A limited packet length covert wireless communication method assisted by truncated interference

Abstract

A method for covert wireless communication of limited-length data packets assisted by truncated interference relates to the technical field of secure transmission of wireless network information. The system of the present invention includes a source node, a destination node, an interference node and a monitoring node, all of which are equipped with a single antenna and operate in half-duplex mode. When there is private information to be sent, the source node sends its encoded limited-length data packet to the destination node, and the monitoring node observes the wireless transmission environment to determine whether the source node has sent a private data packet to the destination node. The interference node determines its working state according to the channel gain between it and the destination node, and sends interference when the channel gain is less than a set threshold, otherwise it remains silent. While utilizing interference to enhance the concealment of communication, the present invention reduces its impact on the decoding of the destination node, thereby improving the covert transmission performance of limited-length data packets.

Description

Technical Field

[0001] The present invention relates to the technical field of wireless network information security transmission, and in particular to a limited packet length covert wireless communication method assisted by truncation interference. Background Art

[0002] The Internet of Things (IoT) connects all objects—people, machines, and objects—in a specific spatial environment on demand for information transmission and collaborative interaction, giving rise to a vast array of emerging military and civilian applications, including smart transportation, e-health, and battlefield situation monitoring. Unlike traditional human-centric networks, IoT nodes typically transmit relatively small amounts of information, such as environmental information (such as temperature and humidity), location information, and vital signs, making them suitable for communication using finite-length packets. Furthermore, ultra-reliable low-latency communication, one of the three major 5G application scenarios, is primarily targeted at real-time applications such as autonomous driving, telemedicine, and industrial automation, requiring user-level latency to be under 1 millisecond. Driven by this, finite-length packet transmission can effectively reduce packet transmission latency by controlling packet encoding length, and will play a crucial role in future wireless communications.

[0003] Due to the open and broadcast nature of wireless channels, wireless communication signals are often more susceptible to intentional or unintentional detection, eavesdropping, or interference by devices other than the communicating parties, compared to traditional wired communications. Traditional information security technologies primarily rely on upper-layer key encryption techniques, leveraging the computational complexity required to crack the key to ensure secure information transmission. However, with the continuous advancement of computer technology and the emergence of powerful computers, even the most robust encryption algorithms are at risk of being cracked. Meanwhile, physical layer security technologies have taken a different approach, leveraging the inherent security properties of wireless channels and their inherent randomness to ensure secure information transmission. It is worth noting that both of these security technologies only guarantee the security of the communication content, meaning that an adversary cannot decipher the information from the received signal. However, in some scenarios, simply protecting the communication content is insufficient; it is necessary to ensure that the communication signals remain undetectable. For example, for patients with medical conditions, signals from implantable medical devices could potentially leak health information. In such cases, ensuring that information transmission is undetectable—that is, concealing wireless communication signals—is crucial for achieving secure information transmission and protecting user privacy.

[0004] Covert wireless communication technology has attracted widespread attention from researchers by exploiting inherent or artificial uncertainty in the received signal at monitoring nodes to conceal wireless communication signals, ensuring that information transmission is undetectable. The paper "Delay-intolerant covert communications with either fixed or random transmit power" (IEEE Trans. Inf. Forensics Secur., vol. 14, no. 1, pp. 129-140, Jan. 2019) first investigated the problem of covert wireless communication for finite-length packets. The results show that when using finite-length coding, monitoring nodes can only obtain a limited number of observation samples, which can enhance the concealment of information transmission while satisfying transmission delay constraints. The paper "Delay-constrained covert communications with a full-duplex receiver," IEEE Wirel. Commun. Lett., vol. 8, no. 3, pp. 813–816, June 2019, investigates the problem of covert communication assisted by interference from a full-duplex destination node. The paper demonstrates that, unlike the case of infinite-length packets, where random power interference is required to create uncertainty at the monitoring node, fixed-power interference can improve communication covertness in the case of finite-length packet transmission. It is worth noting that the full-duplex destination node employed in the paper can mitigate the impact of interference on its decoding through self-interference cancellation. However, for general user scenarios and energy-constrained IoT scenarios, using terminal devices to continuously transmit interference to improve communication covertness is not practical. The inventor's previous work, "Probabilistic Jamming Aided Covert Communication in the Finite Blocklength Regime (submitted to IEEE WCSP2022 for review)," proposed using cooperative nodes to send interference with a certain probability to enhance the concealment of wireless information transmission. This method is applicable to scenarios where the destination node has weak capabilities, and the results show that probabilistic jamming can improve communication concealment performance by reducing the adverse effects of interference on the destination node's decoding. However, the proposed probabilistic jamming method still reduces communication reliability when the channel between the interfering node and the destination node is strong. Summary of the Invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a finite-length data packet covert wireless communication method assisted by truncated interference. The method is based on finite block length coding and utilizes truncated interference to achieve the goal of enhancing communication concealment while reducing the adverse effects of interference on decoding of the destination node.

[0006] To achieve the above-mentioned object, the covert wireless communication method of limited-length data packets assisted by truncation interference of the present invention comprises the following steps:

[0007] Step 1: Codebook Sharing Before transmitting a private data packet, the source node and the destination node generate a key using the characteristics of their wireless channel. The source node then uses the key-encrypted information to inform the destination node in advance of the codebook used to encode the private data packet and the transmission cycle occupied by the transmission.

[0008] Step 2: Interference Interference node determines its working state according to the channel gain between it and the destination node. The specific method is as follows: the destination node periodically broadcasts a pilot signal to the surrounding area. According to the channel reciprocity, the interference node estimates the current channel between it and the destination node based on the received pilot signal. When the channel gain between the interference node and the destination node is less than a certain threshold, the interference node cuts off the channel with power P. j The interference signal is sent; if the channel gain does not meet the conditions, it is not sent. Then, the interference transmission probability is the probability that the channel gain between the interfering node and the destination node is less than the set truncation threshold.

[0009] Step 3: Information Encoding The source node encodes the privacy data packet to be transmitted. The length of the encoded data packet is N, which means that the source node can send out all the limited-length data packets after N channel uses.

[0010] Step 4: The source node transmits information with power P a Send privacy data packets. In order to achieve covert transmission, the sending power P a The communication concealment constraints should be met:

[0011]

[0012] in, represents the exponential integral function; μ aw and μ jw denote the mean of small-scale fading between the source node, interference node and monitoring node respectively; d aw and d jw Represent the distances between the source node and the interference node and the monitoring node respectively; α represents the exponential parameter of large-scale fading; p represents the probability of interference transmission, which is related to the channel gain between the interference node and the destination node and the set truncation threshold; σ 2 represents the noise power; ε represents the preset covert communication tolerance value, which is usually a very small positive real number.

[0013] Step 5: Information decoding The destination node decodes the received signal. The average effective concealment throughput from the source node to the destination node is:

[0014]

[0015] Among them, R represents the amount of information transmitted per channel. Indicates the average packet error rate of the system.

[0016] With the goal of maximizing the average effective concealment throughput of the system, the optimal truncation threshold τ * It can be calculated according to the following equation:

[0017]

[0018] A covert wireless communication method using finite-length data packets assisted by truncated interference includes a source node, a destination node, an interfering node, and a monitoring node. All nodes are equipped with a single antenna and operate in half-duplex mode. When the source node has private information to send, it encodes it into a finite-length data packet with a channel usage number N and sends it. The monitoring node observes the wireless transmission environment to determine whether the source node has sent a private data packet to the destination node. To enhance concealment performance, the interfering node sends an interference signal with a certain probability to degrade the detection performance of the monitoring node. To mitigate the impact of interference on the destination node's decoding, the interfering node only sends interference when the channel gain between it and the destination node is less than a certain threshold. If the channel gain does not meet the condition, no interference is sent (i.e., interference is truncated).

[0019] Compared with existing transmission methods, the present invention has the following advantages and significant effects: in the specific operation of the truncated interference-assisted limited-length data packet covert wireless communication method described in the present invention, the destination node periodically broadcasts a pilot signal to the surrounding area, and the interfering node estimates the current channel gain between it and the destination node based on the pilot signal. When the channel gain is less than a certain threshold, the interfering node sends interference, otherwise it remains silent. Among them, the interfering node sends interference with a certain probability, which increases the uncertainty of the monitoring node about the signal it receives. At the same time, the interfering node only sends interference when the channel gain between it and the destination node is small, which reduces the adverse effect of interference on the decoding of the destination node. Compared with the traditional use of full-duplex destination nodes to continuously send interference, the present invention has lower requirements on terminal equipment and can be applied to energy-constrained scenarios such as the Internet of Things. Compared with traditional probabilistic interference methods, the truncated interference provided by the present invention can achieve higher concealed throughput. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The diagram is a schematic diagram of a system model of a truncated interference-assisted covert wireless communication method for limited-length data packets designed by the present invention.

[0021] Figure 2 This is a comparison diagram of the average effective concealment throughput that can be achieved by the system corresponding to different truncation thresholds.

[0022] Figure 3 The figure is a comparison diagram of the average effective concealed throughput that can be achieved by the method proposed in the present invention and the traditional probabilistic interference method system under different interference transmission probabilities. DETAILED DESCRIPTION

[0023] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0024] like Figure 1 The illustrated system employs a finite-length packet covert wireless communication system assisted by truncated interference, comprising a source node, a destination node, an interfering node, and a monitoring node. All nodes are equipped with a single antenna and operate in half-duplex mode. When a source node has private information to transmit, it encodes it into a finite-length packet with a channel usage number N and transmits it. The monitoring node observes the wireless transmission environment to determine whether the source node has sent a private packet to the destination node. To enhance concealment performance, the interfering node transmits interference signals with a certain probability, degrading the monitoring node's detection performance. To mitigate the impact of interference on the destination node's decoding, the interfering node transmits interference only when the channel gain between it and the destination node is less than a certain threshold. If the channel gain does not meet the condition, no interference is transmitted (i.e., interference is truncated).

[0025] The present invention provides a method for covert wireless communication using truncated interference-assisted limited-length data packets, comprising the following steps:

[0026] Step 1: Codebook Sharing: Before transmitting a private data packet, the source and destination nodes use their wireless channel characteristics to generate a key. The source node then uses the key-encrypted information to inform the destination node in advance of the codebook used to encode the private data packet and the transmission cycle occupied by the transmission.

[0027] Step 2: Interference cutoff: The interfering node determines its working state according to the channel gain between it and the destination node. The destination node periodically broadcasts a pilot signal to the surrounding area. According to the channel reciprocity, the interfering node estimates the current channel between it and the destination node based on the received pilot signal. When the channel gain between the interfering node and the destination node is less than a certain threshold, the interfering node cuts off the signal with a power of P. j Send an interference signal; if the channel gain does not meet the conditions, it will not be sent; then, the interference transmission probability is the probability that the channel gain between the interfering node and the destination node is less than the set truncation threshold;

[0028] For a quasi-static Rayleigh fading channel, the probability that an interfering node sends interference is expressed as

[0029]

[0030] Among them, d jbrepresents the distance between the interference node and the destination node; α represents the exponential parameter of large-scale fading; |h jb | 2 represents small-scale fading that obeys exponential distribution; μ jb represents the mean of small-scale fading between the interfering node and the destination node; τ represents the set truncation threshold.

[0031] Step 3: Information encoding: The source node encodes the privacy data packet to be transmitted. The length of the encoded data packet is N, which means that the source node sends all the limited-length data packets after N channel uses.

[0032] Step 4: Information transmission: To achieve covert transmission, the transmission power P a The communication concealment constraints should be met:

[0033]

[0034] in, and They represent the probability distribution of the monitoring node observation samples when the source node sends and does not send privacy data packets respectively; express and relative entropy between represents the expectation; ε represents the preset covert communication tolerance value, which is usually a very small positive real number;

[0035] Using Gaussian mixture model Approximating this, the communication concealment constraint is further derived as:

[0036]

[0037] in, represents the exponential integral function; μ aw represents the mean value of small-scale fading between the source node and the monitoring node; d aw represents the distance between the source node and the monitoring node; the interference transmission probability p is given by formula (4); σ 2 Represents the noise power.

[0038] Furthermore, the source node uses power P a Send privacy data packets; in order to achieve covert transmission, the sending power P a The communication concealment constraint should be satisfied, that is, formula (1):

[0039]

[0040] in, represents the exponential integral function; μ aw represents the mean value of small-scale fading between the source node and the monitoring node; μjw represents the mean value of small-scale fading between the interference node and the monitoring node; d aw Indicates the distance between the source node and the monitoring node; d jw represents the distance between the interfering node and the monitoring node; α represents the exponential parameter of large-scale fading; p represents the probability of interference transmission, which is related to the channel gain between the interfering node and the destination node and the set truncation threshold; P j represents the power of the interfering node; σ 2 represents the noise power; ε represents the preset covert communication tolerance value, which is usually a very small positive real number.

[0041] Step 5: Information decoding: The destination node decodes the received signal. Since the interfering node sends interference with a certain probability, the received signal-to-noise ratio of the destination node is expressed as:

[0042]

[0043] Among them, d ab Represents the distance between the source node and the destination node; d jb represents the distance between the interference node and the destination node; |h ab | 2 represents the small-scale fading between the source node and the destination node; |h jb | 2 represents the small-scale fading between the interfering node and the destination node; κ∈{0,1} represents the working state of the interfering node, κ=0 means the interfering node remains silent, and κ=1 means the interfering node sends interference;

[0044] The use of finite block length coding inevitably results in decoding errors at the destination node, and its packet error rate is expressed as

[0045]

[0046] in, represents the Gaussian Q function; R represents the amount of information transmitted per channel; the average packet error rate is expressed as:

[0047]

[0048] in, represents the received signal-to-noise ratio at the destination node when the interfering node sends interference, that is, κ = 1 in formula (7); represents the received signal-to-noise ratio at the silent destination node of the interference node, that is, κ = 0 in formula (7); f(x) represents the probability density function of the variable x;

[0049] Only when the data packets are correctly decoded can they contribute to the system's concealed throughput; then, the average effective concealed throughput from the source node to the destination node is expressed as:

[0050]

[0051] The average effective concealed throughput from the source node to the destination node is:

[0052]

[0053] Among them, R represents the amount of information transmitted per channel. Indicates the average packet error rate of the system;

[0054] With the goal of maximizing the average effective concealment throughput of the system, the optimal truncation threshold τ * Calculated according to the following equation:

[0055]

[0056] The simulation of the change of the average effective concealment throughput with the truncation threshold in the method of the present invention is as follows: Figure 2 As shown, the channel coding rate is R = 0.1 bit per channel, the coding length is N = 200 channels, the concealment tolerance is ε = 0.1, and the distance between nodes is d ab =d jb =d aw =d jw = 30 meters, the large-scale fading parameter is α = 2.2, and the small-scale fading coefficient is μ ab =μ aw =μ jw =1, noise power The interference transmission power is P j =-30dBm, the source node's transmission power is the maximum transmission power that satisfies the concealment constraint. Figure 2 It can be seen from the figure that there is an optimal truncation threshold that maximizes the average effective concealment throughput of the system, and the optimal truncation threshold is related to the channel quality between the interfering node and the destination node.

[0057] The comparison simulation of the average effective concealment throughput of the method of the present invention and the traditional probabilistic interference method (i.e., the interference node only sends interference with a certain probability regardless of the current channel quality between it and the destination node) is shown in the following figure: Figure 3 As shown, the channel coding rate is R = 0.1 bit per channel, the coding length is N = 200 channels, and the distance between nodes is d ab =d jb =d aw =d jw = 30 meters, the large-scale fading parameter is α = 2.2, and the small-scale fading coefficient is μ ab =μ jb =μ aw =μ jw =1, noise power The interference transmission power is P j =-30dBm, the source node's transmission power is the maximum transmission power that satisfies the concealment constraint. Figure 3 It can be seen from the figure that the average effective concealment throughput of the method of the present invention is significantly better than that of the traditional probabilistic jamming method.

[0058] The description of the above embodiment is relatively specific and detailed, but it only expresses one feasible implementation method of the present invention and does not limit the scope of the patent of the present invention. It should be pointed out that researchers and engineers in this field may add several variations or improvements based on this embodiment within the framework of the present invention, but these are all within the scope of protection of the patent of the present invention. The scope of protection of the patent of the present invention shall be based on the appended claims.

Claims

1. A method for covert wireless communication of limited-length data packets assisted by truncation interference, characterized in that: The method of the present invention comprises the following steps: Step 1: Codebook Sharing: Before transmitting a private data packet, the source and destination nodes use their wireless channel characteristics to generate a key. The source node then uses the encrypted information to inform the destination node in advance of the codebook used to encode the private data packet and the transmission cycle occupied by the transmission. Step 2: Interference cutoff: The interfering node determines its working state according to the channel gain between it and the destination node. That is, when the channel gain between the interfering node and the destination node is less than a certain threshold, the interfering node cuts off the interference with power P. j Send interference signal; if the channel gain does not meet the conditions, do not send; the destination node periodically broadcasts the pilot signal to the surrounding area; Step 3: Information encoding: The source node encodes the private data packet to be transmitted. The length of the encoded data packet is N, which means that the source node sends all the limited-length data packets after using the channel N times. Step 4: Information transmission: The source node transmits information with power P. a Send privacy data packets; in order to achieve covert transmission, the sending power P a The communication concealment constraints should be met: Where N represents the number of channels occupied by the data packet; represents the exponential integral function; μ aw represents the mean value of small-scale fading between the source node and the monitoring node; μ jw represents the mean value of small-scale fading between the interference node and the monitoring node; d aw Indicates the distance between the source node and the monitoring node; d jw represents the distance between the interfering node and the monitoring node; α represents the exponential parameter of large-scale fading; p represents the probability of interference transmission, which is related to the channel gain between the interfering node and the destination node and the set truncation threshold; P j represents the power of the interfering node; σ 2 represents the noise power; ε represents the preset covert communication tolerance value, which is a very small positive real number; Step 5: Information decoding: The destination node decodes the received signal. The average effective concealment throughput from the source node to the destination node is: Among them, R represents the amount of information transmitted per channel. Indicates the average packet error rate of the system; With the goal of maximizing the average effective concealment throughput of the system, the optimal truncation threshold τ * Calculated according to the following equation:

2. The method for covert wireless communication using truncated interference-assisted limited-length data packets according to claim 1, wherein: According to the channel reciprocity, the interfering node estimates the current channel between it and the destination node based on the received pilot signal; when the channel gain between the interfering node and the destination node is less than a certain threshold, the interfering node uses power P j Send an interference signal; if the channel gain does not meet the conditions, it will not be sent; then, the interference transmission probability is the probability that the channel gain between the interfering node and the destination node is less than the set truncation threshold; For a quasi-static Rayleigh fading channel, the probability that an interfering node sends interference is expressed as Among them, d jb represents the distance between the interference node and the destination node; α represents the exponential parameter of large-scale fading; |h jb | 2 represents small-scale fading that obeys exponential distribution; μ jb represents the mean of small-scale fading between the interfering node and the destination node; τ represents the set truncation threshold.

3. The method for covert wireless communication using truncated interference-assisted limited-length data packets according to claim 1, wherein: In order to achieve concealed transmission, the transmission power P a The communication concealment constraints should be met: in, and They represent the probability distribution of the monitoring node observation samples when the source node sends and does not send privacy data packets respectively; express and relative entropy between represents the expectation; ε represents the preset covert communication tolerance value, which is a very small positive real number; Using Gaussian mixture model Approximating this, the communication concealment constraint is further derived as: in, represents the exponential integral function; μ aw represents the mean value of small-scale fading between the source node and the monitoring node; d aw represents the distance between the source node and the monitoring node; the interference transmission probability p is given by formula (4); σ 2 represents the noise power, further, the transmission power P a Formula (1) should be satisfied.

4. The method for covert wireless communication using truncated interference-assisted limited-length data packets according to claim 1, wherein: Since the interfering node sends interference with a certain probability, the received signal-to-noise ratio of the destination node is expressed as: Among them, d ab Represents the distance between the source node and the destination node; d jb represents the distance between the interference node and the destination node; |h ab | 2 represents the small-scale fading between the source node and the destination node; |h jb | 2 represents the small-scale fading between the interfering node and the destination node; κ∈{0,1} represents the working state of the interfering node, κ=0 means the interfering node remains silent, and κ=1 means the interfering node sends interference; The use of finite block length coding inevitably results in decoding errors at the destination node, and its packet error rate is expressed as in, represents the Gaussian Q function; R represents the amount of information transmitted per channel; the average packet error rate is expressed as: in, represents the received signal-to-noise ratio at the destination node when the interfering node sends interference, that is, κ = 1 in formula (7); represents the received signal-to-noise ratio at the silent destination node of the interference node, that is, κ = 0 in formula (7); f(x) represents the probability density function of the variable x; Only when the data packets are correctly decoded can they contribute to the system's concealed throughput; then, the average effective concealed throughput from the source node to the destination node is expressed as:

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