JPH0446393B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention aims at a flying object such as an aircraft, and uses wideband modulation of the emitted radio waves in a transmitting/receiving device that tracks Doppler frequency displacement of reflected waves from the target. The present invention relates to a transmitting/receiving device that uses waves to receive reflected waves from a target in a narrow band.

[Conventional technology]

FIG. 3 shows a conventional transmitting/receiving device. In the figure, 1 is an antenna, 2 is a transmitting/receiving switch, 3 is a transmitter, 4a is a phase modulator that modulates the phase of the output of this transmitter 3, and 5 is this phase. a phase modulation code generator that generates a modulation code for the modulator; 6 is a pulse modulator that pulse-modulates the output of the phase modulator 4a;
7 is a pulse modulation signal generator that generates a pulse modulation signal for this pulse modulator 6; 8 is a local oscillator; 9
is a phase demodulation code generator, 4b, 4c, 4d are:
Phase modulators 10a, 10b, and 10c phase modulate the output of the local oscillator 8 with a demodulation code that is the output of the phase demodulation code generator 9, and the outputs of the phase modulators 4b, 4c, and 4d and the transmission/reception switching. a mixer 11 for mixing the received signal which is the output of the device 2;
A timing discriminator 12a detects a timing difference between the phase modulation code of the received signal and the phase demodulation code output from the phase demodulation code generator 9 using the outputs of the mixers 10a, 10b, and 10c; 13 is a demodulation clock generator that supplies a reference clock to the phase demodulation code generator 9; 14a supplies a voltage that controls the frequency of this demodulation clock generator 13; amplifier,
15 is a timing search voltage generator that changes the output frequency of the demodulation clock generator 13 by a predetermined frequency in order to search for the timing of the phase modulation code of the received signal; a timing search controller that stops the output of the timing search voltage generator when the signal matches the modulation code; 17 is a frequency discriminator that receives the output of the mixer 10a and detects a Doppler frequency shift of the received signal; 12b is a A filter 14b filters the output of the frequency discriminator, and an amplifier 18 supplies a voltage for controlling the oscillation frequency of the local oscillator. The generated sharp tooth wave generator 19 is a Doppler frequency search controller that controls the operation of the sharp tooth wave generator 18 according to the timing of the output of the frequency discriminator 17 during the Doppler frequency displacement search.

Next, the operation will be explained.

Based on the phase modulation code output from the phase modulation code generator 5, the transmission carrier output from the transmitter 3 is converted into a phase modulation code "1" by the phase modulator 4a.
Corresponding to “0”, phase modulation of “0” and “π” radians is applied. Thereafter, the transmitted wave pulse-modulated by the pulse modulator 6 passes through the transmitter/receiver switch 2 and is irradiated from the antenna 1 toward the target. The radio waves reflected by the target undergo a Doppler frequency shift and are received by the antenna 1 with a delay corresponding to the time required to travel the distance to and from the target. The received signal is transferred to the transmitter/receiver switch 2.
and is supplied to mixers 10a, 10b, and 10c. On the other hand, on the receiving side, phase modulation is applied to the output of the local oscillator 8 by phase modulators 4b, 4c, and 4d using a demodulation code output from a phase demodulation code generator 9. The three outputs of the phase demodulation code generator 9 are the same as the phase modulation code, but are shifted by 1/2 bit. The three demodulated waves phase-modulated by phase modulators 4b, 4c, and 4d are sent to mixers 10a, 10b, and 4d, respectively.
10c. Mixer 10a, 10b, 1
The envelope of the output of 0c has the waveform shown in FIG. 4 depending on the timing of the code of the received signal and the code of the demodulated signal. In the figure, 20a is the mixer 10
This is the envelope of the output of a, the peak is when the phase modulation code of the received signal and the demodulation code of the phase modulator 4b match, and the width of the output is 2 bits.
Similarly, 20b is the envelope of the output of mixer 10b,
20c is the envelope of the output of mixer 10c. 2
1 is the output characteristic of the timing discriminator 11, which becomes 0 when the output of the mixer 10a reaches its peak. A filter 12 filters the output of the timing discriminator 11 and outputs a timing error signal,
This timing error signal is amplified by an amplifier 14a, controls the clock frequency of the demodulation clock generator 13, and controls the demodulation code, which is the output of the phase demodulation code generator 9, so that the output of the mixer 10a reaches its peak. do. Further, when the timing of the phase modulation code of the received signal is initially unknown, a predetermined voltage is output from the timing search voltage generator 15,
As a result, the demodulation code that is the output of the phase demodulation code generator 9 moves at a predetermined speed relative to the phase modulation code of the received signal, and the timing discriminator 11 moves in the vicinity where the timings of these codes match. A waveform 21 is output as an output, and the timing search controller 16 uses this output to cut off the output of the timing search voltage generator 15 when the timings match. Thereafter, as described above, the phase modulation code of the received signal is tracked so that the output of the mixer 10a reaches its peak.

On the other hand, regarding tracking of Doppler frequency displacement, the frequency discriminator 17 detects a Doppler frequency tracking error using the output of the mixer 10a, this tracking error is filtered by the filter 12b, and the amplifier 14
control the oscillation frequency of the local oscillator 8 through b,
Doppler frequency tracking is performed so that the output frequency of the mixer 10a is constant. Further, when the Doppler frequency displacement of the received signal is initially unknown, a sharp tooth wave with a predetermined waveform is output from the clean tooth wave generator 18, and this clean tooth wave is sent to the local oscillator 8 through the amplifier 14b. is added to change the output frequency of the local oscillator 8 within a predetermined range.

At this time, the output frequency of the mixer 10a changes similarly, and the output of the frequency discriminator 19 also changes accordingly. The frequency search controller is a frequency discriminator 1
Using the output of the mixer 10a, when the output of the mixer 10a reaches a predetermined frequency, the voltage of the tooth-tooth wave generator is fixed. After this, as mentioned above, the frequency discriminator 1
7. Through a series of operations of the filter 12b, the amplifier 14b, and the local oscillator 8, the Doppler frequency of the received signal is tracked so that the output of the mixer 10a becomes a predetermined frequency.

[Problem that the invention seeks to solve]

Conventional transmitting/receiving devices are configured as described above, so before searching, detecting, capturing, and tracking the Doppler frequency displacement, it is necessary to search, detect, capture, and track the timing at which the demodulation code is generated. Therefore, when searching and detecting the timing of the demodulated code, the bandwidth of the timing discriminator needs to be set as wide as the Doppler frequency displacement is uncertain. Therefore, the equivalent noise bandwidth of the timing discriminator is widened, making it impossible to perform narrow band reception, resulting in a problem that the minimum reception sensitivity is degraded.

Furthermore, since timing tracking and Doppler frequency tracking are performed using separate circuits, if there is interference with each tracking, one of the tracking will be lost.
The problem was that it was susceptible to interference because it could not continue to track the received signal.

This invention was made to solve the above-mentioned problems, and by simultaneously searching, detecting, capturing, and tracking the timing and Doppler frequency, it is possible to perform narrowband reception. The purpose of this invention is to obtain a transmitting/receiving device that is resistant to interference.

[Means for solving problems]

The transmitter/receiver according to the present invention samples a phase demodulated signal, converts it to digital, performs fast Fourier transform, and uses the fast Fourier transform output to perform timing discrimination and Doppler frequency discrimination. This is how it was done.

[Effect]

In this invention, by using fast Fourier transform, it is possible to perform timing discrimination and Doppler frequency discrimination at the same time. Therefore, even if one discrimination is disturbed, the other discrimination is normal. If so, you can continue tracking,
Furthermore, narrowband reception is also possible.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. In Figure 1, 1, 2, 3, 4a, 4b,
4c, 4d, 5, 6, 7, 8, 9, 10a, 10
b, 10c, and 13 are the same as the conventional transmitting/receiving device. 22 is a sampler that samples the outputs of the mixers 10a, 10b, and 10c; 23 is an A/D converter that digitally converts the output of this sampler 22; and 24 is a high-speed converter that converts the output of this A/D converter 23. A Fourier transformer 25 that performs Fourier transform uses the output of the Fourier transformer 24 to perform timing and Doppler frequency discrimination, and performs search, acquisition, and
A controller 26a performs calculations necessary for tracking, and a D/A converter 26a converts the output of the controller 25 into analog to generate a voltage for controlling the demodulation clock generator 13. A controller 26b performs calculations necessary for tracking. This is a D/A converter that converts the output into analog and generates a voltage that controls the local oscillator 8.

Next, the operation will be explained.

By operating in the same manner as a conventional transmitting/receiving device, the output of the local oscillator 8 is supplied with a demodulation code that is the same as the phase modulation code outputted from the phase demodulation code generator 9 and shifted by 1/2 bit, and the phase modulators 4b and 4
Phase modulation is applied with c and 4d. Phase modulator 4b, 4
The three demodulated waves phase-modulated by signals c and 4d are supplied to mixers 10a, 10b, and 10c, respectively, and mixed with the received signal. Mixer 10a, 10b, 10
The output of c becomes a video signal based on the same principle as heterodyne detection, and the amplitude of this video signal is 20a, 20b in FIG. The waveform is shown in 20c. The video signal is sampled by a sampler 22,
The A/D converter 23 converts it into a digital signal. The signals converted to digital signals are combined into a number of signals for a time N/B determined by the processing band B and the number of fast Fourier transform points N, and are processed by a Fourier transformer 24 composed of a pipeline processor or a parallel processor. The data is fast Fourier transformed and converted to data on the frequency axis. mixer 1
The outputs of 0a, 10b, and 10c are each subjected to fast Fourier transform as described above, and as shown in Fig. 2, the target is Both the received signal and unnecessary signals such as noise can be obtained. In the figure, a is the output obtained by fast Fourier transforming the output of the mixer 10a, b is the output of the mixer 10b, and c is the result obtained by fast Fourier transforming the output of the mixer 10c, and 27a, 27b, 27c is a target received signal. Note that the horizontal axis represents frequency and the vertical axis represents amplitude. The controller 25 uses this output to search, detect, capture, and track the timing and Doppler frequency of the received signal.

First, in search and detection, the timing and Doppler frequency are set to preset values as initial values or values measured by other equipment (such as a location radar), and the output of the Fourier transformer 24 of the received signal is set to the target value. Until 27a to 27c are detected, the timing and Doppler frequency are changed and reset by a preset change width, and the above detection operation is repeated.

Next, after the received signal is detected, acquisition is performed. The timing is captured using the fast Fourier transformed result of the detected received signal so that the output of the mixer 10a is maximized. In FIG. 2, 27a, 27b, and 27c are spectra of detected received signals. The amplitudes of spectra 27a, 27b, 27c are A, B, C
Then, the autocorrelation timing shift DT is
It is detected as an amount proportional to (B-C). That is, the amplitudes A, B, and C of the mixer 10 shown in FIG.
Output waveforms 20a, 20b, a, 10b, 10c,
20c at the same timing, 1/2
Bit advanced 20b and 1/2 bit delayed 2
The value (B-C) obtained by subtracting 0c has an S-shaped characteristic with respect to time as shown in 21, and realizes a timing discriminator. Therefore, capturing the timing is
This can be achieved by correcting the timing by an amount obtained by multiplying (B-C) by a predetermined coefficient. On the other hand, the Doppler frequency is captured using the spectrum 27a obtained by fast Fourier transform of the target received signal shown in FIG. The deviation DF between the preset frequency and the frequency of the spectrum 27a of the target received signal subjected to fast Fourier transform is calculated, and the Doppler frequency is corrected by this deviation DF so that the frequency is located at the center frequency of the processing band B. This is achieved by setting. For both timing capture and Doppler frequency capture, the respective deviations DT and DF from the previously set values are
is added and output through the D/A converters 26a and 29b to control the frequencies of the demodulation clock generator 13 and local oscillator 8.Finally, tracking, detection of tracking error is based on the calculation performed at the time of acquisition. The same is true. In tracking, a predetermined filter calculation is performed on this deviation, and the output of this filter is added to the previously set value and output. The output controls the frequency of demodulation clock generator 13 and local oscillator 8 through D/A converters 26a and 26b.

〔Effect of the invention〕

As described above, according to the present invention, the fast Fourier transform is used to perform timing control and Doppler frequency control at all times. This has the effect that the minimum receiving sensitivity can be lowered, and that the received signal can be continued to be tracked even if either the timing or the Doppler frequency is interfered with.

[Brief explanation of drawings]

FIG. 1 shows a transmitting/receiving device according to an embodiment of the present invention, FIG. 2 shows a spectrum of the result of fast Fourier transform, FIG. 3 shows a conventional transmitting/receiving device, and FIG. 4 shows an envelope of demodulated signal output. be. In the figure, 1 is an antenna, 2 is a transmitter/receiver switch, 3 is a transmitter, 4a, 4b, 4c, 4d are phase modulators, 5 is a phase modulation code generator, 6 is a pulse modulator, and 7 is a pulse modulation signal. generator, 8 is a local oscillator, 9 is a phase demodulation code generator, 10a, 10
b, 10c are mixers, 11 is a timing discriminator,
12a and 12b are filters, 13 is a demodulation clock generator, 14a and 14b are amplifiers, 15 is a timing search voltage generator, 16 is a timing search controller, 17 is a frequency discriminator, 18 is a sharp tooth wave generator, 19 are frequency search controllers, 20a, 20b,
20c is an envelope of the output of the mixer, 21 is the output characteristic of the mixer, 22 is a sampler, 23 is an A/D converter, 24 is a Fourier transformer, 25 is a discriminator, 26
a, 26b are D/A converters, 27a, 27b, 2
7c is the spectrum of the received signal, and a, b, and c are the results of fast Fourier transform. In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. An antenna, a transmitter/receiver switch, a transmitter, a phase modulator and a phase modulation code generator for phase modulating the output of this transmitter, a pulse modulator and a pulse modulation signal generator for pulse modulating the received signal, A local oscillator to demodulate, a demodulation clock generator for phase demodulating the output of this local oscillator, 1/
A phase demodulation code generator that generates three systems of phase demodulation codes shifted by 2 bits, three systems of phase modulators, three systems of mixers that mix the received signal and the demodulated signal, and using the output of the mixer, a timing discriminator, a filter, a timing search controller, a timing search voltage generator and an amplifier for controlling the timing of demodulating the phase modulation of a received signal;
In a transmitting/receiving device composed of a frequency discriminator, a filter, a frequency search controller, a tooth-tooth wave generator, and an amplifier for demodulating the Doppler frequency shift of the received signal, the output of the mixer is sampled. three systems of A/D converters that convert the outputs of the above samplers into digital signals, three systems of Fourier transformers that perform fast Fourier transforms of the outputs of the above A/D converters, and +1/ of the above Fourier transformers. A controller that uses the 2-bit shift and -1/2-bit shift outputs to control the timing, and the remaining unshifted output to control the Doppler frequency, and converts the output of this controller into an analog signal. A transmitting/receiving device equipped with a D/A converter.