Covert communication method and device based on public signal carrying

Abstract

A covert communication method and device based on public signal carrying belong to the field of satellite communication, in the embodiment, covert signals are carried in non-cooperative public signals for carrying transmission, no negotiation relation exists between signal sending ends, the carried public signal receiving and sending ends do not know the existence of the covert signals, and the transmission safety of the covert signals is ensured; extra spectrum resources are not needed when the hidden signal is carried by the carried public signal; determining that the signal-to-noise ratio for demodulating the carried public signal is not less than a preset signal-to-noise ratio threshold and the detection probability of the monitoring end is less than a preset detection probability threshold according to the carried public signal; the packet length, the transmitting power and the transmission rate of the hidden signal meet the communication quality requirement that the demodulation bit error rate of the hidden signal is smaller than a preset bit error rate threshold value, so that the transmission quality of the carried public signal and the transmission concealment of the hidden signal are ensured; and a basis is provided for maximizing the hidden transmission rate.

Description

Technical Field

[0001] This article relates to satellite communication technology, and more particularly to a method and device for covert communication based on public signals. Background Technology

[0002] Satellite communication boasts numerous advantages, including wide coverage, large communication capacity, high transmission quality, and flexible signal configuration, leading to its widespread application in communication, positioning, and navigation. However, satellite communication signals are easily exposed to unauthorized interceptors during propagation in wide-area open space, posing security risks such as vulnerability to detection or interception by malicious users and potential information leakage. Covert communication, a low-probability-of-detection communication method, reduces the probability of detection by unauthorized users during transmission through physical layer technologies such as encoding, modulation, and waveform design of the transmitted signal. Compared to security technologies based on information complexity, it can ensure the security of the communication process at its source, making it a crucial technology that urgently needs research and development in future wireless communication.

[0003] The implementation of covert communication in related technologies mainly relies on spread spectrum communication technology, which requires additional spectrum resources and is difficult to cope with the resource-scarce space-to-ground communication scenarios. Furthermore, covert communication is not efficient in terms of covertness, and the effective covert transmission capacity is very limited, making it difficult to improve covertness while ensuring communication performance. In summary, how to improve the efficiency of spectrum resource utilization and covert communication capabilities in space-to-ground covert communication to meet the challenges of covert transmission in satellite communication has become an issue that needs to be addressed. Summary of the Invention

[0004] This application provides a method for covert communication based on publicly available signals, including: The covert signal transmitter selects a public signal to be carried from one or more pre-determined candidate public signals. There is no negotiation service between the candidate public signal and the covert signal. The transmitters of each candidate public signal and the transmitters of each covert signal are within the communication coverage area of ​​the same relay satellite. The receivers of each candidate public signal and the receivers of each covert signal are within the communication coverage area of ​​the same relay satellite. Based on the determined publicly available signal being carried, the packet length, transmission power, and maximum covert transmission rate of the covert signal are determined. The determined packet length, transmission power, and maximum covert transmission rate of the covert signal enable the covert signal obtained by the covert signal receiver from the publicly available signal to meet predetermined communication quality requirements. The communication quality requirements include: the signal-to-noise ratio of the demodulated publicly available signal at the covert signal receiver is greater than or equal to a predetermined signal-to-noise ratio threshold; the detection probability at the listening end is less than a predetermined detection probability threshold; and the demodulation bit error rate of the covert signal is less than a predetermined bit error rate threshold. The covert signal transmitter sends a covert signal to the relay satellite according to the determined packet length, transmission power and maximum covert transmission rate. The covert signal is carried on top of the public signal during the communication transmission through the relay satellite.

[0005] On the other hand, embodiments of this application also provide a computer storage medium storing a computer program, which, when executed by a processor, implements the aforementioned method for covert communication based on publicly available signals.

[0006] Furthermore, embodiments of this application also provide a terminal, including: a memory and a processor, wherein the memory stores a computer program; wherein, The processor is configured to execute computer programs in memory; When the computer program is executed by the processor, it implements the covert communication method based on public signals as described above.

[0007] Furthermore, embodiments of this application provide a method for covert communication based on publicly available signals, comprising: The covert signal receiver receives a publicly transmitted signal carrying a covert signal from a relay satellite; The received public signal is processed by serial interference cancellation method to obtain the hidden signal carried in the public signal. The public signal to be carried is obtained by the covert signal receiver through the following process: from one or more pre-determined candidate public signals, the public signal to be carried is selected for carrying the covert signal. There is no negotiation service between the candidate public signal and the covert signal, and the transmitter of each candidate public signal and the transmitter of each covert signal are within the communication coverage of the same relay satellite, and the receiver of each candidate public signal and the receiver of each covert signal are within the communication coverage of the same relay satellite.

[0008] In this embodiment, the covert signal is transmitted by being carried within the carried public signal. Regardless of which candidate public signal is selected as the carried public signal, it can be ensured that there is no negotiation relationship between the transmitter of the covert signal and the transmitter of the carried public signal. Therefore, neither the transmitter nor the receiver of the carried public signal is aware of the existence of the covert signal, ensuring the security of data transmission via the carried public signal carrying the covert signal. Transmitting the covert signal by carrying it within the carried public signal does not require additional spectrum resources, improving spectrum efficiency and the universality of covert signal communication transmission. Based on the determined carried public signal... The covert signal is carried by a public signal. The signal-to-noise ratio (SNR) of the carried public signal is determined to be greater than or equal to a preset SNR threshold at the receiver, the detection probability at the listening end is less than a preset detection probability threshold, and the demodulation bit error rate (BER) of the covert signal is less than a preset BER threshold. The packet length, transmission power, and transmission rate of the covert signal are determined to ensure the transmission quality of the carried public signal and the covert signal transmission covertness. Furthermore, based on the SNR of the carried public signal and the BER of the covert signal transmission, a basis is provided for maximizing the covert transmission rate.

[0009] Other features and advantages of this application will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the application. Other advantages of this application can be realized and obtained by means of the solutions described in the description and the accompanying drawings. Attached Figure Description

[0010] The accompanying drawings are used to provide an understanding of the technical solutions of this application and constitute a part of the specification. They are used together with the embodiments of this application to explain the technical solutions of this application and do not constitute a limitation on the technical solutions of this application.

[0011] Figure 1 This is a flowchart of a method for covert communication based on a public signal, according to Embodiment 1 of this disclosure; Figure 2 This is a schematic diagram of the transmission time slot of the concealed signal carried on the disclosed signal according to an embodiment of this disclosure; Figure 3 This is a flowchart of another method for covert communication based on publicly disclosed signals, according to an embodiment of this disclosure; Figure 4 The concealed signal transmission power and coded packet length are specified in the embodiments of this disclosure. Relationship diagram; Figure 5 A schematic diagram illustrating the relationship between the demodulation bit error rate of concealed signals and the effective concealment capacity; Figure 6 This is a structural block diagram of a device for covert communication based on a public signal, according to an embodiment of this disclosure. Detailed Implementation

[0012] This application describes several embodiments, but these descriptions are exemplary and not restrictive, and it will be apparent to those skilled in the art that many more embodiments and implementations are possible within the scope of the embodiments described herein. Although many possible combinations of features are shown in the drawings and discussed in the detailed description, many other combinations of the disclosed features are also possible. Unless specifically limited, any feature or element of any embodiment may be used in combination with, or may replace, any feature or element of any other embodiment.

[0013] This application includes and contemplates combinations of features and elements known to those skilled in the art. The embodiments, features, and elements disclosed in this application can also be combined with any conventional features or elements to form unique inventive solutions. Any feature or element of any embodiment can also be combined with features or elements from other inventive solutions to form another unique inventive solution. Therefore, it should be understood that any feature shown and / or discussed in this application can be implemented individually or in any suitable combination.

[0014] Furthermore, in describing illustrative embodiments, the specification may have presented methods and / or processes as a specific sequence of steps. However, the method or process should not be limited to the specific order of steps described herein, to the extent that it does not depend on such a specific order. As will be understood by those skilled in the art, other sequences of steps are also possible. Therefore, the specific order of steps set forth in the specification should not be construed as a limitation on the technical solution. Moreover, the method and / or process should not be limited to the steps performed in the written order; those skilled in the art will readily understand that these orders can be varied and still remain within the spirit and scope of the embodiments of this application.

[0015] Figure 1 This is a flowchart of a method for covert communication based on publicly disclosed signals, as described in Embodiment 1 of this disclosure. Figure 1 As shown, it includes: Step 101: The covert signal transmitter selects a public signal to be carried from one or more pre-determined candidate public signals. There is no negotiation service between the candidate public signal and the covert signal. The transmitter of each candidate public signal and the transmitter of each covert signal are within the communication coverage of the same relay satellite. The receiver of each candidate public signal and the receiver of each covert signal are within the communication coverage of the same relay satellite. Step 102: Determine the packet length, transmission power, and maximum covert transmission rate of the covert signal. The determined packet length, transmission power, and maximum covert transmission rate of the covert signal enable the covert signal obtained by the covert signal receiver from the carried public signal to meet predetermined communication quality requirements. The communication quality requirements include: the signal-to-noise ratio of the demodulated public signal at the covert signal receiver is greater than or equal to a predetermined signal-to-noise ratio threshold; the detection probability at the listening end is less than a predetermined detection probability threshold; and the demodulation bit error rate of the covert signal is less than a predetermined bit error rate threshold. Step 103: The covert signal transmitter sends a covert signal to the relay satellite according to the determined packet length, transmission power and maximum covert transmission rate. The covert signal is carried on the public signal during the communication transmission through the relay satellite.

[0016] In this embodiment, the covert signal is transmitted by being carried within the carried public signal. Regardless of which candidate public signal is selected as the carried public signal, it can be ensured that there is no negotiation relationship between the transmitter of the covert signal and the transmitter of the carried public signal. Therefore, neither the transmitter nor the receiver of the carried public signal is aware of the existence of the covert signal, ensuring the security of data transmitted by carrying the covert signal within the carried public signal. Transmitting the covert signal by carrying it within the carried public signal does not require additional spectrum resources, improving spectrum efficiency and the universality of covert signal communication transmission. According to the determined... The communication quality requirements for the concealed signal are determined by the following: the signal-to-noise ratio (SNR) of the concealed signal demodulated by the concealed signal receiver is greater than or equal to a preset SNR threshold; the detection probability at the listening end is less than a preset detection probability threshold; and the demodulation bit error rate (BER) of the concealed signal is less than a preset BER threshold. The packet length, transmission power, and transmission rate of the concealed signal ensure the transmission quality of the concealed signal and the concealment of the concealed signal transmission. Furthermore, based on the SNR of the concealed signal demodulated and the BER of the concealed signal transmission, a foundation is provided for maximizing the concealed transmission rate.

[0017] In this embodiment of the disclosure, the candidate public signal and the covert signal do not have any negotiated business, that is, the candidate public signal and the covert signal are non-cooperative, and the candidate public signal is a non-cooperative public signal of the covert signal; the candidate public signal in this embodiment of the disclosure can be determined based on related technologies, for example, based on the geographical locations of the public signal's sending end, the public signal's receiving end, the covert signal's sending end, and the covert signal's receiving end.

[0018] This embodiment of the disclosure increases the detection difficulty at the listening end by mounting the concealed signal on the high-power public signal being transmitted in the transmission system, effectively concealing the concealed signal and thereby improving the effective concealment capacity and concealed transmission efficiency; the concealed signal is randomly mounted on the public signal, and by utilizing the uncertainty of residual errors generated during the demodulation and elimination process of the public signal, the effective concealment capacity is improved by controlling the transmission power of the concealed signal.

[0019] To facilitate understanding of the embodiments of this disclosure, the relevant models of the monitoring end are briefly described below: Unauthorized eavesdropping detection model: To achieve optimal detection performance, after receiving information, the unauthorized eavesdropping party first performs public signal cancellation, and then uses an optimal detector (i.e., an energy detector) for hypothesis testing; where, Public signal cancellation includes: the illegal eavesdropping end first uses its knowledge of public signals to eliminate them using a serial interference cancellation algorithm; however, due to the uncertainty inherent in public signal cancellation, imperfect cancellation occurs, resulting in information remaining after public signal cancellation. It can be represented as: ; In the formula, and These represent the presence and absence of concealed information, respectively. The channel response of the open signal transmitter and the covert signal detector. The recovery of the public signal depends primarily on the distance between the receiving parties, where i represents the i-th transmission time slot. This represents the public signal of the i-th time slot. This represents the concealed signal in the i-th time slot. This represents the noise from the listener in the i-th time slot.

[0020] Assumption verification includes: the illegal eavesdropping end uses an energy detector to measure the observed signal energy. With detection threshold To compare and determine whether concealed information has been transmitted, the signal energy expression is as follows: ; In the formula, This indicates that the judgment result is that a covert signal transmission occurred. This indicates that the judgment result is that no covert signal transmission occurred. This indicates the information after the monitoring party has publicly disclosed the signal. The threshold value for the eavesdropping energy detector is represented by , and 'n' represents the length of the coded block of the concealed signal. There are two types of false detections in the detection of illegal eavesdropping devices: false alarm rate and false alarm rate. and false alarm rate , respectively represented as: ; ; The probability of incorrect detection of an unauthorized eavesdropping end is: To ensure the system's concealment requirements, the probability of false detection by the unauthorized eavesdropping party needs to be sufficiently high. In one exemplary instance, before the concealed signal transmitter selects the carried public signal from one or more predetermined candidate public signals, the method of this disclosure embodiment further includes: The covert signal transmitter encodes the original covert information into packets with a length of [missing information]. The hidden signal.

[0021] In this embodiment of the disclosure, the covert signal transmitter can encode the original covert information into a packet length. The hidden signal.

[0022] In one exemplary instance, this disclosure embodiment is carried by a disclosed signal via Figure 2 The method of this disclosure further includes transmitting data through the T transmission time slots shown in the figure: Determine whether to transmit a covert signal in each transmission time slot of the carried public signal, so as to carry the covert signal through the carried public signal in the determined transmission time slot; The transmission time slot for sending the covert signal is stored in the key of the covert signal so that the covert signal receiver can parse the covert signal according to the key.

[0023] This embodiment of the disclosure transmits the covert signal by embedding it in the time slot of the public signal and using a key, thus ensuring the security of the covert communication. This embodiment of the disclosure can also refer to the communication standards in related technologies to share the transmission time slot for transmitting the covert signal at the covert signal transmitter and the covert signal receiver.

[0024] In one exemplary embodiment, this disclosure can determine with probability p whether a covert signal is transmitted in each transmission time slot carrying the public signal. This disclosure can also employ other methods to determine whether a covert signal is transmitted in each transmission time slot carrying the public signal.

[0025] After the covert signal is emitted in this embodiment, the transmitter carrying the public signal simultaneously emits the public signal. There is no need to process the covert signal and the public signal carrying it. The covert signal is naturally carried over the public signal and sent to the relay satellite.

[0026] In some exemplary instances, the transmission power of the covert signal in this disclosure embodiment is The concealed signal can be represented as The transmission power of the publicly available signal carried is The publicly available signal can be represented as: ,in, The public signal transmitted from the carrier signal transmitter to the relay satellite can be represented as: (The public signal is an independent, identically distributed Gaussian random variable.) ; In the formula, , i represents the i-th transmission time slot, This indicates that the publicly transmitted signal in the current transmission time slot carries a hidden signal. This indicates that the currently transmitted time slot carries a public signal but not a concealed signal.

[0027] In one exemplary instance, the method of this disclosure embodiment further includes: Based on a pre-determined detection probability threshold of the listening end Demodulate the lowest signal-to-noise ratio of the publicly available signal. Determine the transmission power of the concealed signal. The constraints to be met include the minimum value of the first term (which is independent of the packet length) and the second term (which is related to the packet length). The first term is that the transmission power must ensure the reliable transmission of the public signal carried by the concealed signal. The second term is that the transmission power must ensure the concealment of the concealed signal transmission. In the second term, the larger the packet length, the smaller the transmission power. The minimum signal-to-noise ratio of the public signal being demodulated is the signal-to-noise ratio threshold. Demodulation bit error rate based on a predetermined concealed signal Determine the maximum covert transmission rate of the covert signal. The constraints to be met are determined based on the packet length and the transmit power. The higher the transmit power, the higher the maximum covert transmission rate. The higher the packet length, the higher the maximum covert transmission rate. Based on the constraints that the transmit power of the concealed signal must meet and the constraints that the transmission rate of the maximum concealed signal must meet, the optimal packet length and transmit power can be determined through a parameter optimization selection algorithm, and then the maximum concealed transmission rate of the concealed signal can be determined based on the determined packet length and transmit power.

[0028] This disclosure embodiment can refer to related technologies, and in order to ensure the concealment of covert signal transmission, a detection probability of the listening end is set. (Detection probability threshold at the monitoring end); To ensure the reliability of the transmission of the public signal, a minimum signal-to-noise ratio (SNR) requirement for demodulating the public signal is set. (Signal-to-noise ratio threshold); To ensure the reliability of concealed signal recovery, set the demodulation bit error rate of the concealed signal. ; Detect probability through the listening end Signal-to-noise ratio threshold Transmission power of covert signals Constraints were imposed on the demodulation bit error rate of the concealed signal. Transmission rate of covert signals Constraints were imposed.

[0029] In this embodiment of the disclosure, under the framework of covert communication carried by the disclosed signal, the probability of detection by an eavesdropper is less than a detection probability threshold. Set the minimum signal-to-noise ratio (SNR) requirement for demodulating the publicly available signal. Demodulation bit error rate of concealed signals When considering constraints, select the optimal grouping length. And the maximum covert signal transmission power within the constraints. .

[0030] This disclosure assumes that both the concealed signal and the carried public signal follow a Gaussian distribution, and the channel is an additive white Gaussian noise (AWGN) channel. Under these assumptions, the method of this disclosure embodiment can be quantitatively analyzed: assuming the listening end eliminates interference from the carried public signal, an energy detector and hypothesis testing algorithm are applied to determine whether a concealed signal is being transmitted in the system. The decoding criterion adopts the ML decoding rule, for a given detection probability index... > 0, to ensure the covert transmission of signals, the detection error probability of the detection party must be guaranteed. At this point, to ensure the covert transmission of the signal, the transmission power of the covert signal is... Must meet: ; In the formula, Indicates the detection probability threshold. The channel impulse response at the monitoring end is given, and n represents the packet length of the concealed signal. This represents the noise power at the receiver of the concealed signal. This represents the demodulation bit error rate of the concealed signal receiver on the overlay of the publicly transmitted signal. The transmission power of the publicly available signal being carried.

[0031] In one exemplary instance, for a concealed signal carried by a publicly transmitted signal, the reliability of the transmitted publicly transmitted signal should be guaranteed, meaning that the normal recovery of the transmitted publicly transmitted signal should not be affected; a signal-to-noise ratio (SNR) of demodulated transmitted publicly transmitted signal greater than or equal to a SNR threshold is defined as... The signal-to-noise ratio (SNR) of a covert signal receiver is used to measure its reception quality, which can be expressed as: ; To ensure reliable transmission of a concealed signal carried by a publicly available signal, the transmission power of the concealed signal must meet the following requirements: ; in, The channel coefficients are those of the publicly available signal being carried. This indicates the lowest signal-to-noise ratio (SNR) of the demodulated signal. The channel coefficients are those of the publicly available signal being carried. This indicates the noise power at the receiver of the public signal.

[0032] In summary, to simultaneously achieve the covert transmission of the concealed signal and the reliable transmission of the publicly available signal carrying the covert signal, the transmission power of the covert signal in this embodiment must meet the following requirements: ; In the formula, This is to ensure the reliable transmission of overt signals carrying covert signals. The conditions that the transmit power of the concealed signal must meet are: the equivalent residual interference coefficient of the publicly carried signal, which is predetermined based on the coding and modulation method of the publicly carried signal; This indicates the conditions that the transmission power of the covert signal must meet to ensure the covert transmission of the covert signal.

[0033] For a given hidden signal demodulation bit error rate index To ensure the reliability of covert signal transmission, the demodulation bit error rate during covert signal demodulation must be guaranteed. Both the concealed signal and the carried public signal follow a Gaussian distribution. When the channel is an additive white Gaussian noise (AWGN) channel, assuming the concealed signal decoding criterion uses the ML decoding rule, according to the finite-length channel coding theorem, the transmission rate of the concealed signal is... Must meet: ; in, This indicates the signal-to-noise ratio (SNR) of the concealed signal reception. , The channel coefficients for the concealed signal. The demodulation bit error rate of the concealed signal. Here, represents the channel coefficients of the covert signal, and n represents the packet length of the covert signal. This indicates that the demodulation bit error rate of the concealed signal is guaranteed to not exceed [a certain value]. The minimum required signal-to-noise ratio threshold.

[0034] In this embodiment of the present disclosure, the covert signal is carried on the carried public signal and sent to a relay satellite. The relay satellite forwards the received carried public signal. After the covert signal is carried on the carried public signal, it is forwarded to the covert signal receiving end by the relay satellite, thereby realizing the transmission of the covert signal from the sending end to the receiving end.

[0035] This disclosure also provides a computer storage medium storing a computer program, which, when executed by a processor, implements the aforementioned method for covert communication based on publicly available signals.

[0036] This disclosure also provides a terminal, including: a memory and a processor, wherein the memory stores a computer program; wherein, The processor is configured to execute computer programs in memory; When a computer program is executed by a processor, it implements the covert communication method described above, which is based on public signals.

[0037] Figure 3 This is a flowchart of another method for covert communication based on publicly disclosed signals, as described in this embodiment. Figure 3 As shown, it includes: Step 301: The covert signal receiver receives the publicly transmitted signal carrying the covert signal from the relay satellite; Step 302: Process the received carried public signal using a serial interference cancellation method to obtain the concealed signal carried in the carried public signal; The public signal to be carried is obtained by the covert signal receiver through the following process: from one or more pre-determined candidate public signals, the public signal to be carried is selected for carrying the covert signal. There is no negotiation service between the candidate public signal and the covert signal, and the transmitter of each candidate public signal and the transmitter of each covert signal are within the communication coverage of the same relay satellite, and the receiver of each candidate public signal and the receiver of each covert signal are within the communication coverage of the same relay satellite.

[0038] In this embodiment of the present disclosure, after the concealed signal receiver receives the carried public signal, it processes the carried public signal by a serial interference cancellation method to obtain the concealed signal carried by the carried public signal.

[0039] Based on related technologies, the embodiments disclosed herein allow the covert signal receiver to determine the carried public signal either through a sharing method or by pre-storing.

[0040] The transmission rate of the concealed signal in the embodiments of this disclosure The signal-to-noise ratio at the covert signal receiver Group length and bit error rate requirements (The demodulation error rate of the concealed signal) is related to the transmission time slot in which the concealed signal is transmitted. After the concealed signal receiver performs serial interference cancellation on the received signal, it obtains the concealed signal.

[0041] The disclosed signal transmitted from the transmitter to the relay satellite in this embodiment can be represented as: ; In the formula, , i represents the i-th transmission time slot, This indicates that the publicly transmitted signal in the current transmission time slot carries a hidden signal. This indicates that the currently transmitted time slot carries a public signal but not a concealed signal; Correspondingly, the covert signal receiver receives the carried public signal as The expression is: ; In the transmission time slot for transmitting covert signals, the covert signal receiver receives the carried public signal as follows: ; In one exemplary instance, the covert signal receiver of this disclosure embodiment can employ a serial interference cancellation algorithm to eliminate the public signal and obtain the covert signal at the receiving end. Decoding the covert information by parsing the covert signal at the receiving end includes: Channel coefficients obtained from channel estimation Based on this, the publicly available signals are demodulated. The expression representing the estimation of a concealed signal carried by a publicly displayed signal is as follows: ; in, This indicates that the estimation of the publicly available signal being carried is correct. ; This indicates an error in the estimation of the publicly available signal; the event... The probability of this occurring is also known as the bit error rate (BER) of demodulating a publicly available signal, denoted as . , Signal-to-noise ratio compared to the publicly available signal And it is related to the selected modulation and coding modes.

[0042] Based on the expressions of the public signal without concealed signals and the public signal with concealed signals, the concealed signal is obtained after performing serial interference cancellation processing on the public signal with concealed signals. The concealed signal reception failure and subsequent recovery of the concealed signal in this embodiment of the disclosure can be represented as follows: ; In this embodiment of the present disclosure, the covert signal receiver performs serial interference cancellation on the received public signal to obtain the covert signal carried on the public signal, and demodulates the obtained covert signal to obtain covert information.

[0043] Based on the aforementioned constraints on transmission power and transmission rate, when the distance between the satellite and the onboard public signal receiver... The distance between the relay satellite and the listening end Considering only free space transmission loss and noise power When the results of this embodiment are as follows: at different detection probability thresholds Below, concealed signal transmission power With group length Relationship such as Figure 4 As shown in the figure, curve 4-1 represents the detection probability threshold. Covert signal transmission power at =0.05 With group length The relationship is shown in curve 4-2, which represents the detection probability threshold. Covert signal transmission power at =0.01 With group length The relationship is shown in curve 4-3, which represents the detection probability threshold. Covert signal transmission power at =0.005 With group length The relationship is shown in curve 4-4, which represents the detection probability threshold. Covert signal transmission power at =0.001 With group length The relationship when the detection probability threshold When fixed, for longer group lengths Due to the limitations imposed by concealment constraints, the transmission power of concealed signals is limited. With group length The decrease is due to the increase; while for shorter group lengths... To ensure that the demodulation of the overt signals is not interfered with, the transmission power of the covert signals is... It will remain a constant value; under different reliability indicators For each (demodulation bit error rate of the concealed signal), there exists an optimal block length. Corresponding to the maximum effective concealment capacity ,like Figure 5 As shown, curve 5-1 represents Effective concealment capacity at =0.01 With the length of the encoded block The relationship is represented by curve 5-2. Effective concealment capacity at =0.005 With the length of the encoded block The relationship is represented by curve 5-3. Effective concealment capacity at =0.001 With the length of the encoded block The relationship, with reliability indicators The reduction in reliability, due to stricter constraints, results in a decrease in the optimal effective concealment capacity. Reduced; however, excessively high reliability indicators This will also reduce its corresponding optimal effective concealment capacity. This is because when the encoded block length... When the signal-to-interference-plus-noise ratio (SIR) of the received public signal is relatively small, it is subject to the lower limit of the SIR. This limitation restricts the power of covert signal transmission. The increase in [something], in turn, limits the effective concealment capacity. .

[0044] This disclosure also provides a computer storage medium storing a computer program, which, when executed by a processor, implements the aforementioned method for covert communication based on publicly available signals.

[0045] This disclosure also provides a terminal, including: a memory and a processor, wherein the memory stores a computer program; wherein, The processor is configured to execute computer programs in memory; When a computer program is executed by a processor, it implements the covert communication method described above, which is based on public signals.

[0046] Figure 6 This is a structural block diagram of a device for covert communication based on a publicly disclosed signal, as described in an embodiment of this disclosure. Figure 6 As shown, it includes: a selection unit, a parameter determination unit, and a transmission unit; wherein, The selection unit is configured to: select a public signal to be carried for carrying a covert signal from one or more pre-determined candidate public signals, wherein there is no negotiated service between the candidate public signal and the covert signal, and the transmitter of each candidate public signal and the transmitter of the covert signal are within the communication coverage of the same relay satellite, and the receiver of each candidate public signal and the receiver of the covert signal are within the communication coverage of the same relay satellite. The parameter determination unit is set to determine the packet length, transmission power, and maximum covert transmission rate of the covert signal. The determined packet length, transmission power, and maximum covert transmission rate of the covert signal enable the covert signal obtained by the covert signal receiver from the carried public signal to meet the predetermined communication quality requirements. The communication quality requirements include: the signal-to-noise ratio of the demodulated public signal by the covert signal receiver is greater than or equal to a predetermined signal-to-noise ratio threshold; the detection probability of the listening end is less than a predetermined detection probability threshold; and the demodulation bit error rate of the covert signal is less than a predetermined bit error rate threshold. The transmitting unit is configured to transmit a covert signal to the relay satellite according to the determined packet length, transmission power and maximum covert transmission rate, wherein the covert signal is carried on top of the public signal during the communication transmission through the relay satellite.

[0047] In one exemplary instance, the carried signal in this embodiment of the disclosure is transmitted through T transmission time slots, and the selection unit in this embodiment of the disclosure is further configured as follows: Determine whether to transmit a covert signal in each transmission time slot of the carried public signal, so as to carry the covert signal through the carried public signal in the determined transmission time slot; The transmission time slot for sending the covert signal is stored in the key of the covert signal so that the covert signal receiver can parse the covert signal according to the key.

[0048] In one exemplary instance, the communication quality requirements in this disclosure embodiment further include: The detection probability of the listening end is less than the preset detection probability threshold. Demodulation bit error rate of concealed signals It is less than the preset bit error rate threshold.

[0049] In one exemplary instance, the parameter unit of this disclosure is set as follows: Based on detection probability threshold Demodulate the lowest signal-to-noise ratio of the publicly available signal. Determine the transmission power of the concealed signal. The constraints to be met include the minimum value of the first term (which is independent of the packet length) and the second term (which is related to the packet length). The first term is that the transmission power must ensure the reliable transmission of the public signal carrying the concealed signal. The second term is that the transmission power must ensure the concealment of the concealed signal transmission. In the second term, the larger the packet length, the smaller the transmission power. The minimum signal-to-noise ratio of the demodulated public signal is the preset signal-to-noise ratio threshold of the demodulated public signal. Demodulation bit error rate based on a predetermined concealed signal Determine the maximum covert transmission rate of the covert signal. The constraints to be met are determined based on the packet length and the transmit power. The higher the transmit power, the higher the maximum covert transmission rate. The higher the packet length, the higher the maximum covert transmission rate. Based on the constraints that the transmit power of the concealed signal must meet and the constraints that the transmission rate of the maximum concealed signal must meet, the optimal packet length and transmit power are determined, and then the maximum concealed transmission rate of the concealed signal is determined based on the determined packet length and transmit power.

[0050] In one exemplary instance, when both the concealed signal and the carried public signal follow a Gaussian distribution, and the channel is an additive white Gaussian noise (AWGN) channel, the transmission power of the concealed signal in this embodiment satisfies: ; In the formula, This indicates the conditions that the transmission power of the concealed signal must meet to ensure the reliable transmission of the concealed signal over a publicly transmitted signal. This represents the transmission power of the covert signal, and n represents the packet length of the covert signal. This indicates the transmission power of the publicly disclosed signal. This indicates the lowest signal-to-noise ratio (SNR) of the demodulated signal. The channel coefficients are those of the publicly available signal being carried. Indicates the noise power at the receiver of the public signal; This indicates the conditions that the transmission power of a covert signal must meet to ensure its covert transmission. Indicates the detection probability threshold. The channel impulse response at the monitoring end is given, and n represents the packet length of the concealed signal. This represents the noise power at the receiver of the concealed signal. This represents the demodulation bit error rate of the concealed signal receiver on the overlay of the publicly transmitted signal. The equivalent residual interference coefficient of the public signal is predetermined based on the coding and modulation method of the public signal being carried.

[0051] In one exemplary instance, when both the concealed signal and the carried public signal follow a Gaussian distribution, and the channel is an additive white Gaussian noise (AWGN) channel, the transmission rate of the concealed signal in this embodiment of the disclosure is... satisfy: ; in, This indicates the received signal-to-noise ratio of the concealed signal. Let be the demodulation bit error rate of the concealed signal, and n represent the block length of the concealed signal. This indicates that the demodulation bit error rate of the concealed signal is guaranteed to not exceed [a certain value]. The minimum required signal-to-noise ratio threshold.

[0052] This disclosure also provides another covert communication apparatus, comprising: a receiving unit and a processing unit; wherein, The receiving unit is configured to receive publicly available signals carried by relay satellites. The processing unit is configured to process the received carried public signal using a serial interference cancellation method to obtain the concealed signal carried in the carried public signal; The public signal to be carried is obtained by the covert signal receiver through the following process: from one or more pre-determined candidate public signals, the public signal to be carried is selected for carrying the covert signal. There is no negotiation service between the candidate public signal and the covert signal, and the transmitter of each candidate public signal and the transmitter of each covert signal are within the communication coverage of the same relay satellite, and the receiver of each candidate public signal and the receiver of each covert signal are within the communication coverage of the same relay satellite.

[0053] It will be understood by those skilled in the art that all or some of the steps, systems, or apparatuses disclosed above, and their functional modules / units, can be implemented as software, firmware, hardware, or suitable combinations thereof. In hardware implementations, the division between functional modules / units mentioned above does not necessarily correspond to the division of physical components; for example, a physical component may have multiple functions, or a function or step may be performed collaboratively by several physical components. Some or all components may be implemented as software executed by a processor, such as a digital signal processor or microprocessor, or as hardware, or as an integrated circuit, such as an application-specific integrated circuit (ASIC). Such software may be distributed on a computer-readable medium, which may include computer storage media (or non-transitory media) and communication media (or transient media). As is known to those skilled in the art, the term "computer storage medium" includes volatile and non-volatile, removable and non-removable media implemented in any method or technology for storing information (such as computer-readable instructions, data structures, program modules, or other data). Computer storage media include, but are not limited to, RAM, ROM, EEPROM, flash memory or other memory technologies, CD-ROM, digital versatile disc (DVD) or other optical disc storage, magnetic cartridges, magnetic tape, disk storage or other magnetic storage devices, or any other medium that can be used to store desired information and can be accessed by a computer. Furthermore, it is well known to those skilled in the art that communication media typically contain computer-readable instructions, data structures, program modules, or other data in modulated data signals such as carrier waves or other transmission mechanisms, and may include any information delivery medium.

Claims

1. A method for covert communication based on piggybacking on a public signal, characterized in that, The method comprises the steps of: a covert signal sending terminal selects a carried public signal for carrying a covert signal from one or more predetermined candidate public signals, wherein the candidate public signals do not have a negotiated service with the covert signal, and the sending terminal of each candidate public signal and the sending terminal of the covert signal are within the communication coverage of the same relay satellite, and the receiving terminal of each candidate public signal and the receiving terminal of the covert signal are within the communication coverage of the same relay satellite; determining the packet length, transmission power and maximum covert transmission rate of the covert signal according to the determined carried public signal, wherein the determined packet length, transmission power and maximum covert transmission rate of the covert signal enable the covert signal received by the receiving terminal to meet the predetermined communication quality requirement, and the communication quality requirement comprises that the signal-to-noise ratio of the carried public signal demodulated by the receiving terminal is greater than or equal to a preset signal-to-noise ratio threshold, the detection probability of the listening terminal is less than a preset detection probability threshold, and the demodulation bit error rate of the covert signal is less than a preset bit error rate threshold; the covert signal sending terminal sends the covert signal to the relay satellite according to the determined packet length, transmission power and maximum covert transmission rate, wherein the covert signal is carried on the carried public signal in the process of communication transmission through the relay satellite.

2. The method of claim 1, wherein, The carried public signal is transmitted through T transmission time slots, and the method further comprises the steps of: determining whether the covert signal is sent in each transmission time slot of the carried public signal, so as to carry the covert signal on the carried public signal in the determined transmission time slot; storing the transmission time slot for sending the covert signal in the key of the covert signal, so that the receiving terminal of the covert signal parses the covert signal according to the key.

3. The method of claim 1, wherein, The determination of the packet length, transmission power and maximum covert transmission rate of the covert signal comprises the steps of: determining a constraint condition that the transmission power of the covert signal needs to meet based on the detection probability threshold and the minimum signal-to-noise ratio of the demodulated carried public signal, wherein the constraint condition comprises a first term irrelevant to the packet length and a second term related to the packet length, the first term is a constraint condition that the transmission power needs to meet to ensure the reliable transmission of the carried public signal carrying the covert signal, the second term is a constraint condition that the transmission power needs to meet to ensure the concealment of the covert signal transmission, the second term is smaller when the packet length is larger, and the minimum signal-to-noise ratio of the demodulated carried public signal is the preset signal-to-noise ratio threshold of the demodulated carried public signal; determining a constraint condition that the maximum covert transmission rate of the covert signal needs to meet based on the preset demodulation bit error rate of the covert signal, wherein the constraint condition is determined based on the packet length and the transmission power, and the maximum covert transmission rate is larger when the transmission power is larger and the packet length is larger; determining the optimal packet length and transmission power based on the constraint condition that the transmission power of the covert signal needs to meet and the constraint condition that the maximum covert transmission rate of the covert signal needs to meet, and then determining the maximum covert transmission rate of the covert signal based on the determined packet length and transmission power.

4. The method of claim 3, wherein, The covert signal and the carried public signal are subject to Gaussian distribution, and when a channel is an additive white Gaussian noise (AWGN) channel, the transmission power of the covert signal satisfies: ； In the formula, denotes the condition that the transmission power of the hidden signal needs to meet to ensure reliable transmission of the piggybacked open signal carrying the hidden signal, denotes the transmission power of the hidden signal, and n denotes the packet length of the hidden signal, denotes the transmission power of the piggybacked open signal, denotes the minimum signal-to-noise ratio for demodulating the piggybacked open signal, is the channel coefficient of the piggybacked open signal, denotes the noise power of the open signal receiver; is the equivalent residual interference coefficient of the piggybacked open signal determined in advance according to the encoding modulation mode of the piggybacked open signal; denotes the condition that the transmission power of the hidden signal needs to meet to ensure reliable transmission of the piggybacked open signal carrying the hidden signal, denotes the detection probability threshold, is the channel impulse response of the monitoring end, denotes the noise power of the hidden signal receiver, denotes the demodulation bit error rate of the piggybacked open signal by the hidden signal receiver.

5. The method of claim 3, wherein, The covert signal and the piggybacked open signal both obey Gaussian distribution, when a channel is an additive white Gaussian noise (AWGN) channel, a transmission rate of the covert signal satisfies: ； wherein denotes the received signal-to-noise ratio of the covert signal, denotes the demodulation error rate of the covert signal, n denotes the packet length of the covert signal, denotes the minimum signal-to-noise ratio threshold required to ensure that the demodulation error rate of the covert signal does not exceed the critical value.

6. A method of covert communication based on piggybacking on a public signal, characterized in that, The method comprises the steps of: The covert signal receiving end receives the carried public signal carrying the covert signal from the relay satellite; The received carried public signal is processed by a serial interference cancellation method to obtain the covert signal carried in the carried public signal; The carried public signal is obtained by the covert signal receiving end through the following processing: from one or more pre-determined candidate public signals, a carried public signal for carrying the covert signal is selected, the candidate public signals do not have a negotiated service with the covert signal, and the transmission end of each candidate public signal and the transmission end of the covert signal are within the communication coverage of the same relay satellite, and the receiving end of each candidate public signal and the receiving end of the covert signal are within the communication coverage of the same relay satellite.

7. A computer storage medium having stored therein a computer program, characterized in that, The computer program is executed by the processor to implement the method of covert communication based on a public signal carrying according to any one of claims 1 to 5 or 6.

8. A terminal, characterized by comprising: The method comprises the steps of: The memory and the processor, the memory has a computer program; wherein The processor is configured to execute the computer program in the memory; The computer program is executed by the processor to implement the method of covert communication based on a public signal carrying according to any one of claims 1 to 5 or 6.

9. An apparatus for covert communication, the apparatus comprising: The method comprises the steps of: The selection unit, the determination parameter unit and the transmission unit; wherein The selection unit is configured to select a carried public signal for carrying the covert signal from one or more pre-determined candidate public signals, wherein the candidate public signals do not have a negotiated service with the covert signal, and the transmission end of each candidate public signal and the transmission end of the covert signal are within the communication coverage of the same relay satellite, and the receiving end of each candidate public signal and the receiving end of the covert signal are within the communication coverage of the same relay satellite; The determination parameter unit is configured to determine the packet length, transmission power and maximum covert transmission rate of the covert signal according to the determined carried public signal, wherein the determined packet length, transmission power and maximum covert transmission rate of the covert signal enable the covert signal received by the covert signal receiving end from the carried public signal to satisfy the pre-determined communication quality requirement, the communication quality requirement includes: the signal-to-noise ratio of the covert signal receiving end demodulating the carried public signal is greater than or equal to a pre-set signal-to-noise ratio threshold, the detection probability of the listening end is less than a pre-set detection probability threshold, and the demodulation bit error rate of the covert signal is less than a pre-set bit error rate threshold, and the determined packet length and transmission power of the covert signal are used to determine the maximum covert transmission rate; The transmission unit is configured to transmit the covert signal to the relay satellite according to the determined packet length, transmission power and maximum covert transmission rate, wherein the covert signal is carried in the carried public signal during communication transmission by the relay satellite.

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