CN114244420B - Satellite communication Chirp signal tracking receiver - Google Patents
Satellite communication Chirp signal tracking receiver Download PDFInfo
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- H—ELECTRICITY
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- H04B7/185—Space-based or airborne stations; Stations for satellite systems
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B7/00—Radio transmission systems, i.e. using radiation field
- H04B7/14—Relay systems
- H04B7/15—Active relay systems
- H04B7/185—Space-based or airborne stations; Stations for satellite systems
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Abstract
The invention discloses a satellite communication Chirp signal tracking receiver, which relates to the field of satellite communication and mainly comprises the following components: determining the signal form and time domain and frequency domain characteristics of satellite communication, and establishing a simulation model according to a tracking mode; designing intermediate frequency and sampling rate, and performing digital down-conversion, extraction and low-pass filtering after A/D sampling; designing a matched filter to obtain signal peak distribution and performing frequency coarse estimation on Chirp signal frequency offset; storing the single-period Chirp signal, obtaining a frequency accurate estimation result through frequency scanning, and carrying out frequency correction; and (3) carrying out locking judgment on the signal subjected to frequency correction according to the signal characteristics, synchronously demodulating the single-channel single-pulse signal, separating the sum signal and the difference signal, and sending the obtained error information to an antenna servo system for self-tracking. The invention combines Chirp signal extraction with a single-channel single-pulse tracking mode, can ensure that the antenna system achieves high-precision tracking performance, and is suitable for self-tracking of beaconing satellite signals.
Description
Technical Field
The invention relates to a self-tracking system in the field of satellite communication, in particular to a tracking method for satellite communication signals using Chirp signals as frequency correction signals, which adopts single-channel single-pulse tracking, and is particularly suitable for the design of a high-precision tracking receiver of a beaconing-free satellite communication system.
Background
In the conventional satellite communication system, the self-tracking technology of the antenna ensures that the beam of the communication antenna assembled on a moving carrier such as an airplane, a ship, a car and the like is always aligned with the satellite by a certain tracking means, so that the communication is ensured to be carried out stably. The antenna self-tracking system can be roughly divided into a program tracking system, a stepping tracking system, a cone scanning tracking system and a single pulse tracking system, and the tracking modes have various characteristics in the aspects of performance, implementation method and the like, but have respective advantages and disadvantages.
(1) The program tracking system calculates the difference between the angle value of the antenna to be pointed and the angle value of the actual pointing obtained by the current sensor according to the actual time, and controls the servo unit by using the difference value to make the difference value zero. The tracking mode does not need signal feedback and has the simplest equipment, in other tracking modes, program guidance is generally used as an initial capturing means of a satellite communication antenna, but the tracking precision is low when the tracking mode is used alone, the depth in the mobile carrier tracking application depends on high-precision inertial navigation, and the tracking performance requirement of a system cannot be met generally.
(2) Step tracking is also called extremum tracking, which is based on the maximum level of the received beacon signal when the antenna points to the satellite, and belongs to maximum tracking. The tracking mode is used as an antenna tracking closed-loop basis through signal feedback, a step tracking receiver is needed to calculate the signal power, but the tracking speed is low because the maximum value of the signal is needed to be found through step motion, so that the tracking precision is higher than that of program tracking, and the requirements can not be met in certain application occasions needing quick and high-precision tracking.
(3) The basic idea of the cone scanning tracking system is that an antenna feed source is artificially deviated from the visual axis of the antenna by an angle, and is rotated around the visual axis of the antenna, when the satellite deviates from the visual axis, a beacon signal received by a receiving channel is added with an amplitude modulation which is the same as the rotation frequency of a wave beam compared with an original signal, a tracking receiver obtains azimuth and pitching error voltages through synchronous demodulation, and a servo system drives the antenna to move towards the direction of error reduction until the error is minimum, and the antenna is aligned with the satellite. The cone scanning tracking mode is the earliest differential self-tracking mode, the tracking precision is higher than that of stepping tracking, but because the antenna feed source is always deviated from the visual axis, the gain is reduced, and meanwhile, the equipment quantity is increased because the mechanical rotation of the antenna auxiliary surface is required.
(4) The single pulse tracking system is divided into a comparison single pulse and a comparison single pulse in a comparison mode, and is divided into multi-mode single pulse tracking and multi-horn single pulse tracking in a feed source mode. The principle is that the self-tracking is realized by utilizing the characteristic that the electric field pattern of the antenna is zero in the axial direction of the antenna and has polarity in the direction of the off-axis, and the self-tracking system is a high-precision difference self-tracking system, and is particularly suitable for satellite antenna tracking which needs rapid high-precision tracking.
However, in the above tracking modes, besides program tracking, the stepping tracking, cone scanning tracking and single pulse tracking modes of the conventional satellite communication system all need to use the level of a beacon (single carrier) received when an antenna beam points to a satellite as a basis, and signal maximum value, azimuth and elevation error information are obtained through modes such as maximum value searching, amplitude or phase modulation signal synchronous demodulation and the like, so that the antenna beam is aligned to the satellite direction.
With the satellite mobile communication systems such as the Tiantong series and the like put into use, new signal tracking requirements appear, and the satellite channels do not have traditional beacon (single carrier) signals, so that the traditional beacon tracking mode loses the judgment basis.
Disclosure of Invention
In view of this, the invention provides a satellite communication Chirp signal tracking receiver, which finds that the frequency correction Chirp signal in the channel can be used for antenna tracking by analyzing the channel characteristics, and can make the antenna system achieve higher tracking performance by combining a single-channel single-pulse tracking mode, thereby solving the problem of rapid and high-precision tracking of the beaconing-free satellite signal.
In order to solve the technical problems, the invention adopts the following technical scheme:
a satellite communication chirp signal tracking receiver comprises an A/D sampling module, a first digital down-conversion module, a first extraction and filtering module, a data storage module, a frequency scanning and frequency offset estimation module, a second digital down-conversion module, a second extraction and filtering module, a first matched filtering module, a signal peak extraction module, a quadrature demodulation module, a synchronous modulation signal generator, a low-pass filtering module, a azimuth difference and pitch difference signal normalization module, a digital phase correction module, a signal characteristic detection module, a locking detection module and a signal to noise ratio detection module;
the A/D sampling module receives an intermediate frequency signal at the radio frequency front end of the antenna, performs A/D sampling and then outputs the signal to the first digital down-conversion module without distortion; the first digital down-conversion module performs first-stage digital down-conversion on the digital signal and then outputs the digital signal to the second digital down-conversion module and the first extraction and filtering module respectively; the first extraction and filtering module extracts and filters the input signal in a low-pass mode, and then stores the input signal into the data storage module; the frequency scanning and frequency offset estimation module extracts stored data to carry out matched filtering, frequency coarse estimation and frequency fine estimation, a matched filtering result is output to the signal characteristic detection module, and a frequency offset estimation result is output to the second digital down-conversion module; the signal characteristic detection module detects signal characteristics of the signals subjected to the matched filtering, and outputs signal frequency offset to the locking detection module and the servo control unit; the second digital down-conversion module carries out secondary down-conversion on the signal output by the first digital down-conversion module and outputs the baseband signal subjected to frequency offset correction to the second extraction and filtering module; the second extraction and filtering module extracts and filters the input signal in a low-pass mode, and then outputs the input signal to the first matched filtering module; the first matched filtering module performs time domain matched filtering on the input signal according to the signal characteristics and outputs the result to the sum signal peak value extraction module; the sum signal peak value extraction module carries out peak value detection on an input signal and then outputs a sum signal peak value to the signal-to-noise ratio detection module, the quadrature demodulation module, the azimuth difference and pitch difference signal normalization module and the servo control unit respectively; the signal-to-noise ratio detection module estimates the signal-to-noise ratio of the peak detected signal and outputs the signal-to-noise ratio of the Chirp signal to the lock detection module and the servo control unit; the lock detection module performs lock judgment by utilizing the signal-to-noise ratio and the signal frequency offset and outputs a lock instruction to the servo control unit; the quadrature demodulation module carries out quadrature demodulation by utilizing the sum signal peak value and the synchronous modulation signal output by the synchronous modulation signal generator, and outputs a quadrature demodulation result to the low-pass filtering module; after the low-pass filtering module filters out the high-frequency components, outputting a azimuth difference signal and a pitching difference signal to the azimuth difference signal normalization module; the azimuth difference and pitch difference signal normalization module normalizes azimuth difference signals, pitch difference signals and sum signal peaks and outputs normalization results to the digital phase correction module; the digital phase correction module receives the calibration phase sent by the servo control unit, performs phase correction on the phase difference and pitch difference signals, removes cross coupling influence, and outputs the phase difference and pitch difference to the servo control unit.
The frequency estimation function is completed by a data storage module and a frequency scanning and frequency deviation estimation module, wherein the data storage module comprises a data buffer module, a DPRAM and a data selection module, and the frequency scanning and frequency deviation estimation module comprises a frequency deviation correction module, a second matched filtering module, a peak value detection module, a frequency deviation estimation module and a DDS module;
the data buffer module receives the digital signal output by the first extraction and filtering module, stores the data into the DPRAM, and outputs a data scanning mark to the data selecting module after the data is fully written; the data selection module reads signals stored in the DPRAM according to the scanning marks and outputs the signals to the frequency offset correction module; the frequency offset correction module corrects the frequency according to the frequency control word output by the DDS module, and outputs corrected data to the second matched filtering module; the second matched filtering module performs time domain matched filtering on the corrected data according to the Chirp signal characteristics and outputs the result to the peak detection module; the peak detection module carries out peak detection on the matched filtering output signal and outputs the time interval between peaks to the frequency offset estimation module; the frequency offset estimation module estimates a frequency difference delta f through a time interval delta t between peaks, and outputs the updated frequency difference to the DDS module; the DDS module outputs a frequency control word according to the frequency difference control, and performs 4 frequency stepping scans, wherein the maximum value of the stepping is 8.192kHz, and the minimum value of the stepping is 0.25Hz.
The first matched filtering module and the second matched filtering module are obtained by cascading 8 groups of filters, and each group of filters is provided with a feedback port.
The synchronous modulation signal input by the quadrature demodulation module is synchronous with the modulation square wave, and the frequency of the modulation square wave is more than or equal to 16kHz.
The DPRAM storage depth in the data caching module is 64ms, the DPRAM storage depth is divided into four areas, each area comprises an 8ms non-overlapping data area, an overlapping data area overlapping with other areas is arranged in front of and behind the non-overlapping data area, and after the data of a certain 24ms area is fully written, a data scanning mark is output to the data selecting module.
Compared with the background technology, the invention has the following beneficial effects:
(1) The invention uses the Chirp signal in the satellite FCCH channel to track, is suitable for the tracking of the beaconing-free satellite signal, and provides a solution for the tracking of time division and linear frequency modulation signals in the satellite channel.
(2) The method carries out frequency offset estimation on the Chirp signal by using the full time domain matched filtering method, and simultaneously extracts signal power by using peak level, thereby reducing the digital signal processing operand.
(3) In the invention, the time division characteristic of signals in a satellite communication channel is utilized to carry out high-speed signal processing in a time gap, and the sampling data is subjected to frequency scanning for a plurality of times, so that the frequency offset estimation precision is improved, more accurate signal peaks are obtained, and the method can be used for initial signal capturing and coordinate calibration correction in an un-calibrated state.
(4) According to the invention, the tracking error signal level of the azimuth and elevation directions of the antenna is obtained by combining Chirp signal calculation with a single pulse tracking mode, so that the automatic tracking of the mobile carrier is not dependent on high-precision inertial navigation any more, and the tracking precision of the antenna is improved.
(5) The tracking of the Chirp signal can be realized by utilizing the traditional satellite communication antenna tracking platform, the algorithm implementation mode is simple and feasible, the updating is convenient, and the system cost is effectively reduced.
In a word, the invention has ingenious conception, clear thought and easy realization, solves the problem of self-tracking of the antenna of the beaconing-free satellite signal, improves the tracking precision, effectively saves the cost and is an important improvement on the prior art.
Drawings
FIG. 1 is a schematic diagram of a typical signal of a satellite broadcast channel according to the present invention;
FIG. 2 is a schematic block diagram of a Chirp signal tracking receiver of the present invention;
FIG. 3 is a schematic block diagram of frequency estimation according to an embodiment of the present invention;
FIG. 4 is a schematic block diagram of a matched filter in an embodiment of the invention;
FIG. 5 shows the result of the matched filtering output being bimodal due to the presence of Chirp signal frequency differences in an embodiment of the present invention;
FIG. 6 shows the result of the single peak output of the matched filtering after the frequency scanning and the frequency offset estimation after the Chirp signal frequency offset estimation is completed in the embodiment of the invention;
fig. 7 is a result of synchronously demodulating a single-channel single-pulse signal to obtain sum and difference signals and maintaining the sum and difference signals in the embodiment of the present invention.
Detailed Description
The invention is further described below with reference to the drawings and detailed description.
Before tracking the receiver, determining the signal form, time domain and frequency domain characteristics of satellite communication, analyzing a Chirp signal expression and establishing a simulation model;
fig. 1 is a schematic diagram of a typical signal of a satellite broadcast channel in an embodiment, where signal 1 is an FCCH, i.e., a Chirp signal, with a time length of 7.5ms, a bandwidth of 15.36kHz, and a period of 480ms; signal 2 is pi/4-CQPSK signal, time is 15ms, period is 480ms, symbol rate is 16KBps, bandwidth is 21.6kHz; other time signals vary with traffic. In the embodiment, a Chirp signal is selected as a tracking object, a simulation model is built in Matlab according to a signal expression, and FIG. 2 is a schematic block diagram of a Chirp signal tracking receiver.
And then determining a tracking mode according to the tracking precision requirement, and determining a single-channel modulation signal form.
In the embodiment, a high-precision single-channel single-pulse tracking mode is used, and the single-channel converter in the radio frequency front end of the antenna is designed to modulate a signal waveform into a square wave with the square wave frequency not less than 16kHz by referring to the Chirp signal bandwidth.
And the proper intermediate frequency and sampling rate are designed, so that the signal enters the tracking receiver after A/D sampling without distortion.
In the embodiment, the intermediate frequency signal enters the tracking receiver to start a digital signal processing flow after A/D sampling, and the embodiment selects a band-pass sampling mode for processing because the signal bandwidth is smaller than the intermediate frequency.
As shown in fig. 2, the embodiment of the present invention includes an a/D sampling module, a first digital down-conversion module, a first decimation and filtering module, a data storage module, a frequency scanning and frequency offset estimation module, a second digital down-conversion module, a second decimation and filtering module, a first matched filtering module, a signal peak extraction module, a quadrature demodulation module, a synchronous modulation signal generator, a low-pass filtering module, a level difference and pitch difference signal normalization module, a digital phase correction module, a signal feature detection module, a lock detection module, and a signal to noise ratio detection module;
the A/D sampling module receives an intermediate frequency signal at the radio frequency front end of the antenna, performs A/D sampling and then outputs the signal to the first digital down-conversion module without distortion; the first digital down-conversion module performs first-stage digital down-conversion on the digital signal and then outputs the digital signal to the second digital down-conversion module and the first extraction and filtering module respectively; the first extraction and filtering module extracts and filters the input signal in a low-pass mode, and then stores the input signal into the data storage module; the frequency scanning and frequency offset estimation module extracts stored data to carry out matched filtering, frequency coarse estimation and frequency fine estimation, a matched filtering result is output to the signal characteristic detection module, a frequency offset estimation result is output to the second digital down-conversion module, the frequency offset exists due to Chirp signal frequency difference before frequency scanning and frequency offset estimation, the output of the matched filter is bimodal, as shown in fig. 5, and the output of the matched filter is unimodal after the frequency scanning and frequency offset estimation is completed, as shown in fig. 6; the signal characteristic detection module detects signal characteristics of the signals subjected to the matched filtering, and outputs signal frequency offset to the locking detection module and the servo control unit; the second digital down-conversion module carries out secondary down-conversion on the signal output by the first digital down-conversion module and outputs the baseband signal subjected to frequency offset correction to the second extraction and filtering module; the second extraction and filtering module extracts and filters the input signal in a low-pass mode, and then outputs the input signal to the first matched filtering module; the first matched filtering module performs time domain matched filtering on the input signal according to the signal characteristics and outputs the result to the sum signal peak value extraction module; the sum signal peak value extraction module carries out peak value detection on an input signal and then outputs a sum signal peak value to the signal-to-noise ratio detection module, the quadrature demodulation module, the azimuth difference and pitch difference signal normalization module and the servo control unit respectively; the signal-to-noise ratio detection module estimates the signal-to-noise ratio of the peak detected signal and outputs the signal-to-noise ratio of the Chirp signal to the lock detection module and the servo control unit; the lock detection module performs lock judgment by utilizing the signal-to-noise ratio and the signal frequency offset and outputs a lock instruction to the servo control unit; the quadrature demodulation module performs quadrature demodulation by using the sum signal peak value and the synchronous modulation signal output by the synchronous modulation signal generator, and outputs a quadrature demodulation result to the low-pass filtering module, wherein the quadrature demodulation result is shown in fig. 7; after the low-pass filtering module filters out high-frequency components, outputting a position difference signal and a pitching difference signal to the position difference and pitching difference signal normalization module, wherein an input synchronous modulation signal is required to be synchronous with a modulation square wave, and the frequency of the modulation square wave is more than or equal to 16kHz; the azimuth difference and pitch difference signal normalization module normalizes azimuth difference signals, pitch difference signals and sum signal peaks and outputs normalization results to the digital phase correction module; the digital phase correction module receives the calibration phase sent by the servo control unit, performs phase correction on the phase difference and pitch difference signals, removes cross coupling influence, and outputs the phase difference and pitch difference to the servo control unit.
As shown in fig. 3, the frequency estimation function is completed by a data storage module and a frequency scanning and frequency offset estimation module, wherein the data storage module comprises a data buffer module, a DPRAM and a data selection module, and the frequency scanning and frequency offset estimation module comprises a frequency offset correction module, a second matched filtering module, a peak detection module, a frequency offset estimation module and a DDS module;
the data buffer module receives the digital signal output by the first extraction and filtering module, stores the data into the DPRAM, the storage depth of the DPRAM is 64ms, the DPRAM is divided into four areas, each area comprises an 8ms non-overlapping data area, an overlapping data area overlapping with other areas is respectively arranged in front of and behind the non-overlapping data area, and after the data of a certain 24ms area is fully written, a data scanning mark is output to the data selecting module; the data selection module reads signals stored in the DPRAM according to the scanning marks and outputs the signals to the frequency offset correction module; the frequency offset correction module corrects the frequency according to the frequency control word output by the DDS module, and outputs corrected data to the second matched filtering module; the second matched filtering module performs time domain matched filtering on the corrected data according to the Chirp signal characteristics and outputs the result to the peak detection module; the peak detection module carries out peak detection on the matched filtering output signal and outputs the time interval between peaks to the frequency offset estimation module; the frequency offset estimation module estimates a frequency difference delta f through a time interval delta t between peaks, and outputs the updated frequency difference to the DDS module; the DDS module outputs a frequency control word according to the frequency difference control, and performs 4 frequency stepping scans, wherein the maximum value of the stepping is 8.192kHz, and the minimum value of the stepping is 0.25Hz.
Fig. 4 is a schematic block diagram of a matched filter, where the first matched filter module and the second matched filter module are cascaded by 8 sets of filters, each set of filters having a feedback port.
The foregoing description is only the preferred embodiment of the present invention, and is not intended to limit the present invention, and any simple modification, variation and equivalent change of the above embodiment according to the technical matter of the present invention still fall within the scope of the technical solution of the present invention.
Claims (5)
1. The satellite communication chirp signal tracking receiver is characterized by comprising an A/D sampling module, a first digital down-conversion module, a first extraction and filtering module, a data storage module, a frequency scanning and frequency offset estimation module, a second digital down-conversion module, a second extraction and filtering module, a first matched filtering module, a signal peak value extraction module, a quadrature demodulation module, a synchronous modulation signal generator, a low-pass filtering module, a position difference and pitch difference signal normalization module, a digital phase correction module, a signal characteristic detection module, a locking detection module and a signal-to-noise ratio detection module;
the A/D sampling module receives an intermediate frequency signal at the radio frequency front end of the antenna, performs A/D sampling and then outputs the signal to the first digital down-conversion module without distortion; the first digital down-conversion module performs first-stage digital down-conversion on the digital signal and then outputs the digital signal to the second digital down-conversion module and the first extraction and filtering module respectively; the first extraction and filtering module extracts and filters the input signal in a low-pass mode, and then stores the input signal into the data storage module; the frequency scanning and frequency offset estimation module extracts stored data to carry out matched filtering, frequency coarse estimation and frequency fine estimation, a matched filtering result is output to the signal characteristic detection module, and a frequency offset estimation result is output to the second digital down-conversion module; the signal characteristic detection module detects signal characteristics of the signals subjected to the matched filtering, and outputs signal frequency offset to the locking detection module and the servo control unit; the second digital down-conversion module carries out secondary down-conversion on the signal output by the first digital down-conversion module and outputs the baseband signal subjected to frequency offset correction to the second extraction and filtering module; the second extraction and filtering module extracts and filters the input signal in a low-pass mode, and then outputs the input signal to the first matched filtering module; the first matched filtering module performs time domain matched filtering on the input signal according to the signal characteristics and outputs the result to the sum signal peak value extraction module; the sum signal peak value extraction module carries out peak value detection on an input signal and then outputs a sum signal peak value to the signal-to-noise ratio detection module, the quadrature demodulation module, the azimuth difference and pitch difference signal normalization module and the servo control unit respectively; the signal-to-noise ratio detection module estimates the signal-to-noise ratio of the peak detected signal and outputs the signal-to-noise ratio of the Chirp signal to the lock detection module and the servo control unit; the lock detection module performs lock judgment by utilizing the signal-to-noise ratio and the signal frequency offset and outputs a lock instruction to the servo control unit; the quadrature demodulation module carries out quadrature demodulation by utilizing the sum signal peak value and the synchronous modulation signal output by the synchronous modulation signal generator, and outputs a quadrature demodulation result to the low-pass filtering module; after the low-pass filtering module filters out the high-frequency components, outputting a azimuth difference signal and a pitching difference signal to the azimuth difference signal normalization module; the azimuth difference and pitch difference signal normalization module normalizes azimuth difference signals, pitch difference signals and sum signal peaks and outputs normalization results to the digital phase correction module; the digital phase correction module receives the calibration phase sent by the servo control unit, performs phase correction on the phase difference and pitch difference signals, removes cross coupling influence, and outputs the phase difference and pitch difference to the servo control unit.
2. The satellite communication chirp signal tracking receiver of claim 1, characterized in that the frequency estimation function is performed by a data storage module together with a frequency scanning and frequency offset estimation module, wherein the data storage module comprises a data buffer module, a DPRAM and a data selection module, and the frequency scanning and frequency offset estimation module comprises a frequency offset correction module, a second matched filtering module, a peak detection module, a frequency offset estimation module and a DDS module;
the data buffer module receives the digital signal output by the first extraction and filtering module, stores the data into the DPRAM, and outputs a data scanning mark to the data selecting module after the data is fully written; the data selection module reads signals stored in the DPRAM according to the scanning marks and outputs the signals to the frequency offset correction module; the frequency offset correction module corrects the frequency according to the frequency control word output by the DDS module, and outputs corrected data to the second matched filtering module; the second matched filtering module performs time domain matched filtering on the corrected data according to the Chirp signal characteristics and outputs the result to the peak detection module; the peak detection module carries out peak detection on the matched filtering output signal and outputs the time interval between peaks to the frequency offset estimation module; the frequency offset estimation module estimates a frequency difference delta f through a time interval delta t between peaks, and outputs the updated frequency difference to the DDS module; the DDS module outputs a frequency control word according to the frequency difference control, and performs 4 frequency stepping scans, wherein the maximum value of the stepping is 8.192kHz, and the minimum value of the stepping is 0.25Hz.
3. The satellite communication chirp signal tracking receiver of claim 1, wherein the first and second matched filter modules are each cascaded from 8 sets of filters, each set of filters having a feedback port.
4. The satellite communication chirp signal tracking receiver of claim 1, characterized in that the synchronous modulation signal input by the quadrature demodulation module is to be synchronized with a modulation square wave frequency not less than 16kHz.
5. The satellite communication chirp signal tracking receiver according to the previous claim 2, characterized in that the storage depth of the DPRAM in the data buffer module is 64ms, and the data buffer module is divided into four areas, each area comprises a non-overlapping data area of 8ms, the non-overlapping data area is respectively provided with an overlapping data area overlapping with other areas, and after the data of a certain 24ms area is fully written, the data scanning mark is output to the data selecting module.
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