CN114827991B - A concealed wireless communication method and system - Google Patents
A concealed wireless communication method and system Download PDFInfo
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- CN114827991B CN114827991B CN202210422427.5A CN202210422427A CN114827991B CN 114827991 B CN114827991 B CN 114827991B CN 202210422427 A CN202210422427 A CN 202210422427A CN 114827991 B CN114827991 B CN 114827991B
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W12/00—Security arrangements; Authentication; Protecting privacy or anonymity
- H04W12/02—Protecting privacy or anonymity, e.g. protecting personally identifiable information [PII]
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- H—ELECTRICITY
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- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/69—Spread spectrum techniques
- H04B1/713—Spread spectrum techniques using frequency hopping
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- H—ELECTRICITY
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- Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
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- Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks
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Abstract
The embodiment of the invention provides a method for transmitting wireless signals, which comprises the steps of obtaining a frequency hopping rate, expected detection probability and detection performance parameters of a monitoring end, determining a time hopping duty ratio according to the detection performance parameters, a detection threshold value set based on the detection performance parameters and the expected detection probability, obtaining a frequency hopping key, generating frequency hopping map information according to the frequency hopping rate and the frequency hopping key, generating a time hopping transmission sequence according to the time hopping duty ratio, carrying out up-conversion on baseband signals according to the frequency hopping map information to obtain band-pass signals to be transmitted, and controlling the band-pass signals to be transmitted through an antenna according to the time hopping transmission sequence. According to the technical scheme provided by the embodiment of the invention, the frequency hopping rate is set, so that certain concealment is improved, meanwhile, the expected detection probability possibly achieved in a reasonable parameter range and the detection performance of the monitoring end are considered, and the proportion of the transmitted wireless signals is reduced by the obtained time hopping duty ratio, so that the concealment is further improved.
Description
Technical Field
The present invention relates to the field of wireless communication technologies, and in particular, to a concealed wireless communication method and system.
Background
With the continuous development of wireless communication technology, more and more wireless devices enter the life of people, thereby bringing convenience to the life of people. However, with the expansion of the application range of wireless communication, more and more private information needs to be transmitted, such as physical health information, personal location, identity information, and the like. Because of the open space transmission characteristic of electromagnetic waves, wireless signals are easy to be intercepted by non-cooperators, so that privacy leakage is caused, and the safety of users is threatened. In military scenarios, communication security is particularly important, and once my communication facts are detected by non-cooperators, malicious attacks or information leakage of the non-cooperators are caused, so that situations are changed. Therefore, in order to maintain the security of the communication user, the transmission information needs to be protected for covert communication. If the monitoring end interferes with the sending signal in a mode of tracking interference, once the sending signal is detected, the sending signal is interfered, and communication of a legal communication party is interrupted. In the scene, the sending end makes the probability of the signal detected by the monitoring end as low as possible through a reasonable hidden communication technical means. The hidden communication is also called low probability detection (Low Probability Detection, LPD) communication, and the communication signal is hidden by a reasonable technical means, so that a listener cannot find the communication facts of both communication parties, and interference or information theft cannot be generated.
The prior hidden communication key technology research mainly takes the sum of false alarm probability and missing detection probability under an energy detection algorithm as a hidden evaluation index, wherein the false alarm probability refers to the probability that a monitoring end judges that a transmission signal exists under the condition that no signal is transmitted, and the missing detection probability refers to the probability that the monitoring end judges that the transmission signal does not exist under the condition that the transmission end transmits the signal. Although the sum of the false alarm probability and the missed detection probability under the optimal detection threshold condition is the lowest, the false detection probability of the monitoring end can be the lowest, in the actual application scene, the monitoring end can make useless work due to the fact that the false alarm probability is too large, and therefore the monitoring end can make the false alarm probability as low as possible by adjusting the detection threshold. In order to meet specific false alarm probability requirements, the detection threshold set by the monitoring end is not an optimal detection threshold. The adjustment of the detection threshold value can enable the sum of the false alarm and the missing detection probability to be larger than the sum of the false alarm and the missing detection probability under the condition of the optimal detection threshold value. In addition, for the transmitting end, in some specific application scenarios, the transmitting end is more concerned about the probability that the transmitted signal is detected, that is, the probability of missing detection of the monitoring end is expected to be as large as possible. Therefore, the sum of false alarm probability and missing detection probability under the optimal detection threshold in the existing hidden communication key technology research can not well describe the working mode of a monitoring end in an actual communication system.
In addition, the existing key technology research of the covert communication can also reduce the probability of detecting the signal by using a time hopping technology. If the transmitting end divides the transmitting time into N time slots and randomly selects one of the time slots for transmitting, the monitoring end needs to detect the transmitting signal in one complete data transmission time slot because the time slot where the transmitting signal is located cannot be determined, and as the number of the optional time slots increases, the uncertainty of the receiving signal of the monitoring end increases, and the capacity of a hidden channel increases until complete hidden transmission is realized for all transmitting information. In an actual communication system, an energy detection algorithm adopted by a monitoring end has high efficiency, millisecond detection can be realized, if a time slot occupied by transmitted data is larger than the time range, the monitoring end can detect a transmitted signal in a multi-detection mode, and at the moment, the time hopping technology cannot improve the concealment of the system. Therefore, for the fixed-frequency transmission system adopting the time hopping technology, as the observation time of the detector increases, the detection probability of the monitoring end increases, so in some scenes with higher security level, the time hopping technology needs to make the sending time slot of the sending signal sufficiently low in order to reach the expected hidden transmission requirement, so that the signal power input by the monitoring end to the detector can be ensured to be smaller than the detection threshold.
Finally, the frequency hopping technology is widely applied to communication scenes, and the capability of the system for resisting fixed frequency interference can be effectively improved. The frequency hopping signal carries out frequency hopping in a plurality of selectable frequency points, so that the probability that the transmitting signal falls into the working bandwidth of the detector at the monitoring end can be reduced, the concealment of the system can be improved to a certain extent, meanwhile, as the frequency hopping rate is increased, the residence time of each frequency hopping signal on a fixed frequency point is reduced, the power of the transmitting signal falling into the detector is reduced, and the concealment of the system is improved.
Based on the above analysis, in the existing hidden communication technology, firstly, the conventional encryption-based information security scheme can only protect the transmission signal from the calculation angle, and along with the enhancement of the hardware processing capability, the conventional encryption scheme based on calculation may fail, and cannot effectively protect the transmission information. Secondly, the application scenario of the prior covert evaluation is not the same as that of the actual communication system, so that the covert communication design scheme taking the prior covert evaluation index as a criterion cannot provide the optimal theoretical guidance for the actual covert communication system. In addition, in an actual communication system, the energy detection algorithm adopted by the monitoring end has high efficiency in a mode of realizing hidden communication through a time hopping technology, and the transmitted signal can be detected through a mode of detecting for many times, so that the time hopping technology cannot improve the concealment of the system. Therefore, in order to further meet the expected requirement of hidden transmission, the time slot for transmitting the signal needs to be low enough, and the throughput of the system is obviously reduced by the scheme, so that the requirement of the communication system on the transmission rate cannot be met. Thus, the time-hopping technique alone has limited utility in improving system concealment. Finally, frequency hopping techniques may improve the system's ability to resist fixed frequency interference, however, in practical communication systems, the frequency hopping signal rate is limited due to hardware level limitations, and thus, the ability of individual frequency hopping techniques to improve the system's concealment is limited.
Accordingly, there is a need for improvements over the prior art.
Disclosure of Invention
It is therefore an object of the present invention to overcome the above-mentioned drawbacks of the prior art and to provide a concealed wireless communication method and system.
The invention aims at realizing the following technical scheme:
According to a first aspect of the present invention, there is provided a method for transmitting a wireless signal, including obtaining a frequency hopping rate, an expected detection probability, and a detection performance parameter of a listening end, determining a time hopping duty cycle according to the detection performance parameter, a detection threshold set based on the detection performance parameter, and the expected detection probability, obtaining a frequency hopping key, generating frequency hopping pattern information according to the frequency hopping rate and the frequency hopping key, and generating a time hopping transmission sequence according to the time hopping duty cycle, up-converting a baseband signal according to the frequency hopping pattern information to obtain a band-pass signal to be transmitted, and controlling the band-pass signal to be transmitted through an antenna at a designated time according to the time hopping transmission sequence.
In some embodiments of the present invention, the detection performance parameter includes a signal-to-noise ratio of a received signal, and the method for obtaining the signal-to-noise ratio of the received signal includes obtaining a monitoring parameter of a monitoring end and a communication parameter of a transmitting end and a receiving end, calculating a minimum transmission signal power of the transmitting end based on the communication parameters of the transmitting end and the receiving end, and calculating the signal-to-noise ratio of the received signal according to the monitoring parameter and the minimum transmission signal power.
In some embodiments of the invention, the monitoring parameters comprise a minimum monitorable distance between a monitoring end and a transmitting end, a channel fading factor, channel noise power, carrier wave wavelength, a receiving antenna gain of the monitoring end and a transmitting antenna gain of the transmitting end, and calculating the receiving signal to noise ratio comprises calculating the receiving signal power of the monitoring end according to the minimum transmitting signal power, the minimum monitorable distance, the channel fading factor, the transmitting antenna gain of the transmitting end, the receiving antenna gain of the monitoring end and the carrier wave wavelength, and calculating the receiving signal to noise ratio based on the receiving signal power of the monitoring end and the channel noise power.
In some embodiments of the present invention, the detection performance parameter further includes a preset false alarm probability value and a detection time window length, where the detection time window length determining manner includes setting a signal sampling frequency of the listening end, obtaining an optimal detection time based on the frequency hopping rate, and determining the detection time window length according to the optimal detection time and the signal sampling frequency.
In some embodiments of the present invention, the setting of the detection threshold based on the detection performance parameter includes:
Wherein epsilon is a detection threshold, Q is a complementary cumulative distribution function, P f is a preset false alarm probability value, L=τf s, L is a detection time window length, optimal detection time τ=1/v hop,vhop is a frequency hopping rate, f s is a signal sampling frequency, Is the channel noise power of the listening end.
In some embodiments of the invention, the time-hopping duty cycle is determined as follows:
Wherein ρ is a time hopping duty cycle, Q is a complementary cumulative distribution function, P d is a desired detection probability, γ is a signal-to-noise ratio of a received signal at a listening end, l=τf s, L is a detection time window length, optimal detection time τ=1/v hop,vhop is a frequency hopping rate, f s is a signal sampling frequency, ε is a detection threshold, Is the channel noise power of the listening end.
In some embodiments of the present invention, the communication parameters include a target data transmission rate of the transmitting end and a transmitting antenna gain of the transmitting end, a minimum receiving signal-to-noise ratio of the receiving end and a receiving antenna gain of the receiving end, a distance between the transmitting end and the receiving end, a channel fading factor, and a carrier wavelength.
In some embodiments of the present invention, the minimum transmit signal power calculation method includes calculating a minimum receive signal power of a receiving end based on a target data transmission rate and a minimum receive signal to noise ratio, and calculating a minimum transmit signal power based on the minimum receive signal power, a distance between the transmitting end and the receiving end, a channel fading factor, a carrier wavelength, a transmit antenna gain, and a receiving end receive antenna gain.
In some embodiments of the present invention, the time-hopping transmission sequence includes a number of time chips indicating whether to transmit the band-pass signal, wherein the time-hopping transmission sequence indicates that a number ratio of the time chips transmitting the band-pass signal to all the time chips corresponds to a time-hopping duty cycle, and the time chips indicating to transmit the band-pass signal are arranged before the time chips indicating not to transmit the band-pass signal.
According to a second aspect of the present invention, there is provided a method of acquiring a wireless signal, comprising acquiring a frequency hopping rate, a frequency hopping key and a time hopping duty cycle employed when the wireless signal is transmitted according to the first aspect of the present invention, generating frequency hopping pattern information according to the frequency hopping rate and the frequency hopping key, and generating a time hopping reception sequence according to the time hopping duty cycle, controlling an antenna to receive the wireless signal at a specified time based on the time hopping reception sequence, acquiring the received wireless signal, and down-converting the wireless signal with the frequency hopping pattern information to obtain a baseband signal.
In some embodiments of the present invention, the time-hopping reception sequence includes a number of time chips indicating whether to receive the wireless signal, wherein a number ratio of the time chips indicating to receive the wireless signal and all the time chips corresponds to a time-hopping duty cycle, and the time chips indicating to receive the wireless signal are arranged before the time chips indicating to not receive the wireless signal.
According to a third aspect of the present invention, there is provided a wireless transmitting terminal for the method according to the first aspect of the present invention, including a frequency hopping time hopping parameter configuration module configured to obtain a frequency hopping rate, an expected detection probability, and a detection performance parameter of a listening terminal, determine a time hopping duty cycle according to the detection performance parameter, a detection threshold set based on the detection performance parameter, and the expected detection probability, a frequency hopping time hopping module configured to obtain a frequency hopping key, generate frequency hopping pattern information according to the frequency hopping rate and the frequency hopping key, generate a time hopping transmission sequence according to the time hopping duty cycle, a first mixer configured to up-convert a baseband signal according to the frequency hopping pattern information to obtain a band-pass signal to be transmitted, and a first high frequency switch configured to control the band-pass signal to be transmitted through an antenna at a specified time according to the time hopping transmission sequence to obtain a wireless signal.
According to a fourth aspect of the present invention, there is provided a wireless receiving terminal for the method according to the second aspect of the present invention, including a time hopping frequency hopping parameter synchronization module for acquiring a frequency hopping rate, a frequency hopping key and a time hopping duty cycle employed when transmitting a wireless signal according to the method according to the first aspect of the present invention, a frequency hopping time hopping receiving module for generating frequency hopping pattern information according to the frequency hopping rate and the frequency hopping key and generating a time hopping receiving sequence according to the time hopping duty cycle, a second high frequency switch for controlling an antenna to receive the wireless signal at a designated time based on the time hopping receiving sequence, and a second mixer for acquiring the received wireless signal, down-converting the wireless signal using the frequency hopping pattern information to obtain a baseband signal.
According to a fifth aspect of the present invention, there is provided a wireless communication system comprising a wireless transmitting end according to the third aspect of the present invention and a wireless receiving end according to the fourth aspect of the present invention.
Compared with the prior art, the invention has the advantages that:
1. Before the wireless signals are sent, the expected detection probability possibly achieved in a reasonable parameter range and the detection performance of the monitoring end are considered to obtain the time-hopping duty ratio, the time-hopping sending sequence generated by the time-hopping duty ratio controls the band-pass signals to be sent out through the antenna at the appointed time, the proportion of the wireless signals to be sent is reduced to improve the concealment, and the appropriate time-hopping duty ratio can meet the requirement of the data transmission rate to a certain extent. The detection performance of the detector at the monitoring end is limited to a certain extent through the set frequency hopping rate. Thus, the combination of time hopping techniques and frequency hopping rates also improves concealment during wireless communications to a greater extent.
2. The invention combines each detection performance parameter of the monitoring end to set the detection threshold value, improves the accuracy of the detection condition of the monitoring end in the obtained actual communication system, can effectively improve the communication concealment of the sending end and the receiving end, maps one information symbol into a plurality of time chips, only sends information in the time with the chip sequence of 1, and because the transmission rate of the information symbol is generally in microsecond level, the energy detection algorithm adopted by the monitoring end can only realize millisecond detection, thus the invention still keeps the concealment under the high-efficiency energy detection algorithm. Finally, since the detection result of the detector is irrelevant to the form of the input signal, the time hopping transmission sequences are arranged in the order of 1 at the front and 0 at the rear, for example 111000, so that the complexity of time hopping synchronization of the receiving end is reduced.
Drawings
Embodiments of the invention are further described below with reference to the accompanying drawings, in which:
Fig. 1 is a schematic diagram of a scenario simulation of a transmitting end, a receiving end and a listening end according to an embodiment of the present invention;
fig. 2 is a flow chart of a method of transmitting a wireless signal according to one embodiment of the present invention;
FIG. 3 is a schematic diagram of a frequency hopping period versus frequency synthesis time relationship according to one embodiment of the present invention;
fig. 4 is a waveform diagram of an original transmission wireless signal according to an embodiment of the present invention;
Fig. 5 is a schematic diagram of a time-hopping transmission sequence generated according to a time-hopping duty cycle and a time-hopping signal waveform diagram for bandpass signal transmission according to the time-hopping transmission sequence according to an embodiment of the present invention;
FIG. 6 is a schematic diagram of occupied time slots for transmitting bandpass signals and occupied frequency bands for transmitting bandpass signals according to one embodiment of the invention;
fig. 7 is a flowchart of a method of acquiring a wireless signal according to one embodiment of the present invention;
Fig. 8 is a schematic diagram of a configuration of a transmitting end for transmitting a wireless signal according to an embodiment of the present invention;
Fig. 9 is a schematic structural diagram of a receiving end for acquiring a wireless signal according to an embodiment of the present invention;
FIG. 10 is a comparison of simulation results in accordance with one embodiment of the present invention.
Detailed Description
For the purpose of making the technical solutions and advantages of the present invention more apparent, the present invention will be further described in detail by way of specific embodiments with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
As mentioned in the background section, in the existing covert communication technology, firstly, the conventional encryption-based information security scheme can only protect the transmission signal from the calculation perspective, and with the enhancement of the hardware processing capability, the conventional encryption scheme based on calculation may fail, and cannot effectively protect the transmission information. Secondly, the application scenario of the prior covert evaluation is not the same as that of the actual communication system, so that the covert communication design scheme taking the prior covert evaluation index as a criterion cannot provide the optimal theoretical guidance for the actual covert communication system. In addition, in an actual communication system, the energy detection algorithm adopted by the monitoring end has high efficiency in a mode of realizing hidden communication through a time hopping technology, and the transmitted signal can be detected through a mode of detecting for many times, so that the time hopping technology cannot improve the concealment of the system. Therefore, in order to further meet the expected requirement of hidden transmission, the time slot for transmitting the signal needs to be low enough, and the throughput of the system is obviously reduced by the scheme, so that the requirement of the communication system on the transmission rate cannot be met. Thus, the time-hopping technique alone has limited utility in improving system concealment. Finally, frequency hopping techniques may improve the system's ability to resist fixed frequency interference, however, in practical communication systems, the frequency hopping signal rate is limited due to hardware level limitations, and thus, the ability of individual frequency hopping techniques to improve the system's concealment is limited. Therefore, there is a need for a method for designing time-hopping and frequency-hopping parameters in a targeted manner by combining time-hopping and frequency-hopping technologies, so that both communication parties can effectively improve the communication concealment capability under the condition of ensuring the data transmission rate.
In order to solve the problems, the invention provides a method for transmitting and receiving wireless signals, which is used for acquiring a frequency hopping rate, expected detection probability and detection performance parameters of a monitoring end when the wireless signals are transmitted, determining a time hopping duty ratio according to the detection performance parameters, a detection threshold set based on the detection performance parameters and the expected detection probability, acquiring a frequency hopping secret key, generating frequency hopping map information according to the frequency hopping rate and the frequency hopping secret key, generating a time hopping transmission sequence according to the time hopping duty ratio, carrying out up-conversion on a baseband signal according to the frequency hopping map information to obtain band-pass signals, and controlling the band-pass signals to be transmitted through an antenna at appointed time according to the time hopping transmission sequence. When a wireless signal is acquired, the frequency hopping rate, the frequency hopping key and the time hopping duty ratio adopted when the wireless signal is transmitted are acquired, frequency hopping map information is generated according to the frequency hopping rate and the frequency hopping key, a time hopping receiving sequence is generated according to the time hopping duty ratio, the antenna is controlled to receive the wireless signal at a designated time based on the time hopping receiving sequence, and finally the acquired wireless signal is subjected to down-conversion by utilizing the frequency hopping map information to obtain a baseband signal. Before the wireless signals are sent, the expected detection probability possibly achieved in a reasonable parameter range and the detection performance of the monitoring end are considered to obtain the time-hopping duty ratio, the time-hopping sending sequence generated by the time-hopping duty ratio controls the band-pass signals to be sent out through the antenna at the appointed time, the proportion of the wireless signals to be sent is reduced to improve the concealment, and the appropriate time-hopping duty ratio can meet the requirement of the data transmission rate to a certain extent. Thus, the combination of time hopping techniques and frequency hopping rates also improves concealment during wireless communications to a greater extent.
Before describing embodiments of the present invention in detail, some of the terms used therein are explained as follows:
the time-hopping duty cycle is the ratio of the actual transmission time of a transmitted wireless signal in one symbol period to the symbol period, i.e., the time required for continuous transmission of one information symbol.
And the false alarm probability value is the probability that the monitoring end erroneously judges that the sending end sends the signal under the influence of the noise signal received by the monitoring end when the sending end does not send the signal.
And the detection probability is the probability that the monitoring end detects the existence of the transmission signal under the condition that the transmission end transmits the signal.
Firstly, a wireless communication scene is simulated and set, and a transmitting end for transmitting wireless signals, a receiving end for receiving wireless signals and a monitoring end for detecting wireless signals in the wireless communication scene are described. According to an embodiment of the present invention, the arrangement manner of the transmitting end a, the receiving end B and the monitoring end W is shown in fig. 1, where the transmitting end a transmits a signal to the receiving end B through a transmitting channel, and the monitoring end W analyzes a signal received by the monitoring channel to detect whether the transmitting end transmits information, and meanwhile, the transmitting channel and the monitoring channel may be both AWGN channels, and the transmitting end and the receiving end share a section of infinitely long key for ensuring successful establishment of a communication link, and the key information is not known by the monitoring end.
In order to increase the concealment of the wireless signal by the transmitting end to reduce the probability of the transmitted wireless signal being detected by the listening end, according to an embodiment of the present invention, a method for transmitting a wireless signal is provided, see fig. 2, including steps S1, S2, S3, S4. For a better understanding of the present invention, each step is described in detail below in connection with specific examples.
Step S1, obtaining a frequency hopping rate, expected detection probability and detection performance parameters of a monitoring end, and determining a time hopping duty ratio according to the detection performance parameters, a detection threshold set based on the detection performance parameters and the expected detection probability.
According to one embodiment of the present invention, the higher the frequency hopping rate, the lower the probability that the signal is detected, however, limited by the hardware level, there is a frequency switching time in which no information can be transmitted and the frequency hopping performance loss occurs, see fig. 3, for example, generally, the frequency synthesis time is required to be not more than 20% of the frequency hopping period in engineering, so after the hardware frequency synthesis time is determined, the highest frequency hopping rate is limited, and the frequency hopping rate can be set to 2000hop/s, which is only illustrative herein, and the implementation can set according to specific situations and needs, which is not limited in this respect. The expected detection probability is the optimal detection probability possibly achieved by the monitoring end when the sending end and the receiving end communicate by fully considering the actual working mode of the monitoring end. The actual working mode of the monitoring end can be that the monitoring end divides the monitoring channel into a plurality of sub-channels by adopting a channelized receiver and using a plurality of filters with the bandwidth of M, so that the monitoring end can detect wireless signals received by the sub-channels at the same time. The channelized receiver can intercept and receive wireless signals of different frequency bands at the same time, after intercepting and receiving the wireless signals, the monitoring end firstly calculates the wireless signal energy received by each sub-channel, compares the obtained maximum wireless signal energy and the corresponding frequency point with a preset threshold value, confirms that a transmitting signal exists on the frequency band when the wireless signal energy is larger than the preset threshold value, and further understands the received wireless signals or generates interference on the frequency point.
According to one embodiment of the invention, the detection performance parameter comprises a signal-to-noise ratio of a receiving signal of a monitoring end, and the signal-to-noise ratio obtaining mode of the receiving signal of the monitoring end comprises steps a1 and a2, wherein,
Step a1, acquiring monitoring parameters of a monitoring end and communication parameters of a sending end and a receiving end. The monitoring parameters comprise the minimum monitoring distance between the monitoring end and the transmitting end, channel fading factors, channel noise power, carrier wave wavelength, receiving antenna gain of the monitoring end and transmitting antenna gain of the transmitting end. The communication parameters comprise a target data transmission rate of a transmitting end and a transmitting antenna gain of the transmitting end, a minimum receiving signal-to-noise ratio of a receiving end and a receiving antenna gain of the receiving end, a distance between the transmitting end and the receiving end, a channel fading factor and a carrier wave wavelength.
And a2, calculating the minimum transmission signal power of the transmitting end based on the communication parameters of the transmitting end and the receiving end, and calculating the signal-to-noise ratio of the receiving signal of the monitoring end according to the monitoring parameters and the minimum transmission signal power.
According to one embodiment of the invention, step a2 further comprises the steps of:
And a step a21 of calculating the minimum transmission signal power of the transmitting end based on the communication parameters. The preferred calculation method includes calculating the minimum received signal power of the receiving end based on the target data transmission rate and the minimum received signal to noise ratio, and calculating the minimum transmitted signal power based on the minimum received signal power, the distance between the transmitting end and the receiving end, the channel fading factor, the carrier wavelength, the transmitting antenna gain, and the receiving end receiving antenna gain. Wherein, the communication parameters are the communication performance parameters of both legal communication parties (a sending end and a receiving end).
According to one embodiment of the invention, given the target data transmission rate R, the minimum receiving signal-to-noise ratio of the receiving end is determined according to shannon channel capacity formula r=log (1+snr), and the determining formula is as follows:
Wherein snr is the minimum received signal-to-noise ratio of the receiving end, P r_receiver is the minimum received signal power of the receiving end, The channel noise power is received for the receiving end.
The minimum received signal power of the receiving end is determined according to the minimum received signal-to-noise ratio of the receiving end, and the determination formula is as follows:
and finally, combining a free space loss model to calculate and obtain the minimum transmitting signal power of the transmitting end, wherein the calculation formula is as follows:
Wherein, P t_min is the minimum transmitting signal power of the transmitting end, P r_receiver is the minimum receiving signal power of the receiving end, d tr is the distance between the transmitting end and the receiving end, l is the channel fading factor, G t is the transmitting antenna gain of the transmitting end, G r is the receiving antenna gain of the receiving end, Λ is the carrier wavelength, c=3×10 8 m/s is the speed at which light propagates in vacuum, and f is the carrier frequency.
And a step a22, calculating the signal-to-noise ratio of the received signal of the monitoring end according to the monitoring parameter and the minimum transmission signal power. The specific calculation mode comprises the steps of calculating the received signal power of the monitoring end according to the minimum transmitted signal power of the transmitting end, the transmitting antenna gain of the transmitting end, the receiving antenna gain of the monitoring end, the minimum monitoring distance between the monitoring end and the transmitting end, the channel fading factor and the carrier wave wavelength between the monitoring end and the transmitting end, and calculating the signal-to-noise ratio of the received signal based on the received signal power and the channel noise power of the monitoring end.
After the minimum transmission signal power is calculated according to the step a21, the received signal power of the monitoring end can be calculated through a free space loss model, and the calculation formula is as follows:
Wherein, P r_warden is the received signal power of the monitor, G r' is the receiving antenna gain of the monitor, and d min is the minimum monitorable distance between the monitor and the transmitting end.
Further, according to the received signal power of the monitoring end, the signal to noise ratio gamma of the received signal of the monitoring end is calculated, and the calculation formula is as follows:
wherein, gamma is the signal-to-noise ratio of the signal received by the monitoring end, And monitoring the channel noise power for the monitoring end.
Since the higher the frequency hopping rate is, the lower the probability of signal detection is, so the performance of the detector is limited by the set frequency hopping rate in a manner of limiting the optimal detection time of the detector at the monitoring end on a single frequency band to a certain extent. According to one embodiment of the invention, the detection performance parameter further comprises a preset false alarm probability value and a detection time window length, wherein the detection time window length determining mode comprises the steps of setting a signal sampling frequency of a monitoring end, obtaining optimal detection time based on a frequency hopping rate, and determining the detection time window length according to the optimal detection time and the signal sampling frequency.
According to one embodiment of the present invention, the obtaining method for obtaining the optimal detection time based on the frequency hopping rate includes:
τ=1/vhop,
Where τ is the optimal detection time and v hop is the frequency hopping rate.
Determining a detection time window length according to the optimal detection time and the signal sampling frequency, including:
L=τfs,
wherein L is the detection time window length, and f s is the signal sampling frequency.
For the monitoring end, in order to reduce the invalid working influence of the false alarm probability value on the monitoring end, the detection threshold is adjusted to enable the false alarm probability value to be as low as possible, and the detection threshold at the moment is not an optimal detection threshold for enabling the sum of the false alarm probability and the missed detection probability to be minimum. For the transmitting end, if the transmitting end pays more attention to whether the transmitting signal can be detected, the probability of missing detection of the monitoring end is more desirable. Therefore, the sum of the false alarm probability and the missing detection probability under the optimal detection threshold cannot well obtain the detection condition of the monitoring end in the actual communication system. Therefore, according to one embodiment of the present invention, the detection threshold is set according to the detection performance parameter of the listening end, including the following setting manners:
wherein epsilon is a detection threshold value, Q is a complementary cumulative distribution function, P f is a preset false alarm probability value, L is a detection time window length, Is the channel noise power of the listening end. The detection threshold is set by combining with each detection performance parameter of the monitoring end, so that the accuracy of the detection condition of the monitoring end in the obtained actual communication system is improved, and the communication concealment of the sending end and the receiving end can be effectively improved.
At present, in order to meet the expected requirement of hidden transmission, the transmission time slot of a transmission signal needs to be low enough, so that the system throughput caused by quite small time-hopping duty ratio is obviously reduced, and the requirement of data transmission rate in communication cannot be met. To set the appropriate time-hopping duty cycle, according to one embodiment of the invention, the time-hopping duty cycle is determined as follows:
Wherein ρ is the time-hopping duty cycle, Q is the complementary cumulative distribution function, P d is the desired detection probability, γ is the signal-to-noise ratio of the received signal at the listening end, L is the detection time window length, ε is the detection threshold, Is the channel noise power of the listening end. After the optimal detection time of the detector of the monitoring end and the detection threshold value in the actual communication system are given, the invention can set the proper time-hopping duty ratio by the time-hopping technology, properly reduce the proportion of the transmission signals input into the detector, not only meet the requirement of the data transmission rate in communication, but also further reduce the detection probability of the monitoring end on the transmission signals.
And S2, acquiring a frequency hopping key, generating frequency hopping map information according to the frequency hopping rate and the frequency hopping key, and generating a time hopping transmission sequence according to the time hopping duty ratio.
According to one embodiment of the present invention, before generating the hopping pattern information, a plurality of sets of hopping keys are generally set in practice, and different hopping keys correspond to different hopping patterns and are selected for use, so that one of the hopping keys needs to be acquired, and the generation of the hopping pattern information is controlled according to the hopping keys and the hopping rate.
According to one embodiment of the invention, the time hopping transmission sequence comprises a plurality of time chips indicating whether to transmit the band-pass signal, wherein the time hopping transmission sequence indicates that the number ratio of the time chips transmitting the band-pass signal to all the time chips accords with the time hopping duty ratio, and the time chips indicating that the band-pass signal is transmitted are arranged before the time chips indicating that the band-pass signal is not transmitted. In addition, a time Chip is also commonly called a Chip (Chip), and in the field of wireless communication, a time for transmitting one information symbol in a band-pass signal is divided into m (m is an integer greater than 1) short intervals, which are called chips. For example, assuming that m is 10, the time of transmitting 1 information symbol is divided into 10 time chips, and the information symbol may be indicated to be transmitted in some of the time chips by the time hopping transmission sequence, so that the band-pass signal is controlled to be transmitted through the antenna at a designated time according to the time hopping transmission sequence.
According to one embodiment of the present invention, each information symbol in the band-pass signal is mapped into a time-hopping transmission sequence according to a time-hopping duty cycle, and it is required to be clear that a symbol period is larger than a period of a time chip, for example, the symbol period of one information symbol in the transmission band-pass signal is 1ms, the time-hopping duty cycle is 0.5, and the period of the time chip may be defined to be 0.1ms, and the information symbol is mapped into a time-hopping transmission sequence in the form of 1111100000 according to the time-hopping duty cycle, wherein the first 5 time chips of the time-hopping transmission sequence are time chips indicating that the band-pass signal is transmitted, and the last 5 time chips are time chips indicating that the band-pass signal is not transmitted. Since the transmission rate of the information symbol is generally in microsecond level, in an actual communication system, the energy detection algorithm adopted by the monitoring end can only realize millisecond level detection. Therefore, a plurality of information symbols are included in the detection time range of the detector at one monitoring end, so that the concealment is still kept under the high-efficiency detection algorithm.
According to one embodiment of the invention, the time chips indicating to transmit the band-pass signal are arranged before the time chips indicating to not transmit the band-pass signal, thereby reducing the complexity of time-hopping synchronization of the receiving end.
Before the time-hopping duty cycle is not set, referring to fig. 4, the abscissa of the coordinate system represents time, the ordinate represents amplitude, and the original transmission wireless signal waveform in the coordinate system represents continuous transmission wireless signal in one symbol period. After setting the time-hopping duty cycle, see fig. 5, which includes two coordinate systems, wherein the abscissa of each coordinate system represents time, the ordinate represents amplitude, the upper coordinate system is a time-hopping transmission sequence when the time-hopping duty cycle is 0.5, and the time-hopping signal waveform of the corresponding coordinate system below the time-hopping transmission sequence represents that the first half symbol period in one symbol period is transmitting a wireless signal, and the second half symbol period is in an idle state. In a section of time-hopping signal waveform of 0, only noise signals detected by a detector of the monitoring end are reduced to a certain extent, so that the detection probability of the monitoring end is reduced, and the concealment of communication signals is improved.
And step S3, up-converting the baseband signal according to the frequency hopping pattern information to obtain a band-pass signal to be transmitted.
According to one embodiment of the invention, the baseband signal is obtained by the transmitting end sequentially encoding and modulating the received information bits.
And S4, controlling the band-pass signal to be sent out through the antenna at the appointed time according to the time-hopping sending sequence to obtain the wireless signal.
According to one embodiment of the present invention, referring to fig. 6, the band-pass signal obtained according to the frequency hopping pattern information and the time hopping transmission sequence obtained according to the time hopping duty ratio are included, and the time occupied slot and the frequency occupied distribution diagram when the band-pass signal is transmitted are represented by time on the abscissa, and the frequency hopping point on the corresponding time on the ordinate is represented by F.
According to an embodiment of the present invention, there is provided a method for acquiring a wireless signal, see fig. 7, including steps A1, A2, A3, A4.
Step A1, obtaining the frequency hopping rate, the frequency hopping key and the time hopping duty ratio adopted when the wireless signal is transmitted according to the above embodiment of the present invention.
And A2, generating frequency hopping map information according to the frequency hopping rate and the frequency hopping key, and generating a time hopping receiving sequence according to the time hopping duty ratio.
And step A3, controlling the antenna to receive the wireless signal at the appointed time based on the time hopping receiving sequence.
According to one embodiment of the present invention, frequency hopping pattern information and a time hopping reception sequence including a number of time chips indicating whether to receive a wireless signal are generated in the same manner as a transmitting end, wherein the number ratio of the time chips indicating to receive the wireless signal and all the time chips corresponds to a time hopping duty ratio, and the time chips indicating to receive the wireless signal are arranged before the time chips indicating not to receive the wireless signal. The time-hopped receive sequence of claim 1111100000 wherein the first 5 time chips of the time-hopped receive sequence are time chips indicating receipt of a wireless signal and the last 5 time chips are time chips indicating no receipt of a wireless signal.
And step A4, acquiring a received wireless signal, and performing down-conversion on the wireless signal by using the frequency hopping pattern information to obtain a baseband signal.
According to an embodiment of the present invention, there is provided a wireless transmitting end (corresponding to the transmitting end) for the above-mentioned method for transmitting a wireless signal of the present invention, referring to fig. 8, including an encoder and a modulator, encoding information bits by the encoder, and modulating the encoded information bits by the modulator to obtain a baseband signal. In addition, the device also comprises a frequency hopping and time hopping parameter configuration module which is used for acquiring the frequency hopping rate, the expected detection probability and the detection performance parameter of the monitoring end, and determining the time hopping duty ratio according to the detection performance parameter, the detection threshold value set based on the detection performance parameter and the expected detection probability. The frequency hopping and time hopping module is used for acquiring the frequency hopping secret key, generating frequency hopping map information according to the frequency hopping rate and the frequency hopping secret key, and generating a time hopping transmission sequence according to the time hopping duty ratio. And the first mixer is used for carrying out up-conversion on the baseband signal according to the frequency hopping pattern information to obtain a band-pass signal to be transmitted. And the first high-frequency switch is used for controlling the band-pass signal to be sent out through the sending antenna at the appointed time according to the time hopping sending sequence to obtain a wireless signal. And a transmitting antenna for transmitting the band-pass signal, the frequency hopping rate, the frequency hopping key and the time hopping duty ratio at a designated time.
According to one embodiment of the invention, the band-pass signal is controlled to be sent out through the antenna at a designated time according to the time hopping sending sequence, wherein the time hopping sending sequence is utilized to control the on-off of the first high-frequency switch, the first high-frequency switch is turned on when the time hopping sending sequence is 1, the band-pass signal is sent, and the first high-frequency switch is turned off when the time hopping sending sequence is 0, and the band-pass signal is not sent.
According to an embodiment of the present invention, there is provided a wireless receiving terminal (corresponding to a receiving terminal) for the above-described method of acquiring a wireless signal of the present invention, referring to fig. 9, including a receiving antenna for receiving a wireless signal, a frequency hopping rate, a frequency hopping key, and a time hopping duty ratio at a designated time. The time hopping frequency hopping parameter synchronization module is used for acquiring the frequency hopping rate, the frequency hopping key and the time hopping duty ratio adopted when the wireless signal is transmitted according to the method of the invention, and simultaneously, synchronizing the frequencies of the receiving end and the transmitting end and synchronizing the time of the receiving end and the transmitting end. And the frequency hopping time hopping receiving module is used for generating frequency hopping map information according to the frequency hopping rate and the frequency hopping key and generating a time hopping receiving sequence according to the time hopping duty ratio. And a second high frequency switch for controlling the receiving antenna to receive the wireless signal at a specified time based on the time hopping receiving sequence. And the second mixer is used for acquiring the received wireless signal, and performing down-conversion on the wireless signal by utilizing the frequency hopping pattern information to obtain a baseband signal. In addition, a demodulator is included for demodulating the baseband signal. And the decoder is used for decoding the demodulated baseband signal to obtain information bits.
According to one embodiment of the invention, controlling the antenna to receive the wireless signal at the designated time according to the time hopping reception sequence includes controlling on/off of the second high frequency switch by using the time hopping reception sequence, turning on the second high frequency switch when the time hopping reception sequence is 1, receiving the wireless signal, and turning off the second high frequency switch when the time hopping reception sequence is 0, not receiving the wireless signal.
According to an embodiment of the present invention, there is provided a wireless communication system including a transmitting end of the method of transmitting a wireless signal according to the above embodiment of the present invention and a receiving end of the method of acquiring a wireless signal according to the above embodiment of the present invention.
To illustrate the effect of the present invention, the inventors performed simulation verification on the method of the present invention, and simulation parameters are shown in table 1.
TABLE 1 simulation parameter settings
Parameter description:
And the false alarm probability value is that the monitoring end adopts a sampling rate which is 2 times of the bandwidth of the transmitted wireless signal to sample according to the Nyquist theorem, and can obtain all information of the transmitted wireless signal. Therefore, the false alarm probability value is generally set to 0.05 in the simulation practice process.
The minimum interception distance between the sending end and the interception end is generally considered that the interception end can be discovered by the sending end when the distance between the interception end and the sending end is smaller than d min, so that the sending end can take measures to attack or avoid the interception end. D min was set to 6km during simulation practice.
According to the simulation parameters, simulation practice is carried out on the method for transmitting the wireless signals of the transmitting end:
After the target data transmission rate R is given, determining the minimum receiving signal-to-noise ratio of a receiving end according to a shannon channel capacity formula, wherein R=log (1+snr), and the determining formula is as follows:
Wherein snr is the minimum received signal-to-noise ratio of the receiving end, P r_receiver is the minimum received signal power of the receiving end, The channel noise power is received for the receiving end.
The minimum received signal power of the receiving end is determined according to the minimum received signal-to-noise ratio of the receiving end, and the determination formula is as follows:
and finally, combining a free space loss model to calculate and obtain the minimum transmitting signal power P t_min =1.09 w of the transmitting end.
Combining the minimum signal power of the transmitting end, the minimum interception distance d min between the transmitting end and the interception end can calculate the received signal power of the interception end according to the free space loss model
Further, the signal-to-noise ratio of the receiving signal of the monitoring end is calculated according to the power of the receiving signal of the monitoring end
From l=τf s,τ＝1/vhop, the listening end detection time window length (i.e., the number of sampling points) l=3000 can be determined.
Given a false alarm probability value of P f =0.05, the detection threshold is known
Further, to make the expected detection probability of the monitoring end lower than 0.5, according to the formula
It is possible to obtain the simulation practice that, when the expected detection probability P d =0.5, Q -1(Pd) =0,The time-hopping duty cycle ρ= 0.673103156641033 satisfying the demand is calculated.
The simulation practice results are shown in fig. 10, the abscissa is the detection time of the communication signal detected by the monitoring end, the ordinate is the detection probability of the monitoring end at the corresponding detection time, and fig. 10 comprises the detection probabilities corresponding to three methods for transmitting wireless signals, wherein the detection probabilities are respectively that a frequency hopping communication system which adopts a frequency hopping signal (the frequency hopping rate is 2000 hop/s) is only set, a time hopping communication system which only sets a time hopping signal (the time hopping duty ratio is 0.67) is set, and a time hopping communication system which sets a time hopping frequency signal (the frequency hopping rate is 2000hop/s and the time hopping duty ratio is 0.67) are set, the detection probabilities of the communication signals of the monitoring end on all the communication systems are compared, and according to the illustration results, compared with the independent time hopping communication system and the frequency hopping communication system, the time hopping frequency hopping communication system combines the advantages of the time hopping technology and the frequency hopping technology, and the concealment of the communication signals can be effectively improved.
It should be noted that, although the steps are described above in a specific order, it is not meant to necessarily be performed in the specific order, and in fact, some of the steps may be performed concurrently or even in a changed order, as long as the required functions are achieved.
The present invention may be a system, method, and/or computer program product. The computer program product may include a computer readable storage medium having computer readable program instructions embodied thereon for causing a processor to implement aspects of the present invention.
The computer readable storage medium may be a tangible device that retains and stores instructions for use by an instruction execution device. The computer readable storage medium may include, for example, but is not limited to, an electronic storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of the computer-readable storage medium include a portable computer diskette, a hard disk, a Random Access Memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), a Static Random Access Memory (SRAM), a portable compact disc read-only memory (CD-ROM), a Digital Versatile Disc (DVD), a memory stick, a floppy disk, a mechanical encoding device, punch cards or intra-groove protrusion structures such as those having instructions stored thereon, and any suitable combination of the foregoing.
The foregoing description of embodiments of the invention has been presented for purposes of illustration and description, and is not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the various embodiments described. The terminology used herein was chosen in order to best explain the principles of the embodiments, the practical application, or the technical improvements in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.
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