Beam forming method and system with adjustable RIS enhanced beam width, medium and equipment

Abstract

The invention relates to the technical field of beam forming, and discloses an RIS enhanced beam-width-adjustable beam forming method, system, medium and equipment, and the method comprises the steps: constructing an RIS-assisted ISAC system, constructing a sensing channel model in the system, and calculating the phase shift of standard beam forming; calculating the sensing gain of the potential target by combining the position of the sensing target relative to the user center based on the phase shift of the standard beam forming; reconstructing the sensing gain of the potential target by using a stationary phase method, and solving an ideal beam forming phase shift when the sensing gain of the reconstructed potential target is optimal; adjustment of the beam width and the channel gain is realized by adjusting the expression form of the ideal beam forming phase shift. According to the invention, the width of the sensing beam can be adjusted and is used for replacing resource-intensive narrow beam scanning sensing, so that the resource utilization rate is improved, the interference is reduced, and the calculation complexity is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of beamforming, and in particular to a beamforming method, system, medium and device with adjustable beam width enhanced by RIS. Background Art

[0002] Integrated sensing and communications (ISAC) is a transformative approach that integrates sensing and communication functions in wireless networks and has potential advantages in enhancing communication capabilities and supporting various emerging applications. The large-scale deployment of ISAC still depends on the comprehensive design of aspects such as sensing mode, frame structure, and beamforming. In particular, beamforming has always been a key focus of extensive research in ISAC systems. However, a major challenge in beamforming design lies in its high complexity, which has promoted the application of reconfigurable intelligent surfaces (RIS), an auxiliary communication device, in ISAC systems.

[0003] RIS can intelligently control numerous reflection units to effectively concentrate the diffused electromagnetic waves in space to areas with weak signals, achieving more efficient and uniform signal coverage and having the potential to independently or jointly manage sensing tasks. In the prior art, there are joint design schemes for active beamforming on the base station (BS) side and passive beamforming on the RIS side, aiming to improve sensing performance while maintaining the communication experience. There are also RIS-based self-sensing systems, where the RIS controller transmits detection signals, and dedicated sensors on the RIS estimate the target position by analyzing the reflected signals. However, existing research mainly focuses on using RIS to assist ISAC systems and knowing in advance whether there is a sensing target. However, the problems of whether there is a sensing target and whether timely detection is required to achieve ISAC still exist. To solve this problem, in the prior art, there is a practice of using frequent sensing beam scanning as a solution, and on this basis, a RIS beam scanning program using the prior information of the target cluster is used to achieve high-resolution sensing. There is also a RIS-assisted bistatic ISAC system that jointly optimizes the RIS phase and analog beamforming to suppress composite path interference while balancing the performance of sensing and communication.

[0004] However, most of these beamforming methods in the prior art use resource-intensive narrow beams for scanning to sense potential targets. The resource utilization efficiency of the beam scanning method is low, and it is necessary to fundamentally update the current transmission protocol with high complexity. Moreover, there is interference between the sensing beam and the communication beam, and the balance between sensing and communication further increases the complexity of beamforming design. Summary of the Invention

[0005] To this end, the technical problem to be solved by the present invention is to overcome the deficiencies in the prior art, and provide a beamforming method, system, medium and device with adjustable beam width enhanced by RIS, which can adjust the width of the sensing beam and use a wide beam to sense potential targets instead of resource-intensive narrow beam scanning sensing, improve resource utilization efficiency, reduce interference between the sensing beam and the communication beam, and reduce computational complexity.

[0006] To solve the above technical problem, the present invention provides a beamforming method with adjustable beam width enhanced by RIS, including:

[0007] Construct an ISAC system assisted by RIS, build a sensing channel model in the system and calculate the phase shift of the standard beamforming;

[0008] Based on the phase shift of the standard beamforming, calculate the sensing gain of potential targets in combination with the position of the sensing target relative to the user center;

[0009] Use the stationary phase method to reconstruct the sensing gain of potential targets and solve the phase shift of the ideal beamforming when the reconstructed sensing gain of potential targets is optimal;

[0010] By adjusting the expression form of the phase shift of the ideal beamforming, the adjustment of the beam width and the channel gain is realized.

[0011] Further, the constructing a sensing channel model in the system and calculating the phase shift of the standard beamforming includes:

[0012] Establish a Cartesian coordinate system in the system, and the center of RIS is located at the coordinate origin o r =[0, 0, 0], the wavelength is λ = c / f, where f is the carrier frequency and c is the speed of light; assume that the shape of RIS is a disk with a radius of R and is located in the xy plane of the coordinate system; RIS is composed of N ris reflective units, and the interval between adjacent two RIS units is Δ = λ / 2; each reflective unit corresponds to a three-dimensional coordinate, and the three-dimensional coordinates (x, y, z) of all reflective units form a 3D coordinate set, denoted as S ris , satisfying x 2 +y 2 ≤R 2 and z = 0;

[0013] Use α ru to represent the elevation angle of the UE to the RIS plane, draw a zero-crossing line l ru on the RIS plane, and the phases of the received beams of the reflective units on the zero-crossing line are the same. Take the zero-crossing line as the reference line, which is expressed as:

[0014] lru ={(x,y):y - x tanα ru = 0} (1);

[0015] Taking the zero - crossing line as a reference, the phase of the reflection unit at the point (x,y,0) is:

[0016]

[0017] where h ru (x,y,φ ru ) is the phase of the reflection unit at the point (x,y,0), φ ru represents the angle between the link between the UE and the RIS and the xy - plane, Δd ru represents the perpendicular distance from the RIS unit to the reference line, α ru is the AOE from the RIS to the UE;

[0018] The channel from the BS to the RIS is described as:

[0019]

[0020] where h br (x,y,φ br ) is the channel representation from the BS to the RIS, α br is the AOE from the RIS to the BS, φ br represents the angle between the link between the BS and the RIS and the xy - plane;

[0021] The channel from the RIS to the UE is described as:

[0022] h(x,y)=h ru (x,y,φ ru )h br (x,y,φ br ) (4),

[0023] where h(x,y) is the channel representation from the RIS to the UE;

[0024] When considering the entire RIS plane, the entire sensing channel is:

[0025]

[0026] where, is the entire sensing channel representation, h(x n ,y n ) is the channel representation from the n - th reflection unit of the RIS to the UE, is the phase shift of the n - th reflection unit;

[0027] Each RIS unit can act as a phase shifter where x n and y n are the coordinates of the n-th reflecting unit; assuming that the RIS integrates an uncountable and infinitesimal number of reflecting units, the summation in formula (5) can be approximated as:

[0028]

[0029] where is the approximation of the entire sensing channel, is the phase shift at each point in the RIS plane;

[0030] The offset is of the same order as and can be ignored when the number of units is large; sample N ris elements from and select according to the corresponding coordinates Using this continuous model, with the UE as the target, the phase shift of the standard beamforming is:

[0031]

[0032] where is the phase shift of the standard beamforming,

[0033] Furthermore, the phase shift based on the standard beamforming, combined with the position of the sensing target relative to the user center to calculate the sensing gain of the potential target, includes:

[0034] Introduce a phase shift to adjust the beam width Construct the overall phase shift after reflection by the RIS as:

[0035]

[0036] where is the overall phase shift after reflection by the RIS, is the additional phase shift;

[0037] Use φ rs to represent the angle between the link between the potential target and the RIS and the xy plane of the RIS, and use α rs to represent the elevation angle, then the sensing gain of the potential target is:

[0038]

[0039] where is the sensing gain of the potential target, Δd rsTo represent the vertical distance from the RIS unit to the reference line,

[0040] transform the in the rectangular coordinate system into the in the polar coordinate system. Transform formula (9) into polar form to obtain:

[0041]

[0042] Due to the radial symmetry, the design only varies with r and is independent of θ. Assuming that the phase shift of the reflection unit of the RIS is consistent at a distance r from the origin, then there is:

[0043]

[0044] Then the integral of formula (10) can be equivalent to:

[0045]

[0046] where χ is the position of the perceived target relative to the user center, and χ 2 = η 2 + ξ 2 represents the spatial offset. Integrating over the entire θ gives:

[0047]

[0048] where g(χ) is the perceived gain of the potential target represented by the position of the perceived target relative to the user center, R is the radius of the RIS, and J0 is the zero-order function of the Bessel function of the first kind.

[0049] Furthermore, the position χ of the perceived target relative to the user center satisfies:

[0050] The range of the variable χ in three-dimensional space can be regarded as a circle centered at and is represented as:

[0051]

[0052] where χ * is the required beam width; let where it can be obtained:

[0053]

[0054] Furthermore, the reconstruction of the perceived gain of the potential target using the stationary phase method includes:

[0055] Let \(p(r,\chi)=rJ_0(r\kappa\chi)\), then formula (12) can be rewritten as:

[0056]

[0057] Based on the SPM, the integral around the stationary phase point dominates, that is, let:

[0058]

[0059] where, is the first derivative of the additional phase shift

[0060] Assume \(r\) e is the stationary phase point. Using at \(r\) e Taylor expansion and ignoring the high-order terms above the second order, we can get:

[0061]

[0062] where, is the second derivative of the additional phase shift;

[0063] Substituting formula (17) into formula (15), we can get:

[0064]

[0065] where, \(\delta\) is a constant;

[0066] Let We can get Relating \(u = r - r\) e and the upper and lower bounds of the integral of formula (18), we can get Therefore, the upper and lower bounds of the new integral are Also, since is an even function, let We can convert formula (18) to:

[0067]

[0068] where, Then, further simplifying formula (19), the perceptual gain of the reconstructed potential target is:

[0069]

[0070] Furthermore, the ideal beamforming phase shift when solving for the optimal perceptual gain of the reconstructed potential target includes:

[0071] The ideal beamforming satisfies:

[0072]

[0073] and \(p(r e ,\chi)\neq0\), that is where \(j (0,n) represents the \(n\)th zero of \(J_0(\cdot)\);

[0074] Let be set as a constant, then is a second-order polynomial about \(r\), so the for beamforming design is:

[0075]

[0076] where \(a\) and \(r o are parameters to be optimized;

[0077] When \(r o \neq0\) and \(r o = 0\), find the channel gain with respect to \(\chi\) and the optimal solutions of \(a\) and \(r o respectively;

[0078] Take the o when \(a\) and \(r\) take the optimal solutions as the phase shift of the ideal beamforming.

[0079] Furthermore, when \(r o \neq0\), substitute formula (25) into formula (19), then the channel gain with respect to \(\chi\) is:

[0080]

[0081] When \(r o \neq0\), denote the optimal \(r o as Denote the optimal \(a\) as \(a * , and \(a * are:

[0082]

[0083] where \(\eta\lt1\) is the attenuation with respect to \(J_0(0)\), and \(J_0(0)\) is the value of the zero-order function of the Bessel function of the first kind at 0; \(J_0 -1 (\eta)\) is the inverse function of \(J_0(\cdot)=\eta\), and \(L\) is a constant.

[0084] Furthermore, when \(r o = 0\), the channel gain with respect to \(\chi\) is:

[0085]

[0086] When \(r o = 0\), the optimal \(ro That is, r o = 0, and the optimal a is denoted as a'.

[0087] Furthermore, by adjusting the expression form of the phase shift of the ideal beamforming, the adjustment of the beam width and channel gain is achieved, including:

[0088] When r o ≠ 0, by jointly optimizing a and r o to flexibly adjust the beam width and channel gain;

[0089] When r o = 0, at this time the beamforming design is The optimal a' does not exceed Moreover, a' satisfies:

[0090]

[0091] In the direction of χ = 0, the integral formula (15) can be transformed into:

[0092]

[0093] Substituting formula (34) into formula (35) gives that the sensing beam achieves zero gain in the user direction.

[0094] The present invention also provides a RIS-enhanced beamwidth-adjustable beamforming system, including:

[0095] A system construction module for constructing a RIS-assisted ISAC system, constructing a sensing channel model in the system, and calculating the phase shift of the standard beamforming;

[0096] A sensing gain construction module for calculating the sensing gain of potential targets based on the phase shift of the standard beamforming and the position of the sensing target relative to the user center;

[0097] A beam solving module for reconstructing the sensing gain of potential targets using the stationary phase method and solving the phase shift of the ideal beamforming when the reconstructed sensing gain of potential targets is optimal;

[0098] A beam adjustment module for adjusting the beam width and channel gain by adjusting the expression form of the phase shift of the ideal beamforming.

[0099] The present invention also provides a computer-readable storage medium, on which a computer program is stored, and when the computer program is executed by a processor, the RIS-enhanced beamwidth-adjustable beamforming method described above is implemented.

[0100] The present invention also provides a beamforming device with adjustable RIS-enhanced beam width, including a memory, a processor, and a computer program stored on the memory and executable on the processor. When the processor executes the computer program, the RIS-enhanced beam width adjustable beamforming method as described above is implemented.

[0101] The above technical solution of the present invention has the following beneficial effects compared with the prior art:

[0102] By constructing an expression form of the phase shift for ideal beamforming, the present invention can flexibly adjust the perceived beam width with low computational complexity. By realizing the flexible adjustment of the perceived beam width, potential targets in a wider area can be perceived around the user's direction, thereby realizing efficient wide-area detection around the user. Wide-beam sensing of potential targets is used to replace resource-intensive narrow-beam scanning sensing, solving the problem of low resource utilization efficiency caused by the scanning method and improving resource utilization rate. Beamforming allows zero gain at the center of the sensing beam under specific configurations, effectively reducing interference to the communication beam. BRIEF DESCRIPTION OF THE DRAWINGS

[0103] In order to make the content of the present invention easier to be clearly understood, the following further details the present invention according to specific embodiments of the present invention in conjunction with the drawings, where:

[0104] Figure 1 is a flowchart of the method in the preferred embodiment of the present invention.

[0105] Figure 2 is a schematic diagram of RIS-assisted ISAC detection in the preferred embodiment of the present invention.

[0106] Figure 3 is a comparison result graph of the digital integration method and the method of the present invention in the simulation experiment in the preferred embodiment of the present invention.

[0107] Figure 4 is a sensing gain graph with respect to the spatial offset χ at different frequencies in the simulation experiment in the preferred embodiment of the present invention.

[0108] Figure 5 is a 3dB beam width graph in different directions at 30 GHz in three-dimensional space in the simulation experiment in the preferred embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0109] The following further illustrates the present invention in conjunction with the drawings and specific embodiments, so that those skilled in the art can better understand the present invention and be able to implement it, but the examples given are not intended to limit the present invention.

[0110] Embodiment 1

[0111] Refer to Figure 1As shown in the figure, the present invention discloses a beamforming method with adjustable RIS-enhanced beam width, comprising the following steps:

[0112] S1: Construct an RIS-assisted ISAC system as shown in Figure 2 the figure, establish a sensing channel model in the system and calculate the phase shift of the standard beamforming; Figure 2 Fig. is a schematic diagram of RIS-assisted ISAC detection, where BS and RIS generate communication beams and sensing beams respectively.

[0113] BS provides services for communication users, while RIS undertakes the sensing task. The goal is to design an adjustable wide sensing beamforming to detect potential sensing targets. The establishment of a sensing channel model in the system and the calculation of the phase shift of the standard beamforming include:

[0114] S1-1: Establish a Cartesian coordinate system in the system, with the center of RIS located at the coordinate origin o r = [0, 0, 0], the wavelength is λ = c / f, where f is the carrier frequency and c is the speed of light; assume that the shape of RIS is a disc with a radius of R and is located in the xy plane of the coordinate system; RIS is composed of N ris reflecting units, and the interval between two adjacent RIS units is Δ = λ / 2; each reflecting unit corresponds to a three-dimensional coordinate, and the three-dimensional coordinates (x, y, z) of all reflecting units form a 3D coordinate set, denoted as S ris , satisfying x 2 + y 2 ≤ R 2 and z = 0.

[0115] S1-2: The present invention considers a far-field millimeter-wave scenario, and only line-of-sight propagation is considered for channel propagation. Here, the angle of arrival (AOAs) from a specified user to each reflecting unit of RIS is the same. Use α ru to represent the elevation angle of arrival (AOE) from the UE (user equipment) to the RIS plane, draw a zero-crossing line l ru on the RIS plane, and the phases of the received beams of the reflecting units on the zero-crossing line are the same. Take the zero-crossing line as the reference line, which is expressed as:

[0116] l ru = {(x, y): y - x tanα ru = 0} (1).

[0117] S1-3: Taking the zero-crossing line as the reference, the phase of the reflecting unit at the point (x, y, 0) is:

[0118]

[0119] where h ru (x, y, φ ru ) is the phase of the reflection unit at the point (x, y, 0), and φ ru represents the angle between the link between the UE and the RIS and the xy plane. Δd ru represents the perpendicular distance from the RIS unit to the reference line. Analogous to the angle formed by a plane wave illuminating a linear array, α ru is the AOE from the RIS to the UE.

[0120] S1-4: The channel from the BS to the RIS is described as:

[0121]

[0122] where h br (x, y, φ br ) is the channel representation from the BS to the RIS. α br is the AOE from the RIS to the BS, and φ br represents the angle between the link between the BS and the RIS and the xy plane; then this cascaded channel, i.e., from the BS to the RIS.

[0123] The channel from the RIS to the UE is described as:

[0124] h(x, y) = h ru (x, y, φ ru )h br (x, y, φ br ) (4).

[0125] where h(x, y) is the channel representation from the RIS to the UE.

[0126] S1-5: Since the above equation only considers the case of a single RIS reflection unit, when considering the entire RIS plane, the entire sensing channel is:

[0127]

[0128] where is the entire sensing channel representation, h(x n , y n ) is the channel representation from the nth reflection unit of the RIS to the UE, is the phase shift of the nth reflection unit. h(x n , y n)It means that if the nth RIS reflection unit does not modify the signal at all, then for the signal from the base station to the RIS and then reflected by the RIS to the user, the signal phase shift generated by the signal itself; however, the presence of the RIS can modify the phase of this signal. h(x n ,y n )is the representation of the nth RIS reflection unit modifying the signal phase.

[0129] S1-6: Each RIS unit can act as a phase shifter where x n and y n are the coordinates of the nth reflection unit; assuming that the RIS integrates an uncountable and infinitesimal number of reflection units, the summation in formula (5) can be approximated as a Riemann sum:

[0130]

[0131] where, is the approximation of the entire sensing channel, is the phase shift at each point in the RIS plane. When the RIS units are infinitesimal and very numerous, it can be regarded as a large plane, and the values of x and y become continuous.

[0132] S1-7: The magnitude of the offset is the same as . When the number of units is large, this deviation becomes negligible; this approximation enables the design of beamforming to be carried out in a continuous manner. Subsequently, N ris elements are sampled from , and is selected according to the corresponding coordinates. Using this continuous model and aiming at the UE, the phase shift of the standard beamforming is:

[0133]

[0134] where, is the phase shift of the standard beamforming, It should be noted that and are both constants and can be understood as known quantities because the positions of the BS and the RIS are fixed, and the natural angles are known.

[0135] S2: Based on the phase shift of the standard beamforming, calculate the sensing gain of potential targets by combining the position of the sensing target relative to the user center.

[0136] S2-1: To effectively design a sensing beam with adjustable beam width, it is necessary to design the phase shift to compensate for the phase change Ensure consistent performance across the entire beamwidth (this phase change is compared to the BS-to-UE. Starting from Figure 2 As can be seen, the original BS-to-UE beam is a narrow beam. Now, what needs to be done is to first direct the beam to the RIS, and then the RIS directs this beam to the UE. A phase is generated from the BS to the RIS, and a phase is also generated from the RIS to the UE. If this phase is compensated, then the beam directed from the BS to the RIS and then from the RIS to the UE is the same as the beam directly generated from the BS to the RIS, both being the same narrow beam). To transition from a narrow beamwidth to a wide beamwidth, after compensating for this phase change, an additional phase shift for adjusting the beamwidth needs to be introduced Then, the overall phase shift after reflection by the RIS is constructed as:

[0137]

[0138] Where, is the overall phase shift after reflection by the RIS, is the additional phase shift.

[0139] S2-2: Use φ rs to represent the angle between the potential target and RIS link and the xy plane of the RIS, and use α rs to represent the elevation angle (AOE). Then, the sensing gain of the potential target is:

[0140]

[0141] Where, is the sensing gain of the potential target, Δd rs represents the vertical distance from the RIS element to the reference line,

[0142] Convert in the rectangular coordinate system to in the polar coordinate system. Formula (9) is transformed into polar form to obtain:

[0143]

[0144] S2-3: Due to radial symmetry, then The design of only varies with r and is independent of θ. In addition, assuming that the phase shift of the reflection element of the RIS at a distance r from the origin is consistent, then there is:

[0145]

[0146] Then, the integral of formula (10) can be equivalent to:

[0147]

[0148] where χ is the position of the perceived target relative to the user center, χ 2 = η 2 + ξ 2 denotes the spatial offset, and integrating over the entire θ gives:

[0149]

[0150] where g(χ) is the perceived gain of the potential target expressed by the position of the perceived target relative to the user center, R is the radius of the RIS, and J0 is the zero-order function of the Bessel function of the first kind.

[0151] The position χ of the perceived target relative to the user center satisfies:

[0152] The range of the variable χ in three-dimensional space can be regarded as a circle centered at which is expressed as:

[0153]

[0154] where χ * is the required beamwidth; from the perspective of angles, a more intuitive result can be obtained. Let where According to and definitions, after some calculations, we can get:

[0155]

[0156] S3: Use the stationary phase method to reconstruct the perceived gain of the potential target.

[0157] S3-1: The goal of this paper is to design wide-sensing beamforming to detect potential targets in a wide range centered on the user. To achieve this goal, it is necessary to design to obtain a relatively large and flat gain |g(χ)| 2 , and the stationary phase method (SPM) is used to solve it. Let p(r, χ) = rJ0(rκχ), then formula (12) can be rewritten as:

[0158]

[0159] Based on SPM, the integral around the stationary point dominates, that is, let:

[0160]

[0161] where is the first derivative of the additional phase shift.

[0162] S3-2: Assume r e is the stationary point, and using the Taylor expansion of e at r and neglecting the high-order terms above the second order, we can obtain:

[0163]

[0164] where is the second derivative of the additional phase shift

[0165] S3-3: Substituting Equation (17) into Equation (15), we can obtain:

[0166]

[0167] where δ is a constant and a very small positive value;

[0168] Then let u = r - r e , we can get Relating u = r - r e and the upper and lower bounds of the integral in Equation (18), we can obtain Therefore, the upper and lower bounds of the new integral are Also, since is an even function, let we can transform Equation (18) into:

[0169]

[0170] where c is usually a very small value; then further simplifying Equation (19), the perceptual gain of the reconstructed potential target is:

[0171]

[0172] S4: Solve for the phase shift of the ideal beamforming when the perceptual gain of the reconstructed potential target is optimal.

[0173] S4-1: Since the goal is to obtain a large and flat-changing gain |g(χ)| min within the range (χ max ), then based on Equation (20), the ideal beamforming design should satisfy: 2 And it should be noted that the key to applying the stationary phase method lies in the establishment of Equation (17), that is, p(r

[0174]

[0175] e , χ) ≠ 0, that is where j​(0,n) denote the nth zero of J0(·). Moreover, the variation of the beam shape characteristic is related to whether r e is 0, which will be discussed for r e ≠0 and r e = 0 below.

[0176] For comparison, two methods will be used to solve One is to use the digital integration method, which has a large amount of calculation. The present invention proposes a low-complexity method to solve At the same time, these two methods will be tested and a comparison will be given.

[0177] First is the first one, using the digital integration method. To satisfy the conditions of the second-order differential equation in formula (21) and stipulate that the equation holds within the entire [0, R] range, that is:

[0178]

[0179] where k is a positive value. The first-order differential equation can be obtained through where the values of k and c are determined by the conditions and and then according to the obtained c = 0 and it can be concluded that:

[0180]

[0181] The numerator in formula (23) has no closed-form solution, but it can be obtained through digital integration, and then the for beamforming design can be obtained using formula (23) as:

[0182]

[0183] Formula (24) can also be obtained through digital integration.

[0184] Since the above method has a large computational complexity, a low computational complexity method will be proposed next.

[0185] S4-2: First, from the expression of the channel gain, that is, formula (19), it can be seen that the upper bound m of the integral contains This will cause fluctuations in the Fresnel integral. In addition, as the denominator, it has a high complexity in the beamforming design. From a more engineering perspective, can be set as a constant, then is a second-order polynomial about r, so the for beamforming design can be obtained as:

[0186]

[0187] Among them, a and r o are parameters to be optimized during the design process.

[0188] r e is obtained based on the first derivative of which is equal to 0. The first method is to use the stationary phase method and then use numerical integration to find The second method is to first assume and then find a and r according to the conditions o . For take the first derivative and then set the first derivative equal to 0. That is, according to formula (16), r o = r e .

[0189] S4-3: As described above, the change in the shape characteristics of the beam is related to whether r e is 0. Therefore, the following discussion is carried out. In the two cases of r o ≠0 and r o = 0, find the channel gain with respect to X and the optimal solutions of a and r o respectively.

[0190] (1) As described above, when r o ≠0, that is, p(r, X)≠0, which satisfies the principle of using the SPM method. Formula (25) can be substituted into formula (19), and the channel gain with respect to χ is:[[]]

[0191]

[0192] Substitute the optimal r o when r o ≠0 and denote it as The optimal a is denoted as a * , and a * are:[[]]

[0193]

[0194] Among them, η < 1 is the attenuation with respect to J0(0), and J0(0) is the value of the zero-order function of the Bessel function of the first kind at 0; J0 -1 (η) is the inverse function of J0(·)=η, and L is a constant.

[0195] The proofs of the above formulas (27) and (28) will be given below:[[]]

[0196] It can be seen from formula (26) that r oIs inversely proportional to the spatial offset χ and directly proportional to the perceived channel gain |g(χ)|, which indicates that the optimal Should be the maximum value under the condition of ensuring the required beam width. Then, given a desired beam width χ * And an attenuation value η, the optimal Can be obtained through Obtained.

[0197] To obtain the optimal a, use And Respectively represent the spatial Fourier transform (SFT) of p(r, χ) and , where k r Represents the wave number, then formula (15) is equivalent to:

[0198]

[0199] For |k r | < κχ and In the case of, satisfying the complex Chirp signal form, then Then the integral of formula (19) can be approximately equivalent to:

[0200]

[0201] For The SFT of is without a closed-form solution. However, since The cut-off frequency of is The main spectra of these two SFTs are concentrated in a finite frequency band, so this effective approximate estimation can be carried out. In addition, the cut-off frequency of the Chrip signal increases linearly with the size of the RIS, which is crucial for the application of SPM because the application of SPM depends on The phase of changes faster than the phase of p(r, χ), that is Equation (28) can be obtained therefrom.

[0202] (2) When r o = 0, the beamforming design can achieve a flat and large channel gain near the user direction and ensure zero gain in the user direction. Then, since r o = 0, the condition for using SPM cannot be satisfied. Next, another alternative method for beamforming design will be described. Here, the following conclusion is given first. The channel gain regarding χ is:

[0203]

[0204] r o = 0, the optimal ro That is, r o = 0, and the optimal a is denoted as a'.

[0205] Next, the proof of the conclusion will be carried out. First, the integral formula (15) is calculated under the conditions of R→∞ and r o = 0, and the result is obtained as follows:

[0206]

[0207] where a' is the optimal a when r o = 0; similar to formula (30), since the upper limit R is increased, the cut-off frequency of... will also increase, which enhances the elimination of sine components in the range [R, ∞]. Mathematically, this condition indicates that:

[0208]

[0209] If a' is given by formula (28), then within the range formula (33) holds.

[0210] The above introduced the design of beamforming with adjustable beam width under the conditions of r e ≠0 and r e = 0, which is carried out around the design of... Next, it will be explained how to achieve zero gain in the user direction under a specific configuration.

[0211] S4-4: Take the o values of a and r when they are the optimal solutions as the phase shifts of the ideal beamforming.

[0212] S5: Adjust the beam width and channel gain by adjusting the expression form of the phase shifts of the ideal beamforming.

[0213] When r o ≠0, flexibly adjust the beam width and channel gain by jointly optimizing a and r o ;

[0214] When r o = 0, at this time the beamforming design is such that the optimal a' does not exceed and a' satisfies:

[0215]

[0216] In the direction of χ = 0, the integral formula (15) can be transformed into:

[0217] ​

[0218] Substituting formula (34) into formula (35) gives that the sensing beam achieves zero gain in the user direction.

[0219] It can be seen from this that regardless of whether r o ≠0 or r o =0, the width of the sensing beam can be extended to a wider range. Especially when r o =0, the beam width and channel gain can be controlled by adjusting only one parameter a′. Although this method has low flexibility, it can achieve zero gain in the user direction by adjusting an appropriate a′, thus effectively reducing the interference to the communication beam.

[0220] Embodiment 2

[0221] The present invention also discloses a beamforming system with adjustable RIS enhanced beam width, including:

[0222] A system construction module, configured to construct an ISAC system assisted by RIS, construct a sensing channel model in the system, and calculate the phase shift of the standard beamforming;

[0223] A sensing gain construction module, configured to calculate the sensing gain of potential targets based on the phase shift of the standard beamforming and in combination with the position of the sensing target relative to the user center;

[0224] A beam solving module, configured to reconstruct the sensing gain of potential targets using the stationary phase method and solve the ideal beamforming phase shift when the reconstructed sensing gain of potential targets is optimal;

[0225] A beam adjustment module, configured to adjust the beam width and channel gain by adjusting the expression form of the ideal beamforming phase shift.

[0226] Embodiment 3

[0227] The present invention also discloses a computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, it implements the RIS enhanced beam width adjustable beamforming method in Embodiment 1.

[0228] Embodiment 4

[0229] The present invention also discloses a device, including a memory, a processor, and a computer program stored on the memory and executable on the processor. When the processor executes the computer program, it implements the RIS enhanced beam width adjustable beamforming method in Embodiment 1.

[0230] Beamforming has a wide range of applications in actual environments such as autonomous driving perception, disaster search and rescue, intelligent obstacle avoidance, and vehicle-to-everything (V2X) with strict communication isolation. In these actual environments, the sensing targets are usually located near communication users. This requires designing a sensing beam with a wide beam to cover the target area, laying a foundation for detecting potential sensing targets.

[0231] The present invention proposes a beamforming technology for the ISAC system, which has the following advantages compared with the prior art:

[0232] (1) An ideal expression form of the phase shift of beamforming is constructed, which can flexibly adjust the width of the sensing beam. When adjusting the width, the problem is simplified and the computational complexity is low.

[0233] (2) By flexibly adjusting the width of the sensing beam, it is possible to sense potential targets in a wider area around the user direction, thereby realizing efficient wide-area detection around the user. Using a wide beam to sense potential targets instead of resource-intensive narrow beam scanning sensing solves the problem of low resource utilization efficiency caused by the scanning method and improves resource utilization rate.

[0234] (3) The constructed channel model can clearly capture the relationship between the sensing channel gain and the spatial offset in the RIS-assisted communication system.

[0235] (4) Beamforming allows the realization of zero gain at the center of the sensing beam (i.e., consistent with the direction of the communication user) under specific configurations, effectively reducing interference to the communication beam, which is very suitable for the requirements of the ISAC system.

[0236] To further illustrate the beneficial effects of the present invention, the present invention verifies the effects of the present invention through simulation experiments. First, set the radius R of the RIS to 0.5 meters, and compare the frequencies of 30 GHz and 100 GHz respectively. The variation of the sensing gain at different frequencies with respect to the spatial offset χ is compared. The results are as Figure 3 shown. Figure 3 is the comparison result between the digital integration and the proposed low-complexity calculation method, which is the result when r o = 0.1 in formula (26); Figure 3 (a) in it is the performance at 30 GHz, Figure 3 (b) in it is the performance at 100 GHz. It can be seen from Figure 3 that for r o ≠0, near χ = 0, the results of these two methods are closely fitted. Although the accuracy of the theoretical method declines as χ increases, from an engineering perspective, within the limited beam width, the theoretical method model is accurate enough for solving the sensing gain result. When r oWhen = 0, by selecting an appropriate a, the theoretical model calculation result can obtain zero gain in the direction of χ=0.

[0237] Figure 4 This is the sensing gain graph with respect to the spatial offset χ at different frequencies in the simulation experiment of the preferred embodiment of the present invention. Figure 4 In (a), it is the performance at 30 GHz. Figure 4 In, it is the performance at 100 GHz, where a=a * , and the Rician factor is set to 6 dB. Figure 4 It demonstrates that taking the results as a benchmark, for a given beamwidth and different frequencies, when different schemes are all optimally configured, the performance is as follows. From Figure 4 it can be seen that whether it is the beamforming of the theoretical method or the beamforming of the digital integration method, the calculated gain results are very approximate. In addition, taking the results of the Rician channel as a benchmark, when the NLoS CSI is unknown at the receiving end, it can be seen that the NLoS CSI has limited influence within the widened beamwidth, which shows the robustness of the proposed beamforming method. The proposed beamwidth broadening method of beamforming is effective throughout the millimeter-wave frequency band. Although the sensing gain experiences a sharp drop at χ=0.1, the gain results calculated by the proposed beamforming design are acceptable compared with the benchmark.

[0238] Figure 5 This is the 3 dB beamwidth graph in different directions at 30 GHz in three-dimensional space. Figure 5 It shows the signal broadened profile of the 3 dB beamwidth in different directions in 3D space obtained based on formula (14). It can be seen that for different signal directions (φ rs , α rs ), the beamwidth coverage is different. The coverage range in the higher "latitude" direction is significantly smaller than that in the lower "latitude" direction. In addition, the difference in beam distribution between (a) and (b) stems from their different coordinate systems. The sensing gain exhibits spatial asymmetry in all configurations, which results from the RIS direction and its inherent non-uniform radiation pattern.

[0239] Those skilled in the art should understand that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the present application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present application can take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk memory, CD-ROM, optical memory, etc.) containing computer-usable program code.

[0240] This application is described with reference to the flowcharts and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the present application. It should be understood that each flow and / or block in the flowcharts and / or block diagrams, and the combination of flows and / or blocks in the flowcharts and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to the processors of general-purpose computers, special-purpose computers, embedded processors, or other programmable data processing devices to generate a machine, such that the instructions executed by the processors of the computer or other programmable data processing devices generate means for implementing the functions specified in one or more flows and / or blocks Figure 1 in one or more flows and / or blocks Figure 1 or multiple blocks.

[0241] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing device to work in a specific manner, such that the instructions stored in the computer-readable memory generate a manufactured article including instruction means that implement the functions specified in one or more flows and / or blocks Figure 1 in one or more flows and / or blocks Figure 1 or multiple blocks.

[0242] These computer program instructions can also be loaded onto a computer or other programmable data processing device, such that a series of operation steps are executed on the computer or other programmable device to generate a computer-implemented process, and thus the instructions executed on the computer or other programmable device provide steps for implementing the functions specified in one or more flows and / or blocks Figure 1 in one or more flows and / or blocks Figure 1 or multiple blocks.

[0243] Obviously, the above embodiments are only examples for clear illustration and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A beamforming method for enhancing beam width adjustable of RIS, characterized in that, Including: Construct an RIS-assisted ISAC system, build a sensing channel model in the system, and calculate the phase shift of the standard beamforming; Based on the phase shift of the standard beamforming, calculate the sensing gain of potential targets in combination with the position of the sensing target relative to the user center; Use the stationary phase method to reconstruct the sensing gain of potential targets and solve for the ideal beamforming phase shift when the reconstructed sensing gain of potential targets is optimal; By adjusting the expression form of the ideal beamforming phase shift, adjust the beam width and channel gain.

2. The beamforming method for RIS enhanced beamwidth adjustable according to claim 1, wherein: The constructing a sensing channel model in the system and calculating the phase shift of the standard beamforming includes: Establish a Cartesian coordinate system in the system, with the center of the RIS located at the coordinate origin o r = [0, 0, 0], and the wavelength is λ = c / f, where f is the carrier frequency and c is the speed of light; assume that the shape of the RIS is a disk with a radius of R and is located in the xy plane of the coordinate system; the RIS is composed of N ris reflecting elements, and the interval between two adjacent RIS elements is Δ = λ / 2; each reflecting element corresponds to a three-dimensional coordinate, and the three-dimensional coordinates (x, y, z) of all reflecting elements form a 3D coordinate set, denoted as S ris , satisfying x 2 + y 2 ≤ R 2 and z = 0; Use α ru to represent the elevation angle of the UE to the RIS plane. Draw a zero-crossing line l on the RIS plane ru . The phases of the received beams of the reflection units on the zero-crossing line are the same. Take the zero-crossing line as the reference line and denote it as: Taking the zero-crossing line as a reference, the phase of the reflection unit at the point (x, y, 0) is: where h ru (x, y, φ ru ) is the phase of the reflection unit at the point (x, y, 0), and φ ru represents the angle between the link between the UE and the RIS and the xy plane, Δd ru represents the vertical distance from the RIS unit to the reference line, α ru is the AOE from the RIS to the UE; The channel from the BS to the RIS is described as: where h br (x, y, φ br ) represents the channel from the BS to the RIS, α br is the AOE from the RIS to the BS, and φ br represents the angle between the link between the BS and the RIS and the xy plane; The channel from the RIS to the UE is described as: h(x,y) = h ru (x,y,φ ru )h br (x,y,φ br ) (4) Where h(x, y) is the channel representation from the RIS to the UE; When considering the entire RIS plane, the entire sensing channel is: Among them, is the entire perception channel representation, h(x n , y n ) is the channel representation from the RIS to the UE for the nth reflection unit, is the phase shift of the nth reflection unit; Each RIS unit can act as a phase shifter where x n and y n are the coordinates of the n-th reflecting unit; assuming that the RIS integrates an uncountable and infinitesimal number of reflecting units, the summation in formula (5) can be approximated as: wherein, is an approximation of the entire sensing channel, is the phase shift at each point in the RIS plane; Offset is of the same order of magnitude as and can be ignored when the number of units is large; For N ris elements are sampled from and selected according to the corresponding coordinates Using this continuous model, with the UE as the target, the phase shift of the standard beamforming is: Among them, is the phase shift of the standard beamforming, 3. The beamforming method for enhancing the beam width adjustable of RIS according to claim 2, wherein: The calculating the sensing gain of potential targets based on the phase shift of the standard beamforming in combination with the position of the sensing target relative to the user center includes: Introduce the phase shift for adjusting the beam width Construct the overall phase shift after reflection by the RIS as follows: Among them, is the overall phase shift after reflection by RIS, is the additional phase shift; Use φ rs to represent the angle between the potential target and the xy plane of the RIS link and the RIS, and use α rs to represent the elevation angle. Then, the sensing gain of the potential target is as follows: Among them, is the sensing gain of the potential target, Δd rs represents the vertical distance from the RIS unit to the reference line, Convert the in the rectangular coordinate system to in the polar coordinate system. Formula (9) is converted to the polar coordinate form to obtain: Due to the radial symmetry, the design only varies with r and is independent of θ. Assuming that the phase shift of the reflection unit of the RIS is consistent at a distance r from the origin, we have: Then the integral of formula (10) can be equivalent to: where χ is the position of the perceived target relative to the user center, χ 2 = η 2 + ξ 2 represents the spatial offset, and integrating over the entire θ gives: Where g(χ) is the sensing gain of potential targets represented by the position of the sensing target relative to the user center, R is the radius of the RIS, and J0 is the zero-order function of the Bessel function of the first kind.

4. The beamforming method for adjusting the beam width of RIS enhancement according to claim 3, wherein: The position χ of the sensing target relative to the user center satisfies: The range of the variable χ can be regarded as a circle centered at in three-dimensional space, which is expressed as: where χ * is the required beam width; let where θ ∈ [0, 2π), we can obtain:

5. The beamforming method for enhancing the beam width adjustable of RIS according to claim 3, wherein: The using the stationary phase method to reconstruct the sensing gain of potential targets includes: Let p(r, χ) = rJ0(rκκ), then formula (12) can be rewritten as: Based on the SPM, the integral around the stationary point dominates, that is, let: wherein, is the first derivative of the additional phase shift Suppose r e is a stationary point. Using the Taylor expansion of e at r and neglecting the higher-order terms of the second order and above, we can obtain: wherein, is the second derivative of the additional phase shift; Substituting formula (17) into formula (15) gives: Where δ is a constant; Let We can obtain The associated \(u = r - r\) e And the upper and lower bounds of the integral in formula (18), we can obtain Therefore, the upper and lower bounds of the new integral are Also, since is an even function, let We can transform formula (18) into:[[]] Among them, The perceptual gain of the reconstructed potential target is obtained by further simplifying formula (19) as follows:

6. The RIS-enhanced beamwidth-adjustable beamforming method according to claim 5, wherein: The solving for the ideal beamforming phase shift when the reconstructed sensing gain of potential targets is optimal includes: The ideal beamforming satisfies: and p(r e , χ) ≠ 0, that is where j (0,n) denotes the n-th zero of J0(·); Set as a constant, then is a second-order polynomial of r, so the for beamforming design is: Among them, a and r o are parameters to be optimized; For \(r\) o \(\neq0\) and \(r\) o \(=0\), respectively find the optimal solutions for the channel gain with respect to \(\chi\) and \(a\), \(r\) o ; Take a and r o When the values are optimal As the phase shift of the ideal beamforming 7. The beamforming method for RIS enhanced beamwidth adjustable according to claim 6, characterized in that: When r o ≠ 0, substituting formula (25) into formula (19), the channel gain with respect to χ is as follows: Let r o When r ≠ 0, the optimal r o is denoted as r o * and the optimal a is denoted as a * , r o * and a * are as follows: where η < 1 is the attenuation with respect to J0(0), where J0(0) is the value of the zero-order function of the Bessel function of the first kind at 0; J0 -1 (η) is the inverse function of J0(·) = η, and L is a constant.

8. The beamforming method for enhancing the beam width adjustable of RIS according to claim 7, characterized in that: When r o = 0, the channel gain with respect to χ is: r o When r = 0, the optimal r o That is, r o = 0, and the optimal a is denoted as a'.

9. The beamforming method with adjustable beam width enhanced by RIS according to claim 8, characterized in that: The adjusting the beam width and channel gain by adjusting the expression form of the ideal beamforming phase shift includes: When r o ≠ 0, by jointly optimizing a and r o to flexibly adjust the beam width and channel gain; When r o = 0, the beamforming design is then The optimal a' will not exceed Moreover, a' satisfies: In the direction of χ = 0, the integral formula (15) can be transformed into: Substituting formula (34) into formula (35) gives that the sensing beam achieves zero gain in the user direction.

10. A beamforming system with adjustable beam width enhanced by RIS, characterized in that, Including: A system construction module, used to construct an RIS-assisted ISAC system, build a sensing channel model in the system, and calculate the phase shift of the standard beamforming; A sensing gain construction module, used to calculate the sensing gain of potential targets based on the phase shift of the standard beamforming in combination with the position of the sensing target relative to the user center; A beam solving module, used to use the stationary phase method to reconstruct the sensing gain of potential targets and solve for the ideal beamforming phase shift when the reconstructed sensing gain of potential targets is optimal; A beam adjustment module, used to adjust the beam width and channel gain by adjusting the expression form of the ideal beamforming phase shift.

11. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, it implements the RIS enhanced beam width adjustable beamforming method according to any one of claims 1-9.

12. A beamforming device with adjustable beam width enhanced by RIS, characterized in that: It includes a memory, a processor, and a computer program stored on the memory and executable on the processor. When the processor executes the computer program, it implements the RIS enhanced beamwidth adjustable beamforming method according to any one of claims 1-9.

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