A shortwave frequency selection system based on time-varying multi-subband pilot

Abstract

The present invention discloses a shortwave frequency selection system based on time-varying multi-subband pilot, which comprises: an analog-to-digital conversion module, which is used to perform data sampling on a radio frequency analog signal received by an antenna module to generate a radio frequency digital signal after analog-to-digital conversion, and then send the generated radio frequency digital signal to a down-conversion processing module of N*2 independent digital channels at the back end; a carrier frequency set generation module, which is used to collect carrier frequencies and send them to the down-conversion processing module; the carrier frequency set comprises N*2 carrier frequencies consisting of N preset carrier frequencies and N pseudo-randomly changing spare frequencies that correspond one to one based on time changes; and a down-conversion processing module, which is used to generate independent digital carrier signals according to the N preset carrier frequencies and the N pseudo-randomly changing spare frequencies, and generate N*2 digital baseband signals after digital mixing with the radio frequency digital signal, and transmit the generated digital baseband signals to a spectrum detection module for frequency domain analysis to obtain N*2 electromagnetic 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 radio waves travel long distances through the ionosphere, they are subject to the time-varying characteristics of the ionosphere and the complex electromagnetic environment surrounding the shortwave band. To ensure normal communication, backup frequencies are typically used. However, when no interoperable frequencies are initially available, the real-time selection of interoperable shortwave frequencies is crucial. If information exchange can be accomplished using short pulse signals during the frequency selection process, it would not only allow detection of as many selected frequencies as possible within a limited timeframe, but also prevent tracking and identification, further fulfilling the need for covert frequency selection.

[0003] Existing technology uses a scan-and-receive method that polls several pre-set carrier operating frequencies within a limited timeframe (e.g., 1 second). Once a call signal is received and the signal-to-noise ratio (SNR) is sufficient for communication, the scan results are transmitted back to notify the receiver of the available frequencies. Because single-channel reception is used, the receiver employs time-slot cyclic scanning, which can easily lead to missed detection of the first and last frequencies. To ensure this, the transmission frequency slots need to be increased (e.g., the transmission time of a single frequency must be set to no less than 200ms), or multiple rounds of useful information must be sent. This reduces the number of frequencies detected across different carrier frequencies within a limited timeframe, reducing the number of possible frequency detection attempts.

[0004] However, existing hardware platforms monitor channels in a narrowband environment and scan by varying the center frequency. This results in excessively long channel detection times, which not only prevents the transmission and reception of useful information in the shortest possible time, but also makes it difficult for the detection signal to be intercepted, hindering covert communications.

[0005] In short, for receivers using 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. For single-channel scanning reception, it 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 pilots, 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, perform data sampling, and generate a RF digital signal, which is then sent to the down-conversion processing module of the N*2 independent digital channels at the back end;

[0011] A carrier frequency set generation module is used to generate a carrier frequency set and send it to the down-conversion processing module; the carrier frequency set includes N*2 carrier frequency points consisting of N preset carrier frequency points and N pseudo-randomly changing spare frequency points that correspond to each other 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 backup 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 standby carrier frequency and the corresponding preset carrier frequency 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-path electromagnetic spectrum detection information is passed to the discrimination module based on the sub-band frequency set.

[0018] Preferably, it further comprises: 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 using 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 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. When dual-tone is used as the detection baseband signal, two groups of different single tones are selected from the 1000n / m+1 groups of single tones as the synthetic sub-band.

[0022] Preferably, the system further comprises: a time-agreement-based transmit / receive control module and a transmit channel single-channel digital signal processing module; the time-agreement-based transmit / receive control module is connected to the sub-band frequency set-based discrimination module and the transmit channel single-channel digital signal processing module, and sends transmit / receive control instructions to the two modules to achieve 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, frequencies that fall in the same band and are closely spaced are grouped into a same-time transmission group.

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

[0026] Generate time-varying sub-band baseband signals, which are converted into high-speed RF digital signals S after digital up-conversion processing 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 radio frequency digital signal S containing time-varying sub-band baseband information is generated. mix ;

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

[0030] Digital-to-analog converter, used to convert RF digital signal S mix After 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 a transmitting state.

[0032] Preferably, the transmitting channel single-channel digital signal processing module is further 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 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 change, 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 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 frequency with relatively small electromagnetic environment interference is selected 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, further improving 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 effective reception of autocorrelation signals. This is not conducive to tracking and analysis for incoherent reception, further enhancing the stealth 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 pilots provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below in conjunction with the 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 radio frequency analog signals and send them to the analog-to-digital conversion module 20 when the shortwave radio 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 set the carrier frequency 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 N corresponding pseudo-randomly changing backup frequencies based on time variations. In the detection and scanning states, the N*2 carrier frequency information is distributed to the down-conversion processing module 40 for the N*2 independent digital channels and the single-channel RF digital signal transmission module 90.

[0043] In order to make full use of the timeliness of the preset frequency points, the interval between the backup carrier frequency points based on time changes and the corresponding preset carrier frequency points 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 backup 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 employs software-defined radio technology and uses a high-real-time FPGA chip to down-convert the RF digital signal collected by the analog-to-digital conversion module 20 into (N*2) independent digital channels. Specifically, independent digital carrier signals are generated from the agreed N carrier frequency points and the N pseudo-randomly changing backup frequency points that vary over time. These signals are digitally mixed with the high-speed RF digital signal collected by the analog-to-digital conversion module 20. The signals are then extracted and filtered using multi-stage down-conversion to convert them into low-speed digital baseband signals (e.g., a baseband signal with an 8kHz sampling rate). The generated digital baseband signals are then transmitted to the spectrum detection module, which performs frequency domain analysis on the N*2 digital baseband signals to obtain N*2 channels of electromagnetic spectrum detection information.

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

[0047] N*2 independent baseband signal monitoring module 50 is 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

[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.

[0050] For N pre-set carrier frequencies, due to the time-varying and harsh local electromagnetic environment of shortwave, if strong interference is present at one of the pre-set frequencies, the common approach is to discard that frequency. For shortwave long-distance communications, which are limited by the ionosphere, the number of available frequencies is limited. Using a time-based pseudo-random backup carrier frequency strategy can further improve the effective detection of available frequencies. Therefore, real-time monitoring and assessment of the electromagnetic environment surrounding the N*2 carrier frequencies is required to determine the selection of the operating carrier frequency for 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 comparison with the relevant time-varying sub-band frequency set, it is determined which channel among 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, two different single-tone groups 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 a composition similar to 300Hz and 600Hz dual-tones. You can transform them 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 switching period 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.

[0055] The sub-band frequency set-based determination module 60 is configured 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 communications, given that both the sender and receiver experience frequency offsets in their crystal oscillator clocks, a common approach is to transmit a fixed waveform, perform autocorrelation detection, and perform frequency correction. To achieve covert detection communication, the present invention employs a common carrier plus single-sideband modulation architecture. After performing a fast Fourier transform on the received baseband signal, the useful subband spectrum frequency is compared with the carrier frequency. Since the frequency difference between the two is fixed, if it corresponds to a time-based pseudo-random subband frequency set, the received signal is considered to be 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, the system further includes: a time-agreement-based transmit / receive control module 80 and a transmit channel single-channel digital signal processing module 90; the time-agreement-based transmit / receive control module 80 is connected to the sub-band frequency set-based discrimination module 60 and the transmit channel single-channel digital signal processing module 90, and sends transmit / receive control instructions to the two modules to achieve 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, frequencies that fall in the same band and are closely spaced are grouped into a same-time transmission group.

[0061] Among them, in the process of detection and frequency selection, there are two working states: one is a monitoring state only, without sending detection signals 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 time for sending signals at each frequency point is 100ms, the time for transmitting useful signals is 80ms. The time for the receiver to stably receive signals after down-conversion 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). A 1024-point FFT transform is performed at the baseband receiving end (if the number of input data points of the FFT is insufficient, the spectrum resolution can be improved by zero padding, which only affects the phase information of the signal but not the frequency value). 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. 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 required to be less than 30ms.

[0065] When transmitting, if the transmission frequency is across bands, it is easily limited by the time consumption of the tuning circuit, which takes up the limited time to send useful signals. Therefore, according to the preset N frequencies, the frequencies that fall in the same band and are closely spaced are grouped into the same transmission group.

[0066] For example, a maximum of 3 frequency points can be transmitted each time, that is, after sending for 300ms, it will switch to the receiving state for 300ms, and then enter the transmitting state for 300ms. After this 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), it is possible to realize the autonomous transmission of 15 different carrier frequencies and the parallel reception of 30 frequencies. If the detection time is appropriately extended, the number of detectable frequencies can also be easily increased.

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

[0069] Generate time-varying sub-band baseband signals, which are converted into high-speed RF digital signals S after digital up-conversion processing 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 radio frequency digital signal S containing time-varying sub-band baseband information is generated. mix ;

[0072] Combined with the time-based receiving / transmitting control module, 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 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 N*2 frequency point environmental monitoring, 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 radio frequency 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 radio frequency 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 backup frequency f n备用 (f n备用 =f n +f Δ ) electromagnetic environment, and select the carrier frequency used in the call, f ΔThe range is a frequency value based on time change, 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 point of the nth channel, after comparing the electromagnetic characteristics with the preset backup frequency point of the nth channel, the decision is made based on which frequency point has the smallest local electromagnetic interference. 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 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 frequency with relatively small electromagnetic environment interference is selected 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, further improving 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 effective reception of autocorrelation signals. This is not conducive to tracking and analysis for incoherent reception, further enhancing the stealth 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 this understanding, the present invention implements all or part of the process in the above-mentioned embodiment method, and can also be completed by a computer program to instruct the relevant hardware. The computer program can be stored in a computer-readable storage medium. When the computer program is executed by the processor, it can implement the steps of the above-mentioned various method embodiments. 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, USB flash drive, mobile hard disk, magnetic disk, optical disk, computer memory, read-only memory (ROM), random access memory (RAM), 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 illustrative, wherein the units described as separate components may or may not be physically separate, 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 across 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 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 can be specifically implemented as one or more communication buses or signal lines. A person of ordinary skill in the art can understand and implement the present invention without inventive work.

[0081] The above are only preferred embodiments 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, perform data sampling, and generate a RF digital signal, which is then sent to the down-conversion processing module of the N*2 independent digital channels at the back end; A carrier frequency set generation module is used to generate a carrier frequency set and send it to the down-conversion processing module; the carrier frequency set includes N*2 carrier frequency points consisting of N preset carrier frequency points and N pseudo-randomly changing spare frequency points that correspond to each other 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 backup 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, 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, 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-path electromagnetic spectrum detection information is passed 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, 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 using 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 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, characterized in that: For the time-varying sub-band baseband signal generation module, the frequency interval between useful signals is set to mHz, so there are (1000n / m+1) groups of single-tone frequencies within the nkHz bandwidth range. When dual-tone is used as the detection baseband signal, two different single-tone groups 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, characterized in that: Also includes: Time-agreement-based receive / transmit control module and transmit channel single-channel digital signal processing module; The time-agreement-based transmit / receive control module is connected to the sub-band frequency set-based discrimination module and the transmit channel single-channel digital signal processing module, and sends transmit / receive control instructions to the two modules to achieve 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, frequencies that fall in the same band and are closely spaced are grouped into a same-time transmission group.

7. The shortwave frequency selection system based on time-varying multi-subband pilot according to claim 6, characterized in that: The single-channel digital signal processing module is used for: Generate time-varying sub-band baseband signals, which are converted into high-speed RF digital signals S after digital up-conversion processing 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 radio frequency digital signal S containing time-varying sub-band baseband information is generated. mix ; Combined with the time-based receiving / transmitting control module, when the shortwave radio is in the transmitting state, the RF digital signal S mix passed to the digital-to-analog converter; Digital-to-analog converter, used to convert RF digital signal S mix After 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 further 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 change, f n备用 =f n +f Δ .

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