A Backscatter Communication Method and System for Concealed Environments

Abstract

The present invention provides a method and system for backscatter communication in a covert environment, which relates to the field of wireless communication. The backscatter communication system in a covert environment includes an environmental radio frequency source, a monitor, a receiving end, and a backscatter tag including multiple antennas. The environmental radio frequency source is used to send radio frequency signals to the backscatter tag. For any preset transmission gap, when in an active state, the backscatter tag is used to perform backscatter processing on the radio frequency signals to obtain backscatter signals; the backscatter signals include covert information to be transmitted. The receiving end is used to convert the backscatter signals and radio frequency signals to obtain the covert information. The monitor is used to acquire and detect whether the backscatter tag transmits covert information based on the power of the backscatter signals. Based on this, the present invention can effectively increase the channel capacity while ensuring communication concealment without increasing the additional power consumption of the backscatter device.

Description

Technical Field

[0001] The present invention relates to the field of wireless communication, and particularly to a backscatter communication method and system in a covert environment. Background Art

[0002] As a new emerging ultra-low power communication paradigm, backscatter devices draw energy from ambient electromagnetic waves to activate circuits, and adjust the reflection coefficient of the antenna by switching the antenna impedance according to the information bits to be transmitted, and then bounce the incident signal through different reflection coefficients to complete passive information transmission. In the prior art, backscatter devices collect ambient electromagnetic wave energy, do not rely on battery power supply, can reduce system power consumption and system maintenance cost. The backscatter communication method abandons the traditional radio frequency link, greatly reduces the transmission power consumption, and solves the device cost. However, its extremely simplified design principle makes its protocol stack simple and the computing power limited, unable to ensure the security of the communication process, and there is a large monitoring risk.

[0003] Generally, backscatter communication schemes include two types. One is artificial noise injection. For example, a covert communication method for an ambient backscatter system with an uncontrollable radio frequency source is to design an optimal communication strategy and detection scheme using a full-duplex receiver that emits artificial noise. The other is beamforming. For example, the spatial selectivity of multi-antenna tags is used to ensure the concealment of the ambient backscatter system.

[0004] However, due to the uncontrollability of the ambient radio frequency source and the limited power of the backscatter tag, the artificial noise injection scheme depends on a full-duplex receiver. The artificial noise injection method cannot be compatible with the existing ambient backscatter communication system, and will increase the system power consumption, unable to meet the ultra-low power requirement of the system. And the beamforming scheme requires the backscatter device to accurately estimate the channel state information and time synchronization, and due to the limited power of the backscatter tag, it is almost impossible for the backscatter device to achieve.

[0005] Based on this, there is an urgent need for an ultra-low power and high-rate covert backscatter transmission scheme. Summary of the Invention

[0006] In view of the above deficiencies in the prior art, the present invention provides a backscatter communication method and system in a covert environment, which can ensure communication concealment and effectively increase the channel capacity without increasing the additional power consumption of the backscatter device.

[0007] In order to achieve the above invention object, the technical solution adopted by the present invention is:

[0008] In a first aspect, the present invention provides a backscatter communication system for a concealed environment, comprising an environmental radio frequency source, a monitor, a receiving end, and a backscatter tag including multiple antennas; the environmental radio frequency source is communicatively connected to the monitor, the receiving end, and the backscatter tag respectively; the backscatter tag is also communicatively connected to the monitor and the receiving end;

[0009] The environmental radio frequency source is configured to send a radio frequency signal to the backscatter tag;

[0010] For any preset transmission gap, when the backscatter tag is in an active state, it is configured to perform backscatter processing on the radio frequency signal to obtain a backscattered signal; the backscattered signal includes concealed information to be transmitted;

[0011] The receiving end is configured to convert the backscattered signal and the radio frequency signal to obtain the concealed information;

[0012] The monitor is configured to obtain and detect whether the backscatter tag transmits concealed information based on the power of the backscattered signal.

[0013] Preferably, at least one of the antennas is a target antenna; for any preset transmission gap, the backscatter tag is further configured to transmit the concealed information of the tag through the radio frequency signal using the target antenna according to a first reflection coefficient; and transmit the public information of the tag through the radio frequency signal using the remaining antennas except the target antenna according to a second reflection coefficient to obtain a backscattered signal; wherein the first reflection coefficient and / or the second reflection coefficient is a random variable subject to a continuous uniform distribution.

[0014] Preferably, the backscatter tag is further configured to convert the bit sequence corresponding to the concealed information to be transmitted according to a preset rule to obtain a backscattered signal.

[0015] Preferably, when determining the target antenna according to the antenna index, the backscatter tag is further configured to map some bit information in the bit sequence to spatial constellation points; and map the remaining bit information in the bit sequence except the some bit information to signal constellation points to obtain a backscattered signal.

[0016] Preferably, when there are four antennas and each antenna index includes two-bit information, the backscatter tag is further configured to map at least the first two bit information in the bit sequence to spatial constellation points; and map the bit information in the bit sequence except at least the first two bit information to signal constellation points to obtain a backscattered signal.

[0017] Preferably, the expression of the first reflection coefficient satisfies:

[0018]

[0019] where Γ 1max is the maximum change value of the first reflection coefficient; is the first reflection coefficient value when the change amount γ is in the interval [0, Γ 1max .

[0020] Preferably, the monitor is also used to determine that the backscatter tag transmits hidden information when the average power of the backscattered signal under a preset transmission gap is greater than the threshold value; and determine that the backscatter tag does not transmit hidden information when the average power of the backscattered signal under the preset transmission gap is less than or equal to the threshold value.

[0021] Preferably, the monitor is also used to obtain a probability constraint function based on the error probability when detecting the hidden information transmission of the backscatter tag, so as to measure the concealment performance of the backscatter communication system in the hidden environment through the threshold value and / or the probability constraint function.

[0022] Preferably, when the error probability includes the miss detection probability and the false alarm probability, where the miss detection probability is the probability that the hidden transmission occurs but is not detected; and the false alarm probability is the probability that the detection result indicates the occurrence when the hidden transmission does not occur, the received signal of the monitor in different test states is expressed as:

[0023]

[0024] where, H0 means that the backscatter tag does not send hidden information to the receiving end; H1 means that the backscatter tag sends hidden information to the receiving end; Γ1 is the first reflection coefficient; Γ2 is the second reflection coefficient; P a is the transmission power of the RF signal, x, s, c are the RF signal, the hidden information of the tag, and the public information of the tag respectively, h aw , h at , h tw are the channel coefficients from the environmental RF source to the monitor, from the environmental RF source to the backscatter tag, and from the backscatter tag to the monitor respectively, n w is the additive Gaussian noise of the monitor; k is the first matrix, k c is the second matrix.

[0025] In a second aspect, the present invention also provides a backscatter communication method in a hidden environment, which is applied to a backscatter communication system in a hidden environment. The backscatter communication system in a hidden environment includes an environmental RF source, a monitor, a receiving end, and a backscatter tag including multiple antennas; the environmental RF source is communicatively connected to the monitor, the receiving end, and the backscatter tag respectively; the backscatter tag is also communicatively connected to the monitor and the receiving end;

[0026] Use the environmental RF source to send an RF signal to the backscatter tag;

[0027] For any preset transmission gap, when the backscatter tag is in the active state, it performs backscatter processing on the radio frequency signal to obtain a backscattered signal; the backscattered signal includes the covert information to be transmitted.

[0028] The receiving end is used to convert the backscattered signal and the radio frequency signal to obtain the covert information.

[0029] The monitor is used to obtain and detect whether the backscatter tag transmits covert information based on the power of the backscattered signal.

[0030] In summary, a covert environment backscatter communication method and system provided by the present invention have the following

[0031] Beneficial effects:

[0032] The present invention provides a covert environment backscatter communication system, including an environmental radio frequency source, a monitor, a receiving end, and a backscatter tag including multiple antennas; the environmental radio frequency source is communicatively connected to the monitor, the receiving end, and the backscatter tag respectively; the backscatter tag is also communicatively connected to the monitor and the receiving end. The environmental radio frequency source is used to send a radio frequency signal to the backscatter tag; for any preset transmission gap, the backscatter tag is used to perform backscatter processing on the radio frequency signal when in the active state to obtain a backscattered signal; the backscattered signal includes the covert information to be transmitted; the receiving end is used to convert the backscattered signal and the radio frequency signal to obtain the covert information; the monitor is used to obtain and detect whether the backscatter tag transmits covert information based on the power of the backscattered signal. Based on this, a covert environment backscatter communication method and system provided by the present invention can ensure communication concealment and effectively increase the channel capacity while not increasing the additional power consumption of the backscatter device.

[0033] To make the above objects, features, and advantages of the present invention more obvious and understandable, the following specific preferred embodiments are given below and are described in detail in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts.

[0035] Figure 1 FIG. 1 shows one of the schematic structural diagrams of a covert environment backscatter communication system provided by an embodiment of the present invention;

[0036] Figure 2Shows the second structural schematic diagram of the backscatter communication system in a covert environment provided by an embodiment of the present invention;

[0037] Figure 3 Shows the step schematic diagram of a backscatter communication method in a covert environment provided by an embodiment of the present invention;

[0038] Figure 4 Shows the second step schematic diagram of a backscatter communication method in a covert environment provided by an embodiment of the present invention.

[0039] Icons: 100 - Backscatter communication system in a covert environment; 101 - Environmental radio frequency source; 102 - Monitor; 103 - Receiver; 104 - Multi-antenna backscatter tag. Detailed implementation manners

[0040] The following describes the detailed implementation manners of the present invention to facilitate those skilled in the art of the present technology to understand the present invention. However, it should be clear that the present invention is not limited to the scope of the detailed implementation manners. For those of ordinary skill in the art of the present technology, as long as various changes are within the spirit and scope of the present invention defined and determined by the appended claims, these changes are obvious, and all inventions created using the concept of the present invention are within the scope of protection.

[0041] Generally, there are two types of backscatter communication schemes. First, for the covert communication method of the backscatter system in an environment with an uncontrollable radio frequency source, an optimal communication strategy and detection scheme are designed using a full-duplex receiver that emits artificial noise. Second, the spatial selectivity of multi-antenna tags is used to ensure the concealment of the backscatter system in the environment.

[0042] However, due to the uncontrollability of the environmental radio frequency source and the limited power of the backscatter tag, the artificial noise injection scheme depends on a full-duplex receiver. The artificial noise injection method cannot be compatible with the existing backscatter communication system in the environment and will increase the system power consumption, unable to meet the ultra-low power consumption requirements of the system; while the beamforming scheme requires the backscatter device to accurately estimate the channel state information and perform time synchronization. Due to the limited power of the backscatter tag, it is almost impossible for the backscatter device to achieve.

[0043] Based on this, the present invention provides an ultra-low power and high-rate covert backscatter transmission scheme.

[0044] Please refer to Figure 1, In a first aspect, the present invention provides a backscatter communication system 100 in a covert environment, including an environmental radio frequency source 101, a monitor 102, a receiving end 103, and a backscatter tag including multiple antennas, that is, a multi-antenna backscatter tag 104. Among them, the environmental radio frequency source 101 is respectively communicatively connected to the monitor 102, the receiving end 103, and the backscatter tag; the multi-antenna backscatter tag 104 is also communicatively connected to the monitor 102 and the receiving end 103, that is, the multi-antenna backscatter tag 104 communicates with the monitor 102 and the receiving end 103 through the antennas.

[0045] In this embodiment, the environmental radio frequency source 101 is used to send a radio frequency signal to the backscatter tag; in a possible implementation manner, the environmental radio frequency source can be a cellular signal or a Wi-Fi signal, etc., to provide energy and a radio frequency carrier for the tag.

[0046] For any preset transmission gap, the multi-antenna backscatter tag 104 is used to perform backscatter processing on the radio frequency signal when in an active state to obtain a backscatter signal; the backscatter signal includes the covert information to be transmitted.

[0047] Specifically, the multi-antenna backscatter tag 104 first absorbs the signal energy from the environmental radio frequency source 101 to activate its circuit, and then uses spatial modulation technology, that is, only one tag antenna is activated in each time slot, and the covert information of the tag is transmitted through random reflection coefficients and antenna indices, and the remaining antennas transmit public information through random reflection systems to confuse the detection of the malicious monitor 102.

[0048] The receiving end 103 is used to convert the backscatter signal and the radio frequency signal to obtain the covert information. In a possible implementation manner, the receiving end 103 can perform joint detection on the backscatter index, the reflection coefficient, and the excitation source signal, that is, the radio frequency signal, etc. At the same time, when the receiving end converts the backscatter signal and the radio frequency signal, it can also analyze the covert capacity of the backscatter signal, including the channel capacity corresponding to the tag impedance modulation and the channel capacity corresponding to the spatial modulation.

[0049] The monitor 102 is used to obtain and detect whether the backscatter tag transmits covert information based on the power of the backscatter signal.

[0050] In this embodiment, the monitor 102 monitors the transmission of the backscatter covert communication through energy detection, such as power.

[0051] Based on this, a backscatter communication system 100 in a covert environment provided in this embodiment can achieve covert communication while improving the transmission rate of the tag.

[0052] In a possible implementation manner, at least one of the antennas includes a target antenna; for any preset transmission gap, the multi-antenna backscatter tag is further configured to transmit the hidden information of the tag through a radio frequency signal by using the target antenna according to a first reflection coefficient; and transmit the public information of the tag through a radio frequency signal by using the antennas other than the target antenna according to a second reflection coefficient to obtain a backscatter signal; wherein, the first reflection coefficient and / or the second reflection coefficient is a random variable subject to a continuous uniform distribution.

[0053] Please refer to Figure 2 , in a possible implementation manner, the signal can be loaded onto the incident signal through impedance matching to complete signal transmission. For example, the resistance or impedance of the corresponding antenna can be adjusted by a controller.

[0054] Preferably, the expression of the first reflection coefficient satisfies:

[0055]

[0056] wherein, Γ 1max is the maximum change value of the first reflection coefficient; is the value of the first reflection coefficient when the change amount γ is in the interval [0, Γ 1max .

[0057] Similarly, the expression of the second reflection coefficient satisfies:

[0058]

[0059] wherein, Γ 2max is the maximum change value of the second reflection coefficient; is the value of the first reflection coefficient when the change amount γ is in the interval [0, Γ 2max .

[0060] In a possible implementation manner, the backscatter tag is further configured to convert the bit sequence corresponding to the hidden information to be transmitted according to a preset rule to obtain a backscatter signal.

[0061] In this embodiment, when the target antenna is determined according to the antenna index, the backscatter tag is further configured to map some bit information in the bit sequence to spatial constellation points; and map the remaining bit information in the bit sequence except for some bit information to signal constellation points to obtain a backscatter signal.

[0062] For example, when there are four antennas and each antenna index includes two-bit information, the backscatter tag is further configured to map at least the first two-bit information in the bit sequence to spatial constellation points; and map the bit information in the bit sequence except for at least the first two-bit information to signal constellation points to obtain a backscatter signal.

[0063] In a possible implementation, the monitor 102 is further configured to determine that the backscatter tag performs covert information transmission when the average power of the backscatter signal under a preset transmission gap is greater than a threshold value; and determine that the backscatter tag does not perform covert information transmission when the average power of the backscatter signal under the preset transmission gap is less than or equal to the threshold value.

[0064] Specifically, the monitor determines whether the backscatter tag performs covert information transmission according to the observed signal. In a possible implementation, the monitor can use a radiometer to monitor the transmission energy of its backscatter signal, and then judge the method of covert information transmission. A threshold value can be preset in advance. When the average received power of an observation time slot is greater than the threshold value, it is determined that there is covert transmission. If the average received power is less than the threshold value, it is determined that there is no covert transmission.

[0065] Furthermore, the monitor 102 is further configured to obtain a probability constraint function based on the error probability obtained by detecting the backscatter tag during covert information transmission, so as to measure the covert performance of the backscatter communication system in the covert environment through the threshold value and / or the probability constraint function.

[0066] In this embodiment, please continue to refer to Figure 2 , the monitor performs a binary hypothesis test on the received signal (ideally, the received signal is the backscatter signal). When the error probability or the detection error probability includes the miss detection probability and the false alarm probability, and the sum of the miss detection probability value and the false alarm probability value is used as the detection error probability value, the miss detection probability is the probability that the covert transmission occurs but is not detected; the false alarm probability is the probability that the detection result is that the covert transmission occurs when the covert transmission does not occur. The received signal of the monitor in different test states is expressed as:

[0067]

[0068] where, H0 is that the backscatter tag does not send covert information to the receiving end; H1 is that the backscatter tag sends covert information to the receiving end; Γ1 is the first reflection coefficient; Γ2 is the second reflection coefficient; P a is the transmission power of the RF signal, x, s, c are the RF signal, the covert information of the tag, and the public information of the tag respectively, h aw , h at , h tw are the channel coefficients from the environmental RF source to the monitor, from the environmental RF source to the backscatter tag, and from the backscatter tag to the monitor respectively, n w is the additive Gaussian noise of the monitor; k is the first matrix. For example, k = diag[0, 0, 0, … 1 t …, 0, 0, 0], k c is the second matrix. For example, k c= diag[1, 1, 1, … 0 t …, 1, 1, 1]。

[0069] In this embodiment, please continue to refer to Figure 2 , the receiver can use techniques such as maximum likelihood or successive interference cancellation to jointly detect the tag signal corresponding to the backscatter signal. Among them, when the tag performs covert transmission, the received signal at the receiver (ideally, the received signal is the backscatter signal) can be expressed as:

[0070]

[0071] where h ab , h at , h tb are the channel coefficients from the ambient RF source to the receiver, from the ambient RF source to the backscatter tag, and from the backscatter tag to the receiver respectively, and n b is the additive Gaussian noise at the receiver.

[0072] Among them, for the covert environment backscatter communication system provided in this embodiment, to ensure the transmission effectiveness of the covert information under the covertness constraint conditions, the receiver can also analyze the covert capacity of the above system based on the received signal. Specifically, when the covert capacity includes the channel capacity corresponding to the tag impedance modulation and the channel capacity corresponding to the antenna index modulation, let X represent the signal information corresponding to the tag impedance modulation, X a represent the signal information corresponding to the antenna index, and Y b represent the signal information received by the legitimate receiver, then the covert capacity can be specifically expressed as:

[0073]

[0074] where, according to the chain rule of mutual information, C b can be decomposed into the form of the sum of mutual information. C1 represents the channel capacity corresponding to the tag impedance modulation, and C a represents the channel capacity corresponding to the antenna index modulation, and can be specifically expressed as:

[0075]

[0076] where π is the pi, e is the natural constant, N t is the total number of antennas. When the selected antenna index is x a = m, (m ∈ {1, 2, … N t}), the received signal will satisfy the complex Gaussian distribution, and its probability density function is: where Correspondingly, the average probability density function of the received signal is: P aRepresents the source signal transmission power, N b Represents the additive Gaussian noise power. Since the radio frequency signal x, the covert information s of the tag, and the public information c of the tag follow a circularly symmetric complex Gaussian distribution, then E{|x| 2} = 1, E{|s| 2} = 1, E{|c| 2} = 1.

[0077] Based on this, under the covert constraint, the covert ambient backscatter communication system provided in this embodiment can also construct a problem of maximizing the covert capacity by optimizing the range of variation of the power reflection coefficient. Furthermore, by using the monotonicity of the objective function and the constraint conditions, an iterative optimization algorithm is adopted to derive the optimal range of variation of the power reflection coefficient and the corresponding covert capacity.

[0078] In summary, the present invention provides a covert ambient backscatter communication system, including an ambient radio frequency source, a monitor, a receiving end, and a backscatter tag including multiple antennas; the ambient radio frequency source is communicatively connected to the monitor, the receiving end, and the backscatter tag respectively; the backscatter tag is also communicatively connected to the monitor and the receiving end. The ambient radio frequency source is used to send a radio frequency signal to the backscatter tag; for any preset transmission gap, the backscatter tag is used to perform backscatter processing on the radio frequency signal when in an active state to obtain a backscatter signal; the backscatter signal includes the covert information to be transmitted; the receiving end is used to convert the backscatter signal and the radio frequency signal to obtain the covert information; the monitor is used to obtain and detect whether the backscatter tag transmits the covert information based on the power of the backscatter signal. Based on this, a covert ambient backscatter communication method and system provided by the present invention can effectively increase the channel capacity while ensuring communication concealment without increasing the additional power consumption of the backscatter device.

[0079] In a second aspect, please refer to Figure 3 , the present invention also provides a covert ambient backscatter communication method, which is applied to a covert ambient backscatter communication system. The covert ambient backscatter communication system includes an ambient radio frequency source, a monitor, a receiving end, and a backscatter tag including multiple antennas; the ambient radio frequency source is communicatively connected to the monitor, the receiving end, and the backscatter tag respectively; the backscatter tag is also communicatively connected to the monitor and the receiving end; the covert ambient backscatter communication method includes steps 201 to step 204.

[0080] Step 201: Use the ambient radio frequency source to send a radio frequency signal to the backscatter tag.

[0081] Step 202: For any preset transmission gap, use the backscatter tag to perform backscatter processing on the radio frequency signal when in an active state to obtain a backscatter signal; the backscatter signal includes the covert information to be transmitted.

[0082] Step 203: Use the receiving end to convert the backscattered signal and the radio frequency signal to obtain the covert information.

[0083] Step 204: Use the monitor to obtain and detect whether the backscatter tag transmits covert information based on the power of the backscattered signal.

[0084] In this embodiment, the backscatter processing in Step 202 can be understood as quadratic modulation, which includes spatial modulation and impedance modulation to obtain the backscattered signal. In Step 203, when the receiving end converts the backscattered signal and the radio frequency signal, the covert capacity of the backscattered signal can also be analyzed, including the channel capacity corresponding to the tag impedance modulation and the channel capacity corresponding to the spatial modulation.

[0085] In a possible implementation manner, on the basis of Figure 3 , please refer to Figure 4 , the present invention also provides another covert environment backscatter communication method, that is, Step 205 is further included after Step 204.

[0086] Step 205: Use the monitor to analyze the detection threshold and the minimum detection error probability based on binary hypothesis testing to achieve covert transmission of backscatter.

[0087] Based on this, in this embodiment, the covert environment backscatter communication system can optimize the maximum change value of the power reflection coefficient according to the minimum detection error probability and the covert capacity to achieve covert transmission of backscatter. In a possible implementation manner, the method for obtaining the maximum change value of the covert capacity-optimized power reflection coefficient can be: under the covert constraint, by optimizing the power reflection coefficient change range, a covert capacity maximization problem is constructed. Using the monotonicity of the objective function and the constraint conditions, an iterative optimization algorithm is used to derive the optimal power reflection coefficient change range and the corresponding covert capacity.

[0088] In the present invention, specific embodiments are used to elaborate on the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to the present invention.

[0089] Those of ordinary skill in the art will realize that the embodiments described herein are for helping readers understand the principle of the present invention, and it should be understood that the protection scope of the present invention is not limited to such specific statements and embodiments. Those of ordinary skill in the art can make various other specific deformations and combinations that do not deviate from the essence of the present invention based on the technical revelations disclosed in the present invention, and these deformations and combinations are still within the protection scope of the present invention.

Claims

1. A concealed environment backscatter communication system, characterized in that: It includes an environmental radio frequency source, a monitor, a receiving end, and a backscatter tag including multiple antennas; the environmental radio frequency source is respectively connected to the monitor, the receiving end, and the backscatter tag; the backscatter tag is also connected to the monitor and the receiving end; The environmental radio frequency source is used to send a radio frequency signal to the backscatter tag; For any preset transmission gap, the backscatter tag is used to perform backscatter processing on the radio frequency signal when in an activated state to obtain a backscatter signal; the backscatter signal includes the hidden information to be transmitted; The receiving end is used to convert the backscattered signal and the radio frequency signal to obtain hidden information; The monitor is used to obtain and detect whether the backscatter tag transmits concealed information according to the power of the backscatter signal; Each of the antennas includes at least a target antenna; For any preset transmission gap, the backscatter tag is also used to use the target antenna to transmit the hidden information of the tag through the radio frequency signal according to the first reflection coefficient; and use the remaining antennas except the target antenna to transmit the public information of the tag through the radio frequency signal according to the second reflection coefficient to obtain a backscatter signal; wherein the first reflection coefficient and / or the second reflection coefficient are random variables that obey a continuous uniform distribution.

2. The concealed environment backscatter communication system according to claim 1, characterized in that: The backscatter tag is further used to convert the bit sequence corresponding to the concealed information to be transmitted according to a preset rule to obtain a backscatter signal.

3. The concealed environment backscatter communication system according to claim 2, characterized in that: When the target antenna is determined according to the antenna index, the backscatter tag is also used to map part of the bit information in the bit sequence into a spatial constellation point; and map the remaining bit information in the bit sequence except the part of the bit information into a signal constellation point to obtain a backscatter signal.

4. The concealed environment backscatter communication system according to claim 3, characterized in that: When four antennas are included and each antenna index includes two bits of information, the backscatter tag is also used to map at least the first two bits of information in the bit sequence into spatial constellation points; and map the bit information in the bit sequence except the at least the first two bits of information into signal constellation points to obtain a backscatter signal.

5. The concealed environment backscatter communication system according to claim 1, characterized in that: The expression of the first reflection coefficient satisfies: ； in, is the maximum change value of the first reflection coefficient; For the change In the interval [0, ] is the first reflection coefficient value under .

6. The concealed environment backscatter communication system according to claim 1, characterized in that: The monitor is further used to determine that the backscatter tag transmits concealed information when the average power of the backscatter signal in a preset transmission interval is greater than a threshold value; When the average power of the backscatter signal in the preset transmission interval is less than or equal to the threshold value, it is determined that the backscatter tag does not transmit concealed information.

7. The concealed environment backscatter communication system according to claim 6, characterized in that: The monitor is also used to obtain a probability constraint function based on the error probability of the backscatter tag when transmitting covert information, so as to measure the concealment performance of the concealed environment backscatter communication system through the threshold value and / or the probability constraint function.

8. The concealed environment backscatter communication system according to claim 7, characterized in that: When the error probability includes missed detection probability and false alarm probability, the missed detection probability is the probability that concealed transmission is not detected when it occurs; the false alarm probability is the probability that concealed transmission does not occur but the detection result is that it occurs, the received signal of the monitor in different inspection states is expressed as: ； ； in, Because the backscatter tag does not send hidden information to the receiver; Sending covert information to the receiver for the backscatter tag; is the first reflection coefficient; is the second reflection coefficient; is the transmission power of the RF signal, , , They are radio frequency signal, hidden information of tag, and public information of tag. , , are the channel coefficients from the ambient RF source to the monitor, from the ambient RF source to the backscatter tag, and from the backscatter tag to the monitor, respectively. is the additive Gaussian noise of the monitor; is the first matrix, is the second matrix.

9. A concealed environment backscatter communication method, characterized in that: The invention is applied to a concealed environment backscatter communication system, wherein the concealed environment backscatter communication system comprises an environment radio frequency source, a monitor, a receiving end and a backscatter tag comprising multiple antennas; the environment radio frequency source is respectively connected to the monitor, the receiving end and the backscatter tag in communication; the backscatter tag is also connected to the monitor and the receiving end in communication; Using the ambient radio frequency source to send a radio frequency signal to the backscatter tag; For any preset transmission gap, the backscatter tag is used to perform backscatter processing on the radio frequency signal when it is in an activated state to obtain a backscatter signal; the backscatter signal includes the hidden information to be transmitted; Using the receiving end to convert the backscattered signal and the radio frequency signal to obtain concealed information; Using the monitor to obtain and detect whether the backscatter tag transmits concealed information based on the power of the backscatter signal; Each of the antennas includes at least a target antenna; For any preset transmission gap, using the backscatter tag to transmit the hidden information of the tag through the radio frequency signal based on the target antenna according to the first reflection coefficient; A backscattered signal is also obtained based on the public information of the radio frequency signal transmission tag transmitted by the remaining antennas except the target antenna according to the second reflection coefficient; wherein the first reflection coefficient and / or the second reflection coefficient are random variables that obey a continuous uniform distribution.

Images