A multi-user cooperative reception method for air-earth vortex wave communication

Abstract

The present invention provides a multi-user cooperative reception method for air-ground vortex wave communication, specifically: according to the intensity distribution of the vortex beam, the optimal radial position corresponding to the maximum intensity is derived, and thus a search ring is set, and the radial angle difference closest to an arithmetic progression is selected within the search ring to select cooperative users. The present invention supports high-capacity long-distance transmission, and the present invention can also expand the virtual antenna array as the distance increases, so as to obtain a stable channel capacity in long-distance transmission.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrical communication. Background Art

[0002] In a wireless communication system that utilizes traditional orthogonal resources (such as time, frequency, etc.), it is difficult to significantly improve the spectral efficiency, thus unable to meet the rapidly growing real-time data acquisition requirements of future wireless communication. Vortex wave modes can provide a new orthogonal resource for wireless communication to multiply improve the spectral efficiency. The application of Orbital Angular Momentum (OAM) mode resources has attracted much attention in future wireless communication research.

[0003] Different from the Spin Angular Momentum (SAM) used to describe the polarization state of electromagnetic waves, OAM can indicate the spatial distribution of the electromagnetic field, that is, a helical transverse phase structure. Due to the hollow divergence characteristics of vortex waves, it is difficult to achieve long-distance multiplexing communication of OAM mode resources, especially in the radio frequency band. Generally, traditional receiving schemes use reflector antennas and centralized antenna arrays to complete the reception of OAM wave signals. In 2011, Tamburini successfully conducted a transmission experiment of 442 m vortex wave communication using a reflector antenna. In 2018, by using a centralized uniform circular array, NTT Corporation successfully achieved a multiplexing communication experiment of 10 m OAM. As the communication distance increases, the energy ring generated by the OAM beam expands rapidly, and the traditional full-circle receiving scheme will make the size of the UCA at the receiving end too large to bear.

[0004] In order to achieve OAM multiplexing communication, there is an urgent need to design a compact and easy-to-implement long-distance transmission and reception scheme. The distributed antenna receiving scheme uses multiple distributed antennas independently arranged on the helical phase plane, which is a potential way to achieve long-distance reception of vortex wave signals. Y. Zhao and C. Zhang designed a brand-new frame format for multiplexed OAM signals in "Distributed Antennas Scheme For Orbital Angular Momentum Long-Distance Transmission" published in IEEE Antennas and Wireless Propagation Letters, which can effectively obtain different OAM modes during long-distance transmission. It should be noted that the size of the user equipment is limited and there is only one antenna, which makes it difficult to achieve vortex wave communication in general. Summary of the Invention

[0005] Objective of the Invention: To solve the problems existing in the above-mentioned prior art, the present invention provides a multi-user cooperative receiving method for air-ground vortex wave communication.

[0006] Technical Solution: The present invention provides a multi-user cooperative receiving method for air-ground vortex wave communication, which specifically includes the following steps:

[0007] Step 1: Set the cooperative user set as an empty set, and set the number of cooperative users to be L;

[0008] Step 2: Set the initial search radius r(A) = r fea (A) + σ, where σ is a positive real number, where A is the vertical distance from the air base station to the ground, λ represents the wavelength of the Laguerre-Gaussian beam, and l represents the OAM mode of the Laguerre-Gaussian beam;

[0009] Step 3: If there are users in the search ring [r(A), σ], and the number of users is L, then take these L users as cooperative users and put them into the cooperative user set, and go to Step 8; if the number of users in the search ring [r(A), σ] is less than L, then go to Step 5; if the number of users in the search ring [r(A), σ] is greater than L, then go to Step 4; the search ring [r(A), σ] is a circular ring area with an inner diameter of r(A) - σ and an outer diameter of r(A) + σ;

[0010] Step 4: Take all users in the search ring as potential users, sort the actual radial angles of all potential users in ascending order to form a potential user set, and calculate the maximum radial angle difference φ p , take the first potential user and the last potential user as candidate cooperative users, and sequentially select L - 2 potential users between the first potential user and the last potential user to form several groups of candidate cooperative user groups with the candidate cooperative users; sort the L candidate cooperative users in each group of candidate cooperative user groups in ascending order according to the actual radial angle and number them; based on φ p calculate the ideal radial angle of each candidate cooperative user in each group of candidate cooperative user groups, and select a group of candidate cooperative user groups with the principle that the angular square difference between the ideal radial angle and the actual radial angle is the smallest, and take the users in this group of candidate cooperative user groups as cooperative users and put them into the cooperative user set, and go to Step 8;

[0011] Step 5: Judge whether the current search radius r(A) is greater than D max - σ, if so, go to Step 6, otherwise update r(A), let: r(A) = r(A) + 2σ, and go to Step 3; D max is a preset maximum threshold;

[0012] Step 6: Judge the current cooperative user set Whether it is an empty set. If so, go to Step 7; otherwise, go to Step 8;

[0013] Step 7: Update σ, let σ = 2σ, and go to Step 2;

[0014] Step 8: Adjust the waist radius w0 of the Laguerre-Gaussian beam so that the maximum energy of the Laguerre-Gaussian beam hits the cooperative user.

[0015] Furthermore, the specific content of Step 4 is as follows:

[0016] Step 4.1: Calculate the ideal radial angle of each candidate cooperative user in each group of candidate cooperative user groups

[0017]

[0018] Among them, represents the ideal radial angle of the l c th candidate cooperative user, l c = 1, 2, 3,..., L; θ1 represents the radial angle of the first potential user in the set of potential users;

[0019] Step 4.2: Calculate the angular mean square difference of each group of candidate cooperative user groups:

[0020]

[0021] Among them, represents the ideal radial angle of the i-th candidate cooperative user, θ i represents the radial angle of the first potential user in the set of potential users.

[0022] Furthermore, in Step 8, the waist radius w0 is adjusted according to the following formula:

[0023]

[0024] Among them, r max (A) represents the radius when the intensity distribution of the Laguerre-Gaussian beam is the largest, and the expression is as follows;

[0025]

[0026] Among them, w(z) is the Laguerre beam radius, and the expression is z R represents the Rayleigh range, z represents the distance from the aerial base station to the target user with coordinates (0, 0, 0), z = A, and r max (A) ≥ r fea (A).

[0027] Beneficial effects:

[0028] 1. Based on the hollow divergence characteristics and amplitude distribution of the vortex wave, the present invention derives the optimal radial position, and then selects the cooperative users closest to an arithmetic progression based on the radial angle, thereby breaking through the communication distance limit through multi-user cooperation and achieving long-distance transmission of OAM multiplexing communication.

[0029] 2. At the same time, as the height of the ABS increases, the channel capacity under the fixed UCA scheme decreases rapidly, while the channel capacity of the scheme of this embodiment can remain unchanged. Compared with the fixed UCA scheme, the virtual antenna array composed of cooperative users will expand with the increase of the distance, thus supporting high-capacity long-distance transmission.

[0030] 3. The scheme of the present invention can expand the virtual antenna array with the increase of the distance, so as to obtain a stable channel capacity in long-distance transmission. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a schematic diagram of selecting cooperative users by using the method of the present invention.

[0032] Figure 2 It is a capacity performance diagram under the MUCR scheme.

[0033] Figure 3 It is a curve graph of the channel capacity varying with the ABS altitude under different modes. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0034] The accompanying drawings forming a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention.

[0035] To explain the MUCR scheme of the present invention, Figure 1 the selected cooperative GUs (users) are shown. The 40 GUs marked by are evenly distributed in a 20m×20m area, and the dashed circular rings are the search rings determined according to the MUCR scheme. The GUs in the search rings are potential GUs, and ☆ are the selected cooperative GUs. Inside the dashed ring with radius r min the waist radius cannot be measured.

[0036] The system considered in the present invention consists of an Aerial Base Station (ABS) and K + 1 Ground Users (GUs), represented by the set The 0th GU is the target GU and the other GUs are potential GUs. The ABS is configured with a Uniform Circular Array (UCA), and there are M array elements in the array, represented by the set representation. All GUs are equipped with an antenna. Taking the target user as the origin, a three-dimensional cylindrical coordinate system is established; in the three-dimensional cylindrical coordinate system, the coordinates of the ABS and the k-th GU are (0, 0, A) and (r k , θ k , 0) respectively, where r k represents the distance from the k-th user to the origin in the three-dimensional cylindrical coordinate system, and θ k represents the angle between the k-th user and the x-axis in the three-dimensional cylindrical coordinate system. The ABS is at a height of z = A from the ground. All GUs are randomly distributed on the ground (i.e., the horizontal plane z = 0). The z-axis is a straight line connecting the target GU and the ABS, perpendicular to the ground. The radius of the UCA and the central angle between adjacent two antenna elements are R and The coordinates of the m-th element are (R, A), where represents the angle between the m-th antenna element and the x-axis in the three-dimensional cylindrical coordinate system. In this embodiment, it is assumed that the communication channel between the aerial base station and the ground users is mainly the line-of-sight path, and the free space path loss model is adopted. The distance from the m-th element to the k-th GU is denoted by D m,k , and its expression is as follows:

[0037]

[0038] Assume that the position information of the GU is known to the ABS. The distance from the target GU to the k-th potential GU is r k .

[0039] In the three-dimensional cylindrical coordinate system, the expression of the complex amplitude distribution of the Laguerre Gaussian (LG) beam propagating along the z-axis is as follows:

[0040]

[0041] where z represents the distance from the ABS to the target GU, the coordinates of the target GU are (0, 0, 0), r represents the radius of the ring on the receiving surface where the Laguerre Gaussian beam is incident, θ is the azimuth angle, is the beam radius, w0 is the waist radius of the Laguerre Gaussian beam, is the Rayleigh range, α is the wave number, L p |l| is the associated Laguerre polynomial, (2p + |l| + 1)tan -1 (z / z R) is the Gouy phase, and \(i\) is the imaginary unit. It can be found that the LG beam is related to two parameters: the azimuthal index \(l\) and the radial index \(p\). The azimuthal index \(l\) is the topological charge, also known as the OAM mode. The radial index \(p\) is the number of radial nodes in the cross-section of the LG beam intensity. The radial and azimuthal directions of the LG beam wavefront can be characterized by the indices \(l\) and \(p\) respectively.

[0042] The intensity distribution of the LG beam when \(p = 0\), i.e., the vortex beam, is shown as follows

[0043]

[0044] To obtain the l radial position of the maximum value of \(I\) l (r, z), the partial derivative of \(I\)

[0045]

[0046] Let formula (4) be equal to zero, and we can get

[0047]

[0048] \(r\) max (z) is the maximum radius of the LG beam intensity distribution.

[0049] It can be found that the max \(I_{l}(r,z)\) corresponding to \(r\)

[0050]

[0051] The energy of the vortex beam is mainly concentrated in the energy ring with an inner diameter of \(r\) max (z) - \(\sigma\) and an outer diameter of \(r\) max (z) + \(\sigma\). \(\sigma\) is a preset value, a positive real number close to 0.

[0052] For the ABS, the position coordinates of the target GU are known to be (0, 0, 0), and the distance from the ABS to the target GU is \(A\), i.e., \(z = A\). According to formula (5), \(r\) max (A) can be obtained. The vortex beam presents an energy ring with inner and outer diameters of \(r\) max (A) - \(\sigma\) and \(r\) max (A) + \(\sigma\) respectively. Obviously, the cooperative GU should be selected from the potential GUs within the energy ring located in the interval [r max (A) - \(\sigma\), r max (A) + \(\sigma\)].

[0053] For a fixed value of \(r\) max(A), the potential GUs in the energy ring may not meet the antenna requirements for vortex wave communication during orthogonal transmission. In other words, there is a lack of sufficient cooperative GUs to complete orthogonal communication. Therefore, the waist radius w0 should be adjusted to change r max (A) to ensure that there are sufficient GUs in the energy ring to assist the target GU in vortex wave multiplexing communication.

[0054] Generally, the transmitter is an ABS and the receiver is a size-limited device. Therefore, the available number of transmission modes L requires L, that is, in air-to-ground vortex wave communication, L OAM mode multiplexing requires L cooperative GUs. It should be noted that when the waist radius is w0, the GUs in the energy ring may not meet the antenna requirements for orthogonal transmission of air-to-ground vortex wave communication. That is to say, in the vortex wave multiplexing communication with L OAM mode multiplexing, there are no L cooperative GUs to assist the target GU. Therefore, the waist radius w0 needs to be adjusted to ensure that there are L cooperative GUs in the adjusted energy ring to help the target GU achieve air-to-ground vortex wave communication.

[0055] The ABS is located at the position (0, 0, A), and all GUs are located on the ground. Based on formula (5), the waist radius w0 corresponding to the optimal radial radius r max (A) can be derived as

[0056]

[0057] where λ represents the wavelength of the Laguerre-Gaussian beam.

[0058] For simplicity, the radial radius of the feasible radial radius Laguerre-Gaussian beam is defined as

[0059]

[0060] To make the waist radius w0 exist, the following conditions should be met.

[0061] r max (A) ≥ r fea (A). (9)

[0062] Due to the size limitation of the ABS, in this embodiment, a relatively small value of the waist radius w0 is taken, that is,

[0063]

[0064] The energy ring with an inner diameter of r(A) - σ and an outer diameter of r(A) + σ is defined as the [r(A), σ] ring. From formula (3), it can be seen that the received power of the cooperative GU close to r max (A) is large. Therefore. It can be adjusted according to formula (10) through the waist radius w0, that is, by adjusting the waist radius w0 to change the search radius r(A) so that r(A) = rmax (A).

[0065] The potential GUs in the ring [r(A), σ] (a ring region with an inner diameter of r(A) - σ and an outer diameter of r(A) + σ), where the GUs falling within the [r(A), σ] ring are all called potential GUs, can be represented as the set L P denotes the L P th potential GU and also indicates that there are a total of L P potential GUs in the set of potential GUs. Sort the actual radial angles of all potential users in ascending order and calculate the maximum radial angle difference φ of the set p :

[0066] φ p = θ Lp - θ1

[0067] θ Lp represents the radial angle of the L P th potential GU after sorting in ascending order, and θ1 represents the radial angle of the 1st potential GU after sorting in ascending order.

[0068] The cardinality of the set is i.e., the number of GUs belonging to the set of potential GUs. Similarly, for the set of cooperative GUs L c denotes the L c th cooperative GU and also indicates that there are a total of L c cooperative GUs in the set of cooperative GUs. Sort the cooperative users in ascending order of their radial angles; the cardinality of the set is Therefore, in the [r(A), σ] ring, L p cooperative GUs should be found from L c potential GUs. To achieve L-mode air-to-ground vortex wave communication, the minimum angular mean square difference should be calculated based on the radial angle to select L cooperative GUs for communication, and L c = L, that is, the radial angles of the selected cooperative GUs belonging to the [r(A), σ] ring should satisfy the following conditions.

[0069]

[0070] Among them, represents the ideal radial angle of the L c th cooperative user, L c = 1, 2, 3, …, L c, the selected L cooperative GUs should have the minimum Angle Square Difference (ASD). :

[0071]

[0072] represents the ideal radial angle of the i-th cooperative GU, θ i represents the actual radial angle of the i-th cooperative GU.

[0073] Based on the above analysis, L cooperative GUs with the minimum ASD (Angle Square Difference in Chinese) should be selected from the set of potential GUs. In addition, the [r(A), σ] ring can be changed to update the set of potential GUs, which can be achieved by adjusting the waist radius w0. The MUCR scheme proposed by the present invention is implemented as follows:

[0074] Step 1: Determine the user location and initialize the parameters.

[0075] 1a. Obtain the user coordinates (r k , θ k , 0) of k GUs within the coverage of the base station, and set the cooperative GU set Set the number L of cooperative users to be selected;

[0076] Step 2: Select L cooperative users, which specifically includes the following steps:

[0077] 2a. Set σ as a positive real number approaching 0, set the initial search radius r(A) = r fea (A) + σ, and set the maximum value of the search radius to D max ;

[0078] 2b. When the cooperative user set is an empty set, that is go to step 2c, otherwise go to step 2k;

[0079] 2c. When (r(A) ≤ D max - σ), go to step 2d, otherwise go to step 2j;

[0080] 2d. Find the potential users falling within the [r(A), σ] ring, add the potential user coordinates to the set of potential GUs and find the maximum radial angle difference φ according to formula (11) p , and go to step 2e;

[0081] 2e. Determine whether the number of potential users is L. If so, go to step 2f, otherwise go to step 2g

[0082] 2f. Set the set at this time Set the potential GU at this time as the collaborative GU and go to step 2k;

[0083] 2g. Judge | > L, if yes, go to step 2h, otherwise go to step 2i;

[0084] 2h. Sort the actual radial angles of all potential users in ascending order to form a set of potential users, and calculate the maximum radial angle difference φ p , take the first potential user and the last potential user as candidate collaborative users, and sequentially select L - 2 potential users between the first potential user and the last potential user to form several groups of candidate collaborative user groups with the candidate collaborative users; sort and number the L candidate collaborative users in each group of candidate collaborative user groups according to the actual radial angle; based on φ p Calculate the ideal radial angle of each candidate collaborative user in each group of candidate collaborative user groups, and select a group of candidate collaborative user groups with the principle of the minimum angular square difference between the ideal radial angle and the actual radial angle, put the L candidate collaborative users as collaborative users into the collaborative user set, and go to step 2k;

[0085] 2i. Set r(A) = r(A) + 2σ, go to step 2c;

[0086] 2j. Set σ = 2σ, go to step 2a;

[0087] 2k. Obtain the collaborative GU set Adjust the beam waist radius so that r(A) = r max (A), that is, make the maximum energy of the Laguerre - Gaussian beam hit on the collaborative users.

[0088] The following is the verification of the communication capacity of this embodiment

[0089] Based on the MUCR scheme, the frame format and synchronization method proposed by Y. Zhao can be used. After phase estimation, the signal compensation matrix is as follows

[0090]

[0091] where is the amplitude compensation amount, is the phase compensation amount of the collaborative GU. In addition, where is obtained according to the standard uniform distribution angle. Then, the selected L collaborative GUs can be regarded as an antenna array with L receiving antennas evenly deployed at the radian position. Therefore, by demultiplexing the OAM signal through the phase - shift network, the result is as follows:

[0092]

[0093] Among them, is the phase estimator using the OAM mode L, represents the phase estimator of the plane wave at the nth cooperative GU. The demultiplexing of the OAM signal can be achieved by compensating the phase shift network of the target GU, that is:

[0094]

[0095] where represents the output signal, s u is the user data, and n represents the noise. According to formula (3), the (l, k) - th element of H can be expressed as follows

[0096]

[0097] where, e represents the excited OAM mode. The communication capacity expression of the vortex wave is as follows

[0098]

[0099] where, P e represents the power allocated to the e - th OAM channel based on the water - filling algorithm, σ 2 is the noise variance, represents the singular value corresponding to the e - th OAM channel.

[0100] The beneficial effects brought by the method of the present invention can be further illustrated by the following simulation.

[0101] I. Simulation conditions

[0102] GUs are uniformly distributed in a 20m×20m area. Let the allocated bandwidth, ABS transmit power, and noise power be B = 1, P = 30dBm, and σ 2 =-90dBm. The operating frequency of the air - to - ground vortex wave communication is 1GHz.

[0103] Simulation content and simulation results

[0104] Compare the MUCR scheme with the traditional fixed UCA scheme.

[0105] Simulation 1, compare the capacity performance of the MUCR scheme and the fixed UCA scheme under different GU conditions.

[0106] Simulation results: Figure 2 is the capacity performance under the MUCR scheme. The fixed UCA scheme has 4 antennas to receive the vortex wave signal. From Figure 2In [the specific situation], it can be observed that under the conditions of having 4, 5, and 6 GUs, the MUCR scheme all shows better performance than the fixed UCA scheme. In addition, as the altitude of the ABS increases, the channel capacity under the fixed UCA scheme decreases rapidly, while the channel capacity of the MUCR scheme can remain unchanged. This is because compared with the fixed UCA scheme, the virtual antenna array formed by the collaborative users will expand with the increase of the distance, thus supporting high-capacity long-distance transmission.

[0107] Simulation 2: Compare the channel capacities of the MUCR scheme and the fixed UCA scheme under different modes.

[0108] Simulation results: Figure 3 [The figure] shows the channel capacity curves under different modes. The channel capacity of the MUCR scheme in each mode is greater than that of the fixed UCA scheme. This is because the MUCR scheme can expand the virtual antenna array with the increase of the distance, thus obtaining a stable channel capacity in long-distance transmission. From Figure 3 it can be seen that the larger the number of modes, the smaller the channel capacity. This is because compared with the small-mode system, the system divergence is more serious in the large-mode case.

[0109] In addition, it should be noted that, in the various specific technical features described in the above specific embodiments, without contradiction, they can be combined in any appropriate way. To avoid unnecessary repetition, the present invention will not separately describe various possible combination methods.

Claims

1. A multi-user cooperative receiving method for air-ground vortex wave communication, characterized in that, Specifically, it includes the following steps: Step 1: Set the collaborative user set as an empty set, and set the number of collaborative users to L; Step 2: Set the initial search radius r(A) = r fea (A)+σ, where σ is a positive real number, where A is the vertical distance from the aerial base station to the ground, λ represents the wavelength of the Laguerre-Gaussian beam, and l represents the orbital angular momentum mode of the Laguerre-Gaussian beam; Step 3: If there are users in the search ring [r(A), σ] and the number of users is L, then these L users are taken as collaborative users and put into the collaborative user set, and go to Step 8; if the number of users in the search ring [r(A), σ] is less than L, then go to Step 5; if the number of users in the search ring [r(A), σ] is greater than L, then go to Step 4; the search ring [r(A), σ] is an annular region with an inner diameter of r(A) - σ and an outer diameter of r(A) + σ; Step 4: Take all users within the search ring as potential users, sort all potential users in ascending order according to the actual radial angle to form a set of potential users, and calculate the maximum radial angle difference φ p , take the first potential user and the last potential user as candidate collaborative users, and sequentially select L - 2 potential users between the first potential user and the last potential user to form several groups of candidate collaborative user groups with the candidate collaborative users; sort the L candidate collaborative users in each group of candidate collaborative user groups in ascending order according to the actual radial angle and number them; based on φ p calculate the ideal radial angle of each candidate collaborative user in each group of candidate collaborative user groups, and select a group of candidate collaborative user groups on the principle that the angular square difference between the ideal radial angle and the actual radial angle is the smallest, and take the users in this group of candidate collaborative user groups as collaborative users and put them into the collaborative user set, and go to Step 8; Step 5: Determine whether the search radius r(A) is greater than D at this time max -σ. If so, go to Step 6; otherwise, update r(A) and let: r(A) = r(A) + 2σ, and go to Step 3; D max is the preset maximum threshold value; Step 6: Determine the collaborative user set at this time Is it an empty set? If so, go to Step 7; otherwise, go to Step 8; Step 7: Update σ, let σ = 2σ, and go to Step 2; Step 8: Adjust the waist radius w0 of the Laguerre-Gaussian beam so that the maximum energy of the Laguerre-Gaussian beam hits the collaborative users; In Step 8, the waist radius w0 is adjusted according to the following formula: where r max (A) represents the radius when the Laguerre-Gaussian beam intensity distribution is at its maximum, and the expression is as follows; Among them, w(z) is the Laguerre beam radius, and the expression is z R represents the Rayleigh range, z represents the distance from the air base station to the target user at the coordinate (0, 0, 0), z = A, and r max (A) ≥ r fea (A).

2. The multi-user cooperative receiving method for air-ground vortex wave communication according to claim 1, characterized in that, Specifically, Step 4 is as follows: Step 4.1: Calculate the ideal radial angle of each candidate collaborative user in each group of candidate collaborative user groups Among them, represents the ideal radial angle of the l c -th candidate collaborative user, where l c = 1, 2, 3, ..., L; θ1 represents the radial angle of the first potential user in the set of potential users; L c represents the total number of collaborative GUs in the collaborative GU set; Step 4.2: Calculate the angular mean square difference of each group of candidate collaborative user groups: Among them, represents the ideal radial angle of the i-th candidate collaborative user, θ i represents the radial angle of the i-th potential user in the set of potential users.

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