Backscatter communication method and system in hidden environment

Abstract

The invention provides a hidden environment backscatter communication method and system, and relates to the field of wireless communication. The hidden environment backscatter communication system comprises an environment radio frequency source, a monitor, a receiving end and a backscatter tag comprising a plurality of antennas. The environment radio frequency source is used for sending a radio frequency signal to the backscattering tag. Aiming at any preset transmission gap, the backscattering label is used for performing backscattering processing on the radio frequency signal when the backscattering label is in an activated state to obtain a backscattering signal; the backscattering signal comprises hidden information to be transmitted. And the receiving end is used for converting the backscattering signal and the radio frequency signal to obtain hidden information. And the monitor is used for acquiring the power of the backscattering signal and detecting whether the backscattering label transmits the hidden information or not according to the power of the backscattering signal. On the basis, under the condition that extra power consumption of backscattering equipment is not increased, the channel capacity can be effectively increased while the communication concealment is ensured.

Description

Technical Field

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

[0002] As an emerging ultra-low power communication paradigm, backscatter devices draw energy from environmental electromagnetic waves to activate circuits, and switch antenna impedance according to the information bits to be sent to adjust the antenna's reflection coefficient, and then bounce the incident signal through different reflection coefficients to complete passive information transmission. In the prior art, backscatter devices collect environmental electromagnetic wave energy and do not rely on battery power, which can reduce system power consumption and system maintenance costs. The backscatter communication method abandons the traditional RF link, greatly reduces transmission power consumption, and solves the device cost. However, its extremely simplified design principle makes its protocol stack simple and its computing power limited. It cannot guarantee the security of the communication process and there is a greater risk of monitoring.

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

[0004] However, due to the uncontrollable environmental RF sources and the limited power of backscatter tags, the artificial noise injection scheme relies on a full-duplex receiver. The artificial noise injection method is not compatible with the existing environmental backscatter communication system and will increase the system power consumption, which cannot meet the ultra-low power consumption requirements of the system. The beamforming scheme requires the backscatter device to accurately estimate the channel state information and time synchronize, which is almost impossible to achieve due to the limited power of the backscatter tag.

[0005] Based on this, there is an urgent need for an ultra-low power consumption and high-speed covert backscatter transmission solution. Summary of the invention

[0006] In view of the above-mentioned deficiencies in the prior art, the present invention provides a concealed environment backscatter communication method and system, which can effectively increase the channel capacity while ensuring the communication concealment without increasing the extra power consumption of the backscatter equipment.

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

[0008] In a first aspect, the present invention provides a concealed environment backscatter communication system, comprising 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; the backscatter tag is also connected to the monitor and the receiving end;

[0009] An ambient RF source, used to send RF signals to the backscatter tags;

[0010] 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;

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

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

[0013] Preferably, each antenna includes at least a target antenna; for any preset transmission gap, the backscatter tag is also used to transmit the hidden information of the tag through a radio frequency signal using the target antenna according to a first reflection coefficient; the remaining antennas except the target antenna transmit the public information of the tag through a radio frequency signal according to a 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.

[0014] Preferably, 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.

[0015] Preferably, when the target antenna is determined based on the antenna index, the backscatter tag is also used to map part of the bit information in the bit sequence to a spatial constellation point; and map the remaining bit information in the bit sequence except for part of the bit information to a signal constellation point to obtain a backscatter signal.

[0016] Preferably, 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 to spatial constellation points; and map the bit information in the bit sequence except for at least the first two bits of information to signal constellation points to obtain a backscatter signal.

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

[0018]

[0019] Among them, Γ 1max is the maximum change value of the first reflection coefficient; is the variation γ in the interval [0,Γ 1max ] is the first reflection coefficient value under .

[0020] Preferably, the monitor is also used to determine that the backscatter tag is transmitting covert information when the average power of the backscatter signal in the preset transmission interval is greater than a threshold value; and to determine that the backscatter tag is not transmitting covert information when the average power of the backscatter signal in the preset transmission interval 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 backscatter tag for covert information transmission, so as to measure the concealment performance of the backscatter communication system in a concealed environment through a threshold value and / or a probability constraint function.

[0022] Preferably, when the error probability includes the missed detection probability and the false alarm probability, the missed detection probability is the probability that the concealed transmission is not detected when it occurs; the false alarm probability is the probability that the concealed transmission does not occur but the detection result is the occurrence, the monitor, the received signal in different inspection states is expressed as:

[0023]

[0024] Wherein, H0 means that the backscatter tag does not send hidden information to the receiver; H1 means that the backscatter tag sends hidden information to the receiver; 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, and h aw 、h at 、h tw 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. 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 further provides a concealed environment backscatter communication method, which is applied to a concealed environment backscatter communication system, wherein the concealed environment backscatter communication system comprises an environmental radio frequency source, a monitor, a receiving end, and a backscatter tag comprising multiple antennas; the environmental 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;

[0026] Using the ambient RF source to send RF signals to the backscatter tag;

[0027] 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;

[0028] The backscattered signal and the radio frequency signal are converted by the receiving end to obtain the hidden information;

[0029] The monitor obtains and detects whether the backscatter tag transmits covert information based on the power of the backscatter signal.

[0030] In summary, the present invention provides a concealed environment backscatter communication method and system having the following features:

[0031] Beneficial effects:

[0032] The present invention provides a concealed 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 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 backscatter the radio frequency signal when it is in an activated state to obtain a backscatter signal; the backscatter signal includes concealed information to be transmitted; the receiving end is used to convert the backscatter signal and the radio frequency signal to obtain the concealed information; the monitor is used to obtain and detect whether the backscatter tag transmits the concealed information based on the power of the backscatter signal. Based on this, the present invention provides a concealed environment backscatter communication method and system, which can effectively increase the channel capacity while ensuring the communication concealment without increasing the extra power consumption of the backscatter device.

[0033] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, preferred embodiments are given below and described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0035] Figure 1 One of the structural schematic diagrams of a concealed environment backscatter communication system provided by an embodiment of the present invention is shown;

[0036] Figure 2The second structural schematic diagram of the concealed environment backscatter communication system provided by the embodiment of the present invention is shown;

[0037] Figure 3 A schematic diagram showing the steps of a concealed environment backscatter communication method provided by an embodiment of the present invention is shown;

[0038] Figure 4 The second schematic diagram of the steps of a concealed environment backscatter communication method provided by an embodiment of the present invention is shown.

[0039] Icons: 100 - concealed environment backscatter communication system; 101 - environmental radio frequency source; 102 - monitor; 103 - receiving end; 104 - multi-antenna backscatter tag. DETAILED DESCRIPTION

[0040] The specific implementation modes of the present invention are described below so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation modes. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

[0041] Generally speaking, there are two types of backscatter communication schemes. The first is a covert communication method for environmental backscatter systems with uncontrollable RF sources, which uses a full-duplex receiver that emits artificial noise to design the optimal communication strategy and detection scheme. The second is to use the spatial selectivity of multi-antenna tags to ensure the concealment of environmental backscatter systems.

[0042] However, due to the uncontrollable environmental RF sources and the limited power of backscatter tags, the artificial noise injection scheme relies on a full-duplex receiver. The artificial noise injection method is not compatible with the existing environmental backscatter communication system and will increase the system power consumption, which cannot meet the ultra-low power consumption requirements of the system. The beamforming scheme requires the backscatter device to accurately estimate the channel state information and time synchronize, which is almost impossible to achieve due to the limited power of the backscatter tag.

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

[0044] Please refer to Figure 1In a first aspect, the present invention provides a concealed environment backscatter communication system 100, comprising an environment RF source 101, a monitor 102, a receiving end 103, and a backscatter tag comprising multiple antennas, i.e., a multi-antenna backscatter tag 104. The environment RF source 101 is respectively connected to the monitor 102, the receiving end 103, and the backscatter tag; the multi-antenna backscatter tag 104 is also connected to the monitor 102 and the receiving end 103, i.e., the multi-antenna backscatter tag 104 is connected to the monitor 102 and the receiving end 103 through the antenna.

[0045] In this embodiment, the ambient RF source 101 is used to send a RF signal to the backscatter tag. In one possible implementation, the ambient RF source may be a cellular signal or a Wi-Fi signal to provide energy and a RF carrier to 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 activated state to obtain a backscatter signal; the backscatter signal includes the hidden information to be transmitted.

[0047] Specifically, the multi-antenna backscatter tag 104 first absorbs the signal energy from the ambient RF 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 tag's hidden information is transmitted through random reflection coefficients and antenna indexes, while the remaining antennas transmit public information through a random reflection system 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 hidden information. In a possible implementation, 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. At the same time, when the receiving end converts the backscatter signal and the radio frequency signal, the hidden capacity of the backscatter signal can also be analyzed, 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 according to the power of the backscatter signal.

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

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

[0052] In one possible implementation, each antenna includes at least a target antenna; for any preset transmission gap, the multi-antenna backscatter tag is also used to use the target antenna to transmit the tag's hidden information through a radio frequency signal based on a first reflection coefficient; and use the remaining antennas except the target antenna to transmit the tag's public information through a radio frequency signal based on a 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.

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

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

[0055]

[0056] Among them, Γ 1max is the maximum change value of the first reflection coefficient; is the variation γ in the interval [0,Γ 1max ] is the first reflection coefficient value under .

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

[0058]

[0059] Among them, Γ 2max is the maximum change value of the second reflection coefficient; is the variation γ in the interval [0,Γ 2max ] is the first reflection coefficient value under .

[0060] In a possible implementation, the backscatter tag is further used to convert a 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 also used to map part of the bit information in the bit sequence to a spatial constellation point; and map the remaining bit information in the bit sequence except for part of the bit information to a signal constellation point to obtain a backscatter signal.

[0062] For example, 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 to spatial constellation points; and map the bit information in the bit sequence except for at least the first two bits of information to signal constellation points to obtain a backscatter signal.

[0063] In one possible implementation, the monitor 102 is also used to determine that the backscatter tag is transmitting covert information when the average power of the backscatter signal in a preset transmission interval is greater than a threshold value; and to determine that the backscatter tag is not transmitting covert information when the average power of the backscatter signal in the preset transmission interval is less than or equal to the threshold value.

[0064] Specifically, the monitor determines whether the backscatter tag transmits covert information based on the observed signal. In one possible implementation, the monitor can use a radiometer to monitor the transmission energy of the backscatter signal, and then determine the method of covering information transmission. A threshold value can be set 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 also used to obtain a probability constraint function based on the error probability of the detected backscatter tag when performing covert information transmission, so as to measure the concealment performance of the backscatter communication system in a concealed environment through a threshold value and / or a probability constraint function.

[0066] In this embodiment, please continue to refer to Figure 2 , the monitor performs a double-choice hypothesis test on the received signal (in an ideal state, the received signal is the backscattered signal). When the error probability or detection error probability includes the missed detection probability and the false alarm probability, and the sum of the missed detection probability and the false alarm probability is taken as the detection error probability value, the missed detection probability is the probability that the covert transmission occurs but is not detected; the false alarm probability is the probability that the covert transmission does not occur but the detection result is the occurrence, the monitor, the received signal under different test states is expressed as:

[0067]

[0068] Wherein, H0 means that the backscatter tag does not send hidden information to the receiver; H1 means that the backscatter tag sends hidden information to the receiver; 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, and h aw 、h at 、h tw 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. 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 receiving end can use the maximum likelihood or serial interference cancellation technology to jointly detect the tag signal corresponding to the backscattered signal. Among them, when the tag performs covert transmission, the receiving signal at the receiving end (in an ideal state, the received signal is the backscattered signal) can be expressed as:

[0070]

[0071] Among them, 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. b is the additive Gaussian noise at the receiving end.

[0072] In the concealed environment backscatter communication system provided in this embodiment, in order to ensure the transmission effectiveness of concealed information under the concealment constraint condition, the receiving end can also analyze the concealed capacity of the above system based on the received signal. Specifically, when the concealed capacity includes the channel capacity corresponding to the tag impedance modulation and the channel capacity corresponding to the antenna index modulation, X can be used to represent the signal information corresponding to the tag impedance modulation, and X a Indicates the signal information corresponding to the antenna index, Y b represents the signal information received by the legitimate receiving end, then the concealed capacity can be specifically expressed as:

[0073]

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

[0075]

[0076] Among them, π is the circumference of a circle, e is a 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: in, 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 RF signal x, the tag’s hidden information s, and the tag’s public information c obey circularly symmetric complex Gaussian distribution, then E{|x| 2}=1,E{|s| 2}=1,E{|c| 2}=1.

[0077] Based on this, under the concealment constraint, the concealed environment backscatter communication system provided in this embodiment can also construct the concealment capacity maximization problem by optimizing the power reflection coefficient variation range. Then, by utilizing the monotonicity and constraint conditions of the objective function, an iterative optimization algorithm is used to derive the optimal power reflection coefficient variation range and the corresponding concealment capacity.

[0078] In summary, the present invention provides a concealed 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 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 backscatter the radio frequency signal when it is in an activated state to obtain a backscatter signal; the backscatter signal includes concealed information to be transmitted; the receiving end is used to convert the backscatter signal and the radio frequency signal to obtain the concealed information; the monitor is used to obtain and detect whether the backscatter tag transmits the concealed information based on the power of the backscatter signal. Based on this, the present invention provides a concealed environment backscatter communication method and system, which can effectively increase the channel capacity while ensuring the communication concealment without increasing the extra power consumption of the backscatter device.

[0079] Second, please refer to Figure 3 The present invention also provides a concealed environment backscatter communication method, which is applied to a concealed environment backscatter communication system. The concealed environment backscatter communication system 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 concealed environment backscatter communication method includes steps 201 to 204.

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

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

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

[0083] Step 204: Utilize the monitor to obtain and detect whether the backscatter tag is transmitting covert information based on the power of the backscatter signal.

[0084] In this embodiment, the backscattering processing in step 202 can be understood as secondary modulation, which includes spatial modulation and impedance modulation to obtain a backscattering signal. In step 203, when the receiving end converts the backscattering signal and the RF signal, the concealed capacity of the backscattering 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 one possible implementation, Figure 3 Based on Figure 4 The present invention also provides another concealed environment backscatter communication method, that is, step 204 also includes step 205.

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

[0087] Based on this, the concealed environment backscatter communication system in this embodiment can optimize the maximum change value of the power reflection coefficient according to the minimum detection error probability and the concealed capacity to achieve the concealed transmission of backscatter. In a possible implementation method, the maximum change value of the power reflection coefficient optimized by the concealed capacity can be obtained by: under the concealment constraint, by optimizing the power reflection coefficient variation range, constructing the concealed capacity maximization problem. By using the monotonicity and constraint conditions of the objective function, the optimal power reflection coefficient variation range and the corresponding concealed capacity are derived by using an iterative optimization algorithm.

[0088] The present invention uses specific embodiments to illustrate the principles and implementation methods 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 skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as a limitation on the present invention.

[0089] Those skilled in the art will appreciate that the embodiments described herein are intended to help readers understand the principles of the present invention, and should be understood that the protection scope of the present invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific variations and combinations that do not deviate from the essence of the present invention based on the technical revelations disclosed by the present invention, and these variations 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 based on the power of the backscatter signal.

2. The concealed environment backscatter communication system according to claim 1, characterized in that: 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.

3. The concealed environment backscatter communication system according to claim 2, 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.

4. The concealed environment backscatter communication system according to claim 3, 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.

5. The concealed environment backscatter communication system according to claim 4, 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.

6. The concealed environment backscatter communication system according to claim 2, characterized in that: The expression of the first reflection coefficient satisfies: Among them, Γ 1max is the maximum change value of the first reflection coefficient; f Γ1 (γ) is the change γ in the interval [0,Γ 1max ] is the first reflection coefficient value under .

7. 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.

8. The concealed environment backscatter communication system according to claim 7, 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.

9. The concealed environment backscatter communication system according to claim 8, 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: H0: H1: Wherein, H0 means that the backscatter tag does not send hidden information to the receiver; H1 means that the backscatter tag sends hidden information to the receiver; 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, and h aw 、h at 、h tw 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. w is the additive Gaussian noise of the monitor; k is the first matrix, k c is the second matrix.

10. 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; The monitor is used to obtain and detect whether the backscatter tag transmits concealed information based on the power of the backscatter signal.

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