A method for randomly selecting a single sub-channel for short-packet covert wireless communication

Abstract

A method for randomly selecting a single sub-channel for short-packet covert wireless communication belongs to the technical field of secure transmission of privacy information in wireless networks. It includes the following steps: Key exchange and codebook sharing: Before data packet transmission, a key is generated between the source node and the destination node using the wireless channel, and the codebook for encoding privacy data packets is shared after encryption using the key; Information encoding: The source node encodes the privacy information to be transmitted using the codebook shared with the destination node, indicating that the source node completely sends the privacy information through channel usage; Information transmission: The source node randomly selects one sub-channel out of K sub-channels to send the privacy information to be transmitted with the optimal transmission power; Information decoding: The destination node decodes using the codebook shared with the source node in each transmission period. The present invention makes full use of the uncertainty of the selected sub-channel in a multi-channel system to improve the covert communication performance between the source node and the destination node.

Description

Technical Field

[0001] The present invention belongs to the technical field of secure transmission of wireless network privacy information, and relates to a method for randomly selecting a single sub-channel for short-packet covert wireless communication. Background Art

[0002] With the rapid development of technology, more and more confidential and sensitive data (such as health records, identity authentication, etc.) are transmitted through wireless channels. Data from the Australian Cyber Awareness Index 2019, https: / / channellife.com.au / story / eset-releases-aus-tralian-cyberawareness-index-2019-results, Accessed: 2019-12-13, shows that nearly 94% of the surveyed subjects have conducted financial transactions online, including online banking, paying bills, and online shopping, which means that people are more reliant on modern wireless communication systems in terms of exchanging sensitive and private information. Thus, it can be seen that wireless communication systems have penetrated all aspects of our daily lives, and their security and privacy have also occupied an unparalleled priority in our society. However, due to the open nature of wireless channels (which can be received by both legitimate and illegal users), the security of wirelessly transmitted data has always been a key research area in the industry. Traditionally, the industry has protected data content through technical means to improve the security of wireless transmission. However, in recent years, with the proliferation of wireless devices and the advancement of computing technology, communication security has faced significant challenges. In particular, the breakthrough of quantum computing has greatly increased the computing resources available to potential adversaries, thereby increasing the likelihood of breaking traditional wireless information transmission security technologies. As an effective complement to traditional security mechanisms, physical layer security technology ensures the security of information transmission by leveraging the fading characteristics of wireless channels, achieving absolute security in the sense of Shannon's information theory. It is worth noting that information security transmission mechanisms based on traditional encryption and physical layer security only protect the content of information from being deciphered by illegal eavesdropping nodes, paying more attention to the security of the transmitted information itself, but neglecting the undetectability of the information transmission process. In fact, the basis for an eavesdropping node to decipher information is the correct detection of the information transmission behavior. Therefore, hiding the wireless transmission behavior can achieve stronger security performance. And in some special scenarios, such as military command scenarios, not only the privacy and integrity of information are important, but also the behavior of transmitting information and the location of the transmitter itself are information that cannot be exposed. Once the occurrence of the information transmission process is detected, the monitor may take measures such as full-band high-power interference or even physical attacks to disrupt the information transmission process. At this time, ensuring the undetectability of the information transmission behavior is of great significance for protecting user privacy and information transmission security.

[0003] In this context, covert communication, also known as low-probability-of-detection (LPD) communication, has attracted increasing attention from scholars. Covert communication aims to make wireless communication signals or communication behaviors have a low probability of detection and avoid being detected by the enemy. There are many application scenarios for covert wireless communication, especially in military communication. Signals with a low probability of detection can prevent the enemy's electronic reconnaissance equipment from obtaining intelligence, thus making military operations more covert. Covert wireless communication can be traced back to the spread-spectrum communication that emerged in the early 20th century. When transmitting information, the spread-spectrum technology actually uses a bandwidth much larger than the bandwidth required by the information itself, which can make the transmitted power spectral density lower than the background noise, thus having the ability of covert transmission. However, the theoretical mechanism of the concealment of the spread-spectrum technology has not been rigorously proven. It was not until the literature "Limits of Reliable Communication with Low Probability of Detection on AWGN Channels," in IEEE Journal on Selected Areas in Communications, vol. 31, no. 9, pp. 1921–1930, Sep. 2013, that the basic performance bounds of covert communication in an additive white Gaussian noise (AWGN) channel were first studied in detail, laying the information-theoretic foundation for covert wireless communication. The literature "Delay-Intolerant Covert Communications with Either Fixed or Random Transmit Power," in IEEE Transactions on Information Forensics and Security, vol. 14, no. 1, pp. 129-140, Jan. 2019, studied covert wireless communication with finite blocklength. The research shows that by using the analysis error caused by the limited samples of the monitor, information can be reliably transmitted to the destination node on the basis of meeting the covert conditions. However, the source nodes considered in the above literature all send information through a single-channel system; due to the advantage of high transmission efficiency, multi-channel systems have been widely used in wireless communication. A multi-channel system contains multiple sub-channels, enabling the transmitter to select one of the sub-channels to transmit information, thus providing another degree of freedom to confuse the monitor and improve communication concealment. Therefore, in a multi-channel system, it is of great significance to explore how to effectively improve the system's covert rate, but no relevant research has appeared yet. Summary of the Invention

[0004] The present invention provides a method for randomly selecting a single sub-channel short-packet covert wireless communication, which makes full use of the uncertainty of the selected sub-channel in a multi-channel system to improve the covert communication performance between the source node and the destination node.

[0005] A method for randomly selecting a single sub-channel short-packet covert wireless communication includes the following steps:

[0006] Step S1: Key exchange and codebook sharing: Before data packet transmission, a key is generated between the source node and the destination node using the wireless channel, and the codebook for encrypting and sharing private data packets is encrypted using the key.

[0007] Step S2: Information encoding: The source node encodes the private information to be transmitted using the codebook shared with the destination node. The encoding length is N, indicating that the source node will send the private information with Dnats information volume completely after N channel uses.

[0008] Step S3: Information transmission: The source node uses the optimal transmission power Among K sub-channels, randomly select a sub-channel to send the private information to be transmitted.

[0009] Step S4: Information decoding: The destination node decodes using the codebook shared with the source node in each transmission period.

[0010] A method for randomly selecting a single sub-channel short-packet covert wireless communication, the system consists of a pair of legitimate transceiver pairs (source node and destination node), and there is also a monitor constantly observing the environment and detecting whether the source node transmits information. All nodes are configured with single antennas and operate in half-duplex mode. Specifically, the source node randomly selects a sub-channel from multiple sub-channels to send information, and shares keys and codebooks between the source node and the destination node; in order to achieve the purpose of low-latency tolerance, the sender uses a limited number of channel uses (for example, in scenarios such as connected vehicles, smart meters, and automated factories, about 150 channel uses) to transmit information in each time slot; due to the limited channel uses, there are inevitable errors in the monitor's analysis of the signal, making the monitor misjudge whether the sender transmits information, and finally achieving the purpose of covertly transmitting information within the tolerable exposure probability range when it is known that there is a monitor.

[0011] When the method for randomly selecting a single sub-channel short-packet covert wireless communication described in the present invention is specifically operated, the source node increases the uncertainty of channel selection at the source node by randomly selecting sub-channels among multiple sub-channels, further confusing the monitor, and achieving the purpose of enhancing the concealment of wireless transmission behavior. Compared with the covert wireless communication method of single-channel covert transmission, the present invention can obtain a higher average effective covert rate. Description of the Drawings

[0012] Figure 1 It is a schematic diagram of the system model of the method for randomly selecting a single sub-channel short-packet covert wireless communication of the present invention. Detailed Implementation Manner

[0013] As Figure 1 shown, a method for randomly selecting a single sub-channel short-packet covert wireless communication, the system consists of a pair of legitimate transceiver pairs (source node and destination node), and there is also a monitor constantly observing the environment and detecting whether the source node transmits information. All nodes are configured with single antennas and operate in a half-duplex mode. Specifically, the source node selects the sub-channel with the largest channel coefficient from multiple sub-channels to send information, and shares the secret key and codebook between the source node and the destination node; in order to achieve the purpose of low-latency tolerance, the sender uses a limited number of channel uses (for example, in scenarios such as connected vehicles, smart meters, and automated factories, about 150 channel uses) to transmit information in each time slot; due to the limited channel uses, there are inevitable errors in the monitor's analysis of the signal, resulting in misjudgment when the monitor determines whether the sender transmits information.

[0014] A method for randomly selecting a single sub-channel short-packet covert wireless communication includes the following steps:

[0015] Step S1: Secret key exchange and codebook sharing: Before data packet transmission, the source node and the destination node generate a secret key using the wireless channel and share the codebook encoded with the secret key for the private data packet.

[0016] Step S2: Information encoding: The source node encodes the private information to be transmitted using the codebook shared with the destination node, and the encoding length is N, indicating that the source node can completely send the private information after N channel uses. The number of channel uses in the present invention corresponds to and is equal to the encoding length.

[0017] Step S3: Information transmission: The source node uses the optimal transmission power P a Among K sub-channels, randomly select a sub-channel to send the private information to be transmitted. In order to maximize the transmission rate between the source node and the destination node under the condition of meeting the communication concealment constraint, the transmission power P a should satisfy:

[0018]

[0019] Among them, represents the optimal transmission power.

[0020] With the goal of maximizing the system average covert rate, the optimal number of sub-channels of the system can be calculated according to the following equation:

[0021]

[0022] Among them, ∈ is an arbitrarily small real number, representing the tolerance value of covert communication exposure, representing the minimum misjudgment probability of the monitor, then it describes that the minimum misjudgment probability of the monitor is greater than the probability value required for covertness between the source node and the destination node (for example: the exposure tolerance value ∈ = 0.05, indicating that the communication behavior of the source node needs to have a probability of 0.95 of not being exposed), which is the covert constraint (the requirement for the covert and secret transmission of the communication behavior of the source node); P a > 0 constrains the transmission power to be a positive value; K max refers to the maximum value that the number of sub-channels can reach, K = 1, 2,..., K max constrains the number of sub-channels K to be a positive integer less than K max of.

[0023] To solve the above optimization problem, we need to solve the minimum misjudgment probability of the monitor

[0024] At the end of a transmission period (one time slot), the monitor needs to determine whether the source node sends information, so the monitor faces a binary decision. Since the monitor has limited observed values (a limited number of channel uses), there are judgment errors when judging the communication behavior of the source node And consists of the false alarm probability and the missed detection probability . Without loss of generality, assume that Through calculation, it can be obtained that:

[0025]

[0026] Among them, represents the noise variance received by the monitor. By setting the optimal threshold τ * the minimum missed detection probability is obtained The missed detection probability is a convex function of τ and the optimal threshold τ * can be obtained through a simple one-dimensional search.

[0027] Through a simple analysis of the optimization problem, we find that decreases with the monotonic increase of P a and increases with the monotonic increase of K; the average effective covert rate η increases with the monotonic increase of P a and decreases with the monotonic increase of K. Therefore, we can find the solution K of the optimization problem through a two-dimensional search * and

[0028] Up to here, we can know that when the source node uses K * sub-channels to send information with the transmission power, the transmission rate between the source node and the destination node can be maximized under the condition of being within the exposure tolerance (covert).

[0029] Step S4: Information decoding: The destination node decodes the received signal using the codebook shared with the source node in each transmission period. In each transmission period T, the received signal at the destination node can be expressed as:

[0030]

[0031] where i = 1, 2, …, N represents the channel use index; x a [i] is a complex Gaussian random variable with a mean of zero and a variance of 1, representing the symbol sent by the source node at the i-th channel use; n b [i] is a complex Gaussian random variable with a mean of zero and a variance of , representing the noise observed by the destination node when the source node uses the channel for the i-th time.

[0032] The destination node decodes using the codebook shared with the source node in each transmission period, and the average effective covert rate of the system can be expressed as:

[0033]

[0034] where, represents the system packet error rate, and R represents the transmission rate, which can be calculated according to the following equation:

[0035]

[0036] where

[0037] The description of the above embodiments is relatively specific and detailed, but it only represents a feasible implementation manner of the present invention, and does not limit the scope of the patent of the present invention. It should be noted that those skilled in scientific research and engineering in this field can add several deformations or improvements on the basis of this embodiment within the framework of the present invention, but these are all within the protection scope of the patent of the present invention, and the protection scope of the patent of the present invention is subject to the claims.

Claims

1. A method for short-packet covert wireless communication by randomly selecting a single sub-channel, characterized in that it includes the following steps: Step S1: Key exchange and codebook sharing: Before data packet transmission, a key is generated between the source node and the destination node using the wireless channel, and the codebook for encoding the private data packet is shared after encryption using the key; Step S2: Information encoding: The source node encodes the private information to be transmitted using the codebook shared with the destination node. The encoding length is N, indicating that the source node will completely send the private information containing D nats of information after N channel uses; Step S3: Information transmission: The source node uses the optimal transmission power to randomly select one sub-channel among the K sub-channels to transmit the privacy information to be transmitted; The specific steps for obtaining the optimal transmission power are as follows: Maximize the average effective secrecy rate η between the source node and the destination node under the condition of satisfying the communication secrecy constraint, and the average effective rate where R represents the expected communication rate, and δ m represents the system outage probability Optimize the transmission power P a and the number of sub-channels K for the source node to send information, and establish the following optimization problem: where ∈ is an arbitrarily small real number, representing the tolerance value of covert communication exposure, representing the minimum misjudgment probability of the monitor, then describes that the minimum misjudgment probability of the monitor is greater than the probability value required for covertness between the source node and the destination node, which is the covert constraint; P a > 0 constrains the transmission power to be a positive value; K max refers to the maximum value that the number of sub-channels can reach, K = 1, 2,..., K max constrains the number of sub-channels K to be a positive integer less than K max ; Step S4: Information decoding: The destination node decodes using the codebook shared with the source node in each transmission period.

2. The method for short-packet covert wireless communication by randomly selecting a single sub-channel according to claim 1, characterized in that At the end of a transmission cycle, the monitor needs to determine whether the source node has sent information. Thus, the monitor faces a binary decision determined by the detection threshold τ. Since the monitor has limited observed values, there are judgment errors when determining the communication behavior of the source node. And It consists of the false alarm probability and the miss detection probability Without loss of generality, assume that Through calculation, it can be obtained that: Among them, represents the noise variance received by the monitor; by setting the optimal threshold τ * the minimum misjudgment probability is obtained 3. The method for short-packet covert wireless communication by randomly selecting a single sub-channel according to claim 2, characterized in that For the information decoding in the above step S4, the average effective covert rate is expressed as: wherein, represents the system mispacket rate, and R represents the expected communication rate, which is calculated according to the following equation: wherein represents the signal-to-noise ratio of the destination node, represents the noise variance received by the destination node; θ and ζ are intermediate variables of the formula, θ = exp(D / N) - 1,

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