A DOA Estimation Method for OAM Communication

Abstract

The present invention discloses a DOA estimation method for OAM communication, including: the transmitting end estimates the elevation angle θ0 with OAM beams of different radii and different modes; the transmitting end fixes the elevation angle θ0 and estimates the deflection angle φ0 with beams of different radii and mode 0; the transmitting end obtains the beam deflection angles (θ0, φ0) to achieve the DOA estimation of the transmitting end. The present invention performs DOA estimation in two stages. First, the θ angle is estimated with OAM beams of different radii and different modes, and then the φ angle is estimated with mode 0 beams of different radii. The method is simple to implement and has low complexity.

Description

Technical Field

[0001] The present invention relates to the field of wireless communication technologies, and in particular, to a DOA estimation method for OAM communication. Background Art

[0002] The uniform circular antenna array (UCA) is often used in orbital angular momentum (OAM) multiplexing communication systems in the microwave and millimeter wave frequency bands due to its flexible modulation and multiplexing characteristics. OAM is related to the spatial distribution of the wave function and is a fundamental property of all "vortex electromagnetic waves", manifested as the beam having a helical equiphase surface and propagating along a helix. OAM has an infinite number of orthogonal modes and theoretically can carry an infinite number of information channels for simultaneous and co-frequency multiplexing transmission, thus providing a new degree of freedom for information multiplexing independent of time, frequency, and polarization, and is expected to multiply increase the network capacity, spectral efficiency, anti-interference, and anti-interception capabilities of wireless communication systems. In 2007, B. thide et al. demonstrated through experiments that feeding the UCA with signals of equal amplitude and equal phase difference can generate OAM. As shown. Currently, most of the research on OAM communication based on UCA focuses on the scenario where the transmitting and receiving UCAs are coaxial. However, coaxiality greatly limits the application scenarios of OAM communication. Therefore, it is necessary to study OAM communication in non-coaxial scenarios.

[0003] Currently, there is still relatively little research on non-coaxial OAM communication scenarios. In the paper "Achieving Practical OAM Based Wireless Communications with Misaligned Transceiver" by CHENG W, for non-coaxial OAM communication scenarios, a "precoding - post-processing" coding scheme was proposed, which can restore the channel into non-interfering parallel sub-channels. However, when this method is adopted, OAM communication based on UCA degenerates into general MIMO communication and loses the characteristics of OAM communication. To maintain the beam characteristics of OAM, CHEN R proposed an OAM beam deflection method in the paper "Beam Steering for the Misalignment in UCA-Based OAM Communication Systems", which realizes beam deflection by adding deflection phase shifts to the UCA array elements at the transceiver. This method only considers the general deflection characteristics and does not consider the constraints of OAM beam generation on the geometric structure of the transceiver array elements. When the method in the paper is adopted, due to only adding deflection phases to the array elements, the deflected OAM beam is distorted. When the beam deflection angle is large, the distortion of the OAM beam intensifies and the modal orthogonality decreases. Therefore, this type of method is not essentially an effective method for OAM beam deflection. Regarding the above problems, YU W comprehensively considered the requirements of OAM beam deflection for phase and antenna array geometric structure in the paper "UCA-Based OAM Beam Steering with High Mode Isolation[J]. IEEE Wireless Communications Letters". For a specific deflection angle, the positions of the transceiver array elements are first adjusted to form a specified elliptical array, and based on the specific array element structure, a one-dimensional linear phase weighting method is proposed to achieve OAM beam deflection. Simulations show that this method can ensure the orthogonality of each OAM mode while achieving beam deflection. To achieve generality, a square grid array (SGA) is adopted in the paper to realize elliptical arrays at arbitrary angles, and multi-angle OAM communication is carried out by selecting elliptical arrays with different aspect ratios on the square grid array. However, the prerequisite for specific-angle OAM communication is that the transceiver obtains the deflection angle of the other party relative to itself.

[0004] The prerequisite for OAM beam deflection is that the transceiver can obtain the deflection angle of the other party relative to itself, so as to implement the beam deflection method for the known deflection angle. Therefore, the estimation of the direction of arrival (DOA) by the transceiver is the prerequisite for OAM deflection beam communication. The current DOA estimation methods are mainly for the MIMO millimeter-wave DOA estimation in general cases. DOA estimation is generally implemented at the base station end. The base station estimates the angles of each terminal based on its powerful digital and analog processing capabilities, so as to achieve high-speed communication with mobile terminals. The traditional DOA estimation methods generally define a function, and give the estimation of the arrival angle according to the relationship between the maximum value of the function and the angle. This function is habitually called the pseudo-spectrum. The ways to define the pseudo-spectrum include: Bartlett method, minimum variance distortionless response method, maximum entropy method, Pisarenko harmonic decomposition method, minimum norm method, multiple signal classification (MUSIC) method, etc. These methods are applied to general forms of antenna arrays and have high complexity. For the OAM communication scenario based on UCA, it is necessary to design a more efficient DOA estimation method by combining the specific geometric structure of UCA. There is less research in this area currently, and researchers at Xidian University have done some work in this field. CHEN R proposed an OAM arrival angle estimation method based on UCA in the paper "Multi-mode OAM Radio Waves: Generation, Angle of Arrival Estimation and Reception With UCAs", and used multiple sub-carriers of OFDM and multiple modes of OAM for DOA estimation. The method in the paper combines the geometric structure of UCA. However, as mentioned before, it is impossible to achieve strict OAM beam deflection by using UCA. Therefore, it is necessary to study an efficient OAM beam DOA estimation method based on SGA, so that the transceiver can adaptively achieve OAM high-speed communication at any angle in real time. Summary of the Invention

[0005] Objective of the Invention: Aiming at the defect that strict OAM beam deflection cannot be achieved by using UCA in the prior art, the present invention discloses a DOA estimation method for OAM communication, which performs DOA estimation in two stages. First, the elevation angle θ0 is estimated by using OAM beams with different radii and different modes, and then the azimuth angle φ is estimated by using 0-mode beams with different radii. The method is simple to implement and has low complexity.

[0006] Technical Solution: To achieve the above technical objectives, the present invention adopts the following technical solutions.

[0007] A DOA estimation method for OAM communication includes the following steps:

[0008] The transmitting end estimates the elevation angle θ0 with OAM beams of different radii and different modes;

[0009] The transmitting end fixes the elevation angle θ0 and estimates the deflection angle φ0 with beams of different radii and mode 0;

[0010] The transmitting end obtains the beam deflection angles (θ0, φ0) to achieve the DOA estimation of the transmitting end.

[0011] Preferably, the coordinate construction of the beam deflection angle is as follows: both the transmitting end antenna and the receiving end antenna adopt square grid arrays. At the transmitting end, the center point of the SGA is selected as the coordinate origin o, the plane where the SGA is located is the xoy plane, the x-axis and the y-axis are respectively selected as the straight lines parallel to two perpendicular sides of the SGA, and both are in the positive direction from the origin o to the edge of the SGA; the straight line passing through the o point and perpendicular to the xoy plane is the z-axis, and the positive direction of the z-axis is upward. The beam deflection angle (θ0, φ0) of the receiving end relative to the transmitting end is defined as the angle of the vector v formed by the connection line of the center points of the receiving end SGA and the transmitting end SGA in the transmitting coordinate system z - xoy. The direction of the vector v is from the transmitting center point to the receiving center point. The elevation angle θ0 is defined as the angle between the vector v and the z-axis; the deflection angle φ0 is defined as the angle between the projection line of the vector v on the xoy plane and the y-axis.

[0012] Preferably, the transmitting end estimates the elevation angle with OAM beams of different radii and different modes, specifically including:

[0013] The transmitting end scans with OAM beams of different radii and different modes and sends the first scanning beam to the receiving end;

[0014] The transmitting end obtains the elevation angle θ0 fed back by the receiving end, and the elevation angle θ0 is calculated by the receiving end through the received first scanning beam.

[0015] Preferably, the transmitting end scans with OAM beams of different radii and different modes and sends the first scanning beam to the receiving end, specifically including:

[0016] At the transmitting end, assume that the radii of the uniform circular array antennas (UCA) supported by the SGA from small to large are r0, r1... r N-1 , for the UCA with radius r n , the effective OAM modes it can support are 0... l n , let the radius index be n and the mode index be l;

[0017] Select the UCA with radius r n , for the selected UCA, set the phase offset of each array element of the UCA according to the feeding method of mode l, and the transmitting end transmits the first scanning beam with the selected UCA and the specified OAM mode; until all OAM beam scans of all radii and all modes with l = 0... l n , n = 0... N - 1 are completed.

[0018] Preferably, the elevation angle θ0 is calculated by the receiving end based on the received first scanning beam, and the steps include:

[0019] The receiving end receives the first scanning beam and records the signal-to-noise ratio s measured each time by itself. n，l , and simultaneously records the radius-mode combination (r n , l) corresponding to this measurement.

[0020] The receiving end compares a number of recorded signal-to-noise ratios s n，l , and selects the radius-mode combination corresponding to the maximum signal-to-noise ratio Calculate the elevation angle θ0 through the radius-mode combination .

[0021] Preferably, the calculation of the elevation angle θ0 through the radius-mode combination includes the following calculation formula:

[0022]

[0023] where is the wave number and λ is the wavelength.

[0024] Preferably, the transmitting end fixes the elevation angle θ0 and estimates the deflection angle φ0 with beams of different radii and 0 mode, specifically including:

[0025] The transmitting end fixes the elevation angle θ0, scans with beams of different radii and 0 mode, and sends out the second scanning beam to the receiving end;

[0026] The transmitting end obtains the deflection angle φ0 fed back by the receiving end, and the deflection angle φ0 is calculated by the receiving end based on the received second scanning beam.

[0027] Preferably, the design process of the second scanning beam includes:

[0028] The transmitting end selects a UCA with a preset radius, calculates and configures the phase for each antenna element in the UCA, sets the variable φ to traverse in segments within [0, 2π] according to the UCA pattern, and sends out the second scanning beam; the second scanning beam is a 0-mode OAM beam; the number of the second scanning beams is the number of segments of the direction angle φ;

[0029] The receiving end receives all the second scanning beams, records the signal-to-noise ratio corresponding to each second scanning beam, and selects the variable φ corresponding to the maximum signal-to-noise ratio as the deflection angle φ0 and feeds it back to the transmitting end.

[0030] Preferably, the setting of the variable φ to traverse in segments within [0, ۲π] according to the UCA pattern and sending out the second scanning beam includes:

[0031] Coarse Scanning: The transmitting end selects a UCA with the minimum radius r0, calculates the configured phase for each antenna element in the UCA, and traverses the variable φ in segments within [0, 2π] according to the UCA pattern. The number of scanning segments for coarse scanning is M, and the scanning step size is Transmit the second scanning beam;

[0032] The receiving end receives the M second scanning beams during the coarse scanning process, records the signal-to-noise ratio corresponding to each second scanning beam, selects the maximum signal-to-noise ratio, and records the coarse scanning angle range corresponding to the maximum signal-to-noise ratio and feeds it back to the transmitting end;

[0033] Fine Scanning: The transmitting end selects a UCA with the maximum radius r N-1 , calculates the configured phase for each antenna element in the UCA, and traverses φ in segments within the coarse scanning angle range according to the UCA pattern. The number of scanning segments for fine scanning is Q, and the scanning step size is Δ φ , and emits the second scanning beam;

[0034] The receiving end receives the Q second scanning beams during the fine scanning process, records the signal-to-noise ratio corresponding to each second scanning beam, and selects the φ corresponding to the maximum signal-to-noise ratio as φ0 and feeds it back to the transmitting end.

[0035] Preferably, for calculating the configured phase for each antenna element in the UCA, its calculation formula includes:

[0036] α i = kr0sinθ0cos(φ - φ i )

[0037] where α i is the phase of the i-th antenna element, and φ is the variable used to determine the deflection angle.

[0038] Beneficial Effects: The present invention performs DOA estimation in two stages. First, the θ angle is estimated using OAM beams with different radii and different modes, and then the φ angle is estimated using the 0-mode beams with different radii. The method is simple to implement and has low complexity, and is applicable to the deflection OAM beam communication system based on SGA. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 is the overall method flow chart of the present invention;

[0040] Figure 2 is the schematic diagram of the deflection beam OAM communication scenario based on SGA in Embodiment 1;

[0041] Figure 3 ]>is the schematic diagram of the beam divergence angle θ of different modes in Embodiment 1;

[0042] Figure 4Schematic diagram of the OAM non-zero mode circular beam in Embodiment 1;

[0043] Figure 5 Schematic diagram of the 0-mode beam scanning with a fixed θ angle in Embodiment 1. Detailed implementation manners

[0044] The following further illustrates and explains a DOA estimation method for OAM communication according to the present invention in conjunction with the accompanying drawings and embodiments.

[0045] Explanation of basic terms: An antenna element (or antenna, antenna array element) refers to a single antenna. Multiple antenna elements are uniformly arranged in a circular shape to form a UCA, so it is called a uniform circular array antenna. In the present invention, the SGA is adopted at both the transmitting and receiving ends, that is, the antenna elements at both the transmitting and receiving ends are deployed on a square grid to form a square grid array (SGA). The central element refers to the antenna element at the center of the SGA. For example, assuming that the number of antenna elements of the SGA adopted in the present invention is odd, such as a 5*5 SGA, the position of the central element is (3,3). In the present invention, it is assumed that the central element of the SGA is the center of the UCA (i.e., the center of the circle), and an approximate UCA is selected on the SGA.

[0046] Embodiment 1:

[0047] As shown in the Figure 2 accompanying Figure 2 drawings, the accompanying drawings give a schematic diagram of the deflected beam OAM communication scenario based on the SGA (square grid array) in the embodiment of the present invention. If deflected beam OAM communication is to be performed, the transmitting and receiving ends first need to obtain the beam deflection angles (θ, φ) of the other party relative to themselves.

[0048] This embodiment discloses a DOA estimation method for OAM communication, including the following steps:

[0049] The transmitting end estimates the elevation angle θ0 with OAM beams of different radii and different modes;

[0050] The transmitting end fixes the elevation angle θ0 and estimates the deflection angle φ0 with beams of different radii and 0 mode;

[0051] The transmitting end obtains the beam deflection angle (θ0, φ0) to achieve the DOA estimation of the transmitting end.

[0052] In an actual communication scenario, the beam deflection angles are independently estimated by both the transmitting and receiving ends, that is, there is a beam deflection angle of the transmitting end relative to the receiving end, and there is also a beam deflection angle of the receiving end relative to the transmitting end. The estimation methods of both are the same. Therefore, the present invention only analyzes the beam deflection angle of the receiving end relative to the transmitting end as an example. For the convenience of variable distinction and expression, the beam deflection angle of the receiving end relative to the transmitting end is denoted as (θ0, φ0) here. As shown in the Figure 2As shown in the figure, the method for establishing the coordinate system is as follows: Both the transmitting end antenna and the receiving end antenna adopt a square grid array (SGA). At the transmitting end, the center point of the SGA is selected as the coordinate origin o, the plane where the SGA is located is taken as the xoy plane, the x-axis and the y-axis are respectively selected as the straight lines parallel to two perpendicular sides of the SGA, and the positive directions of both are from the origin o to the edge of the SGA. The straight line passing through point o and perpendicular to the xoy plane is the z-axis, and the positive direction of the z-axis is upward. The specific coordinate system is as shown in the appendix Figure 2 shown

[0053] The beam deflection angles (θ0, φ0) of the receiving end relative to the transmitting end are defined as the angles of the vector v formed by the connection line between the center points of the receiving end SGA and the transmitting end SGA (the vector direction is: from the transmitting center point to the receiving center point) in the transmitting coordinate system z - xoy. θ0 is the elevation angle, defined as the angle between the vector v and the z-axis. φ0 is the deflection angle, defined as the angle between the projection line of the vector v on the xoy plane and the y-axis

[0054] The feature of using SGA to select array elements for OAM communication is that multiple circles with different radii or ellipses with different major and minor axis lengths can be selected for OAM deflection beam communication at multiple angles. The present invention utilizes this characteristic to perform DOA estimation in two stages. First, the θ angle is estimated using OAM beams with different radii and different modes, and then the φ angle is estimated using the 0-mode beam with different radii. The method of this patent is simple to implement and has low complexity. It is applicable to all deflection OAM beam communication systems based on SGA

[0055] As shown in the appendix Figure 1 shown, a DOA estimation method for OAM communication includes the following steps

[0056] S1. The transmitting end scans with OAM beams of different modes and emits the first scanning beam

[0057] S2. The transmitting end obtains the elevation angle θ0 fed back by the receiving end, and the elevation angle θ0 is calculated from the first scanning beam received by the receiving end

[0058] S3. The transmitting end fixes the elevation angle θ0 and scans in the φ direction with a 0-mode beam to emit the second scanning beam

[0059] S4. The transmitting end obtains the deflection angle φ0 fed back by the receiving end, determines the arrival angle (θ0, φ0), and completes the DOA estimation of the receiving end relative to the transmitting end; the deflection angle φ0 is calculated from the second scanning beam received by the receiving end

[0060] The transmitting end obtains the beam deflection angles (θ0, φ0) to achieve the DOA estimation of the transmitting end. There is only one beam deflection angle (θ0, φ0), which refers to the overall relative angle between the transmitting and receiving ends

[0061] In this embodiment, the specific steps of step S1 include:

[0062] At the transmitting end, assume that the radii of the UCA (Uniform Circular Array) supported by the SGA (Square Grid Array) from small to large are r0, r1... r N-1 , for the UCA with radius r n , the effective OAM (Orbital Angular Momentum) modes it can support are 0... l n (Since the radiation patterns of positive and negative OAM modes are the same, only the positive mode is needed to transmit data here). Let the radius index be n and the mode index be l.

[0063] Step S11: Select the UCA with radius r n . For the selected UCA, set the phase offset of each array element of the UCA according to the feeding method of mode l. Among them, the phase setting method based on the OAM of the UCA is well-known in the art and can refer to the paper "UCA Based OAM Beam Steering with High Mode Isolation[J].IEEE WirelessCommunications Letters" by YU W.

[0064] Step S12: The transmitting end transmits the first scanning beam with the UCA selected in step S11 and the specified OAM mode;

[0065] Step S13: Repeat steps S11 and S12 for l = 0... l n , n = 0... N - 1. Among them, N is determined by the number of UCAs supported by the SGA, and l n is determined by the number of antenna array elements included in the nth UCA.

[0066] The specific steps of step S2 include:

[0067] Step S21: The central array element at the receiving end receives the first scanning beam and records the signal-to-noise ratio s n，l measured each time by itself, and at the same time records the radius-mode combination (r n , l) corresponding to this measurement. One radius and one mode, that is, one (r n , l) corresponds to one first scanning beam, and each first scanning beam has a corresponding signal-to-noise ratio. At the same radius, that is, when r n is fixed, multiple adjustments correspond to multiple first scanning beams, and there are multiple signal-to-noise ratios.

[0068] Step S22: The receiving end compares the recorded several signal-to-noise ratios s n，l , and selects the radius-mode combination corresponding to the maximum signal-to-noise ratio Through the radius-mode combination Calculate the elevation angle θ0;

[0069] Through the radius mode combination The calculation formula for the elevation angle θ0 is:

[0070]

[0071] Wherein, is the wave number, which is a parameter of the electromagnetic wave used in OAM communication. The wave numbers at the receiving end and the transmitting end are the same, independent of the first scanning beam. λ is the wavelength, which is a parameter of the electromagnetic wave used in OAM communication. The wave numbers at the receiving end and the transmitting end are the same, independent of the first scanning beam. l is the OAM mode, and r is the UCA radius. Here, substitute the radius mode combination into formula (1) for calculation to obtain the elevation angle θ0.

[0072] The OAM beam has two significant characteristics: the main lobe gain of the beam is symmetric in the φ direction, that is, at the same θ angle, the gain at any φ angle position is the same; when the UCA is fixed, the OAM beam divergence angle increases with the increase of the mode.

[0073] From the appendix Figure 3 It can be seen that the divergence angle θ of the OAM beam increases with the increase of the mode. Therefore, the beam scanning in the θ direction can be performed by adjusting the mode. Appendix Figure 4 is a schematic diagram of the OAM three-dimensional circular beam. It can be seen from the figure that since the non-0 mode OAM beam is a circular beam, at the same θ, the gain at any φ angle position is the same. This characteristic also holds for the 0 mode of non-circular beams. In addition, the width of the main lobe of the OAM beam will decrease with the increase of the UCA radius. Therefore, the beam scanning accuracy can be further improved by adjusting the size of the UCA radius.

[0074] According to the above principle, the transmitting end antenna array can select UCAs with different radii and transmit pilot signals in different OAM modes. The receiving end receives the signals and calculates the signal-to-noise ratio, selects the OAM mode and UCA radius corresponding to the beam with the maximum signal-to-noise ratio, and substitutes the mode and radius values into formula (1) to calculate the corresponding θ, which is the estimated θ0, that is, the elevation angle of the receiving array relative to the transmitting array in the θ direction.

[0075] Step S23: The receiving end feeds back the calculated θ0 to the transmitting end.

[0076] The specific steps of step S3 and step S4 include: after obtaining the θ0 obtained in the above steps, the transmitting end performs scanning with a 0-mode beam to determine the φ0 angle, that is:

[0077] The transmitting end fixes the elevation angle θ0 and scans with beams of different radii and 0 mode to send out the second scanning beam to the receiving end; as shown in the appendix Figure 2 As shown, it scans in the φ direction with beams of different radii and 0 mode to determine φ0. The φ direction is the azimuth angle direction in the horizontal plane. The second 0-mode scanning beam scans the variable φ from 0 to 2π under the condition of determining the elevation angle. The actual scanning range is a fixed elevation angle, and φ takes a circular ring from 0 to 2π.

[0078] The transmitting end obtains the deflection angle φ0 fed back by the receiving end, and the deflection angle φ0 is calculated by the receiving end through the received second scanning beam.

[0079] After determining the elevation angle θ0, the 0 mode can be used to further determine the φ0 angle at this time. The 0-mode beam does not diverge, and there is a main lobe with the strongest gain in the deflected beam direction. This characteristic can be used to determine the complete deflection angle information. The UCA pattern function is shown in formula (2):

[0080]

[0081] where (θ, φ) is the beam deflection angle, α i is the phase of the i-th antenna element, and I is the number of antennas in the selected UCA. φ′ i is the azimuth angle of the i-th antenna element, i = 1…I. The azimuth angles of the antenna elements of their respective SGAs (UCAs) at the transmitting and receiving ends are known, so φ′ i here is known. At this time, the previously obtained θ0 angle can be substituted into θ in the above formula, and then φ is traversed from 0 to 2π. At this time, the main lobe of the 0-mode beam will also scan from 0 to 2π, as shown in the appendix Figure 5 As shown.

[0082] The design process of the second scanning beam includes:

[0083] The transmitting end selects a UCA with a preset radius, calculates and configures the phase for each antenna element in the UCA, sets the variable φ to traverse in segments within [0, 2π] according to the UCA pattern, and sends the second scanning beam; the second scanning beam is a 0-mode OAM beam; the number of the second scanning beams is the number of segments of the direction angle φ;

[0084] The receiving end receives all the second scanning beams, records the signal-to-noise ratio corresponding to each second scanning beam, and selects the variable φ corresponding to the maximum signal-to-noise ratio as the deflection angle φ0 and feeds it back to the transmitting end.

[0085] When the variable φ traverses in segments within [0, 2π], if only one scan traversal is performed, in order to obtain a more accurate result, the number of scan segments required is relatively high and the time consumption is long. In addition, since the main lobe width decreases as the radius of the UCA increases, that is, the larger the radius of the UCA, the smaller the main lobe width. Under the condition of the same number of scan segments, the complexity of beam scanning is higher. Based on this characteristic, the present invention adopts a coarse scan - fine scan method. First, select a UCA with a smaller radius on the SGA. The 0 - mode main lobe of this UCA is relatively wide. Use this 0 - mode main lobe to scan in the φ direction. At this time, the scan step size can be relatively large. After determining the rough range of the φ angle, then use the largest UCA that can be supported to perform a fine scan within the rough range obtained above. Adopting this beam scanning method from coarse to fine can greatly reduce the beam scanning complexity. Similar to the estimation of the θ angle, for the 0 - mode scanning beams at different angles, the receiving end receives the signal and calculates the signal - to - noise ratio, and takes the φ angle corresponding to the maximum signal - to - noise ratio as the estimated φ0 angle.

[0086] Specifically:

[0087] Step S3l: Select a UCA with a radius of r 0 (the minimum radius). The phases of the selected antenna elements are configured according to the UCA pattern function of formula (2) as:

[0088] α i =kr0sinθ0cos(φ - φ′ i ) (3)

[0089] α i is the phase of the i - th antenna element, φ′ i is the azimuth angle of the i - th antenna element, i = 1…I, φ′ i is known; the variable φ in formula (3) is set to (M can be determined according to the UCA radius to ensure that the main lobe width in the φ direction is approximately equal to j = 0…M - 1). M is the number of scan segments, that is, the 2π angle is divided into M segments for scanning. According to M, the scan step size is set to For all modes of beams, all elements of the selected UCA need to adjust their phases according to formula (3) respectively, that is, all elements of the UCA jointly adjust their phases to emit the scanning beam.

[0090] According to the UCA, the beam width of the 0 - mode can be determined (the specific method refers to the paper "Analyze UCA - Based OAM Communication From Spatial Correlation[J].IEEE Access" by YU W). Assume that the beam width of the 0 - mode when the radius is r is B r , then

[0091] The transmitting end configures the phase for j = 0…M - 1 according to Equation 3, that is, the phase configuration of the 0-mode beam sets the antenna elements of the UCA to transmit the second scanning beam, where j is the beam index of the 0-mode scanning.

[0092] Step S32: The receiving end receives all the second scanning beams and records the signal-to-noise ratio as s′0. ，j， Select the maximum signal-to-noise ratio.

[0093] Assume that the scanning angle index corresponding to the maximum signal-to-noise ratio is j0, and the receiving end feeds back the coarse scanning angle range to the transmitting end.

[0094] Step S33: The transmitting end selects a UCA with a radius of r N-1 (maximum radius). When θ in Equation (3) is set to θ0, φ is set within the range to perform beam scanning in 0 mode (the scanning step size is set according to the accuracy requirement). In the present invention, it is assumed that the step size is Δ φ , then the φ angle for each scan is q = 0…Q - 1,

[0095] Step S34: The receiving end receives the Q second scanning beams during the fine scanning process, records the signal-to-noise ratio corresponding to each second scanning beam, and selects the φ corresponding to the maximum signal-to-noise ratio and feeds it back to the transmitting end as φ0.

[0096] Step S35: The transmitting end receives φ0, selects the array elements in combination with the existing θ0 and sets the array element phases, thereby completing all the settings for the deflected beam OAM communication. In this embodiment, the specific process implemented in Step S35 can refer to the paper “UCA-Based OAM Beam Steering with High Mode Isolation[J].IEEE Wireless Communications Letters” by YU W.

[0097] Both beam scans use OAM beams. Among them, the first scanning beam scans by continuously traversing all the OAM beams of the supported modes, and the second scanning beam only uses the 0-mode beam to perform multiple-direction scans.

[0098] The receiving end can also perform DOA estimation using the above steps, and then select the array elements and set the phases. When the transceiver is set up, the deflected beam OAM communication can be carried out.

[0099] The present invention performs DOA estimation through two stages. First, the θ angle is estimated using OAM beams with different radii and different modes, and then the φ angle is estimated using the 0-mode beams with different radii. The method is simple to implement and has low complexity, and is applicable to the deflected OAM beam communication system based on SGA.

[0100] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A DOA estimation method for OAM communication, characterized in that, It includes the following steps: Both the transmitting end antenna and the receiving end antenna adopt a square grid array, that is, SGA; The transmitting end estimates the elevation angle θ0 with OAM beams of different radii and different modes, including: the transmitting end scans with OAM beams of different radii and different modes and sends the first scanning beam to the receiving end; the transmitting end obtains the elevation angle θ0 fed back by the receiving end, and the elevation angle θ0 is calculated by the receiving end through the received first scanning beam, and its steps include: The receiving end receives the first scanning beam and records the signal-to-noise ratio s measured each time by itself n，l , and at the same time records the corresponding transmitter radius mode combination (r n , l) for this measurement; The receiving end compares a number of recorded signal-to-noise ratios s n，l , and selects the radius-mode combination corresponding to the maximum signal-to-noise ratio Based on the radius-mode combination calculate the elevation angle θ0; The transmitting end fixes the elevation angle θ0 and estimates the deflection angle φ0 with beams of different radii and mode 0, including: the transmitting end fixes the elevation angle θ0, scans with beams of different radii and mode 0, and sends the second scanning beam to the receiving end by the coarse scanning - fine scanning method; the transmitting end obtains the deflection angle φ0 fed back by the receiving end, and the deflection angle φ0 is calculated by the receiving end through the received second scanning beam; The transmitting end obtains the beam deflection angle (θ0, φ0) to achieve the DOA estimation of the transmitting end.

2. The DOA estimation method for OAM communication according to claim 1, characterized in that The coordinate construction of the beam deflection angle is as follows: both the transmitting end antenna and the receiving end antenna adopt a square grid array. At the transmitting end, the center point of the SGA is selected as the coordinate origin o, the plane where the SGA is located is the xoy plane, the x - axis and the y - axis are respectively selected as the straight lines parallel to two perpendicular sides of the SGA, and both are in the positive direction from the origin o to the edge of the SGA; the straight line passing through the o point and perpendicular to the xoy plane is the z - axis, and the positive direction of the z - axis is upward. The beam deflection angle (θ0, φ0) of the receiving end relative to the transmitting end is defined as the angle of the vector v formed by the connection line of the center points of the receiving - end SGA and the transmitting - end SGA in the transmitting coordinate system z - xoy, the direction of the vector v is from the transmitting center point to the receiving center point, the elevation angle θ0 is defined as the included angle between the vector v and the z - axis; the deflection angle φ0 is defined as the included angle between the projection line of the vector v on the xoy plane and the y - axis.

3. A DOA estimation method for OAM communication according to claim 1, characterized in that The transmitting end scans with OAM beams of different radii and different modes and sends the first scanning beam to the receiving end, specifically including: At the transmitting end, assume that the radii of the UCAs supported by the SGA are r0, r1... r from small to large N-1 , where UCA is the Uniform Circular Array; for the UCA with radius r n , the valid OAM modes it can support are 0... l n . Let the radius index be n and the mode index be l; Select a UCA with a radius of r n For the selected UCA, set the phase offset of each element of the UCA according to the feeding method of mode l, and the transmitting end transmits the first scanning beam with the selected UCA and the specified 0AM mode; until all the OAM beam scans of all radii and all modes of l = 0... l n , n = 0... N-1 are completed.

4. A DOA estimation method for OAM communication according to claim 1, characterized in that Said by combining the radius modes Calculate the elevation angle θ0, and its calculation formula includes: where, is the wave number and λ is the wavelength.

5. A DOA estimation method for OAM communication according to claim 1, characterized in that, The design process of the second scanning beam includes: The transmitting end selects a UCA with a preset radius, calculates and configures the phase for each antenna element in the UCA, sets the variable φ to traverse in segments within [0, 2π] according to the UCA pattern, and sends the second scanning beam; the second scanning beam is a mode - 0 OAM beam; the number of the second scanning beams is the number of segments of the variable φ; The receiving end receives all the second scanning beams, records the signal - to - noise ratio corresponding to each second scanning beam, and selects the variable φ corresponding to the maximum signal - to - noise ratio as the deflection angle φ0 and feeds it back to the transmitting end.

6. The DOA estimation method for OAM communication according to claim 5, characterized in that, The setting of the variable φ to traverse in segments within [0, 2π] according to the UCA pattern and sending the second scanning beam includes: Coarse scan: The UCA with the minimum radius r0 is selected at the transmitting end, the configuration phase is calculated for each antenna element in the UCA, and the variable φ is traversed in segments within [0, 2π] according to the UCA pattern. The number of scan segments for the coarse scan is M, and the scan step size is Transmit the second scan beam; The receiving end receives M second scanning beams during the coarse scanning process, records the signal - to - noise ratio corresponding to each second scanning beam, selects the maximum signal - to - noise ratio, and records the range of the coarse scanning angle corresponding to the maximum signal - to - noise ratio and feeds it back to the transmitting end; Fine scan: The transmitting end selects a UCA with the maximum radius r N-1 and calculates the configured phase for each antenna element in the UCA. According to the UCA radiation pattern, φ is set to traverse in segments within the coarse scan angle range. The number of scan segments for the fine scan is Q, and the scan step size is Δ φ , and emits the second scan beam; The receiving end receives Q second scanning beams during the fine scanning process, records the signal - to - noise ratio corresponding to each second scanning beam, and selects the φ corresponding to the maximum signal - to - noise ratio as φ0 and feeds it back to the transmitting end.

7. A DOA estimation method for OAM communication according to claim 5, characterized in that Calculating the configured phase for each antenna element in the UCA, and its calculation formula includes: α i = kr0sinθ0 cos(φ - φ i ) where α i is the phase of the i-th antenna element, and φ is a variable used to determine the deflection angle.

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