CN110995299A - Electromagnetic wave orbital angular momentum transmission method and system based on dimension expansion interference code - Google Patents

Abstract

The invention relates to an electromagnetic wave orbital angular momentum transmission method and system based on a spread-dimensional interference code. In the system, the signal transmission terminal system includes a data generation module, a serial-to-parallel conversion module, an interference code expansion module, an OAM mode selection module and a signal transmission antenna module. The data generation module outputs the modulated serial user data; the serial-parallel conversion module converts the serial user data into multi-row parallel data; the interference code expansion module multiplies the parallel data and the interference code to form an expansion matrix; the mode selection module converts the The elements of each column vector of the expanded-dimensional matrix are added separately and fed to the antenna element through different modes, which are converted into space electromagnetic waves and sent out. At the receiving end, the signal receiving terminal system includes a receiving antenna array and a data demodulation module, and the receiving antenna array sends the received space transmission electromagnetic waves to the demodulation module. The demodulation module restores the transmitted signal to user data. The invention improves the signal-to-noise ratio of the receiving end, reduces the computational complexity of the receiving end, and can be applied to multi-user transmission.

Description

Method and system for electromagnetic wave orbital angular momentum transmission based on spread-dimensional interference code

technical field

The present invention relates to the technical field of orbital angular momentum electromagnetic wave communication, in particular to a method and system for electromagnetic wave orbital angular momentum transmission based on extended-dimensional interference codes.

Background technique

Orbital Angular Momentum (OAM) of electromagnetic waves is another important physical quantity that is different from the electric field strength of electromagnetic waves. The electromagnetic wave with OAM is also called "vortex electromagnetic wave", and its phase plane presents a spiral shape along the propagation direction, which is no longer a traditional plane electromagnetic wave. Electromagnetic waves of different OAMs can be transmitted at the same frequency and orthogonally, opening a new dimension for electromagnetic wave multiplexing. It is expected to be applied to communication, navigation and radar, which can not only greatly improve the communication transmission capacity, but also improve the navigation accuracy and radar detection accuracy. It is an important direction for the future development of electromagnetic wave applications.

The research on orbital angular momentum (OAM) of electromagnetic waves has a history of more than 30 years. It was initially mainly focused on the field of optical communication. It was not until the last decade that it was gradually extended to the field of low-frequency electromagnetic waves, namely microwave, millimeter wave and terahertz bands, which have electromagnetic waves. The communication system of OAM can greatly improve the transmission capacity of the system by relying on the orthogonality of OAM. The orthogonality of OAM modes brings additional spectral efficiency and energy efficiency, first realized and applied in optical communication. Due to the orthogonality between OAMs of different orders, the OAM modes in the fiber are also orthogonal to each other, and multiple spatially superimposed OAM modes can be demodulated into Gaussian modes using reversed phase plates, so that the Separated from each other in space, the demodulation system saves complex DSP algorithms and greatly reduces the complexity of the system. OAM modal multiplexing can be used to increase the number of channels and improve communication capacity. Circularly polarized light with spin OAM was first predicted by Poynting in 1909. The mechanical effects of circularly polarized light were first observed in experiments in 1936. Since then, the scientific community's research on electromagnetic wave OAM has almost stagnated. It wasn't until 1992 that Allen proposed that the Laguerre Gaussian laser beam had an OAM that could be used as an optical wrench or to increase transmission channel capacity. In 2012, Jian Wang et al. achieved a transmission rate of 1.37Tbps using the orbital angular momentum properties of lasers. In 2013, Nenad B. et al. used two OAM mode multiplexing and polarization state multiplexing to achieve a transmission distance of 1.1km and a transmission rate of 400Gbit/s, and combined with wavelength division multiplexing of ten wavelengths to achieve 1.6Tbit/s. s transmission rate, and the communication system does not use DSP algorithm demodulation, which simplifies the complexity of the receiver. In December 2018, the team of Jin Xianmin from Shanghai Jiao Tong University developed the first optical waveguide that can carry the photonic OAM degree of freedom in an optical chip, and realized the efficient and high-fidelity transmission of photonic OAM in the waveguide.

Compared with optical communication, it is more difficult to generate and apply orbital angular momentum quantum states for radio frequency electromagnetic waves (below 300 GHz), and the long-distance transmission of radio frequency OAM beams in free space is difficult due to beam divergence. In 2007, B.Thide et al. extended the OAM in the optical field to the microwave band for the first time, and proposed that the uniform circular array (UCA) antenna can generate microwave orbital angular momentum. Massive occupancy problem. Because the uniform circular antenna array can easily generate orbital angular momentum carrying different modes, many subsequent studies are also based on the uniform circular antenna array scheme. In 2010, Mohammadi analyzed in detail the generation and detection of different OAM electromagnetic waves using uniform circular antenna arrays. The receiving end uses the receiving antenna with the opposite OAM mode of the transmitting end to receive the entire ring beam energy from space, and the transmitted OAM electromagnetic wave is phase-compensated by the receiving antenna and becomes a regular plane electromagnetic wave. The number of states increases proportionally, and the conventional electromagnetic waves after phase compensation can be separated by space division. This all-spatial reception method is borrowed from optical OAM. In 2014, Yan Yan et al. used the full-space reception method to multiplex four OAM modes at a distance of 2.5m, with a transmission rate of 32Gbit/s and a spectral efficiency of 16bit/s/Hz. Analyzing the existing coaxial transmission mode of OAM all-phase plane of electromagnetic wave, it can be found that as the number of OAM modes increases, the divergence angle of OAM electromagnetic wave increases, and the electromagnetic wave beam emitted from the transmitting antenna is in the shape of an inverted cone. diverge. If the coaxial receiving method of the all-phase plane in the fiber is adopted, a huge annular receiving antenna coaxial with the propagation direction is required, which cannot be realized in the actual environment. Therefore, the full airspace reception method is only suitable for short-range point-to-point transmission. Since the phase of the OAM electromagnetic wave is linearly distributed along the circumference on the annular beam section, there is a phase difference between any two points on the annular beam section, and the electromagnetic waves of different OAM modes produce different phase differences. When the antenna spacing is fixed, the phase difference between the antennas is proportional to the OAM mode. Therefore, an antenna array can be arranged on a part of the ring beam to receive the signal, and the Fourier transform of the received signal can complete the detection of different phase differences, and then complete the detection and separation of different OAM modes. In 2016, Zhang Xianmin's research group of Zhejiang University and others used partial reception to complete the experiment of 4 channels of OAM electromagnetic waves for 10m and transmission rate of 160Mbit/s. However, phase gradient detection requires that both receiving points are located on the same circle perpendicular to the propagation axis, and the center of the circle coincides with the propagation axis. Phase misalignment will reduce the correctness of OAM modal detection. Moreover, the detection accuracy decreases with the decrease of the opening angle between the two antennas, that is, when the distance between the antennas is fixed, the detection accuracy decreases as the transmission distance increases. In addition, the detection performance is greatly affected by noise. In 2016, the Avionics Laboratory of Tsinghua University used part of the phase plane to receive OAM electromagnetic waves, and realized the OAM mapping to the second frequency domain by rotating the OAM electromagnetic waves, and completed a 27.5-kilometer long-distance (Tsinghua University to Qianling Mountain) 10GHz OAM electromagnetic wave transmission experiment; And in April 2018, the 172 km (Mangshan to Renqiu) airborne OAM multiplexing transmission experiment was successfully carried out.

The orbital angular momentum transmission scheme using UCA antenna is considered to be an effective line-of-sight MIMO scheme with high spectral efficiency. However, multi-antenna joint demodulation needs to process multi-antenna signals, resulting in high complexity of receiver solution. In order to overcome the interference between modes, the MIMO scheme using the OAM receiver structure needs to introduce a complex interference cancellation mechanism and cannot perform multi-user transmission. Inter-modal interference is particularly pronounced in the case of non-coaxial antennas between the transmit (Tx) and receive (Rx) array antennas. Therefore, in the present invention, an electromagnetic wave orbital angular momentum transmission method and system based on a dimension-expanding interference code is innovatively proposed, and the interference code is used to expand in different modes of multiplexing transmission. Due to the orthogonality of the interference code, the final transmitted OAM beam self-interferes to form a space-division beam, and the energy of each beam is concentrated in the direction of a corresponding receiving antenna, which can be easily received by the corresponding antenna in the UCA, improving the receiving end. Signal-to-noise ratio (SNR), which simplifies the receiver structure. In addition, the scheme does not need to consider inter-modal interference, and the space division beams can be allocated to multiple users to form a multi-user OAM transmission scheme.

SUMMARY OF THE INVENTION

The present invention aims to solve the problem of high solution complexity of multi-antenna joint demodulation in the UCA antenna scheme described in the background, and the problem of OAM inter-modal interference when the transceiver ends are not coaxial.

To this end, the purpose of the present invention is to propose a method and system for electromagnetic wave orbital angular momentum transmission based on the expanded dimension interference code. Multi-user transmission, and greatly suppress the problem of interference between modes when the transceiver ends are not coaxial.

An electromagnetic wave orbital angular momentum transmission system based on a spread-dimensional interference code, comprising a signal transmitting terminal system and a signal receiving terminal system, wherein:

The signal transmission terminal system includes a data generation module, a data serial-to-parallel conversion module, an interference code expansion module, an OAM mode selection module and a signal transmission antenna module connected in sequence, wherein,

A data generation module for receiving user data and outputting modulated serial user data;

a data serial-to-parallel conversion module, for converting the serial user data into multi-row parallel data according to the number of OAM modes;

The interferometric code expansion module is used to multiply the parallel data and the interference code, and perform a dimension expansion operation on the parallel data to become a dimension expansion matrix with the same dimension as the OAM modal number, and the interference code is an orthogonal Sequences of quasi-orthogonality or quasi-orthogonality;

The OAM mode selection module adds the elements of each column vector of the dimension expansion matrix respectively and selects different OAM modes to feed to the uniform circular array antenna elements of different OAM modes of the signal transmitting antenna module, forming different OAM modes. The OAM modal carrier signal;

The signal transmitting antenna module is used to convert different OAM modal carrier signals into space electromagnetic waves and send them out.

The signal receiving terminal system includes a receiving antenna array and a data demodulation module. The receiving antenna array is located on the same annular section where different OAM modal beams converge. Each beam corresponds to a receiving antenna, and each receiving antenna converts the received space electromagnetic waves into The radio frequency signal is sent to the data demodulation module, and the data demodulation module restores the radio frequency signal to each channel of user data.

A method for transmitting electromagnetic wave orbital angular momentum based on a dimension-expanding interference code, using the above-mentioned transmission system to carry out the following steps:

The data generation module receives user data and outputs the modulated serial user data;

The data serial-parallel conversion module converts the serial user data into multi-line parallel data according to the number of OAM modes;

The interferometric code expansion module multiplies the parallel data with the interference code, performs a dimension expansion operation on the parallel data, and becomes a dimension expansion matrix with the same dimension as the OAM modal number, and the interference code is orthogonal or quasi. Orthogonal sequence;

The OAM mode selection module adds the elements of each column vector of the expansion matrix respectively and selects different OAM modes to feed to the antenna elements of the uniform circular array of different OAM modes of the signal transmitting antenna module, forming different OAM modes. The OAM modal carrier signal;

The signal transmitting antenna module converts different OAM modal carrier signals into space electromagnetic waves and sends them out;

The receiving antenna array is located on the same annular section where different OAM modal beams converge. Each beam corresponds to a receiving antenna. Each receiving antenna converts the received space transmission electromagnetic waves into radio frequency signals and sends them to the data demodulation module. Data demodulation The module restores the radio frequency signal to each user data.

The present invention aims to solve the problems of low receiving signal-to-noise ratio and high receiver complexity of MIMO scheme due to beam divergence in free space electromagnetic wave orbital angular momentum transmission described in the background, as well as the inter-modal interference and User receives questions. Therefore, the purpose of the present invention is to propose a method and system for electromagnetic wave orbital angular momentum transmission based on expanded-dimensional interference code, which can improve the signal-to-noise ratio of the receiving end of electromagnetic wave orbital angular momentum transmission and reduce the complexity of receiver solution. In addition, this scheme suppresses the OAM inter-modal interference of UCA, and solves the problem that it can only be used for single-user reception. The solution proposed in this patent can be applied to multi-user transmission, which will be specifically described in the following examples.

Description of drawings

The above-described features and technical advantages of the present invention will become more clearly and easily understood by describing its embodiments in conjunction with the following drawings.

Fig. 1 is the structural representation of the electromagnetic wave orbital angular momentum transmission system based on the dimension-expanding interference code of the present invention;

Figure 2-1 is a schematic diagram of the planar coaxial UCA mode;

Figure 2-2 is a schematic diagram of a circular longitudinal coaxial UCA mode;

3 is a schematic diagram of the coaxial transmission and reception structure of multiple longitudinal uniform circular antenna arrays according to the present invention;

4 is a spatial energy distribution diagram of a single shaped beam in OAM multiplexing transmission according to an embodiment of the present invention;

5 is a circular cross-sectional view of a multiplexed beam directional energy distribution according to an embodiment of the present invention;

Fig. 6-1 is a graph showing the distribution curve of the received energy of users in adjacent positions of the beam pointing position according to an embodiment of the present invention;

Fig. 6-2 is a graph showing the user's received energy distribution curve at the diagonal position of the beam pointing position according to an embodiment of the present invention;

FIG. 7 is a schematic diagram of multi-user transmission according to an embodiment of the present invention.

Detailed ways

Embodiments of the method and system for transmitting electromagnetic wave orbital angular momentum based on the spread-dimensional interference code according to the present invention will be described below with reference to the accompanying drawings. As those of ordinary skill in the art would realize, the described embodiments may be modified in various different ways or combinations thereof, all without departing from the spirit and scope of the present invention. Accordingly, the drawings and description are illustrative in nature and are not intended to limit the scope of protection of the claims. Furthermore, in this specification, the drawings are not drawn to scale, and the same reference numerals refer to the same parts.

As shown in Figures 1, 2-1 and 2-2, the electromagnetic wave orbital angular momentum transmission system based on the expanded dimension interference code includes a signal transmitting terminal system and a signal receiving terminal system. The signal transmission terminal system includes a data generation module 101, a data serial-to-parallel conversion module 102, an interference code expansion module 103, an OAM mode selection module 104 and a signal transmission antenna module 105, wherein the signal transmission antenna module 105 includes a planar coaxial UCA Pattern 109 and circular longitudinal coaxial UCA pattern 110 ; the signal receiving terminal system includes a receiving antenna array 106 , a data demodulation module 107 and a user receiving end module 108 . The configuration of each subsystem will be described below.

1. Signal transmission subsystem

(1) Data generation module 101: Generate user data and output modulated serial user data. The modulation method can be amplitude keying (ASK), frequency shift keying (FSK), phase shift keying (PSK), or quadrature amplitude modulation (QAM), minimum frequency shift keying (MSK), quadrature Frequency Division Multiplexing Modulation (OFDM), etc.

(2) data serial-to-parallel conversion module 102: converts serial user data into multi-line parallel data according to the number of OAM modes;

(3) Interference code expansion module 103: multiply the parallel data by the interference code, perform a dimension expansion operation on the parallel data, and become a dimension expansion matrix with the same dimension as the OAM modal number, and the interference code has A sequence with a certain orthogonality or quasi-orthogonality, due to the orthogonality of the interference code, the final transmitted OAM beam self-interferes to form a space-division beam, and the energy of each beam is concentrated in a corresponding receiving antenna direction, which can be easily It is received by the corresponding antenna in the UCA at the receiving end.

The interference code is a sequence group with a certain orthogonality. Without loss of generality, the following takes the carrier interference code (CI code) as an example to describe the expansion process. The process of forming the CI code from the vectors of the Fourier transform matrix is:

F _N =[W _i,k ] _N×N (2)

在N＝2ⁿ,n∈Z⁺的情况下，F_N为DFT(离散傅里叶变换)矩阵，它的行向量之间两两正交。CI码包括干涉码1至干涉码N-1,可以表示为in,

In the case of N=2 ⁿ , n∈Z ⁺ , F _N is a DFT (Discrete Fourier Transform) matrix, and its row vectors are orthogonal to each other. The CI code includes interference code 1 to interference code N-1, which can be expressed as

C=[c ₀ ,c ₁ ,...,c _N-1 ] ^T (3)

Wherein, c _i =[W _i,0 ,W _i,1 ,...,W _i,N-1 ], 0≤i≤N-1. As shown in Figure 1, it is assumed that the user data is parallel data D=[d ₀ , d ₁ ,..., d _N-1 ] ^T after serial-to-parallel conversion, that is, symbols 1 to N-1 in Figure 1, after Interference code expansion module, the transmitted CI-OAM signal (dimension expansion signal matrix) S is the Hadamard product of D and C

表示哈达玛积，C表示CI码扩维矩阵，S矩阵每列在一个OAM模态发送，则第k行扩维信号矩阵在OAM模态l上发射信号为in,

Represents the Hadamard product, C represents the CI code expansion matrix, and each column of the S matrix is transmitted in an OAM mode, then the kth row of the expanded dimension signal matrix transmits the signal in the OAM mode l as

(4) OAM modal selection module 104: superimpose the parallel data transmitted by the same OAM modal, that is, add the input expansion matrix to the column vector, select the corresponding OAM modal, and feed it to the UCA of different OAM modalities On the antenna element, different OAM modal carrier signals are formed, that is, the addition of elements in the first column of S is sent by OAM mode 0, the addition of elements in the second column is sent by OAM mode 1, and so on, all the time. Element-wise addition to column N is sent by OAM modality N-1.

It should be noted that the above is only to form multi-row parallel data, and expand the parallel data into an expanded dimension matrix, and the columns of the expanded dimension matrix are orthogonal to each other. It is also possible to form multi-column parallel data, expand the parallel data into an expanded matrix, and then the rows of the expanded matrix are orthogonal. The principles and methods are the same, and will not be repeated here.

(5) Signal transmitting antenna module 105 : used to convert different OAM modal carrier signals into space electromagnetic waves, which includes any one of the planar coaxial UCA mode 109 and the longitudinal coaxial UCA mode 110 .

Among them, the planar coaxial UCA module 109 is shown in Fig. 2-1, which includes a plurality of coaxial (that is, around the same propagation axis) uniform circular antenna arrays in the same plane, wherein the antennas in the same circle are exactly the same, The amplitude of the feed signal is equal, the phase is uniformly delayed once, and the phase is delayed by l·2π in one rotation around the propagation axis, where l is the number of OAM modes. Each ring generates different OAM modes, so that different OAM modes can occur on one substrate, but the radius of each circular antenna array needs to be calculated accurately, so that the beams of different OAM modes finally converge on the same ring section, Each UCA radius can be calculated by Equation 6 from the same beam divergence angle and electromagnetic wave frequency for different OAM modes coaxial in the same plane.

为波矢，λ为电磁波波长，

a为发射端UCA天线阵的半径，θ为OAM波束发散角。例如已知相同的波束发散角、电磁波频率和最终要汇聚到的同一环形截面，可以根据公式6计算出每个发射端UCA半径，再根据最终将要汇聚到同一环形截面，即可定位发射端位置。Equation 6 is the electric field expression of the OAM based on UCA in the spherical coordinate system (r, θ, φ), where the OAM airspace electric field strength E, r represents the straight-line distance from the center of the circular array to the observation point, and l is the OAM mode number, N represents the number of antenna elements in UCA, J _l (·) is the first-order Bessel function of the first order,

is the wave vector, λ is the wavelength of the electromagnetic wave,

a is the radius of the UCA antenna array at the transmitting end, and θ is the OAM beam divergence angle. For example, knowing the same beam divergence angle, electromagnetic wave frequency and the same annular section to be converged, the UCA radius of each transmitting end can be calculated according to formula 6, and then the position of the transmitting end can be located according to the final convergence to the same annular section. .

Among them, the longitudinal coaxial UCA mode 110, as shown in Figure 2-2, is composed of multiple identical longitudinal uniform circular antenna arrays, each uniform circular antenna array generates different OAM modes, because each OAM mode is different , the beam divergence angle is different, and the precise antenna placement position is required. Firstly, the beam divergence angles of different OAM modes are calculated according to the frequency of the electromagnetic wave and the radius of the uniform circular antenna array. The divergence angles of the electromagnetic waves can be calculated according to Equation 6. The beam divergence angle corresponding to the antenna array and the position of the same ring section to be converged can be determined by the geometric relationship of the position of each ring antenna array;

The signal transmitting antenna module 105 can generate a helical phase plane through a helical phase plate, a helical reflection surface or a ring phased array, so as to obtain an electromagnetic wave signal with orbital angular momentum. The signal transmitting antenna module 105 can coaxially generate OAM electromagnetic waves of multiple modes. The OAM electromagnetic waves of different modes are orthogonal to each other during space transmission. The energy of the signal is mainly concentrated in the ring formed by the main lobe, and the multiple modes The OAM phase planes with orthogonal states are also uniformly distributed on the ring, so that the beams of different OAM modes are finally converged on the same ring section at the receiving end.

2. Signal receiving subsystem

(1) Receiving antenna array 106: The receiving antenna array is located on the same annular section where different OAM modal beams converge, and is used to convert space-transmitted electromagnetic waves (electromagnetic waves transmitted in free space) into radio-frequency signals (that is, conductors in the transmission line). The traveling electromagnetic wave) is sent to the data demodulation module, corresponding to the previous modal signals of 1 to N-1, there are 1 to N-1 antennas on the same annular section, and each modal beam corresponds to a different receiving antenna;

(2) Data demodulation module 107: demodulate the received radio frequency signal and restore it to user data;

(3) User receiving end module 108: send the demodulation module data to the user receiving end.

The implementation principle of signal reception is described below. The transmitting end can adopt either the longitudinal coaxial UCA mode 110 or the planar coaxial UCA module 109, and the UCA antenna elements including M antennas are coaxially arranged at the receiving end, and the M antennas are evenly distributed on the phase plane. For mode l, the phase difference between adjacent antennas is c. Without loss of generality, it is assumed that the No. 0 antenna is exactly in the initial phase direction of the transmitted signals in all modes (here, No. 0 is used as an example only for the convenience of illustration. In fact, the No. 0 antenna can also be other numbers. The initial phase direction of the transmitted signal of all modes), the phase factor matrix corresponding to the receiving antenna array can be expressed as:

当M＝N时，

很容易可看出，当接收天线小于发射天线个数时，即M<N，接收未知量个数小于发射数据个数，为欠定方程，无解。当接收天线个数多于发射天线个数时，即M>N，接收未知量个数大于发射数据个数，为超定方程，可求其最小二乘解。为了简化计算和讨论，下面仅考察M＝N时各个接收天线上接收的信号。根据公式(5)，第0号接收天线所收到的信号为：Among them, the phase factor of the l-th modal signal corresponding to the m-th antenna is

When M=N,

It is easy to see that when the number of receiving antennas is less than the number of transmitting antennas, that is, M<N, and the number of received unknowns is less than the number of transmitted data, it is an underdetermined equation with no solution. When the number of receiving antennas is more than the number of transmitting antennas, that is, M>N, and the number of received unknowns is greater than the number of transmitted data, it is an overdetermined equation, and its least squares solution can be obtained. In order to simplify the calculation and discussion, the following only considers the signal received on each receiving antenna when M=N. According to formula (5), the signal received by the No. 0 receiving antenna is:

Antenna i, its received signal is:

是第i个接收机的加性高斯白噪声，0为噪声均值，

为噪声方差。因此，第i号每个接收天线上只剩下对应数据d_i的信号，其他数据信号都随着相位因子矩阵行列的正交性而相互抵消了。从整个系统来看，数据d_i好像沿着单独的信道发送给了接收天线r_i，体现出了扩维码在波束赋形和波束调控中的作用。in,

is the additive white Gaussian noise of the ith receiver, 0 is the noise mean,

is the noise variance. Therefore, only the signal corresponding to the data d _i remains on each receiving antenna of the ith, and other data signals cancel each other with the orthogonality of the rows and columns of the phase factor matrix. From the perspective of the whole system, the data _di seems to be sent to the receiving antenna _ri along a separate channel, which reflects the role of the spreading code in beamforming and beam steering.

则接收天线阵在t时刻接收的信号可以表示为：If the No. 0 antenna is not aligned in the initial phase direction of all modal transmission signals, let the offset angle be φ, and

Then the signal received by the receiving antenna array at time t can be expressed as:

where ri ^(φ) (t) represents the signal received from the _i -th receive antenna. Assuming that the previous formula (8) and formula (9) indicate that the received vector when φ=0 is r(t)=[r ₀ (t),r ₁ (t),...,r _N-1 (t)], then The correlation matrix of the received vector is:

R=E[r(t) ^rH (t)] (11)

矩阵p_i表示偏移角度φ后第i个天线信号与接收信号向量r(t)之间的互相关矩阵：The elements of the i ₁ row and i ₂ column of the matrix R are

The matrix p _i represents the cross-correlation matrix between the ith antenna signal and the received signal vector r(t) after the offset angle φ:

According to the minimum mean square error criterion, the optimal weighting coefficient vector can be obtained as:

w(φ,t)=R ^-1 p _i (13)

Thus, the output signal after the receiving antenna is deflected by φ is:

Take the alignment of the initial phase (ie, the starting phase) of all modes as an example: for parallel data sent by a longitudinally coaxial UCA pattern 110 comprising a plurality of identical circular antenna arrays, as shown in FIG. 3, four identical UCA along the The axes are placed in different positions, and each UCA produces a modal OAM. Along the longitudinal axis, the number of OAM modes generated by each UCA are l=1, l=2, l=3, l=4, respectively, and the corresponding beam divergence angles are θ ₁ =11.26o, θ ₂ =18.91 o, θ ₃ =26.47o, θ ₄ =34.35o. The spacing between transmit UCAs and between receive UCAs are d ₁ , d ₂ , d ₃ and d ₄ , respectively. According to the system structure shown in Figure 3, the positional relationship can be calculated as

The ring radius of the receiving antenna is R=1m, and the positions of each UCA are calculated as d ₁ =2.1m, d ₂ =0.91m, d ₃ =0.55m and d ₄ =1.46m, respectively.

和

上每个接收天线乘上对应的相位因子只剩下对应天线阵子发送的数据，实现了OAM波束赋形指向不同位置。在波束赋形指向位置上放置接收天线，用户即可得到远场接收最大信噪比。图6-1为波束指向天线1时，相邻天线2方向的接收功率曲线；图6-2为波束指向天线1时，对角线天线3方向的接收功率曲线。可见，不同天线之间接收也会存在干扰，只要接收机SNR允许，该干扰可以通过调制和编码进行简单抑制。另外，根据本发明的基于扩维干涉码的电磁波轨道角动量传输方法与系统还可以具有以下附加的技术特征：By simulating a single assignment of multiplexing when the number of OAM modalities is l=1, l=2, l=3, and l=4 (at the receiving end, the beams of each modal are accumulated with a starting phase aligned with 0 phase). The far-field pattern of the shaped beam is shown in Figure 4. It can be seen that each shaped beam points to a specific direction, and the receiving antenna is placed in this direction to obtain the maximum signal-to-noise ratio of far-field reception. Figure 5 is the far-field pattern of the multiplexing when four OAM modes are sent by four antennas as l=1, l=2, l=3, and l=4. It can be seen that the four phase directions of the torus are

and

Multiplying each receiving antenna by the corresponding phase factor only leaves the data sent by the corresponding antenna element, realizing OAM beamforming pointing to different positions. By placing the receiving antenna at the beamforming pointing position, the user can obtain the maximum signal-to-noise ratio for far-field reception. Figure 6-1 shows the received power curve of the adjacent antenna 2 when the beam is directed to antenna 1; Figure 6-2 is the received power curve of the diagonal antenna 3 when the beam is directed to antenna 1. It can be seen that there will also be interference in reception between different antennas. As long as the receiver SNR allows, the interference can be simply suppressed by modulation and coding. In addition, the electromagnetic wave orbital angular momentum transmission method and system based on the expanded dimension interference code according to the present invention may also have the following additional technical features:

Since the energy of the final transmitted OAM beam at the receiving end is concentrated in one direction, the antenna placed at the receiving end improves the signal-to-noise ratio (SNR) of the receiving end, and the user end directly performs demodulation and reception, which simplifies the receiver structure and reduces the complexity. As shown in Figure 4, due to the phase cancellation between the electromagnetic beams, the beam energy finally converges to a point direction, and there is only one user data information in this direction, which is directly demodulated and sent to the user end, which simplifies the receiver structure.

方向上放置接收天线，用户1直接接收天线1数据并解调；在接收端环面的

方向上放置接收天线，波束赋形后指向用户2直接接收天线2数据并解调；在接收端环面相位为

和

上放置接收天线，波束赋形后分别指向用户3和用户4接收天线3和天线4并解调。An antenna mentioned above can represent a user. By adjusting the antenna position of the transmitter, different users can receive and transmit information under different transmission distances and different distributions, which is convenient for distributed transmission and reception, thus becoming a multi-user system. As an example, as shown in Figure 7, after 4 OAM modal beamforming, the torus at the receiving end

Place the receiving antenna in the direction, user 1 directly receives the data of antenna 1 and demodulates;

The receiving antenna is placed in the direction, and the beam is pointed to user 2 to directly receive the data of antenna 2 and demodulate; the torus phase at the receiving end is

and

The receiving antenna is placed on the top, and the beam is directed to user 3 and user 4 to receive antenna 3 and antenna 4 respectively and demodulate.

In an optional embodiment, the antenna in the transmitting antenna array and/or the receiving antenna array is one of a horn antenna, a parabolic antenna, a Cassegrain antenna, a patch antenna, and an array antenna.

In an alternative embodiment, orbital angular momentum electromagnetic waves are generated using one or more of helical phase plates, specific reflector antennas, specific feed antennas, phased array antennas, spatial light modulators, diffraction gratings, and metamaterials .

It can be known from the above analysis that the method and system for electromagnetic wave orbital angular momentum transmission based on the expanded dimension interference code proposed by the present invention, the final transmitted OAM beam is self-interference to form a space-division beam, and the energy of each beam is concentrated in a direction corresponding to the receiving antenna , which can be easily received by the corresponding antenna in the UCA, which improves the signal-to-noise ratio at the receiving end and simplifies the receiver structure. In addition, the scheme does not need to consider inter-modal interference, and also has broad application prospects in the downlink beamforming of the multi-user OAM scheme.

In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", " Rear, Left, Right, Vertical, Horizontal, Top, Bottom, Inner, Outer, Clockwise, Counterclockwise, Axial, The orientations or positional relationships indicated by "radial direction", "circumferential direction", etc. are based on the orientations or positional relationships shown in the accompanying drawings, which are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying the indicated devices or elements. It must have a specific orientation, be constructed and operate in a specific orientation, and therefore should not be construed as a limitation of the present invention.

In addition, the terms "first" and "second" are only used for descriptive purposes, and should not be construed as indicating or implying relative importance or implying the number of indicated technical features. Thus, a feature delimited with "first", "second" may expressly or implicitly include at least one of that feature. In the description of the present invention, "plurality" means at least two, such as two, three, etc., unless otherwise expressly and specifically defined.

In the present invention, unless otherwise expressly specified and limited, the terms "installed", "connected", "connected", "fixed" and other terms should be understood in a broad sense, for example, it may be a fixed connection or a detachable connection , or integrated; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between the two elements, unless otherwise specified limit. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

In the present invention, unless otherwise expressly specified and limited, a first feature "on" or "under" a second feature may be in direct contact between the first and second features, or the first and second features indirectly through an intermediary touch. Also, the first feature being "above", "over" and "above" the second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is level higher than the second feature. The first feature being "below", "below" and "below" the second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature has a lower level than the second feature.

In the description of this specification, description with reference to the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples", etc., mean specific features described in connection with the embodiment or example , structure, material or feature is included in at least one embodiment or example of the present invention. In this specification, schematic representations of the above terms are not necessarily directed to the same embodiment or example. Furthermore, the particular features, structures, materials or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, those skilled in the art may combine and combine the different embodiments or examples described in this specification, as well as the features of the different embodiments or examples, without conflicting each other.

Although the embodiments of the present invention have been shown and described above, it should be understood that the above-mentioned embodiments are exemplary and should not be construed as limiting the present invention. Embodiments are subject to variations, modifications, substitutions and variations.

Claims (10)

1. an electromagnetic wave orbital angular momentum transmission system based on dimension-expanding interference code, is characterized in that, comprises signal transmitting terminal system and signal receiving terminal system, wherein: The signal transmission terminal system includes a data generation module, a data serial-to-parallel conversion module, an interference code expansion module, an OAM mode selection module and a signal transmission antenna module connected in sequence, wherein, A data generation module for receiving user data and outputting modulated serial user data; a data serial-to-parallel conversion module, for converting the serial user data into multi-row parallel data according to the number of OAM modes; The interferometric code expansion module is used to multiply the parallel data and the interference code, and perform a dimension expansion operation on the parallel data to become a dimension expansion matrix with the same dimension as the OAM modal number, and the interference code is an orthogonal Sequences of quasi-orthogonality or quasi-orthogonality; The OAM mode selection module adds the elements of each column vector of the dimension expansion matrix respectively and selects different OAM modes to feed to the uniform circular array antenna elements of different OAM modes of the signal transmitting antenna module, forming different OAM modes. The OAM modal carrier signal; The signal transmitting antenna module is used to convert different OAM modal carrier signals into space electromagnetic waves and send them out. The signal receiving terminal system includes a receiving antenna array and a data demodulation module. The receiving antenna array is located on the same annular section where different OAM modal beams converge. Each beam corresponds to a receiving antenna, and each receiving antenna converts the received space electromagnetic waves into The radio frequency signal is sent to the data demodulation module, and the data demodulation module restores the radio frequency signal to each channel of user data. 2. the electromagnetic wave orbital angular momentum transmission system based on the dimension-expanding interference code according to claim 1, is characterized in that, the signal transmitting antenna module comprises any one in plane coaxial UCA mode and longitudinal coaxial UCA mode, Among them, the plane coaxial UCA mode includes a plurality of uniform circular antenna arrays coaxial in the same plane, in which the amplitudes of the feed signals of the antenna elements in the same circle are equal, and the phases are uniformly delayed in turn. Different OAM modes, according to the same beam divergence angle corresponding to different OAM modes, calculate the radius of the uniform circular antenna array, and by presetting the radius of each circle of circular antenna array, make the different OAM mode beams converge to the same annular section on the receiving antenna array; Among them, the longitudinal coaxial UCA mode includes multiple longitudinal coaxial circular antenna arrays, each circular antenna array generates different OAM modes, and the beam divergence of different OAM modes is calculated according to the frequency of electromagnetic waves and the radius of each circular antenna array The position of each circular antenna array is determined according to the beam divergence angle corresponding to each circular antenna array and the position of the same annular section to be converged. By presetting the distance between each circular antenna array and the receiving antenna array, the different The OAM modal beams are focused on the receiving antenna arrays located in the same annular cross-section. 3. the electromagnetic wave orbital angular momentum transmission system based on the dimension-expanded interference code according to claim 1, is characterized in that, the antenna in described transmitting antenna array and/or described receiving antenna array is horn antenna, parabolic antenna, card One of the Segron antennas and patch antennas. 4. the electromagnetic wave orbital angular momentum transmission system based on the dimension-expanding interference code according to claim 1, is characterized in that, utilizes helical phase plate, specific reflector antenna, specific feed antenna, phased array antenna, spatial light modulator One or more of , diffraction gratings, and metamaterials generate orbital angular momentum electromagnetic waves. 5 . The electromagnetic wave orbital angular momentum transmission system based on the expanded dimension interference code according to claim 1 , wherein the electromagnetic wave comprises one or more of light waves, microwaves, millimeter waves and terahertz waves. 6 . 6. an electromagnetic wave orbital angular momentum transmission method based on dimension-expanding interference code, is characterized in that, applying the described transmission system of claim 1 to carry out the following steps: The data generation module receives user data and outputs the modulated serial user data; The data serial-parallel conversion module converts the serial user data into multi-line parallel data according to the number of OAM modes; The interferometric code expansion module multiplies the parallel data with the interference code, performs a dimension expansion operation on the parallel data, and becomes a dimension expansion matrix with the same dimension as the OAM modal number, and the interference code is orthogonal or quasi. Orthogonal sequence; The OAM mode selection module adds the elements of each column vector of the expansion matrix respectively and selects different OAM modes to feed to the antenna elements of the uniform circular array of different OAM modes of the signal transmitting antenna module, forming different OAM modes. The OAM modal carrier signal; The signal transmitting antenna module converts different OAM modal carrier signals into space electromagnetic waves and sends them out; The receiving antenna array is located on the same annular section where different OAM modal beams converge. Each beam corresponds to a receiving antenna. Each receiving antenna converts the received space transmission electromagnetic waves into radio frequency signals and sends them to the data demodulation module. Data demodulation The module restores the radio frequency signal to each user data. 7. the electromagnetic wave orbital angular momentum transmission method based on the dimension-expanding interference code according to claim 6, is characterized in that, by changing the initial phase of the different OAM modes that the signal transmitting antenna module produces, makes the OAM received at the receiving end The modal information is aligned with different initial phases to realize the OAM beamforming pointing to different positions, and the receiving antenna is placed on the beamforming pointing position to receive the radio frequency signal. 8. the electromagnetic wave orbital angular momentum transmission method based on spread dimension interference code according to claim 6, is characterized in that, the method for modulation comprises amplitude keying, frequency shift keying, phase shift keying, quadrature amplitude modulation, minimum Either frequency shift keying or orthogonal frequency division multiplexing modulation. 9. the electromagnetic wave orbital angular momentum transmission method based on the expanded dimension interference code according to claim 6, is characterized in that, The signal transmitting antenna module includes a planar coaxial UCA mode, Among them, the planar coaxial UCA mode includes a plurality of uniform circular antenna arrays coaxial in the same plane, in which the amplitudes of the feed signals of the antenna elements in the same circle are equal, and the phases are uniformly delayed in turn, and each circle of UCA produces different OAM modes. By presetting the radius of each circular antenna array, the beams of different OAM modes are converged on the receiving antenna array located in the same circular section, For the planar coaxial UCA mode, formula 6 is used to calculate the radius of the uniform circular antenna array according to the electromagnetic wave frequencies of different OAM modes and the same beam divergence angle,

Equation 6 is the electric field expression of the OAM based on UCA in the spherical coordinate system (r, θ, φ), where E is the electric field intensity in the OAM airspace, r is the straight-line distance from the center of the circular array to the observation point, and l is the OAM modulus. is the number of states, N represents the number of antenna elements in UCA, J _l ( ) is the first-class Bessel function of order l,

is the wave vector, λ is the wavelength of the electromagnetic wave, a is the radius of the UCA at the transmitting end, θ is the OAM beam divergence angle,

10. The electromagnetic wave orbital angular momentum transmission method based on dimension-expanding interference code according to claim 6, is characterized in that, The signal transmitting antenna module includes longitudinal coaxial UCA mode, The longitudinal coaxial UCA mode includes multiple identical or different longitudinal coaxial circular antenna arrays, each circular antenna array generates a different OAM mode, and the distance between each circular antenna array and the receiving antenna array is preset by presetting the distance between the circular antenna array and the receiving antenna array. , so that the different OAM modal beams converge on the receiving antenna array located in the same annular section, For the longitudinal coaxial UCA mode, formula 6 is used to calculate different beam divergence angles according to the frequency of the electromagnetic wave and the radius of the uniform circular antenna array. Determine the position of each circular antenna array,

Equation 6 is the electric field expression of the OAM based on UCA in the spherical coordinate system (r, θ, φ), where E is the electric field intensity in the OAM airspace, r is the straight-line distance from the center of the circular array to the observation point, and l is the OAM modulus. is the number of states, N represents the number of antenna elements in UCA, J _l ( ) is the first-class Bessel function of order l,

is the wave vector, λ is the wavelength of the electromagnetic wave, a is the radius of the UCA at the transmitting end, θ is the OAM beam divergence angle,

Images