Design system and method for reflector-assisted SWIPT system communication based on directional modulation

Abstract

The invention provides a design method for reflector-assisted SWIPT system communication based on directional modulation. The design method comprises the following steps: a transmitting end sends a wireless signal to a reflector; after the reflecting surface receives a signal from a transmitting end, the phase of each reflecting element is adjusted according to a preset phase shift mode, the wavefront shape and the transmission direction of the reflected signal are changed, and the reflected signal is directionally transmitted to a receiving end; and the receiving end is responsible for receiving the signal reflected by the reflecting surface and generating different wave beam responses to carry out information decoding and energy collection. According to the invention, simultaneous transmission of wireless information and energy can be realized, and the energy efficiency and reliability of the network are improved. In addition, through the direction modulation and beam forming technology, the security of the system can be enhanced, and the risk of security threats such as eavesdropping can be reduced.

Description

Technical Field

[0001] The invention belongs to the field of communications, and in particular relates to a design system and method for reflective surface-assisted SWIPT system communications based on directional modulation. Background Art

[0002] Directional Modulation (DM), as a physical layer security technology, has received increasing attention in recent years. Different from the strategy of relying on interference to solve security problems in traditional physical layer security methods, directional modulation technology directly realizes customized symbol design at the receiving end of communication. This technology accurately maps the digital modulated constellation signal to a pre-set spatial direction, which is defined as a legal and secure communication direction, and deliberately introduces confusion of the constellation signal in an unexpected free space area. Specifically, the receiving beam of the legitimate user will have amplitude and phase characteristics that fully match the expected transmission data symbol. Even in the case where the eavesdropper's channel is correlated with the legitimate user's channel, the eavesdropper's receiving performance will be significantly reduced due to the destructive interference intentionally imposed on the eavesdropper by the directional modulation technology, thereby ensuring the high security of the communication process.

[0003] An intelligent reflecting surface (IRS) is a planar array composed of a large number of low-value reconfigurable passive elements. It can improve the propagation of reflected signals by causing phase shifts in the incident signal. The entire process does not require the participation of baseband and RF processing. Since the intelligent reflecting surface has a thin and light structure, controllable cost and low power consumption, it can achieve wireless signal coverage at a low cost. In recent years, there has been an increasing number of studies on the application of IRS in wireless communication systems. These studies have shown that by properly designing and configuring IRS, the wireless propagation environment between communication devices can be actively improved, and there is great potential in improving the transmission rate, coverage and energy efficiency of land mobile communication systems. This will have a positive impact on multiple key performance indicators of wireless communication systems.

[0004] Simultaneous Wireless Information and Power Transfer (SWIPT) is a recently developed technology among various wireless power transfer (WPT) technologies. It can simultaneously transmit information and power wirelessly. The concept of SWIPT was first proposed by Varshney, who used the capacity energy function to combine the performance optimization formula of wireless information and power transmission to analyze it theoretically. Traditional wireless communication is just a simple information exchange, while SWIPT technology can transmit the energy-carrying information part to the terminal node while transmitting information. Then, after a series of signal adjustments, the received wireless energy will be stored in the battery of the terminal device to compensate for the energy loss caused by the daily information exchange and transmission of the terminal device. Summary of the invention

[0005] The purpose of the present invention is to prevent eavesdroppers from stealing information while ensuring that legitimate users receive information, and at the same time support the legitimate user receiving end to simultaneously perform energy harvesting (EH) and information decoding (ID).

[0006] The technical solution of the present invention is as follows:

[0007] A design method for reflector-assisted SWIPT system communication based on directional modulation includes the following steps:

[0008] The transmitter sends a wireless signal to the reflecting surface;

[0009] After receiving the signal from the transmitting end, the reflecting surface adjusts the phase of each reflecting element according to the preset phase shift mode, changes the wavefront shape and transmission direction of the reflected signal, and the reflected signal is transmitted to the receiving end in a direction;

[0010] The receiving end is responsible for receiving the signal reflected by the reflecting surface and generating different beam responses for information decoding and energy collection.

[0011] Furthermore, the wireless signal is transmitted in a specific direction.

[0012] Furthermore, the receiving end includes a user and an eavesdropper.

[0013] Furthermore, the beam response of the receiving end includes:

[0014] User's beam response:

[0015] Eavesdropper's beam response:

[0016] Among them, · is the dot product, is the weight vector of the transmitter, s(f,θ) is the steering vector from the transmitter to the reflection surface, θ is the transmission direction of the signal from the user to the reflection surface, is the weight vector of the reflection surface, is the steering vector from the reflective surface to the user, is the transmission direction of the signal from the reflecting surface to the user, s(f,ζ) is the steering vector from the reflecting surface to the eavesdropper, and ζ is the transmission direction of the signal from the reflecting surface to the eavesdropper.

[0017] Furthermore, the formula of the steering vector s(f,θ) from the transmitter to the reflecting surface is:

[0018]

[0019] Among them, f is the signal frequency, c is the wave speed, d n (n=0, 1, ..., N-1) is the distance between the zeroth antenna and the Nth antenna, and N is the number of antennas equipped in the BS.

[0020] Furthermore, the steering vector from the reflective surface to the user The formula is:

[0021]

[0022] Furthermore, the formula for the steering vector s(f,ζ) from the reflecting surface to the eavesdropper is:

[0023]

[0024] Where f is the signal frequency, c is the wave speed, and x y (y=0, 1, ..., Y-1) is the distance between the zeroth electromagnetic unit and the Yth electromagnetic unit on the reflection surface, and Y is the number of electromagnetic units.

[0025] The present invention also provides a design system for reflective surface-assisted SWIPT system communication based on directional modulation, the system comprising:

[0026] Transmitter, reflector and receiver;

[0027] Wherein, the transmitting end is used to send wireless signals to the reflecting surface;

[0028] The reflective surface is used to adjust the reflection angle and reflection intensity of the incident signal;

[0029] The receiving end is responsible for receiving the signal reflected by the reflecting surface and generating different beam responses for information decoding and energy collection.

[0030] Furthermore, the transmitting end is equipped with N transmitting antennas arranged in a uniform linear array.

[0031] Furthermore, the reflecting surface is composed of a plurality of passive reflecting elements.

[0032] Compared with the prior art, the present invention has the following advantages:

[0033] The present invention can realize the simultaneous transmission of wireless information and energy, improve the energy efficiency and reliability of the network. In addition, through directional modulation and beamforming technology, the security of the system can be enhanced and the risk of security threats such as eavesdropping can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The accompanying drawings generally illustrate various embodiments by way of example and not limitation, and together with the description and claims, serve to illustrate the embodiments of the invention. Where appropriate, the same reference numerals are used throughout the drawings to refer to the same or similar parts. Such embodiments are illustrative and are not intended to be exhaustive or exclusive embodiments of the present apparatus or method.

[0035] Figure 1 A schematic diagram showing a comparison between the directional modulation system of the present invention and a traditional transmitter architecture;

[0036] Figure 2 A schematic diagram of a scene model of the present invention is shown;

[0037] Figure 3 A schematic diagram of a system model of the present invention is shown;

[0038] Figure 4 A schematic diagram of the constraint algorithm flow of the present invention is shown;

[0039] Figure 5 The eavesdropper amplitude of the present invention is shown;

[0040] Figure 6 The eavesdropper phase value of the present invention is shown;

[0041] Figure 7 An iteration diagram of the objective function of the present invention is shown. DETAILED DESCRIPTION

[0042] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0043] The embodiment of the present invention provides a design method for reflective surface assisted SWIPT system communication based on directional modulation, comprising the following steps:

[0044] Step 1: The transmitting array includes N transmitting antennas arranged in a uniform linear array. The BS transmits to the reflection surface in the direction θ∈[0°,180°]. The transmission angles reflected by the reflection surface to the user USER and the eavesdropper EVE are respectively ζ, respectively represent the steering vectors from BS to the reflection surface, from the reflection surface to USER, and from the reflection surface to EVE:

[0045]

[0046] Among them, f is the signal frequency, c is the wave speed, d n (n=0,1,…,N-1) is the distance between the zeroth antenna and the Nth antenna, x y (y=0, 1, ..., Y-1) is the distance between the zeroth electromagnetic unit and the Yth electromagnetic unit on the reflecting surface.

[0047] Step 2: The beam responses at the user USER and the eavesdropper EVE can be expressed as:

[0048]

[0049] w l =[w0,w1,…,w N-1 ] T is the weight vector of the BS corresponding to l symbols, is the weight vector of the reflection surface corresponding to l symbols, [] H is the conjugate transpose operation, such as w l Obtained by transposing.

[0050] In practice, the precision of the phase shift of the smart reflective surface is limited. The present invention takes this practical problem into consideration and adjusts the phase of each electromagnetic unit from is selected from , where B0 (γ=0,1,…,B0-1) is the number of bits.

[0051] Step 3: Construct an optimization problem based on the above structure. The optimization equation of the present invention can be expressed as:

[0052]

[0053] C4:0<ρ<1

[0054] C5:α y ∈Φ,|β y |=1

[0055] for y=0,1,…,Y-1;l=0,1,…,L-1

[0056] Constraint (C1) is the desired symbol synthesized by the ID end in the direction of the user USER, where ρ is the power allocation ratio (PS ratio) of the receiving end; constraint (C2) refers to the minimum energy reception requirement that needs to be met at the EH end in the direction of the user USER; constraint (C3) is the transmission power constraint of the transmitting end; constraint (C4) is the value range constraint of the power allocation ratio; constraint (C5) is the adjustable amplitude and phase of the electromagnetic unit of the smart reflector.

[0057] Constraint (C2) cannot be solved directly using the CVX toolbox, so this experiment uses the geometric scaling method and relaxes the constraints to approximately equal, so that the CVX toolbox can be used to solve it.

[0058] Constraint (C5) is a non-convex constraint. In order to solve this problem, a corresponding iterative optimization algorithm is proposed. The algorithm flow chart is as follows Figure 4 As shown. Where C f (min) is the cost function value calculated based on the initial value, Φ(l) is the lth element of Φ, C f (α y,l ) is α y Take the objective function value obtained by Φ(l), C f (α y ) is the maximum objective function value obtained by traversing all elements in Φ.

[0059] Example 1

[0060] In this embodiment, we set the number of antennas of the ULA transmitter to N = 20, d = λ / 2; the number of elements of the smart reflector is M = 15, and the distance between adjacent antennas is x = λ / 2. A desired receiver is located at the center of the circle, the distance from BS to IRS reflector is H = 1000λ, the distance from IRS to USER is D1 = 900λ, h = 200λ, and the minimum energy collection requirement is E min dBm.

[0061] The received energy value of the receiving end calculated after optimization is about E = -1.42dBn, which is greater than the minimum energy collection requirement E min , that is, the minimum threshold constraint of received energy is reached.

[0062] The expected response value at the user receiving end is an amplitude of 0.1 (gain is 0dB) and a phase shift of 90°, that is, the symbols '00', '01', '11', '10' correspond to 45°, 135°, -135° and -45° respectively, while at the eavesdropper position the phases of the symbols '00', '01', '11', '10' are disturbed.

[0063] The final amplitude value of the eavesdropper around the legitimate receiver is as follows Figure 5, the beam response level of all eavesdropping devices is lower than 0dB, which is the amplitude response required to achieve the invention effect in this experiment. However, the special thing is that when the eavesdropping device and the legitimate receiver are in the same straight line, the beam response level of the eavesdropping device will be equal to 0dB. This is also the problem we need to solve in the next work. Phase response of eavesdropping devices around legitimate receivers Figure 6 As shown, it can be seen that the signal phase of the eavesdropper is randomly disordered.

[0064] The above comparison of the amplitude and phase at the eavesdropper shows that while the legitimate user receives the correct information, the surrounding eavesdroppers cannot receive the correct information.

[0065] Figure 7 The figure is the relationship between the objective function value and the number of iterations. It can be seen that the cost function value shows a decreasing trend. From the third iteration to the fifth iteration, the function value no longer changes; that is, the objective function is convergent, which illustrates the effectiveness of the proposed design.

[0066] In summary, in this experiment, the legitimate user receiving end can receive the correct information signal under the condition of meeting the minimum energy reception requirement, that is, the legitimate user end can ensure the security of information transmission while realizing the energy supply function. Therefore, it is of practical significance to apply directional modulation technology to the SWIPT system.

[0067] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A design method for reflector-assisted SWIPT system communication based on directional modulation, characterized in that: The steps include: The transmitter sends a wireless signal to the reflecting surface; After receiving the signal from the transmitting end, the reflecting surface adjusts the phase of each reflecting element according to the preset phase shift mode, changes the wavefront shape and transmission direction of the reflected signal, and the reflected signal is transmitted to the receiving end in a direction; The receiving end is responsible for receiving the signal reflected by the reflecting surface and generating different beam responses for information decoding and energy collection.

2. The design method of the reflector-assisted SWIPT system communication based on directional modulation according to claim 1 is characterized in that: The wireless signal is transmitted in a specific direction.

3. The design method of the reflector-assisted SWIPT system communication based on directional modulation according to claim 1 is characterized in that: The receiving end includes a user and an eavesdropper.

4. The design method of the reflector-assisted SWIPT system communication based on directional modulation according to claim 1 is characterized in that: The beam response at the receiver includes: User's beam response: Eavesdropper's beam response: Where, · is the dot product, s(f,θ) is the steering vector from the transmitter to the reflector, is the weight vector of the reflection surface, is the steering vector from the reflective surface to the user, is the transmission direction of the signal from the reflecting surface to the user, s(f,ζ) is the steering vector from the reflecting surface to the eavesdropper, ζ is the transmission direction of the signal from the reflecting surface to the eavesdropper, is the weight vector of the transmitter.

5. The design method of the reflector-assisted SWIPT system communication based on directional modulation according to claim 4 is characterized in that: The formula for the steering vector s(f,θ) from the transmitter to the reflector is: Among them, f is the signal frequency, c is the wave speed, d n (n=0, 1, ..., N-1) is the distance between the zeroth antenna and the Nth antenna of the transmitting end, and N is the number of antennas equipped by the BS.

6. The design method of the reflector-assisted SWIPT system communication based on directional modulation according to claim 4 is characterized in that: Steering vector from reflective surface to user The formula is: The formula for the steering vector s(f,ζ) from the reflecting surface to the eavesdropper is: Where f is the signal frequency, c is the wave speed, and x y (y=0, 1, ..., Y-1) is the distance between the zeroth electromagnetic unit and the Yth electromagnetic unit on the reflection surface, and Y is the number of electromagnetic units.

7. A design system for reflector-assisted SWIPT system communication based on directional modulation, characterized in that: The system comprises: Transmitter, reflector and receiver; Wherein, the transmitting end is used to send wireless signals to the reflecting surface; The reflective surface is used to adjust the reflection angle and reflection intensity of the incident signal; The receiving end is responsible for receiving the signal reflected by the reflecting surface and generating different beam responses for information decoding and energy collection.

8. The design system of the reflector-assisted SWIPT system communication based on directional modulation according to claim 7, characterized in that: The transmitting end is equipped with N transmitting antennas arranged in a uniform linear array.

9. The design system of the reflector-assisted SWIPT system communication based on directional modulation according to claim 1, characterized in that: The reflecting surface is composed of a plurality of passive reflecting elements.

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