Short-wave frequency selection system based on time-varying multi-sub-band pilot frequency

Abstract

The invention discloses a short-wave frequency selection system based on time-varying multi-subband pilot frequency, which comprises an analog-to-digital conversion module used for performing analog-to-digital conversion on a radio frequency analog signal received by an antenna module, performing data sampling to generate a radio frequency digital signal, and sending the radio frequency digital signal to a down-conversion processing module of N * 2 independent digital channels at the rear end; the carrier frequency set generation module is used for generating a carrier frequency set and sending the carrier frequency set to the down-conversion processing module; the carrier frequency set comprises N * 2 paths of carrier frequency points formed by N paths of preset carrier frequency points and N paths of pseudo-random change standby frequency points which are in one-to-one correspondence based on time change; the down-conversion processing module is used for respectively generating independent digital carrier signals according to N paths of preset carrier frequency points and N paths of standby carrier frequency points in pseudo random change, and generating N * 2 paths of digital baseband signals after carrying out digital frequency mixing on the digital carrier signals and the radio frequency digital signals, and the generated digital baseband signal is transmitted to a frequency spectrum detection module for frequency domain analysis to obtain N * 2 paths of electromagnetic frequency spectrum detection information.

Description

Technical Field

[0001] The present application relates to the field of communications, and in particular to a shortwave frequency selection system based on time-varying multi-subband pilots. Background Art

[0002] When shortwave is used for long-distance communication through the ionosphere, it is subject to the time-varying characteristics of the ionosphere and the influence of the complex electromagnetic environment around the shortwave frequency band. In order to ensure normal communication of shortwave, the general measures taken include the use of backup frequencies. However, when there are no passable frequencies at the beginning, it is crucial to select the shortwave frequencies that can be passed between the sender and the receiver in real time. If information exchange can be completed with short-time pulse signals during the frequency selection process, it can not only complete the detection of as many selected frequency points as possible in a limited short time, but also prevent being tracked and identified, further realizing the needs of covert frequency selection.

[0003] The existing technology uses a method of scanning and receiving by polling several pre-set carrier working frequencies within a limited time (such as 1 second). When a call signal is received and the signal-to-noise ratio can meet the communication requirements, the scanning result is transmitted back to notify the passable frequency. Because single-channel reception is adopted, time slot cycle scanning reception is adopted at the receiver end, which is prone to missed detection of the first and last frequencies. To ensure that there is no missed detection of the frequency, it is necessary to increase the time slot of the sending frequency (such as setting the single frequency transmission time to not less than 200ms), or repeat multiple rounds of sending useful information, thereby reducing the number of frequencies of different carrier frequencies to be detected within a limited time, and reducing the number of detections of passable frequencies.

[0004] However, existing hardware platforms monitor channels in narrowband and scan by changing the center frequency. This will result in a long channel detection time, which cannot meet the requirement of sending and receiving useful information in the shortest possible time. On the other hand, the long detection time will cause the detection signal to be intercepted, which is not conducive to covert communication.

[0005] In short, for receivers that use a single-channel cyclic scanning reception architecture, in scenarios where covert communication is required, the shorter the residence time of the signal sent on a single channel, the less likely it is to be intercepted; while shortening the residence time of the transmitted signal, it also increases the real-time processing requirements of the receiver. Single-channel scanning reception can no longer meet the requirements of covert detection communication. Summary of the invention

[0006] The present invention provides a shortwave frequency selection system based on time-varying multi-subband pilots to improve the above problems.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] A shortwave frequency selection system based on time-varying multi-subband pilot, comprising:

[0009] The antenna module is used to receive the radio frequency analog signal and send it to the analog-to-digital conversion module when the shortwave radio station is in the receiving state;

[0010] The analog-to-digital conversion module is used to convert the RF analog signal received by the antenna module into a digital signal after data sampling, and then send it to the down-conversion processing module of the N*2 independent digital channels at the back end;

[0011] A carrier frequency set generation module, used for generating a carrier frequency set and sending it to a down-conversion processing module; the carrier frequency set includes N*2 carrier frequency points consisting of N preset carrier frequency points and one-to-one corresponding N pseudo-randomly changing spare frequency points based on time changes;

[0012] The down-conversion processing module is used to generate independent digital carrier signals according to N preset carrier frequencies and N pseudo-randomly changing standby carrier frequencies, and after digital mixing with the radio frequency digital signal, use multi-stage down-conversion digital signal extraction and filtering to generate low-speed N*2 digital baseband signals, and transmit the generated digital baseband signals to the spectrum detection module;

[0013] The spectrum detection module is used to perform frequency domain analysis on N*2 digital baseband signals to obtain N*2 electromagnetic spectrum detection information.

[0014] Preferably, the interval between the backup carrier frequency point and the corresponding preset carrier frequency point is no more than 100 kHz.

[0015] Preferably, it also includes:

[0016] N*2 independent baseband signal monitoring modules are used to monitor and evaluate the electromagnetic environment around N*2 carrier frequencies in real time to determine the selection of the working carrier frequency of the transmission path, and

[0017] The N*2-channel electromagnetic spectrum detection information is transmitted to the discrimination module based on the sub-band frequency set.

[0018] Preferably, it also includes: a discrimination module based on a sub-band frequency set and a time-varying sub-band baseband signal generation module; wherein:

[0019] The time-varying sub-band baseband signal generating module is used to generate a time-varying sub-band frequency set and send it to the discrimination module based on the sub-band frequency set, wherein the time-varying sub-band frequency set is modulated by a carrier plus single sideband modulation method;

[0020] The sub-band frequency set-based discrimination module is used to compare the N*2 channels of electromagnetic spectrum detection information with the time-varying sub-band frequency set, and then determine the number of channels containing useful detection related information among the N*2 channels received simultaneously.

[0021] Preferably, for the time-varying sub-band baseband signal generating module, the frequency interval between useful signals is set to mHz, then there are (1000n / m+1) groups of single-tone frequencies within the bandwidth range of nkHz, and when dual-tone is used as the detection baseband signal, 2 groups of different single tones are selected from the 1000n / m+1 groups of single tones as the synthetic sub-band.

[0022] Preferably, it further comprises: a receiving / transmitting control module based on time agreement and a transmitting channel single-channel digital signal processing module; the receiving / transmitting control module based on time agreement is connected with the discrimination module based on sub-band frequency set and the transmitting channel single-channel digital signal processing module, and sends receiving / transmitting control instructions to the two to realize waveform detection and transmission;

[0023] For the detection waveform, a pseudo-random combination tone based on time variation is used to distinguish whether the received signal is an interference signal or a detection signal;

[0024] For the transmission waveform, according to the preset frequencies of N carrier waves, the frequencies that fall in the same band and are closely spaced are grouped into the same transmission group.

[0025] Preferably, the single-channel digital signal processing module is used for:

[0026] Generate a time-varying sub-band baseband signal, which is converted into a high-rate RF digital signal S after digital up-conversion using software radio technology. rf ;

[0027] Through environmental monitoring of N*2 frequency points, the time-division digital phase-locked loop technology is used to generate N*2 digital carrier signals f c ;

[0028] S rf With f c After digital mixing, a RF digital signal S containing time-varying sub-band baseband information is generated. mix ;

[0029] Combined with the receive / transmit control module based on time agreement, when the shortwave radio is in the transmitting state, the RF digital signal S mix to the digital-to-analog converter;

[0030] Digital-to-analog converter, used to convert RF digital signal S mix After the digital-to-analog conversion, the RF analog signal is obtained and transmitted to the antenna module;

[0031] The antenna module is also used to transmit the radio frequency analog signal transmitted by the digital-to-analog converter when the shortwave radio station is in the transmitting state.

[0032] Preferably, the transmitting channel single-channel digital signal processing module is also used for:

[0033] When in the detection state, for the preset N carrier frequencies, when at a certain set frequency f n When there is a strong interference source at (1≤n≤N), the n f Δ The spare frequency point f n备用 The carrier frequency used in the call is selected by comparing the electromagnetic environment. Δ The range is the frequency value based on time variation, f n备用 =f n +f Δ .

[0034] To sum up, in this embodiment, a pseudo-random time-varying pulse detection waveform is used to detect as many shortwave carrier preset frequencies as possible within a limited time, and through the real-time monitoring technology of the local electromagnetic environment around the preset carrier frequency, the preset working frequency point and the corresponding backup frequency point are automatically compared with the local electromagnetic environment, and the electromagnetic environment interference is relatively small as the sending carrier frequency; in this way, this embodiment not only utilizes the effective reference of the preset frequency point, but also realizes the autonomous selection of the sending frequency point according to the actual electromagnetic environment, and further improves the efficiency of the preset frequency point.

[0035] In addition, this embodiment utilizes a short pseudo-random time-varying waveform combination to send only 100ms of information at a fixed single-point carrier frequency while ensuring that the autocorrelation signal can be effectively received. This is not conducive to tracking and analysis for incoherent reception, further enhancing the concealment of detection frequency selection. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 A schematic structural diagram of a shortwave frequency selection system based on time-varying multi-subband pilot provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0038] See also Figure 1 The first embodiment of the present invention discloses a shortwave frequency selection system based on time-varying multi-subband pilot, which includes:

[0039] The antenna module 10 is used to receive the radio frequency analog signal and send it to the analog-to-digital conversion module 20 when the shortwave radio station is in a receiving state.

[0040] The analog-to-digital conversion module 20 is used to perform data sampling on the radio frequency analog signal received by the antenna module 10 to generate a radio frequency digital signal after analog-to-digital conversion, and then send it to the down-conversion processing module 40 of the back-end N*2 independent digital channels.

[0041] The carrier frequency set generating module 30 is used to generate a carrier frequency set and send it to the down-conversion processing module 40 .

[0042] In this embodiment, the carrier frequency set includes N*2 carrier frequencies consisting of N preset carrier frequencies and one-to-one corresponding N pseudo-randomly changing spare frequencies based on time changes. In the detection and scanning state, the N*2 carrier frequency information is distributed to the down-conversion processing module 40 of the N*2 independent digital channels and the single-channel RF digital signal module 90.

[0043] In order to make full use of the timeliness of the preset frequency, the interval between the backup carrier frequency based on time change and the corresponding preset carrier frequency is no more than 100kHz.

[0044] The down-conversion processing module 40 is used to generate independent digital carrier signals according to N preset carrier frequencies and N pseudo-randomly changing spare carrier frequencies, and after digital mixing with the RF digital signal, use multi-stage down-conversion digital signal extraction and filtering to generate low-speed N*2 digital baseband signals, and transmit the generated digital baseband signals to the spectrum detection module.

[0045] In this embodiment, the down-conversion processing module 40 adopts software radio technology and uses a high-real-time FPGA chip to perform down-conversion processing on (N*2) independent digital channels of the radio frequency digital signal collected by the analog-to-digital conversion module 20. Specifically, the agreed N carrier frequency points and the N pseudo-randomly changing spare frequency points that change with time are respectively generated as independent digital carrier signals, which are digitally mixed with the high-speed radio frequency digital signal collected by the analog-to-digital conversion module 20, and then multi-stage down-conversion digital signal extraction and filtering are used to convert it into a low-speed digital baseband signal (such as a baseband signal with a sampling rate of 8kHz); the generated digital baseband signal is transmitted to the spectrum detection module, and the spectrum detection module performs frequency domain analysis on the N*2 digital baseband signals to obtain N*2 electromagnetic spectrum detection information.

[0046] In this embodiment, in particular, it also includes:

[0047] N*2 independent baseband signal monitoring module 50, used for real-time monitoring and evaluation of the electromagnetic environment around the N*2 carrier frequency points, so as to determine the selection of the working carrier frequency points of the transmission path, and

[0048] The N*2 channels of electromagnetic spectrum detection information are transmitted to the discrimination module 60 based on the sub-band frequency set.

[0049] Among them, under the condition that the transmission power of shortwave radio stations is limited, in order to make the shortwave information propagate as far as possible through the ionosphere, single-carrier transmission is generally adopted. When the radio station is in the detection state, the more carrier paths that can be sent within a limited time, the more predictable frequency points that can be detected will be.

[0050] For N pre-set carrier frequencies, since the local electromagnetic environment of shortwave is time-varying and harsh, if there is strong interference at some preset frequencies, the general measure is to discard the frequency; for shortwave long-distance communication limited by the ionosphere, the passable frequencies are few in themselves, and the use of time-based pseudo-random standby carrier frequency measures can further improve the effective detection of passable frequencies. In this way, the electromagnetic environment around the N*2 carrier frequencies must be monitored and evaluated in real time to determine the selection of the working carrier frequency of the transmission path.

[0051] At the same time, the electromagnetic spectrum detection information of N*2 channels is transmitted to the discrimination module 60 based on the sub-band frequency set, and after being compared with the relevant time-varying sub-band frequency set, it is determined which channel of the (N+N) channels received at the same time contains useful detection related information.

[0052] The time-varying sub-band baseband signal generating module 70 is used to generate a time-varying sub-band frequency set and send it to the sub-band frequency set based determination module 60. The time-varying sub-band frequency set is modulated using a carrier plus single sideband modulation method.

[0053] Among them, under a certain power, in order to make the shortwave transmitter send out useful signals as much as possible, the commonly used shortwave working bandwidth is about 2.7kHz (300Hz~3000Hz). In order to meet the frequency resolution requirement of ±15Hz, the frequency interval between useful signals can be set to 50Hz. Then, there are 55 groups of single-tone frequencies ((3000-300) / 50+1=55) within the bandwidth of 2.7kHz. When dual-tone is used as the detection baseband signal, 2 different single-tones are selected from the 55 groups of single-tones as the synthetic sub-bands. The following situations can be formed: When designing dual-tones, pay attention to the relationship between the two single tones being integer multiples. For example, avoid the composition of 300Hz and 600Hz dual tones, which can be transformed into 315Hz and 600Hz to prevent serious interference between the two waveforms.

[0054] In the case of a certain reference time as the standard, if every Y time1 The baseband dual tone is switched once every second. If Y time1If the one-way switching repetition period based on the standard time is 3 seconds, then the one-way switching repetition period based on the standard time is 4455 seconds (3 seconds*1485=4455 seconds). In order to enable the receiving end to automatically correct the frequency of the received sub-band signal, the modulation method of carrier plus single sideband is adopted for modulation processing.

[0055] The sub-band frequency set-based determination module 60 is used to compare the N*2 channels of electromagnetic spectrum detection information with the time-varying sub-band frequency set, and determine the number of channels containing useful detection related information among the N*2 channels received simultaneously.

[0056] In shortwave communication, since both the shortwave sender and the receiver will have a frequency offset of the crystal clock, the general mode is to use a fixed waveform for transmission, autocorrelation detection, and frequency correction. In the present invention, in order to achieve covert detection communication, the industry-wide common carrier plus single-sideband signal modulation architecture is adopted. After the received baseband signal is fast Fourier transformed, the useful sub-band spectrum frequency is compared with the carrier frequency. Since the frequency difference between the two is fixed, if it can correspond to the time-based pseudo-random sub-band frequency set, it is considered that the received signal is a useful detection signal.

[0057] In addition, at the receiving end, in order to further enhance the reliability of receiving the baseband signal, not only the relative frequency difference between the sub-band frequency value and the carrier frequency value is determined, but also the amplitude values ​​of the carrier and sub-band can be compared to distinguish whether the received signal is a useful signal or a noise interference signal.

[0058] Preferably, it further comprises: a receiving / transmitting control module 80 based on time agreement and a transmitting channel single-channel digital signal processing module 90; the receiving / transmitting control module 80 based on time agreement is connected with the discrimination module 60 based on sub-band frequency set and the transmitting channel single-channel digital signal processing module 90, and sends receiving / transmitting control instructions to the two to realize waveform detection and transmission;

[0059] For the detection waveform, a pseudo-random combination tone based on time variation is used to distinguish whether the received signal is an interference signal or a detection signal;

[0060] For the transmission waveform, according to the preset frequencies of N carrier waves, the frequencies that fall in the same band and are closely spaced are grouped into the same transmission group.

[0061] Among them, in the process of detection and frequency selection, there are two working states: one is a monitoring state only, and no detection signal is sent for external calls; the other is a combination state of time slot monitoring and calling, which can be manually set according to actual needs.

[0062] For the detection waveform, a pseudo-random combination tone based on time variation is used to distinguish whether the received signal is an interference signal or a detection signal.

[0063] In foreign shortwave radio stations, the reception-transmission time is required to be no more than 10ms, and the transmission-reception time is no more than 10ms. If the signal transmission time of each frequency point is 100ms, the useful signal transmission time is 80ms, and the time for the receiver to stably receive the signal after down-conversion processing is about 70ms; if the sampling rate of the received baseband signal is 8ksps, the number of data points of the useful baseband signal that can be collected is about 560 points (8000*0.07=560), and a 1024-point FFT transformation is performed at the baseband receiving end (when the number of input data points of FFT is insufficient, the spectrum resolution can be improved by zero padding, which will only affect the phase information of the signal but not the frequency value), and the spectrum resolution is about 7.8125Hz (f s / N=8000 / 1024, f s is the sampling frequency, N is the number of FFT points), and the instantaneous spectrum information within the 3kHz bandwidth is obtained.

[0064] In order to control the amplitude of the data receiving baseband signal, the digital baseband signal after down-conversion needs to be processed by data AGC, and the trigger time of data AGC (RF signal increases by 60dB) is required to be less than 10ms, and the release time of data AGC (RF signal decreases by 60dB) is less than 30ms.

[0065] In the transmitting state, if the transmitting frequency is in a cross-band state, it is easily limited by the time consumption of the tuning circuit, which takes up the limited time for sending useful signals. For this reason, according to the preset N frequencies, the frequencies that fall in the same band and are closely spaced are grouped into the same sending group.

[0066] For example, a maximum of 3 frequency points can be transmitted each time, that is, after sending for 300ms, it switches to the receiving state for 300ms, and then enters the transmitting state for 300ms. After a cycle of 3 seconds, 5 transmissions can be completed, and 15 frequency points can be transmitted on one side.

[0067] In this way, on the basis of being able to complete the electromagnetic environment monitoring of 30 different carrier frequencies within a short time (such as 3 seconds), the autonomous transmission of 15 different carrier frequencies and the parallel reception of 30 frequencies can be achieved. If the detection time is appropriately extended, the number of detectable frequencies can be easily increased.

[0068] The transmitting channel single-channel digital signal processing module 90 is used for:

[0069] Generate a time-varying sub-band baseband signal, which is converted into a high-rate RF digital signal S after digital up-conversion using software radio technology. rf ;

[0070] Through environmental monitoring of N*2 frequency points, the time-division digital phase-locked loop technology is used to generate N*2 digital carrier signals fc ;

[0071] S rf With f c After digital mixing, a RF digital signal S containing time-varying sub-band baseband information is generated. mix ;

[0072] Combined with the receive / transmit control module based on time agreement, when the shortwave radio is in the transmitting state, the RF digital signal S mix transmitted to the digital-to-analog converter 100;

[0073] The digital-to-analog converter 100 is used to convert the radio frequency digital signal S mix After the digital-to-analog conversion, the radio frequency analog signal is obtained and transmitted to the antenna module 10;

[0074] The antenna module 10 is also used to transmit the radio frequency analog signal transmitted by the digital-to-analog converter 100 when the shortwave radio station is in a transmitting state.

[0075] The single-channel digital signal processing module 90 is mainly divided into a digital baseband part and a digital radio frequency part: a time-varying sub-band baseband signal is generated, and after digital up-conversion processing using software radio technology, it is converted into a high-speed radio frequency digital signal S rf ; Through environmental monitoring of N*2 frequency points, the time-division digital phase-locked loop technology is used to generate N*2 digital carrier signals f c , S rf With f c After digital mixing, a RF digital signal S containing time-varying sub-band baseband information is generated. mix , combined with the time-based transceiver conversion module, the RF digital signal S mix The digital-to-analog converter 100 converts the RF digital signal S mi After the digital-to-analog conversion, the radio frequency analog signal is obtained and transmitted to the antenna module 10, and the antenna module 10 transmits the radio frequency analog signal when the shortwave radio station is in the transmitting state.

[0076] When in the detection state, for the preset N frequency points, when at a certain set frequency point f n When there is a strong interference source at (1≤n≤N), the n f Δ The spare frequency point f n备用 (f n备用 =f n +f Δ ) electromagnetic environment, and select the carrier frequency used in calling, f ΔThe range is a frequency value based on time changes, which further enhances the concealment of the detection working frequency. If radio station A receives the detection signal f sent by radio station B at the backup frequency of the preset frequency of the nth channel, n备用 , then the default communication frequency of radio station A and radio station B is preferably f n备用 ; When no frequency selection information is received, if radio station A detects a strong interference signal at the preset frequency of the nth channel, after comparing the electromagnetic characteristics with the preset backup frequency of the nth channel, the frequency with the smaller local electromagnetic interference is used as the judgment standard to decide whether to use f when sending. n , or f n备用 frequency.

[0077] To sum up, in this embodiment, a pseudo-random time-varying pulse detection waveform is used to detect as many shortwave carrier preset frequencies as possible within a limited time, and through the real-time monitoring technology of the local electromagnetic environment around the preset carrier frequency, the preset working frequency point and the corresponding backup frequency point are automatically compared with the local electromagnetic environment, and the electromagnetic environment interference is relatively small as the sending carrier frequency; in this way, this embodiment not only utilizes the effective reference of the preset frequency point, but also realizes the autonomous selection of the sending frequency point according to the actual electromagnetic environment, and further improves the efficiency of the preset frequency point.

[0078] In addition, this embodiment utilizes a short pseudo-random time-varying waveform combination to send only 100ms of information at a fixed single-point carrier frequency while ensuring that the autocorrelation signal can be effectively received. This is not conducive to tracking and analysis for incoherent reception, further enhancing the concealment of detection frequency selection.

[0079] In the present invention, it should be understood that if the implemented module is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on such an understanding, the present invention implements all or part of the processes in the above-mentioned embodiment method, and can also be completed by instructing the relevant hardware through a computer program. The computer program can be stored in a computer-readable storage medium, and the computer program can implement the steps of the above-mentioned various method embodiments when executed by the processor. Among them, the computer program includes computer program code, and the computer program code can be in source code form, object code form, executable file or some intermediate form. The computer-readable medium may include: any entity or device capable of carrying the computer program code, recording medium, U disk, mobile hard disk, magnetic disk, optical disk, computer memory, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), electric carrier signal, telecommunication signal and software distribution medium. It should be noted that the content contained in the computer-readable medium can be appropriately increased or decreased according to the requirements of legislation and patent practice in the jurisdiction. For example, in some jurisdictions, according to legislation and patent practice, computer-readable media do not include electric carrier signals and telecommunication signals.

[0080] It should be noted that the device embodiments described above are merely schematic, wherein the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules may be selected according to actual needs to implement the scheme of this embodiment. In addition, in the accompanying drawings of the device embodiments provided by the present invention, the connection relationship between the modules indicates that there is a communication connection between them, which may be specifically implemented as one or more communication buses or signal lines. A person of ordinary skill in the art may understand and implement it without creative work.

[0081] The above are only preferred implementations of the present invention. The protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention.

Claims

1. A shortwave frequency selection system based on time-varying multi-subband pilot, characterized in that: include: The antenna module is used to receive the radio frequency analog signal and send it to the analog-to-digital conversion module when the shortwave radio station is in the receiving state; The analog-to-digital conversion module is used to convert the RF analog signal received by the antenna module into a digital signal after data sampling, and then send it to the down-conversion processing module of the N*2 independent digital channels at the back end; A carrier frequency set generation module, used for generating a carrier frequency set and sending it to a down-conversion processing module; the carrier frequency set includes N*2 carrier frequency points consisting of N preset carrier frequency points and one-to-one corresponding N pseudo-randomly changing spare frequency points based on time changes; The down-conversion processing module is used to generate independent digital carrier signals according to N preset carrier frequencies and N pseudo-randomly changing standby carrier frequencies, and after digital mixing with the radio frequency digital signal, use multi-stage down-conversion digital signal extraction and filtering to generate low-speed N*2 digital baseband signals, and transmit the generated digital baseband signals to the spectrum detection module; The spectrum detection module is used to perform frequency domain analysis on N*2 digital baseband signals to obtain N*2 electromagnetic spectrum detection information.

2. The shortwave frequency selection system based on time-varying multi-subband pilot according to claim 1 is characterized in that: The interval between the standby carrier frequency point and the corresponding preset carrier frequency point is no more than 100 kHz.

3. The shortwave frequency selection system based on time-varying multi-subband pilot according to claim 1 is characterized in that: Also includes: N*2 independent baseband signal monitoring modules are used to monitor and evaluate the electromagnetic environment around N*2 carrier frequencies in real time to determine the selection of the working carrier frequency of the transmission path, and The N*2-channel electromagnetic spectrum detection information is transmitted to the discrimination module based on the sub-band frequency set.

4. The shortwave frequency selection system based on time-varying multi-subband pilot according to claim 3 is characterized in that: Also includes: A discrimination module based on a sub-band frequency set and a time-varying sub-band baseband signal generation module; wherein: The time-varying sub-band baseband signal generating module is used to generate a time-varying sub-band frequency set and send it to the discrimination module based on the sub-band frequency set, wherein the time-varying sub-band frequency set is modulated by a carrier plus single sideband modulation method; The sub-band frequency set-based discrimination module is used to compare the N*2 channels of electromagnetic spectrum detection information with the time-varying sub-band frequency set, and then determine the number of channels containing useful detection related information among the N*2 channels received simultaneously.

5. The shortwave frequency selection system based on time-varying multi-subband pilot according to claim 4 is characterized in that: For the time-varying sub-band baseband signal generation module, the frequency interval between useful signals is set to mHz, then there are (1000n / m+1) groups of single-tone frequencies within the bandwidth range of nkHz. When dual-tone is used as the detection baseband signal, 2 different groups of single tones are selected from the (1000n / m+1) groups of single tones as the synthetic sub-band.

6. The shortwave frequency selection system based on time-varying multi-subband pilot according to claim 4 is characterized in that: Also includes: A receiving / transmitting control module based on time agreement and a single-channel digital signal processing module for the transmitting channel; The receiving / transmitting control module based on time agreement is connected with the discrimination module based on sub-band frequency set and the transmitting channel single-channel digital signal processing module, and sends receiving / transmitting control instructions to the two modules to realize waveform detection and transmission; For the detection waveform, a pseudo-random combination tone based on time variation is used to distinguish whether the received signal is an interference signal or a detection signal; For the transmission waveform, according to the preset frequencies of N carrier waves, the frequencies that fall in the same band and are closely spaced are grouped into the same transmission group.

7. The shortwave frequency selection system based on time-varying multi-subband pilot according to claim 6 is characterized in that: The single-channel digital signal processing module is used for: Generate a time-varying sub-band baseband signal, which is converted into a high-rate RF digital signal S after digital up-conversion using software radio technology. rf ; Through environmental monitoring of N*2 frequency points, the time-division digital phase-locked loop technology is used to generate N*2 digital carrier signals f c ; S rf With f c After digital mixing, a RF digital signal S containing time-varying sub-band baseband information is generated. mix ; Combined with the receive / transmit control module based on time agreement, when the shortwave radio is in the transmitting state, the RF digital signal S mix to the digital-to-analog converter; Digital-to-analog converter, used to convert RF digital signal S mix After the digital-to-analog conversion, the RF analog signal is obtained and transmitted to the antenna module; The antenna module is also used to transmit the radio frequency analog signal transmitted by the digital-to-analog converter when the shortwave radio station is in a transmitting state.

8. The shortwave frequency selection system based on time-varying multi-subband pilot according to claim 7, characterized in that: The single-channel digital signal processing module is also used for: When in the detection state, for the preset N carrier frequencies, when at a certain set frequency f n When there is a strong interference source at (1≤n≤N), the n f Δ The backup frequency f n备用 The carrier frequency used in the call is selected by comparing the electromagnetic environment. Δ The range is the frequency value based on time variation, f n备用 =f n +f Δ .

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