Device-to-device covert communication system jointly assisted by unmanned aerial vehicle and intelligent reflecting surface

Abstract

The invention discloses a device-to-device covert communication system jointly assisted by an unmanned aerial vehicle (UAV) and an intelligent reflector (UIRS), and the system comprises the steps: building a D2D covert communication model jointly assisted by the UAV and the UIRS, including communication links between entities, and calculating an average minimum error detection probability and a maximum communication rate; the sender sends the hidden signals to the UIRS, the UIRS forwards the hidden signals to the receiver, and the UIRS changes the angles of the corresponding incident hidden signals and the angles of the corresponding reflected hidden signals through component elements; a frequency spectrum sharing cellular user sends a cellular signal to a base station, meanwhile, the base station sends an interference signal, an uncertain factor is introduced at a Willie receiving end of an eavesdropper, and the concealment of a UIRS combined auxiliary D2D communication link is realized; the eavesdropper Willie monitors whether the UIRS combined auxiliary D2D communication link transmits the hidden signal or not; the concealment is measured through the average minimum error detection probability; the maximum communication rate of the UIRS combined auxiliary D2D communication link is obtained under multiple constraints such as the average minimum error detection probability, the cellular communication link outage probability, the sending power and the sending power of interference signals, and the communication rate of the system is effectively improved under the combined assistance of the unmanned aerial vehicle and the intelligent reflector UIRS.

Description

Technical Field

[0001] The present invention belongs to wireless communication technology, and in particular relates to a device-to-device covert communication system jointly assisted by an unmanned aerial vehicle and an intelligent reflective surface. Background Art

[0002] Device-to-device (D2D) communication allows end users to communicate directly without forwarding by base stations or access devices, thereby effectively improving the spectrum utilization efficiency of the network. In harsh communication environments, relay-assisted D2D communication becomes an effective solution to extend the communication range and alleviate connection barriers. Due to the limitations of traditional ground relays in terms of flexibility and mobility, drone relay-assisted D2D communication has gradually received more and more attention and research.

[0003] Unmanned aerial vehicles (UAVs) can establish line-of-sight links with ground communication nodes, have advantages such as high mobility and on-demand deployment capabilities, and are widely used in wireless communication networks. However, due to the complex environment, UAV communications may be blocked and eavesdropped in actual scenarios. Using intelligent reflecting surfaces (IRS) to adjust the angles of component elements to change the incident signal and reflected signal and reconfigure the transmission environment can effectively enhance the transmission signal and improve the communication quality. Therefore, by loading IRS on UAVs, the UAV and intelligent reflecting surface UIRS-assisted D2D communication system can expand the wireless communication range and improve the communication quality by combining the mobility of UAVs and the beamforming capability of IRS, and is widely used in disaster relief, Internet of Things, and intelligent transportation.

[0004] The D2D link assisted by drones and smart reflective surfaces is vulnerable to monitoring by eavesdroppers due to the open nature and visibility of signal propagation. Traditional encryption measures and physical layer security methods focus on protecting the content of communication, but the existence of the link is still exposed to the wireless environment. Covert communication is committed to protecting the existence of the link or signal. Therefore, combining D2D communication assisted by drones and smart reflective surfaces with covert communication can effectively hide the communication link between the sender and the receiver in the D2D pair. At the same time, the cellular user link sends interference signals, which can effectively confuse the monitoring of eavesdroppers, thereby enhancing the concealment of the communication link.

[0005] Patent CN2021102655224 discloses a joint power control and channel allocation method for drone-based D2D communication, Patent 2024104223106 discloses a multi-resource joint optimization method for maximizing energy efficiency in intelligent reflective surface-assisted D2D communication, and Patent CN2024107232978 involves a D2D covert communication method based on intelligent reflective surface, which improves the covert communication performance and the performance of the D2D system. However, Patent 2021102655224 and Patent CN2024104223106 use drones and intelligent reflective surfaces to assist D2D communication, but do not consider the concealment of the channel; Patent CN2024107232978 uses intelligent reflective surfaces to assist D2D covert communication, but the fixed ground IRS deployment flexibility is limited and cannot adapt to changing environmental conditions.

[0006] Therefore, it is necessary and feasible to study the device-to-device covert communication system and its communication method assisted by UAVs and intelligent reflective surfaces, and to optimize and analyze its concealment and communication rate. Summary of the invention

[0007] Purpose of the invention: The purpose of the present invention is to solve the deficiencies in the prior art and to provide a device-to-device covert communication system assisted by a drone and an intelligent reflective surface.

[0008] Technical solution: The present invention is a device-to-device covert communication system assisted by a UAV and an intelligent reflective surface, and the entities involved include a UAV and an intelligent reflective surface UIRS, a full-duplex base station B s and a half-duplex communication terminal, the half-duplex communication terminal comprising a half-duplex cellular user C using a single antenna u , half-duplex D2D sender D t , half-duplex D2D receiver D r and half-duplex eavesdropper Willie; the following communication links are formed between each entity;

[0009] Link 1), UIRS joint assisted D2D hidden link D t →UIRS→D r ; The sender D in this link t Send a covert signal to the drone and the intelligent reflective surface UIRS, and the UIRS will send the D t The sent covert signal is forwarded to the receiver D r ; Cellular user C u Send cellular signal to base station B s , forming an uplink cellular link C u →B s ; Cellular user C uThe uplink and downlink of the transmission network use orthogonal spectrum resources and there is no interference between them. t →UIRS→D r With uplink cellular link C u →B s Shared spectrum resources;

[0010] Link 2), Base Station B s In order to counter the eavesdropper Willie and improve the system's stealth, artificial noise is sent to the eavesdropper Willie to build an artificial noise link B. s →Willie; Base Station B s The artificial noise emitted also affects the receiver D r Generate interference and form link B s →D r , and causes the base station B s The self-interference of link B s →B s ; Link 2) Base station B s Use the same spectrum resources to send and receive information at the same time;

[0011] Link 3), the randomly distributed eavesdropper Willie attempts to monitor the UIRS joint assisted D2D covert link D t →UIRS→D r , detect whether a covert signal is being sent, involving eavesdropping on link D t →Willie and UIRS→Willie;

[0012] Link 4), Base Station B s To sender D t Send information to form a downlink cellular link B s →D t ;

[0013] Calculate the average minimum false detection probability of the eavesdropper Willie in link 3) Using the mean minimum false detection probability To measure the link 1) UIRS joint assisted D2D hidden link D t →UIRS→D r The concealment of

[0014] At the same time, the uplink cellular link C is calculated u →B s The probability of interruption

[0015] Finally, the average minimum false detection probability is calculated and cellular communication link C u →Bs Probability of interruption Constrained communication rate R r , and the communication rate R r Perform constraint optimization to obtain the maximum communication rate of link 1)

[0016] Furthermore, the minimum error detection probability ξ is calculated * and the average minimum false detection probability The method is as follows:

[0017] Consider the eavesdropper Willie's false detection probability satisfies ξ=P FA +P MD ;

[0018]

[0019] P FA is the false alarm probability of the eavesdropper Willie, P MD is the probability of missed alarm of eavesdropper Willie;

[0020] H0 indicates that the UIRS joint assisted D2D communication link does not transmit concealed signals, and H1 indicates that the UIRS joint assisted D2D communication link transmits concealed signals; P b For full-duplex base station B s The transmission power of the interference signal, P t For sender D t The transmission power, h bw Interference signal communication link B s → Willie's small-scale fading parameter, h ur UIRS→D r Small-scale fading parameter of the communication link, h tu D t →Small-scale fading parameter of UIRS communication link, h tw D t →Small-scale fading parameter of Willie communication link; τ is the detection threshold of Willie, is the noise power received by the eavesdropper Willie;

[0021] Next, calculate the minimum error detection probability ξ * There are two situations:

[0022]

[0023] Case 1), if the intermediate parameter ψ1 = ψ2, then the average minimum error detection probability Equal to the constant value 1-(1 / e);

[0024] in,

[0025]

[0026] The intermediate parameter ψ1 reflects the full-duplex base station B s The interference signal strength between the eavesdropper Willie and the full-duplex base station B is considered. s The transmission power of the interference signal P b , full-duplex base station B s The distance to the eavesdropper Willie and the path loss exponent α bw The intermediate parameter ψ2 reflects the signal strength between the UAV-IRS-assisted D2D communication link and the eavesdropper Willie, taking into account the UAV and the intelligent reflective surface UIRS to the receiver D r The distance d ur , human-machine and intelligent reflective surface UIRS to sender D t The distance d tu , sender D t The distance d to the eavesdropper Willie tw , transmission power P t And human-machine and intelligent reflective surface UIRS to receiver D r , UAV and intelligent reflective surface UIRS to sender D t and sender D t Path loss exponent α to the eavesdropper Willie ur , α tu and α tw .d bw For full-duplex base station B s The distance to the eavesdropper Willie, d ur For UAVs with intelligent reflective surfaces UIRS to receiver D r The distance, d tu For UAVs with smart reflective surfaces UIRS to sender D t The distance, d tw For sender D t The distance to the eavesdropper Willie; α bw , α ur , α tu and α tw They are full-duplex base station B s To the eavesdropper Willie, the drone and the intelligent reflective surface UIRS to the receiver D r , UAV and intelligent reflective surface UIRS to sender D t and sender D t Path loss exponent to eavesdropper Willie; α bw =α ur =αtu =α tw ; g ur , g tu and g tw Each element of follows an independent complex Gaussian distribution; β0 is the channel gain at a reference distance of 1m;

[0027] Case 2), if the intermediate parameter ψ1≠ψ2, the average minimum error detection probability It is divided into the following two cases: Case A), if the cellular link has priority communication protection zone O b At sender D t The coverage area is centered on O t Calculate the corresponding average minimum error detection probability

[0028] Case B): If the cellular link has priority in communication protection zone O b At sender D t The coverage area is centered on O t Otherwise, calculate the corresponding average minimum false detection probability The expression is as follows:

[0029]

[0030] Among them, ξ * is the minimum false detection probability of the eavesdropper Willie, which is about the sender D t The transmission power P t and full-duplex base station B s The transmission power P of the interference signal b The function of tw From the eavesdropper Willie to the sender D of D2D t The distance, d bt For full-duplex base station B s To sender D t The distance, r w is the straight-line distance of the eavesdropper Willie, θ w is the azimuth of the eavesdropper Willie, R t For sender D t The coverage area is centered on O t Radius, r b is the cellular communication link C u →B s Priority communication protection zone O b radius.

[0031] Furthermore, we can obtain the minimum error detection probability that satisfies the average and cellular communication link C u →B s Probability of interruption Constrained communication rate R r After that, according to the half-duplex D2D sender D t The transmission power P t , the transmission power of the interference signal P b , Cellular communication link C u →B s Probability of interruption and the average minimum error detection probability of the half-duplex eavesdropper Willie at the receiving end These four constraints are finally optimized to obtain the maximum communication rate.

[0032] Furthermore, in the case of UAV and intelligent reflective surface UIRS assisted transmitter D t and receiver D r During D2D communication, it is assumed that the UIRS is hovering at a height H, the IRS is equipped with K reflective elements, and the effective phase shift of all reflective elements of the IRS is Θ; then the UIRS joint assisted D2D covert link D t →UIRS→D r The modeling is as follows:

[0033]

[0034] j is a complex number, θ i represents the phase shift of the ith element, θ i ∈[0,2π], i=1,2,…,K; h tu D t →Small-scale fading parameter of UIRS communication link, h ur UIRS→D r The small-scale fading parameter of the communication link, β0 is the channel gain at a reference distance of 1m, d tu For UAVs with smart reflective surfaces UIRS to sender D t The distance, d ur For UAVs with intelligent reflective surfaces UIRS to receiver D r distance, λ is the carrier wavelength, d is the distance between the reflective elements, φ tu ,φ ur For sender D t to the cosine of the launch angle between the drone and the intelligent reflector UIRS, α tu , α ur For UAVs with smart reflective surfaces UIRS to sender D t and UAV with intelligent reflective surface UIRS to receiver D r The path loss exponent.

[0035] Furthermore, the eavesdropping link UIRS→Willie in link 3) is modeled as follows:

[0036]

[0037] In the above formula, d uw is the distance between the UAV and the intelligent reflective surface UIRS and the half-duplex eavesdropper Willie, α uw UIRS for drones with smart reflective surfaces to eavesdropper Willie and sender D t The path loss exponent to the eavesdropper Willie, g uw Each element of follows an independent complex Gaussian distribution, that is Here, m represents the mth element of the communication link from the human-machine interface to the intelligent reflective surface UIRS to the half-duplex eavesdropper Willie, m = 1, 2, …, K, K means that the IRS is equipped with K reflective elements.

[0038] Furthermore, the full-duplex base station B s Configure two antennas, one antenna receives half-duplex cellular user C u One wire is used to send cellular signals, and the other wire is used for downlink cellular links and to send interference signals. Self-interference is generated between the two wires and cannot be eliminated. represents the self-interference coefficient;

[0039] Full-duplex base station B s By sending jamming signals, the eavesdropper Willie interferes with the UIRS joint assisted D2D covert link D t →UIRS→D r For covert communication detection, the transmission power of the interference signal obeys uniform distribution;

[0040] The uplink cellular link C u →B s The probability of interruption The calculation formula is:

[0041]

[0042] In the above formula, P c For half-duplex cellular user C u The transmission power, h cb C u →B s Small-scale fading parameter of the communication link, h bb For B s →B s Small-scale fading parameter of the communication link, h bt For B s →D t Small-scale fading parameters of the communication link, For half-duplex cellular user C u Received noise power; R c is the target communication rate.

[0043] Furthermore, the maximum communication rate is obtained The specific method is as follows:

[0044] Step (1), calculate the cellular communication link C u →B s Probability of interruption

[0045]

[0046] Among them, P c For cellular user C u The transmission power, h cb C u →B s Small-scale fading parameter of the communication link, h bb For B s →B s Small-scale fading parameter of the communication link, h bt For B s →D t Small-scale fading parameters of the communication link, For cellular user C u Received noise power; R c is the target communication rate, η is the intermediate auxiliary amount, η=2 Rc -1;

[0047] Step (2): Calculate the maximum communication rate

[0048] Step (2.1), according to Solve for the half-duplex D2D sender D t The transmission power P t And the transmission power of the interference signal P b ;γ is the given target interruption probability;

[0049] Step (2.2), based on the given allowed error detection probability ∈, according to the average minimum error detection probability For sender D t The transmission power P t The monotonically decreasing function and the transmission power P of the interference signal b A monotonically increasing function to solve the sender D t The maximum transmit power P that can be obtained tm and full-duplex base station B s The maximum transmit power P of the interference signal that can be obtainedbm ; The calculation formula is as follows:

[0050]

[0051] Step (2.3), use the search algorithm in the interval (0,P tm ]and In, get half sender D t Optimal transmit power and the optimal transmission power of the interference signal Make formula (8) obtain the maximum value, that is, the maximum communication rate

[0052] R * r =maxR r , (8)

[0053] In the above formula, R r It means that the average minimum false detection probability and cellular communication link C u →B s Probability of interruption Constrained communication rate;

[0054]

[0055] Among them, P t For sender D t The transmission power, P b For full-duplex base station B s The transmission power of the interference signal, h ur UIRS→D r Small-scale fading parameter of the communication link, h tu D t →Small-scale fading parameter of UIRS communication link, h br For B s →D r The small-scale fading parameter of the communication link, Θ is the effective phase shift of all elements of the IRS, For the receiver D r Received noise power.

[0056] Furthermore, for the maximum communication rate The constraints are as follows:

[0057]

[0058] where Θ is the effective phase shift of all components of the IRS, and h br For B s →D r Small-scale fading parameters of the communication link, For the receiver D r The received noise power, For sender D t The maximum transmit power determined by itself, For full-duplex base station B s The maximum transmission power of the interference signal determined by itself.

[0059] Beneficial effect: The present invention can achieve the maximum communication rate under multiple constraints such as the average minimum error detection probability, the probability of cellular communication link interruption, the transmission power and the transmission power of the interference signal. With the joint assistance of UAV and intelligent reflective surface UIRS, the communication rate of the system is effectively improved. The advantages are as follows:

[0060] 1. The D2D sender Dt of the present invention sends a covert signal to the UIRS, which is forwarded by the UIRS to the half-duplex D2D receiver Dr. The UIRS changes the angles of the corresponding incident covert signal and the reflected covert signal through the constituent elements; the spectrum-sharing half-duplex cellular user Cu sends a cellular signal to the full-duplex base station Bs, and the full-duplex base station Bs sends an interference signal at the same time.

[0061] 2. The present invention introduces an uncertainty factor at the receiving end of the half-duplex eavesdropper Willie to achieve the concealment of the UIRS joint assisted D2D communication link; the half-duplex eavesdropper Willie monitors whether the UIRS joint assisted D2D communication link transmits a concealed signal.

[0062] 3. In the calculation of the average minimum error detection probability, the present invention considers two cases of intermediate parameters ψ1=ψ2 and ψ1≠ψ2. In the case of ψ1≠ψ2, the cellular link priority communication protection zone O is considered. b In the coverage area O centered at the sender Dt t The average minimum false detection probability is obtained for the two cases of inside and outside, thus measuring the concealment.

[0063] 4. In the calculation of the maximum communication rate, the present invention obtains the maximum communication rate of the UIRS jointly assisted D2D communication link under the four constraints of satisfying the average minimum error detection probability, the cellular communication link interruption probability, the transmission power and the transmission power of the interference signal. The communication rate of the system is effectively improved under the joint assistance of the drone and the intelligent reflective surface UIRS. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Figure 1 This is a device-to-device covert communication model diagram of a drone and an intelligent reflective surface jointly assisted by the present invention.

[0065] Figure 2It is an overall flow chart of the device-to-device covert communication model of the present invention.

[0066] Figure 3 is the average minimum error detection probability of the device-to-device covert communication model when ψ1=ψ2 of the present invention Calculation flow chart.

[0067] Figure 4 is the average minimum error detection probability of the device-to-device covert communication model when ψ1≠ψ2 of the present invention Calculation flow chart.

[0068] Figure 5 It is a flow chart of calculating the maximum communication rate of the device-to-device covert communication model of the present invention.

[0069] Figure 6 It is the full-duplex base station B of the present invention. s The transmission power P of the interference signal b The mean minimum false detection probability Relationship simulation diagram.

[0070] Figure 7 is the half-duplex D2D sender D of the present invention t The transmission power P t The mean minimum false detection probability Relationship simulation diagram.

[0071] Figure 8 is the half-duplex D2D sender D of the present invention t The transmission power P t Probability of interruption of cellular communication link Relationship simulation diagram.

[0072] Fig. 9 It is the full-duplex base station B of the present invention. s The interference signal P b Probability of interruption of cellular communication link Relationship simulation diagram.

[0073] Fig.10 is the half-duplex D2D sender D of the present invention t Maximum transmit power With the maximum communication rate Relationship simulation diagram.

[0074] Fig.11 It is the cellular link priority communication protection zone of the present invention. b In the sender D t The coverage area is centered on O t Half-duplex D2D sender D t The transmission power P tWith the communication rate R r Relationship simulation diagram.

[0075] Fig.12 It is the cellular link priority communication protection zone of the present invention. b In the sender D t The coverage area is centered on O t Half-duplex D2D sender D t The transmission power P t With the communication rate R r Relationship simulation diagram. DETAILED DESCRIPTION

[0076] The technical solution of the present invention is described in detail below, but the protection scope of the present invention is not limited to the embodiments.

[0077] The device-to-device covert communication system of the UAV and intelligent reflective surface combined with the present invention includes the UAV and the intelligent reflective surface UIRS, a full-duplex base station B s and a half-duplex communication terminal, wherein the half-duplex communication terminal includes a cellular user C using a single antenna and half-duplex u , half-duplex D2D sender D t , half-duplex D2D receiver D r and half-duplex eavesdropper Willie; the following communication links are formed between each entity.

[0078] Link 1), UIRS joint assisted D2D hidden link D t →UIRS→D r ; The sender D in this link t Send a covert signal to the drone and the intelligent reflective surface UIRS, and the UIRS will send the D t The sent covert signal is forwarded to the receiver D r ; Cellular user C u Send cellular signal to base station B s , forming an uplink cellular link C u →B s ; Cellular user C u The uplink and downlink of the transmission network use orthogonal spectrum resources and there is no interference between them. t →UIRS→D r With uplink cellular link C u →B s Shared spectrum resources;

[0079] Link 2), Base Station B s In order to counter the eavesdropper Willie and improve the system's stealth, artificial noise is sent to the eavesdropper Willie to build an artificial noise link B.s →Willie; Base Station B s The artificial noise emitted also affects the receiver D r Generate interference and form link B s →D r , and causes the base station B s The self-interference of link B s →B s ; Link 2) Base station B s Use the same spectrum resources to send and receive information at the same time;

[0080] Link 3), the randomly distributed eavesdropper Willie attempts to monitor the UIRS joint assisted D2D covert link D t →UIRS→D r , detect whether a covert signal is being sent, involving eavesdropping on link D t →Willie and UIRS→Willie;

[0081] Link 4), Base Station B s To sender D t Send information to form a downlink cellular link B s →D t .

[0082] The relationship between the communication links is as follows: Figure 1 As shown. The UIRS-assisted D2D hidden link obeys the distribution of formula (3), formula (4) and formula (5), and the other ground communication links obey independent quasi-static Rayleigh block fading, and their corresponding small-scale fading parameters are independent and identically distributed cyclically symmetric complex Gaussian random variables. The small-scale fading parameters and distances between each communication terminal are expressed as: D t →UIRS is h tu and d tu , UIRS→D r h ur and d ur ,UIRS→Willie is h uw and d uw , C u →B s h cb and d cb , B s →D t h bt and d bt , D t →Willie is h tw and d tw , B s →Willie is h bw and d bw, B s →D r h br and d br , B s →B s h bb and d bb The channel noise of each communication link obeys the complex Gaussian distribution, and the receiving noise power of the cellular communication link is The receiving noise power of the UIRS joint assisted D2D communication link is The received noise power of half-duplex eavesdropper Willie is Full-duplex base station B s The self-interference coefficient is Full-duplex base station B s The transmission power of the interference signal is uniformly distributed, and its maximum transmission power is Half-duplex D2D sender D t Its maximum transmission power is is the interruption probability of the cellular communication link, R r is the communication rate of the UIRS joint assisted D2D communication link, The corresponding maximum communication rate.

[0083] Calculate the average minimum false detection probability of the eavesdropper Willie in link 3) Using the mean minimum false detection probability To measure the link 1) UIRS joint assisted D2D hidden link D t →UIRS→D r The concealment of

[0084] At the same time, the uplink cellular link C is calculated u →B s The probability of interruption like Figure 5 shown.

[0085] Finally, the average minimum false detection probability is calculated and cellular communication link C u →B s Probability of interruption Constrained communication rate R r , and the communication rate R r Perform constraint optimization to obtain the maximum communication rate of link 1)

[0086] like Figures 2 to 4 As shown, the half-duplex eavesdropper Willie collects the signal of a single block fading and calculates the power average value Y of the collected signal. wCompare with its detection threshold τ; the second step, based on the power average value Y when n→∞ w , calculate the false alarm probability P under the premise of H0 FA , calculate the missed alarm probability P under the premise of H1 MD ; The third step, according to the formula ξ=P FA +P MD , calculate the error detection probability, and on this basis, find the minimum error detection probability; the fourth step, based on the uncertainty of the half-duplex eavesdropper Willie on the relevant communication link and the cellular link priority communication protection zone O b In half-duplex D2D sender D t The coverage area is centered on O t The average minimum error detection probability is calculated for both the inside and outside cases.

[0087] The false detection probability of the eavesdropper Willie satisfies ξ=P FA +P MD ;

[0088]

[0089] P FA is the false alarm probability of the eavesdropper Willie, P MD is the probability of missed alarm of eavesdropper Willie;

[0090] H0 indicates that the UIRS joint assisted D2D communication link does not transmit concealed signals, and H1 indicates that the UIRS joint assisted D2D communication link transmits concealed signals; P b For full-duplex base station B s The transmission power of the interference signal, P t For sender D t The transmission power, h bw Interference signal communication link B s → Willie's small-scale fading parameter, h ur UIRS→D r Small-scale fading parameter of the communication link, h tu D t →Small-scale fading parameter of UIRS communication link, h tw D t →Small-scale fading parameter of Willie communication link; τ is the detection threshold of Willie, is the noise power received by the eavesdropper Willie;

[0091] Furthermore, the minimum error detection probability ξ is calculated * There are two situations:

[0092]

[0093] Case 1), if the intermediate parameter ψ1 = ψ2, then the average minimum error detection probability Equal to the constant value 1-(1 / e);

[0094] in,

[0095]

[0096] d bw For full-duplex base station B s The distance to the eavesdropper Willie, d ur For UAVs with intelligent reflective surfaces UIRS to receiver D r The distance, d tu For UAVs with smart reflective surfaces UIRS to sender D t The distance, d tw For sender D t The distance to the eavesdropper Willie; α bw , α ur , α tu and α tw They are full-duplex base station B s To the eavesdropper Willie, the drone and the intelligent reflective surface UIRS to the receiver D r , UAV and intelligent reflective surface UIRS to sender D t and sender D t Path loss exponent to eavesdropper Willie; α bw =α ur =α tu =α tw ; g ur , g tu and g tw Each element of follows an independent complex Gaussian distribution.

[0097] Case 2), if the intermediate parameter ψ1≠ψ2, the average minimum error detection probability It is divided into the following two cases: Case A), if the cellular link has priority communication protection zone O b At sender D t The coverage area is centered on O t Calculate the corresponding average minimum error detection probability

[0098] Case B): If the cellular link has priority in communication protection zone O b At sender D t The coverage area is centered on O t Otherwise, calculate the corresponding average minimum false detection probability The expression is as follows:

[0099]

[0100] Among them, ξ * is the minimum false detection probability of the eavesdropper Willie, which is about the sender D t The transmission power P t and full-duplex base station B s The transmission power P of the interference signal b The function of tw From the eavesdropper Willie to the sender D of D2D t The distance, d bt For full-duplex base station B s To sender D t The distance, r w is the straight-line distance of the eavesdropper Willie, θ w is the azimuth of the eavesdropper Willie, R t For sender D t The coverage area is centered on O t Radius, r b is the cellular communication link C u →B s Priority communication protection zone O b radius.

[0101] This embodiment obtains the minimum error detection probability that satisfies the average and cellular communication link C u →B s Probability of interruption Constrained communication rate R r After that, according to the half-duplex D2D sender D t The transmission power P t , the transmission power of the interference signal P b , Cellular communication link C u →B s Probability of interruption and the average minimum error detection probability of the half-duplex eavesdropper Willie at the receiving end These four constraints are finally optimized to obtain the maximum communication rate.

[0102] The device-to-device covert communication system jointly assisted by the UAV and the intelligent reflective surface of this embodiment is characterized in that, during the D2D communication between the UAV and the intelligent reflective surface UIRS assisted sender Dt and receiver Dr, assuming that the UIRS is hovering at a height H, the IRS is equipped with K reflective elements, and the effective phase shift of all reflective elements of the IRS is θ; then the UIRS jointly assisted D2D covert link D t→UIRS→D r The modeling is as follows:

[0103]

[0104]

[0105] j is a complex number, θ i represents the phase shift of the ith element, θ i ∈[0,2π], i=1,2,…,K; h tu D t →Small-scale fading parameter of UIRS communication link, h ur UIRS→D r The small-scale fading parameter of the communication link, β0 is the channel gain at a reference distance of 1m, d tu For UAVs with smart reflective surfaces UIRS to sender D t The distance, d ur For UAVs with intelligent reflective surfaces UIRS to receiver D r distance, λ is the carrier wavelength, d is the distance between the reflective elements, φ tu ,φ ur For sender D t to the cosine of the launch angle between the drone and the intelligent reflector UIRS, α tu , α ur For UAVs with smart reflective surfaces UIRS to sender D t and UAV with intelligent reflective surface UIRS to receiver D r The path loss exponent.

[0106] In this embodiment, the eavesdropping link UIRS→Willie in link 3) is modeled as follows:

[0107]

[0108] In the above formula, d uw is the distance between the UAV and the intelligent reflective surface UIRS and the half-duplex eavesdropper Willie, α uw UIRS for drones with smart reflective surfaces to eavesdropper Willie and sender D t The path loss exponent to the eavesdropper Willie, g uw Each element of follows an independent complex Gaussian distribution, that is Here, m represents the mth element of the communication link from the human-machine interface to the intelligent reflective surface UIRS to the half-duplex eavesdropper Willie, m = 1, 2, …, K, K means that the IRS is equipped with K reflective elements.

[0109] In this embodiment, the full-duplex base station B sConfigure two antennas, one antenna receives half-duplex cellular user C u One wire is used to send cellular signals, and the other wire is used for downlink cellular links and to send interference signals. Self-interference is generated between the two wires and cannot be eliminated. represents the self-interference coefficient;

[0110] Full-duplex base station B s By sending jamming signals, the eavesdropper Willie interferes with the UIRS joint assisted D2D covert link D t →UIRS→D r For covert communication detection, the transmission power of the interference signal obeys uniform distribution;

[0111] The uplink cellular link C u →B s The probability of interruption The calculation formula is:

[0112]

[0113] In the above formula, P c For half-duplex cellular user C u The transmission power, h cb C u →B s Small-scale fading parameter of the communication link, h bb For B s →B s Small-scale fading parameter of the communication link, h bt For B s →D t Small-scale fading parameters of the communication link, For half-duplex cellular user C u Received noise power; R c is the target communication rate.

[0114] This embodiment obtains the maximum communication rate The specific method is as follows:

[0115] Step (1), calculate the cellular communication link C u →B s Probability of interruption

[0116]

[0117] Among them, P c For cellular user C u The transmission power, h cb C u →B s Small-scale fading parameter of the communication link, h bb For Bs →B s Small-scale fading parameter of the communication link, h bt For B s →D t Small-scale fading parameters of the communication link, For cellular user C u Received noise power; R c is the target communication rate, η is the intermediate auxiliary amount, η=2 Rc -1;

[0118] Step (2): Calculate the maximum communication rate

[0119] Step (2.1), according to Solve for half-duplex D2D sender D t The transmission power P t And the transmission power of the interference signal P b ;γ is the given target interruption probability;

[0120] Step (2.2), based on the given allowed error detection probability ∈, according to the average minimum error detection probability For sender D t The transmission power P t The monotonically decreasing function and the transmission power P of the interference signal b A monotonically increasing function to solve the sender D t The maximum transmit power P that can be obtained tm and full-duplex base station B s The maximum transmit power P of the interference signal that can be obtained bm ; The calculation formula is as follows:

[0121]

[0122] Step (2.3), use the search algorithm in the interval (0,P tm ]and In, get half sender D t Optimal transmit power and the optimal transmission power of the interference signal Make formula (17) obtain the maximum value, that is, the maximum communication rate

[0123] R * r =maxR r , (17)

[0124] In the above formula, R r It means that the average minimum false detection probability and cellular communication link Cu →B s Probability of interruption Constrained communication rate;

[0125]

[0126] Among them, P t For sender D t The transmission power, P b For full-duplex base station B s The transmission power of the interference signal, h ur UIRS→D r Small-scale fading parameter of the communication link, h tu D t →Small-scale fading parameter of UIRS communication link, h br For B s →D r The small-scale fading parameter of the communication link, Θ is the effective phase shift of all elements of the IRS, For the receiver D r Received noise power.

[0127] For the maximum communication rate The constraints are as follows:

[0128]

[0129] where Θ is the effective phase shift of all components of the IRS, and h br For B s →D r Small-scale fading parameters of the communication link, For the receiver D r The received noise power, For sender D t The maximum transmit power determined by itself, For full-duplex base station B s The maximum transmission power of the interference signal determined by itself.

[0130] Embodiment: In order to verify the performance of the method proposed in the present invention, the following simulation experiments are carried out:

[0131] like Figures 6 to 10 As shown, the simulation environment is as follows: the receiving noise of each communication link obeys the complex Gaussian distribution, and the setting Path loss exponent α=4.

[0132] Figure 6 The full-duplex base station B s The transmission power of the interference signal P b and the average minimum false detection probability The relationship between the different transmission powers P of the interference signal is studied. b The impact on the average minimum false detection probability. Figure 6 The following conclusions can be drawn: When ψ1=ψ2, the average minimum error detection probability is 1-(1 / e). When ψ1≠ψ2, as the transmission power P of the interference signal increases, b As the average minimum error detection probability increases, it also increases, indicating that in the half-duplex D2D sender D t The transmission power P t When the transmission power of the interference signal is fixed, P b Increasing it will reduce the detection performance of half-duplex eavesdropper Willie.

[0133] Figure 7 Given a half-duplex D2D sender D t Different transmission power P t Average minimum false detection probability In the case of ψ1=ψ2, the average minimum error detection probability is 1-(1 / e). In the case of ψ1=ψ2, the transmission power P of the interference signal is b is a fixed value, with the half-duplex D2D sender D t The transmission power P t As the average minimum error detection probability increases, the half-duplex D2D sender D t The transmission power P t The increase of will make the half-duplex eavesdropper Willie's power at the receiving end relative to the transmission power P of the interference signal b Therefore, the half-duplex D2D sender D t The transmission power P t The increase of will increase the detection probability of the signal and reduce the average minimum false detection probability.

[0134] Figure 8 Given a half-duplex cellular user C u Different transmission powers[ c Half-duplex D2D sender D t Transmit power P t and cellular communication link interruption probability Here we assume that the target communication rate is R c is 1, the transmission power of the interference signal is P b Given as 25dB, the self-interference coefficient is 0.4. It can be obtained that in the half-duplex cellular user C u The transmission power P c The interruption probability of the cellular communication link under the conditions of 25dB, 27.5dB and 30dB respectively With half-duplex D2D sender D t The transmission power P t This indicates that the increase in the transmit power of the IRS-assisted D2D communication link may lead to increased interference to the cellular link, thereby increasing the interruption probability of the cellular communication link.

[0135] Fig. 9 The transmission power P of the interference signal under different conditions is studied. b and cellular communication link interruption probability Assuming that the half-duplex D2D sender D t The transmission power P t When the B / s of the half-duplex D2D sender are 29dB and 30dB respectively, t The transmission power P t Increase the probability of causing interruption Assume that the half-duplex D2D sender D t The transmission power P t When the half-duplex cellular user C u The transmission power P c 29dB and 30dB respectively, half-duplex cellular user C u The transmission power P c The smaller the value, the greater the interruption probability. c 0.9 and 1 respectively, which can give a smaller target communication rate R c Reduce the probability of causing interruptions The increase indicates that a stable communication rate can lead to a lower interruption probability.

[0136] Fig.10 Compared with the half-duplex D2D sender D t Maximum transmit power and maximum communication rate The relationship between . Four specific situations are given, respectively. In the cellular link priority communication protection zone O b In half-duplex D2D sender D t The coverage area is centered on O t Within and cellular link priority communication protection zone O b In half-duplex D2D sender D t The coverage area is centered on O t By comparing the other two cases, we can get the half-duplex D2D sender D t The transmission power P t The increase in the value range corresponds to the maximum communication rate will also increase, indicating that the transmission power P of the fixed interference signal b, maximum transmit power With the maximum communication rate Proportional to the increase in half-duplex D2D sender D t The transmission power P t The signal strength can be improved, and the communication rate will also increase relatively when the concealment requirements are reduced.

[0137] Fig.11 and Fig.12 The half-duplex D2D sender Dt with different transmission power P is shown respectively. t With the communication rate R r relationship diagram. Fig.11 Corresponding to the cellular link priority communication protection zone O b In the coverage area O centered at the sender Dt t Simulation results when other than Fig.12 Cellular link priority communication protection zone O b In the coverage area O centered at the sender Dt t The two figures compare the performance of four different schemes. The results show that in the trade-off between concealment and communication rate, the communication rate considering concealment is significantly lower than that without considering concealment. However, in order to improve the concealment of the system, a proper reduction in the communication rate is acceptable. Compared with the schemes that only consider full-duplex UAV and fixed-position IRS, the method proposed by the present invention significantly improves the communication rate while improving the concealment of the system, proving its effectiveness in optimizing system performance.

[0138] Figure 6 , Figure 7 , Figure 8 , Fig. 9 , Fig.10 , Fig.11 and Fig.12 The simulation results show that the present invention constrains the transmission power and the transmission power of the interference signal by analyzing the average minimum error detection probability and the interruption probability of the cellular communication link, and obtains the maximum communication rate of the UIRS jointly assisted D2D communication link. The communication rate of the system is effectively improved under the joint assistance of the UAV and the intelligent reflector UIRS.

Claims

1. A device-to-device covert communication system assisted by a drone and an intelligent reflective surface, characterized in that: The entities involved include the drone, the intelligent reflector UIRS, and the full-duplex base station B s and a half-duplex communication terminal, wherein the half-duplex communication terminal includes a half-duplex cellular user C u , half-duplex D2D sender D t , half-duplex D2D receiver D r and half-duplex eavesdropper Willie; the following communication links are formed between each entity; Link 1), UIRS joint assisted D2D hidden link D t →UIRS→D r ; The sender D in this link t Send a covert signal to the drone and the intelligent reflective surface UIRS, and the UIRS will send the D t The sent covert signal is forwarded to the receiver D r ; Cellular user C u Send cellular signal to base station B s , forming an uplink cellular link C u →B s ; Cellular user C u The uplink and downlink of the transmission network use orthogonal spectrum resources and there is no interference between them. t →UIRS→D r With uplink cellular link C u →B s Shared spectrum resources; Link 2), Base Station B s In order to counter the eavesdropper Willie and improve the system's stealth, artificial noise is sent to the eavesdropper Willie to build an artificial noise link B. s →Willie; Base Station B s The artificial noise emitted also affects the receiver D r Generate interference and form link B s →D r , and causes the base station B s The self-interference of link B s →B s ; Link 2) Base station B s Use the same spectrum resources to send and receive information at the same time; Link 3), the randomly distributed eavesdropper Willie attempts to monitor the UIRS joint assisted D2D covert link D t →UIRS→D r , detect whether a covert signal is being sent, involving eavesdropping on link D t →Willie and UIRS→Willie; Link 4), Base Station B s To sender D t Send information to form a downlink cellular link B s →D t ; Calculate the average minimum false detection probability of the eavesdropper Willie in link 3) Using the mean minimum false detection probability To measure the link 1) UIRS joint assisted D2D hidden link D t →UIRS→D r The concealment of At the same time, calculate the uplink cellular link C u →B s The probability of interruption Finally, the average minimum false detection probability is calculated and cellular communication link C u →B s Probability of interruption Constrained communication rate R r , and the communication rate R r Perform constraint optimization to obtain the maximum communication rate of link 1) 2. The device-to-device covert communication system assisted by a drone and a smart reflective surface according to claim 1, characterized in that: Calculate the minimum false detection probability ξ * and the average minimum false detection probability The method is as follows: The false detection probability of the eavesdropper Willie satisfies ξ=P FA +P MD ; P FA is the false alarm probability of the eavesdropper Willie, P MD is the probability of missed alarm of eavesdropper Willie; H0 indicates that the UIRS joint assisted D2D communication link does not transmit concealed signals, and H1 indicates that the UIRS joint assisted D2D communication link transmits concealed signals; P b For full-duplex base station B s The transmission power of the interference signal, P t For sender D t The transmission power, h gw Interference signal communication link B s → Willie's small-scale fading parameter, h ur UIRS→D r Small-scale fading parameter of the communication link, h tu D t →Small-scale fading parameter of UIRS communication link, h tw D t →Small-scale fading parameter of Willie communication link; τ is the detection threshold of Willie, is the noise power received by the eavesdropper Willie; Next, calculate the minimum error detection probability ξ * , including two situations: Case 1), if the intermediate parameter ψ1 = ψ2, then the average minimum error detection probability is equal to the constant value 1-(1 / e); where, The intermediate parameter ψ1 reflects the full-duplex base station B s The intermediate parameter ψ2 reflects the signal strength between the UAV-IRS-assisted D2D communication link and the eavesdropper Willie; d bw For full-duplex base station B s The distance to the eavesdropper Willie, d ur For UAVs with intelligent reflective surfaces UIRS to receiver D r The distance, d tu For UAVs with smart reflective surfaces UIRS to sender D t The distance, d tw For sender D t The distance to the eavesdropper Willie; α bw , α ur , α tu and α tw They are full-duplex base station B s To the eavesdropper Willie, the drone and the intelligent reflective surface UIRS to the receiver D r , UAV and intelligent reflective surface UIRS to sender D t and sender D t Path loss exponent to eavesdropper Willie; α bw =α ur =α tu =α tw ; g ur , g tu and g tw Each element of follows an independent complex Gaussian distribution; β0 is the channel gain at a reference distance of 1m; Case 2), if the intermediate parameter ψ1≠ψ2, the average minimum error detection probability It is divided into the following two cases: Case A), if the cellular link has priority communication protection zone O b At sender D t The coverage area is O t Calculate the corresponding average error detection probability Case B): If the cellular link has priority in communication protection zone O b At sender D t The coverage area is centered on O t Otherwise, the corresponding average error detection probability is calculated The expression is as follows: Among them, ξ * is the minimum false detection probability of the eavesdropper Willie, which is about the sender D t The transmission power P t and full-duplex base station B s The transmission power P of the interference signal b The function of tw From the eavesdropper Willie to the sender D of D2D t The distance, d bt For full-duplex base station B s To sender D t The distance, r w is the straight-line distance of the eavesdropper Willie, θ w is the azimuth of the eavesdropper Willie, R t For sender D t The coverage area is centered on O t Radius, r b is the cellular communication link C u →B s Priority communication protection zone O b radius.

3. The device-to-device covert communication system assisted by a drone and a smart reflective surface according to claim 1, characterized in that: Get the minimum error detection probability that satisfies the average and cellular communication link C u →B s Probability of interruption Constrained communication rate R r After that, according to the half-duplex D2D sender D t The transmission power P t , the transmission power of the interference signal P b , Cellular communication link C u →B s Probability of interruption and the average minimum error detection probability of the half-duplex eavesdropper Willie at the receiving end These four constraints are finally optimized to obtain the maximum communication rate.

4. The device-to-device covert communication system assisted by a drone and a smart reflective surface according to claim 1, characterized in that: UIRS-assisted transmitter in UAV with intelligent reflective surface t and receiver D r During D2D communication, it is assumed that the UIRS is hovering at a height H, the IRS is equipped with K reflective elements, and the effective phase shift of all reflective elements of the IRS is Θ; then the UIRS joint assisted D2D covert link D t →UIRS→D r The modeling is as follows: j is a complex number, θ i represents the phase shift of the ith element, θ i ∈[0,2π], i=1,2,…,K; h tu D t →Small-scale fading parameter of UIRS communication link, h ur UIRS→D r The small-scale fading parameter of the communication link, β0 is the channel gain at a reference distance of 1m, d tu For UAVs with smart reflective surfaces UIRS to sender D t The distance, d ur For UAVs with intelligent reflective surfaces UIRS to receiver D r distance, λ is the carrier wavelength, d is the distance between the reflective elements, φ tu ,φ ur For sender D t to the cosine of the launch angle between the drone and the intelligent reflector UIRS, α tu , α ur For UAVs with smart reflective surfaces UIRS to sender D t and UAV with intelligent reflective surface UIRS to receiver D r The path loss exponent.

5. The device-to-device covert communication system assisted by a drone and a smart reflective surface according to claim 1, characterized in that: The eavesdropping link UIRS→Willie in link 3) is modeled as follows: In the above formula, d uw is the distance between the UAV and the intelligent reflective surface UIRS and the half-duplex eavesdropper Willie, α uw UIRS for drones with smart reflective surfaces to eavesdropper Willie and sender D t The path loss exponent to the eavesdropper Willie, g uw Each element of follows an independent complex Gaussian distribution, that is Here, m represents the mth element of the communication link from the human-machine interface to the intelligent reflective surface UIRS to the half-duplex eavesdropper Willie, m = 1, 2, …, K, K means that the IRS is equipped with K reflective elements.

6. The device-to-device covert communication system assisted by a drone and a smart reflective surface according to claim 1, characterized in that: The full-duplex base station B s Configure two antennas, one antenna receives half-duplex cellular user C u One wire is used to send cellular signals, and the other wire is used for downlink cellular links and to send interference signals. Self-interference is generated between the two wires and cannot be eliminated. represents the self-interference coefficient; Full-duplex base station B s By sending jamming signals, the eavesdropper Willie interferes with the UIRS joint assisted D2D covert link D t →UIRS→D r For covert communication detection, the transmission power of the interference signal obeys uniform distribution; The uplink cellular link C u →B s The probability of interruption The calculation formula is: In the above formula, P c For half-duplex cellular user C u The transmission power, h cb C u →B s Small-scale fading parameter of the communication link, h bb For B s →B s Small-scale fading parameter of the communication link, h bt For B s →D t Small-scale fading parameters of the communication link, For half-duplex cellular user C u Received noise power; R c is the target communication rate.

7. The communication method of the device-to-device covert communication system with the joint assistance of a drone and an intelligent reflective surface according to claim 1, characterized in that: Get the maximum communication rate The specific method is as follows: Step (1), calculate the cellular communication link C u →B s Probability of interruption Among them, P c For cellular user C u The transmission power, h cb C u →B s Small-scale fading parameter of the communication link, h bb For B s →B s Small-scale fading parameter of the communication link, h bt For B s →D t Small-scale fading parameters of the communication link, For cellular user C u Received noise power; R c is the target communication rate, η is the intermediate auxiliary amount, η=2 Rc -1; Step (2): Find the maximum communication rate Step (2.1), according to Solve for half-duplex D2D sender D t The transmission power P t And the transmission power of the interference signal P b γ is the given target interruption probability; Step (2.2), based on the given allowed error detection probability ∈, according to the average minimum error detection probability For sender D t The transmission power P t The monotonically decreasing function and the transmission power P of the interference signal b A monotonically increasing function to solve the sender D t The maximum transmit power P that can be obtained tm and full-duplex base station B s The maximum transmit power P of the interference signal that can be obtained bm ; The calculation formula is as follows: Step (2.3), use the search algorithm in the interval (0,P tm ]and In, get half sender D t Optimal transmit power and the optimal transmission power of the interference signal Make formula (8) obtain the maximum value, that is, the maximum communication rate R * r =maxR r ,(8) In the above formula, R r It means that the average minimum false detection probability and cellular communication link C u →B s Probability of interruption Constrained communication rate; Among them, P t For sender D t The transmission power, P b For full-duplex base station B s The transmission power of the interference signal, h ur UIRS→D r Small-scale fading parameter of the communication link, h tu D t →Small-scale fading parameter of UIRS communication link, h br For B s →D r The small-scale fading parameter of the communication link, Θ is the effective phase shift of all elements of the IRS, For the receiver D r Received noise power.

8. The communication method of the device-to-device covert communication system with the joint assistance of a drone and an intelligent reflective surface according to claim 1 or 7, characterized in that: For the maximum communication rate The constraints are as follows: where Θ is the effective phase shift of all components of the IRS, and h br For B s →D r Small-scale fading parameters of the communication link, For the receiver D r The received noise power, For sender D t The maximum transmit power determined by itself, For full-duplex base station B s The maximum transmission power of the interference signal determined by itself.

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