.

Next, the operation shown in FIG. 10 will be explained.

As above, the 5cpc signal is sent to the frequency converter 3L 51
Enter. Since the receiving station oscillation signal from the corresponding synthesizer 32.52 is also added to the frequency converter 31.51, the signals S N and S out of the 5 cpc signals are intermediate frequency band signals (for example, the same as 70 MHz). ).

Therefore, the signal S14 is demodulated by a quadrature detector consisting of two detectors 33a and 33b and a 90 degree hybrid 48,
Low pass filters 34a, 34b and A/D converter 3
Demodulated data r and Q are obtained via 5a and 35b.

The demodulated data is sent to polarity determiners 41a, 41b, and coefficient unit 42.
a42b and an adder 43, which is a known Costas type phase comparator. The phase error signal from the Costas type phase comparator is passed through a loop filter 45. The regenerated carrier wave is applied to the VCO 47 via the D/A converter 46 and outputted from the VCO to the 90-degree hybrid 48 .

Incidentally, the error state monitoring section 44 monitors the error state of the demodulated data, and when the number of errors increases, it is determined that synchronization has been lost, and a sweep signal is applied to the loop filter.

On the other hand, the signal S from the frequency converter 51 is subjected to quadrature detection in a quasi-synchronous manner by a quadrature detector consisting of detectors 53a, 53b and a 90-degree hybrid 56 using the regenerated carrier wave of the VCO 47. Here, the reason why "quasi" is added is because there remains a difference in transmission frequency due to the difference in transmitters.

And low pass filters 54a, 54b and A/D
Demodulated data i and q are obtained via converters 55a and 55b, and this data is superimposed with a complex component rotating at a period corresponding to the frequency difference (hereinafter referred to as one-phase rotation). Therefore, this phase rotation is calculated by the coefficient units 61a, 61b,
62a, 62b Correct demodulated data I, Q by canceling with a phase rotation unit consisting of a subtracter 63a and an adder 63b
get.

Note that if the phase rotation is θ, sfn θ is given to the coefficient multipliers 61a and 61b, and cos θ is given to the coefficient multipliers 62a and 62b, respectively.

Demodulated data I and Q are sent to polarity determiners 64a and 64b.
It is input to a Costas type phase comparator consisting of coefficient units 65a, 65b and an adder 66. The error signal from the Costas type phase comparator is sent to an adder 73. Delay circuit 71. Coefficient unit 72
The signal is input to a variable frequency digital oscillator through a well-known loop filter consisting of:

Here, the output of the loop filter corresponds to the frequency difference between the signal SR and the signal S, and is nothing but frequency difference information between the reproduction reference carrier wave for demodulation and the reference carrier wave for quasi-synchronization.

Now, in the variable frequency digital oscillator, the output of the loop filter is added to the adder 74, and added to the previous addition value held in the delay circuit 75 at predetermined clock intervals. This added value is input as an address to the sine table 76 and the cosine table 77, so from these tables the sine value corresponding to the phase θ expressed in 8 bits is calculated.
The values of θ and cos θ are calculated using the coefficient multipliers 61a, b and 62a.
, b.

In other words, this phase tracking means constitutes a phase-locked loop based on complex processing of the baseband signal, but the control value of the variable frequency digital oscillator indicates a frequency difference,
By extracting this control value, the frequency difference can be obtained. This embodiment has a feature that it does not require any hardware other than the hardware required for demodulating the original received signal.

That is, when detecting the frequency, detection errors are reduced and the circuit scale can be reduced.

[Effects of the Invention] As described in detail above, according to the present invention, it is possible to reduce detection errors and reduce the circuit scale when detecting a frequency.

2 is a frequency discriminator, 11 is a first frequency conversion means; 12 is a first demodulator; 13 is a second frequency conversion means; 14 indicates a second demodulator.

[Brief explanation of drawings]

FIG. 1 is a block diagram of the principle of the first invention, and FIG. 2 is a block diagram of the principle of the second invention.
FIG. 3 is a block diagram of the principle of the third invention, and FIG. 4 is a block diagram of the principle of the third invention. A block diagram of the principle of the fifth present invention, FIG. 5 is a block diagram of an embodiment of the first present invention,
FIG. 6 is an example of the frequency arrangement of a 5cpc signal, FIG. 7 is a block diagram of the second embodiment of the present invention, FIG. 8 is a block diagram of the third embodiment of the present invention, and FIG. 9 is a block diagram of the eighth embodiment of the present invention. 10 is a block diagram of the embodiment of the present invention shown in FIGS. 4 and 5, and FIG. 11 is a block diagram of the conventional example. In the figure, the third principle block diagram of the present invention No. ¥34. Qi 5's uninvented 7 principles Block Diagram 1 Block diagram of the embodiment of the present invention 5 CPC signal question He E arrangement - example (f2) 8th Kan's first work Evening prisoner (b) Conventional example block prisoner

Claims (1)

[Claims] 1. In a receiving device that receives digitally modulated waves generated by digitally modulating a plurality of carrier waves having different frequencies, the first and second digitally modulated waves are transmitted to first and second receiving stations. First and second frequency conversion means (11, 1
3), and first and second demodulators that reproduce the first and second reference carrier waves from the outputs of the first and second frequency conversion means and demodulate the first and second digitally modulated waves. (12, 14), and a frequency discriminator (2) that compares the frequencies of the reproduced first and second reference carrier waves and sends out an output corresponding to the frequency difference.
1. A frequency detection method, comprising: obtaining frequency difference information between first and second carrier waves that have generated the first and second digital modulated waves from the output of the frequency discriminator. 2. The frequency discriminator includes branching/product calculation means (which performs multiplication with the in-phase branch component and the orthogonal branch component after in-phase branching the reproduced first reference carrier wave and orthogonal branching the second reference carrier wave). 21), a differentiator (22) for differentiating one of the product outputs from the branching/product calculating means, and a differentiator (22) for calculating the product of the other output of the branching/product calculating means and the output of the differentiator. Product operator (23)
2. The frequency detection method according to claim 1, comprising: 3. Among the outputs from the branch/product calculation means, one product output is passed through a low pass filter (24), and the other product output is passed through a high pass filter having the same cutoff frequency as the low pass filter. (2
3. The frequency detection method according to claim 2, wherein after passing through 5), a product calculation unit (23) performs a product calculation. 4. The receiving device according to claim 1, further comprising orthogonal detection means (3) for orthogonally detecting a digitally modulated wave generated by digitally modulating a specific carrier wave using a reproduced reference carrier wave and outputting demodulated data; carrier wave reproducing means (4) for generating the reproduced reference carrier wave using the carrier wave reproducing means; and phase tracking means (6) for outputting demodulated data by canceling the phase rotation of the demodulated output of the quasi-synchronous quadrature detection means, and the phase tracking means outputs demodulated data. A frequency detection method characterized by extracting frequency difference information of carrier waves other than the specific carrier wave. 5. The frequency detection method according to claim 4, wherein the frequency difference information is extracted from the output side of a phase tracking loop filter in the phase tracking means.