Unauthorized satellite covert communication system and communication method

Abstract

The invention provides an unauthorized satellite covert communication system and communication method, and relates to the field of satellite communication, and the system comprises a user terminal device, a ground terminal device and a transparent forwarding satellite. The user side equipment comprises a communication application program and a satellite communication terminal; the communication application program configures service parameters; the satellite communication terminal carries out baseband signal processing and transmitting power adjustment on the service signals based on the service parameters and then sends the service signals to the ground end equipment; the ground end equipment receives and analyzes the service signal, generates a feedback sending signal, carries out frequency conversion amplification on the feedback sending signal, and sends the feedback sending signal to the user end equipment; the satellite communication terminal receives a feedback sending signal sent by the ground end equipment, deframes the feedback sending signal and then transmits the feedback sending signal to the communication application program through Bluetooth; and the transparent forwarding satellite carries out transparent forwarding on signals interacted between the user end equipment and the ground end equipment according to a preset mapping relation. Therefore, high-reliability stable communication is realized, and the spectrum utilization efficiency of the shared channel is improved.

Description

Technical Field

[0001] This invention relates to the field of satellite communication technology, and in particular to an unauthorized satellite covert communication system and communication method. Background Technology

[0002] With the rapid development of satellite communication technology, spectrum resources are becoming increasingly scarce, and the traditional fixed allocation model of licensed spectrum can no longer meet diverse communication needs. Unlicensed spectrum sharing access technology, due to its flexibility and low cost, has gradually become a research hotspot in the field of wireless communication.

[0003] However, the utilization of unlicensed spectrum in satellite communication scenarios still faces significant challenges: on the one hand, satellite communication systems are extremely sensitive to interference, and disorderly access by unlicensed users can easily lead to a decline in the communication quality of licensed users (such as normal satellite services); on the other hand, traditional unlicensed communication technologies (such as contention-based random access) are difficult to meet the needs of covert communication, and their signal characteristics are easily detected and interfered with.

[0004] Spread spectrum communication technology has advantages such as low probability of intercept (LPI) and strong anti-interference capability, providing a feasible solution for satellite covert communication. In the existing technology, some studies have attempted to apply spread spectrum technology to satellite unlicensed spectrum sharing, but the following problems are common: (1) no effective interference avoidance mechanism has been established, making it difficult to ensure the communication quality of licensed users; (2) the power control strategy is crude, resulting in low spectrum utilization efficiency; (3) it lacks adaptability to the time-varying characteristics of satellite channels (such as Doppler shift and atmospheric attenuation), affecting the reliability of covert communication. Summary of the Invention

[0005] This invention provides an unlicensed satellite covert communication system and method to address the shortcomings of existing technologies, such as difficulty in ensuring communication quality for licensed users, low spectrum utilization efficiency, and low reliability of covert communication. It enables highly reliable and stable communication by utilizing the bandwidth of unlicensed satellite communication and adopting covert communication methods.

[0006] This invention provides an unauthorized satellite covert communication system, comprising: User terminal equipment, ground terminal equipment, and transparent relay satellites; The user terminal equipment includes a communication application and a satellite communication terminal; The communication application is used to configure service parameters and transmit service signals to the satellite communication terminal via Bluetooth; the satellite communication terminal performs baseband signal processing and transmission power adjustment on the service signals based on the service parameters configured by the communication application, and sends the service signals after baseband signal processing and transmission power adjustment to the ground terminal equipment. The ground terminal equipment is used to receive and parse the service signals sent by the user terminal equipment, generate a response signal, and perform frequency conversion and amplification on the response signal, and send the frequency conversion and amplified response signal to the user terminal equipment. The satellite communication terminal is also used to receive the echo transmission signal sent by the ground terminal equipment, deframe the echo transmission signal, and transmit the deframed echo transmission signal to the communication application via Bluetooth; The transparent relay satellite is used to transparently relay signals exchanged between the user terminal equipment and the ground terminal equipment according to a preset mapping relationship.

[0007] According to the unauthorized satellite covert communication system provided by the present invention, the ground terminal equipment is further used for: Based on satellite channel communication capabilities, frequency selection frames are periodically sent to multiple candidate frequency points through a polling mechanism; The user terminal device is specifically used for: The frequency selection frames sent by the ground terminal device are captured in a polling manner at the multiple candidate frequency points; The target frequency is selected based on the capture result of the frequency selection frame; the target frequency is used to transmit the service signal.

[0008] According to the present invention, an unauthorized satellite covert communication system is provided, wherein the satellite communication terminal is specifically used for: The service signals are framed to generate service frames; The service frame is sequentially subjected to convolutional coding, low-density parity-check coding (LDPC), direct sequence spread spectrum (DSSS), and binary phase shift keying (BPSK) modulation operations to obtain the service signal after baseband signal processing.

[0009] According to the present invention, an unauthorized satellite covert communication system is provided, wherein the satellite communication terminal is specifically used for: The transmission power of the service signal after baseband signal processing is dynamically adjusted based on the noise floor of the satellite channel.

[0010] According to the present invention, an unauthorized satellite covert communication system is provided, wherein the service frame is composed of a pilot header, a frame synchronization header, a service segment, and multiple data segments; The pilot header is formed by spreading with all-1 symbols; The frame synchronization header is a preset m-sequence used to separate the pilot header from the service segment; The service segment contains information related to the service parameters, and the service segment uses convolutional coding. The data segment contains frame information from the Media Access Control (MAC) layer and valid transmission data. The data segment has multiple rate levels and uses LDPC encoding.

[0011] According to the present invention, an unauthorized satellite covert communication system is provided, wherein the ground terminal equipment includes an antenna system, a radio frequency transceiver unit, a signal processor, and a host computer; The antenna system is connected to the signal processor through the radio frequency transceiver unit, and the signal processor communicates with the host computer through the network port; The host computer is used to parse the service signals processed by the signal processor and generate the return command configuration; The signal processor is used to generate a callback transmission signal based on the callback configuration and send it to the radio frequency transceiver unit, and to perform frame deframe processing on the service signal processed by the radio frequency transceiver unit. The radio frequency transceiver unit is used to amplify the service signals and the echo transmission signals sent by the user terminal equipment. The antenna system is used to convert the service signal sent by the user terminal equipment and send it to the radio frequency transceiver unit, and to convert the amplified echo transmission signal from the radio frequency transceiver unit and send it to the user terminal equipment.

[0012] The present invention also provides a communication method applied to an unauthorized satellite covert communication system as described in any of the preceding inventions, comprising the following steps: Using the user terminal equipment, based on the service parameters configured in the communication application, the service signal is processed in baseband and the transmission power is adjusted. The service signal after baseband signal processing and transmission power adjustment is then sent to the ground terminal equipment. The ground terminal equipment receives and parses the service signals sent by the user terminal equipment, generates a response signal, performs frequency conversion and amplification on the response signal, and sends the frequency conversion and amplification response signal to the user terminal equipment. The user terminal device deframes the echo transmission signal and transmits the deframed echo transmission signal to the communication application via Bluetooth. The signals exchanged between the user terminal equipment and the ground terminal equipment are transparently forwarded by a transparent relay satellite according to a preset mapping relationship.

[0013] According to a communication method provided by the present invention, the method further includes: Based on satellite channel communication capabilities, the ground-based equipment periodically sends frequency selection frames to multiple candidate frequency points through a polling mechanism. The user terminal device polls and captures the frequency selection frames sent by the ground terminal device at the multiple candidate frequency points. The user terminal device selects a target frequency point based on the capture result of the frequency selection frame; the target frequency point is used to transmit the service signal.

[0014] According to a communication method provided by the present invention, baseband signal processing is performed on service signals, including: The service signals are framed to generate service frames; The service frame is sequentially subjected to convolutional coding, low-density parity-check coding (LDPC), direct sequence spread spectrum (DSSS), and binary phase shift keying (BPSK) modulation operations to obtain the service signal after baseband signal processing.

[0015] According to a communication method provided by the present invention, baseband signal processing and transmit power adjustment are performed on service signals, including: The transmission power of the service signal after baseband signal processing is dynamically adjusted based on the noise floor of the satellite channel.

[0016] The unlicensed satellite covert communication system and method provided by this invention achieve flexible configuration of service parameters and signal transmission between user-end equipment and satellite communication terminals through Bluetooth short-range communication. It combines baseband signal processing and dynamic transmit power adjustment technology to adapt to complex transmission environments, utilizes the preset frequency band mapping relationship of transparent relay satellites to complete unresolved signal relay, and ensures reliable long-distance signal return through frequency conversion amplification and echo generation mechanisms at the ground-end equipment. Finally, closed-loop communication is completed through frame de-framing processing and Bluetooth backhaul at the satellite communication terminal. This achieves highly adaptable covert communication in unlicensed frequency bands, enhances signal anti-interference capabilities, and enables covert, stable, and efficient data communication in complex electromagnetic environments. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the structure of the unauthorized satellite covert communication system provided by the present invention.

[0019] Figure 2 This is a flowchart illustrating the communication method provided by the present invention.

[0020] Figure 3 This is a schematic diagram of an embodiment of the unauthorized satellite covert communication system provided by the present invention.

[0021] Figure 4 This is a schematic diagram of the autonomous frequency selection process provided by the present invention.

[0022] Figure 5This is a schematic diagram of the business communication process provided by the present invention.

[0023] Figure 6 This is a schematic diagram of the structure of the frequency selection frame provided by the present invention.

[0024] Figure 7 This is a schematic diagram of the structure of the service frame provided by the present invention. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0026] Figure 1 This is a schematic diagram of the unauthorized satellite covert communication system provided by the present invention, as shown below. Figure 1 As shown, the system includes: User terminal equipment 100, ground terminal equipment 110, and transparent relay satellite 120; The user terminal device 100 includes a communication application 101 and a satellite communication terminal 102; The communication application 101 is used to configure service parameters and transmit service signals to the satellite communication terminal 102 via Bluetooth. Based on the service parameters configured by the communication application 101, the satellite communication terminal 102 performs baseband signal processing and transmission power adjustment on the service signals and sends the service signals after baseband signal processing and transmission power adjustment to the ground terminal equipment 110. Ground terminal equipment 110 is used to receive and parse the service signals sent by user terminal equipment 100, generate a response signal, and perform frequency conversion and amplification on the response signal, and send the frequency conversion and amplified response signal to user terminal equipment 100. Satellite communication terminal 102 is also used to receive the echo transmission signal sent by ground terminal equipment 110, deframe the echo transmission signal, and transmit the deframed echo transmission signal to communication application 101 via Bluetooth. The transparent relay satellite 120 is used to transparently relay signals exchanged between the user terminal equipment 100 and the ground terminal equipment 110 according to a preset mapping relationship.

[0027] Specifically, the unlicensed satellite covert communication system provided in this embodiment of the invention comprises three core components: user terminal equipment, ground terminal equipment, and transparent relay satellite, which form a closed-loop communication through signal interaction.

[0028] The user terminal equipment includes communication applications and satellite communication terminals.

[0029] The communication application (APP) serves as the user's interface, used to configure service parameters (such as communication rate, frequency selection, etc.) and transmit the service signals (service data) to be sent to the satellite communication terminal via Bluetooth.

[0030] The satellite communication terminal is the core processing unit of the user terminal equipment. After receiving the configured service parameters and service signals from the communication application, it can perform baseband signal processing and transmit power adjustment on the service signals according to these parameters. Baseband signal processing may include digital signal processing processes such as channel coding and modulation, with the aim of converting the raw data into an anti-interference signal suitable for satellite transmission. The transmit power adjustment process can dynamically adjust the radio frequency transmit power according to preset power parameters, thereby ensuring the adaptability of the transmitted signal in different transmission environments. The service signal, after baseband signal processing and transmit power adjustment, is transmitted to the transparent relay satellite via the antenna of the satellite communication terminal, completing the uplink transmission from the user terminal equipment to the satellite link.

[0031] Transparent relay satellites, acting as relay nodes, can transparently forward service signals according to a pre-defined frequency mapping relationship (e.g., uplink frequency f1 → downlink frequency f2). Here, "transparent" means the satellite does not analyze the signal content but only performs physical layer forwarding. Transparent relay satellites can use directional beamforming based on the geographical location of user equipment to accurately cover the area where the user equipment is located with the service signals transmitted by the user equipment.

[0032] After receiving the signal relayed by the transparent relay satellite, the ground equipment first performs signal parsing (including demodulation, channel decoding and other reverse processes) to extract the original service information, and then generates the corresponding feedback transmission signal (such as acknowledgment response, control command and other feedback information).

[0033] After generating the corresponding echo transmission signal, the ground equipment can perform frequency conversion and amplification processing on the echo transmission signal (up-convert to the radio frequency band and amplify the power), and transmit it to the transparent relay satellite via the antenna. The frequency conversion and amplified echo transmission signal is then returned to the user equipment via the transparent relay satellite, forming a complete communication closed loop.

[0034] After sending a service signal, the satellite communication terminal enters a waiting state for a response. It captures the response signal transmitted by the ground equipment via a transparent relay satellite through the receiving link. The satellite communication terminal performs deframe processing on the response signal, decomposing the received frame structure data into information units that can be recognized by the application layer, and transmits them back to the communication application via Bluetooth. Finally, the result is displayed on the user interface of the communication application, completing the two-way communication process.

[0035] The unlicensed satellite covert communication system provided by this invention achieves flexible configuration of service parameters and signal transmission between user-end equipment and satellite communication terminals through Bluetooth short-range communication. It combines baseband signal processing and dynamic transmit power adjustment technology to adapt to complex transmission environments, utilizes the preset frequency band mapping relationship of transparent relay satellites to complete unresolved signal relay, and ensures reliable long-distance signal return through frequency conversion amplification and echo generation mechanisms at the ground-end equipment. Finally, closed-loop communication is completed through frame de-framing processing and Bluetooth backhaul at the satellite communication terminal. This achieves highly adaptable covert transmission in unlicensed frequency bands, enhances signal anti-interference capabilities, and enables covert, stable, and efficient data communication in complex electromagnetic environments.

[0036] According to the unauthorized satellite covert communication system provided by the present invention, the ground terminal equipment is also used for: Based on satellite channel communication capabilities, frequency selection frames are periodically sent to multiple candidate frequency points through a polling mechanism; The user terminal device is specifically used for: Polling and capturing frequency selection frames sent by ground-based devices at multiple candidate frequencies; The target frequency is selected based on the capture results of the frequency selection frame; the target frequency is used to transmit service signals.

[0037] Specifically, ground-based equipment can periodically send frequency selection frames to multiple candidate frequency points through a polling mechanism, based on the communication capabilities of the satellite channel.

[0038] Specifically, ground-based equipment can generate frequency-selective frames based on the satellite channel status (such as available frequencies, signal quality, etc.), and then transmit them to a transparent relay satellite after modulation and amplification. The transparent relay satellite then forwards these frequency-selective frames to the area where the user equipment is located according to a preset frequency mapping relationship, with the beam pointing to the corresponding beam area.

[0039] In some implementations, the frequency-selective frame is a service frame sent from the ground equipment to the user equipment and transparently forwarded by the satellite. It is spread entirely by all-1 symbols and has not undergone channel coding.

[0040] User-end equipment can poll and capture frequency selection frames sent by ground-end equipment on multiple candidate frequency points, and select the target frequency point based on the capture results.

[0041] Specifically, when the user terminal equipment (satellite communication terminal) is powered on or needs to initiate communication, it can sequentially scan all candidate frequency points (e.g., f1~f7) to detect and capture the frequency selection frames transmitted by the ground end. Based on the capture results of the frequency selection frames, the user terminal equipment can determine the coverage beam of its geographical location and thus select a suitable target frequency point as the frequency point for subsequent service signal transmission.

[0042] This process ensures that user-end equipment can select the optimal beam frequency under current satellite channel conditions, thereby improving the reliability and stealth of communication.

[0043] According to the present invention, an unauthorized satellite covert communication system is provided, wherein the satellite communication terminal is specifically used for: Perform framing processing on the service signals to generate service frames; The service frame is sequentially subjected to convolutional coding, low-density parity-check coding (LDPC), direct sequence spread spectrum (DSSS), and binary phase shift keying (BPSK) modulation operations to obtain the service signal after baseband signal processing.

[0044] Specifically, in the unauthorized satellite covert communication system provided by this invention, the baseband signal processing flow of the satellite communication terminal adopts multi-level coding and modulation technology to achieve reliable signal transmission.

[0045] First, the satellite communication terminal performs frame processing on the original service signals, and constructs a standardized service frame structure by adding frame headers and check fields, thereby providing basic data units for subsequent encoding and modulation processing.

[0046] In some implementations, a service frame consists of a pilot header, a frame synchronization header, a service segment, and multiple data segments; The pilot header is formed by spreading with all-1 symbols; The frame synchronization header is a preset m-sequence used to separate the pilot header from the service segment; The service segment contains information related to business parameters, and the service segment uses convolutional coding. The data segment contains frame information from the Media Access Control (MAC) layer and valid transmitted data. The data segment has multiple rate levels and uses LDPC encoding.

[0047] Specifically, in the embodiments of the present invention, the service frame may consist of a pilot header, a frame synchronization header, a service segment, and multiple data segments.

[0048] The pilot header is generated using all-1 symbols spread spectrum without channel coding. Due to the periodicity of the all-1 symbols, the receiver can quickly acquire the signal and make a preliminary estimate of the channel state through correlation operations.

[0049] The frame synchronization header can use a preset small m-sequence, which has not been channel-coded, to separate the pilot header and the service segment as an isolation marker. Frame synchronization is achieved through the autocorrelation characteristics of the m-sequence, ensuring that the receiver can accurately separate the pilot header and the service segment.

[0050] The service segment carries key information about service parameters, including frame type, rate level, source ID, and number of data packets. This information can be enhanced with convolutional coding to improve error resilience, ensuring that the receiving end can reliably parse the configuration parameters and providing a basis for demodulation and decoding of subsequent data segments.

[0051] The data segment contains Media Access Control (MAC) layer frame information and the user's valid transmission data. It can support multiple rate matching and achieve efficient error correction through Low Density Parity Check (LDPC) encoding.

[0052] After framing is completed, the satellite communication terminal sequentially performs convolutional code encoding, LDPC encoding, direct sequence spread spectrum (DSSS) and binary phase shift keying (BPSK) modulation operations to obtain the service signal after baseband signal processing.

[0053] Among them, convolutional coding can perform forward error correction coding on service frames through a sliding window mechanism to generate redundant parity bits to enhance random error correction capability; LDPC coding can improve coding gain through sparse matrix parity relation, especially for effective correction of burst errors; then, the encoded signal can be multiplied with pseudo-random code through DSSS to spread the signal energy to a wider frequency band, which reduces power spectral density to enhance stealth and improves anti-interference capability through spread spectrum gain; finally, BPSK modulation is used to convert the spread spectrum digital signal into a phase-modulated analog baseband signal to adapt it to the physical transmission requirements of satellite communication.

[0054] According to the present invention, an unauthorized satellite covert communication system is provided, wherein the satellite communication terminal is specifically used for: The transmission power of the service signal after baseband signal processing is dynamically adjusted based on the noise floor of the satellite channel.

[0055] Specifically, satellite communication terminals can dynamically adjust their transmission power based on the real-time noise floor of the satellite channel to ensure signal concealment and reliability.

[0056] The noise floor of a satellite channel refers to the lowest power spectral density of background noise in the satellite channel. Satellite communication terminals can detect the noise level of the current frequency in real time and, in conjunction with preset stealth thresholds (such as signal power needing to be at least 3dB below the noise floor), calculate the maximum allowable transmit power.

[0057] Based on the noise floor, the maximum allowable transmit power is dynamically adjusted. On the one hand, the signal power can be suppressed below the noise floor, so that its power spectral density blends with the noise background and avoids being identified by conventional user detection equipment, thereby achieving covert communication. On the other hand, it can ensure that the signal can still be correctly demodulated by the target receiver after spreading gain compensation, maintaining communication reliability.

[0058] According to the present invention, an unauthorized satellite covert communication system includes ground-end equipment comprising an antenna system, a radio frequency transceiver unit, a signal processor, and a host computer. The antenna system is connected to the signal processor via a radio frequency transceiver unit, and the signal processor communicates with the host computer via a network port. The host computer is used to parse the service signals processed by the signal processor and generate the return command configuration; The signal processor is used to generate a return message transmission signal based on the return message configuration and send it to the radio frequency transceiver unit, and to perform frame deframe processing on the service signal processed by the radio frequency transceiver unit. The radio frequency transceiver unit is used to amplify and process the service signals and feedback transmission signals sent by the user terminal equipment; The antenna system is used to convert the service signals sent by the user terminal equipment to the frequency transceiver unit and then transmit them to the radio frequency transceiver unit, and to convert the amplified return signal from the radio frequency transceiver unit to the frequency and then transmit it to the user terminal equipment.

[0059] Specifically, the ground-based equipment in an unlicensed satellite covert communication system may include an antenna system, a radio frequency transceiver unit, a signal processor, and a host computer, which work together to receive, parse, and generate service signals.

[0060] The antenna system serves as the physical interface for signal transmission and reception of ground-end equipment; the radio frequency transceiver unit, as the core module for signal amplification in ground-end equipment, performs power adjustment for bidirectional signals; the signal processor is used for baseband signal processing tasks; and the host computer, as the control and analysis center, interacts with the signal processor through the network port.

[0061] In the receiving link, the antenna system performs frequency conversion processing on the service signal relayed by the user terminal equipment via the satellite, and then transmits the frequency-converted signal to the radio frequency transceiver unit; the radio frequency transceiver unit amplifies the frequency-converted service signal and transmits the amplified service signal to the signal processor; the signal processor performs deframe operations (such as extracting frame headers, demodulation and decoding, etc.) on the amplified service signal, and transmits the deframed data to the host computer through the network port; the host computer parses the deframed data and generates response configurations (such as response commands, parameter adjustment commands, etc.) based on the parsing results or external inputs.

[0062] In the transmission link, the host computer feeds back the generated echo configuration to the signal processor. The signal processor generates an echo transmission signal that conforms to the transmission protocol according to the echo configuration (this process includes frame structure encapsulation, encoding and modulation, etc.), and then transmits the generated signal to the radio frequency transceiver unit. The radio frequency transceiver unit amplifies the power of the echo transmission signal generated by the signal processor to ensure that the signal remains detectable after being transmitted by satellite. The antenna system performs frequency conversion processing on the echo transmission signal amplified by the radio frequency transceiver unit and finally radiates it to the user terminal equipment.

[0063] Figure 2 This is a flowchart illustrating the communication method provided by the present invention, as shown below. Figure 2 As shown, this method, applied to any of the previously described unauthorized satellite covert communication systems, includes the following steps: Step 200: Using the user terminal equipment, based on the service parameters configured in the communication application, perform baseband signal processing and transmit power adjustment on the service signal, and send the service signal after baseband signal processing and transmit power adjustment to the ground terminal equipment.

[0064] Step 201: Receive and parse the service signals sent by the user terminal equipment through the ground terminal equipment, generate a response signal, amplify the response signal by frequency conversion, and send the amplified response signal to the user terminal equipment.

[0065] Step 202: Deframe the echo transmission signal through the user terminal device, and transmit the deframed echo transmission signal to the communication application via Bluetooth.

[0066] In this process, the signals exchanged between the user terminal equipment and the ground terminal equipment are transparently forwarded by the transparent relay satellite according to the preset mapping relationship.

[0067] Specifically, the unlicensed satellite covert communication system provided in this embodiment of the invention comprises three core components: user terminal equipment, ground terminal equipment, and transparent relay satellite, which form a closed-loop communication through signal interaction.

[0068] The user-end equipment includes communication apps and satellite communication terminals.

[0069] The communication APP serves as the user interface, used to configure service parameters (such as communication rate, frequency selection, etc.) and transmit the service signals (service data) to be sent to the satellite communication terminal via Bluetooth.

[0070] The satellite communication terminal is the core processing unit of the user terminal equipment. After receiving the configured service parameters and service signals from the communication application, it can perform baseband signal processing and transmit power adjustment on the service signals according to these parameters. Baseband signal processing may include digital signal processing processes such as channel coding and modulation, with the aim of converting the raw data into an anti-interference signal suitable for satellite transmission. The transmit power adjustment process can dynamically adjust the radio frequency transmit power according to preset power parameters, thereby ensuring the adaptability of the transmitted signal in different transmission environments. The service signal, after baseband signal processing and transmit power adjustment, is transmitted to the transparent relay satellite via the antenna of the satellite communication terminal, completing the uplink transmission from the user terminal equipment to the satellite link.

[0071] Transparent relay satellites, acting as relay nodes, can transparently forward service signals according to a pre-defined frequency mapping relationship (e.g., uplink frequency f1 → downlink frequency f2). Here, "transparent" means the satellite does not analyze the signal content but only performs physical layer forwarding. Transparent relay satellites can use directional beamforming based on the geographical location of user equipment to accurately cover the area where the user equipment is located with the service signals transmitted by the user equipment.

[0072] After receiving the signal relayed by the transparent relay satellite, the ground equipment first performs signal parsing (including demodulation, channel decoding and other reverse processes) to extract the original service information, and then generates the corresponding feedback transmission signal (such as acknowledgment response, control command and other feedback information).

[0073] After generating the corresponding echo transmission signal, the ground equipment can perform frequency conversion and amplification processing on the echo transmission signal (up-convert to the radio frequency band and amplify the power), and transmit it to the transparent relay satellite via the antenna. The frequency conversion and amplified echo transmission signal is then returned to the user equipment via the transparent relay satellite, forming a complete communication closed loop.

[0074] After sending a service signal, the satellite communication terminal enters a waiting state for a response. It captures the response signal transmitted by the ground equipment via a transparent relay satellite through the receiving link. The satellite communication terminal performs deframe processing on the response signal, decomposing the received frame structure data into information units that can be recognized by the application layer, and transmits them back to the communication application via Bluetooth. Finally, the result is displayed on the user interface of the communication application, completing the two-way communication process.

[0075] The communication method provided by this invention performs baseband signal processing and dynamic transmit power adjustment based on service parameters configured in the communication application by the user terminal equipment. This adapts to complex transmission environments. It utilizes the preset frequency band mapping relationship of transparent relay satellites to achieve unresolved signal relay, and ensures reliable long-distance signal return transmission through frequency conversion amplification and echo generation mechanisms on the ground terminal equipment. Finally, closed-loop communication is completed through frame de-framing processing and Bluetooth backhaul communication application on the user terminal equipment. This achieves highly adaptable transmission for covert communication in unlicensed frequency bands, enhances signal anti-interference capabilities, and enables covert, stable, and efficient data communication in complex electromagnetic environments.

[0076] According to a communication method provided by the present invention, the method further includes: Using ground-based equipment and based on satellite channel communication capabilities, frequency selection frames are periodically sent to multiple candidate frequency points through a polling mechanism. The user terminal equipment polls and captures frequency selection frames sent by the ground terminal equipment at multiple candidate frequency points. The target frequency is selected by the user terminal equipment based on the capture result of the frequency selection frame; the target frequency is used to transmit service signals.

[0077] Specifically, ground-based equipment can periodically send frequency selection frames to multiple candidate frequency points through a polling mechanism, based on the communication capabilities of the satellite channel.

[0078] Specifically, ground-based equipment can generate frequency-selective frames based on the satellite channel status (such as available frequencies, signal quality, etc.), and then transmit them to a transparent relay satellite after modulation and amplification. The transparent relay satellite then forwards these frequency-selective frames to the area where the user equipment is located according to a preset frequency mapping relationship, with the beam pointing to the corresponding beam area.

[0079] In some implementations, the frequency-selective frame is a service frame sent from the ground equipment to the user equipment and transparently forwarded by the satellite. It is spread entirely by all-1 symbols and has not undergone channel coding.

[0080] User-end equipment can poll and capture frequency selection frames sent by ground-end equipment on multiple candidate frequency points, and select the target frequency point based on the capture results.

[0081] Specifically, when the user terminal equipment (satellite communication terminal) is powered on or needs to initiate communication, it can sequentially scan all candidate frequency points (e.g., f1~f7) to detect and capture the frequency selection frames transmitted by the ground end. Based on the capture results of the frequency selection frames, the user terminal equipment can determine the coverage beam of its geographical location and thus select a suitable target frequency point as the frequency point for subsequent service signal transmission.

[0082] This process ensures that user-end equipment can select the optimal beam frequency under current satellite channel conditions, thereby improving the reliability and stealth of communication.

[0083] According to a communication method provided by the present invention, baseband signal processing is performed on service signals, including: Perform framing processing on the service signals to generate service frames; The service frame is sequentially subjected to convolutional coding, low-density parity-check coding (LDPC), direct sequence spread spectrum (DSSS), and binary phase shift keying (BPSK) modulation operations to obtain the service signal after baseband signal processing.

[0084] Specifically, in the unauthorized satellite covert communication system provided by this invention, the baseband signal processing flow employs multi-level coding and modulation technology to achieve reliable signal transmission.

[0085] First, the user terminal equipment performs frame processing on the original service signal, and constructs a standardized service frame structure by adding frame headers and check fields, thereby providing basic data units for subsequent encoding and modulation processing.

[0086] In some implementations, a service frame consists of a pilot header, a frame synchronization header, a service segment, and multiple data segments; The pilot header is formed by spreading with all-1 symbols; The frame synchronization header is a preset m-sequence used to separate the pilot header from the service segment; The service segment contains information related to business parameters, and the service segment uses convolutional coding. The data segment contains frame information from the Media Access Control (MAC) layer and valid transmitted data. The data segment has multiple rate levels and uses LDPC encoding.

[0087] Specifically, in the embodiments of the present invention, the service frame may consist of a pilot header, a frame synchronization header, a service segment, and multiple data segments.

[0088] The pilot header is generated using all-1 symbols spread spectrum without channel coding. Due to the periodicity of the all-1 symbols, the receiver can quickly acquire the signal and make a preliminary estimate of the channel state through correlation operations.

[0089] The frame synchronization header can use a preset small m-sequence, which has not been channel-coded, to separate the pilot header and the service segment as an isolation marker. Frame synchronization is achieved through the autocorrelation characteristics of the m-sequence, ensuring that the receiver can accurately separate the pilot header and the service segment.

[0090] The service segment carries key information about service parameters, including frame type, rate level, source ID, and number of data packets. This information can be enhanced with convolutional coding to improve error resilience, ensuring that the receiving end can reliably parse the configuration parameters and providing a basis for demodulation and decoding of subsequent data segments.

[0091] The data segment contains MAC layer frame information and the user's valid transmitted data. It can support multiple rate matching levels and achieve efficient error correction through LDPC encoding.

[0092] After framing is completed, the user terminal equipment sequentially performs convolutional code encoding, LDPC encoding, DSSS and BPSK modulation operations to obtain the service signal after baseband signal processing.

[0093] Among them, convolutional coding can perform forward error correction coding on service frames through a sliding window mechanism to generate redundant parity bits to enhance random error correction capability; LDPC coding can improve coding gain through sparse matrix parity relation, especially for effective correction of burst errors; then, the encoded signal can be multiplied with pseudo-random code through DSSS to spread the signal energy to a wider frequency band, which reduces power spectral density to enhance stealth and improves anti-interference capability through spread spectrum gain; finally, BPSK modulation is used to convert the spread spectrum digital signal into a phase-modulated analog baseband signal to adapt it to the physical transmission requirements of satellite communication.

[0094] According to a communication method provided by the present invention, baseband signal processing and transmit power adjustment are performed on service signals, including: The transmission power of the service signal after baseband signal processing is dynamically adjusted based on the noise floor of the satellite channel.

[0095] Specifically, user-end equipment can dynamically adjust its transmission power based on the real-time noise floor of the satellite channel to ensure signal concealment and reliability.

[0096] The noise floor of a satellite channel refers to the lowest power spectral density of background noise in the satellite channel. User-end equipment can detect the noise level at the current frequency in real time and, in conjunction with a preset concealment threshold (such as the signal power needing to be at least 3dB below the noise floor), calculate the maximum allowable transmit power.

[0097] Based on the noise floor, the maximum allowable transmit power is dynamically adjusted. On the one hand, the signal power can be suppressed below the noise floor, so that its power spectral density blends with the noise background and avoids being identified by conventional user detection equipment, thereby achieving covert communication. On the other hand, it can ensure that the signal can still be correctly demodulated by the target receiver after spreading gain compensation, maintaining communication reliability.

[0098] The following examples, through specific application scenarios, further illustrate the unauthorized satellite covert communication system and communication method provided by the present invention.

[0099] Figure 3 This is a schematic diagram of an embodiment of the unauthorized satellite covert communication system provided by the present invention, as shown below. Figure 3As shown, the unauthorized satellite covert communication system described in this embodiment includes: 1. User terminal equipment: (1) Communication APP: Configure service parameters (communication rate, file transfer, frequency, etc.) and interact with satellite communication terminal via Bluetooth.

[0100] (2) Satellite communication terminal: integrated baseband processing unit (PS, PL), AD9361 radio frequency transceiver chip, radio frequency processing unit.

[0101] 2. Ground-based equipment (ground station): (1) Antenna system: including high-gain feedforward directional antenna, power amplifier, low-noise amplifier, supporting uplink and downlink frequency conversion.

[0102] (2) Radio frequency transceiver unit (radio frequency transmitting unit and radio frequency receiving unit): bidirectional amplification link, including mixer and filter.

[0103] (3) Signal processor: The complete system has a total of 8 signal processors, which complete the signal acquisition, despreading, and frame synchronization of all beam directions, and integrate the network port to communicate with the host computer.

[0104] (4) Host computer: parses service instructions, generates response configuration (frequency point, content), and interacts with signal processor through TCP / IP protocol.

[0105] 3. Transparent relay satellite: The GEO geostationary orbit satellite is equipped with a broadband transparent transponder, supports frequency mapping (uplink f1 → downlink f2) and power amplification, and achieves geographic location positioning based on onboard GPS.

[0106] The communication process of an unauthorized satellite covert communication system is as follows: Autonomous frequency selection (ground end → satellite → user end): Figure 4 This is a schematic diagram of the autonomous frequency selection process provided by the present invention, such as... Figure 4 As shown, autonomous frequency selection is an operation that is performed automatically after the terminal is powered on. The satellite communication terminal polls and acquires frequency points f1-f7. Within the frequency selection time limit, the terminal can perform autonomous frequency selection based on the frequency selection frame sent by the ground equipment and select a better beam to ensure subsequent communication.

[0107] The specific signal flow and implementation details are as follows: Step 1: The host computer generates a frequency selection frame. The host computer polls and sends frequency-selected frames based on the satellite channel's communication capabilities, and then sends them to the signal processor via the network port.

[0108] Step 2: Generate the frequency-selective frame baseband waveform The signal processor modulates the long pilot data (DSSS-BPSK) to generate a frequency-selective signal → radio frequency transceiver unit.

[0109] Step 3: Frequency conversion and amplification of the RF transceiver unit The radio frequency transceiver unit amplifies the signal, which is then amplified by the antenna system power amplifier before being transmitted to the satellite.

[0110] Step 4: Satellite Retransmission Transparent satellite relay: the transponder switches the uplink frequency to the downlink frequency (based on a preset mapping relationship), and the beam points to the corresponding beam area.

[0111] Step 5: Frequency selection on the user end When the selected frequency frame arrives, the user terminal captures the signal, analyzes it, determines the beam state based on the capture result, selects the optimal beam and the best frequency point to complete the frequency selection, and uploads it to the APP via Bluetooth.

[0112] Figure 5 This is a schematic diagram of the business communication process provided by the present invention, such as... Figure 5 As shown, the complete business communication process can be broken down into two parts: sending services via the return link and sending feedback via the forward link. The specific signal flow and implementation details are as follows: Return link (user terminal → satellite → ground terminal): Step 1: User-side signal generation: The communication app sends configurations via Bluetooth: transmission rate (adjustable from 1kbps to 4kbps), file (string, text, voice, image), and frequency (7 selectable frequency points, with the best frequency point selected based on the user's frequency selection results).

[0113] Step 2: Baseband Processing The satellite communication terminal performs framing (including synchronization header, service segment, and data segment) → convolutional code encoding → LDPC encoding → DSSS spread spectrum → BPSK modulation.

[0114] Step 3: Radio Frequency Transmission: Power control (3 adjustable levels) is transmitted to the satellite via antenna.

[0115] Step 4: Transparent Satellite Forwarding The transponder detects the uplink frequency (the frequency selected by the user from f1 to f7), maps it to the downlink frequency according to the preset relationship, and directs the beam to the area where the ground terminal is located based on the geographical location of the user terminal.

[0116] Step 5: Ground-end receiver frequency converter: The antenna system's low-noise amplifier provides amplification gain, which is then converted to intermediate frequency (IF) → amplified by the RF transceiver unit → signal processor.

[0117] Step 6: Ground station signal processing: The signal processor performs acquisition → despreading and tracking → frame synchronization → demodulation and decoding → service segment convolutional code decoding → data segment LDPC decoding.

[0118] Step 7: Business Output: After the signal processor decodes the frames, the data is transmitted to the host computer via the network port, and the host computer parses the data frames.

[0119] Forward link (ground end → satellite → user end): Step 1: Ground-end response generation: The host computer parses the service content, generates the response configuration (uplink frequency point), and sends it to the signal processor through the network port.

[0120] Step 2: Generate the echo signal: Signal processor: Same as the uplink encoding and modulation process, generates the echo signal → radio frequency transceiver unit.

[0121] Step 3: Baseband signal frequency conversion and amplification: The radio frequency transceiver unit amplifies the signal, which is then amplified by the antenna system power amplifier and transmitted to the satellite.

[0122] Step 4: Satellite secondary relay: The transponder switches the uplink frequency to the downlink frequency (the corresponding frequency in f1~f7), and the beam is directed towards the area where the user is located.

[0123] Step 5: User-side reception and processing: The satellite communication terminal follows the same receiving process as the ground terminal. After frame de-framing, the return message is transmitted to the communication APP via Bluetooth to display service confirmation information.

[0124] The following are the specific parameters for the waveform and frame structure design in this embodiment.

[0125] 1. Waveform parameters: Communication system: DSSS-BPSK; Speed: 3 adjustable levels; Spread ratio: 3 adjustable levels; Forming method: root-lifted cosine; Channel coding and decoding: convolutional codes, LDPC codes.

[0126] 2. Frequency-selective frame structure Figure 6 This is a schematic diagram of the structure of the frequency-selective frame provided by the present invention, as shown below. Figure 6As shown, the frequency-selective frame is a service frame that is transparently forwarded from the ground equipment to the terminal via satellite. It is entirely spread by all-1 symbols and has not undergone channel coding. The terminal can poll and capture the frequency points f1~f7 that are accessible by the frequency-selective frame, and determine the coverage beam of its geographical location based on the capture results, and select a suitable frequency point for service communication.

[0127] 3. Service Frame Structure Figure 7 This is a schematic diagram of the structure of the service frame provided by the present invention, as shown below. Figure 7 As shown, a service frame consists of a pilot header, a frame identifier, a service segment, and multiple data segments. The pilot header is spread using all-1 symbols and is not channel-coded. The frame synchronization header is a preset small m-sequence, also not channel-coded, used to separate the pilot header and the service segment as an isolation identifier. The service segment contains configuration parameters for service frame transmission, including frame type, rate level, source ID, and number of data packets. The service segment uses convolutional coding. The data segments contain MAC layer frame information and valid transmitted data, have three rate levels, and use LDPC coding.

[0128] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Those skilled in the art can understand and implement this without any creative effort.

[0129] Through the above description of the embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus necessary general-purpose hardware platforms, and of course, it can also be implemented by hardware. Based on this understanding, the above technical solutions, in essence or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods described in the various embodiments or some parts of the embodiments.

[0130] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An unauthorized satellite covert communication system, characterized in that, include: User terminal equipment, ground terminal equipment, and transparent relay satellites; The user terminal equipment includes a communication application and a satellite communication terminal; The communication application is used to configure service parameters and transmit service signals to the satellite communication terminal via Bluetooth; the satellite communication terminal performs baseband signal processing and transmission power adjustment on the service signals based on the service parameters configured by the communication application, and sends the service signals after baseband signal processing and transmission power adjustment to the ground terminal equipment. The ground terminal equipment is used to receive and parse the service signals sent by the user terminal equipment, generate a response signal, and perform frequency conversion and amplification on the response signal, and send the frequency conversion and amplified response signal to the user terminal equipment. The satellite communication terminal is also used to receive the echo transmission signal sent by the ground terminal equipment, deframe the echo transmission signal, and transmit the deframed echo transmission signal to the communication application via Bluetooth; The transparent relay satellite is used to transparently relay signals exchanged between the user terminal equipment and the ground terminal equipment according to a preset mapping relationship.

2. The unauthorized satellite covert communication system according to claim 1, characterized in that, The ground terminal equipment is also used for: Based on satellite channel communication capabilities, frequency selection frames are periodically sent to multiple candidate frequency points through a polling mechanism; The user terminal device is specifically used for: The frequency selection frames sent by the ground terminal device are captured in a polling manner at the multiple candidate frequency points; The target frequency is selected based on the capture result of the frequency selection frame; the target frequency is used to transmit the service signal.

3. The unauthorized satellite covert communication system according to claim 1, characterized in that, The satellite communication terminal is specifically used for: The service signals are framed to generate service frames; The service frame is sequentially subjected to convolutional coding, low-density parity-check coding (LDPC), direct sequence spread spectrum (DSSS), and binary phase shift keying (BPSK) modulation operations to obtain the service signal after baseband signal processing.

4. The unauthorized satellite covert communication system according to claim 1 or 3, characterized in that, The satellite communication terminal is specifically used for: The transmission power of the service signal after baseband signal processing is dynamically adjusted based on the noise floor of the satellite channel.

5. The unauthorized satellite covert communication system according to claim 3, characterized in that, The service frame consists of a pilot header, a frame synchronization header, a service segment, and multiple data segments. The pilot header is formed by spreading with all-1 symbols; The frame synchronization header is a preset m-sequence used to separate the pilot header from the service segment; The service segment contains information related to the service parameters, and the service segment uses convolutional coding. The data segment contains frame information from the Media Access Control (MAC) layer and valid transmission data. The data segment has multiple rate levels and uses LDPC encoding.

6. The unauthorized satellite covert communication system according to claim 1, characterized in that, The ground-based equipment includes an antenna system, a radio frequency transceiver unit, a signal processor, and a host computer. The antenna system is connected to the signal processor through the radio frequency transceiver unit, and the signal processor communicates with the host computer through the network port; The host computer is used to parse the service signals processed by the signal processor and generate the return command configuration; The signal processor is used to generate a callback transmission signal based on the callback configuration and send it to the radio frequency transceiver unit, and to perform frame deframe processing on the service signal processed by the radio frequency transceiver unit. The radio frequency transceiver unit is used to amplify the service signals and the echo transmission signals sent by the user terminal equipment. The antenna system is used to convert the service signal sent by the user terminal equipment and send it to the radio frequency transceiver unit, and to convert the amplified echo transmission signal from the radio frequency transceiver unit and send it to the user terminal equipment.

7. A communication method, characterized in that, Applied to any one of claims 1 to 6, the unauthorized satellite covert communication system includes: Using the user terminal equipment, based on the service parameters configured in the communication application, the service signal is processed in baseband and the transmission power is adjusted. The service signal after baseband signal processing and transmission power adjustment is then sent to the ground terminal equipment. The ground terminal equipment receives and parses the service signals sent by the user terminal equipment, generates a response signal, performs frequency conversion and amplification on the response signal, and sends the frequency conversion and amplification response signal to the user terminal equipment. The user terminal device deframes the echo transmission signal and transmits the deframed echo transmission signal to the communication application via Bluetooth. The signals exchanged between the user terminal equipment and the ground terminal equipment are transparently forwarded by a transparent relay satellite according to a preset mapping relationship.

8. The communication method according to claim 7, characterized in that, The method further includes: Based on satellite channel communication capabilities, the ground-based equipment periodically sends frequency selection frames to multiple candidate frequency points through a polling mechanism. The user terminal device polls and captures the frequency selection frames sent by the ground terminal device at the multiple candidate frequency points. The user terminal device selects a target frequency point based on the capture result of the frequency selection frame; the target frequency point is used to transmit the service signal.

9. The communication method according to claim 7, characterized in that, Baseband signal processing is performed on the service signals, including: The service signals are framed to generate service frames; The service frame is sequentially subjected to convolutional coding, low-density parity-check coding (LDPC), direct sequence spread spectrum (DSSS), and binary phase shift keying (BPSK) modulation operations to obtain the service signal after baseband signal processing.

10. The communication method according to claim 7 or 9, characterized in that, Baseband signal processing and transmit power adjustment for service signals, including: The transmission power of the service signal after baseband signal processing is dynamically adjusted based on the noise floor of the satellite channel.

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